Masaki Yokokawa

Usefulness of direct-conversion flat-panel detector system as a quality assurance tool for high-dose-rate 192Ir source.

The routine quality assurance (QA) procedure for a high‐dose‐rate (HDR) 192Ir radioactive source is an important task to provide appropriate brachytherapy. Traditionally, it has been difficult to obtain good quality images using the 192Ir source due to irradiation from the high‐energy gamma rays. However, a direct‐conversion flat‐panel detector (d‐FPD) has made it possible to confirm the localization and configuration of the 192Ir source. The purpose of the present study was to evaluate positional and temporal accuracy of the 192Ir source using a d‐FPD system, and the usefulness of d‐FPD as a QA tool. As a weekly verification of source positional accuracy test, we obtained 192Ir core imaging by single‐shot radiography for three different positions (1300/1400/1500 mm) of a check ruler. To acquire images for measurement of the 192Ir source movement distance with varying interval steps (2.5/5.0/10.0 mm) and temporal accuracy, we used the high‐speed image acquisition technique and digital subtraction. For accuracy of the 192Ir source dwell time, sequential images were obtained using various dwell times ranging from 0.5 to 30.0 sec, and the acquired number of image frames was assessed. Analysis of the data was performed using the measurement analysis function of the d‐FPD system. Although there were slight weekly variations in source positional accuracy, the measured positional errors were less than 1.0 mm. For source temporal accuracy, the temporal errors were less than 1.0%, and the correlation between acquired frames and programmed time showed excellent linearity (R2=1). All 192Ir core images were acquired clearly without image halation, and the data were obtained quantitatively. All data were successfully stored in the picture archiving and communication system (PACS) for time‐series analysis. The d‐FPD is considered useful as the QA tool for the 192Ir source. PACS number: 87.56.FcThe routine quality assurance (QA) procedure for a high-dose-rate (HDR) 192Ir radioactive source is an important task to provide appropriate brachytherapy. Traditionally, it has been difficult to obtain good quality images using the 192Ir source due to irradiation from the high-energy gamma rays. However, a direct-conversion flat-panel detector (d-FPD) has made it possible to confirm the localization and configuration of the 192Ir source. The purpose of the present study was to evaluate positional and temporal accuracy of the 192Ir source using a d-FPD system, and the usefulness of d-FPD as a QA tool. As a weekly verification of source positional accuracy test, we obtained 192Ir core imaging by single-shot radiography for three different positions (1300/1400/1500 mm) of a check ruler. To acquire images for measurement of the 192Ir source movement distance with varying interval steps (2.5/5.0/10.0 mm) and temporal accuracy, we used the high-speed image acquisition technique and digital subtraction. For accuracy of the 192Ir source dwell time, sequential images were obtained using various dwell times ranging from 0.5 to 30.0 sec, and the acquired number of image frames was assessed. Analysis of the data was performed using the measurement analysis function of the d-FPD system. Although there were slight weekly variations in source positional accuracy, the measured positional errors were less than 1.0 mm. For source temporal accuracy, the temporal errors were less than 1.0%, and the correlation between acquired frames and programmed time showed excellent linearity (R2=1). All 192Ir core images were acquired clearly without image halation, and the data were obtained quantitatively. All data were successfully stored in the picture archiving and communication system (PACS) for time-series analysis. The d-FPD is considered useful as the QA tool for the 192Ir source. PACS number: 87.56.Fc.

Dosimetry advantages of intraoperatively built custom-linked seeds compared with loose seeds in permanent prostate brachytherapy

Purpose The aim of this study was to compare the implant quality between intraoperatively built custom-linked seeds (IBCL) and loose seeds (LS) retrospectively. Material and methods This study included 74 prostate cancer patients who were treated with permanent prostate brachytherapy (PPB) using IBCL (n = 37) or LS (n = 37) between July 2014 and June 2016. Dose-volume histogram (DVH) parameters, seed migration, and operation time were compared between the IBCL and LS groups. In addition to the standard target volume of the whole prostate gland, DVH parameters for prostate plus a 3 mm margin (CTV) were evaluated. Results In intraoperative planning, prostate V150 was lower (54.8% vs. 59.6%, p = 0.027), and CTV V100 (88.1% vs. 85.6%, p = 0.019) and D90 (98.5% vs. 92.6%, p = 0.0033) were higher in the IBCL group compared with in the LS group. In post-implant dosimetry, prostate V100 (96.9% vs. 95.2%, p = 0.020), CTV V100 (85.6% vs. 81.7%, p = 0.046), and CTV D90 (94.2% vs. 86.5%, p < 0.001) were higher, and prostate V150 (57.1% vs. 64.5%, p = 0.0051) and CTV V150 (31.5% vs. 35.7%, p = 0.046) were lower in the IBCL group compared with in the LS group. Regarding DVH changes between intraoperative planning and post-implant dosimetry, the decrease in prostate D90 was significantly lower in the IBCL group than in the LS group (–1.16% vs. –4.17%, p < 0.001). For the IBCL group, the operation time was slightly but significantly longer than that for the LS group (50.5 minutes vs. 43.7 minutes, p = 0.011). However, the seed migration rate was significantly lower in the IBCL group than in the LS group (5% vs. 41%, p < 0.001). Conclusions Intraoperatively built custom-linked is more advantageous than LS in terms of dosimetric parameters and migration.

A Phase I/II Trial of Radiotherapy Concurrent with TS-1 Plus Cisplatin in Patients with Clinically Resectable Type 4 or Large Type 3 Gastric Cancer: Osaka Gastrointestinal Cancer Chemotherapy Study Group OGSG1205

A Phase I/II trial of radiotherapy administered concurrently with TS-1 plus cisplatin has been initiated in Japanese patients with clinical resectable type 4 or large type 3 gastric cancer. The aim of this trial is to determine the recommended dose of TS-1 and cisplatin combined with radiotherapy at a fixed dose in the Phase I study, and to evaluate the efficacy and safety in the Phase II study. The primary endpoint for Phase II is the pathological complete response rate, assessed using surgically resected specimens. Secondary endpoints are the response rate, progression-free survival, overall survival, operation transitional rate, R0 resection rate, rate of treatment completion, rate of down-staging and rates of postoperative complications and adverse events. In Phase II, a total of 30 patients will be enrolled in the Osaka Gastrointestinal Cancer Chemotherapy Study Group trial over a period of 6 years.