Renaud James, Yartsev Slav, Dar A Rashid, Van Dyk Jake
Department of Physics and Engineering, London Regional Cancer Program, London Health Sciences Centre, London, Ontario, Canada.
Med Dosim. 2009 Fall;34(3):233-42. doi: 10.1016/j.meddos.2008.10.002. Epub 2008 Nov 24.
The purpose of this study was to compare 2 adaptive radiotherapy strategies with helical tomotherapy. A patient having mesothelioma with mediastinal nodes was treated using helical tomotherapy with pretreatment megavoltage CT (MVCT) imaging. Gross tumor volumes (GTVs) were outlined on every MVCT study. Two alternatives for adapting the treatment were investigated: (1) keeping the prescribed dose to the targets while reducing the dose to the OARs and (2) escalating the target dose while maintaining the original level of healthy tissue sparing. Intensity modulated radiotherapy (step-and-shoot IMRT) and 3D conformal radiotherapy (3DCRT) plans for the patient were generated and compared. The primary lesion and nodal mass regressed by 16.2% and 32.5%, respectively. Adapted GTVs and reduced planning target volume (PTV) margins of 4 mm after 22 fractions decrease the planned mean lung dose by 19.4%. For dose escalation, the planned prescribed doses may be increased from 50.0 to 58.7 Gy in PTV(1) and from 60.0 to 70.5 Gy in PTV(2). The step-and-shoot IMRT plan was better in sparing healthy tissue but did not provide target coverage as well as the helical tomotherapy plan. The 3DCRT plan resulted in a prohibitively high planned dose to the spinal cord. MVCT studies provide information both for setup correction and plan adaptation. Improved healthy tissue sparing and/or dose escalation can be achieved by adaptive planning.
本研究的目的是将两种自适应放疗策略与螺旋断层放疗进行比较。一名患有间皮瘤并伴有纵隔淋巴结的患者接受了螺旋断层放疗，并在治疗前进行了兆伏级CT（MVCT）成像。在每次MVCT检查中勾勒出大体肿瘤体积（GTV）。研究了两种治疗适应方案：（1）在降低危及器官（OAR）剂量的同时保持对靶区的处方剂量，以及（2）在维持原有健康组织保护水平的同时提高靶区剂量。生成并比较了该患者的调强放疗（静态调强IMRT）和三维适形放疗（3DCRT）计划。原发灶和淋巴结肿块分别缩小了16.2%和32.5%。22次分割后，适应后的GTV和4mm的计划靶区（PTV）边界缩小使计划平均肺剂量降低了19.4%。对于剂量递增，PTV（1）的计划处方剂量可从50.0Gy增加到58.7Gy，PTV（2）的计划处方剂量可从60.0Gy增加到70.5Gy。静态调强IMRT计划在保护健康组织方面更好，但靶区覆盖不如螺旋断层放疗计划。3DCRT计划导致脊髓的计划剂量过高。MVCT研究为摆位校正和计划适应提供了信息。通过自适应计划可以实现更好的健康组织保护和/或剂量递增。
