SU-F-T-37: Dosimetric Evaluation of Planned Versus Decay Corrected Treatment Plans for the Treatment of Tandem-Based Cervical HDR Brachytherapy.

PURPOSE: This study evaluated dosimetric parameters for actual treatment plans versus decay corrected treatment plans for cervical HDR brachytherapy.

METHODS: 125 plans of 25 patients, who received 5 fractions of HDR brachytherapy, were evaluated in this study. Dose was prescribed to point A (ICRU-38) and High risk clinical tumor volume (HR-CTV) and organs at risk (OAR) were, retrospectively, delineated on original CT images by treating physician. First HDR plan was considered as reference plan and decay correction was applied to calculate treatment time for subsequent fractions, and was applied, retrospectively, to determine point A, HR-CTV D90, and rectum and bladder doses.

RESULTS: The differences between mean point A reference doses and the point A doses of the plans computed using decay times were found to be 1.05%±0.74% (-2.26% to 3.26%) for second fraction; -0.25%±0.84% (-3.03% to 3.29%) for third fraction; 0.04%±0.70% (-2.68% to 2.56%) for fourth fraction and 0.30%±0.81% (-3.93% to 2.67%) for fifth fraction. Overall mean point A dose difference, for all fractions, was 0.29%±0.38% (within ± 5%). Mean rectum and bladder dose differences were calculated to be -3.46%±0.12% and -2.47%±0.09%, for points, respectively, and -1.72%±0.09% and -0.96%±0.06%, for D2cc, respectively. HR-CTV D90 mean dose difference was found to be -1.67% ± 0.11%. There was no statistically significant difference between the reference planned point A doses and that calculated using decay time to the subsequent fractions (p<0.05).

CONCLUSION: This study reveals that a decay corrected treatment will provide comparable dosimetric results and can be utilized for subsequent fractions of cervical HDR brachytherapy instead of actual treatment planning. This approach will increase efficiency, decrease workload, reduce patient observation time between applicator insertion and treatment delivery. This would be particularly useful for institutions with limited resources or large patient populations with limited access to care.