TITLE:
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
AUTHORS:
Jardel L. Thalhofer, Wilson F. Rebello, Samanda A. Correa, Ademir X. Silva, Edmilson M. Souza, Delano V. Batista
KEYWORDS:
Radiotherapy; Prostate; MCNPX; MAX and Linac
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.2 No.2,
May
24,
2013
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.