RESUMO
Spot-scanning particle therapy possesses advantages, such as high conformity to the target and efficient energy utilization compared with those of the passive scattering irradiation technique. However, this irradiation technique is sensitive to target motion. In the current clinical situation, some motion management techniques, such as respiratory-gated irradiation, which uses an external or internal surrogate, have been clinically applied. In surrogate-based gating, the size of the gating window is fixed during the treatment in the current treatment system. In this study, we propose a dynamic gating window technique, which optimizes the size of gating window for each spot by considering a possible dosimetric error. The effectiveness of the dynamic gating window technique was evaluated by simulating irradiation using a moving target in a water phantom. In dosimetric characteristics comparison, the dynamic gating window technique exhibited better performance in all evaluation volumes with different effective depths compared with that of the fixed gate approach. The variation of dosimetric characteristics according to the target depth was small in dynamic gate compared to fixed gate. These results suggest that the dynamic gating window technique can maintain an acceptable dose distribution regardless of the target depth. The overall gating efficiency of the dynamic gate was approximately equal or greater than that of the fixed gating window. In dynamic gate, as the target depth becomes shallower, the gating efficiency will be reduced, although dosimetric characteristics will be maintained regardless of the target depth. The results of this study suggest that the proposed gating technique may potentially improve the dose distribution. However, additional evaluations should be undertaken in the future to determine clinical applicability by assuming the specifications of the treatment system and clinical situation.
Assuntos
Neoplasias Pulmonares/radioterapia , Pulmão/efeitos da radiação , Imagens de Fantasmas , Radiometria/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Intensidade Modulada/métodos , Algoritmos , Simulação por Computador , Humanos , Pulmão/diagnóstico por imagem , Doses de RadiaçãoRESUMO
PURPOSE: While a large amount of experimental data suggest that the proton relative biological effectiveness (RBE) varies with both physical and biological parameters, current commercial treatment planning systems (TPS) use the constant RBE instead of variable RBE models, neglecting the dependence of RBE on the linear energy transfer (LET). To conduct as accurate a clinical evaluation as possible in this circumstance, it is desirable that the dosimetric parameters derived by TPS ( D RBE = 1.1 ) are close to the "true" values derived with the variable RBE models ( D v RBE ). As such, in this study, the closeness of D RBE = 1.1 to D v RBE was compared between planning target volume (PTV)-based and robust plans. METHODS: Intensity-modulated proton therapy (IMPT) treatment plans for two Radiation Therapy Oncology Group (RTOG) phantom cases and four nasopharyngeal cases were created using the PTV-based and robust optimizations, under the assumption of a constant RBE of 1.1. First, the physical dose and dose-averaged LET (LETd ) distributions were obtained using the analytical calculation method, based on the pencil beam algorithm. Next, D v RBE was calculated using three different RBE models. The deviation of D v RBE from D RBE = 1.1 was evaluated with D99 and Dmax , which have been used as the evaluation indices for clinical target volume (CTV) and organs at risk (OARs), respectively. The influence of the distance between the OAR and CTV on the results was also investigated. As a measure of distance, the closest distance and the overlapped volume histogram were used for the RTOG phantom and nasopharyngeal cases, respectively. RESULTS: As for the OAR, the deviations of D max v RBE from D max RBE = 1.1 were always smaller in robust plans than in PTV-based plans in all RBE models. The deviation would tend to increase as the OAR was located closer to the CTV in both optimization techniques. As for the CTV, the deviations of D 99 v RBE from D 99 RBE = 1.1 were comparable between the two optimization techniques, regardless of the distance between the CTV and the OAR. CONCLUSION: Robust optimization was found to be more favorable than PTV-based optimization in that the results presented by TPS were closer to the "true" values and that the clinical evaluation based on TPS was more reliable.
Assuntos
Transferência Linear de Energia , Terapia com Prótons/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Intensidade Modulada/métodos , Eficiência Biológica Relativa , Algoritmos , Humanos , Neoplasias Nasofaríngeas/radioterapia , Órgãos em Risco , Imagens de Fantasmas , Radiometria , Dosagem RadioterapêuticaRESUMO
We developed a synchrotron-based real-time-image gated-spot-scanning proton-beam therapy (RGPT) system and utilized it to clinically operate on moving tumors in the liver, pancreas, lung, and prostate. When the spot-scanning technique is linked to gating, the beam delivery time with gating can increase, compared to that without gating. We aim to clarify whether the total treatment process can be performed within approximately 30 min (the general time per session in several proton therapy facilities), even for gated-spot-scanning proton-beam delivery with implanted fiducial markers. Data from 152 patients, corresponding to 201 treatment plans and 3577 sessions executed from October 2016 to June 2018, were included in this study. To estimate the treatment process time, we utilized data from proton beam delivery logs during the treatment for each patient. We retrieved data, such as the disease site, total target volume, field size at the isocenter, and the number of layers and spots for each field, from the treatment plans. We quantitatively analyzed the treatment process, which includes the patient load (or setup), bone matching, marker matching, beam delivery, patient unload, and equipment setup, using the data obtained from the log data. Among all the cases, 90 patients used the RGPT system (liver: n = 34; pancreas: n = 5; lung: n = 4; and prostate: n = 47). The mean and standard deviation (SD) of the total treatment process time for the RGPT system was 30.3 ± 7.4 min, while it was 25.9 ± 7.5 min for those without gating treatment, excluding craniospinal irradiation (CSI; head and neck: n = 16, pediatric: n = 31, others: n = 15); for CSI (n = 11) with two or three isocenters, the process time was 59.9 ± 13.9 min. Our results demonstrate that spot-scanning proton therapy with a gating function can be achieved in approximately 30-min time slots.
