Room: Karl Dean Ballroom A1
Purpose: Estimation of isoeffective biological dose (EQD) for outcomes prediction, i.e., TCP and NTCP, requires knowledge of multiple parameters including the radiosensitivity parameter (Î±/Î²). This can be challenging if the number of events (toxicity/recurrence) is limited. Here, we explore the use of imbalance correction by Synthetic Minority Over-sampling Technique (SMOTE) and show its application to maximum likelihood estimates (MLE) of TCP/NTCP with unknown Î±/Î² ratio and generalized equivalent uniform dose (gEUD) parameters.
Methods: 192 hepatocellular cancer patients treated with radiotherapy (146 SBRT and 46 IMRT) to a physical dose of 50 Gy were evaluated. NTCP was modeled using the LKB model and TCP by Poisson model. Toxicity was assessed by Child-Pugh changes (17% rate) and failure as recurrence within the field (7% rate) with a follow-up of 1 year. Data imbalance was corrected using SMOTE, which employs a k-nearest neighbor algorithm with perturbation in the feature space of the minority group. Features were selected as mean EQD2 dose, number of fractions, and dose per fraction. Modeling parameters (D50, Î³50, Î±/Î², a_gEUD) were estimated using MLE and confidence intervals (CI) were calculated by likelihood profiling.
Results: Three-parameters LKB (D50, Î³50, Î±/Î²) estimates yielded an Î±/Î²=2.63 (95%CI: 0.914-7.49). The use of SMOTE resulted in a tighter CI with Î±/Î²=2.70 (95%CI: 1.49-4.95). Similar trend was noted in the case of 4-parameters LKB (added a_gEUD) yielded Î±/Î²= 1.50 (95%CI: 0.282-5.99) and a_gEUD=0.714 (95%CI:0.467-0.944), which improved with SMOTE into Î±/Î²= 3.02 (95%CI: 1.78-5.37) and a_gEUD=1.05 (95%CI:0.897-1.23). In case of TCP with 3-parameters Poisson model, SMOTE slightly improved Î±/Î²=17.1 (95%CI: -78-181) to Î±/Î²= 12.7 (95%CI: -104-153). In case of 4-parameters Poisson model, estimates with SMOTE had wide CIs and an average Î±/Î² above 10.
Conclusion: Machine learning techniques can aid in the estimation of traditional radiosensitivity parameters and improve accuracy for EQD conversion and TCP/NTCP predictions.
Not Applicable / None Entered.