Linearization of EBT3 film dose response and virtual film dosimetry for SBRT quality assurance

Micro-Mini & Nano-Dosimetry & Innovative Technologies in Radiation Therapy

Cai, M.^1 ; Archibald-Heeren, B.^1,2 ; Wang, Y.^2 ; Metcalfe, P.^1

Center of Medical Radiation Physics, University of Wollongong, Northfields Ave, Wollongong

NSW

2522, Australia^1

Physics Department, Radiation Oncology Institute, 185 Fox Valley Rd, Wahroonga

NSW

2076, Australia^2

关键词: Calibration curves;    Dose measurement;    Dose normalization;    Film dosimetry;    High spatial resolution;    Intensity values;    Patient specific;    Reference points;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/777/1/012005/pdf
DOI  :  10.1088/1742-6596/777/1/012005

来源: IOP

【 摘 要 】

EBT3 film offers high spatial resolution and low energy dependence, making it a suitable choice for quality assurance where high dose gradients are present, such as the case for SBRT. This work presents a simple method to adjust scanner settings so that dose response becomes linear. This linearity eliminates the need to obtain a calibration curve and associated uncertainties in curve fitting. Relative dosimetry can be performed after dose normalization to a reference point. Linearity is also a more robust condition than calibration curve with respect to scanner warm-up conditions, resulting in reduced uncertainty in dose measurement. An in-house developed program reads the film scan and a 2D dose map then constructs both to virtual films using grayscale values. Film intensity value was normalized to dose at reference point. Relative dosimetry was performed by comparing the two resulting images. Patient specific quality assurance was conducted for two SBRT cases. In both plans more than 95% gamma function points passed the gamma criteria of 2%/3mm.