Combined HDR brachytherapy boost plus external beam radiotherapy by IMRT versus external beam radiotherapy alone IMRT in intermediate- and high-risk prostate cancer: Dosimetric analysis from a randomized control trial.

Abstract

134 Background: Dose escalation by IMRT or brachytherapy significantly improves biochemical control in localized prostate cancer. In this prospective randomized study we compared dose conformity between two modalities HDR brachytherapy and IMRT to deliver a boost to the prostate after External beam Radiotherapy (EBRT). Methods: 20 patients with localized prostate cancer were randomized to receive IMRT alone or IMRT plus brachytherapy. After randomization, all patients received EBRT 45Gy/25#/5 weeks by IMRT in phase I. In phase II patients received either HDR brachytherapy 19Gy/2# (Arm A) or EBRT 29Gy/15#/3weeks (Arm B) and EQD2–DVH parameters were calculated for comparison. EQD2 was calculated with α/β ratio of 1.5Gy and 3Gy for prostate & 3Gy for rectum and bladder. Results: The median age, stage distribution, Gleason score, PSA and prostate volume of the cohort were 69.5 years, T2b–T3b, 7, 38.5ng/ml and 47.4cc respectively.The HDR BT delivered higher mean doses to PTV. In phase II, HDR BT vs IMRT the mean EQD2 for 95% of prostate volume, 33% of rectal volume was 45.7Gy vs 28.4Gy, 6.8Gy vs 17.4 Gy respectively; Dmean of rectum and bladder was 7.4 Gy vs 13.5Gy and 5.4Gy vs 12.7Gy respectively. Conclusions: HDR BT produced more conformal plan and lower OAR doses than IMRT. Dose escalation for prostate tumors by HDR BT may be preferred as easily achievable. [Table: see text]