Room: Exhibit Hall | Forum 4
Purpose: Most commercially available treatment planning systems for brachytherapy operate based on physical dose and do not incorporate fractionation or tissue-specific response. We present an methodology for incorporating biological dose calculations into the IPSA (Inverse Planning Simulated Annealing) optimization algorithm for brachytherapy treatment planning.
Methods: IPSA-Bio was built to optimize based on tissue- and fractionation- specific parameters. This allows for incorporation of prior external beam dose into the brachytherapy optimization. The code structure was built to allow plug-and-play functionality for various biological dose calculation models. For this work, EQD2 (equivalent dose in 2 Gy fractions) and EUBED (equivalent uniform biologically effective dose) were explicitly incorporated. In the case of EQD2, the number of fractions is accounted for in the formula for EQD2, thus the dose per fraction can be directly optimized. IPSA-Bio was applied to the clinical scenario in which extensive hypofractionation was desireable for cervical cancer patients. Different fractionation schemes were tested on 6 cervical cancer patient datasets. Hypofractionated plans (1-4 fractions) were generated and compared to 5-fraction planning.
Results: IPSA-Bio has similar functionality to physical-dose planning with the additional ability to account for fractionation effects. It was shown that hypofractionated plans consisting of 3 and 4 fractions can have comparable target coverage with equivalent normal tissue exposure. In some specific cases, further fractionation may present acceptable target coverage as well.
Conclusion: An algorithm incorporating radiobiology has clinically acceptable performance. As new/different biological models gain acceptance, the plug-and-play functionality allows for various biological models to be incorporated. It is shown that further hypofractionation may be possible for cervical cancer patients. When implemented clinically, this algorithm would allow for expanded treatment fractionation options to be evaluated on a patient-specific basis, potentially allowing for shorter hospital stays and fewer surgical implants for the patient.
Brachytherapy, Treatment Planning, Radiobiology