Evaluation of Cardiac Dose Distribution and Prediction of Cardiovascular Risk Increase in Breast Cancer Radiotherapy for Georgian Women

Abstract

This study aims to evaluate cardiac dose distribution in breast cancer radiotherapy and predict the increase in cardiovascular risk among the Georgian female population.
Patients: We analyzed the treatment records of 100 female patients (40 with right-sided breast cancer, and 60 with left-sided) who underwent radiation therapy at the Kutaisi Christina Kiri Cancer Centre between 2017 and 2018.
Dose Evaluation: Radiotherapy was planned using conformal 3D and intensity-modulated radiation therapy (IMRT) techniques (ZXOX20) on the Eclipse planning system, based on diagnostic CT scans and virtual simulations (ZXOX30). A total dose of 50Gy was delivered in 2Gy fractions, with an additional 10Gy boost. Multi-leaf collimators (MLC) were used to protect surrounding tissues. The minimum, maximum, and mean heart doses were recorded.
Data Analysis: To enhance the accuracy of the results, Bayesian statistical approach was applied. We employed a hierarchical Bayesian model with lognormal distribution assumptions for heart dose data, using prior information from European studies (1977–2017) on cardiac doses in breast cancer radiotherapy. Posterior distributions, updated with clinical data, were used to estimate cardiac dose distributions for Georgian patients. Statistical significance was assessed using ANOVA, Chi-square, Shapiro-Wilk test for normality, and Grubbs' test.
Results: The mean heart doses for left-sided patients were 2.95Gy (SD =2.69), and for right-sided patients, 1.30Gy (SD = 0.80). Lognormal approximation yielded mean heart doses of 0.87 (SD=0.69) for left-sided and -0.23 (SD=0.82) for right-sided patients. The predicted increase in cardiovascular risk was 19% for left-sided and 6% for right-sided breast cancer patients.
Conclusion: Left-sided breast cancer radiotherapy is associated with a higher cardiovascular risk. Further research is needed to refine the "benefit-risk" assessment in radiotherapy and validate these findings.