Radiation Dose-Response Model for Locally Advanced Rectal Cancer After Preoperative Chemoradiation Therapy

PURPOSE: Preoperative chemoradiotherapy (CRT) is part of the standard treatment of locally advanced rectal cancers. Tumour regression at the time of operation is desirable, but not much is known about the relationship between radiation dose and tumour regression. In the present study we estimated radiation dose-response curves for various grades of tumour regression after preoperative CRT. METHODS AND MATERIALS: A total of 222 patients, treated with consistent chemotherapy and radiotherapy techniques, were considered for the analysis. Radiotherapy consisted of a combination of external beam radiotherapy and brachytherapy. Response at the time of operation was evaluated from the histopathological specimen and graded on a five point scale (TRG1-5). The probability of achieving complete, major and partial response was analyzed using ordinal logistic regression, and the effect of including clinical parameters in the model was examined. The radiation dose response relationship for a specific grade of histopathological tumour regression was parameterized in terms of the dose required for 50% response, D(50,i), and the normalized dose-response gradient, γ(50,i). RESULTS: A highly significant dose–response relationship was found (p=0.002). For complete response (TRG1) the dose-response parameters were D(50,TRG1)=92.0 Gy (95% CI: 79.3 to 144.9 Gy), γ(50,TRG1)=0.982 (0.533 to 1.429), and for major response (TRG1-2) D(50,TRG1&2)=72.1 Gy (65.3 to 94.0 Gy), γ(50,TRG1&2)=0.770 (0.338 to 1.201). Tumour size and N-category both had a significant effect on the dose-response relationships. CONCLUSIONS: This study has demonstrated a significant dose-response relationship for tumour regression after preoperative CRT for locally advanced rectal cancer for tumour dose levels in the range of 50.4 to 70 Gy, which is higher than the dose-range usually considered

Application of Synchronization to Formation Flying Spacecraft: Lagrangian Approach

This article presents a unified synchronization framework with application to precision formation flying spacecraft. Central to the proposed innovation, in applying synchronization to both translational and rotational dynamics in the Lagrangian form, is the use of the distributed stability and performance analysis tool, called contraction analysis that yields exact nonlinear stability proofs. The proposed decentralized tracking control law synchronizes the attitude of an arbitrary number of spacecraft into a common time-varying trajectory with global exponential convergence. Moreover, a decentralized translational tracking control law based on phase synchronization is presented, thus enabling coupled translational and rotational maneuvers. While the translational dynamics can be adequately controlled by linear control laws, the proposed method permits highly nonlinear systems with nonlinearly coupled inertia matrices such as the attitude dynamics of spacecraft whose large and rapid slew maneuvers justify the nonlinear control approach. The proposed method integrates both the trajectory tracking and synchronization problems in a single control framework.Comment: This paper has been withdrawn by the authors. updated version published. Journal of Guidance, Control, and Dynamics, Vol. 32, No. 2, March-April 2009, pp. 512-52