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A note on modeling of tumor regression for estimation of radiobiological parameters
Author(s) -
Zhong Hualiang,
Chetty Indrin
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4884019
Subject(s) - jacobian matrix and determinant , mathematics , estimation theory , regression analysis , dosimetry , statistics , nuclear medicine , medicine
Purpose: Accurate calculation of radiobiological parameters is crucial to predicting radiation treatment response. Modeling differences may have a significant impact on derived parameters. In this study, the authors have integrated two existing models with kinetic differential equations to formulate a new tumor regression model for estimation of radiobiological parameters for individual patients. Methods: A system of differential equations that characterizes the birth‐and‐death process of tumor cells in radiation treatment was analytically solved. The solution of this system was used to construct an iterative model (Z‐model). The model consists of three parameters: tumor doubling time T d , half‐life of dead cells T r , and cell survival fraction SF D under dose D. The Jacobian determinant of this model was proposed as a constraint to optimize the three parameters for six head and neck cancer patients. The derived parameters were compared with those generated from the two existing models: Chvetsov's model (C‐model) and Lim's model (L‐model). The C‐model and L‐model were optimized with the parameter T d fixed. Results: With the Jacobian‐constrained Z‐model, the mean of the optimized cell survival fractions is 0.43 ± 0.08, and the half‐life of dead cells averaged over the six patients is 17.5 ± 3.2 days. The parameters T r and SF D optimized with the Z‐model differ by 1.2% and 20.3% from those optimized with the T d ‐fixed C‐model, and by 32.1% and 112.3% from those optimized with the T d ‐fixed L‐model, respectively. Conclusions: The Z‐model was analytically constructed from the differential equations of cell populations that describe changes in the number of different tumor cells during the course of radiation treatment. The Jacobian constraints were proposed to optimize the three radiobiological parameters. The generated model and its optimization method may help develop high‐quality treatment regimens for individual patients.