Assuntos
Neoplasias Hepáticas/diagnóstico por imagem , Neoplasias Pulmonares/diagnóstico por imagem , Neoplasias Pancreáticas/diagnóstico por imagem , Neoplasias da Próstata/diagnóstico por imagem , Terapia com Prótons/métodos , Radioterapia Guiada por Imagem/métodos , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Criança , Pré-Escolar , Feminino , Marcadores Fiduciais , Humanos , Lactente , Recém-Nascido , Modelos Lineares , Neoplasias Hepáticas/radioterapia , Neoplasias Pulmonares/radioterapia , Masculino , Pessoa de Meia-Idade , Neoplasias Pancreáticas/radioterapia , Neoplasias da Próstata/radioterapia , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador , Reprodutibilidade dos Testes , Síncrotrons , Fatores de Tempo , Adulto JovemRESUMO
A synchrotron-based real-time image gated spot-scanning proton beam therapy (RGPT) system with inserted fiducial markers can irradiate a moving tumor with high accuracy. As gated treatments increase the beam delivery time, this study aimed to investigate the frequency of intra-field adjustments corresponding to the baseline shift or drift and the beam delivery efficiency of a synchrotron-based RGPT system. Data from 118 patients corresponding to 127 treatment plans and 2810 sessions between October 2016 and March 2019 were collected. We quantitatively analyzed the proton beam delivery time, the difference between the ideal beam delivery time based on a simulated synchrotron magnetic excitation pattern and the actual treatment beam delivery time, frequency corresponding to the baseline shift or drift, and the gating efficiency of the synchrotron-based RGPT system according to the proton beam delivery machine log data. The mean actual beam delivery time was 7.1 min, and the simulated beam delivery time in an ideal environment with the same treatment plan was 2.9 min. The average difference between the actual and simulated beam delivery time per session was 4.3 min. The average frequency of intra-field adjustments corresponding to baseline shift or drift and beam delivery efficiency were 21.7% and 61.8%, respectively. Based on our clinical experience with a synchrotron-based RGPT system, we determined the frequency corresponding to baseline shift or drift and the beam delivery efficiency using the beam delivery machine log data. To maintain treatment accuracy within ± 2.0 mm, intra-field adjustments corresponding to baseline shift or drift were required in approximately 20% of cases. Further improvements in beam delivery efficiency may be realized by shortening the beam delivery time.
Assuntos
Neoplasias , Terapia com Prótons , Marcadores Fiduciais , Humanos , Neoplasias/radioterapia , Cintilografia , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador , SíncrotronsRESUMO
To improve the penumbra of low-energy beams used in spot-scanning proton therapy, various collimation systems have been proposed and used in clinics. In this paper, focused on patient-specific brass collimators, the collimator-scattered protons' physical and biological effects were investigated. The Geant4 Monte Carlo code was used to model the collimators mounted on the scanning nozzle of the Hokkaido University Hospital. A systematic survey was performed in water phantom with various-sized rectangular targets; range (5-20 cm), spread-out Bragg peak (SOBP) (5-10 cm), and field size (2 × 2-16 × 16 cm2 ). It revealed that both the range and SOBP dependences of the physical dose increase had similar trends to passive scattering methods, that is, it increased largely with the range and slightly with the SOBP. The physical impact was maximized at the surface (3%-22% for the tested geometries) and decreased with depth. In contrast, the field size (FS) dependence differed from that observed in passive scattering: the increase was high for both small and large FSs. This may be attributed to the different phase-space shapes at the target boundary between the two dose delivery methods. Next, the biological impact was estimated based on the increase in dose-averaged linear energy transfer (LETd ) and relative biological effectiveness (RBE). The LETd of the collimator-scattered protons were several keV/µm higher than that of unscattered ones; however, since this large increase was observed only at the positions receiving a small scattered dose, the overall LETd increase was negligible. As a consequence, the RBE increase did not exceed 0.05. Finally, the effects on patient geometries were estimated by testing two patient plans, and a negligible RBE increase (0.9% at most in the critical organs at surface) was observed in both cases. Therefore, the impact of collimator-scattered protons is almost entirely attributed to the physical dose increase, while the RBE increase is negligible.
