Sharma S, Manigandan D, Gandhi A, Subramani V, Sharma D, Kumar P, Julka P, Rath G
All India Institute of Medical Sciences (AIIMS), New Delhi, Delhi.
Med Phys. 2012 Jun;39(6Part19):3840-3841. doi: 10.1118/1.4735676.
To dosimetrically compare the whole-IMRT, hybrid-IMRT (combination of IMRT and 3D-CRT) and 3D-conformal radiotherapy (3D- CRT) plans for larger targets.
Five previously treated patients of carcinoma cervix with para-aortic lymph-nodes (target length 33-34cm) were selected. PTV-P (PTV-Primary), PTV-PA (PTV-para-aortic) and organ at risks (OARs) were defined. Three plans were generated using Eclipse TPS for Varian CL2300C/D linear accelerator using 6MV photon beam. Three plans were: (i) Whole-IMRT: IMRT for both PTV-P and PTV-PA (ii) Hybrid-IMRT: IMRT for PTV-P and 3D-CRT for PTV-PA (iii) 3D-CRT: 3D-CRT for both PTV-P and PTV-PA. Prescription dose for PTV-P is 50.4Gy and PTV-PA is 45Gy in 28 fractions. Coverage index (CI=Target volume covered by prescription dose/Target volume), mean doses to bladder, rectum and bowel were used for plan comparison by using DVH. Integral dose (liter-Gray) to normal tissue (i.e., patient volume minus PTV-P and PTV-PA) and total monitor units (MUs) required to deliver a plan was also noted.
The CI for PTV-P is 0.98±0.20, 0.96±0.09, and 0.95±0.01 for Whole-IMRT, Hybrid-IMRT and 3D-CRT plan and for PTV- PA is 0.98±0.01, 0.98±0.01, and 0.97±0.20. Maximum doses to PTV-P are 5660.85±90.85cGy, 5640.35±70.35cGy and 5813.80±97.40cGy. Maximum doses to PTV-PA are 5000.60±109.10cGy, 5079.85±20.25cGy and 5092.25±19.75cGy. Mean doses to the bladder are 3810±225.80cGy, 3842.10±182.70cGy and 5204±98.25cGy for Whole-IMRT, Hybrid-IMRT and 3D-CRT plan, respectively. Mean doses to rectum are 3955.35±324.95cGy, 3971.15±354.15cGy and 4741.20±371.60cGy. Mean doses to bowel are 2623.35±320.85cGy, 2855.30±371.05cGy and 3011.7±433.80cGy. Average MUs required to deliver one fraction is 1285±87, 1585±186, 485±46 for Whole-IMRT, Hybrid-IMRT and 3D-CRT plans, respectively. Higher integral doses to normal tissue were observed for whole-IMRT (267.60±76 liter-Gy) followed by hybrid-IMRT (259.20±53 liter-Gy) and 3D-CRT (186.30±33 liter-Gy).
Whole-IMRT is useful for larger targets compared to hybrid-IMRT in terms of dose conformity, lesser MUs and reduced critical organ doses with little compromise on integral dose, where 3D-CRT sacrificed the OAR sparing.
通过剂量学方法比较大靶区的全容积调强放疗（whole-IMRT）、混合调强放疗（IMRT与3D适形放疗[3D-CRT]相结合）及3D适形放疗（3D-CRT）计划。
选取5例先前接受过治疗的伴有主动脉旁淋巴结转移的宫颈癌患者（靶区长33 - 34cm）。定义了计划靶区-原发灶（PTV-P）、计划靶区-主动脉旁（PTV-PA）及危及器官（OARs）。使用Eclipse治疗计划系统（TPS）针对瓦里安CL2300C/D直线加速器，采用6MV光子束生成三种计划。三种计划分别为：（i）全容积调强放疗：PTV-P和PTV-PA均采用调强放疗（ii）混合调强放疗：PTV-P采用调强放疗，PTV-PA采用3D适形放疗（iii）3D适形放疗：PTV-P和PTV-PA均采用3D适形放疗。PTV-P的处方剂量为50.4Gy，PTV-PA为45Gy，分28次照射。通过剂量体积直方图（DVH），使用覆盖指数（CI = 处方剂量覆盖的靶区体积/靶区体积）、膀胱、直肠和肠道的平均剂量进行计划比较。还记录了正常组织（即患者体积减去PTV-P和PTV-PA）的积分剂量（升-戈瑞）以及实施一个计划所需的总监测单位（MUs）。
全容积调强放疗、混合调强放疗和3D适形放疗计划中，PTV-P的CI分别为0.98±0.20、0.96±0.09和0.95±0.01，PTV-PA的CI分别为0.98±0.01、0.98±0.01和0.97±0.20。PTV-P的最大剂量分别为5660.85±90.85cGy、5640.35±70.35cGy和5813.80±97.40cGy。PTV-PA的最大剂量分别为5000.60±109.10cGy、5079.85±20.25cGy和5092.25±19.75cGy。全容积调强放疗、混合调强放疗和3D适形放疗计划中，膀胱的平均剂量分别为3810±225.80cGy、3842.10±182.70cGy和5204±98.25cGy。直肠的平均剂量分别为3955.35±324.95cGy、3971.15±354.15cGy和4741.20±371.60cGy。肠道的平均剂量分别为2623.35±320.85cGy、2855.30±371.05cGy和3011.7±433.80cGy。全容积调强放疗、混合调强放疗和3D适形放疗计划中，每次照射所需的平均MUs分别为1285±87、1585±186、485±46。观察到全容积调强放疗对正常组织的积分剂量较高（267.60±76升-戈瑞），其次是混合调强放疗（259.20±53升-戈瑞）和3D适形放疗（186.30±33升-戈瑞）。
与混合调强放疗相比，全容积调强放疗在剂量适形性、较少的MUs以及降低危及器官剂量方面对大靶区更有用，且在积分剂量上几乎没有妥协，而3D适形放疗则牺牲了危及器官的保护。
