Reliability of algebraic sum to evaluate adjuvant pelvic radiotherapy and vaginal cuff brachytherapy cumulative doses in uterine cancers

PURPOSE: To evaluate the reliability of algebraic sum with respect to rigid fusion of treatment plans related to adjuvant external beam pelvic radiotherapy (APR) and vaginal cuff high-dose-rate brachytherapy (BT) in uterine cancer patients. MATERIAL AND METHODS: For algebraic sum, APR and BT doses were mathematically added. Rigid fusion was realized overlapping computed tomography (CT) images of APR and BT treatment plans. Rectum and bladder were considered reference organs at risk (OARs). Following dose (D) parameters were examined: D(max) (0.5 cc), D(20%) and D(50%) for rectum, D(max) (0.5 cc) and D(50%) for bladder; for each parameter, differences between the two adopted methods were reported as Δ-values. RESULTS: Twenty uterine cancer patients submitted to radical surgery followed by APR plus vaginal cuff BT were reviewed. APR was done with a dose of 25 × 2 Gy. All patients also receveid a vaginal cuff boost with BT at the dose of 2 × 5 Gy. Differences between mean cumulative doses calculated with rigid fusion and algebraic sum were evaluated. For the rectum and bladder ΔD(50%), there were no significant differences, and BT contribution resulted minimal. An apparent significant difference value was registered in bladder ΔD(max) (0.5 cc). No toxicity was observed. CONCLUSIONS: In uterine cancer patients submitted to APR and vaginal cuff BT, algebraic sum and rigid plan fusion of doses allowed to obtain similar results in evaluating cumulative OARs’ doses. Further investigations and increased number of patients are recommended to confirm our findings.