A commercial optically stimulated luminescence (OSL) system developed for radiation protection dosimetry by Landauer, Inc., the InLight microStar reader, was tested for dosimetry procedures in radiotherapy. The system uses carbon-doped aluminum oxide, Al2O3:C, as a radiation detector material. Using this OSL system, a percent depth dose curve for 60Co gamma radiation was measured in solid water. Field size and SSD dependences of the detector response were also evaluated. The dose response relationship was investigated between 25 and 400 cGy. The decay of the response with time following irradiation and the energy dependence of the Al2O3:C OSL detectors were also measured. The results obtained using OSL dosimeters show good agreement with ionization chamber and diode measurements carried out under the same conditions. Reproducibility studies show that the response of the OSL system to repeated exposures is 2.5% (1sd), indicating a real possibility of applying the Landauer OSL commercial system for radiotherapy dosimetric procedures.

No abstract

O objetivo deste trabalho é submeter filmes radiocrômicos, dosímetros termoluminescentes e câmara de ionização a situações idênticas de irradiação, com a finalidade de se avaliarem as suas capacidades em medir doses periféricas. O crescente aumento de sobreviventes ao câncer infantil tem criado a necessidade de se investigarem as causas das sequelas do tratamento. Mensurações de radiações periféricas à região alvo da radioterapia incrementam o conhecimento do assunto e auxiliam na elaboração de métodos de proteção. Como o espectro da radiação na periferia é diferente do encontrado no feixe, a independência energética supostamente oferecida em filmes radiocrômicos pode suplantar a dependência energética encontrada em câmaras de ionização e TLDs, de forma a descartar a necessidade de correções de valores se filmes forem utilizados. Neste trabalho os três dosímetros foram submetidos às doses decorrentes da emissão de feixes de 6 MV, campo 10 cm x 10 cm e 500 UM. Os dosímetros foram posicionados a 0, 10, 17,5 e 30 cm do raio central, sempre sob 5 cm de água. Os resultados encontrados mostraram que os valores apresentados pelos filmes possuem alto desvio padrão da média e que para resultados mais conclusivos é necessário prosseguir com as irradiações, empregando feixes mais intensos.

Electron beams are applied in radiotherapy treatments where superficialized doses are desirable as well as deeper tissues sparing. Monte Carlo method has been recently implemented in the TPS as the algorithm for electron beam isodoses calculation at the National Institute of Cancer in Brazil. This work comprises an additional method of evaluation of the isodoses generated by the TPS, considering the irradiation of a non-flat surface. A 6-Gy electron beam breast irradiation was planned and delivered to an anthropomorphic phantom into which 36 capsules with TLD100 were inserted. The TLD calibration curve was performed from 100 cGy to 700 cGy. In an overall analysis, eMC algorithm isodose distribution results agreed with TLD measured doses. 75% of measured data met the 5% accuracy criteria, which can be considered in good agreement with the recommended uncertainties involved in a radiotherapy treatment. Considered all collected data, 8 TLDs received extremely low doses and due to tissue attenuation of the electron beam, the TLD measurements might have additional uncertainties. If these data are not taken into account, 100% of the measured doses, considering the uncertainties, meet the 5% accuracy criteria. About the 3 methods for isodose smoothing available in the eMC algorithm, the low level of dose smoothing option provides the best matching with measured data, consisting of the most reliable option. Considering the AAPM recommendations eMC algorithm offers an accurate solution for isodoses calculation, within a 5% accuracy.