Assessing Heterogeneity Effects on Points A, B, and Organs at Risk Doses in High-dose-Rate Brachytherapy for Cervical Cancer - A Comparison of Ir and Co Sources Using Monte Carlo N-Particle 5.

Purpose: The present article deals with investigating the effects of tissue heterogeneity consideration on the dose distribution of Ir and Co sources in high-dose-rate brachytherapy (HDR-BT).

Materials And Methods: A Monte Carlo N-Particle 5 (MCNP5) code was developed for the simulation of the dose distribution in homogeneous and heterogeneous phantoms for cervical cancer patients. The phantoms represented water-equivalent and human body-equivalent tissues. Treatment data for a patient undergoing HDR-BT with a Ir source were used as a reference for validation, and for Co, AAPM Task Group 43 methodology was also applied. The dose values were calculated for both source types in the phantoms.

Results: The results showed a good agreement between the calculated dose in the homogeneous phantom and the real patient's treatment data, with a relative difference of less than 5% for both sources. However, when comparing the absorbed doses at critical points such as Point A right, Point A left, Point B right, Point B left, bladder International Commission on Radiation Units and Measurement (ICRU) point, and recto-vaginal ICRU point, the study revealed significant percentage differences (approximately 5.85% to 12.02%) between the homogeneous and heterogeneous setups for both Ir and Co sources. The analysis of dose-volume histograms (DVH) indicated that organs at risk, notably the rectum and bladder, still received doses within recommended limits.

Conclusions: The study concludes that Co and Ir sources can be effectively used in HDR-BT, provided that careful consideration is given to tissue heterogeneity effects during treatment planning to ensure optimal therapeutic outcomes.