Room: Exhibit Hall | Forum 3
Purpose: Small animal image-guided radiotherapy (SA-IGRT) systems closely emulate the clinical radiotherapy environment and process. The dose delivery accuracy of these systems depends on a number of operator- and system-related factors which can individually or cumulatively contribute to significant dosimetric errors. Since tumor response and normal tissue toxicity are radiation dose-dependent, accurate treatment dose verification is important in pre-clinical studies. Here, we develop an EPID transmission and in-phantom exit dosimetry method for kilovoltage (kV) x-ray beam dose verification in SA-IGRT systems.
Methods: We calibrated the in-built EPID on the small animal radiation research platform (SARRP, XSTRAHL, Inc.) to measure transmission dose at the detector plane. Accuracy of two-dimensional (2D) transmission dose distributions against ion chamber (IC) and film measurements was validated for a range of x-ray tube currents, object thicknesses, and collimator sizes. To calculate the dose delivered to an object, the EPID transmission dose was back-projected to the beamâ€™s exit surface. Accuracy of the dose distribution was then compared against IC and film measurements for several collimators at varying thicknesses of homogeneous and inhomogeneous phantoms.
Results: Transmission dose values measured with the EPID showed close agreement with film and IC measurements, for tube currents higher than 10 mA (â‰¤0.4%), various phantom thicknesses (â‰¤2.4%), and multiple cone sizes (â‰¤2.9%). For phantom thicknesses â‰¥15 mm, calculated exit doses agreed with IC and film values within â‰¤2.5% and â‰¤3.2%, respectively. As small animals typically have â‰¥15 mm thickness, these results imply that the EPID is capable of accurate exit dose calculation in preclinical studies. For inhomogeneous phantom, the EPID and film exit dose measurements agreed within â‰¤2.7%.
Conclusion: We developed and validated a novel 2D transit/exit dosimetry in kV x-ray energies using an EPID. This system shows promising potential for performing in-vivo kV x-ray dose verification in pre-clinical studies.