Small field dosimetry employing the thermoluminescence technique using a 3D printed phantom

Abstract

With the advent of new radiotherapy modalities, it has become necessary to apply relatively small fields that are dynamic or static. The use of these field sizes can cause uncertainty in dosimetry, requiring special attention in small field dosimetry. With these mentioned challenges, it is difficult to select a detector with good performance for dosimetry in small fields. TLDs have advantages because they have characteristics such as high spatial resolution and dose response, they offer a promising opportunity to measure the absorbed dose in a small field. The objective of this study is to evaluate the performance of CaSO4:Dy, LiF:Mg,Ti and μLiF:Mg,Ti thermoluminescent dosimeters for clinical photon beams in small field dosimetry using a 3D printed phantom. For clinical application the 6EX linear accelerator from Varian Medical System and the Multillif collimator from BrainLab were used. The 3D printed phantom was subjected to real treatment conditions. The dynamic arc 3D radiosurgery technique was adopted, with a dose of 7 Gy. To decrease statistical variation, the treatment simulation was repeated three times for each dosimeter. The results obtained demonstrated the viability of TLDs for clinical applications from photon beams to small fields. The values showed agreement in percentage terms below ±5% as recommended by the ICRU. The greatest percentage difference found was 1.2% (LiF:Mg;Ti) in relation to the planning system. All thermoluminescent dosimeters presented an uncertainty relatively low, with good stability and reproducibility in all measurements. The 3D printed phantom showed the possibility of achieving real treatment conditions.