A preliminary study on rectal dose reduction associated with hyaluronic acid implantation in brachytherapy for prostate cancer.

Objectives: Hydrogel spacer (HS) was developed to reduce rectal toxicities caused by radiotherapy, but has been reported to cause major adverse events. Our institute has attempted to introduce a hyaluronic acid (HA) as an alternative spacer. This study aimed to compare rectal doses and geometric distributions between the HS and HA implantation in prostate cancer. Methods: HS and HA were inserted in 20 and 18 patients undergoing high-dose brachytherapy, respectively. The rectum spacer volumes injected were 10 mL and 22 mL, respectively. In the treatment planning system, 13.5 Gy was administered with common catheter positions. The rectal dose indices were assessed between the spacer groups for dosimetry evaluation. Distances between the prostate and rectum and configurations of the spacers were compared. Results: The mean doses irradiated to 0.1 and 2 mL of the rectum were 10.45 Gy and 6.71 Gy for HS, and 6.73 Gy and 4.90 Gy for HA (p<0.001). The mean minimum distances between the prostate and rectum were 1.23 cm and 1.79 cm for HS and HA, respectively (p<0.05). Geometrical configuration comparisons revealed that HA has a higher ability to expand the space than HS. Conclusion: The rectal dose reduction ability of HA is significantly greater than that of HS, suggesting its potential as a new spacer.

Relative biological effectiveness for epithermal neutron beam contaminated with fast neutrons in the linear accelerator-based boron neutron capture therapy system coupled to a solid-state lithium target.

This study aimed to quantify the relative biological effectiveness (RBE) for epithermal neutron beam contaminated with fast neutrons in the accelerator-based boron neutron capture therapy (BNCT) system coupled to a solid-state lithium target. The experiments were performed in National Cancer Center Hospital (NCCH), Tokyo, Japan. Neutron irradiation with the system provided by Cancer Intelligence Care Systems (CICS), Inc. was performed. X-ray irradiation, which was assigned as the reference group, was also performed using a medical linear accelerator (LINAC) equipped in NCCH. The four cell lines (SAS, SCCVII, U87-MG and NB1RGB) were utilized to quantify RBE value for the neutron beam. Before both of those irradiations, all cells were collected and dispensed into vials. The doses of 10% cell surviving fraction (SF) (D10) were calculated by LQ model fitting. All cell experiments were conducted in triplicate at least. Because the system provides not only neutrons, but gamma-rays, the contribution from the gamma-rays to the survival fraction were subtracted in this study. D10 value of SAS, SCCVII, U87-MG and NB1RGB for the neutron beam was 4.26, 4.08, 5.81 and 2.72 Gy, respectively, while that acquired by the X-ray irradiation was 6.34, 7.21, 7.12 and 5.49 Gy, respectively. Comparison of both of the D10 values, RBE value of SAS, SCCVII, U87-MG and NB1RGB for the neutron beam was calculated as 1.7, 2.2, 1.3 and 2.5, respectively, and the average RBE value was 1.9. This study investigated RBE of the epithermal neutron beam contaminated with fast neutrons in the accelerator-based BNCT system coupled to a solid-state lithium target.

Film measurement and analytical approach for assessing treatment accuracy and latency in a magnetic resonance-guided radiotherapy system.

PURPOSE: We measure the dose distribution of gated delivery for different target motions and estimate the gating latency in a magnetic resonance-guided radiotherapy (MRgRT) system. METHOD: The dose distribution accuracy of the gated MRgRT system (MRIdian, Viewray) was investigated using an in-house-developed phantom that was compatible with the magnetic field and gating method. This phantom contains a simulated tumor and a radiochromic film (EBT3, Ashland, Inc.). To investigate the effect of the number of beam switching and target velocity on the dose distribution, two types of target motions were applied. One is that the target was periodically moved at a constant velocity of 5 mm/s with different pause times (0, 1, 3, 10, and 20 s) between the motions. During different pause times, different numbers of beams were switched on/off. The other one is that the target was moved at velocities of 3, 5, 8, and 10 mm/s without any pause (i.e., continuous motion). The gated method was applied to these motions at MRIdian, and the dose distributions in each condition were measured using films. To investigate the relation between target motion and dose distribution in the gating method, we compared the results of the gamma analysis of the calculated and measured dose distributions. Moreover, we analytically estimated the gating latencies from the dose distributions measured using films and the gamma analysis results. RESULTS: The gamma pass rate linearly decreased with increasing beam switching and target velocity. The overall gating latencies of beam-hold and beam-on were 0.51 ± 0.17 and 0.35 ± 0.05 s, respectively. CONCLUSIONS: Film measurements highlighted the factors affecting the treatment accuracy of the gated MRgRT system. Our analytical approach, employing gamma analysis on films, can be used to estimate the overall latency of the gated MRgRT system.

