SU-E-T-224: An Assessment of EBT2 Gafchromic Film as a Potential Means for Depth Dose Measurement of Radiotherapy Beams

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Abstract

Purpose: The Gafchromic EBT2 film was investigated as a potential mean for depth dose (DD) measurement of broad range of radio-therapy beam-modalities and energies. Methods: Gafchromic EBT2 films were exposed to 6 Gy dose from various beams in water for DD measurements. The beams employed for this study comprised of KV x-rays (75 kVp), 60Co, Mega-voltage x-rays (6 &18MV), electrons (7 & 20 MeV), and spot-scanning proton beams (180 & 150 MeV). Film optical densities (OD) were measured using a flat bed scanner. For each beam, film response measured over the dose range 0.6–6.2 Gy, was employed for OD-to—dose conversion. Results: for all mega-voltage photon & electron beams, percentage depth-doses measured with EBT2 showed an excellent agreement (<1.5%) with those measured with ion chambers. In case of 75 kVp (nominal), a small over-response is observed at deep depths (d > 2 cm) due to beam hardening. In contrast, an under-response in the Bragg-peak region is observed for proton beams due to quenching effects similar to the results published for EBT1. However, the suggested empirical corrections enable good agreement with ion-chamber data for these beams as well. Conclusion: The results indicate that EBT2 is able to serve as a reliable tool for measuring DDs for all radiotherapy beams in general with a high spatial resolution and reproducibility.

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