Satoru Utsunomiya

A study on a dental device for the prevention of mucosal dose enhancement caused by backscatter radiation from dental alloy during external beam radiotherapy

The changes in dose distribution caused by backscatter radiation from a common commercial dental alloy (Au–Ag–Pd dental alloy; DA) were investigated to identify the optimal material and thicknesses of a dental device (DD) for effective prevention of mucositis. To this end, 1 cm3 of DA was irradiated with a 6-MV X-ray beam (100 MU) in a field size of 10 × 10 cm2 using a Novalis TX linear accelerator. Ethylene vinyl acetate copolymer, polyolefin elastomer, and polyethylene terephthalate (PET) were selected as DD materials. The depth dose along the central axis was determined with respect to the presence/absence of DA and DDs at thicknesses of 1–10 mm using a parallel-plate ionization chamber. The dose in the absence of DDs showed the lowest value at a distance of 5 mm from the DA surface and gradually increased with distance between the measurement point and the DA surface for distances of ≥5 mm. Except for PET, no significant difference between the DA dose curves for the presence and absence of DDs was observed. In the dose curve, PET showed a slightly higher dose for DA with DD than for DA without DD for thicknesses of ≥4 mm. The findings herein suggest that the optimal DD material for preventing local dose enhancement of the mucosa caused by DA backscatter radiation should have a relatively low atomic number and physical density and that optimal DD thickness should be chosen considering backscatter radiation and percentage depth dose.

Superiority of a soft tissue-based setup using cone-beam computed tomography over a bony structure-based setup in intensity-modulated radiotherapy for prostate cancer.

The purpose of this study was to test the superiority of a soft tissue‐based setup using cone‐beam computed tomography (CBCT) to a bony structure‐based setup using the ExacTrac system in intensity‐modulated radiotherapy (IMRT) for prostate cancer. We studied 20 patients with localized prostate cancer who received IMRT between November 2010 and February 2012. After the initial setup, the pelvic bony structure‐based setup and ExacTrac system were applied. After that, CBCT and a soft tissue‐based setup were used. A shift in the isocenter between the ExacTrac‐based and CBCT‐based setup was recorded in the anterior–posterior (AP), superior–inferior (SI), and left–right (LR) axes. The shift was considered an interfractional prostate shift. Post‐treatment CBCT was also taken once a week to measure the intrafractional prostate shift, based on the coordinates of the isocenter between pre‐ and post‐treatment CBCT. The planning target volume (PTV) margins were determined using van Herks method. We measured the elapsed time required for soft tissue matching and the entire treatment time using CBCT. The means±standard deviation(SD) of the inter‐ and intrafractional shifts were 0.9±2.8 mm and −0.3±1.4 mm in the AP, 0.9±2.2 mm and −0.1±1.2 mm in the SI, and 0.1±0.7 mm and −0.1±0.7 mm in the LR directions. The PTV margins in the cases of bony structure‐based and soft tissue‐based setups were 7.3 mm and 2.7 mm in the AP, 5.8 mm and 2.3 mm in the SI, and 1.9 mm and 1.2 mm in the LR directions. Even though the median elapsed time using CBCT was expanded in 5.9 min, the PTV margins were significantly reduced. We found the calculated PTV margins in the soft tissue‐based setup using CBCT were small, and this arrangement was superior to the bony structure‐based setup in prostate IMRT. PACS numbers: 87.19.ru, 87.55.T‐

Clinical commissioning of a new patient positioning system, SyncTraX FX4, for intracranial stereotactic radiotherapy