Commissioning and performance evaluation of commercially available mobile imager for image guided total body irradiation.

BACKGROUND: The setup of lung shield (LS) in total body irradiation (TBI) with the computed radiography (CR) system is a time-consuming task and has not been quantitatively evaluated. The TBI mobile imager (TBI-MI) can solve this problem through real-time monitoring. Therefore, this study aimed to perform commissioning and performance evaluation of TBI-MI to promote its use in clinical practice. METHODS: The source-axis distance in TBI treatment, TBI-MI (CNERGY TBI, Cablon Medical B.V.), and the LS position were set to 400, 450, and 358 cm, respectively. The evaluation items were as follows: accuracy of image scaling and measured displacement error of LS, image quality (linearity, signal-to-noise ratio, and modulation transfer function) using an EPID QC phantom, optimal thresholding to detect intra-fractional motion in the alert function, and the scatter radiation dose from TBI-MI. RESULTS: The accuracy of image scaling and the difference in measured displacement of the LS was <4 mm in any displacements and directions. The image quality of TBI imager was slightly inferior to the CR image but was visually acceptable in clinical practice. The signal-to-noise ratio was improved at high dose rate. The optimal thresholding value to detect a 10-mm body displacement was determined to be approximately 5.0%. The maximum fraction of scattering radiation to irradiated dose was 1.7% at patient surface. CONCLUSION: MI-TBI can quantitatively evaluate LS displacement with acceptable image quality. Furthermore, real-time monitoring with alert function to detect intrafraction patient displacement can contribute to safe TBI treatment.

Failure modes and effects analysis study for accelerator-based Boron Neutron Capture Therapy.

BACKGROUND: Boron Neutron Capture Therapy (BNCT) has recently been used in clinical oncology thanks to recent developments of accelerator-based BNCT systems. Although there are some specific processes for BNCT, they have not yet been discussed in detail. PURPOSE: The aim of this study is to provide comprehensive data on the risk of accelerator-based BNCT system to institutions planning to implement an accelerator-based BNCT system. METHODS: In this study, failure mode and effects analysis (FMEA) was performed based on a treatment process map prepared for the accelerator-based BNCT system. A multidisciplinary team consisting of a medical doctor (MD), a registered nurse (RN), two medical physicists (MP), and three radiologic technologists (RT) identified the failure modes (FMs). Occurrence (O), severity (S), and detectability (D) were scored on a scale of 10, respectively. For each failure mode (FM), risk priority number (RPN) was calculated by multiplying the values of O, S, and D, and it was then categorized as high risk, very high risk, and other. Additionally, FMs were statistically compared in terms of countermeasures, associated occupations, and whether or not they were the patient-derived. RESULTS: The identified FMs for BNCT were 165 in which 30 and 17 FMs were classified as high risk and very high risk, respectively. Additionally, 71 FMs were accelerator-based BNCT-specific FMs in which 18 and 5 FMs were classified as high risk and very high risk, respectively. The FMs for which countermeasures were "Education" or "Confirmation" were statistically significantly higher for S than the others (p = 0.019). As the number of BNCT facilities is expected to increase, staff education is even more important. Comparing patient-derived and other FMs, O tended to be higher in patient-derived FMs. This could be because the non-patient-derived FMs included events that could be controlled by software, whereas the patient-derived FMs were impossible to prevent and might also depend on the patient's condition. Alternatively, there were non-patient-derived FMs with higher D, which were difficult to detect mechanically and were classified as more than high risk. In O, significantly higher values (p = 0.096) were found for FMs from MD and RN associated with much patient intervention compared to FMs from MP and RT less patient intervention. Comparing conventional radiotherapy and accelerator-based BNCT, although there were events with comparable risk in same FMs, there were also events with different risk in same FMs. They could be related to differences in the physical characteristics of the two modalities. CONCLUSIONS: This study is the first report for conducting a risk analysis for BNCT using FMEA. Thus, this study provides comprehensive data needed for quality assurance/quality control (QA/QC) in the treatment process for facilities considering the implementation of accelerator-based BNCT in the future. Because many BNCT-specific risks were discussed, it is important to understand the characteristics of BNCT and to take adequate measures in advance. If the effects of all FMs and countermeasures are discussed by multidisciplinary team, it will be possible to take countermeasures against individual FMs from many perspectives and provide BNCT more safely and effectively.

