Emory University, Department of Radiation Oncology, Atlanta, GA 30322, USA.
J Appl Clin Med Phys. 2010 Jun 21;11(3):3040. doi: 10.1120/jacmp.v11i3.3040.
The objective was to evaluate the performance of a high-definition multileaf collimator (MLC) of 2.5 mm leaf width (MLC2.5) and compare to standard 5 mm leaf width MLC (MLC5) for the treatment of intracranial lesions using dynamic conformal arcs (DCA) technique with a dedicated radiosurgery linear accelerator. Simulated cases of spherical targets were created to study solely the effect of target volume size on the performance of the two MLC systems independent of target shape complexity. In addition, 43 patients previously treated for intracranial lesions in our institution were retrospectively planned using DCA technique with MLC2.5 and MLC5 systems. The gross tumor volume ranged from 0.07 to 40.57 cm3 with an average volume of 5.9 cm3. All treatment parameters were kept the same for both MLC-based plans. The plan evaluation was performed using figures of merits (FOM) for a rapid and objective assessment on the quality of the two treatment plans for MLC2.5 and MLC5. The prescription isodose surface was selected as the greatest isodose surface covering >or= 95% of the target volume and delivering 95% of the prescription dose to 99% of target volume. A Conformity Index (CI) and conformity distance index (CDI) were used to quantifying the dose conformity to a target volume. To assess normal tissue sparing, a normal tissue difference (NTD) was defined as the difference between the volume of normal tissue receiving a certain dose utilizing MLC5 and the volume receiving the same dose using MLC2.5. The CI and normal tissue sparing for the simulated spherical targets were better with the MLC2.5 as compared to MLC5. For the clinical patients, the CI and CDI results indicated that the MLC2.5 provides better treatment conformity than MLC5 even at large target volumes. The CI's range was 1.15 to 2.44 with a median of 1.59 for MLC2.5 compared to 1.60-2.85 with a median of 1.71 for MLC5. Improved normal tissue sparing was also observed for MLC2.5 over MLC5, with the NTD always positive, indicating improvement, and ranging from 0.1 to 8.3 for normal tissue receiving 50% (NTV50), 70% (NTV70) and 90% (NTV90) of the prescription dose. The MLC2.5 has a dosimetric advantage over the MLC5 in Linac-based radiosurgery using DCA method for intracranial lesions, both in treatment conformity and normal tissue sparing when target shape complexity increases.
目的是评估具有 2.5 毫米叶片宽度(MLC2.5)的高清多叶准直器(MLC)的性能,并与标准 5 毫米叶片宽度 MLC(MLC5)进行比较,使用专用放射外科直线加速器治疗颅内病变的动态适形弧形(DCA)技术。创建模拟的球形靶区,仅研究靶区体积大小对两种 MLC 系统性能的影响,而不考虑靶区形状复杂性。此外,我们机构对 43 例颅内病变患者进行了回顾性 DCA 技术 MLC2.5 和 MLC5 系统治疗计划。肿瘤总体积范围为 0.07 至 40.57 cm3,平均体积为 5.9 cm3。两种基于 MLC 的计划均保持相同的所有治疗参数。使用快速和客观评估两种 MLC2.5 和 MLC5 治疗计划质量的优点(FOM)进行计划评估。处方等剂量面被选为覆盖>或= 95%的靶区最大等剂量面,并将 95%的处方剂量传递到 99%的靶区。一致性指数(CI)和一致性距离指数(CDI)用于量化目标体积的剂量一致性。为了评估正常组织的保留,定义正常组织差异(NTD)为使用 MLC5 接收一定剂量的正常组织体积与使用 MLC2.5 接收相同剂量的正常组织体积之间的差异。与 MLC5 相比,模拟球形靶区的 CI 和正常组织保留情况更好。对于临床患者,CI 和 CDI 结果表明,即使在大靶区体积下,MLC2.5 也能提供比 MLC5 更好的治疗一致性。CI 的范围为 1.15 至 2.44,中位数为 1.59,对于 MLC2.5,而 MLC5 的范围为 1.60 至 2.85,中位数为 1.71。与 MLC5 相比,MLC2.5 也观察到正常组织保存改善,NTD 始终为正,表明改善,范围为 0.1 至 8.3,用于接受 50%(NTV50)、70%(NTV70)和 90%(NTV90)处方剂量的正常组织。在使用 DCA 方法的基于 Linac 的放射外科治疗颅内病变时,MLC2.5 比 MLC5 在治疗一致性和正常组织保留方面具有剂量学优势,尤其是在靶区形状复杂性增加时。