COMPARATIVE RADIATION DOSIMETRY OF WHOLE BREAST RADIOTHERAPY USING IMRT AND VMAT TECHNIQUES IN LEFT SIDED BREAST CANCER PATIENTS AFTER BREAST CONSERVING SURGERY

Background:The radiotherapy of left sided breast cancers is mandatory and integral part of treatment and challenging because of surrounding critical structures posing increased risk of complications. The main objective of this study was to quantify doses toorgan at risk(OARs) including left lung, heart, contralateral breast, spinal cord, and planning target volume (PTV) using different radiation techniques like Intensity modulated radiation therapy (IMRT)&volumetric modulated arc therapy (VMAT) and comparison of radiation dosimetry.

Methods: A prospective study of 30 patients of left sided breast cancer who had undergone Breast Conservative Surgery (BCS) and chemotherapy was done for adjuvant radiation. For every patient radiation planning was done by two different techniques IMRT and VMAT. Then the comparison of radiation dosimetry parameters was done for all the techniques including the parameters like PTV coverage, doses to OAR like heart, left lung, contralateral breast and spinal cord and head of humerus. The Homogenity Index (HI) were calculated.

Result: The Mean age of the patient was 46.7 years. When comparing the doses delivered in IMRT and VMAT Technique for left sided breast cancer post breast conservation surgery there was significant difference in PTV Breast and axilla V95 Gy. It was 96.2±1.9% (IMRT) vs 94.8±1.71% (VMAT), (p=0.004). However significant sparing of Organs at Risk was seen. With ipsilateral lung dose mean V5 Gy was 77.86± 9.68% (IMRT) v/s 83.04± 9.86 % (VMAT), (p=0.0446). Also mean V30 Gy was 14.6±4.82% with IMRT vs 16.54±5.86% with VMAT, (p=0.0169). Heart mean dose was 8.8±1.49 Gy with IMRT and 10.98±3.7 Gy with VMAT, (p=0.0227). Further V30 Gy for Heart was 4.61±3.8% with IMRT and 6.72±4.0% with VMAT, (p=0.0132).No significant difference was seen with IMRT and VMAT technique for contralateral lung, contralateral breast and spinal cord.

Conclusion: In treatment of patients with radiation with left breast cancer patients post BCS using IMRT and VMAT technique it is seen significant dose reduction with IMRT Technique for ipsilateral lung and Heart as compared to VMAT technique. Significant V95 coverage for PTV Breast and axilla with IMRT as compared to VMAT. Hence in our Study IMRT technique was found to be superior for better sparing of Organ at risk and better PTV coverage.

背景：左侧乳腺癌放射治疗是治疗方案中不可或缺的核心组成部分，同时也是极具挑战性的治疗环节，因病灶周围存在诸多关键危及器官（Organ at Risk, OAR），会提升并发症发生风险。本研究的核心目标为：采用调强放射治疗（Intensity Modulated Radiation Therapy, IMRT）、容积调强弧形治疗（Volumetric Modulated Arc Therapy, VMAT）等不同放射治疗技术，量化左肺、心脏、对侧乳腺、脊髓等危及器官以及计划靶区（Planning Target Volume, PTV）的受照剂量，并对比不同技术的放射剂量学参数。

方法：本研究为前瞻性研究，纳入30例接受保乳手术（Breast Conservative Surgery, BCS）联合化疗的左侧乳腺癌患者，行术后辅助放射治疗。为每位患者分别采用IMRT与VMAT两种技术制定放射治疗计划，随后对比两种技术的放射剂量学参数，包括PTV覆盖度、左肺、心脏、对侧乳腺、脊髓及肱骨小头等危及器官的受照剂量，并计算均匀性指数（Homogeneity Index, HI）。

结果：入组患者的平均年龄为46.7岁。对比保乳术后左侧乳腺癌患者采用IMRT与VMAT技术的受照剂量，二者在乳腺及腋窝PTV的V95Gy剂量体积占比存在显著统计学差异：IMRT组为96.2±1.9%，VMAT组为94.8±1.71%（p=0.004）。但IMRT技术对危及器官的保护效果更优：同侧肺的平均V5Gy占比，IMRT组为77.86±9.68%，VMAT组为83.04±9.86%（p=0.0446）；平均V30Gy占比，IMRT组为14.6±4.82%，VMAT组为16.54±5.86%（p=0.0169）。心脏的平均受照剂量，IMRT组为8.8±1.49Gy，VMAT组为10.98±3.7Gy（p=0.0227）；心脏V30Gy占比，IMRT组为4.61±3.8%，VMAT组为6.72±4.0%（p=0.0132）。而在对侧肺、对侧乳腺及脊髓的受照剂量方面，两种技术未观察到显著统计学差异。

结论：在保乳术后左侧乳腺癌患者的放射治疗中，相较于VMAT技术，IMRT技术可显著降低同侧肺与心脏的受照剂量，同时在乳腺及腋窝PTV的V95Gy覆盖度上更具优势。本研究结果显示，IMRT技术在危及器官保护与PTV覆盖度方面均表现更优。