Department of Radiation Oncology, Kasturba Medical College, Mangalore , Manipal Academy of Higher Education, Manipal, India.
Department of Radiation Physics, Cachar cancer hospital &Research Centre, Silchar, Assam, India.
Asian Pac J Cancer Prev. 2023 May 1;24(5):1659-1666. doi: 10.31557/APJCP.2023.24.5.1659.
To develop a dosimetric tool to estimate the dose delivered in the presence of air pockets with EBT3 film while simulating the conditions of vaginal vault brachytherapy (VVBT) with 3.0 diameter cylindrical applicator at a prescription dose distance of 5mm from the surface of it.
Six acrylic plates (10 cm x 10 cm, 0.5 cm thick) with four different types of slots were designed and produced locally. They can hold a cylindrical vaginal brachytherapy applicator in the centre, air equivalent material from the applicator's surface [(sizes 4.5 mm (A), 3.0 mm (B), and 2.0 mm (C)], EBT3 film at the prescribed dose distance, and holder rods. Plates were layered together with acrylic rods and assembled in a holding box in a water phantom. Three treatment plans done in TPS with prescription doses of 2 Gy, 3 Gy, and 4 Gy at 5.0 mm with a treatment length of 6 cm, and were executed in Co-60-based HDR brachytherapy unit (M/s SagiNova, Germany) with & without the placement of air equivalent material, and the dose received at slot locations A, B, & C were noted.
The mean percentage deviation of measured dose without and with presence of air pocket at A, B and C was 13.9%, 11.0% and 6.4% respectively for all dose prescriptions. As the air pocket size expanded radially from 2.0 mm to 4.5 mm, the increase in dosage ranged from 6.4% to 13.9% which was due to the fact that the film was held at dosage prescription distance and the lack of attenuation of photons radially through air pocket.
The present study can be carried out with a 3D printed phantom that simulates VVBT application having air pockets of different dimensions at different locations and also can be analyzed with Monte Carlo simulations.
开发一种剂量学工具，以在使用 EBT3 膜模拟阴道穹窿近距离放射治疗（VVBT）条件下，测量存在气腔时的剂量，该治疗使用直径为 3.0 厘米的圆柱形施源器，处方剂量距离为 5 毫米。
本地设计并制作了六块带有四个不同类型狭槽的丙烯酸板（10 厘米 x 10 厘米，0.5 厘米厚）。它们可以在中心容纳圆柱形阴道近距离放射治疗施源器、施源器表面的空气等效材料[尺寸为 4.5 毫米（A）、3.0 毫米（B）和 2.0 毫米（C）]、EBT3 膜在规定的剂量距离处，以及保持杆。将板与丙烯酸棒分层，并在水模体中的保持盒中组装在一起。在 TPS 中进行了三个治疗计划，处方剂量分别为 2 Gy、3 Gy 和 4 Gy，在 5.0 毫米处治疗长度为 6 厘米，并在 Co-60 为基础的 HDR 近距离放射治疗单元（M/s SagiNova，德国）中执行，无论是否放置空气等效材料，都记录了在狭槽位置 A、B 和 C 处接收到的剂量。
在所有剂量处方中，没有和存在空气口袋时，在 A、B 和 C 处测量剂量的平均百分比偏差分别为 13.9%、11.0%和 6.4%。随着空气口袋从 2.0 毫米向 4.5 毫米的半径扩展，剂量的增加范围从 6.4%到 13.9%，这是因为胶片保持在处方剂量距离，并且光子径向通过空气口袋时没有衰减。
本研究可以在具有不同尺寸和位置空气口袋的 3D 打印模体上进行，也可以进行蒙特卡罗模拟分析。
