Assessment and validation of glottic motion using cone-beam CT and real-time cine MRI.

PURPOSE: This study aimed to assess the margin for the planning target volume (PTV) using the Van Herk formula. We then validated the proposed margin by real-time magnetic resonance imaging (MRI). METHODS: An analysis of cone-beam computed tomography (CBCT) data from early glottic cancer patients was performed to evaluate organ motion. Deformed clinical target volumes (CTV) after rigid registration were acquired using the Velocity program (Varian Medical Systems, Palo Alto, CA, USA). Systematic (Σ) and random errors (σ) were evaluated. The margin for the PTV was defined as 2.5 Σ + 0.7 σ according to the Van Herk formula. To validate this margin, we accrued healthy volunteers. Sagittal real-time cine MRI was conducted using the ViewRay system (ViewRay Inc., Oakwood Village, OH, USA). Within the obtained sagittal images, the vocal cord was delineated. The movement of the vocal cord was summed up and considered as the internal target volume (ITV). We then assessed the degree of overlap between the ITV and the PTV (vocal cord plus margins) by calculating the volume overlap ratio, represented as (ITV∩PTV)/ITV. RESULTS: CBCTs of 17 early glottic patients were analyzed. Σ and σ were 0.55 and 0.57 for left-right (LR), 0.70 and 0.60 for anterior-posterior (AP), and 1.84 and 1.04 for superior-inferior (SI), respectively. The calculated margin was 1.8 mm (LR), 2.2 mm (AP), and 5.3 mm (SI). Four healthy volunteers participated for validation. A margin of 3 mm (AP) and 5 mm (SI) was applied to the vocal cord as the PTV. The average volume overlap ratio between ITV and PTV was 0.92 (range 0.85-0.99) without swallowing and 0.77 (range 0.70-0.88) with swallowing. CONCLUSION: By evaluating organ motion by using CBCT, the margin was 1.8 (LR), 2.2 (AP), and 5.3 mm (SI). The margin acquired using CBCT fitted well in real-time cine MRI. Given that swallowing during radiotherapy can result in a substantial displacement, it is crucial to consider strategies aimed at minimizing swallowing and related motion.

Development of an anthropomorphic multimodality pelvic phantom for quantitative evaluation of a deep-learning-based synthetic computed tomography generation technique.

PURPOSE: The objective of this study was to fabricate an anthropomorphic multimodality pelvic phantom to evaluate a deep-learning-based synthetic computed tomography (CT) algorithm for magnetic resonance (MR)-only radiotherapy. METHODS: Polyurethane-based and silicone-based materials with various silicone oil concentrations were scanned using 0.35 T MR and CT scanner to determine the tissue surrogate. Five tissue surrogates were determined by comparing the organ intensity with patient CT and MR images. Patient-specific organ modeling for three-dimensional printing was performed by manually delineating the structures of interest. The phantom was finally fabricated by casting materials for each structure. For the quantitative evaluation, the mean and standard deviations were measured within the regions of interest on the MR, simulation CT (CTsim ), and synthetic CT (CTsyn ) images. Intensity-modulated radiation therapy plans were generated to assess the impact of different electron density assignments on plan quality using CTsim and CTsyn . The dose calculation accuracy was investigated in terms of gamma analysis and dose-volume histogram parameters. RESULTS: For the prostate site, the mean MR intensities for the patient and phantom were 78.1 ± 13.8 and 86.5 ± 19.3, respectively. The mean intensity of the synthetic image was 30.9 Hounsfield unit (HU), which was comparable to that of the real CT phantom image. The original and synthetic CT intensities of the fat tissue in the phantom were -105.8 ± 4.9 HU and -107.8 ± 7.8 HU, respectively. For the target volume, the difference in D95% was 0.32 Gy using CTsyn with respect to CTsim values. The V65Gy values for the bladder in the plans using CTsim and CTsyn were 0.31% and 0.15%, respectively. CONCLUSION: This work demonstrated that the anthropomorphic phantom was physiologically and geometrically similar to the patient organs and was employed to quantitatively evaluate the deep-learning-based synthetic CT algorithm.

3D star shot analysis using MAGAT gel dosimeter for integrated imaging and radiation isocenter verification of MR-Linac system.