Abstract Background & Aims A new real‐time tracking radiotherapy (RTRT) system, the SyncTraX FX4 (Shimadzu, Kyoto, Japan), consisting of four X‐ray tubes and four ceiling‐mounted flat panel detectors (FPDs) combined with a linear accelerator, was installed at Uonuma Kikan Hospital (Niigata, Japan) for the first time worldwide. In addition to RTRT, the SyncTraX FX4 system enables bony structure‐based patient verification. Here we provide the first report of this systems clinical commissioning for intracranial stereotactic radiotherapy (SRT). Materials & Methods A total of five tests were performed for the commissioning: evaluations of (1) the systems image quality; (2) the imaging and treatment coordinate coincidence; and (3) the localization accuracy of cone‐beam computed tomography (CBCT) and SyncTraX FX4; (4) the measurement of air kerma; (5) an end‐to‐end test. Results & Discussion The tests revealed the following. (1) All image quality evaluation items satisfied each acceptable criterion in all FPDs. (2) The maximum offsets among the centers were ≤0.40 mm in all combinations of the FPD and X‐ray tubes (preset). (3) The isocenter localization discrepancies between CBCT and preset #3 in the SyncTraX FX4 system were 0.29 ± 0.084 mm for anterior‐posterior, −0.19 ± 0.13 mm for superior‐inferior, 0.076 ± 0.11 mm for left‐right, −0.11 ± 0.066° for rotation, −0.14 ± 0.064° for pitch, and 0.072±0.058° for roll direction. the Pearsons product‐moment correlation coefficient between the two systems was >0.98 in all directions. (4) The mean air kerma value for preset #3 was 0.11 ± 0.0002 mGy in predefined settings (80 kV, 200 mA, 50 msec). (5) For 16 combinations of gantry and couch angles, median offset value in all presets was 0.31 mm (range 0.14–0.57 mm). Conclusion Our results demonstrate a competent performance of the SyncTraX FX4 system in terms of the localization accuracy for intracranial SRT.

Definitive chemoradiotherapy with low-dose continuous 5-fluorouracil reduces hematological toxicity without compromising survival in esophageal squamous cell carcinoma patients

Background and purpose To compare chemoradiotherapy (CRT) with low-dose continuous 5-fluorouracil (5FU) to CRT with 5FU+cisplatin (CDDP) for esophageal squamous cell carcinoma (ESCC) in a retrospective cohort study. Methods and materials We reviewed the cases of Stage I–IV ESCC patients who underwent definitive CRT in 2000–2014. Concomitant chemotherapy was one of the three regimens: (1) high-dose intermittent 5FU and CDDP (standard-dose FP: SDFP), (2) low-dose continuous 5FU and CDDP (LDFP), or (3) low-dose continuous 5FU (LD5FU). The general selection criteria for chemotherapy were: SDFP for patients aged <70 yrs; LDFP for those aged 70–74 yrs; LD5FU for those aged ≥75 yrs or with performance status (PS) ≥3. Propensity scores were derived with chemotherapy (LD5FU vs. 5FU+CDDP) as the dependent variable. Results In a multivariate analysis, chemotherapy (LD5FU vs. SDFP, p = .24; LDFP vs. SDFP, p = .52) did not affect the overall survival (OS). LD5FU caused significantly less grade 3–4 leukopenia (9%) compared to SDFP (47%) and LDFP (44%) (p < .001). In a propensity-matched analysis, LD5FU affected neither OS (HR 1.06; 95%CI 0.55–2.05; p = .87) nor progression-free survival (HR 0.95, 95%CI 0.50–1.81; p = .87). Conclusion CRT with low-dose continuous 5FU may be a less toxic option for elderly ESCC patients.

Respiratory gating and multifield technique radiotherapy for esophageal cancer

PurposeTo investigate the effects of a respiratory gating and multifield technique on the dose-volume histogram (DVH) in radiotherapy for esophageal cancer.Methods and materialsTwenty patients who underwent four-dimensional computed tomography for esophageal cancer were included. We retrospectively created the four treatment plans for each patient, with or without the respiratory gating and multifield technique: No gating-2-field, No gating-4-field, Gating-2-field, and Gating-4-field plans. We compared the DVH parameters of the lung and heart in the No gating-2-field plan with the other three plans.ResultIn the comparison of the parameters in the No gating-2-field plan, there are significant differences in the Lung V5Gy, V20Gy, mean dose with all three plans and the Heart V25Gy–V40Gy with Gating-2-field plan, V35Gy, V40Gy, mean dose with No Gating-4-field plan and V30Gy–V40Gy, and mean dose with Gating-4-field plan. The lung parameters were smaller in the Gating-2-field plan and larger in the No gating-4-field and Gating-4-field plans. The heart parameters were all larger in the No gating-2-field plan.ConclusionThe lung parameters were reduced by the respiratory gating technique and increased by the multifield technique. The heart parameters were reduced by both techniques. It is important to select the optimal technique according to the risk of complications.

