An easy and novel method for safer brachytherapy: real-time fluoroscopic verification of high-dose-rate 192Ir source position using a flat-panel detector.

Takayuki Nose,Hideya Yamazaki,Katsuya Nakata,Yuki Otani,Tadashi Takenaka,Shinichiro Kumita,Koji Masui

doi:10.1093/jrr/rrz013

Abstract

Real-time fluoroscopic verification of the active source position during actual treatment is the only established method to prevent high-dose-rate (HDR) brachytherapy events. The challenge is spurious signals from an HDR 192Ir source that result in image halation, making source positions indiscernible when using a non-modified image intensifier fluoroscope. We have previously reported a method for observing an HDR 192Ir source by using an elaborately modified image intensifier system. The newly developed flat-panel detector fluoroscope is, by contrast, inherently halation-free thanks to the wider dynamic range (12–14 bits), compared with image intensifier fluoroscopes (8 bits). To explore the feasibility, we applied a commercially available flat-panel detector fluoroscope without modification to actual treatment. We successfully observed source positions without halation for all 107 patients, with a total of 522 HDR treatment sessions during a 3-year period from 2014 to 2017. Actual source positions were compared with planned positions on the planning hard copy. With this method, we detected a total of 1 error (0.2%) among the 522 sessions, at a similar detection rate of 0.1% with our previous experience using a modified image intensifier fluoroscope. We found that a commercially available flat-panel detector fluoroscope is ready for use for real-time verification and outweighs the need for elaborate modifications of an image intensifier fluoroscope. A flat-panel detector fluoroscope will help the global radiation oncology community promote real-time verification programs, leading to safer HDR brachytherapy.

Highlights

Rare, events that led to one patient death elsewhere have been reported for high-dose-rate (HDR) brachytherapy treatments [1]
We found that the automatic exposure control function interfered with image quality in the presence of an HDR 192Ir (Fig. 2), so we routinely turned off this function during source fluoroscopy
We detected a total of 1 error (0.2%) among the 522 treatment sessions performed during the 3 years. This error was detected in a patient with gingival osteosarcoma treated with interstitial brachytherapy

Summary

Introduction

Events that led to one patient death elsewhere have been reported for high-dose-rate (HDR) brachytherapy treatments [1]. Real-time fluoroscopic verification of HDR 192Ir source position during treatment using a modified image intensifier (II) system has been the only practically established method for preventing accidents [2]. To observe an HDR 192Ir source, an II system, needs dedicated, elaborate modifications to avoid halation due to scattered photons from the HDR 192Ir source itself [2]. In contrast to II systems (dynamic range, 8 bits), newly developed flat-panel detector (FPD) systems are, thanks to the wider dynamic range (12–14 bits), practically halation-free, with finer gradation processing [3, 4]. At Shimane University Hospital, an FPD system was, for the first time, applied to a routine quality control program to check dwell position accuracy for the HDR 192Ir source. Successful, clear X-ray images resulted from effective use of the FPD system, in which a minimum dislocation of 0.04 mm was detectable [3, 4]

Methods

Results

Conclusion