Program Information
Optimizing Re-Irradiation of Recurrent Nasopharyngeal Carcinoma After Initial Radiation Therapy
A Tai1*, Q Zhou2 , X Deng2 , X Li1 , (1) Medical College of Wisconsin, Milwaukee, WI, (2) Sun Yat-Sen University Cancer Center, Guangzhou, Guangdong
Presentations
WE-G-FS1-5 (Wednesday, August 2, 2017) 4:30 PM - 6:00 PM Room: Four Seasons 1
Purpose: The normal tissue toxicities such as trismus and massive hemorrhage are a serious concern for re-irradiation of recurrent nasopharyngeal carcinoma (NPC). To be able to calculate the tumor control probability (TCP) based on individual patient response to the initial radiation would be useful to optimize re-irradiation aiming to minimizing the normal tissue toxicities.
Methods: A TCP model, called tumor regrowth-gap model, was developed to investigate the dependence of TCP after re-irradiation of recurred NPC on the time interval between the two treatment courses (gap). The time dependence of tumor cell regrowth was modeled by K=K₀e^(γτ)^δ, where γ = ln2⁄Td (Td is tumor potential double time), δ is a fitting parameter characterizing the speed of tumor cell regrowth after RT, and τ is the follow-up time. The model parameters were determined by the TCP data of 295 recurrent NPC patients. The gap ranged from 6 months to 190 months with a median gap of 27 months. The radiation-reduced trismus and massive hemorrhage were also analyzed.
Results: Model fitting showed the prescribed re-irradiation dose and the speed of tumor cell regrowth significantly affected TCP of irradiated NPC patients. The faster the tumor regrowth the earlier the recurrence and the poorer the clinic outcome of re-irradiation. The relationship between δ and the time gap between the initial- and re-irradiations can be fitted by a quadratic function. With the extracted model parameters, TCP at 2 and 5 years for irradiation of the recurred NPC patients are predicted based on the biologically effective dose (BED) and the gap.
Conclusion: The dependence of TCP on BED and the gap was established for re-irradiation of the recurred NPC. The model along with the extracted tumor-specific radiobiological parameters may be used to optimize re-irradiation dose and/or fractionation scheme for individual patients with recurred NPC.
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