Assuntos
Algoritmos , Melanoma/radioterapia , Terapia com Prótons/instrumentação , Terapia com Prótons/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Rabdomiossarcoma/radioterapia , Neoplasias Uveais/radioterapia , Criança , Simulação por Computador , Relação Dose-Resposta à Radiação , Humanos , Método de Monte Carlo , Órgãos em Risco/efeitos da radiação , Eficiência Biológica Relativa , Espalhamento de RadiaçãoRESUMO
Fluorination of resist materials is an effective method used to enhance the energy deposition of extreme ultraviolet (EUV) light in the fabrication of next-generation semiconductor devices. The dynamics of radical ions are important to understand when considering the radiation-chemistry of the resist materials using EUV and electron beam lithography. Here, the dynamics of the radical anions and cations of benzenes with one or two 2-hydroxyhexafluoroisopropyl groups (HFABs) were studied using radiolysis techniques. The formation of dimer radical cations was observed only in the monosubstituted benzene solutions of 1,2-dichloroethane. If the compound contained more than two substituents, it was found to hinder the necessary π-π overlapping. Pulse radiolysis of HFABs in tetrahydrofuran showed a characteristic spectral shift of the radical anion within the region of several hundred nanoseconds. From the results of low-temperature spectroscopy and density functional calculations, it is suggested that excess electrons of the 2-hydroxyhexafluoroisopropyl group of the radical anions cause dissociation into neutral radicals.
RESUMO
PURPOSE: To quantitatively evaluate the achievable performance of volumetric imaging based on lung motion modeling by principal component analysis (PCA). METHODS: In volumetric imaging based on PCA, internal deformation was represented as a linear combination of the eigenvectors derived by PCA of the deformation vector fields evaluated from patient-specific four-dimensional-computed tomography (4DCT) datasets. The volumetric image was synthesized by warping the reference CT image with a deformation vector field which was evaluated using optimal principal component coefficients (PCs). Larger PCs were hypothesized to reproduce deformations larger than those included in the original 4DCT dataset. To evaluate the reproducibility of PCA-reconstructed volumetric images synthesized to be close to the ground truth as possible, mean absolute error (MAE), structure similarity index measure (SSIM) and discrepancy of diaphragm position were evaluated using 22 4DCT datasets of nine patients. RESULTS: Mean MAE and SSIM values for the PCA-reconstructed volumetric images were approximately 80 HU and 0.88, respectively, regardless of the respiratory phase. In most test cases including the data of which motion range was exceeding that of the modeling data, the positional error of diaphragm was less than 5 mm. The results suggested that large deformations not included in the modeling 4DCT dataset could be reproduced. Furthermore, since the first PC correlated with the displacement of the diaphragm position, the first eigenvector became the dominant factor representing the respiration-associated deformations. However, other PCs did not necessarily change with the same trend as the first PC, and no correlation was observed between the coefficients. Hence, randomly allocating or sampling these PCs in expanded ranges may be applicable to reasonably generate an augmented dataset with various deformations. CONCLUSIONS: Reasonable accuracy of image synthesis comparable to those in the previous research were shown by using clinical data. These results indicate the potential of PCA-based volumetric imaging for clinical applications.
Assuntos
Neoplasias Pulmonares , Humanos , Neoplasias Pulmonares/diagnóstico por imagem , Análise de Componente Principal , Reprodutibilidade dos Testes , Movimento (Física) , Diagnóstico por Imagem , Respiração , Tomografia Computadorizada Quadridimensional/métodosRESUMO
Respiratory motion considerably influences dose distribution, and thus clinical outcomes in radiotherapy for lung cancer. Breath holding, breath coaching, respiratory gating with external surrogates, and mathematical predicting models all have inevitable uncertainty due to the unpredictable variations of internal tumor motion. The amplitude of the same tumor can vary with standard deviations > 5 mm occurring in 23% of T1-2N0M0 non-small cell lung cancers. Residual motion varied 1-6 mm (95th percentile) for the 40% duty cycle of respiratory gating with external surrogates. The 4-D computed tomography is vulnerable to problems relating to the external surrogates. Real-time 4-D radiotherapy (4DRT), where the temporal changes in anatomy during the delivery of radiotherapy are explicitly considered in real time, is emerging as a new method to reduce these known sources of uncertainty. Fluoroscopic, real-time tumor-tracking technology using internal fiducial markers near the tumor has ± 2 mm accuracy, and has achieved promising clinical results when used with X-ray therapy. Instantaneous irradiation based on real-time verification of internal fiducial markers is considered the minimal requisite for real-time 4DRT of lung cancers at present. Real-time tracking radiotherapy using gamma rays from positron emitters in tumors is in the preclinical research stage, but has been successful in experiments in small animals. Real-time tumor tracking via spot-scanning proton beam therapy has the capability to cure large lung cancers in motion, and is expected to be the next-generation real-time 4DRT.
