胸腺瘤术后调强放射治疗和容积弧形调强放射治疗剂量学分析

Dosimeter analysis of thymoma postoperative radiotherapy with intensity modulated radiation therapy and volumetric modulated arc therapy

目的研究在胸腺瘤术后放射治疗中分别采取调强放射治疗（IMRT）技术和容积弧形调强放射治疗（VMAT）技术的剂量学特点，并进一步指导胸腺瘤的放射治疗计划设计。方法选择2012年9月至2013年2月10例行放射治疗的胸腺瘤术后的患者，其中男性7例，女性3例：年龄38-63岁。中位年龄56岁。分别在治疗计划系统（TPS）上勾画大体肿瘤靶区（GTV）、临床肿瘤靶区（CTV）和计划肿瘤靶区（P11V）。术后胸腺瘤放射治疗处方剂量为5000cGy，分别采取IMRT和VMAT技术设计治疗计划，由TPS得到正常组织、危及器官的受累剂量和靶区与处方剂量分布的一致性，并列表比较。结果IMRT的计划靶区的适形指数（CI）和均匀性指数（HI）分别为0．78和1．11，VMAT计划的CI和HI为O．87和1．07。VMAT相比较IMRT在靶区剂量的适形性和不均匀性均稍优于IMRT（P=0．012，P=0．047）。在并型器官如肺组织的低剂量体积（V5、V10）上，VMAT比IMRT对肺组织产生更大的损伤，分别为69．26％和64．68％（P〈0．05）、47．52％和44．93％（P〈0．05）。对于脊髓的最大剂量．VMAT为20.51Gy，IMRT为31．66Gy；心脏的V40和V50，VMAT和IMRT相应的值为10．64％和15．08％、4．39％和8．15％；食管的最大剂量，VMAT和IMRT相应的值为38．67Gv和44-30Gy。可以看出VMAT在保护正常器官方面均优于IMRT。结论对于肿瘤靶区偏中心、体积较小、压迫正常肺组织较小的患者，采取IMRT的治疗方式可以更好地保护正常和危及器官：但是对于肿瘤靶区体积较大、中心型、压迫正常肺组织较大的患者，采取照射范围较大的VMAT更加有优势。

Objective To analyze the dosimetry characteristics of thymoma radiotherapy with intensity modulated radiation therapy CIMRT） and volumetric modulated arc therapy （VMAT） technology, and provide further guidance for designing thymoma radiation therapy plan. Methods From September 2012 to February 2013, a total of 10 patients with thymoma were enrolled, which included 7 males and 3 females with ages of 38 - 63 years old. The gross tumor volume（GTV）, clinical target volume（CTV） and planning target volume（PTV） of the target on treatment planning system（TPS） were performed. Prescription dose was 5 000 cGy, and IMRT and VMAT based therapy plan were applied respectively. Finally, the dose of organ involvement, consistency of target and dose distribution were evaluated. Results The conformal index（C0 and homogeneity index（HI） for IMRT were 0.78 and 1.11, respectively, while VMAT were 0.87 and 1.07, respectively, showed the superiority in consistency of target and dose distribution（P = 0.012, P = 0.047）. On the low-dose volume（Vs, V10） at the parallel organs such as lung tissue, VMAT Ied to greater damage than IMRT, which were 69.26 % and 64.68 %（P 〈 0.05）, 47.52 % and 44.93 %, respectively （P 〈 0.05）. For the maximum dose of spinal cord, VMAT was 20.51 Gy and IMRT was 31.66 Gy. VMAT were 10.64 % and 15.08 %, and IMRT were 4.39 % and 8.15 %, respectively, correspondence of the V40 and Vs0 of heart. For the maximum dose of esophagus, VMAT was 38.67 Gy and IMRT was 44.30 Gy. For the protection of normal organs, the VMAT was better than IMRT. Conclusion It is demonstrated that IMRT technology is a better choice for the patient with tumor target off-center type, smaller volume and less oppressed normal lung tissue, and the IMRT treatment could protect the normal and organs at risk. But for the patients with largest target volume, central type and larger oppressed normal lung tissue, VMAT is a better choice for radiation therapy.