PURPOSE: This study aims to investigate a star shot analysis using a three-dimensional (3D) gel dosimeter for the imaging and radiation isocenter verification of a magnetic resonance linear accelerator (MR-Linac). METHODS: A mixture of methacrylic acid, gelatin, and tetrakis (hydroxymethyl) phosphonium chloride, called MAGAT gel, was fabricated. One MAGAT gel for each Linac and MR-Linac was irradiated under six gantry angles. A 6 MV photon beam of Linac and a 6 MV flattening filter free beam of MR-Linac were delivered to two MAGAT gels and EBT3 films. MR images were acquired by MR-Linac with a clinical sequence (i.e., TrueFISP). The 3D star shot analysis for seven consecutive slices of the MR images with TrueFISP was performed. The 2D star shot analysis for the central plane of the gel was compared to the results from the EBT3 films. The radius of isocircle (ICr ) and the distance between the center of the circle and the center marked on the image (ICd ) were evaluated. RESULTS: For MR-Linac with MAGAT gel measurements, ICd at the central plane was 0.46 mm for TrueFISP. Compared to EBT3 film measurements, the differences in ICd and ICr for both Linac and MR-Linac were within 0.11 and 0.13 mm, respectively. For the 3D analysis, seven consecutive slices of TrueFISP images were analyzed and the maximum radii of isocircles (ICr_max ) were 0.18 mm for Linac and 0.73 mm for MR-Linac. The tilting angles of radiation axis were 0.31° for Linac and 0.10° for MR-Linac. CONCLUSION: The accuracy of 3D star shot analysis using MAGAT gel was comparable to that of EBT3 film, having a capability for integrated analysis for imaging isocenter and radiation isocenter. 3D star shot analysis using MAGAT gel can provide 3D information of radiation isocenter, suggesting a quantitative extent of gantry-tilting.

Impact of High-Dose Irradiation on Human iPSC-Derived Cardiomyocytes Using Multi-Electrode Arrays: Implications for the Antiarrhythmic Effects of Cardiac Radioablation.

Cardiac radioablation is emerging as an alternative option for refractory ventricular arrhythmias. However, the immediate acute effect of high-dose irradiation on human cardiomyocytes remains poorly known. We measured the electrical activities of human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) upon irradiation with 0, 20, 25, 30, 40, and 50 Gy using a multi-electrode array, and cardiomyocyte function gene levels were evaluated. iPSC-CMs showed to recover their electrophysiological activities (total active electrode, spike amplitude and slope, and corrected field potential duration) within 3-6 h from the acute effects of high-dose irradiation. The beat rate immediately increased until 3 h after irradiation, but it steadily decreased afterward. Conduction velocity slowed in cells irradiated with ≥25 Gy until 6-12 h and recovered within 24 h; notably, 20 and 25 Gy-treated groups showed subsequent continuous increase. At day 7 post-irradiation, except for cTnT, cardiomyocyte function gene levels increased with increasing irradiation dose, but uniquely peaked at 25-30 Gy. Altogether, high-dose irradiation immediately and reversibly modifies the electrical conduction of cardiomyocytes. Thus, compensatory mechanisms at the cellular level may be activated after the high-dose irradiation acute effects, thereby, contributing to the immediate antiarrhythmic outcome of cardiac radioablation for refractory ventricular arrhythmias.

Feasibility of dosimetric measurements using Al2O3:C OSL dosimeter during fluoroscopy-guided procedures.

This study investigated the feasibility of dosimetric measurements using Al2O3:C optically stimulated luminescence (OSL) dosimeters during fluoroscopy-guided procedures. The linearity and energy dependence of Al2O3:C OSL dosimeters were evaluated, and the air kerma rate at the operator's position was measured. The response of Al2O3:C OSL dosimeters to short, repetitive irradiations was compared to that of long uninterrupted irradiation. The change in response of the Al2O3:C OSL dosimeter under automatic exposure rate control (AERC) was evaluated with the use of various thicknesses of polymethyl-methacrylate (PMMA) plates (15-30 cm). The Al2O3:C OSL dosimeters could detect 5µGy and showed good linearity in doses of ≥10µGy (R2: 0.997-0.999,p< 0.001). The relative response of the Al2O3:C OSL dosimeter normalised to that of 36.8 keV was 0.828-1.101 at the energies investigated (30.6-46.0 keV). The air kerma rate at the operator's position was estimated to be 2.61-7.17µGy min-1depending on the heights representing different body parts. Repetitive short irradiations had no significant impact on the relative response of the Al2O3:C OSL dosimeters (p> 0.05). Despite a high energy dependence on the low energy beam used in fluoroscopy, the change in relative response of the Al2O3:C OSL dosimeter under AERC was within 5.7% depending on the thickness of the PMMA plates. Dosimetric measurement using Al2O3:C OSL dosimeters for patients and operators is feasible. However, one should be cautious about high standard deviations when measuring small doses of ≤20µGy using Al2O3:C OSL dosimeters. It is essential to perform intensive bleaching before measuring very small doses to minimise pre-irradiation counts.

