乳腺癌调强放射治疗和常规切线野治疗的三维剂量学研究

背景与目的:乳房保留治疗已在早期乳腺癌患者中逐渐推广应用,其中全乳根治性放疗的标准技术通常采用常规切线野技术。调强放射治疗(intensity-modulatedradiotherapy,IMRT)技术有望在保障相同疗效的同时进一步减少放疗并发症,提高生活质量。本研究利用三维计划系统评价全乳IMRT的剂量学优势与适应证。方法:选择10例接受保乳手术的Tis～2N0M0早期乳腺癌病例,利用三维治疗计划系统为每例患者设计两种全乳放射治疗计划,切线野常规计划与IMRT计划,处方剂量均为5000cGy。用剂量体积直方图(dosevolumehistograms,DVH)来比较各种计划中计划靶体积(planningtargetvolume,PTV)、危及器官(organsatrisks,OARs)的剂量学差异。结果:靶区覆盖率在两种计划中相似,分别为98.3%和97.7%。与常规计划比较,IMRT计划的PTV接受<95%处方剂量与>103%处方剂量的体积百分比之和(inhomogeneityindex,IHI)从29.9%减少到2.9%,PTV接受至少105%处方剂量照射的体积百分比(V105%)从28.2%减少到0.6%;IMRT计划改善IHI和减少V105%的平均值在PTV较大的患者中优势更明显。左侧患者中冠状动脉的最大剂量(Dmax)以及心脏的平均剂量(Dmean)分别从5057.1cGy减少到4832.9cGy和从629.8cGy到450.7cGy;右侧患者肝脏的Dmean从283.9cGy减少到172.0cGy;所有患者中同侧肺的Dmean、至少接受20Gy照射的体积百分比(V20)分别从925.2cGy减少到765.9cGy,从16.0%到15.3%,Dmean与V20的平均值在IMRT计划中减少的百分比在不同射野中心肺厚度(centrallungdistance,CLD)亚组中分别是14.7%与20.9%,7.0%与12.9%;对侧乳腺和对侧肺的Dmean也分别从75.4cGy减少到20.3cGy和从30.9cGy到16.1cGy。结论:全乳IMRT的剂量学优势主要在于保证靶区覆盖率的前提下,显著改善靶区的剂量分布均匀性并一定程度上降低OARs的受照剂量与容积。乳房体积和CLD较大的病例可以通过IMRT技术获得更好的剂量学结果。

Dosimetric evaluation of intensity-modulated tangential beam versus conventional tangential irradiation for breast cancer

BACKGROUND & OBJECTIVE: Breast-conserving therapy has become a widely accepted treatment option in the management of early-stage breast cancer. Postoperative radiotherapy is conventionally delivered with conventional wedged tangential fields. However, intensity modulation in radiotherapy helps to maximize tumor control while minimizing damage to normal tissues. This study was to evaluate the potential dosimetric benefits and optimal indications of intensity-modulated radiotherapy (IMRT) for the intact breast. METHODS: Ten patients with stage Tis-2N0M0 breast cancer, who received breast-conserving surgery, were selected for this study. A dosimetric comparison of forward planning IMRT with conventional wedged tangential technique was performed on each patient using three-dimensional treatment planning. The total prescribed dose for both plans was 5000 cGy/25 fractions. Dose volume histograms (DVH) were used to compare the planning target volume (PTV) and organs at risks (OARs) such as ipsilateral lung, contralateral breast, contralateral lung for all patients, and coronary arteries, heart for left sided patients, and liver for right sided patients. RESULTS: The PTV coverage in IMRT plan was similar to that of the conventional plan (97.7% vs. 98.3%). A better dose uniformity throughout the whole breast was achieved by IMRT plan. The percentage of PTV receiving less than 95% prescribed dose and more than 103% prescribed dose (inhomogeneity index, IHI) decreased from 29.9% to 2.9%; the percentage of PTV receiving more than 105% prescribed dose (V105%) decreased from 28.2% to 0.6%. A better amelioration of IHI and reduction of V105% in IMRT plans were observed in the relatively large PTV subgroup. Obvious reduction in the doses to OARs was achieved by IMRT plan. The maximum dose (Dmax) of coronary artery decreased from 5057.1 cGy to 4832.9 cGy, and the mean dose (Dmean) of heart decreased from 629.8 cGy to 450.7 cGy; the Dmean of liver decreased from 283.9 cGy to 172.0 cGy for right sided patients; the Dmean and percentage of volume receiving more than 20 Gy (V20) of ipsilateral lung decreased from 925.2 cGy to 765.9 cGy, and from 16.0% to 15.3%, respectively; the Dmean and V20 of different central lung distance (CLD) subgroups decreased by 14.7% and 20.9%, 7.0% and 12.9%, respectively; the Dmean of contralateral breast decreased from 75.4 cGy to 20.3 cGy; the Dmean of contralateral lung decreased from 30.9 cGy to 16.1 cGy. CONCLUSION: Forward planning IMRT based on a standard tangential beam arrangement significantly improves the dose homogeneity throughout the target volume of intact breast, and reduces the dose to OARs, especially in patients with large breast volumes or exceeded CLD, who might be proposed as candidates of IMRT for intact breast.