Dosimetric comparison of target-segmented plan versus conventional IMRT plan for post-mastectomy left-sided breast cancer patients

Objective To compare the dosimetric differences among Target-Segmented Plan (TSP), Non-TSP, and conventional static 8-field intensity modulated radiation therapy (8F-IMRT) plan for post-mastectomy irradiation of left-sided breast cancer patients. Methods This study enrolled thirty consecutive breast cancer patients who underwent radical mastectomy and treated with post-op radiation in Department of Radiation Oncology, Renmin Hospital of Wuhan University from June 2017 to November 2018.The clinical target volume (CTV) included the ipsilateral chest wall, supra/infra-clavicular, high-risk partial axillary in high risk, and internal mammary nodes (IMN). The organs at risk (OARs) near the targets, including ipsilateral lung, heart, contralateral breast, ipsilateral humeral head and spinal cord, were contoured as well. The maximum distance of PTV′s tangent to the outermost side of the affected lung was more than 2 cm. Depending on the maximum distance, the patients were classified into three groups: A( 4 cm), respectively. Three types of treatment plans (TSP, Non-TSP and 8F-IMRT) were created for each patient using the Eclipse treatment planning system with the same dose optimization objective . The dose-volume histograms were compared for the PTVs and OARs. Results All plans achieved the intended dose criteria.The D98% of TSP was lower than that of Non-TSP and 8F-IMRT (Z=-3.294, -3.266, P 0.05). Non-TSP required more Monitor Units (MUs)than the other two plans (Z=-3.04, -2.669, P 0.05). There was no significant difference in spinal cord Dmax among the three plans, but the Dmean of humeral head in 8F-IMRT was higher than that in TSP and Non-TSP (Z=-3.01, -2.442, P<0.05). In the three groups, the mean amplitude of difference comparing Non-TSP and 8F-IMRT with TSP in ipsilateral lung(V5 Gy, V10 Gy, V20 Gy) and heart(V5 Gy, V10 Gy, Dmean) satisfied the relation: D(N-T, A)