Room: Exhibit Hall | Forum 1
Purpose: To quantify the dosimetric differences between two optimization methods to incorporate flash plans for left breast patients in terms dose to critical structures and amount of flash.
Methods: Five patients were planned retrospectively with VMAT radiation therapy to the left breast or chest wall using two methods. The first method utilizes robust optimization to account for target volume motion while the second uses an expanded target volume outside of the external with bolus used during optimization that is removed for the final dose calculation. All treatments delivered a total of 5000cGy in 25 fractions and were normalized to cover 95% of the target volume within the external. Dosimetric comparisons were made for the heart, lungs, and contralateral breast based on the mean dose and relative volume receiving dose levels of interest. The amount of flash delivered was determined by the volume outside of the external ROI that received 90% of the prescription dose.
Results: Dosimetric comparisons of the two methods showed no definitive differences in OAR sparing or amount of incorporated flash. Optimization time was found to be 3.8x longer for robust optimization compared to bolus method.
Conclusion: Preliminary data demonstrates little dosimetric differences between the two optimization methods. Optimization times for the robust method limits the clinical viability of this method over the bolus method. Further investigation, using larger data set is required, however, current data demonstrates both methods are dosimetrically viable.
Breast, Dosimetry, Treatment Planning
TH- External beam- photons: VMAT dose optimization algorithms