Tissue-equivalent dosimeters based on copper doped lithium tetraborate single crystals for radiotherapy

Abstract

Advancements in radiotherapy techniques demand the development of stringent quality assurance (QA) protocols and new dosimeters for achieving better accuracy in the measurement of the delivered dose. The objective of the present study is to assess performance of in-house developed tissue equivalent lithium tetraborate (Li2B4O7) single crystal based thermoluminescent dosimeters (TLDs) for medical dosimetry in radiotherapy. For this, single crystals of copper doped lithium tetraborate, abbreviated as LTB:Cu, were grown using the Czochralski crystal pulling technique and transparent TLDs of the dimensions 3×3x0.6 mm3 in chip form were fabricated in our laboratory. Complete dosimetric characterization of TLDs was done to assess its suitability as a dosimeter for radiotherapy dosimetry. The LTB:Cu TLDs were studied for dosimetric properties such as linearity of response with delivered dose, fading, energy dependence, angular dependence and dose rate dependence. The central-axis depth dose parameters such as percentage depth dose (PDD) and output factors were measured using the developed LTB:Cu TLDs for the clinically relevant depths and field sizes and were compared with the response of commercially established TLD-100 and reference values measured by ionisationchamber.Performance of LTB:Cu TLDs has been assessed for their reliable use in dose verification of treatment planning system (TPS) and QA in radiotherapy. The TLDs were used in the clinical set up for measuring the doses to target and critical organs in the in-house developed thorax phantom and the results were compared with the TPS calculated doses. The doses were delivered using three-dimensional conformal radiotherapy (3D-CRT) and volumetric modulated arc therapy (VMAT) techniques. The planned and measured doses agreed within the acceptable limits of 3%. These studies have shown the great potential for the applicability of the developed TLDs in the radiotherapy dosimetry applications.