Assuntos
Tomografia Computadorizada Quadridimensional , Neoplasias Pulmonares/diagnóstico por imagem , Neoplasias Pulmonares/radioterapia , Animais , HumanosRESUMO
PURPOSE: In accurate proton spot-scanning therapy, continuous target tracking by fluoroscopic x ray during irradiation is beneficial not only for respiratory moving tumors of lung and liver but also for relatively stationary tumors of prostate. Implanted gold markers have been used with great effect for positioning the target volume by a fluoroscopy, especially for the cases of liver and prostate with the targets surrounded by water-equivalent tissues. However, recent studies have revealed that gold markers can cause a significant underdose in proton therapy. This paper focuses on prostate cancer and explores the possibility that multiple-field irradiation improves the underdose effect by markers on tumor-control probability (TCP). METHODS: A Monte Carlo simulation was performed to evaluate the dose distortion effect. A spherical gold marker was placed at several characteristic points in a water phantom. The markers were with two different diameters of 2 and 1.5 mm, both visible on fluoroscopy. Three beam arrangements of single-field uniform dose (SFUD) were examined: one lateral field, two opposite lateral fields, and three fields (two opposite lateral fields + anterior field). The relative biological effectiveness (RBE) was set to 1.1 and a dose of 74 Gy (RBE) was delivered to the target of a typical prostate size in 37 fractions. The ratios of TCP to that without the marker (TCP(r)) were compared with the parameters of the marker sizes, number of fields, and marker positions. To take into account the dependence of biological parameters in TCP model, α∕ß values of 1.5, 3, and 10 Gy (RBE) were considered. RESULTS: It was found that the marker of 1.5 mm diameter does not affect the TCPs with all α∕ß values when two or more fields are used. On the other hand, if the marker diameter is 2 mm, more than two irradiation fields are required to suppress the decrease in TCP from TCP(r) by less than 3%. This is especially true when multiple (two or three) markers are used for alignment of a patient. CONCLUSIONS: It is recommended that 1.5-mm markers be used to avoid the reduction of TCP as well as to spare the surrounding critical organs, as long as the markers are visible on x-ray fluoroscopy. When 2-mm markers are implanted, more than two fields should be used and the markers should not be placed close to the distal edge of any of the beams.
Assuntos
Marcadores Fiduciais , Método de Monte Carlo , Terapia com Prótons , Doses de Radiação , Radioterapia/normas , Humanos , Masculino , Probabilidade , Neoplasias da Próstata/radioterapia , Dosagem RadioterapêuticaRESUMO
PURPOSE: To evaluate the biological effectiveness of magnetic resonance (MR)-guided proton beam therapy, comprehensively characterizing the dose and dose-averaged linear energy transfer (LETd ) distributions under a magnetic field is necessary. Although detailed analysis has characterized curved beam paths and distorted dose distributions, the impact of a magnetic field on LETd should also be explored to determine the proton relative biological effectiveness (RBE). Hence, this initial study aims to present a basic analysis of LETd distributions in the presence of a magnetic field using Monte Carlo simulation (MCS). METHODS: Geant4 MCS (version 10.1.p01) was performed to calculate the LETd distribution of proton beams. The incident beam energies were set to 70.2, 140.8, and 220 MeV, and both zero- and finite-emittance pencil beams as well as scanned field were simulated. A transverse magnetic field of 0-3 T was applied within a water phantom placed at the isocenter, and the three-dimensional dose and LETd distributions in the phantom were calculated. Then, the depth profiles of LETd along the curved trajectory and the lateral LETd profile at the Bragg peak (BP) depth were analyzed under changing energies and magnetic fields. In addition, for zero- and finite-emittance beams, the correlation of the lateral asymmetries between the dose and LETd distributions were analyzed. Finally, spread-out Bragg peak (SOBP) fields were simulated to assess the depth-dependent asymmetry of the LETd distributions. RESULTS: A transverse magnetic field distorted the lateral LETd distribution of a pencil beam at close to the BP, and the magnitude of the distortion at the BP increased for higher energy beams and larger magnetic fields. For a zero-emittance beam, the differences in LETd between the left and right D20 positions were relatively large; the difference in LETd was 1.5 and 2.3 keV/µm at 140.8 and 220 MeV, respectively, at a magnetic field of 1.5 T. These asymmetries were pronounced at positions where the dose asymmetries were large. The size of the asymmetry was less substantial for a finite-emittance beam and even less for a scanned field. However, a 1.5-keV/µm difference still remained between the left and right D20 positions of a scanned field penumbra for a 220 MeV beam under the same magnetic field. For the SOBP field, it was found that the distal region of SOBP had the highest LETd distortions, followed by the central and proximal regions for the middle-sized SOBP (5 × 5 × 5 cm3 ), whereas the degree of LETd distortion did not vary much with depth for the 10 × 10 × 10-cm3 SOBP field. CONCLUSION: Our results indicate that not only the dose but also LETd distortions should be considered to accurately evaluate the biological effectiveness of MR-guided proton beam therapy.
