The effect of endorectal balloon on anorectal dose during postoperative volumetric arc radiotherapy of prostate cancer

Abstract

Purpose: To evaluate the impact of endorectal balloon (ERB) on anorectal dose during postoperative VMAT of prostate cancer.

Methods: In ten patients referred for salvage radiotherapy CTs were obtained without ERB and with air-filled ERB of 50ml and 100ml. CTs were repeated weekly (4-6 control CTs) and registered to the respective planning CT. For each planning CT, a VMAT plan was made with defined anorectal dose constraints and propagated on the respective control CTs. The dose volumes V40Gy, V60Gy and V65Gy of the rectal and anal wall (Rwall and Awall, respectively) and the ERB position were obtained from each plan.

Results: In plans with ERB, the mean Rwall dose volumes V40Gy, V60Gy and V65Gy were higher by 8%, 5% and 2% (ERB 50ml) and 2%, 3% and 3% (ERB 100ml) in comparison to plans without ERB. The respective Awall dose volume differences were 2%, 0%, -1% (ERB 50ml), and -3%, -2%, -2% (ERB 100ml). The dose volume variability of the Rwall was comparable with and without ERB, but was slightly reduced by ERB for the Awall. The mean ERB position variability was >2mm in anterior-posterior and inferior-superior directions.

Conclusion: The use of ERB during post-operative VMAT has no advantages for anorectal dose.

Keywords: Anorectal dose; Endorectal balloon; Post-prostatectomy; VMAT.