Investigation of the Imaging Dose of Various Generation of CBCT Linear Accelerators Sample Abstract
Veni Setyowati1,2, Rory Agustria2, Sri Bintang Arofah2, Syarifatul Ulya2, Supriyanto Ardjo Pawiro1,2

1Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Depok, West Java
2Department of Radiation Oncology, Dharmais Cancer Hospital, Jakarta

Abstract

Integration of Cone-Beam Computed Tomography (CBCT) into Linear Accelerators (LINAC) has been developed as a tool for verifying patient positioning in radiotherapy but may increase the lifetime attributable risk (LAR) of cancer and damage to healthy organs.
This study aimed to evaluate and compare the CBCT imaging dose from four LINACs across different generations (Elekta Synergy versus Versa HD and Varian Trilogy versus TrueBeam) during radiotherapy.
At Dharmais Cancer Hospital, forty five thermoluminescent dosimeter (TLD) chips were calibrated using a Terasix X-ray simulator and measured with a Raysafe multimeter. TLDs are employed and attached to the surface of an Alderson RANDO phantom in three areas: Pelvis (12 points), Thorax (15 points), and Head (18 points). Each LINAC is operated using clinical CBCT parameters. TLD readings in nC were converted to dose (mGy) by multiplying with a calibration factor, then analyzed based on organ localization through TLD points placed on the phantoms anterior, right lateral, and left lateral sides.
In the pelvis, the highest dose was observed with Versa HD 2.94mGy (SD=0.30), whereas the lowest was observed by Trilogy 0.84mGy (SD=0.10). In the thorax, Trilogy yielded the highest dose 1.72mGy (SD=0.40) while TrueBeam yielded the lowest 0.75 mGy (SD=0.06). The highest difference between CBCT was observed with Trilogy and TrueBeam is 0.97mGy. The highest dose in the head was in Trilogy 1.23mGy (SD=0.49), and the lowest dose was in Versa HD 0.47 mGy (SD=0.10).
Variation in imaging dose among LINAC generations does not always indicate that the newer generations deliver lower doses. Trilogy delivered a dose in the thorax 0.97 mGy higher than TrueBeam . However, in the pelvis, Versa HD was delivered a dose 0.85mGy higher than Synergy and even 2.10mGy higher than Trilogy. This indicates that imaging protocols and machine configurations influence differences in CBCT dose more than CBCT Linac generation.

Keywords: Imaging Dose, CBCT, Linac Generation, TLD

Topic: Medical Physics and Biophysics