Assuntos
Transferência Linear de Energia , Terapia com Prótons , Campos Magnéticos , Método de Monte Carlo , Terapia com Prótons/métodos , Prótons , Eficiência Biológica RelativaRESUMO
PURPOSE: In the scanning beam delivery of protons, different portions of the target are irradiated with different linear energy transfer protons with various time intervals and irradiation times. This research aimed to evaluate the spatially dependent biological effectiveness of protracted irradiation in scanning proton therapy. METHODS: One and two parallel opposed fields plans were created in water phantom with the prescribed dose of 2 Gy. Three scenarios (instantaneous, continuous, and layered scans) were used with the corresponding beam delivery models. The biological dose (physical dose × relative biological effectiveness) was calculated using the linear quadratic model and the theory of dual radiation action to quantitatively evaluate the dose delivery time effect. In addition, simulations using clinical plans (postoperative seminoma and prostate tumor cases) were conducted to assess the impact of the effects on the dose volume histogram parameters and homogeneity coefficient (HC) in targets. RESULTS: In a single-field plan of water phantom, when the treatment time was 19 min, the layered-scan scenario showed a decrease of <0.2% (almost 3.3%) in the biological dose from the plan on the distal (proximal) side because of the high (low) dose rate. This is in contrast to the continuous scenario, where the biological dose was almost uniformly decreased over the target by approximately 3.3%. The simulation with clinical geometry showed that the decrease rates in D99% were 0.9% and 1.5% for every 10 min of treatment time prolongation for postoperative seminoma and prostate tumor cases, respectively, whereas the increase rates in HC were 0.7% and 0.2%. CONCLUSIONS: In protracted irradiation in scanning proton therapy, the spatially dependent dose delivery time structure in scanning beam delivery can be an important factor for accurate evaluation of biological effectiveness.
Assuntos
Terapia com Prótons , Humanos , Transferência Linear de Energia , Masculino , Imagens de Fantasmas , Prótons , Planejamento da Radioterapia Assistida por Computador , Eficiência Biológica RelativaRESUMO
The purpose of this work is to show the usefulness of a prediction method of tumor location based on partial least squares regression (PLSR) using multiple fiducial markers. The trajectory data of respiratory motion of four internal fiducial markers inserted in lungs were used for the analysis. The position of one of the four markers was assumed to be the tumor position and was predicted by other three fiducial markers. Regression coefficients for prediction of the position of the tumor-assumed marker from the fiducial markers' positions is derived by PLSR. The tracking error and the gating error were evaluated assuming two possible variations. First, the variation of the position definition of the tumor and the markers on treatment planning computed tomograhy (CT) images. Second, the intra-fractional anatomical variation which leads the distance change between the tumor and markers during the course of treatment. For comparison, rigid predictions and ordinally multiple linear regression (MLR) predictions were also evaluated. The tracking and gating errors of PLSR prediction were smaller than those of other prediction methods. Ninety-fifth percentile of tracking/gating error in all trials were 3.7/4.1 mm, respectively in PLSR prediction for superior-inferior direction. The results suggested that PLSR prediction was robust to variations, and clinically applicable accuracy could be achievable for targeting tumors.
