Verma T R, Painuly N K, Tyagi M, Johny D, Gupta R, Bhatt M L B
PhD, Department of Radiotherapy, King George's Medical University, UP, Lucknow, India.
MSc, Department of Radiology &.
J Biomed Phys Eng. 2019 Dec 1;9(6):629-636. doi: 10.31661/jbpe.v0i0.1177. eCollection 2019 Dec.
In general, radiotherapy treatment planning is performed using the virtual bolus. It is necessary to investigate physical bolus in comparison to virtual one.
In the present study, first, radiological properties of superflab Gel bolus and Paraffin wax bolus was investigated in terms of their relative electron density. Then, dosimetric performance of both the bolus (i.e. Gel and Parafin wax) was compared with Virtual bolus.
In This experimental study, the radiological property of Wax and Gel boluses was investigated using two methods. In one, the relative electron density of both the Gel and Wax boluses was calculated by measuring their linear attenuation coefficient where in another method relative electron density was calculated by recording their CT No directly from their CT scan. Later CT scan of solid water slab phantom (dimension 30x30x15 cm), with physical boluses (i.e. Gel and Wax bolus) of appropriate thicknesses required to deliver a dose of 200 cGy at D using 4 MV, 6 MV and 15 MV photon beams, was taken. These CT data sets were retrieved to TPS. A plan was done to deliver a dose of 200 cGy at D using Single 4 MV, 6 MV and 15 MV photon beams. Dose at depths D, 1 cm, 2 cm, 3 cm, 4 cm and 5 cm was recorded. Using this similar method, doses at depths viz D, 1 cm, 2 cm, 3 cm, 4 cm and 5 cm was recorded for the Gel and Wax boluses. The differences in dose of gel and wax bolus from virtual bolus were recorded for comparison of their dosimetric performance.
The measured (calculated) relative electron density of wax and Gel bolus was found to be 0.958 (0.926) and 0.923 (0.907), respectively. Variation in dosimetric performance of Gel and Wax with reference to Virtual bolus was studied. However, on average, Gel bolus was more consistent with virtual bolus.
To avoid any dose difference between, delivered (using physical bolus) and planned (using virtual bolus), the physical boluses should be investigated for their dosimetric performance in comparison to virtual bolus. The results obtained and methodology used in this study can be applied in routine radiotherapy practices.
一般来说，放射治疗计划是使用虚拟填充物来进行的。有必要将物理填充物与虚拟填充物进行比较研究。
在本研究中，首先，从相对电子密度方面研究了超脂凝胶填充物和石蜡填充物的放射学特性。然后，将这两种填充物（即凝胶和石蜡）的剂量学性能与虚拟填充物进行比较。
在本实验研究中，使用两种方法研究了蜡和凝胶填充物的放射学特性。一种方法是通过测量凝胶和蜡填充物的线性衰减系数来计算它们的相对电子密度，另一种方法是直接从它们的CT扫描记录中读取CT值来计算相对电子密度。随后，对固体水模体（尺寸为30×30×15 cm）进行CT扫描，该模体带有适当厚度的物理填充物（即凝胶和蜡填充物），使用4 MV、6 MV和15 MV光子束在深度D处给予200 cGy剂量。将这些CT数据集导入治疗计划系统（TPS）。制定计划，使用单束4 MV、6 MV和15 MV光子束在深度D处给予200 cGy剂量。记录深度D、1 cm、2 cm、3 cm、4 cm和5 cm处的剂量。使用类似方法，记录凝胶和蜡填充物在深度D、1 cm、2 cm、3 cm、4 cm和5 cm处的剂量。记录凝胶和蜡填充物与虚拟填充物剂量的差异，以比较它们的剂量学性能。
测得（计算得出）蜡和凝胶填充物的相对电子密度分别为0.958（0.926）和0.923（0.907）。研究了凝胶和蜡相对于虚拟填充物的剂量学性能变化。然而，平均而言，凝胶填充物与虚拟填充物更为一致。
为避免（使用物理填充物）实际给予的剂量与（使用虚拟填充物）计划的剂量之间出现任何差异，应将物理填充物与虚拟填充物的剂量学性能进行比较研究。本研究获得的结果和使用的方法可应用于常规放射治疗实践。
