Calculation of Dose in Healthy Organs, during Radiotherapy 4-Field Box 3D Conformal for Prostate Cancer, Simulation of the Linac 2300, Radiotherapy Room and MAX Phantom

Abstract

In men, prostate cancer is one of the most frequent types, and radiotherapy is adopted as a form of treatment. Although there are efforts to minimize the dose in the healthy organ and tissues adjacent to the tumor during radiotherapy, these organs are affected by the secondary scattered and leakage radiation originating from the therapeutic beam and these doses deposited in the healthy organs, can induce the appearance of new focal points of cancer. The aim of this study is to calculate the equivalent and effective doses, due to photons and neutrons, in healthy organs of a patient submitted to radiotherapy treatment for prostate cancer. Computed simulation of radiotherapy treatment for prostate cancer was used to perform the dose calculations, adopting the treatment protocol used at INCA (Brazilian National Cancer Institute). The MCNPX code was employed in the simulation radiation transport while the male voxel MAX phantom was used to represent the patient's human anatomy. The results obtained in this study indicate that the organs close to the irradiated region are predominantly affected by the dose due to photons, with an impact on organs from different systems of the body, such as the bladder, colon, and testicles, besides bone structures such as the femur, pelvis and spinal column. The results obtained from the doses deposited due to neutrons suggest that tibia and fibula, mandible, cranium, brain and thyroid, had the highest dose deposited due to neutrons in relation to photons. The result obtained from the effective dose was 31.47 mSv due to photons, while the dose due to neutrons was 0.42 mSv. Note that the effective dose due to photons is significantly higher than the effective dose due to neutrons. The values calculated in this study were compared with the experimental values obtained in the literature, presenting reasonable concordance. Additionally, as described in the literature, it was verified that the dose due to photons decreases considerably with the increase in the distance of the target organ, while the dose due to neutrons is distributed homogeneously in the organs. It is concluded that the contribution of neutrons to the appearance of secondary cancers is more relevant in the organs furthest from the target volume, and that organs close to the tumor, are affected predominantly by the dose due to photons.