Characteristics of the Exradin W1 scintillator in the magnetic field.

To investigate the angular dependency of the W1 scintillator with and without a magnetic field, the beam incidence angles to the detector varied from 0° to 360° at intervals of 30° when the detector was pointed in both the craniocaudal and right-to-left directions. The beam incidence angles also varied from 0° to 360° at intervals of 45° when the W1 scintillator was in the anterior-to-posterior direction. To investigate the field size dependency of the W1 scintillator with and without a magnetic field, the doses by an identical beam-on time were measured at various square field sizes and the measured doses were normalized to the dose at the field of 10.5 cm × 10.5 cm (FS10.5). With and without a magnetic field, the deviations of the doses to the dose at the beam incident angle of 0° were always less than 1% regardless of the dosimeter positioning relative to the magnetic field direction. When the field sizes were equal to or less than FS10.5, the differences in the output factors with and without a magnetic field were less than 0.7%. However, those were larger than 1% at fields larger than FS10.5, and up to 3.1%. The W1 scintillator showed no angular dependency to the magnetic field. Differences larger than 1% in the output factors with and without a magnetic field were observed at field sizes larger than 10.5 cm × 10.5 cm.

Confidence limits for patient-specific IMRT dose QA: a multi-institutional study in Korea.

This study aims to investigate tolerance levels for patient-specific IMRT dose QA (DQA) using the confidence limits (CL) determined by a multi-institutional study. Eleven institutions participated in the multi-institutional study in Korea. A total of 155 DQA measurements, consisting of point-dose differences (high- and low-dose regions) and gamma passing rates (composite and per-field) for IMRT patients with brain, head and neck (H&N), abdomen, and prostate cancers were examined. The Shapiro-Wilk test was used to evaluate the normality of data grouped by the treatment sites and the DQA methods. The confidence limit coefficients in cases of the normal distribution, and the two-sided Student's t-distribution were applied to determine the confidence limits for the grouped data. The Spearman's test was applied to assess the sensitivity of DQA results within the limited groups. The differences in CLs between the two confidence coefficients based on the normal and t-distributions were negligible for the point-dose data and the gamma passing rates with 3%/3 mm criteria. However, with 2%/2 mm criteria, the difference in CLs were 1.6% and 2.2% for composite and per-field measurements, respectively. This resulted from the large standard deviation and the more sensitive criteria of 2%/2 mm. There was no noticeable correlation among the different QA methods. Our multi-institutional study suggested that the CL was not a suitable metric for defining the tolerance level when the statistics of the sample group did not follow the normality and had a large standard deviation.

Assessment of potential jaw-tracking advantage using control point sequences of VMAT planning.

This study aims to evaluate the potential jaw-tracking advantage using control point sequences of volume volumetric modulated arc therapy (VMAT) planning. VMAT plans for patients with prostate and head and neck (H&N) cancers were converted into new static arc (SA) plans. The SA plan consisted of a series of static fields at each control point of the VMAT plan. All other machine parameters of the SA plan were perfectly identical to those of the original VMAT plan. The jaw-tracking static arc (JTSA) plans were generated with fields that closed the jaws of each SA field into the multileaf collimators (MLCs) aperture. The dosimetric advantages of JTSA over SA were evaluated in terms of a dose-volume histogram (DVH) of organ at risk (OAR) after renormalizing both plans to make the same target coverage. Both plans were delivered to the MatriXX-based COMPASS system for 3D volume dose verification. The average jaw size reduction of the JTSA along the X direction was 3.1 ± 0.9 cm for prostate patients and 6.9 ± 1.9 cm for H&N patients. For prostate patients, the organs far from the target showed larger sparing (3.7%-8.1% on average) in JTSA than the organs adjacent to the target (1.1%-1.5%). For the H&N plans, the mean dose reductions for all organs ranged from 4.3% to 11.9%. The dose reductions were more significant in the dose regions of D80, D90, and D95 than the dose regions of D5, D10, and D20 for all patients. Likewise, the deliverability and reproducibility of jaw-tracking plan were validated. The measured dosimetric advantage of JTSA over SA coincided with the calculated one above.

Improvement of performance for flexible film dosimeter by incorporating additive agents.

