OA153] EBT3 radiochromic film dosimetry in kV X-ray radiation therapy

Abstract

Purpose To evaluate the suitability of EBT3 radiochromic films for the dosimetry of therapeutic kV X-ray beams and particularly examine their potential energy dependence. Methods Film samples from the same batch were irradiated at dose levels of 0.5, 1, 2 and 3 Gy using seven filters/qualities Q (80 ⩽ kVp ⩽ 220, 2.5mmAl ⩽ HVL ⩽ 2mmCu) of a unit calibrated using the in-air method [1] . Pre- and post-irradiation scanning facilitated the calculation of energy response, S AD , W (Q) = netOD(Q)/ D w (Q) for the red channel. S AD , W (Q) equals the inverse product of the intrinsic energy dependence, k bq (Q) = D film (Q)/netOD(Q), by the absorbed dose to water energy dependence, f(Q) = D w (Q)/ D film (Q). The latter was calculated using MCNP6 [2] employing secondary electron tracking in the experimental geometry with beam spectra from SpekCalc [3] and film composition from the literature [4] . k bq (Q) was calculated from experimental [ S AD , W (Q)] and simulation [f(Q)] results. Results EBT3 film does not exhibit energy dependence in the qualities studied. S AD , W (Q) results relative to the highest quality equal unity within 1%, which is well within experimental standard uncertainty (on the order of 4%). An increase of f - 1 (Q) with decreasing quality was found (up to 1.37 relative to the highest quality) suggesting an almost equal film under-response [ k bq - 1 (Q) 1], in accordance with the literature [4] . While S AD , W (Q) varies with dose due to the known non-linearity of film dose response, relative results are in close agreement regardless of dose level. Conclusions The energy dependence of EBT3 films is negligible in the energy range studied. Future studies will extend the studied energy range and focus on reducing experimental uncertainty, studying batch variability, and application of EBT3 for experimental dosimetry.