Background: Radixact Synchrony ® , a real-time motion tracking and compensating modality, is used for helical tomotherapy. Control parameters are used for the accurate application of irradiation. Radixact Synchrony ® uses the potential difference, which is an index of the accuracy of the prediction model of target motion and is represented by a statistical prediction of the 3D distance error. Although there are several reports on Radixact Synchrony ® , few have reported the appropriate settings of the potential difference threshold. Purpose: This study aims to determine the optimal threshold of the potential difference of Radixact Synchrony ® during respiratory tumor-motion-tracking irradiation. Methods: The relationship among the dosimetric accuracy, motion tracking accuracy,and control parameter was evaluated using a moving platform,a phantom with a basic respiratory model (the fourth power of a sinusoidal wave), and several irregular respiratory model waveforms. The dosimetric accuracy was evaluated by gamma analysis (3%, 1 mm, 10% dose threshold). The tracking accuracy was measured by the distance error of the difference between the tracked and driven positions of the phantom. The largest potential difference for 95% of treatment time was evaluated, and its correlation with the gamma-pass ratio and distance error was investigated. The optimal threshold of the potential difference was determined by receiver operating characteristic (ROC) analysis. Results: A linear correlation was identified between the potential difference and the gamma-pass ratio (R = -0.704). A linear correlation was also identified between the potential difference and distance error (R = 0.827). However, as the potential difference increased, it tended to underestimate the distance error. The ROC analysis revealed that the appropriate cutoff value of the potential difference was 3.05 mm. Conclusion:The irradiation accuracy with motion tracking by Radixact Synchrony ® could be predicted from the potential difference, and the threshold of the potential difference should be set to ∼3 mm.

Background/Aim: To investigate the effect of polaprezinc (antioxidant) administration and hyperbaric oxygen therapy on radiation-induced intestinal injury. Materials and Methods: Forty-five C57BL/6J mice underwent total body radiation of 2 Gy. Polaprezinc was given in 12 mice, hyperbaric oxygen in 12 mice, and both in 12 mice. The other 9 mice did not undergo any treatment. Mice were sacrificed 2, 4, and 6 h after radiation, and 9 specimens (3 each from the duodenum, jejunum, and ileum) were harvested. Apoptotic intestinal crypt cells were histologically evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Results: Apoptotic cell number per 1,000 crypt cells was 31.0±6.7 at 2 h, 28.4±5.2 at 4 h, and 32.9±5.1 at 6 h in the mice group treated by radiation alone. Both polaprezinc administration and hyperbaric oxygen therapy significantly suppressed apoptosis. Although the effect of polaprezinc administration on suppressing apoptosis became less over time (4. 9±5.7 and 19.4±13.2 at 2 and 6 h, respectively), that of hyperbaric oxygen therapy was stable regardless of time (23.6±4.8 and 25.8±4.1 at 2 and 6 h). Administration of both polaprezinc and hyperbaric oxygen showed a significant synergetic or additive effect on suppressing apoptosis at 6 h (11.4±10.5, p<0.0035 vs. polaprezinc, p<0.0001 vs. hyperbaric oxygen). Conclusion: Both polaprezinc administration and hyperbaric oxygen therapy are effective in relieving radiation-induced small intestinal damage, and a synergistic or additive effect is expected when using both.

Background/Aim: To evaluate the quality of error detectability with a three-dimensional verification system using isodose volumes as regions of interest (ROIs) in quality assurance (QA) of intensity-modulated radiation therapy. Patients and Methods: Treatment plans with four types of intentional errors were created from the data of 20 patients with localized prostate cancer. These plans underwent QA using the three-dimensional verification system. The datasets of another 30 cases without inserted errors were assessed as controls. The ROIs used in the evaluations were those used in our conventional method (planning target volume, rectum, and bladder). The isodose volume method (5%, 50% and 95% isodose volume) and the error detection rates (measurement above the tolerance values, as set from the other 30 cases) were assessed and compared. Results: There was significantly higher multileaf collimator systematic closed error detectability with the isodose volume method compared to the conventional method (A-side 0.2 mm: p=0.005, A-side 0.35 mm: p=0.002, B-side 0.2 mm: p=0.001 and B-side 0.35 mm: p=0.010). There were no error types for which the error detection rate of the isodose volume method was lower than that of the conventional method. Conclusion: The isodose volume method was able to evaluate the irradiated ROIs that could be delineated, and improved error detectability. This method has the potential to provide a wider margin of safety in intensity-modulated radiation therapy.Intensity modulated radiation therapy (IMRT) is an irradiation technique that can create a steep dose gradient to deliver a high dose to the target while avoiding normal tissue (1, 2). Volumetric-modulated arc therapy (VMAT) is an IMRT technique that uses a dynamic multileaf collimator (MLC) and varies the dose rate while rotating the gantry to rapidly deliver IMRT (3,4). In order to ensure safe delivery of VMAT, it is recommended that each treatment plan created by a treatment planning system (TPS) be verified to detect inherent errors and to verify dose accuracy (5). The IMRT verification methods include absolute dose verification using a dosimeter (6) and dose distribution verification using a two-dimensional detector or radiochromic film (7-11). In absolute dose verification, a phantom is used in a three-dimensional treatment plan. The absolute dose is verified by comparing the results calculated with the phantom's CT scan data with those doses measured using the phantom and a dosimeter. The verification of dose distribution is evaluated comparing distribution recalculated by the TPS with those obtained using radiochromic film or twodimensional detectors. A gamma analysis is often used as the evaluation method (12-14).A recently developed three-dimensional dose verification system can predict the dose distribution in the patient body from the phantom measurement results obtained using a twodimensional detector (15,16). It can be evaluated using a dose volume histogram (DVH), which can predict the dose delivered to organs at risk (OARs)...