The Hybrid Method Can Cover the External Prostatic Region Compared With the Conventional Method in Patients Who Undergo Prostate Low-Dose-Rate Brachytherapy

Abstract

The advantage of low-dose rate (LDR) brachytherapy is the potential ability to cover the external prostatic region with a curative radiation dose. Most external prostatic extension (EPE) is observed (90%) within 5 mm from prostatic capsule. The loose seed which is implanted around prostate often migrates to vessel and lung, while the stranded seed rarely migrates. We hypothesize that the hybrid method (using loose seed in combination of stranded seed) can irradiate with a wide margin (5 mm from prostate capsule) compared with the conventional method (using loose seed alone).A randomized control trial (trial number: UMIN 000012780) was conducted to compare dose evaluation parameters between the conventional method and the hybrid method. Between 2004 and July 2016, a total of 220 patients who underwent LDR-brachytherapy were enrolled. Patients were randomized and allocated to two groups (conventional method vs, hybrid method). We compared dose evaluation (post-dosimetric) parameters (%D90, V100, V150, %UD30, R100) calculated at 1 month after seed implant by CT scan between the two groups, and also compared post-dosimetric parameters using the planning target volume (PTV) with prostate+5mm margin. In the conventional method group, 42 patients received seed implant alone and 68 patients received seed implant in combination with external beam radiation therapy (EBRT), while 43 patients received seed implant alone and 67 in combination with EBRT in the hybrid method group. Regarding dose evaluation parameters, prostate dose (%D90, V100, V150), and urethral dose (%UD30), were not significantly different between 2 groups, while V100 (+5 mm margin) and %D90 (+5 mm margin) were significantly higher in the hybrid method group compared with the conventional method group (P<0.001) (Table 1). The present randomized control trial shows that the hybrid method of LDR-brachytherapy can achieve a higher coverage of peri-prostatic region under keeping a low urethral and rectal dose compared with the conventional method.Abstract 1086; Table 1Comparison of dose evaluation parameters between conventional method and hybrid method%D90 (%)V100 (%)V150 (%)%UD30 (%)R100 (mL)V100 (+5mm margin) (%)%D90 (+5mm margin) (%)Conventional116.896.658.8129.80.0977.279.2Hybrid119.097.259.0131.40.1580.583.4P-value0.0910.0570.7810.4050.0080.001>0.001> Open table in a new tab