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Designing equivalent treatment regimens for prostate radiotherapy based on equivalent uniform dose

¹ Department of Radiation Oncology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, ² Department of Radiation Medicine, Ohio State University, Columbus, OH 43210, ³ School of Health Sciences, Purdue University, West Lafayette, IN 47907-1338, ⁴ Department of Radiation Oncology, Cooper Health System, One Cooper Plaza, Camden, NJ 08103, USA

Correspondence: Prof X A Li, Department of Radiation Oncology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA. E-mail: ali{at}radonc.mcw.edu

The purpose of this work was to determine alternative radiotherapy (RT) regimens that are biologically equivalent to clinically proven treatments using different RT modalities or different fractionation schemes. The concept of equivalent uniform dose (EUD) is used with the linear quadratic model to determine equivalent treatment regimens using two representative sets of parameters derived from clinical data: (i) /β = 3.1 Gy and = 0.15 Gy^–1, and (ii) /β = 1.5 Gy and = 0.04 Gy^–1. The EUD values for the critical structure (rectum) are also calculated. Representative dose volume histograms were used to account for dose inhomogeneities for different RT modalities. A series of alternative and equivalent fractionation regimens that can be used with different radiotherapy modalities for localized prostate cancer were determined. For example, the alternative regimens, calculated with the /β ratio of 3.1 Gy, that would be biologically equivalent to external beam RT (EBRT) of 76 Gy (38x2.0 Gy) include: EBRT hypofractionation of 21x3.0 Gy; I-125 implant of 156 Gy; Pd-103 implant of 128 Gy; high dose rate (HDR) brachytherapy of 4x10.5 Gy; I-125 implant of 65 Gy combined with EBRT of 23x2.0 Gy; and HDR brachytherapy of 3x5.9 Gy combined with EBRT of 23x2.0 Gy. Similar data for other parameters are also presented. With caution, the data presented may be useful in designing clinical trials to explore new RT strategies, such as image-guided intensity-modulated RT.