Optimization and comparison of balloon-based partial breast brachytherapy using a single source, a standard plan line source, and both forward and inverse planned multilumen techniques.

PURPOSE: This study directly compares four dosimetric techniques for balloon-based partial breast brachytherapy: single source, standard line source, and both forward planned and inverse planned multilumen (ML). A standard line source plan is presented to be used in a single catheter or as a starting point for forward planned ML. METHODS AND MATERIALS: The study population consists of 12 patients previously treated with a single lumen. Inverse plans were created for 7 patients and used to create a standard line source plan. ML plans were created on the same patient data sets. The dosimetric aims were as follows: PTV_EVAL (planning target volume for evaluation) D95 (dose received [%] by 95% of PTV_EVAL volume)≥95% of the prescribed dose (PD), the maximum skin and rib dose ≤125% of prescription dose, breast V150 (volume [cc] receiving 150% of the PD)≤50cc, and V200 (volume [cc] receiving 200% of the PD)≤10cc.
RESULTS: The number of patients fulfilling all dosimetric constraints went from 1 patient of 12 with a single catheter to 6 patients of 12 with inverse planned ML and 7 patients of 12 with forward planned ML. PTV_EVAL D95 increased significantly with the standard line source plans and ML plans when compared with the single-source plans. Forward planning took, on average, 7min longer than inverse planning.
CONCLUSION: Multiple sources in a single catheter improve coverage at catheter ends, whereas ML can further improve coverage and reduce dose to organs at risk. Using a standard line source as a starting point for forward planning ML means increase in planning time is kept to a minimum, making it a practicable option for centers without inverse planning software. Patients previously ineligible for treatment with a single catheter may be treated using ML.