Room: AAPM ePoster Library
Purpose: MR-guided online adaptive radiotherapy (MRgOART) allows iso-toxic treatments, i.e., adjusting fraction target dose based on daily anatomic and/or biologic changes while maintaining the same doses for organs at risk (OAR). This work describes a framework for iso-toxic planning in MRgOART using biophysical models.
Methods: adaptive framework focuses on calculating biologically effective dose (BED) for the target (T) and the OARs based on the adaptive plan optimized based on the daily anatomy. The fractional target dose is rescaled such that the same OAR doses are maintained. BED for each fraction is determined using the uncomplicated tumor control probability (UTCP), UTCP=TCPx(1-NTCP), where TCP is tumor control probability and NTCP is normal tissue complication probability. Target and organ specific model parameters derived from published dose-response data are used in the calculation. Data for representative SBRT for prostate and pancreatic cancer patients treated with MRgOART were used to demonstrate the utility of the proposed framework.
Results: The proposed framework allowed to increase/decrease fraction dose based on anatomy change (e.g., OAR moved away from the target), and to estimate fraction doses for the remaining fractions considering total BED. The ratio of daily UTCP to originally planned UTCP ranged from 0.960-1.116 & 0.967-1.127 for the prostate and pancreas cases, respectively.
Conclusion: A framework for iso-toxic adaptive planning is developed to account for biological effect of different fraction doses and to optimize the therapeutic ratio in MRgOART.