Gurjar Om Prakash, Paliwal Radha Kishan, Mishra Surendra Prasad
Roentgen-SAIMS Radiation Oncology Centre, Sri Aurobindo Institute of Medical Sciences, Indore, Madhya Pradesh, India.
Department of Physics, Mewar University, Chittorgarh, Rajasthan, India.
J Med Phys. 2017 Apr-Jun;42(2):80-85. doi: 10.4103/jmp.JMP_125_16.
The aim is to study the density, isodose depths, and doses at different points in slab-pinewood-slab (SPS) phantom, solid phantom SP34 (made up of polystyrene), and chest level of actual patient for developing heterogeneous chest phantom mimicking thoracic region of human body. A 6 MV photon beam of field size of 10 cm × 10 cm was directed perpendicular to the surface of computed tomography (CT) images of chest level of patient, SPS phantom, and SP34 phantom. Dose was calculated using anisotropic analytical algorithm. Hounsfield units were used to calculate the density of each medium. Isodose depths in all the three sets of CT images were measured. Variations between planned doses on treatment planning system (TPS) and measured on linear accelerator (LA) were calculated for three points, namely, near slab-pinewood interfaces (6 and 18 cm depths) and 10 cm depth in SPS phantom and at the same depths in SP34 phantom. Density of pinewood, SP34 slabs, chest wall, lung, and soft tissue behind lung was measured as 0.329 ± 0.08, 0.999 ± 0.02, 0.898 ± 0.02, 0.291 ± 0.12, and 1.002 ± 0.03 g/cc, respectively. Depths of 100% and 90% isodose curves in all the three sets of CT images were found to be similar. Depths of 80%, 70%, 60%, 50%, and 40% isodose lines in SPS phantom images were found to be equivalent to that in chest images, while it was least in SP34 phantom images. Variations in doses calculated at 6, 10, and 18 cm depths on TPS and measured on LA were found to be 0.36%, 1.65%, and 2.23%, respectively, in case of SPS phantom, while 0.24%, 0.90%, and 0.93%, respectively, in case of SP34 slab phantom. SPS phantom seemed equivalent to the chest level of human body. Dosimetric results of this study indicate that patient-specific quality assurance can be done using chest phantom mimicking thoracic region of human body, which has been fabricated using polystyrene and pinewood.
目的是研究平板 - 松木 - 平板（SPS）体模、固体体模SP34（由聚苯乙烯制成）以及实际患者胸部水平处不同点的密度、等剂量深度和剂量，以开发模拟人体胸部区域的非均匀性胸部体模。一束场大小为10 cm×10 cm的6 MV光子束垂直于患者胸部水平、SPS体模和SP34体模的计算机断层扫描（CT）图像表面照射。使用各向异性分析算法计算剂量。利用亨氏单位计算每种介质的密度。测量了所有三组CT图像中的等剂量深度。计算了治疗计划系统（TPS）上计划剂量与直线加速器（LA）上测量剂量在三个点的差异，这三个点分别是靠近平板 - 松木界面处（深度为6 cm和18 cm）以及SPS体模中10 cm深度处和SP34体模中相同深度处。测量得到松木、SP34平板、胸壁、肺以及肺后软组织的密度分别为0.329±0.08、0.999±0.02、0.898±0.02、0.291±0.12和1.002±0.03 g/cc。发现所有三组CT图像中100%和90%等剂量曲线的深度相似。SPS体模图像中80%、70%、60%、50%和40%等剂量线的深度与胸部图像中的相当，而在SP34体模图像中最小。对于SPS体模，在TPS上6 cm、10 cm和18 cm深度处计算的剂量与在LA上测量的剂量差异分别为0.36%、1.65%和2.23%，而对于SP34平板体模，分别为0.24%、0.90%和0.93%。SPS体模似乎与人体胸部水平相当。本研究的剂量学结果表明，可以使用模拟人体胸部区域的胸部体模进行患者特异性质量保证，该体模是用聚苯乙烯和松木制作的。