Objective.To evaluate the reduction in energy dependence and aging effect of the lithium salt of pentacosa-10,-12-diynoic acid (LiPCDA) films with additives including aluminum oxide (Al2O3), propyl gallate (PG), and disodium ethylenediaminetetracetate (EDTA).Approach. LiPCDA films exhibited energy dependence on kilovoltage (kV) and megavoltage (MV) photon energies and experienced deterioration over time. Evaluations were conducted with added Al2O3and antioxidants to mitigate these issues, and films were produced with and without Al2O3to assess energy dependence. The films were irradiated at doses of 0, 3, 6, and 12 cGy at photon energies of 75 kV, 105 kV, 6 MV, 10 MV, and 15 MV. For the energy range of 75 kV to 15 MV, the mean and standard deviation (std) were calculated and compared for the values normalized to the net optical density (netOD) at 6 MV, corresponding to identical dose levels. To evaluate the aging effect, PG and disodium EDTA were incorporated into the films: sample C with 1% PG, sample D with 2% PG, sample E with 0.62% disodium EDTA added to sample D, and sample F with 1.23% disodium EDTA added to sample D.Main results. Films containing Al2O3demonstrated a maximum 15.8% increase in mean normalized values and a 15.1% reduction in std, reflecting a greater netOD reduction at kV than MV energies, which indicates less energy dependence in these films. When the OD of sample 1-4 depending on the addition of PG and disodium EDTA, was observed for 20 weeks, the transmission mode decreased by 8.7%, 8.3%, 29.3%, and 27.3%, respectively, while the reflection mode was 5.4%, 3.0%, 37.0%, and 34.5%, respectively.Significance. Al2O3effectively reduced the voltage and MV energy dependence. PG was more effective than disodium EDTA in preventing the deterioration of film performance owing to the aging effect.

Conversion of single-energy CT to parametric maps of dual-energy CT using convolutional neural network.

OBJECTIVES: We propose a deep learning (DL) multitask learning framework using convolutional neural network for a direct conversion of single-energy CT (SECT) to 3 different parametric maps of dual-energy CT (DECT): virtual-monochromatic image (VMI), effective atomic number (EAN), and relative electron density (RED). METHODS: We propose VMI-Net for conversion of SECT to 70, 120, and 200 keV VMIs. In addition, EAN-Net and RED-Net were also developed to convert SECT to EAN and RED. We trained and validated our model using 67 patients collected between 2019 and 2020. Single-layer CT images with 120 kVp acquired by the DECT (IQon spectral CT; Philips Healthcare, Amsterdam, Netherlands) were used as input, while the VMIs, EAN, and RED acquired by the same device were used as target. The performance of the DL framework was evaluated by absolute difference (AD) and relative difference (RD). RESULTS: The VMI-Net converted 120 kVp SECT to the VMIs with AD of 9.02 Hounsfield Unit, and RD of 0.41% compared to the ground truth VMIs. The ADs of the converted EAN and RED were 0.29 and 0.96, respectively, while the RDs were 1.99% and 0.50% for the converted EAN and RED, respectively. CONCLUSIONS: SECT images were directly converted to the 3 parametric maps of DECT (ie, VMIs, EAN, and RED). By using this model, one can generate the parametric information from SECT images without DECT device. Our model can help investigate the parametric information from SECT retrospectively. ADVANCES IN KNOWLEDGE: DL framework enables converting SECT to various high-quality parametric maps of DECT.

The impact of the new ESTRO-ACROP target volume delineation guidelines for postmastectomy radiotherapy after implant-based breast reconstruction on breast complications.

The European Society for Radiotherapy and Oncology-Advisory Committee in Radiation Oncology Practice (ESTRO-ACROP) updated a new target volume delineation guideline for postmastectomy radiotherapy (PMRT) after implant-based reconstruction. This study aimed to evaluate the impact on breast complications with the new guideline compared to the conventional guidelines. In total, 308 patients who underwent PMRT after tissue expander or permanent implant insertion from 2016 to 2021 were included; 184 received PMRT by the new ESTRO-ACROP target delineation (ESTRO-T), and 124 by conventional target delineation (CONV-T). The endpoints were major breast complications (infection, necrosis, dehiscence, capsular contracture, animation deformity, and rupture) requiring re-operation or re-hospitalization and any grade ≥2 breast complications. With a median follow-up of 36.4 months, the cumulative incidence rates of major breast complications at 1, 2, and 3 years were 6.6%, 10.3%, and 12.6% in the ESTRO-T group, and 9.7%, 15.4%, and 16.3% in the CONV-T group; it did not show a significant difference between the groups (p = 0.56). In multivariable analyses, target delineation is not associated with the major complications (sHR = 0.87; p = 0.77). There was no significant difference in any breast complications (3-year incidence, 18.9% vs. 23.3%, respectively; p = 0.56). Symptomatic RT-induced pneumonitis was developed in six (3.2%) and three (2.4%) patients, respectively. One local recurrence occurred in the ESTRO-T group, which was within the ESTRO-target volume. The new ESTRO-ACROP target volume guideline did not demonstrate significant differences in major or any breast complications, although it showed a tendency of reduced complication risks. As the dosimetric benefits of normal organs and comparable oncologic outcomes have been reported, further analyses with long-term follow-up are necessary to evaluate whether it could be connected to better clinical outcomes.

