Risk estimations of radiation induced malignancies in rectum and bladder following radiotherapy of prostate carcinoma.

[PURPOSE] The purpose of this study was to estimate the risks of radiation-induced rectal and bladder cancers in the case of standard fractionated and hypofractionated radiotherapy for prostate carcinoma using volumetric modulated arc therapy and intensity modulated radiotherapy.

[METHODS] Three plans were generated for twenty-five patients, employing both conventional two-step sequential and simultaneous integrated boost approaches, with prescribed doses of 78 Gy in 39 fractions for CONV-VMAT and 70 Gy in 28 fractions for SIB techniques. The risks of secondary malignancies were estimated based on the organ equivalent doses (OED) and excess absolute risk (EAR) for the bladder and rectum using two radiobiological models: linear-plateau (Plat), and mechanistic (Mech) models.

[RESULTS] Statistically higher OEDs were observed between CONV-VMAT and both SIB-IMRT and SIB-VMAT using Plat (p = 0.012 and p = 0.000) and Mech models (p = 0.000 and p = 0.000) in the case of the rectum. In case of the bladder significantly higher OED values were found when compared CONV-VMAT with SIB-IMRT and SIB-VMAT using Plat model (p = 0.035 and p = 0.008), but no significant difference when analyzed using Mech model (p = 0.470).

[CONCLUSION] These findings highlight the potential benefits of these radiotherapy techniques, suggesting that SIB-VMAT and SIB-IMRT may enhance organ sparing while mitigating long-term oncogenic risks. The study underscores the importance of refining treatment strategies to optimize prostate cancer outcomes while minimizing collateral risks.