ABSTRACT
BACKGROUND: Scattered radiation can be assessed by in vivo dosimetry. Thyroid tissue is sensitive to radiation, even at doses <10 cGy. This study compared the scattered dose to the thyroid measured by thermoluminescent dosimeters (TLDs) and the estimated one by treatment planning system (TPS). METHODS: During radiotherapy to sites other than the thyroid of 16 children and adolescents, seventy-two TLD measurements at the thyroid were compared with TPS estimation. RESULTS: The overall TPS/TLD bias was 1.02 (95% LA 0.05 to 21.09). When bias was stratified by treatment field, the TPS overestimated TLD values at doses <1 cGy and underestimated them at doses >10 cGy. The greatest bias was found in pelvis and abdomen: 15.01 (95% LA 9.16 to 24.61) and 5.12 (95% LA 3.04 to 8.63) respectively. There was good agreement in orbit, head, and spine: bias 1.52 (95% LA 0.48 to 4.79), 0.44 (95% LA 0.11 to 1.82) and 0.83 (0.39 to 1.76) respectively. There was small agreement with broad limits for lung and mediastinum: 1.13 (95% LA 0.03 to 40.90) and 0.39 (95% LA 0.02 to 7.14) respectively. CONCLUSIONS: The scattered dose can be measured with TLDs, and TPS algorithms for outside structures should be improved.
Subject(s)
Neoplasms/radiotherapy , Radiometry , Thyroid Gland/radiation effects , Adolescent , Child , Child, Preschool , Cross-Sectional Studies , Female , Humans , Infant , Male , Neoplasms/pathology , Organs at Risk , Radiation Dosage , Scattering, Radiation , Skin/radiation effectsABSTRACT
A dosimetria in vivo na radioterapia, i.e., a determinação da dose durante o tratamento, proporciona uma verificação da qualidade desse tratamento. Uma rotina de dosimetria in vivo é, incontestavelmente, um benefício direto para o paciente, mas, infelizmente, no Brasil e em toda a América Latina, ainda é um privilégio para poucos. Sabe-se que essa rotina é comum apenas nos países considerados desenvolvidos. Este trabalho demonstrou a viabilidade da implantação de uma rotina de dosimetria in vivo com uso de diodos semicondutores e dosímetros termoluminescentes (TLD), no setor de radioterapia do Instituto Nacional de Câncer (INCA), no caso de tratamento de câncer de cabeça e pescoço. Foram determinadas as características da resposta dos diodos ISORAD-p e detectores termoluminescentes de LiF:Mg;Ti (TLD-100) em forma de pó. Esses detectores foram testados quanto ao seu desempenho para as medidas in vivo no simulador antropomórfico RANDO Alderson e, uma vez comprovada a sua adaptabilidade às medidas propostas foram utilizados na medição de dose no caso de tratamento de tumores na região anatômica da cabeça e pescoço, utilizando irradiadores de Cobalto-60.
In vivo dosimetry in radiotherapy, i. e, the assessment of the doses received by patients during their treatments, permits a verification of the therapy quality. A routine of in vivo dosimetry is, undoubtedly, a direct benefit for the patient. Unfortunately, in Brazil and in Latin America this procedure is still a privilege for only a few patients. This routine is of common application only in developed countries. The aim of this work is to show the viability and implementation of a routine in vivo dosimetry, using diodes semiconductors and thermoluminescent dosimeters (TLD), at the radiotherapy section of the National Institute of Cancer in Brazil, in the case of head and neck cancer treatment. In order to reach that aim, the characteristics of the response of diodes ISORAD-p and LiF:Mg;Ti (TLD-100) thermoluminescent detectors in powder form were determined. The performance of those detectors for in vivo dosimetry was tested using an RANDO Alderson anthropomorfic phantom and, once their adequacy proved for the kind of measurements proposed, they were used for dose assessment in the case of tumour treatments in the head and neck regions, for Cobalt-60 irradiations.