A multi-institutional study for tolerance and action levels of IMRT dose quality assurance measurements in Korea.

The purpose of this study was to suggest tolerance levels for IMRT DQA measurements using confidence limits determined by a multi-institutional study in Korea. Ten institutions were grouped into LINAC (seven linear accelerators) and TOMO (three tomotherapy machines). The DQA processes consisted of point (high- and low-dose regions) and planar (per-field and composite-field) dose measurements using an ion chamber and films (or 2D detector array) inserted into a custom-made acryl phantom (LINAC) or a cheese phantom (TOMO). The five mock structures developed by AAPM TG-119 were employed, but the prostate as well as the H&N structures were modified according to Korean patients' anatomy. The point measurements were evaluated in a ratio of measured and planned doses, while the planar dose distributions were assessed using two gamma criteria of 2 mm/2% and 3 mm/3%. The confidence limit (|mean + 1.96 σ|) for point measurements was determined to be 3.0% in high-dose regions and 5.0% in low-dose regions. The average percentage of points passing the gamma criteria of 2 mm/2% and 3mm/3% for per-field measurements was 92.7 ± 6.5% and 98.2 ± 2.8%, respectively. Thus, the corresponding confidence limit was 79.1% and 92.7%, respectively. The gamma passing rate averaged over all mock tests and institutions for composite-field measurements was 86.1 ± 6.5% at 2 mm/2% and 95.3 ± 3.8% at 3 mm/3%, leading to the confidence limit of 73.3% and 87.9%, respectively. There was no significant difference in the tolerance levels of point dose measurements between LINAC and TOMO groups. In spite of the differences in mock structures and dosimetry tools, our tolerance levels were comparable to those of AAPM and ESTRO guidelines.

Extension of matRad with a modified microdosimetric kinetic model for carbon ion treatment planning: Comparison with Monte Carlo calculation.

BACKGROUND: Treatment planning is essential for in silico particle therapy studies. matRad is an open-source research treatment planning system (TPS) based on the local effect model, which is a type of relative biological effectiveness (RBE) model. PURPOSE: This study aims to implement a microdosimetric kinetic model (MKM) in matRad and develop an automation algorithm for Monte Carlo (MC) dose recalculation using the TOPAS code. In addition, we provide the developed MKM extension as open-source tool for users. METHODS: Carbon beam data were generated using TOPAS MC pencil beam irradiation. We parameterized the TOPAS MC beam data with a double-Gaussian fit and modeled the integral depth doses and lateral spot profiles in the range of 100-430 MeV/u. To implement the MKM, the specific energy data table for Z = 1-6 and integrated depth-specific energy data were acquired based on the Kiefer-Chatterjee track structure and TOPAS MC simulation, respectively. Generic data were integrated into matRad, and treatment planning was performed based on these data. The optimized plan parameters were automatically converted into MC simulation input. Finally, the matRad TPS and TOPAS MC simulations were compared using the RBE-weighted dose calculation results. A comparison was made for three geometries: homogeneous water phantom, inhomogeneous phantom, and patient. RESULTS: The RBE-weighted dose (DRBE ) distribution agreed with TOPAS MC within 1.8% for all target sizes for the homogeneous phantom. For the inhomogeneous phantom, the relative difference in the range of 80% of the prescription dose in the distal fall-off region (R80) between the matRad TPS and TOPAS MC was 0.6% (1.1 mm). DRBE between the TPS and the MC was within 4.0%. In the patient case, the difference in the dose-volume histogram parameters for the target volume between the TPS and the MC was less than 2.7%. The relative difference in R80 was 0.7% (1.2 mm). CONCLUSIONS: The MKM was successfully implemented in matRad TPS, and the RBE-weighted dose was comparable to that of TOPAS MC. The MKM-implemented matRad was released as an open-source tool. Further investigations with MC simulations can be conducted using this tool, providing a good option for carbon ion research.

