[OA088] Prostate HDR brachytherapy: the experience of the team matters

Purpose To evaluate the learning curve of the BT-team performing prostate HDR brachytherapy (BT) at our Institution. Methods Since 2010, 108 prostate BT treatments were performed at our Institution by the same BT-team (2 Radiation Oncologists, 2 Medical Physicists), using transrectal ultrasound-guided real time treatment planning.To evaluate the learning curve of the BT-team, Dose Homogeneity Index (DHI) and Conformity Index (COIN) were evaluated. According to the experienced treatment planning difficulties, a new index called Optimal Plan Index (OPI) was also established and evaluated. OPI was defined as the dose to 95% of the prostate (D95%) divided by the dose to 0.1 cc of the urethra (D0.1 cc). The prescribed dose (Dprescr) was 14 Gy to the prostate surface and the most difficult planning goals were: D95% >95% Dprescr and D0.1 cc <115% Dprescr. The number of needles used for the procedure was also investigated. Results DHI and COIN didn’t show any correlation with the increasing experience of the BT team, whereas OPI resulted to be a good indicator of the learning curve. Average OPI values and number of needles used for the procedure, calculated for every group of 27 patients taken in chronological order, were 0.80 ± 0.05, 0.85 ± 0.06, 0.89 ± 0.03, 0.89 ± 0.02, and 17.6 ± 3.2, 19.4 ± 3.3, 17.2 ± 1.2, 16.8 ± 1.5, for group 1 (G1), 2 (G2), 3 (G3) and 4 (G4), respectively. OPI significantly increased with time (i.e., G1vsG2 p < 0.001, G2vsG3 p < 0.01, G3vsG4 p = 0.67) and number of needles significantly changed over time (i.e., G1vsG2 p = 0.02, G2vsG3 p = 0.005, G3vsG4 p = 0.42), reaching both a plateau and a reduced statistical dispersion after about 50–60 treatments. In fact, within the first 50–60 treatments, some perfectible issues of the procedure were identified and improved (e.g., pre-treatment estimation of pubic arc obstruction, planned and achieved needle positions, dose optimization methods). Attendance of specific courses and conferences helped to achieve this task. Conclusions The quality of HDR prostate BT is operator dependent and the proposed optimal plan index OPI is a good indicator of the learning curve of a BT-team. OPI and needle analysis, combined with a specific education of the involved clinical personnel, was useful to improve some treatment planning strategies at our Institution.