SU‐E‐CAMPUS‐T‐03: Automated Multicriterial Plan Generation for Prostate Cancer Patients with Metal Hip Prostheses: Comparison of Planning Strategies

Purpose: To compare different IMRT planning strategies for patients with metal hip prostheses and to determine the impact of increasing the number of beam directions. Methods: All plans were generated fully automated (i.e., no human trial‐and‐error interaction) using iCycle, our in‐house developed algorithm for multicriterial optimization of beam angles and fluence profiles, allowing objective comparisons of planning strategies. For 18 prostate cancer patients (eight with bilateral hip prostheses, ten with a right‐sided unilateral prosthesis), two planning strategies were evaluated: i) full exclusion of beams containing beamlets that would deliver dose to the target after passing through a prosthesis (IMRTremove, as recommended by AAPM taskgroup 63), and ii) exclusion of those beamlets plus a 5 mm margin only (IMRTcut). Plans with optimized coplanar and non‐coplanar beam arrangements were generated. Differences in PTV coverage and sparing of organs at risk (OARs) were quantified. The impact of beam number on plan quality was evaluated. Results: Especially for patients with bilateral hip prostheses, IMRTcut significantly improved rectum and bladder sparing compared to IMRTremove, while adequate PTV coverage was maintained. For 9‐beam coplanar plans, rectum V60Gy reduced by 17.5% ± 15.0% (maximum 37.4%, p=0.036) and rectum Dmean by 9.4% ± 7.8% (maximum 19.8%, p=0.036). Further improvements in OAR sparing were achievable by using non‐coplanar beam set‐ups, reducing rectum V60Gy by another 4.6% ± 4.9% (p=0.012) for non‐coplanar 9‐beam IMRTcut plans. Larger reductions in rectum V60Gy, by on average 13.5% ± 7.9% (p=0.012), were observed when comparing 7‐and 15‐beam coplanar plans. Conclusion: Excluding only beamlets that pass through a prosthesis prior to delivering dose to the PTV (IMRTcut strategy) significantly improved OAR sparing as opposed to full exclusion of beams containing such beamlets. Application of non‐coplanar beam arrangements and, to a larger extent, an increased number of beams further improved plan quality.