Development of a quasi-3D dosimeter using radiochromic plastic for patient-specific quality assurance.

BACKGROUND: Patient-specific QA verification ensures patient safety and treatment by verifying radiation delivery and dose calculations in treatment plans for errors. However, a two-dimensional (2D) dose distribution is insufficient for detecting information on the three-dimensional (3D) dose delivered to the patient. In addition, 3D radiochromic plastic dosimeters (RPDs) such as PRESAGE® represent the volume effect in which the dosimeters have different sensitivities according to the size of the dosimeters. Therefore, to solve the volume effect, a Quasi-3D dosimetry system was proposed to perform patient-specific QA using predetermined-sized and multiple RPDs. PURPOSE: For patient-specific quality assurance (QA) in radiation treatment, this study aims to assess a quasi-3D dosimetry system using an RPD. METHODS: Gamma analysis was performed to verify the agreement between the measured and estimated dose distributions of intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT). We fabricated cylindrical RPDs and a quasi-3D dosimetry phantom. A practicability test for a pancreatic patient utilized a quasi-3D dosimetry device, an in-house RPD, and a quasi-3D phantom. The dose distribution of the VMAT design dictated the placement of nine RPDs. Moreover, a 2D diode array detector was used for 2D gamma analysis (MapCHECK2). The patient-specific QA was performed for IMRT, VMAT, and stereotactic ablative radiotherapy (SABR) in 20 prostate and head-and-neck patients. For each patient, six RPDs were positioned according to the dose distribution. VMAT SABR and IMRT/VMAT plans employed a 2%/2 mm gamma criterion, whereas IMRT/VMAT plans used a 3%/2 mm gamma criterion, a 10% threshold value, and a 90% passing rate tolerance. 3D gamma analysis was conducted using the 3D Slicer software. RESULTS: The average gamma passing rates with 2%/2 mm and 3%/3 mm criteria for relative dose distribution were 91.6% ± 1.4% and 99.4% ± 0.7% for the 3D gamma analysis using the quasi-3D dosimetry system, respectively, and 97.5% and 99.3% for 2D gamma analysis using MapCHECK2, respectively. The 3D gamma analysis for patient-specific QA of 20 patients showed passing rates of over 90% with 2%/2 mm, 3%/2 mm, and 3%/3 mm criteria. CONCLUSIONS: The quasi-3D dosimetry system was evaluated by performing patient-specific QAs with RPDs and quasi-3D phantom. The gamma indices for all RPDs showed more than 90% for 2%/2 mm, 3%/2 mm, and 3%/3 mm criteria. We verified the feasibility of a quasi-3D dosimetry system by performing the conventional patient-specific QA with the quasi-3D dosimeters.

Evaluation of initial patient setup methods for breast cancer between surface-guided radiation therapy and laser alignment based on skin marking in the Halcyon system.

BACKGROUND: This study was conducted to evaluate the efficiency and accuracy of the daily patient setup for breast cancer patients by applying surface-guided radiation therapy (SGRT) using the Halcyon system instead of conventional laser alignment based on the skin marking method. METHODS AND MATERIALS: We retrospectively investigated 228 treatment fractions using two different initial patient setup methods. The accuracy of the residual rotational error of the SGRT system was evaluated by using an in-house breast phantom. The residual translational error was analyzed using the couch position difference in the vertical, longitudinal, and lateral directions between the reference computed tomography and daily kilo-voltage cone beam computed tomography acquired from the record and verification system. The residual rotational error (pitch, yaw, and roll) was also calculated using an auto rigid registration between the two images based on Velocity. The total setup time, which combined the initial setup time and imaging time, was analyzed to evaluate the efficiency of the daily patient setup for SGRT. RESULTS: The average residual rotational errors using the in-house fabricated breast phantom for pitch, roll, and yaw were 0.14°, 0.13°, and 0.29°, respectively. The average differences in the couch positions for laser alignment based on the skin marking method were 2.7 ± 1.6 mm, 2.0 ± 1.2 mm, and 2.1 ± 1.0 mm for the vertical, longitudinal, and lateral directions, respectively. For SGRT, the average differences in the couch positions were 1.9 ± 1.2 mm, 2.9 ± 2.1 mm, and 1.9 ± 0.7 mm for the vertical, longitudinal, and lateral directions, respectively. The rotational errors for pitch, yaw, and roll without the surface-guided radiation therapy approach were 0.32 ± 0.30°, 0.51 ± 0.24°, and 0.29 ± 0.22°, respectively. For SGRT, the rotational errors were 0.30 ± 0.22°, 0.51 ± 0.26°, and 0.19 ± 0.13°, respectively. The average total setup times considering both the initial setup time and imaging time were 314 s and 331 s, respectively, with and without SGRT. CONCLUSION: We demonstrated that using SGRT improves the accuracy and efficiency of initial patient setups in breast cancer patients using the Halcyon system, which has limitations in correcting the rotational offset.