Assuntos
Sistemas Computacionais , Marcadores Fiduciais , Tomografia Computadorizada Quadridimensional , Processamento de Imagem Assistida por Computador/métodos , Imageamento Tridimensional , Análise dos Mínimos Quadrados , Neoplasias/diagnóstico por imagem , Radiografia Intervencionista , Erros de Diagnóstico , Fluoroscopia , Humanos , Modelos Lineares , Movimento (Física) , Neoplasias/radioterapia , Planejamento da Radioterapia Assistida por Computador , RespiraçãoRESUMO
PURPOSE: To show the feasibility of real-time CT image generation technique utilizing internal fiducial markers that facilitate the evaluation of internal deformation. METHODS: In the proposed method, a linear regression model that can derive internal deformation from the displacement of fiducial markers is built for each voxel in the training process before the treatment session. Marker displacement and internal deformation are derived from the four-dimensional computed tomography (4DCT) dataset. In the treatment session, the three-dimensional deformation vector field is derived according to the marker displacement, which is monitored by the real-time imaging system. The whole CT image can be synthesized by deforming the reference CT image with a deformation vector field in real-time. To show the feasibility of the technique, image synthesis accuracy and tumor localization accuracy were evaluated using the dataset generated by extended NURBS-Based Cardiac-Torso (XCAT) phantom and clinical 4DCT datasets from six patients, containing 10 CT datasets each. In the validation with XCAT phantom, motion range of the tumor in training data and validation data were about 10 and 15 mm, respectively, so as to simulate motion variation between 4DCT acquisition and treatment session. In the validation with patient 4DCT dataset, eight CT datasets from the 4DCT dataset were used in the training process. Two excluded inhale CT datasets can be regarded as the datasets with large deformations more than training dataset. CT images were generated for each respiratory phase using the corresponding marker displacement. Root mean squared error (RMSE), normalized RMSE (NRMSE), and structural similarity index measure (SSIM) between the original CT images and the synthesized CT images were evaluated as the quantitative indices of the accuracy of image synthesis. The accuracy of tumor localization was also evaluated. RESULTS: In the validation with XCAT phantom, the mean NRMSE, SSIM, and three-dimensional tumor localization error were 7.5 ± 1.1%, 0.95 ± 0.02, and 0.4 ± 0.3 mm, respectively. In the validation with patient 4DCT dataset, the mean RMSE, NRMSE, SSIM, and three-dimensional tumor localization error in six patients were 73.7 ± 19.6 HU, 9.2 ± 2.6%, 0.88 ± 0.04, and 0.8 ± 0.6 mm, respectively. These results suggest that the accuracy of the proposed technique is adequate when the respiratory motion is within the range of the training dataset. In the evaluation with a marker displacement larger than that of the training dataset, the mean RMSE, NRMSE, and tumor localization error were about 100 HU, 13%, and <2.0 mm, respectively, except for one case having large motion variation. The performance of the proposed method was similar to those of previous studies. Processing time to generate the volumetric image was <100 ms. CONCLUSION: We have shown the feasibility of the real-time CT image generation technique for volumetric imaging.
Assuntos
Marcadores Fiduciais , Neoplasias , Tomografia Computadorizada Quadridimensional , Humanos , Movimento (Física) , Imagens de FantasmasRESUMO
In spot scanning proton therapy (SSPT), the spot position relative to the target may fluctuate through tumor motion even when gating the radiation by utilizing a fiducial marker. We have established a procedure that evaluates the delivered dose distribution by utilizing log data on tumor motion and spot information. The purpose of this study is to show the reliability of the dose distributions for liver tumors treated with real-time-image gated SSPT (RGPT). In the evaluation procedure, the delivered spot information and the marker position are synchronized on the basis of log data on the timing of the spot irradiation and fluoroscopic X-ray irradiation. Then a treatment planning system reconstructs the delivered dose distribution. Dose distributions accumulated for all fractions were reconstructed for eight liver cases. The log data were acquired in all 168 fractions for all eight cases. The evaluation was performed for the values of maximum dose, minimum dose, D99, and D5-D95 for the clinical target volumes (CTVs) and mean liver dose (MLD) scaled by the prescribed dose. These dosimetric parameters were statistically compared between the planned dose distribution and the reconstructed dose distribution. The mean difference of the maximum dose was 1.3% (95% confidence interval [CI]: 0.6%-2.1%). Regarding the minimum dose, the mean difference was 0.1% (95% CI: -0.5%-0.7%). The mean differences of D99, D5-D95 and MLD were below 1%. The reliability of dose distributions for liver tumors treated with RGPT-SSPT was shown by the evaluation of the accumulated dose distributions.
Assuntos
Neoplasias Hepáticas/radioterapia , Terapia com Prótons , Dosagem Radioterapêutica , Relação Dose-Resposta à Radiação , Humanos , Neoplasias Hepáticas/diagnóstico por imagem , Reprodutibilidade dos Testes , Tomografia Computadorizada por Raios XRESUMO
PURPOSE: Ionoacoustics is one of the promising approaches to verify the beam range in proton therapy. However, the weakness of the wave signal remains a main hindrance to its application in clinics. Here we studied the potential use of a fixed-field alternating gradient accelerator (FFA), one of the accelerator candidates for future proton therapy. For such end, magnitude of the pressure wave and range accuracy achieved by the short-pulsed beam of FFA were assessed, using both simulation and experimental procedure. METHODS: A 100 MeV proton beam from the FFA was applied on a water phantom, through the acrylic wall. The beam range measured by the Bragg peak (BP)-ionization chamber (BPC) was 77.6 mm, while the maximum dose at BP was estimated to be 0.35 Gy/pulse. A hydrophone was placed 20 mm downstream of the BP, and signals were amplified and stored by a digital oscilloscope, averaged, and low-pass filtered. Time-of-flight (TOF) and two relative TOF values were analyzed in order to determine the beam range. Furthermore, an acoustic wave transport simulation was conducted to estimate the amplitude of the pressure waves. RESULTS: The range calculated when using two relative TOF was 78.16 ± 0.01 and 78.14 ± 0.01 mm, respectively, both values being coherent with the range measured by the BPC (the difference was 0.5-0.6 mm). In contrast, utilizing the direct TOF resulted in a range error of 1.8 mm. Fivefold and 50-fold averaging were required to suppress the range variation to below 1 mm for TOF and relative TOF measures, respectively. The simulation suggested the magnitude of pressure wave at the detector exceeded 7 Pascal. CONCLUSION: A submillimeter range accuracy was attained with a pulsed beam of about 21 ns from an FFA, at a clinical energy using relative TOF. To precisely quantify the range with a single TOF measurement, subsequent improvement in the measuring system is required.
