Mattes Malcolm D, Lee Jennifer C, Elnaiem Sara, Guirguis Adel, Ikoro N C, Ashamalla Hani
Department of Radiation Oncology, New York Methodist Hospital, Brooklyn, NY, USA.
Radiat Oncol J. 2014 Mar;32(1):23-30. doi: 10.3857/roj.2014.32.1.23. Epub 2014 Mar 27.
The goal of this study is to determine whether the magnitude of overlap between planning target volume (PTV) and rectum (Rectumoverlap) or PTV and bladder (Bladderoverlap) in prostate cancer volumetric-modulated arc therapy (VMAT) is predictive of the dose-volume relationships achieved after optimization, and to identify predictive equations and cutoff values using these overlap volumes beyond which the Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC) dose-volume constraints are unlikely to be met.
Fifty-seven patients with prostate cancer underwent VMAT planning using identical optimization conditions and normalization. The PTV (for the 50.4 Gy primary plan and 30.6 Gy boost plan) included 5 to 10 mm margins around the prostate and seminal vesicles. Pearson correlations, linear regression analyses, and receiver operating characteristic (ROC) curves were used to correlate the percentage overlap with dose-volume parameters.
The percentage Rectumoverlap and Bladderoverlap correlated with sparing of that organ but minimally impacted other dose-volume parameters, predicted the primary plan rectum V45 and bladder V50 with R(2) = 0.78 and R(2) = 0.83, respectively, and predicted the boost plan rectum V30 and bladder V30 with R(2) = 0.53 and R(2) = 0.81, respectively. The optimal cutoff value of boost Rectumoverlap to predict rectum V75 >15% was 3.5% (sensitivity 100%, specificity 94%, p < 0.01), and the optimal cutoff value of boost Bladderoverlap to predict bladder V80 >10% was 5.0% (sensitivity 83%, specificity 100%, p < 0.01).
The degree of overlap between PTV and bladder or rectum can be used to accurately guide physicians on the use of interventions to limit the extent of the overlap region prior to optimization.
本研究的目的是确定在前列腺癌容积调强弧形放疗（VMAT）中，计划靶区（PTV）与直肠（直肠重叠）或PTV与膀胱（膀胱重叠）之间的重叠程度是否可预测优化后实现的剂量-体积关系，并使用这些重叠体积确定预测方程和临界值，超过该临界值临床正常组织效应定量分析（QUANTEC）剂量-体积限制不太可能得到满足。
57例前列腺癌患者在相同的优化条件和归一化条件下接受VMAT计划。PTV（针对50.4 Gy的主计划和30.6 Gy的追加计划）包括前列腺和精囊周围5至10 mm的边界。使用Pearson相关性分析、线性回归分析和受试者操作特征（ROC）曲线将重叠百分比与剂量-体积参数相关联。
直肠重叠百分比和膀胱重叠百分比与该器官的 sparing 相关，但对其他剂量-体积参数影响极小，分别以R² = 0.78和R² = 0.83预测主计划直肠V45和膀胱V50，并分别以R² = 0.53和R² = 0.81预测追加计划直肠V30和膀胱V30。预测直肠V75>15%的追加直肠重叠的最佳临界值为3.5%（敏感性100%，特异性94%，p<0.01），预测膀胱V80>10%的追加膀胱重叠的最佳临界值为5.0%（敏感性83%，特异性100%，p<0.01）。
PTV与膀胱或直肠之间的重叠程度可用于准确指导医生在优化之前使用干预措施来限制重叠区域的范围。
