Determination of the Absorbed Dose in Water for Small Photon Beams Using Micro-TLDs of LiF:Mg,Ti (Pilot Audit Proposal)

Abstract

Background: Small-field dosimetry remains an open challenge globally. Thus, it is crucial to consider adequate reference codes of practice for the performance of dosimetry. Furthermore, as part of good clinical practice, the implementation of new codes of practice implies the development of a dosimetry audit program. In this work, a pilot dosimetric audit protocol is established for measuring the absolute dose in water for small fields using micro-TLDs LiF:Mg,Ti dosimeters. Methods: The dosimeters were irradiated with a 6 MV X-ray beam in a linear accelerator. The TLDs were calibrated between 0.5 and 3 Gy for different field sizes. For audit, the TLDs were irradiated at 2 Gy for different circular field sizes. The proposed protocol consists of five TLD dosimeters forming a cross with a marked radiochromic film to identify the position of the central dosimeter during irradiation. Only the dosimeter measurement in the center of the field is used. Results: It was found that the percentage difference between the measured dose and the prescribed dose (2 Gy) for irradiation in circular fields is less than 3%. Conclusions: A pilot dosimetric audit was carried out using the proposed protocol over a linear accelerator using small circular collimator photon beams.

Keywords

• micro TLD
• radiotherapy
• small photon beam
• audit
• absorbed dose