Assuntos
Terapia com Prótons , Prótons , Acústica , Imagens de Fantasmas , Dosagem Radioterapêutica , SomRESUMO
PURPOSE: The purpose of this study is to evaluate the sublethal damage (SLD) repair effect in prolonged proton irradiation using the biophysical model with various cell-specific parameters of (α/ß)x and T1/2 (repair half time). At present, most of the model-based studies on protons have focused on acute radiation, neglecting the reduction in biological effectiveness due to SLD repair during the delivery of radiation. Nevertheless, the dose-rate dependency of biological effectiveness may become more important as advanced treatment techniques, such as hypofractionation and respiratory gating, come into clinical practice, as these techniques sometimes require long treatment times. Also, while previous research using the biophysical model revealed a large repair effect with a high physical dose, the dependence of the repair effect on cell-specific parameters has not been evaluated systematically. METHODS: Biological dose [relative biological effectiveness (RBE) × physical dose] calculation with repair included was carried out using the linear energy transfer (LET)-dependent linear-quadratic (LQ) model combined with the theory of dual radiation action (TDRA). First, we extended the dose protraction factor in the LQ model for the arbitrary number of different LET proton irradiations delivered sequentially with arbitrary time lags, referring to the TDRA. Using the LQ model, the decrease in biological dose due to SLD repair was systematically evaluated for spread-out Bragg peak (SOBP) irradiation in a water phantom with the possible ranges of both (α/ß)x and repair parameters ((α/ß)x = 1-15 Gy, T1/2 = 0-90 min). Then, to consider more realistic irradiation conditions, clinical cases of prostate, liver, and lung tumors were examined with the cell-specific parameters for each tumor obtained from the literature. Biological D99% and biological dose homogeneity coefficient (HC) were calculated for the clinical target volumes (CTVs), assuming dose-rate structures with a total irradiation time of 0-60 min. RESULTS: The differences in the cell-specific parameters resulted in considerable variation in the repair effect. The biological dose reduction found at the center of the SOBP with 30 min of continuous irradiation varied from 1.13% to 14.4% with a T1/2 range of 1-90 min when (α/ß)x is fixed as 10 Gy. It varied from 2.3% to 6.8% with an (α/ß)x range of 1-15 Gy for a fixed value of T1/2 = 30 min. The decrease in biological D99% per 10 min was 2.6, 1.2, and 3.0% for the prostate, liver, and lung tumor cases, respectively. The value of the biological D99% reduction was neither in the order of (α/ß)x nor prescribed dose, but both comparably contributed to the repair effect. The variation of HC was within the range of 0.5% for all cases; therefore, the dose distribution was not distorted. CONCLUSION: The reduction in biological dose caused by the SLD repair largely depends on the cell-specific parameters in addition to the physical dose. The parameters should be considered carefully in the evaluation of the repair effect in prolonged proton irradiation.
Assuntos
Terapia com Prótons , Prótons , Relação Dose-Resposta à Radiação , Transferência Linear de Energia , Masculino , Imagens de Fantasmas , Radiação Ionizante , Eficiência Biológica RelativaRESUMO
In contrast to conventional X-ray therapy, proton beam therapy (PBT) can confine radiation doses to tumours because of the presence of the Bragg peak. However, the precision of the treatment is currently limited by the uncertainty in the beam range. Recently, a unique range verification methodology has been proposed based on simulation studies that exploit spherical ionoacoustic waves with resonant frequency (SPIREs). SPIREs are emitted from spherical gold markers in tumours initially introduced for accurate patient positioning when the proton beam is injected. These waves have a remarkable property: their amplitude is linearly correlated with the residual beam range at the marker position. Here, we present proof-of-principle experiments using short-pulsed proton beams at the clinical dose to demonstrate the feasibility of using SPIREs for beam-range verification with submillimetre accuracy. These results should substantially contribute to reducing the range uncertainty in future PBT applications.
