Author: Brian M. Anderson, Simon A. Brundage, Xuguang Scott Chen, Shiva K. Das, Felice Dong, Spencer Lynch, Panayiotis Mavroidis, Ryan Morse Morse, Heidi Urquidi 👨🔬
Affiliation: University of North Carolina Chapel Hill, University of North Carolina at Chapel Hill, University of North Carolina 🌍
Purpose: This study aims at correlating different dosimetric indices of nodal GTV with the regional recurrencies observed after head and neck radiotherapy. Also, to perform a tumor control probability (TCP) modeling by fitting the Poisson model to those dosimetric and outcome data.
Methods: 265 patients with head & neck tumors and complete dosimetric and outcome data were used in this study. The HPV+ patients were prescribed to 60Gy, whereas the rest of the patients to 70Gy in 30 and 35 fractions, respectively. 31 of the patients had recurrencies in the region of the nodal GTV. The Poisson TCP model was used to fit the DVHs of nodal GTV with the regional tumor control data. Metrics like area under the receiver operating characteristic curve (AUC) and odds ratios (OR) were used to evaluate the goodness-of-fit of the model.
Results: Regional recurrencies were observed in 13 (8.8%) and 18 (15.4%) of the patients, who were treated to 60Gy and 70Gy, respectively. For the TCP model, the derived parameter values were D50=32.0Gy and γ=1.63 for the first cohort and 24.0Gy and 0.32 for the second one. The AUC values for the two cohorts were 0.61 and 0.74. The corresponding odds ratios were 2.3 and 9.7, which were associated with a biological effective uniform dose (BEUD) threshold of 45Gy and 60Gy, respectively. Of those ORs, only that corresponding to the 70Gy cohort was found to be statistically significant with a p-value of 0.03.
Conclusion: The dose-response curves of nodal GTV were derived for regional tumor control using the Poisson TCP model. The model parameter values that were derived based on the data of the patients, who were treated to 70Gy showed high predictive value. It was found that a BEUD>60Gy to the nodal GTV may significantly reduce ten-fold the risk of regional recurrency.