An Estimation of Radiobiological Parameters for Head-and-Neck Cancer Cells and the Clinical Implications.

X Sharon Qi,Dian Wang,Steve P Lee,X Allen Li,Qiuhui Yang

doi:10.3390/cancers4020566

Abstract

In vitro survival measurements using two human head-and-neck cancer (HNC) cell lines were performed. The specially designed split-dose surviving fraction was obtained and fitted to the linear-quadratic formalism. The repair halftime (Tr), the potential doubling time (Td), α/β and radiosensitivity α, were estimated. Other radiobiological models: EUD, BED, TCP, etc., were used to examine the potential treatment effectiveness of different IMRT techniques. Our data indicated the repair halftime of ~17 min based on two HNC cell lines. The combined α/β, α and Td are α/β = 8.1 ± 4.1 Gy, α = 0.22 ± 0.08 Gy−1, Td = 4.0 ± 1.8 day, respectively. The prolonged IMRT dose delivery for entire HNC treatment course could possibly result in the loss of biological effectiveness, i.e., the target EUDs decreased by 11% with fraction dose delivery time varying from 5 to 30 min. We determined the sublethal damage repair halftime and other radiobiological parameters for HNC cells, and to evaluate treatment effectiveness of the prolonged dose delivery times associated with different IMRT techniques. The estimated repair halftime for HNC is relatively short and may be comparable to the step-and-shoot IMRT fraction dose delivery time. The effectiveness of IMRT treatment may be improved by reducing the fraction delivery time for HNC treatment.

Highlights

Intensity modulated radiation therapy (IMRT) is becoming the standard technique to treat head-and-neck cancer (HNC) in radiation treatment, since IMRT is capable of delivering highly conformal doses to the target volume while sparing normal structures
The split-doses of 4 Gy + 4 Gy were delivered with time intervals of 0, 0.25, 0.5, 0.75, 1.5, 2.0, 4 and 6 h to the two HNC cell lines
The curves are the fitting results based on Equations (2–4) for each cell line separately

Summary

Introduction

Intensity modulated radiation therapy (IMRT) is becoming the standard technique to treat head-and-neck cancer (HNC) in radiation treatment, since IMRT is capable of delivering highly conformal doses to the target volume while sparing normal structures. The prolonged IMRT dose delivery for HNC treatment could possibly result in the loss of biological effectiveness. There are various IMRT dose delivery techniques available, such as step-and-shot IMRT, dynamic IMRT, helical Tomotherapy (HT) and recently available volumetric modulated arc therapy (VMAT), etc. A Siemens Primus step-and-shoot accelerator, the estimated fraction dose delivery time can be determined primarily by the number of segments and the total number of MUs per fraction [1]. Given a standard fraction size of 2.0 Gy, the dose delivery time may be as long as 20–30 min depending on the total number of segments; while, the dynamic IMRT delivery time is generally believed to be 1/3 to 1/2 of the static method [2]. For VMAT, the dose delivery is supposedly to be much faster than the step-and-shoot IMRT

Results

Discussion

Conclusion