PURPOSE: To estimate the radiation equivalent of the chemotherapy contribution to observed complete response rates in published results of 1-phase radio-chemotherapy of muscle-invasive bladder cancer.
METHODS AND MATERIALS: A standard logistic dose-response curve was fitted to data from radiation therapy-alone trials and then used as the platform from which to quantify the chemotherapy contribution in 1-phase radio-chemotherapy trials. Two possible mechanisms of chemotherapy effect were assumed (1) a fixed radiation-independent contribution to local control; or (2) a fixed degree of chemotherapy-induced radiosensitization. A combination of both mechanisms was also considered.
RESULTS: The respective best-fit values of the independent chemotherapy-induced complete response (CCR) and radiosensitization (s) coefficients were 0.40 (95% confidence interval -0.07 to 0.87) and 1.30 (95% confidence interval 0.86-1.70). Independent chemotherapy effect was slightly favored by the analysis, and the derived CCR value was consistent with reports of pathologic complete response rates seen in neoadjuvant chemotherapy-alone treatments of muscle-invasive bladder cancer. The radiation equivalent of the CCR was 36.3 Gy.
CONCLUSION: Although the data points in the analyzed radio-chemotherapy studies are widely dispersed (largely on account of the diverse range of chemotherapy schedules used), it is nonetheless possible to fit plausible-looking response curves. The methodology used here is based on a standard technique for analyzing dose-response in radiation therapy-alone studies and is capable of application to other mixed-modality treatment combinations involving radiation therapy.
Written by:
Plataniotis GA, Dale RG. Are you the author?
Department of Oncology, Queens Hospital, London, United Kingdom; Department of Surgery and Cancer, Faculty of Medicine, Imperial College, London, United Kingdom.
Reference: Int J Radiat Oncol Biol Phys. 2014 Mar 15;88(4):927-32.
doi: 10.1016/j.ijrobp.2013.11.242
PubMed Abstract
PMID: 24462386
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