The effect of Rectal Retractor, a rectal protector on rectal dose in radical prostate radiotherapy

Introduction: The close proximity of the rectum tissue to the prostate gland results in rectal toxicity during prostate radiotherapy. Rectal Retractor (RR) is a rectal displacement technique that inserts into the rectum, as a result, the lateral and dorsal part of the rectal wall push away from high dose areas. The aim of this study was to investigate the dosimetric consequences and rectal tissue sparing effect of RR during prostate three-dimensional radiotherapy (3DCRT). Materials and Methods: In 15 patients with localized prostate cancer, two planning CT- scans were carried out: without and with RR. The prostate and seminal vesicles plus 5 mm margin were considered as planning target volume (PTV). All patients were treated using 3DCRT with prescription dose of 80 Gy. The inter-fraction setup errors were corrected by electronic portal imaging device (EPID) and fiducial gold markers. Dose volume histograms of the rectum were compared in plan without and with RR. Results: All patients well tolerated RR during first 20-25 fractions. Using RR, mean dose to the rectum was 39 cGy (P <0.001) lower per fraction. Comparison between plan without and with RR indicated that RR resulted in a mean reduction of 57.3%, 63.8%, 71.9% and 72.8% in rectal V50Gy, V60Gy, V70Gy and V75Gy, respectively (P <0.001). Conclusion: The retraction of the rectum is associated with a significant lower dose to the rectum. This may lead to reduction of the rectal toxicity during prostate radiotherapy.