Planning study: prone versus supine position for stereotactic body radiotherapy in prostate by CyberKnife.

This study aimed to clarify the differences in radiotherapy dose characteristics and delivery efficiency between the supine and prone positions in patients with prostate cancer using the CyberKnife. The planning computed tomography (CT) and delineations of the prone position were obtained by rotating the supine CT images with delineations of 180° using image processing software. The optimization parameters for planning target volume (PTV) and organs at risk (OARs) were based on the prone position. The optimization parameters determined for the prone position were applied to the supine position for optimization and dose calculation. The dosimetric characteristics of the PTV and OARs, and delivery efficiency were compared between the two different patient positions. The plans in the prone position resulted in better PTV conformity index (nCI), rectum V90%, V80%, V75%, V50% and bladder V50%. A significant difference was observed in treatment time and depth along the central axis (dCAX) between the two plans. The mean treatment time per fraction and dCAX for the supine and prone positions were 20.9 ± 1.7 min versus 19.8 ± 1.3 min (P = 0.019) and 151.1 ± 33.6 mm versus 233.2 ± 8.8 mm (P < 0.001), respectively. In this study the prone position was found to improve dosimetric characteristics and delivery efficiency compared with the supine position during prostate cancer treatment with the CyberKnife.

Analyzing spatial distribution between 18F-fluorodeoxyglucose and 18F-boronophenylalanine positron emission tomography to investigate selection indicators for boron neutron capture therapy.

BACKGROUND: 18F-FDG PET is often utilized to determine BNCT selection due to the limited availability of 18F-BPA PET, which is performed by synthesizing 18F into the boron drug used for BNCT, although the uptake mechanisms between those are different. Additionally, only a few non-spatial point parameters, such as maximum SUV (SUVmax), have reported a correlation between those in previous studies. This study aimed to investigate the spatial accumulation pattern between those PET images in tumors, which would be expected to either show higher uptake on 18F-BPA PET or be utilized in clinical, to verify whether 18F-FDG PET could be used as a selection indicator for BNCT. METHODS: A total of 27 patients with 30 lesions (11 squamous cell carcinoma, 9 melanoma, and 10 rhabdomyosarcoma) who received 18F-FDG and 18F-BPA PET within 2 weeks were enrolled in this study. The ratio of metabolic tumor volumes (MTVs) to GTV, histogram indices (skewness/kurtosis), and the correlation of total lesion activity (TLA) and non-spatial point parameters (SUVmax, SUVpeak, SUVmin, maximum tumor-to-normal tissue ratio (Tmax/N), and Tmin/N) were evaluated. After local rigid registration between those images, distances of locations at SUVmax and the center of mass with MTVs on each image and similarity indices were also assessed along its coordinate. RESULTS: In addition to SUVmax, SUVpeak, and Tmax/N, significant correlations were found in TLA. The mean distance in SUVmax was [Formula: see text] and significantly longer than that in the center of mass with MTVs. The ratio of MTVs to GTV, skewness, and kurtosis were not significantly different. However, the similarities of MTVs were considerably low. The similarity indices of Dice similarity coefficient, Jaccard coefficient, and mean distance to agreement for MTV40 were [Formula: see text], [Formula: see text], and [Formula: see text] cm, respectively. Furthermore, it was worse in MTV50. In addition, spatial accumulation patterns varied in cancer types. CONCLUSIONS: Spatial accumulation patterns in tumors showed low similarity between 18F-FDG and 18F-BPA PET, although the various non-spatial point parameters were correlated. In addition, the spatial accumulation patterns were considerably different in cancer types. Therefore, the selection for BNCT using 18F-FDG PET should be compared carefully with using 18F-FBPA PET.

