Comparação entre a dose calculada no sistema de plano do tratamento e a dose medida em doentes com cancro do colo do útero no Serviço de Radioterapia do Hospital Central de Maputo

Abstract

For this work, the treatment of cervical cancer was chosen, as it is currently the most common type of cancer among women in Mozambique, and the main objective of the work was to compare the dose calculated in the treatment planning system and the dose mediated in patients with cervical cancer in the radiotherapy service of the Maputo Central Hospital. In order to achieve this objective, data was collected using an ionization chamber and a quality control matrix. Dose distributions were measured in 50 fields in the 10 patients selected for the study using the quality control matrix and compared with the dose distributions calculated in the treatment planning system using the gamma index method with acceptance criteria. ±3% dose difference and ±3 mm agreement distance, which quantitatively compares two dose distributions point by point until at least 95% of the points have the gamma index value between 0,00 to 1,00 (γ ≤ 1), and analysis of the measurements with the quality control matrix showed that the value of γ< 1 for 100% of the data, therefore all are below ±5% dose difference, which was the proposed action level in that work in relation to the planning and treatment system for dose verification. 30 absolute doses were measured with an ionization chamber, these values were corrected to K P,T correction factor values in order to convert the air mass to reference conditions, since the ionization chamber used is open for equilibrium with the environment and the comparison was made between the dose distribution values calculated in the treatment planning system and the dose distribution values corrected by the K P,T correction factor. The analysis of measurements with an ionization chamber showed that the values of the percentage differences of measured and calculated doses are below ±5%, with their maximum deviation being 2,13%. It can be concluded that all values measured with the ionization chamber and the quality control matrix are within the internationally recommended tolerance limits.