Investigation of 2D radiophotoluminescence films in radiotherapy: Multileaf collimator Quality Assurance and small field dosimetry

Luana de Freitas Nascimento, Fabio Castellano, Jo Goossens, Anke van Dijk, Paul Leblans, Marijke De Saint-Hubert

Research outputpeer-review


In radiotherapy, accurate dose determination and precise dose delivery to the tumor are directly associated with better treatment outcomes, such as better tumor control and lower post treatment complications. Challenges in Quality Assurance (QA) are a.o. (1) the varying amounts of primary and secondary scattered photons, the varying gantry angles and the energy heterogeneity and (2) the small field sizes used in Intensity Modulated Radiotherapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT). As alternative to the commonly used GafChromic™ EBT films, radiophotoluminescence (RPL) films gained attention for high resolution 2D dosimetry in radiotherapy thanks to their insensitivity to ambient light, reusability, absence of fading and the few image corrections needed. In this work we characterize the response of improved Al2O3:C,Mg RPL films in a clinical 6 MV beam. Film response was evaluated in terms of uniformity, dose response, minimum detectable dose (MDD), small field dosimetry and its performance was evaluated for multileaf collimator (MLC) QA tests. The new films showed linear dose response up to 8 Gy, followed by supralinear response for higher doses up to 24 % at 20 Gy. QA checks for the MLC, including the chair and the alternating leaves, were compared with calculations from the treatment planning system (TPS) and showed an agreement within 5% for alternating leaves and a deviation in Full Width Half Maximum (FWHM) below 1.5 % for the chair test. The maximum FWHM discrepancy between RPL film results and reference data (diode) for small field sizes (30 × 30, 20 × 20, 10 × 10, 8 × 8, 6 × 6 mm2) was 1.9 %. Notwithstanding the variations in dose response, the studied films exhibit overall good agreement with reference data and demonstrate potential for QA in IMRT and small field radiotherapy

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