Racka Iga, Majewska Karolina, Winiecki Janusz
Medical Physics Department, Prof. Franciszek Łukaszczyk Memorial Oncology Centre in Bydgoszcz, Bydgoszcz, Poland.
Clinic of Oncology and Brachytherapy, Collegium Medicum in Bydgoszcz, Nicholas Copernicus University in Torun, Bydgoszcz, Poland.
Strahlenther Onkol. 2023 Jan;199(1):90-101. doi: 10.1007/s00066-022-01979-2. Epub 2022 Aug 9.
The purpose of this study was to compare two techniques of irradiation of left-sided breast cancer patients who underwent breast-conserving surgery, three-dimensional conformal radiotherapy technique (3D-CRT) and volumetric modulated arc therapy (VMAT), in terms of dose distribution in the planning target volume (PTV) and organs at risk (OARs). The second aim of the study was estimation of the projected risk of radiation-induced secondary cancer for both radiotherapy techniques.
For 25 patients who underwent CT simulation in deep inspiration breath-hold (DIBH), three treatment plans were generated: one using a three-dimensional conformal radiotherapy technique and two using volumetric modulated arc therapy. First VMAT-DIBH geometry consisted of three partial arcs (ARC-DIBH 3A) and second consisted of four partial arcs (ARC-DIBH 4A). Cumulative dose-volume histograms (DVHs) were used to compare dose distributions within the PTV and OARs (heart, left anterior descending coronary artery [LAD], ipsilateral and contralateral lung [IL, CL], and contralateral breast [CB]). Normal tissue complication probabilities (NTCPs) and organ equivalent doses (OEDs) were calculated using the differential DVHs. Excess absolute risks (EARs) for second cancers were estimated using Schneider's full mechanistic dose-response model.
All plans fulfilled the criterium for PTV V95% ≥ 95%. The PTV coverage, homogeneity, and conformity indices were significantly better for VMAT-DIBH. VMAT showed a significantly increased mean dose and V5Gy for all OARs, but reduced LAD D by 15 Gy. For IL, CL, and CB, the 3D-CRT DIBH method achieved the lowest values of EAR: 28.38 per 10,000 PYs, 2.55 per 10,000 PYs, and 4.48 per 10,000 PYs (p < 0.001), compared to 40.29 per 10,000 PYs, 15.62 per 10,000 PYs, and 23.44 per 10,000 PYs for ARC-DIBH 3A plans and 41.12 per 10,000 PYs, 15.59 per 10,000 PYs, and 22.73 per 10,000 PYs for ARC-DIBH 4A plans. Both techniques provided negligibly low NTCPs for all OARs.
The study shows that VMAT-DIBH provides better OAR sparing against high doses. However, the large low-dose-bath (≤ 5 Gy) is still a concern due to the fact that a larger volume of normal tissues exposed to lower doses may increase a radiation-induced risk of secondary cancer.
本研究旨在比较接受保乳手术的左侧乳腺癌患者的两种放疗技术，即三维适形放疗技术（3D-CRT）和容积调强弧形放疗（VMAT），比较其在计划靶区（PTV）和危及器官（OARs）中的剂量分布。本研究的第二个目的是评估两种放疗技术辐射诱发继发性癌症的预计风险。
对25例在深吸气屏气（DIBH）状态下进行CT模拟的患者，制定了三个治疗计划：一个采用三维适形放疗技术，两个采用容积调强弧形放疗。第一个VMAT-DIBH方案由三个部分弧形组成（ARC-DIBH 3A），第二个由四个部分弧形组成（ARC-DIBH 4A）。累积剂量体积直方图（DVHs）用于比较PTV和OARs（心脏、左前降支冠状动脉[LAD]、同侧和对侧肺[IL, CL]以及对侧乳腺[CB]）内的剂量分布。使用微分DVHs计算正常组织并发症概率（NTCPs）和器官等效剂量（OEDs）。使用施奈德的全机制剂量反应模型估计继发性癌症的超额绝对风险（EARs）。
所有计划均满足PTV V95%≥95%的标准。VMAT-DIBH的PTV覆盖度、均匀性和适形指数明显更好。VMAT显示所有OARs的平均剂量和V5Gy显著增加，但LAD的剂量降低了15 Gy。对于IL、CL和CB，3D-CRT DIBH方法的EAR值最低：每10,000人年分别为28.38、2.55和4.48（p<0.001），相比之下，ARC-DIBH 3A计划分别为每10,000人年40.29、15.62和23.44，ARC-DIBH 4A计划分别为每10,000人年41.12、15.59和22.73。两种技术对所有OARs的NTCPs均极低。
研究表明，VMAT-DIBH在避免高剂量照射OARs方面效果更好。然而，由于更大体积的正常组织暴露于较低剂量下可能会增加辐射诱发继发性癌症的风险，大量低剂量区（≤5 Gy）仍是一个问题。
