Characterization and preparation of thermoluminescence dosimeters for surface and in vivo dose measurements

Abstract

Abweichender Titel nach Übersetzung der Verfasserin/des VerfassersDue to their size, reusability and good accuracy thermoluminescent dosimeters (TLDs), are a valuable tool in radiation dosimetry. The properties of TLDs allow a convenient use in radiotherapy and radiation oncology not only for measurements in di↵erent types of phantoms but also for in-vivo dosimetry. The relatively small detectors can be conveniently placed in cavities and/or on surfaces to measure skin dose or dose close to organs at risk. This can help to verify treatment delivery. For future use of thermoluminescent detectors at MedAustron, the center for ion therapy and research in Wiener Neustadt, a set of TLD-100 detectors (LiF:Mg,Ti) was characterized and initial measurements were performed for use of TLDs in in-vivo and surface dose measurements. The sample-to-sample uniformity of TLDs was verified to be within the limits stated by the manufacturer. Individual sensitivity factors for TLDs were determined and the reproducibility limits, given by the manufacturer were fulfilled by most of the investigated TLDs. Furthermore TLDs were calibrated in 60Co and proton beams, where supralinearity was observed for both radiation types starting at the dose level of about 1 Gy. Individual sensitivity factors were applied to correct for varying sensitivity of TLDs. This reduced the standard deviation of measurements by 50 %. To investigate the response of thermoluminescent detectors in changing LET conditions, detectors were placed at several depths of a spread-out Bragg peak. The positioning of TLDs in multiple depths, without mutual shielding, was realized with in-house modified RW3 slabs. TLD results were compared to the response of radiochromic films, i.e. type EBT-3 and EBT-XD. For TLDs no quenching was observed in the investigated region of a spread-out Bragg peak while for EBT-3 and EBT-XD films the known LET dependence was confirmed. The investigated TLDs, corrected with corresponding sensitivity factors, had proven to be well suited for clinical applications. Nevertheless, the consistency in the process of using and treating TLDs is a very crucial aspect. In order to maintain the good outcome, regular quality assurance of all involved parts is strongly recommended.8