Quantitative radiomics approach to assess acute radiation dermatitis in breast cancer patients.

PURPOSE: We applied a radiomics approach to skin surface images to objectively assess acute radiation dermatitis in patients undergoing radiotherapy for breast cancer. METHODS: A prospective cohort study of 20 patients was conducted. Skin surface images in normal, polarized, and ultraviolet (UV) modes were acquired using a skin analysis device before starting radiotherapy ('Before RT'), approximately 7 days after the first treatment ('RT D7'), on 'RT D14', and approximately 10 days after the radiotherapy ended ('After RT D10'). Eighteen types of radiomic feature ratios were calculated based on the values acquired 'Before RT'. We measured skin doses in ipsilateral breasts using optically stimulated luminescent dosimeters on the first day of radiotherapy. Clinical evaluation of acute radiation dermatitis was performed using the Radiation Therapy Oncology Group scoring criteria on 'RT D14' and 'After RT D10'. Several statistical analysis methods were used in this study to test the performance of radiomic features as indicators of radiodermatitis evaluation. RESULTS: As the skin was damaged by radiation, the energy for normal mode and sum variance for polarized and UV modes decreased significantly for ipsilateral breasts, whereas contralateral breasts exhibited a smaller decrease with statistical significance. The radiomic feature ratios at 'RT D7' had strong correlations to skin doses and those at 'RT D14' and 'after RT D10' with statistical significance. CONCLUSIONS: The energy for normal mode and sum variance for polarized and UV modes demonstrated the potential to evaluate and predict acute radiation, which assists in its appropriate management.

Short-term and long-term effects of noninvasive cardiac radioablation for ventricular tachycardia: A single-center case series.

Background: Noninvasive cardiac radioablation is reported to be effective and safe for the treatment of ventricular tachycardia (VT). Objective: This study aimed to analyze the acute and long-term effects of VT radioablation. Methods: Patients with intractable VT or premature ventricular contraction (PVC)-induced cardiomyopathy were included in this study and treated using a single-fraction 25-Gy dose of cardiac radioablation. To quantitatively analyze the acute response after treatment, continuous electrocardiography monitoring was performed from 24 hours before to 48 hours after irradiation and at the 1-month follow-up. Long-term clinical safety and efficacy were assessed 1-year follow-up. Results: From 2019 to 2020, 6 patients were treated with radioablation for ischemic VT (n = 3), nonischemic VT (n = 2), or PVC-induced cardiomyopathy (n = 1). In the short-term assessment, the total burden of ventricular beats decreased by 49% within 24 hours after radioablation and further decreased by 70% at 1 month. The VT component decreased earlier and more dramatically than the PVC component (decreased by 91% and 57% at 1 month, respectively). In the long-term assessment, 5 patients showed complete (n = 3) or partial (n = 2) remission of ventricular arrhythmias. One patient showed recurrence at 10 months, which was successfully suppressed with medical treatment. The posttreatment PVC coupling interval was prolonged (+38 ms at 1 month). Ischemic VT burden decreased more markedly than nonischemic VT burden after radioablation. Conclusion: In this small case series of 6 patients, without a comparison group, cardiac radioablation appeared to decrease the intractable VT burden. A therapeutic effect was apparent within 1-2 days after treatment but was variable by etiology of cardiomyopathy.

Novel tongue-positioning device to reduce tongue motions during radiation therapy for head and neck cancer: Geometric and dosimetric evaluation.

