摘要目的:探讨乳腺癌改良根治术后内乳电子线大分割照射剂量学特征及急性不良反应、近期疗效。方法:选择2018—2020年收治155例乳腺癌改良根治术后患者，Ⅲ期137例(88.4%)，Ⅱ期18例(11.6%)。所有患者均接受规范的化疗、内分泌治疗和抗Her2靶向治疗。按第1、2、3肋间将内乳临床靶体积(CTV im)分为3个亚区(CTV im1、CTV im2、CTV im3)，同时勾画锁骨上下区形成计划靶体积(PTV sc)。胸壁CTV和CTV im采用6~15 MeV电子线照射43.5 Gy分15次，3周完成。PTV sc采用6 MV X线二维放疗或三维放疗43.5 Gy分15次，3周完成。评估内乳、PTV sc及肺、心脏、左前降支(LAD)和右冠脉(RA)的剂量学特征，分析急性不良反应、近期疗效。 结果:CTV im的D mean为(43.3±2.6) Gy，D 95%为(30.5±8.3) Gy，V 90%为(85.0±10.5)%，V 80%为(91.0±7.4)%。CTV im1的相应参数值显著低于CTV im2和CTV im3(均 P<0.001)。体质指数对内乳剂量无影响( P>0.05)。三维放疗比二维放疗技术显著增加CTV im的D mean[(43.4±2.6) Gy∶(41.4±2.3) Gy， P＝0.021]和PTV sc的热点体积[V 110%：(26.7±17.5) cm 3∶(12.5±8.4) cm 3， P＝0.018；V 120%：(6.1±5.3) cm 3∶(2.0±2.6) cm 3， P＝0.023]。患肺D mean为(9.8±1.9) Gy，V 20Gy为(19.7±4.7)%。全组患者心脏D mean为(3.3±1.7) Gy，左乳腺癌为(4.7±1.4) Gy，右乳腺癌为(2.6±1.2) Gy。左乳腺癌患者LADD mean为(13.9±4.9) Gy，右乳腺癌患者RAD mean为(7.5±3.7) Gy。≥2级急性放射性皮炎、放射性食管炎、放射性肺炎发生率分别为19.3%、4.5%、2.6%。中位随访20.5个月(9.9~41.8个月)，2例胸壁复发，2例区域淋巴结复发，6例远处转移，死亡1例。 结论:乳腺癌改良根治术后内乳电子线大分割照射时肺、心、冠脉剂量较低，患者急性不良反应轻且发生率低。但第1肋间的内乳剂量偏低，虽然近期随访疗效较好但需要长期随访。

abstractsObjective:To investigate the dosimetric characteristics, acute toxicity and short-term efficacy of postmastectomy hypofractionated internal mammary (IM) chain irradiation with electrons in patients with high-risk breast cancer.Methods:A total of 155 patients with breast cancer who underwent modified mastectomy between November 2018 and January 2020 were selected. Among them, 137(88.4%) patients were classified as stage Ⅲ and 18(11.6%) as stage Ⅱ. All patients received standard chemotherapy, endocrine therapy and anti-Her2 targeted therapy. CTV im was divided into three subregions: CTV im1, CTV im2 and CTV im3, which represented the first, second and third intercostal IM, respectively. The planning target volume of subraclavicular region (PTV sc) was delineated. CTV cw and CTV im were irradiated with 6-15 MeV electron at 43.5 Gy in 15 fractions over 3 weeks. Moreover, PTV sc was irradiated with 6 MV X-ray at 43.5 Gy in 15 fractions over 3 weeks using two-dimensional radiotherapy (2DRT) or three-dimensional radiotherapy (3DRT). The dosimetric characteristics of CTV im, PTV sc, lung, heart, left anterior descending coronary artery (LAD) and right coronary artery (RA) were evaluated, and the acute toxicity and short-term efficacy were analyzed. Results:The mean dose (D mean) of CTV im was (43.3±2.6) Gy, D 95% was (30.5±8.3) Gy, V 90% was (85.0±10.5)% and V 80% was (91.0±7.4)%, respectively. The corresponding parameters of CTV im1 were significantly lower than those of CTV im2 and CTV im3(all P<0.001). Body mass index exerted no significant effect on IM dose ( P>0.05). Compared with 2DRT, 3DRT for SC significantly increased theD mean of CTV im[(43.4±2.6) Gy vs.(41.4±2.3) Gy, P=0.021], and the hot spot within PTV sc[V 110%: (26.7±17.5) cm 3vs.(12.5±8.4) cm 3, P=0.018; V 120%: (6.1±5.3) cm 3vs.(2.0±2.6) cm 3, P=0.023]. TheD mean of the ipsilateral lung was (9.8±1.9) Gy, and V 20Gy was (19.7±4.7)%. TheD mean of heart was (3.3±1.7) Gy in the whole group, (4.7±1.4) Gy for the left-sided breast cancer and (2.6±1.2) Gy for the right-sided breast cancer, respectively. TheD mean of LAD for the left-sided breast cancer was (13.9±4.9) Gy. TheD mean of RA for the right-sided breast cancer was (7.5±3.7) Gy. The incidence rates of ≥ grade 2 acute radiation dermatitis, esophagitis and pneumonitis were 19.3%, 4.5% and 2.6%, respectively. With a median follow-up time of 20.5 months (range: 9.9-41.8 months), 2 cases of chest wall recurrence, 2 regional lymph node recurrence, 6 distant metastases and 1 death were reported. Conclusions:When hypofractionated internal mammary chain is irradiated by electrons after mastectomy, the doses to the lung, heart and coronary artery are low, and the acute toxicities are mild. However, the dose to CTV im1 is inadequate. Although short-term efficacy is high, long-term follow-up is warranted.