2229 - Evaluation of Automated Whole Breast Tangential Field Technique

C. Busch¹, C. S. Shah¹, P. Xia², and Y. B. Cho¹; ¹Department of Radiation Oncology, Cleveland Clinic Foundation, Cleveland, OH, ²Department of Radiation Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH

Purpose/Objective(s): To evaluate an in-house developed planning scripts for automatic tangent field-in-field technique of whole breast radiotherapy. Materials/

Methods: To automate the planning procedure, an in-house script was developed with open tangential fields as the initial inputs. This script automatically blocked hotspots that were greater than 105% of the prescription dose until the number of segments reached the predefined limits or until no more hotspots exist. Finally, a segment weight optimization was performed. A dataset from 19 patients was used to evaluate the quality of the plans generated by the scripts. The script plans and manually created clinical plans by experienced dosimetrists were compared using 20 Gy to the volume of ipsilateral lung (V20Gy), mean dose of the heart, the volume of PTV receiving 105% of the prescription dose (V105%), and the volume of PTV receiving 90% prescription dose (V90%). In addition, the number of segments and total MU per plan were also compared. A double-sided T test was used for statistical analysis at the 95% confidence interval.
Results: The prescription dose was 40.05 Gy in 15 fractions (16 cases), but cases that prescribed 25Gy (1 case) or 26Gy (2 cases) delivered in 5 fractions were also included. The average PTV breast volume in 19 plans were 1867cc (Range: 435cc – 4347cc). The average mean heart dose was 83.4+/-51.8cGy, and 83.8+/-52.5cGy for the clinical plans and the script plans, respectively without statistical difference (T=0.26). The average V90% of the PTV was 98.8% +/-1.6%, and 99.1% +/-0.9% for the clinical plans and the script plans, respectively without statistical difference (T=0.28). The average V105% of the PTV was 2.0% ± 5.0% and 3.7% +/-6.4% for the clinical plans and the script plans, respectively with statistical difference (T= 0.048). The average V20Gy of the ipsilateral lung were 12.9% +/- 3.4% and 13.0% +/- 3.4% for the clinical plans and the script plans, respectively with statistical difference (T=0.02). The average number of segments were 7.3+/-1.3 and 10.9+/-1.9 for clinical plans and script plans, respectively with statistical difference (T=8E-10). The total MUs were 351.7+/-99.0 for clinical plans and 354.7+/-101.2 for script plans, respectively with statistical difference (T=0.05).
Conclusion: An in-house developed automated tangent planning technique for whole breast is robust and efficient, capable to create a tangent plan within 5 minutes while maintaining consistent plan quality like clinical manual plans.