Author: Dennis A. Cheek, Wei Luo, Cameron Thayer-Freeman, Brien Timothy Washington 👨🔬
Affiliation: UT Southwestern Medical Center, University of Kentucky, Department of Radiation Medicine, University of Kentucky 🌍
Purpose: To investigate the effect of variation in the α/β of cervical cancer on clinical outcome for cervix cancer patients treated with radiation therapy.
Methods: A distribution of experimentally derived α/β values was applied to a reference tumor control probability (TCP) curve generated from cervical cancer patients treated with radiation, using Monte Carlo sampling. An alternate equation for equivalent dose in 2 Gy fractions (EQD2) was derived that considered variance in α/β and was used to generate new values and associated TCP curves. Convolution curves of TCP and normal tissue complication probability (NTCP) were generated to determine potential shifts in optimal dose and probability of risk-free local control (RFLC). Theoretical treatment failure rates were generated to evaluate changes in outcome rates. Alternate fractionations in external beam were calculated that would maintain acceptable tumor control for the new TCP curves.
Results: The α/β distribution produced potential losses in TCP of up to 24% in the clinical range. Convolution curves predicted an optimal treatment dose of 92 Gy EQD2 when applying the most probable α/β of 4.25 Gy, 7 Gy higher than the reference curve. The α/β distribution saw a decrease in RFLC of 10%. To achieve a 90% TCP, fractionations ranged from 70 Gy in 70 fractions to 30 Gy in 3 fractions, with associated increase in normal tissue dose ranging from 8 to 44 Gy EQD2.
Conclusion: The distribution of α/β values from our previous study produced significant changes in tumor control when applied to a reference TCP curve. These results not only demonstrated the potential clinical impact of using α/β = 10 Gy for cervical cancer, but the wide variance of possible clinical uncertainties when applying the α/β distribution. This suggests a potential clinical benefit from looking into alternative radiation treatment schemes for cervical cancer.