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Background Several studies have reported patient-related risk factors for late rectal bleeding following conventionally fractionated radiotherapy for prostate cancer. We investigated patient-related risk factors for late rectal bleeding after hypofractionated radiotherapy. Methods A total of 231 patients with local or locally advanced prostate cancer treated with hypofractionated radiotherapy (70 or 67.2 Gy in 28 fractions) were evaluated retrospectively. All patients received intensity-modulated radiotherapy with daily image guidance. The relationships between late rectal bleeding and risk factors like diabetes, hypertension, cirrhosis, and anticoagulant use were analyzed. Results During a median follow-up of 23 months, the crude rates of grade ≥ 1, grade ≥ 2, and grade ≥ 3 late rectal bleeding were 23.8%, 16.9%, and 9.5%, respectively. Cirrhosis and anticoagulant use predicted an increased risk of grade ≥ 3 rectal bleeding in multivariable analyses (hazard ratio [HR] 14.37, 95% confidence interval [CI] 3.09–66.87, P = 0.001, and HR 2.93, 95% CI 1.14–7.55, P = 0.026, respectively). The non-anticoagulant group had a significantly superior 5-year freedom from grade ≥ 3 bleeding compared to the anticoagulant group in a propensity-weighted log-rank analysis (88.0% vs. 76.7%, P = 0.041). A receiver operating characteristic curve analysis revealed that rectal bleeding was minimized in the anticoagulant group if the equivalent dose at fractionation of 2 Gy (EQD2) V77 Gy of the rectum was < 4.5% or if the EQD2 V8.2 Gy was < 71.0%. Conclusions Patients taking anticoagulants or those with cirrhosis had a significantly higher risk of severe late rectal bleeding than other patients after hypofractionated radiotherapy for prostate cancer in the present study. The bleeding risk could be lowered by minimizing hotspots in patients taking anticoagulants.

Purpose We evaluated the correlation between stomach volume change and interfractional baseline shifts of the diaphragm in image‐guided radiotherapy (IGRT) for hepatocellular carcinoma (HCC). Materials and methods Twenty‐four patients with HCC underwent ten fractions of IGRT, and a total of 240 cone beam computed tomography (CBCT) and on‐board imager (OBI) kV image sets were acquired. These image sets were retrospectively analyzed. Baseline shifts of the diaphragm relative to bone and stomach volume change ratios were evaluated using four‐dimensional simulation CT, kV image, and CBCT images. Associations between baseline shifts and patient physiologic factors were investigated. Results The average baseline shift of the diaphragm in the superior‐inferior (SI) direction was 1.5 mm (standard deviation 4.6 mm), which was higher than the shift in other directions (0.7, 2.0 mm and 0.9, 2.6 mm in right‐left (RL) and anterior‐posterior (AP) directions, respectively). Interfractional baseline shifts of the diaphragm in the SI and AP directions were positively correlated with the stomach volume change ratio (Pearson's r: 0.416 and 0.302, p‐value: <0.001 and <0.001, respectively). Conclusions The interfractional baseline shifts of the diaphragm in the SI and AP directions correlated well with stomach volume changes. Efforts to maintain a constant stomach volume before the simulation and each treatment, such as fasting, may reduce interfractional baseline shifts of liver tumors.

This study was aimed to evaluate the effectiveness of Monte Carlo (MC) method in stereotactic radiotherapy for brain tumor. The difference in doses predicted by the conventional Ray-tracing (Ray) and the advanced MC algorithms was comprehensively investigated through the simulations for phantom and patient data, actual measurement of dose distribution, and the retrospective analysis of 77 brain tumors patients. These investigations consistently showed that the MC algorithm overestimated the dose than the Ray algorithm and the MC overestimation was generally increased as decreasing the beams size and increasing the number of beams delivered. These results demonstrated that the advanced MC algorithm would be inaccurate than the conventional Raytracing algorithm when applied to a (quasi-) homogeneous brain tumors. Thus, caution may be needed to apply the MC method to brain radiosurgery or radiotherapy.

We construct a model of differential K-theory using superbundles with a Z/2Z-graded connection and a differential form on the base manifold and prove that our model is isomorphic to the Freed–Lott–Klonoff model of differential K-theory.

In this study, a radiation detector based on a silicon photomultiplier (SiPM) and large Ce-doped Gd-Al-Ga-grant (Ce:GAGG) scintillator was developed for the gamma spectroscopy observations of radioactivation from linear accelerators (LINACs). The calibration of the detector demonstrated a high energy resolution of 15.89% at 122 keV (gamma-ray emission energy of Co-57), 7.04% at 356 keV (gamma-ray emission energy of 133Ba), 6.17% at 511 keV (gamma-ray emission energy of Na-22), and 5.39% at 662 keV (gamma-ray emission energy of Cs-137). These results indicate that the detector employing a larger Ce:GAGG scintillator provides a higher detection efficiency while maintaining superior energy resolution compared to conventional radiation detectors that use smaller Ce:GAGG scintillators. Furthermore, the energy spectrum measurement of the LINAC revealed detection of neutron and gamma peaks of W-187 and Mn-56, as well as annihilation peaks. Although the energy resolution of the detector was inferior compared to an HPGe detector, it was able to measure similar energy peaks. Therefore, the radiation detector developed in this study, which is characterized by its low cost, decent energy resolution, and high detection efficiency, may be useful for obtaining radiation measurements during the disposal of LINACs.

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