Room: AAPM ePoster Library
Purpose: Adaptive strategies are driven by geometric changes or predetermined time-points due to limited tools to efficiently track changes in normal tissue complication probability (NTCP). The goal of this work is to develop and evaluate the impact of NTCP-based based tools to support risk-based adaptive radiotherapy.
Methods: As part of an ongoing technology development project, 8 patients with daily CBCT images acquired over the course of head and neck radiotherapy (RT) treatment were evaluated under a retrospective IRB for in silico analysis. Deformable registration (DIR)-based dose accumulation was performed using a hybrid intensity based algorithm. NTCP was calculated for each daily computed dose using the Lyman-Kutcher-Burman method with TD50=39.9, m=0.4, n=1, alpha/beta=3 for the parotid glands (PG). PGs were identified as contralateral (cPG) and ipsilateral (iPG). A Pearson’s product-moment correlation was performed between the NTCP change and the GTV volume change. The moving average change, based on the previous 3 fractions, in NTCP was computed for the cPG and iPG across all fractions. The fraction at which the moving average change in NTCP increased by more than 2% from planning was computed.
Results: NTCP at planning and throughout the treatment ranged from 0.8-9% for the cPG and 3-64% for the iPG NTCP, due to proximity to the tumor. NTCP changes were not strongly correlated with changes in GTV volume over the course of treatment, r=0.04 and r=-0.1 for the cPG and iPG, respectively. One patient never exceeded a 2% increase of NTCP for the iPG, 1 patient reached a 2% increase at the final fraction, and the remaining cases exceeded a 2% increase at fraction 4-23 (median=18).
Conclusion: NTCP changes do not strongly correlate with tumor volume changes or fraction number and should be included in the decision making for adaptive strategies when toxicity risk is of importance.
Funding Support, Disclosures, and Conflict of Interest: Research was supported by RaySearch Laboratories, Helen Black Image Guided Fund, Image Guided Cancer Therapy Research Program from The University of Texas MD Anderson Cancer Center, NIH R01DE025248 and NIH R01CA218148. Dr Brock has a licensing agreement with RaySearch Laboratories and Dr. Fuller has received grant support/honoraria/travel funding from Elekta.