Poster — Thur Eve — 73: Follow up of a new bladder preparation protocol when treating the prostate

Background and Purpose: Patients treated for their prostate cancer were put on a bladder preparation protocol to obtain a full bladder. The associated high degree of discomfort forced us to change our practice. The patients were asked to drink 300ml prior to their treatment instead of 750ml. Following this change, a retrospective study was undertaken to assess the dosimetric impact on the bladder. Methods: The first group (patients who drank 750ml) had 10 patients. The second group (patients who drank 300ml) had 14 patients. Planning CT and 8 daily CBCT bladder volumes and DVHs were compared for both groups. Dose optimization constraints where based on PROFIT 78Gy/39 fraction arm. Results: For patients who drank 750ml, the average bladder volume was 377.1±60.9 cc compared with 236.5±31.5 cc for patients who drank 300 ml (p=0.043). Therapists do not report any case of incontinence in the 300 ml group. The achieved bladder wall constraint for V68% went from 23.7±1.7% to 33.8±2.0%, p=0.012, and the V91% went from 14.2±1.1% to 21.8±1.6%, p<0.001. Conclusions: A bladder filling protocol asking patients to drink less before treatment was successfully implemented in our center. We were able to eliminate incontinence during treatment and increase patient comfort. The smaller bladders lead to an increase in dose to the bladder wall, however IMRT optimization was able to produce plans that spared the bladder and were able to pass published protocol guidelines.