SU-C-BRC-05: Monte Carlo Calculations to Establish a Simple Relation of Backscatter Dose Enhancement Around High-Z Dental Alloy to Its Atomic Number

PURPOSE To establish a simple relation of backscatter dose enhancement around a high-Z dental alloy in head and neck radiation therapy to its average atomic number based on Monte Carlo calculations. METHODS The PHITS Monte Carlo code was used to calculate dose enhancement, which is quantified by the backscatter dose factor (BSDF). The accuracy of the beam modeling with PHITS was verified by comparing with basic measured data namely PDDs and dose profiles. In the simulation, a high-Z alloy of 1 cm cube was embedded into a tough water phantom irradiated by a 6-MV (nominal) X-ray beam of 10 cm × 10 cm field size of Novalis TX (Brainlab). The ten different materials of high-Z alloys (Al, Ti, Cu, Ag, Au-Pd-Ag, I, Ba, W, Au, Pb) were considered. The accuracy of calculated BSDF was verified by comparing with measured data by Gafchromic EBT3 films placed at from 0 to 10 mm away from a high-Z alloy (Au-Pd-Ag). We derived an approximate equation to determine the relation of BSDF and range of backscatter to average atomic number of high-Z alloy. RESULTS The calculated BSDF showed excellent agreement with measured one by Gafchromic EBT3 films at from 0 to 10 mm away from the high-Z alloy. We found the simple linear relation of BSDF and range of backscatter to average atomic number of dental alloys. The latter relation was proven by the fact that energy spectrum of backscatter electrons strongly depend on average atomic number. CONCLUSION We found a simple relation of backscatter dose enhancement around high-Z alloys to its average atomic number based on Monte Carlo calculations. This work provides a simple and useful method to estimate backscatter dose enhancement from dental alloys and corresponding optimal thickness of dental spacer to prevent mucositis effectively.

SU-E-T-392: A Sensitivity Analysis for Evaluating Dosimetric Impact of MLC Modeling Parameter Accuracy On IMRT Treatment Plans

PURPOSE To quantify and evaluate the dosimetric impact of MLC modeling parameter accuracy on IMRT treatment plans by performing a sensitivity analysis. METHODS Physician-approved 8 prostate and 4 head-and-neck IMRT treatment plans in which 7 and 9 fields dynamic MLC technique was utilized respectively were retrospectively analyzed. The dose re-calculation was performed with Eclipse treatment planning system (ver.8.9, Varian Medical Systems) after MLC modeling parameters such as leaf transmission factor (LTF) and dosimetric leaf gap (DLG) were manually shifted from the original value. The change in DVH parameters (PTV D95%, rectum wall D25% and bladder wall D35% for prostate cases; PTV D95%, parotid gland mean dose and spinal canal maximum dose for head-and-neck cases) and point doses were plotted as a function of errors in MLC modeling parameters and the dosimetric impact was quantified by sensitivity (slope of an approximate linear function). The 2D map of dose sensitivity to LTF and DLG were created and overlaid onto CT image of the patient using MATLAB software (ver.8.2.0.701, MathWorks). RESULTS The changes in all analyzed DVH parameters had almost linear relationship with errors in LTF and DLG. The sensitivities of DVH parameters for head-and-neck cases were higher than prostate cases overall. For prostate cases, sensitivities of DVH parameters to DLG were higher than LTF and the opposite results were obtained for head-and-neck cases. According to the 2D map, LTF and DLG had high dose sensitivity around PTV edge especially at the overlap between PTV and rectum for a prostate case. The region of high dose sensitivity to LTF was more blurred and widely scattered than DLG. CONCLUSION The dosimetric impact of MLC modeling parameter accuracy on IMRT treatment plans were successfully quantified by a sensitivity analysis of DVH parameters and a 2D map of dose sensitivity overlaid onto CT image of patients.

