Purpose Cardiac implantable electronic devices (CIEDs) were believed to possess a tolerance dose to malfunction during radiotherapy. Although recent studies have qualitatively suggested neutrons as a cause of malfunction, numerical understanding has not been reached. The purpose of this work is to quantitatively clarify the contribution of secondary neutrons from out‐of‐field irradiation to the malfunction of CIEDs as well as to deduce the frequency of malfunctions until completion of prostate cancer treatment as a typical case. Materials and Methods Measured data were gathered from the literature and were re‐analyzed. Firstly, linear relationship for a number of malfunctions to the neutron dose was suggested by theoretical consideration. Secondly, the accumulated number of malfunctions of CIEDs gathered from the literature was compared with the prescribed dose, scattered photon dose, and secondary neutron dose for analysis of their correlation. Thirdly, the number of malfunctions during a course of prostate treatment with high‐energy X‐ray, passive proton, and passive carbon‐ion beams was calculated while assuming the same response to malfunctions, where X‐rays consisted of 6‐MV, 10‐MV, 15‐MV, and 18‐MV beams. Monte Carlo simulation assuming simple geometry was performed for the distribution of neutron dose from X‐ray beams, where normalization factors were applied to the distribution so as to reproduce the empirical values. Results Linearity between risk and neutron dose was clearly found from the measured data, as suggested by theoretical consideration. The predicted number of malfunctions until treatment completion was 0, 0.02 ± 0.01, 0.30 ± 0.08, 0.65 ± 0.17, 0.88 ± 0.50, and 0.14 ± 0.04 when 6‐MV, 10‐MV, 15‐MV, 18‐MV, passive proton, and passive carbon‐ion beams, respectively, were employed, where the single model response to a malfunction of 8.6 ± 2.1 Sv−1 was applied. Conclusions Numerical understanding of the malfunction of CIEDs has been attained for the first time. It has been clarified that neutron dose is a good scale for the risk of CIEDs in radiotherapy. Prediction of the frequency of malfunction as well as discussion of the risk to CIEDs in radiotherapy among the multiple modalities have become possible. Because the present study quantitatively clarifies the neutron contribution to malfunction, revision of clinical guidelines is suggested.

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Cardiac implantable electronic devices (CIEDs) were believed to have a tolerance dose and that direct irradiation has to be avoided. Thus, no clinical guidelines have mentioned the feasibility of total body irradiation (TBI) with a CIED directly. The purpose of this work was to study a feasible and safe condition for TBI using a CIED. Eighteen CIEDs were directly irradiated by a 6-MV X-ray beam, where a non-neutron producible beam was employed for the removal of any neutron contribution to CIED malfunction. Irradiation up to 10 Gy in accumulated dose was conducted with a 100-cGy/min dose rate, followed by up to 20 Gy at 200 cGy/min. An irradiation test of whether inappropriate ventricular shock therapy was triggered or not was also performed by using a 6-MV beam of 5, 10, 20 and 40 cGy/min to two CIEDs. No malfunction was observed during irradiation up to 20 Gy at 100 and 200 cGy/min without activation of shock therapy. These results were compared with typical TBI, suggesting that a CIED in TBI will not encounter malfunction because the prescribed dose and the dose rate required for TBI are much safer than those used in this experiment. Several inappropriate shock therapies were, however, observed even at 10 cGy/min if activated. The present result suggested that TBI was feasible and safe if a non-neutron producible beam was employed at low dose-rate without activation of shock therapy, where it was not inconsistent with clinical and non-clinical data in the literature. The feasibility of TBI while using a CIED was discussed for the first time.

To test the measurement technique of the three-dimensional (3D) dose distribution measured image by capturing the scintillation light generated using a plastic scintillator and a scintillating screen. Methods: Our imaging system constituted a column shaped plastic scintillator covered by a Gd 2 O 2 S:Tb scintillating screen, a conical mirror and a cooled CCD camera. The scintillator was irradiated with 6 MV photon beams. Meanwhile, the irradiated plan was prepared for the static field plans, two-field plan (2F plan) and the conformal arc plan (CA plan). The 2F plan contained 16 mm 2 and 10 mm 2 fields irradiated from gantry angles of 0 • and 25 • , respectively. The gantry was rotated counterclockwise from 45 • to 315 • for the CA plan. The field size was then obtained as 10 mm 2 . A Monte Carlo simulation was performed in the experimental geometry to obtain the calculated 3D dose distribution as the reference data. Dose response was acquired by comparing between the reference and the measurement. The dose rate dependence was verified by irradiating the same MU value at different dose rates ranging from 100 to 600 MU/min. Deconvolution processing was applied to the measured images for the correction of light blurring. The measured 3D dose distribution was reconstructed from each measured image. Gamma analysis was performed to these 3D dose distributions. The gamma criteria were 3% for the dose difference, 2 mm for the distance-to-agreement and 10% for the threshold. Results: Dose response for the scintillation light was linear. The variation in the light intensity for the dose rate ranging from 100 to 600 MU/min was less than 0.5%, while our system presents dose rate independence. For the 3D dose measurement, blurring of light through deconvolution processing worked well. The 3D gamma passing rate (3D GPR) for the 10 × 10 mm 2 , 16 × 16 mm 2 , and 20 × 20 mm 2 fields were observed to be 99.3%, 98.8%, and 97.8%, respectively. Reproducibility of measurement was verified. The 3D GPR results for the 2F plan and the CA plan were 99.7% and 100%, respectively. Conclusions: We developed a plastic scintillation dosimeter and demonstrated that our system concept can act as a suitable technique for measuring the 3D dose distribution from the gamma results. In the future, we will attempt to measure the 4D dose distribution for clinical volumetric modulated arc radiation therapy (VMAT)-SBRTplans.

Background/Aim The aim of this study was to compare volumetric-modulated arc therapy (VMAT) radiation plans between conventional VMAT with flattening filter (cFF-VMAT) and flattening filter-free VMAT (FFF-VMAT) for localized prostate cancer. Materials and methods Ten patients with localized prostate cancer who underwent cFF-VMAT at Yokosuka General Hospital Uwamachi, Yokosuka, Japan, from July 2020 to October 2020 were enrolled. Dose-volume histogram (DVH) parameters of the target volume, normal organs, monitor units (MU), and beam-on time (BOT) were compared between cFF-VMAT and FFF-VMAT plans. Results No significant difference was observed for DVH parameters for the target volume. No significant difference was observed in all parameters for the bladder and rectum between the cFF-VMAT and FFF-VMAT groups. The mean values of MU were 686 ± 52 and 784 ± 80 in cFF-VMAT and FFF-VMAT, respectively (p < 0.001). The mean BOT was 97.0 ± 6.6 s and 72.9 ± 1.4 s for cFF-VMAT and FFF-VMAT, respectively (p < 0.001). Conclusion DVH parameters of the target volume and normal organs were not significantly different between the cFF-VMAT and FFF-VMAT plans. In FFF-VMAT, MU was significantly higher, and the BOT was significantly shorter than those in cFF-VMAT.