Singh S, Raina P, Gurjar O P
PhD, Department of Physics, Ranchi University, Ranchi- 834008, Jharkhand, India.
DipRP, Research Scholars, University Department of Physics, Ranchi University, Ranchi- 834008, Jharkhand State, India.
J Biomed Phys Eng. 2019 Dec 1;9(6):613-620. doi: 10.31661/jbpe.v0i0.1185. eCollection 2019 Dec.
Nowadays, advanced radiotherapy equipment includes algorithms to calculate dose. The verification of the calculated doses is important to achieve accurate results. Mostly homogeneous dosimetric phantoms are available commercially which do not mimic the actual patient anatomy; therefore, an indigenous heterogeneous pelvic phantom mimicking actual human pelvic region has been used to verify the doses calculated by different algorithms.
This study aims to compare the planed dose using different algorithms with measured dose using an indigenous heterogeneous pelvic phantom.
In this experimental study, various three dimensional conformal radiotherapy (3D-CRT) plans were made using different doses calculated by algorithms. The plans were delivered by medical linear accelerator and doses were measured by ion chamber placed in the indigenous pelvic phantom. Planned and measured doses were compared with together and analyzed.
The relative electron densities of different parts in the pelvic phantom were found to be in good agreement with that of actual pelvic parts, including bladder, rectum, fats and bones. The highest percentage deviations between planned and measured dose were calculated in the single field for Superposition algorithm (3.09%) and single field with 45˚wedge for Superposition (3.04%). The least percentage deviation was calculated in the opposite field for Convolution which was - 0.08%. The results were within the range of ±5% as recommended by International Commission on Radiation Units and Measurement.
The cost-effective indigenous heterogeneous pelvic phantom has the density pattern similar to the actual pelvic region; thus, it can be used for routine patient-specific quality assurance.
如今，先进的放射治疗设备包含剂量计算算法。对计算出的剂量进行验证对于获得准确结果至关重要。市面上大多可买到的剂量学模体是均匀的，无法模拟实际患者的解剖结构；因此，一种模仿实际人体盆腔区域的自制非均匀盆腔模体已被用于验证不同算法计算出的剂量。
本研究旨在比较使用不同算法的计划剂量与使用自制非均匀盆腔模体测量的剂量。
在本实验研究中，利用算法计算出的不同剂量制定了各种三维适形放疗（3D - CRT）计划。这些计划由医用直线加速器执行，剂量由置于自制盆腔模体内的电离室测量。将计划剂量和测量剂量进行对比并分析。
发现盆腔模体中不同部位的相对电子密度与实际盆腔部位（包括膀胱、直肠、脂肪和骨骼）的相对电子密度高度一致。叠加算法单野中计划剂量与测量剂量之间的最大百分比偏差为3.09%，叠加算法45˚楔形单野中为3.04%。卷积算法对穿野中的最小百分比偏差为 - 0.08%。结果在国际辐射单位与测量委员会建议的±5%范围内。
这种经济高效的自制非均匀盆腔模体具有与实际盆腔区域相似的密度模式；因此，它可用于常规的患者特异性质量保证。