This study aimed to assess the performance of a tongue-positioning device in interfractional tongue position reproducibility by cone-beam computed tomography (CBCT). Fifty-two patients treated with radiation therapy (RT) while using a tongue positioning device were included in the study. All patients were treated with 28 or 30 fractions using the volumetric modulated arc therapy technique. CBCT images were acquired at the 1st, 7th, 11th, 15th, 19th, 23th, and 27th fractions. Tongues on planning computed tomography (pCT) and CBCT images were contoured in the treatment planning system. Geometric differences in the tongue between pCT and CBCT were assessed by the Dice similarity coefficient (DSC) and averaged Hausdorff distance (AHD). Two-dimensional in vivo measurements using radiochromic films were performed in 13 patients once a week during sessions. The planned dose distributions were compared with the measured dose distributions using gamma analysis with criteria of 3%/3 mm. In all patients, the mean DSC at the 1st fraction (pCT versus 1st CBCT) was 0.80 while the mean DSC at the 27th fraction (pCT versus 27th CBCT) was 0.77 with statistical significance (p-value = 0.015). There was no statistically significant difference in DSC between the 1st fraction and any other fraction, except for the 27th fraction. There was statistically significant difference in AHD between the 1st fraction and the 19th, 23th, and 27th fractions (p-value < 0.05). In vivo measurements showed an average gamma passing rate of 90.54%. There was no significant difference between measurements at the 1st week and those at other weeks. The tongue geometry during RT was compared between pCT and CBCT. In conclusion, the novel tongue-positioning device was found to minimize interfractional variations in position and shape of the tongue.

Image-Guided Versus Conventional Brachytherapy for Locally Advanced Cervical Cancer: Experience of Single Institution with the Same Practitioner and Time Period.

PURPOSE: This study aimed to compare treatment outcomes and toxicity profile between imaged-guided brachytherapy (IGBT) versus conventional brachytherapy (CBT) performed by the same practitioner during the same time period. MATERIALS AND METHODS: Medical records of 104 eligible patients who underwent brachytherapy for locally advanced cervical cancer were retrospectively reviewed. Fifty patients (48.1%) underwent IGBT, and 54 (51.9%) patients underwent CBT. All patients underwent concurrent chemoradiation with cisplatin. High-dose-rate intracavitary brachytherapy with dose prescription of 25-30 Gy in 4-6 fractions was performed for all patients. Late lower gastrointestinal (GI) and urinary toxicities occurred more than 3 months after the end of brachytherapy were included for comparative and dosimetric analyses. RESULTS: The median follow-up period was 18.33 months (range, 3.25 to 38.43 months). There were no differences in oncologic outcomes between the two groups. The IGBT group had lower rate of actuarial grade ≥ 3 toxicity than the CBT group (2-year, 4.5% vs. 25.7%; p=0.030). Cumulative equieffective D2cc of sigmoid colon was significantly correlated with grade ≥ 2 lower GI toxicity (p=0.033), while equieffective D2cc of rectum (p=0.055) and bladder (p=0.069) showed marginal significance with corresponding grade ≥ 2 toxicities in the IGBT group. Half of grade ≥ 3 lower GI toxicities impacted GI tract above the rectum. Optimal thresholds of cumulative D2cc of sigmoid colon and rectum were 69.7 Gy and 70.8 Gy, respectively, for grade ≥ 2 lower GI toxicity. CONCLUSION: IGBT showed superior toxicity profile to CBT. Evaluating the dose to the GI tract above rectum by IGBT might prevent some toxicities.

Scanning methodology for contact lens-type ocular in vivo dosimeter (CLOD) dosimetry applying a silicone material.

PURPOSE: Contact lens-type ocular in vivo dosimeters (CLODs) were recently developed as the first in vivo dosimeter that can be worn directly on the eye to measure the dose delivered to the lens during radiotherapy. However, it has an inherent uncertainty because of its curved shape. Newton's ring effect inevitably occurs because the spacing between the glass window and the active layer is not constant. Furthermore, it involves a large uncertainty because the objective of the CLOD with such morphological characteristics is to measure the dose delivered to an out-of-field lens. In this study, we aimed to investigate the effects of various compensating materials on the sensitivity, accuracy, and uniformity of analysis using a curved CLOD. We developed a new scanning methodology that involves applying a compensating material to reduce the uncertainty caused by the air gap. METHODS: Four compensating materials-Dragon Skin™ 10 (DS), a transparent silicon material, SORTA-Clear™ 40 (SC), optical grease (OG), and air (no compensating material)-were used in this study. The CLOD was scanned in the reflective mode and transmission mode using each compensating material. We then examined the sensitivity, accuracy, and scan uniformity to evaluate the scanning methodology using compensating materials. RESULTS: The increase in sensitivity was the highest for OG compared to that for air in the reflective mode. On average, the sensitivity in the reflective mode was higher than that in the transmission mode by a factor of 2.5 for each dose. Among the four compensating materials, OG had the smallest uncertainty. Therefore, the best scan uniformity was achieved when OG was used. CONCLUSIONS: Scanning methodology was proposed in which a compensating material is applied for a curved lens-type dosimeter. Our results show that OG is the most suitable compensating material to obtain the best accuracy of dose analysis. Following this methodology, the scan uncertainty of curved dosimeters significantly decreased.