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 (T_d), a/β and radiosensitivity a, 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 a/β, a and T_d are a/β = 8.1 ± 4.1 Gy, a = 0.22 ± 0.08 Gy⁻¹, T_d = 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.

Background: Neoadjuvant radiotherapy (NRT) is an effective strategy to treat soft tissue sarcomas (STS). However, the role of neoadjuvant chemoradiotherapy (NCRT) remains to be determined. Methods: From May 1999 to July 2010, 112 patients with localized STS of the extremity and trunk who were treated with NRT or NCRT followed by surgery were retrospectively reviewed. Clinical outcomes including overall survival (OS), disease-free survival (DFS), and distant metastasis free survival (DMFS) were calculated using Kaplan-Meier survival analyses. Prognostic variables were determined by univariate (UVA) and multivariate analyses (MVA). Results: Median follow-up was 37 months. Median RT dose was 50 Gy. Forty-nine patients received NCRT. Overall limb-preservation rate was 99% and local control was 97%. The estimated 3-year OS, DFS, and DMFS were 86%, 68%, and 72%, respectively. Age was the only variable to predict for OS, DFS and DMFS on UVA. Age ≥ 70 predicted for poor OS, stage III disease predicted for poor DFS and DMFS, and the addition of chemotherapy predicted for improved DMFS on MVA. Conclusions: Excellent rates of local control and limb-preservation were observed in patients with primary STS treated with neoadjuvant therapy followed by surgery. Neoadjuvant sequential chemotherapy followed by radiotherapy may be considered for young patients with stage III STS.