Thasasi Phatthraporn, Ruangchan Sirinya, Oonsiri Puntiwa, Oonsiri Sornjarod
Medical Physics Program, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
Division of Radiation Oncology, Department of Radiology, King Chulalongkorn Memorial Hospital, Bangkok, Thailand.
Int J Part Ther. 2022 Jun 3;9(2):1-9. doi: 10.14338/IJPT-22-00006.1. eCollection 2022 Fall.
This study aimed to determine the integral depth-dose curves and assess the geometric collection efficiency of different detector diameters in proton pencil beam scanning.
The Varian ProBeam Compact spot scanning system was used for this study. The integral depth-dose curves with a proton energy range of 130 to 220 MeV were acquired with 2 types of Bragg peak chambers: 34070 with 8-cm diameter and 34089 with 15-cm diameter (PTW), multi-layer ionization chamber with 12-cm diameter (Giraffe, IBA Dosimetry), and PeakFinder with 8-cm diameter (PTW). To assess geometric collection efficiency, the integral depth-dose curves of 8- and 12-cm chamber diameters were compared to a 15-cm chamber diameter as the largest detector.
At intermediate depths of 130, 150, 190, and 220 MeV, PTW Bragg peak chamber type 34089 provided the highest integral depth-dose curves followed by IBA Giraffe, PTW Bragg peak chamber type 34070, and PTW PeakFinder. Moreover, PTW Bragg peak chamber type 34089 had increased geometric collection efficiency up to 3.8%, 6.1%, and 3.1% when compared to PTW Bragg peak chamber type 34070, PTW PeakFinder, and IBA Giraffe, respectively.
A larger plane-parallel ionization chamber could increase the geometric collection efficiency of the detector, especially at intermediate depths and high-energy proton beams.
本研究旨在确定质子笔形束扫描中的积分深度剂量曲线，并评估不同探测器直径的几何收集效率。
本研究使用瓦里安ProBeam紧凑型点扫描系统。采用两种类型的布拉格峰电离室获取质子能量范围为130至220 MeV的积分深度剂量曲线：直径8 cm的34070型和直径15 cm的34089型（PTW）、直径12 cm的多层电离室（长颈鹿型，IBA剂量学公司）以及直径8 cm的PeakFinder（PTW）。为评估几何收集效率，将直径8 cm和12 cm的电离室的积分深度剂量曲线与作为最大探测器的直径15 cm的电离室进行比较。
在130、150、190和220 MeV的中间深度处，PTW 34089型布拉格峰电离室提供的积分深度剂量曲线最高，其次是IBA长颈鹿型、PTW 34070型布拉格峰电离室和PTW PeakFinder。此外，与PTW 34070型布拉格峰电离室、PTW PeakFinder和IBA长颈鹿型相比，PTW 34089型布拉格峰电离室的几何收集效率分别提高了3.8%、6.1%和3.1%。
更大的平行板电离室可提高探测器的几何收集效率，尤其是在中间深度和高能质子束情况下。
