Xin-Ye Ni, Ren Lei, Yan Hui, Yin Fang-Fang
Department of Radiation Oncology, Second People's Hospital of Changzhou, Nanjing Medical University, Changzhou, China
Department of Radiation Oncology, Duke University Medical Center, Durham, NC, USA.
Technol Cancer Res Treat. 2016 Dec;15(6):NP25-NP34. doi: 10.1177/1533034615610251. Epub 2015 Nov 1.
This study aimed to detect the sensitivity of Delt 4 on ordinary field multileaf collimator misalignments, system misalignments, random misalignments, and misalignments caused by gravity of the multileaf collimator in stereotactic body radiation therapy.
(1) Two field sizes, including 2.00 cm (X) × 6.00 cm (Y) and 7.00 cm (X) × 6.00 cm (Y), were set. The leaves of X1 and X2 in the multileaf collimator were simultaneously opened. (2) Three cases of stereotactic body radiation therapy of spinal tumor were used. The dose of the planning target volume was 1800 cGy with 3 fractions. The 4 types to be simulated included (1) the leaves of X1 and X2 in the multileaf collimator were simultaneously opened, (2) only X1 of the multileaf collimator and the unilateral leaf were opened, (3) the leaves of X1 and X2 in the multileaf collimator were randomly opened, and (4) gravity effect was simulated. The leaves of X1 and X2 in the multileaf collimator shifted to the same direction. The difference between the corresponding 3-dimensional dose distribution measured by Delt 4 and the dose distribution in the original plan made in the treatment planning system was analyzed with γ index criteria of 3.0 mm/3.0%, 2.5 mm/2.5%, 2.0 mm/2.0%, 2.5 mm/1.5%, and 1.0 mm/1.0%.
(1) In the field size of 2.00 cm (X) × 6.00 cm (Y), the γ pass rate of the original was 100% with 2.5 mm/2.5% as the statistical standard. The pass rate decreased to 95.9% and 89.4% when the X1 and X2 directions of the multileaf collimator were opened within 0.3 and 0.5 mm, respectively. In the field size of 7.00 (X) cm × 6.00 (Y) cm with 1.5 mm/1.5% as the statistical standard, the pass rate of the original was 96.5%. After X1 and X2 of the multileaf collimator were opened within 0.3 mm, the pass rate decreased to lower than 95%. The pass rate was higher than 90% within the 3 mm opening. (2) For spinal tumor, the change in the planning target volume V under various modes calculated using treatment planning system was within 1%. However, the maximum dose deviation of the spinal cord was high. In the spinal cord with a gravity of -0.25 mm, the maximum dose deviation minimally changed and increased by 6.8% than that of the original. In the largest opening of 1.00 mm, the deviation increased by 47.7% than that of the original. Moreover, the pass rate of the original determined through Delt 4 was 100% with 3 mm/3% as the statistical standard. The pass rate was 97.5% in the 0.25 mm opening and higher than 95% in the 0.5 mm opening A, 0.25 mm opening A, whole gravity series, and 0.20 mm random opening. Moreover, the pass rate was higher than 90% with 2.0 mm/2.0% as the statistical standard in the original and in the 0.25 mm gravity. The difference in the pass rates was not statistically significant among the -0.25 mm gravity, 0.25 mm opening A, 0.20 mm random opening, and original as calculated using SPSS 11.0 software with P > .05.
Different analysis standards of Delt 4 were analyzed in different field sizes to improve the detection sensitivity of the multileaf collimator position on the basis of 90% throughout rate. In stereotactic body radiation therapy of spinal tumor, the 2.0 mm/2.0% standard can reveal the dosimetric differences caused by the minor multileaf collimator position compared with the 3.0 mm/3.0% statistical standard. However, some position derivations of the misalignments that caused high dose amount to the spinal cord cannot be detected. However, some misalignments were not detected when a large number of multileaf collimator were administered into the spinal cord.
本研究旨在检测在立体定向体部放射治疗中，Delta 4对普通射野多叶准直器错位、系统错位、随机错位以及多叶准直器重力导致的错位的敏感性。
（1）设置两种射野尺寸，分别为2.00 cm（X）×6.00 cm（Y）和7.00 cm（X）×6.00 cm（Y）。多叶准直器中的X1和X2叶片同时打开。（2）采用3例脊柱肿瘤的立体定向体部放射治疗病例。计划靶区剂量为1800 cGy，分3次照射。模拟的4种情况包括：（1）多叶准直器中的X1和X2叶片同时打开；（2）仅打开多叶准直器的X1及单侧叶片；（3）多叶准直器中的X1和X2叶片随机打开；（4）模拟重力效应，多叶准直器中的X1和X2叶片向同一方向偏移。采用3.0 mm/3.0%、2.5 mm/2.5%、2.0 mm/2.0%、2.5 mm/1.5%和1.0 mm/1.0%的γ指数标准，分析Delta 4测量的相应三维剂量分布与治疗计划系统中原始计划剂量分布之间的差异。
（1）在2.00 cm（X）×6.00 cm（Y）的射野尺寸下，以2.5 mm/2.5%为统计标准，原始γ通过率为100%。当多叶准直器的X1和X2方向分别打开0.3和0.5 mm时，通过率分别降至95.9%和89.4%。在7.00（X）cm×6.00（Y）cm的射野尺寸下，以1.5 mm/1.5%为统计标准，原始通过率为96.5%。多叶准直器的X1和X2打开0.3 mm后，通过率降至95%以下。在3 mm开口范围内通过率高于90%。（2）对于脊柱肿瘤，使用治疗计划系统计算的各种模式下计划靶区体积V的变化在1%以内。然而，脊髓的最大剂量偏差较高。在重力为-0.25 mm的脊髓中，最大剂量偏差变化最小，比原始值增加了6.8%。在最大开口为1.00 mm时，偏差比原始值增加了47.7%。此外，以3 mm/3%为统计标准，通过Delta 4确定的原始通过率为100%。在0.25 mm开口时通过率为97.5%，在0.5 mm开口A、0.25 mm开口A、整个重力系列和0.20 mm随机开口时通过率高于95%。此外，以2.0 mm/2.0%为统计标准，原始和0.25 mm重力情况下通过率高于90%。使用SPSS 11.0软件计算，-0.25 mm重力、0.25 mm开口A、0.20 mm随机开口和原始情况之间的通过率差异无统计学意义（P>.05）。
在不同射野尺寸下分析Delta 4的不同分析标准，以在90%通过率的基础上提高多叶准直器位置的检测敏感性。在脊柱肿瘤的立体定向体部放射治疗中，与3.0 mm/3.0%统计标准相比，2.0 mm/2.0%标准可揭示多叶准直器轻微位置变化引起的剂量差异。然而，一些导致脊髓高剂量的错位位置偏差无法检测到。然而，当大量多叶准直器应用于脊髓时，一些错位未被检测到。
