Dados do Trabalho

Título

Evaluation of TCP with different radiosensitivities for prostate cancer

Introdução

Radiotherapy is indicated for neoplasm treatment, attenuating tumor growth using ionizing radiation. Such radiation damages cells and can affect healthy tissues around the tumor. Therefore good radiotherapy planning is necessary, aiming to obtain greater tumor control. In these plans, the tumor radiosensitivity must be considered. A way to quantify it is through α and β parameters that are incorporated in the calculation of tumor control probability (TCP). Prostate cancer is the second most common type of cancer in male people. There is a range α and β values for prostate tumor in literature withing a certain range of α/β ratio. In this work, we compare and analyze TCP profiles for different α and β values for a standard irradiation protocol.

Objetivo

Compare and analyze TCP profiles for different α and β values for a standard irradiation protocol.

Método

We obtained the radiosensitivity parameters of prostate cancer (α, β and α/β ) from literature. The α/β ratio ranges from 0.60 Gy to 7.78 Gy, averaging 3.74 Gy. The irradiation protocol used was 70 - 78 Gy delivered in a total treatment time of 42 days. The initial number of cells was 10e9. For calculations, we used Poissonian TCP with the Linear Quadratic Model (LQM) for the surviving fraction. The graphics were obtained using free software Octave. The TCPs were plotted as a function of radiation dose and time of treatment.

Resultados

The graphs analysis shows that changes in radiosensitivity parameters can lead to notorious shifts of TCP curves. For most TCPs there was no dose or time compatibility with the standard protocol. Such behavior is due to the range of α and β values. For the most radiosensitive tumors, lower dose values ensure tumor control. Mean α, β and α/β values obtained from recent literature results in TCPs more similar to protocol predictions.

Conclusão

The α/β ratio which best fits the clinical protocol is high compared to literature findings. The different values interfere in TCP profiles, affecting treatment tumor response. Therefore, attention to these parameters in the clinical scope is necessary.

Palavras-chave

radiosensitivity, TCP, prostate.