Department of Hospital, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
Med Phys. 2013 Jul;40(7):071733. doi: 10.1118/1.4812426.
In broad-beam carbon-ion radiotherapy performed using the heavy-ion medical accelerator in Chiba, the number of monitor units is determined by measuring the physical dose at the center of the spread-out Bragg peak (SOBP) for the treatment beam. The total measurement time increases as the number of treatment beams increases, which hinders the treatment of an increased number of patients. Hence, Kusano et al. [Jpn. J. Med. Phys. 23(Suppl. 2), 65-68 (2003)] proposed a method to calculate the physical dose at the center of the SOBP for a treatment beam. Based on a recent study, the authors here propose a more accurate calculation method.
The authors measured the physical dose at the center of the SOBP while varying the circular field size and range-shifter thickness. The authors obtained the physical dose at the center of the SOBP for an irregularly shaped beam using Clarkson integration based on these measurements.
The difference between the calculated and measured physical doses at the center of the SOBP varied with a change in the central angle of the sector segment. The differences between the calculated and measured physical doses at the center of the SOBP were within ± 1% for all irregularly shaped beams that were used to validate the calculation method.
The accuracy of the proposed method depends on both the number of angular intervals used for Clarkson integration and the fineness of the basic data used for calculations: sampling numbers for the field size and thickness of the range shifter. If those parameters are properly chosen, the authors can obtain a calculated monitor unit number with high accuracy sufficient for clinical applications.
在使用重离子医疗加速器进行的宽束碳离子放射治疗中，通过测量扩展布拉格峰（SOBP）中心的物理剂量来确定治疗束的监测单位数量。随着治疗束数量的增加，总测量时间增加，这阻碍了更多患者的治疗。因此，Kusano 等人[Jpn. J. Med. Phys. 23(Suppl. 2), 65-68 (2003)]提出了一种计算治疗束 SOBP 中心物理剂量的方法。基于最近的一项研究，作者在这里提出了一种更准确的计算方法。
作者通过改变圆形射野大小和射程移位器厚度来测量 SOBP 中心的物理剂量。作者根据这些测量结果，使用 Clarkson 积分法获得了不规则形状射束的 SOBP 中心的物理剂量。
SOBP 中心计算和测量物理剂量之间的差异随扇形段中心角的变化而变化。对于所有用于验证计算方法的不规则形状射束，SOBP 中心计算和测量物理剂量之间的差异均在±1%以内。
所提出方法的准确性取决于用于 Clarkson 积分的角间隔数量以及用于计算的基本数据（射野大小和射程移位器厚度的采样数）的精细程度。如果适当选择这些参数，作者可以获得足够用于临床应用的高精度计算监测单位数量。
