Abstract
The goal of this work is to evaluate the dosimetric accuracy of nanoDot optically stimulated luminescence dosimeters (OSLDs) for small field sizes both at phantom-implant interfaces and deeper depths of a phantom. The central axis percentage depth-dose (PDD) curves were obtained by 6 MV flattening-filter-free (FFF) photon beams in conjunction with the homogeneous and nonhomogeneous RW3 slab phantoms with aluminum (Al), titanium alloy grade 5 (Ti5), and stainless steel grade 316 L (SS) implant material sheets inserted into, in small fields: 2 × 2 cm2 and 4 × 4 cm2. Three different depths were defined within the heterogeneous phantoms created to compare the measured and calculated doses: The soft tissue/metal implant upper interface (level I), metal implant/soft tissue lower interface (level II), and deeper depth from the implant (level III). The assessment of OSLDs was performed at defined depths comparing by Monte Carlo simulation (EGSnrc-based DOSXYZnrc/BEAMnrc) and Acuros XB (AXB) algorithm with GafChromic™ EBT3 film and PTW 31014 pinpoint ion chamber (IC) measurements. The PDDs using OSLDs were compared to those predicted by MC, and AXB, and those measured by EBT3 and IC and found to agree with uncertainty (<3%) in a homogeneous medium. The mean relative differences between OSLD and MC simulation at the level I interface of the Al, Ti5, and SS implants were analyzed as 2.5%, 5.6%, and 9.8% for 2 × 2 cm2 and 3.0%, 5.2%, and 8.8% for 4 × 4 cm2, respectively. When using implant material with lower electron density such as Al, the OSLD measurement values were found to agree with each measurement and calculation technique. At level II, the relative doses measured using OSLDs were similar to those of MC calculations for both field sizes. The maximum difference was found at 3.2% for SS implant. Except for the vicinity of the metal implant/RW3 phantom slab interfaces, the OSLD relative dose values were similar to those of PDD measurements in homogeneous media at depths away from the implant material. The OSLDs present a high capacity for radiotherapy dosimetry in homogeneous medium.But we can not adequately consider the dose to the interface between tissue and high Zeff materials in the case of the Ti5 and SS implant materials for small fields using OSLDs.
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