Technical note: Analysis of brachytherapy source movement by high-speed camera.

PURPOSE: To assess the accuracy of the movement of a brachytherapy source using a high-speed camera for evaluating source position, dwell time, and transit dose. METHODS: A high-speed camera was used to record the source position of an Ir-192 source relative to a ruler within a custom positioning jig in a remote afterloading system. The analyzed frames can be used to assess dwell positions and times. Treatment plans had multiple dwell times equal to 0.1, 0.5, 1.0, and 2.0 s in 2.5- and 5-mm step sizes. Images were acquired at a rate of 146 frames/s. Acquired images were processed to automatically track the actual source using the correlation between a template image and each frame. The brachytherapy dose calculation formalism (AAPM TG43-U1) was applied to each frame to evaluate the transit dose contribution to the total dose. RESULTS: The differences in measured source positions from the nominal for dwell times equal to 0.1, 0.5, 1.0, and 2.0 s in treatment plans were approximately ≤1 mm. The corresponding differences in measured dwell times from the nominal values at 5 mm steps were -15, -9, -5, and 5 ms, respectively. The source velocities at 5 mm steps were approximately 393 mm/s. The dose differences at 5 mm from the source movement with and without the transit dose for these dwell times were 38%, 7%, 3%, and 2%, respectively. CONCLUSIONS: Recording a brachytherapy source using a high-speed camera allowed the evaluation of positional and dwell time accuracies as well as dosimetry assessments, such as the transit dose, based on the application of AAPM TG-43U1.

In vivo dosimetry for testicular and scalp shielding in total skin electron therapy using a radiophotoluminescence glass dosimeter.

Mycosis fungoides (MF) is a common, low-grade non-Hodgkin's lymphoma of skin-homing T lymphocytes that can be treated via skin-directed radiotherapy. Our institution has implemented total skin electron therapy (TSET) with a 4.3 m source-to-surface distance (SSD) and 6 MeV electron beams with a beam spoiler. A 35-year-old male undergoing TSET desired to avoid radiotherapy-induced hair loss and temporary infertility; therefore, leakage dose to scalp and testicles was reduced with a special radiation shield composed of stacked lead sheets. The shields for the scalp and scrotal were of 3 mm and 6 mm, respectively. To assess leakage doses, a radiophotoluminescence glass dosimeter (RPLD) was placed at every fraction. The difference dose between the measured and prescribed dose at the calibration point was 2%. The top of the head and scrotal surface exhibited 18 cGy and 10 cGy, respectively. Thus, the dose to the scrotal surface was not beyond the testicular tolerance dose of 20 cGy. Results of semen analysis two months postradiotherapy were normal. There was no hair loss during or after radiation therapy. Therefore, the RPLD is a useful in vivo dosimeter that provides technical information on radiation shielding to allow for completion of TSET without hair loss or temporary infertility.

The influence of respiratory motion on the cumulative SUV-volume histogram and fractal analyses of intratumoral heterogeneity in PET/CT imaging.

OBJECTIVE: The purpose of this study was to investigate the influence of respiratory motion on the evaluation of the intratumoral heterogeneity of FDG uptake using cumulative SUV-volume histogram (CSH) and fractal analyses. METHODS: We used an NEMA IEC body phantom with a homogeneous hot sphere phantom (HO) and two heterogeneous hot sphere phantoms (HE1 and HE2). The background radioactivity of (18)F in the NEMA phantom was 5.3 kBq/mL. The ratio of radioactivity was 4:2:1 for the HO and the outer rims of the HE1 and HE2 phantoms, the inner cores of the HE1 and HE2 phantoms, and background, respectively. Respiratory motion was simulated using a motion table with an amplitude of 2 cm. PET/CT data were acquired using Biograph mCT in motionless and moving conditions. The PET images were analyzed by both CSH and fractal analyses. The area under the CSH (AUC-CSH) and the fractal dimension (FD) was used as quantitative metrics. RESULTS: In motionless conditions, the AUC-CSHs of the HO (0.80), HE1 (0.75) and HE2 (0.65) phantoms were different. They did not differ in moving conditions (HO, 0.63; HE1, 0.65; HE2, 0.60). The FD of the HO phantom (0.77) was smaller than the FDs of the HE1 (1.71) and HE2 (1.98) phantoms in motionless conditions; however, the FDs of the HO (1.99) and HE1 (2.19) phantoms were not different from each other and were smaller than that of the HE2 (3.73) phantom in moving conditions. CONCLUSION: Respiratory motion affected the results of the CSH and fractal analyses for the evaluation of the heterogeneity of the PET/CT images. The influence of respiratory motion was considered to vary depending on the object size.

