Effects of Interfraction Dose Variations of Target and Organs at Risk on Clinical Outcomes in High Dose Rate Brachytherapy for Cervical Cancer.

Simple Summary: Accurate dose calculation and delivery is critical in treating cancers in radiation therapy. Although high accuracy has been achieved, significant uncertainties or errors still exist in radiation therapy, especially brachytherapy. Various types of uncertainty have been investigated, such as organ filling and organ motion. But interfraction dose variations (IDVs) from the prescribed dose in high dose rate brachytherapy (HDR) resulting from clinical considerations have not been widely discussed. Understanding what IDVs look like and whether or not they would affect clinical outcomes is important to improve the effectiveness of HDR brachytherapy and quality of cervical cancer treatment. We found IVDs followed a left-skewed distribution in our previous study, and we continued to discuss their potential effect on clinical outcomes in this project. In this study, we found that IDVs would reduce tumor control probability and increase treatment failure rate, but a dose escalation could be a remedy for such an effect. Meeting dose prescription is critical to control tumors in radiation therapy. Interfraction dose variations (IDVs) from the prescribed dose in high dose rate brachytherapy (HDR) would cause the target dose to deviate from the prescription but their clinical effect has not been widely discussed in the literature. Our previous study found that IDVs followed a left-skewed distribution. The clinical effect of the IDVs in 100 cervical cancer HDR patients will be addressed in this paper. An in-house Monte Carlo (MC) program was used to simulate clinical outcomes by convolving published tumor dose response curves with IDV distributions. The optimal dose and probability of risk-free local control (RFLC) were calculated using the utility model. The IDVs were well-fitted by the left-skewed Beta distribution, which caused a 3.99% decrease in local control probability and a 1.80% increase in treatment failure. Utility with respect to IDV uncertainty increased the RFLC probability by 6.70% and predicted an optimal dose range of 83 Gy–91 Gy EQD2. It was also found that a 10 Gy dose escalation would not affect toxicity. In conclusion, HRCTV IDV uncertainty reduced LC probabilities and increased treatment failure rates. A dose escalation may help mitigate such effects. [ABSTRACT FROM AUTHOR]