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 50 ml and 100 ml. 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 V40 Gy, V60 Gy and V65 Gy 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 V40 Gy, V60 Gy and V65 Gy were higher by 8%, 5% and 2% (ERB 50 ml) and 2%, 3% and 3% (ERB 100 ml) in comparison to plans without ERB. The respective Awall dose volume differences were 2%, 0%, −1% (ERB 50 ml), and −3%, −2%, −2% (ERB 100 ml). 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 >2 mm in anterior–posterior and inferior–superior directions. Conclusion The use of ERB during post-operative VMAT has no advantages for anorectal dose.