Application of OSL strips in CT dosimetry according to the AAPM methodology

Ricardo Andrade Terini; Johnatan Dias Oliveira; Elisabeth Mateus Yoshimura

doi:10.15392/2319-0612.2023.2259

Autores

Ricardo Andrade Terini Universidade de São Paulo, Instituto de Física
Johnatan Dias Oliveira Universidade Federal do ABC, Centro de Ciências Naturais e Humanas
Elisabeth Mateus Yoshimura Universidade de São Paulo, Instituto de Física

DOI:

https://doi.org/10.15392/2319-0612.2023.2259

Palavras-chave:

dose profiles, OSL strips, equilibrium doses, AAPM methodology

Resumo

Computed tomography (CT) images contribute to high-quality medical diagnosis, but radiation dose can be quite high, requiring accurate assessment. CT dose index (CTDI) was developed for dosimetric purposes, but for scanners operated exclusively in axial mode. Nowadays, CTDI underestimate patient dose in helical CT exams. AAPM report TG111 (2010) suggested a new metric in which the patient's radiation dose is obtained from dose profiles constructed from several measurements made with a small ionization chamber. It is also possible to obtain dose profiles using properly calibrated OSL (optically stimulated luminescence) strips. The main objective of the present work is to contribute to optimizing CT dosimetry, comparing dose profiles obtained with OSL strips with measurements obtained by other authors. In this work, a “pencil” ionization chamber and 20 cm x 0.3 cm OSL strips were X-ray-irradiated, in air and in the holes of two cylindrical CT phantoms, using 100, 120, 140 kV peak voltages, both in lab and in a clinical CT scanner. Irradiated strips were read using an OSL reader built in the GDRFM. OSL profiles were calibrated against ionization chamber. From them, CTDI_w and CTDI_vol values were determined, differing approximately 3.9% from those of the CT scanner. From the profiles, also the planar equilibrium dose D_eq,p(TG111) was evaluated in some CT protocols; D_eq,pexceeded the CTDI values from the CT scanner in every case. E.g.: The percentage difference between D_eq,pand CTDI_vol for the head phantom ranged between 33-25%. Thus, in some cases, it could be advantageous to use calibrated OSL dosimeters instead of ionization chambers to obtain the profiles, saving time, because it is possible to obtain five OSL profiles from a single phantom irradiation.

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Biografia do Autor

Johnatan Dias Oliveira, Universidade Federal do ABC, Centro de Ciências Naturais e Humanas

Aluno de graduação

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