Assuntos
Ouro/efeitos da radiação , Imagens de Fantasmas , Terapia com Prótons/métodos , Prótons , Ouro/química , Humanos , Método de Monte Carlo , Terapia com Prótons/instrumentação , Dosagem Radioterapêutica , Som , Água/químicaRESUMO
UNLABELLED: An autoradiography method revealed intratumoral inhomogeneity in various solid tumors. It is becoming increasingly important to estimate intratumoral inhomogeneity. However, with low spatial resolution and high scatter noise, it is difficult to detect intratumoral inhomogeneity in clinical settings. We developed a new PET system with CdTe semiconductor detectors to provide images with high spatial resolution and low scatter noise. Both phantom images and patients' images were analyzed to evaluate intratumoral inhomogeneity. METHODS: This study was performed with a cold spot phantom that had 6-mm-diameter cold sphenoid defects, a dual-cylinder phantom with an adjusted concentration of 1:2, and an "H"-shaped hot phantom. These were surrounded with water. Phantom images and (18)F-FDG PET images of patients with nasopharyngeal cancer were compared with conventional bismuth germanate PET images. Profile curves for the phantoms were measured as peak-to-valley ratios to define contrast. Intratumoral inhomogeneity and tumor edge sharpness were evaluated on the images of the patients. RESULTS: The contrast obtained with the semiconductor PET scanner (1.53) was 28% higher than that obtained with the conventional scanner (1.20) for the 6-mm-diameter cold sphenoid phantom. The contrast obtained with the semiconductor PET scanner (1.43) was 27% higher than that obtained with the conventional scanner (1.13) for the dual-cylinder phantom. Similarly, the 2-mm cold region between 1-mm hot rods was identified only by the new PET scanner and not by the conventional scanner. The new PET scanner identified intratumoral inhomogeneity in more detail than the conventional scanner in 6 of 10 patients. The tumor edge was sharper on the images obtained with the new PET scanner than on those obtained with the conventional scanner. CONCLUSION: These phantom and clinical studies suggested that this new PET scanner has the potential for better identification of intratumoral inhomogeneity, probably because of its high spatial resolution and low scatter noise.
Assuntos
Neoplasias/diagnóstico por imagem , Neoplasias/patologia , Tomografia por Emissão de Pósitrons/instrumentação , Semicondutores/instrumentação , Adulto , Idoso , Bismuto , Compostos de Cádmio , Carcinoma de Células Escamosas/diagnóstico por imagem , Carcinoma de Células Escamosas/metabolismo , Carcinoma de Células Escamosas/patologia , Feminino , Germânio , Glucose/metabolismo , Humanos , Masculino , Neoplasias Nasofaríngeas/diagnóstico por imagem , Neoplasias Nasofaríngeas/metabolismo , Neoplasias Nasofaríngeas/patologia , Neoplasias/metabolismo , Imagens de Fantasmas , Telúrio , Fatores de TempoRESUMO
Aim: Patients of proton beam therapy (PBT) for prostate cancer had been continuously growing in number due to its promising characteristics of high dose distribution in the tumor target and a sharp distal fall-off. Considering the large number of proton beam facilities in Japan, the further increase of patients undergoing this treatment is due to the emendations by Japanese National Health Insurance (NHI) and the development of medical equipment and technology, it is necessary to know what kind of research and advancements has been done on proton therapy for prostate cancer in the country. For these reasons, this literature review was conducted. The aim of this review is to identify and discuss research studies of proton beam therapy for prostate cancer in Japan. These include observational, interventional, and secondary data analysis of published articles. Method: A literature review on published works related to proton beam therapy for prostate cancer in Japan was conducted using articles that were gathered in the PubMed database of June 2018. We went through abstracts and manuscripts written in English with the keywords 'proton beam therapy', 'prostate cancer', and 'Japan'. Results: A total of 23 articles were included. Fourteen articles were observational studies, most of which focused on the adverse effects of Proton Beam Therapy (PBT). Seven articles were interventional studies related on treatment planning, equipment parts, as well as target positioning. Two were secondary data analysis. The included studies were published in 13 different journals by different institutions using various equipment. Conclusion: Despite the favorable results of proton beam therapy, future research should include more patients and longer follow-up schedules to clarify the definitive role of PBT, yet, up to recent retrospective studies, included in this paper, concluded that PBT can be a suitable treatment option for localized prostate cancer. In addition, interventional studies were conducted by several institutions to further embellish proton therapy.
RESUMO
This study proposes a novel alternative range-verification method for proton beam with acoustic waves generated from spherical metal markers. When proton beam is incident on metal markers, most of the resulting pressure waves are confined in the markers because of the large difference in acoustic impedance between the metal and tissue. However, acoustic waves with frequency equal to marker's resonant frequency escape this confinement; the marker briefly acts as an acoustic transmitter. Herein, this phenomenon is exploited to measure the range of the proton beam. We test the proposed strategy in 3-D simulations, combining the dose calculations with modelling of acoustic-wave propagation. A spherical gold marker of 2.0 mm diameter was placed in water with a 60 MeV proton beam incident on it. We investigated the dependence of pressure waves on the width of beam pulse and marker position. At short beam pulse, specific high-frequency acoustic waves of 1.62 MHz originating from the marker were observed in wave simulations, whose amplitude correlated with the distance between the marker and Bragg peak. Results indicate that the Bragg peak position can be estimated by measuring the acoustic wave amplitudes from the marker, using a single detector properly designed for the resonance frequency.