The edge artifact in the point-spread function-based PET reconstruction at different sphere-to-background ratios of radioactivity.

OBJECTIVE: The aim of this study was to quantitatively evaluate the edge artifacts in PET images reconstructed using the point-spread function (PSF) algorithm at different sphere-to-background ratios of radioactivity (SBRs). METHODS: We used a NEMA IEC body phantom consisting of six spheres with 37, 28, 22, 17, 13 and 10 mm in inner diameter. The background was filled with (18)F solution with a radioactivity concentration of 2.65 kBq/mL. We prepared three sets of phantoms with SBRs of 16, 8, 4 and 2. The PET data were acquired for 20 min using a Biograph mCT scanner. The images were reconstructed with the baseline ordered subsets expectation maximization (OSEM) algorithm, and with the OSEM + PSF correction model (PSF). For the image reconstruction, the number of iterations ranged from one to 10. The phantom PET image analyses were performed by a visual assessment of the PET images and profiles, a contrast recovery coefficient (CRC), which is the ratio of SBR in the images to the true SBR, and the percent change in the maximum count between the OSEM and PSF images (Δ % counts). RESULTS: In the PSF images, the spheres with a diameter of 17 mm or larger were surrounded by a dense edge in comparison with the OSEM images. In the spheres with a diameter of 22 mm or smaller, an overshoot appeared in the center of the spheres as a sharp peak in the PSF images in low SBR. These edge artifacts were clearly observed in relation to the increase of the SBR. The overestimation of the CRC was observed in 13 mm spheres in the PSF images. In the spheres with a diameter of 17 mm or smaller, the Δ % counts increased with an increasing SBR. The Δ % counts increased to 91 % in the 10-mm sphere at the SBR of 16. CONCLUSIONS: The edge artifacts in the PET images reconstructed using the PSF algorithm increased with an increasing SBR. In the small spheres, the edge artifact was observed as a sharp peak at the center of spheres and could result in overestimation.

Improvement in PET/CT image quality in overweight patients with PSF and TOF.

OBJECTIVE: The aim of this study was to evaluate the effect of the point spread function (PSF) and time of flight (TOF) on PET/CT images of overweight patients in relation to the iteration number and the acquisition time. METHODS: This study consisted of a phantom study and a clinical study. The NEMA IEC body phantom and a 40 cm diameter large phantom (LG phantom) simulating an overweight patient were used in this study. Both phantoms were filled with (18)F solution with a sphere to background ratio of 4:1. The PET data were reconstructed with the baseline ordered-subsets expectation maximization (OSEM) algorithm, with the OSEM + PSF model, with the OSEM + TOF model and with the OSEM + PSF + TOF model. The clinical study was a retrospective analysis of 66 patients who underwent (18)F-FDG PET/CT. The image quality was evaluated using the background variability (coefficient of variance, CVphantom and CVliver) and the contrast (CONTHOT and SNR). RESULTS: In phantom study, the CVphantom of the LG phantom was higher than that of the NEMA phantom. The PSF decreased the CVphantom of the LG phantom to the NEMA phantom level. The TOF information accelerated the CVphantom plateau earlier. The best relationship between the CVphantom and the CONTHOT was observed for the OSEM + PSF + TOF. In clinical study, the combination of PSF and TOF decreased the CVliver for overweight patients to that for normal weight patients while it increased the SNR similarly between two patient groups. CONCLUSION: The combination of the PSF and TOF correction improved the image quality of the LG phantom and overweight patients.