Discussion
volume and left-sided tumor
HOT SPOT, BREAST CANCER
To our best knowledge, this is the first study to evaluate the IMRT and VMAT plans regarding regional nodal irradiation including IMNI in the planning benchmark case, and is also the first study to compare the first and revised plans before enrolling patients. The results showed that a number of major deviations were found in the first submission. After revision, the major deviations were corrected; the protocol compliance was significantly improved and was of high level; and the inter-institutional consistency of planning quality was achieved in the revised plans in the benchmark case.Some previous studies showed that a variety of potential protocol deviations and heterogeneities were always detected in the pretrial benchmark case, and many of them could be improved during actual patient enrollment [In our study, the case used for the benchmark planning had a considerably large irradiated volume with left-sided breast cancer, including chest wall, supraclavicular fossa, axilla levels I-III, and IMN region, for which the plan design was very difficult. Various optimization strategies were used by the dosimetrists. In the first submission, insufficient target coverage, hot spot dose, and dose inhomogeneity in PTV were common major deviations. The protocol compliance rates were all low for first PTVcw, PTVsc + ax, and PTVim VGiven that increased radiation-induced heart and lung injury were the main concerns for IMNI [It is worth noting that the use of multi-beam IMRT and VMAT improves homogeneity and conformity at the expense of extending low-dose spread [This study has some limitations. First, there was only one benchmark case in this QA procedure, and the large irradiated volume and left-sided tumor resulted in difficulties for plan design, which might be unrepresentative, but was effective to improve the ability of dosimetrists in individual institutions. Second, owing to the close proximity between the IMN and chest wall, the unintentional IMN dose in the non-IMNI group is an important focus, which might affect the trial results. However, no benchmark case was provided for non-IMNI planning, and the unintentional IMN dose was not evaluated in this study, which would be assessed in individual case review. Third, electron beams were not used in this benchmark case; therefore, careful QA is warranted in subsequent individual case review for the actual enrolled patients. Last, the protocol compliance in other follow-up cases was not evaluated in this paper. We will report the results of subsequent individual case review in the near future and reflect upon the fact that this benchmark planning procedure provided a meaningful contribution to improving the plan qualities for actual enrolled patients.