SU-E-T-465: Dose Calculation Method for Dynamic Tumor Tracking Using a Gimbal-Mounted Linac

PURPOSE Dynamic tumor tracking using the gimbal-mounted linac (Vero4DRT, Mitsubishi Heavy Industries, Ltd., Japan) has been available when respiratory motion is significant. The irradiation accuracy of the dynamic tumor tracking has been reported to be excellent. In addition to the irradiation accuracy, a fast and accurate dose calculation algorithm is needed to validate the dose distribution in the presence of respiratory motion because the multiple phases of it have to be considered. A modification of dose calculation algorithm is necessary for the gimbal-mounted linac due to the degrees of freedom of gimbal swing. The dose calculation algorithm for the gimbal motion was implemented using the linear transformation between coordinate systems. METHODS The linear transformation matrices between the coordinate systems with and without gimbal swings were constructed using the combination of translation and rotation matrices. The coordinate system where the radiation source is at the origin and the beam axis along the z axis was adopted. The transformation can be divided into the translation from the radiation source to the gimbal rotation center, the two rotations around the center relating to the gimbal swings, and the translation from the gimbal center to the radiation source. After operating the transformation matrix to the phantom or patient image, the dose calculation can be performed as the no gimbal swing. The algorithm was implemented in the treatment planning system, PlanUNC (University of North Carolina, NC). The convolution/superposition algorithm was used. The dose calculations with and without gimbal swings were performed for the 3 × 3 cm2 field with the grid size of 5 mm. RESULTS The calculation time was about 3 minutes per beam. No significant additional time due to the gimbal swing was observed. CONCLUSIONS The dose calculation algorithm for the finite gimbal swing was implemented. The calculation time was moderate.

SU‐E‐T‐170: A Survey of Quality Assurance in Intensity‐Modulated Radiation Therapy in Japan

PURPOSE To investigate the status of the implementation of quality assurance (QA) for intensity-modulated radiation therapy (IMRT) in Japan using a questionnaire survey. METHODS The questionnaire consisted of six sections: (1) clinical uses of IMRT; (2) IMRT-related equipment; verification of the (3) absorbed dose; (4) dose distribution; and (5) fluence map; and (6) acceptance criteria for each verification. There were 55 questions in total. RESULTS The questionnaire was completed for 124 institutions. IMRT was performed for prostate cancer in 120 institutions (96.8%), followed by head and neck cancer in 81 (65.3%), and brain tumors in 67 (54.0%). Although at least four individuals were engaged in IMRT QA in 54.0% of the institutions, the number of full-time persons involved in IMRT QA was two or less in 110 institutions (88.7%). This indicated that most institutions in Japan have a staff shortage. Dynamic IMRT was the most common beam delivery technique (52.5%) for prostate cancer, followed by segmental IMRT (25.0%) and volumetric modulated arc radiotherapy (15.0%). Similar tendencies were seen for head and neck cancer and brain tumors. More than 90% of the institutions verified both the absorbed dose and dose distribution. In more than 50% of the institutions, these were verified in each and every beam. The acceptance criterion for the absorbed dose verification was set to +/-3% in at least 80% of the institutions. Gafchromic film was used for the majority of dose distribution verification. The acceptance criteria for dose distribution verification mainly involved gamma analysis and a comparison of dose profiles; however, the judgment of acceptance did not depend on the results of the gamma analysis. CONCLUSION This survey increases our understanding of how institutions currently perform IMRT QA analysis. This understanding will help to move institutions toward more standardization of IMRT QA in Japan. This research was funded by the Japan Society of Medical Physics.