Target coverage and cardiopulmonary sparing with the updated ESTRO-ACROP contouring guidelines for postmastectomy radiation therapy after breast reconstruction: a treatment planning study using VMAT and proton PBS techniques

The European Society for Therapeutic Radiology and Oncology Advisory Committee in Radiation Oncology Practice (ESTRO-ACROP) recently released new contouring guidelines for postmastectomy radiation therapy (PMRT) after implant-based reconstruction (IBR). As compared to prior ESTRO guidelines, the new guidelines primarily redefined the chest wall (CW) target to exclude the breast prosthesis. In this study, we assessed the impact of these changes on treatment planning and dosimetric outcomes using volumetric-modulated arc therapy (VMAT) and proton pencil-beam scanning (PBS) therapy. We performed a treatment planning study of 10 women with left-sided breast cancer who underwent PMRT after IBR. All target structures were delineated first using standard (ESTRO) breast contouring guidelines and then separately using the new (ESTRO-ACROP) guidelines. Standard organs-at-risk (OARs) and cardiac substructures were contoured. Four sets of plans were generated: (1) VMAT using standard ESTRO contours, (2) VMAT using new ESTRO-ACROP contours, (3) PBS using standard contours, and (4) PBS using new contours. VMAT plans using the new ESTRO-ACROP guidelines resulted in modest sparing of the left anterior descending coronary artery (LAD) (mean dose: 6.99 Gy standard ESTRO vs. 6.08 Gy new ESTRO-ACROP, <i>p</i> = 0.010) and ipsilateral lung (V₂₀: 21.66% vs 19.45%, <i>p</i> = 0.017), but similar exposure to the heart (mean dose: 4.6 Gy vs. 4.3 Gy, <i>p</i> = 0.513), with a trend toward higher contralateral lung (V₅: 31.0% vs 35.3%, <i>p</i> = 0.331) and CW doses (V₅: 31.9% vs 35.4%, <i>p</i> = 0.599). PBS plans using the new guidelines resulted in further sparing of the heart (mean dose: 1.05 Gy(RBE) vs. 0.54 Gy(RBE), <i>p</i> p 20: 16.22% vs 6.02%, <i>p</i> PMRT after IBR using the new ESTRO-ACROP contouring guidelines with both VMAT and PBS therapy is associated with significant changes in exposure to several cardiopulmonary structures.

欧洲放射治疗与肿瘤学会（European Society for Therapeutic Radiology and Oncology, ESTRO）放射肿瘤实践咨询委员会（Advisory Committee in Radiation Oncology Practice, ACROP）近日发布了针对基于植入物的乳房重建（implant-based reconstruction, IBR）后乳房切除术后放射治疗（postmastectomy radiation therapy, PMRT）的全新靶区勾画指南。相较于此前的ESTRO指南，新指南主要重新定义了胸壁（chest wall, CW）靶区，将乳房假体排除在外。本研究针对10例接受IBR后PMRT的左侧乳腺癌女性患者，评估了该指南变更对采用容积调强弧形治疗（volumetric-modulated arc therapy, VMAT）与质子笔形束扫描（proton pencil-beam scanning, PBS）的治疗计划及剂量学结局的影响。研究首先分别采用标准ESTRO指南与新版ESTRO-ACROP指南对所有靶区进行勾画，同时勾画标准危及器官（organs-at-risk, OARs）及心脏亚结构。共生成四组治疗计划：（1）采用标准ESTRO靶区的VMAT计划；（2）采用新版ESTRO-ACROP靶区的VMAT计划；（3）采用标准靶区的PBS计划；（4）采用新版靶区的PBS计划。采用新版ESTRO-ACROP指南的VMAT计划可轻度减少左前降支冠状动脉（left anterior descending coronary artery, LAD）的受照剂量（平均剂量：标准ESTRO指南组为6.99 Gy，新版ESTRO-ACROP指南组为6.08 Gy，p=0.010），同侧肺的V20分别为21.66%与19.45%（p=0.017）；但两组的心脏平均受照剂量相近（4.6 Gy vs 4.3 Gy，p=0.513），同时对侧肺V5（31.0% vs 35.3%，p=0.331）及胸壁V5（31.9% vs 35.4%，p=0.599）的受照剂量呈升高趋势。采用新版指南的PBS计划可进一步降低心脏受照剂量（平均剂量：1.05 Gy(RBE) vs 0.54 Gy(RBE)），V20分别为16.22%与6.02%（原文此处p值疑似缺失）。综上，采用新版ESTRO-ACROP靶区勾画指南，联合VMAT与PBS技术开展IBR后PMRT，会使多种心肺结构的受照剂量发生显著改变。