Quality assurance in a phase III, multicenter, randomized trial of POstmastectomy radioThErapy in Node posiTive breast cancer with or without Internal mAmmary nodaL irradiation (POTENTIAL): a planning benchmark case.

PURPOSE: To report the planning benchmark case results of the POTENTIAL trial-a multicenter, randomized, phase 3 trial-to evaluate the value of internal mammary nodal (IMN) irradiation for patients with high-risk breast cancer.

METHODS: All participating institutions were provided the outlines of one benchmark case, and they generated radiation therapy plans per protocol. The plans were evaluated by a quality assurance team, after which the institutions resubmitted their revised plans. The information on beams arrangement, skin flash, inhomogeneity corrections, and protocol compliance was assessed in the first and final submission.

RESULTS: The plans from 26 institutions were analyzed. Some major deviations were found in the first submission. The protocol compliance rates of dose coverage for the planning target volume of chest wall, supraclavicular fossa plus axilla, and IMN region (PTVim) were all significantly improved in the final submission, which were 96.2% vs. 69.2%, 100% vs. 76.9%, and 88.4% vs. 53.8%, respectively. For OARs, the compliance rates of heart Dmean , left anterior descending coronary artery V40Gy , ipsilateral lung V5Gy , and stomach V5Gy were significantly improved. In the first and final submission, the mean values of PTVim V100% were 79.9% vs. 92.7%; the mean values of heart Dmean were 11.5 Gy vs. 9.7 Gy for hypofractionated radiation therapy and 11.5 Gy vs. 11.0 Gy for conventional fractionated radiation therapy, respectively.

CONCLUSION: The major deviations were corrected and protocol compliance was significantly improved after revision, which highlighted the importance of planning benchmark case to guarantee the planning quality for multicenter trials.