Yasutaka Sugano, Presenter: Nothing to Disclose

Masahiro Mizuta, Abstract Co-Author: Nothing to Disclose

Seishin Takao, Abstract Co-Author: Nothing to Disclose

Hiroki Shirato MD, PhD, Abstract Co-Author: Nothing to Disclose

Kenneth Sutherland, Abstract Co-Author: Nothing to Disclose

Hiroyuki Date, Abstract Co-Author: Nothing to Disclose

Purpose/Objectives:Radiotherapy on solid tumors has been performed by various fractionation regimens such as multi- and hypo-fractionation. However, the investigation to optimize the fractionation regimen considering the physical dose distribution remains insufficient. We propose a mathematical method for selecting the optimal number of fractions (n) and dose per fraction (d) based on the physical dose distribution.Materials/Methods:This study adopts the universal survival curve (USC) with tumor repopulation to evaluate the effect on tumor and damage to organ at risks (OARs) in radiation exposure. The USC model provides a rectilinear description of the survival curve in the high dose range while preserving the quadratic nature of the linear quadratic (LQ) model in the low dose range. The essential point in radiation therapy is that the tumor be sterilized to a requisite level while normal tissues or OARs are preserved intact as much as possible. By using a graphical tumor-OAR (TO) plot to illustrate the relationship between the effect on tumor and damage to OARs, the optimal fractionation regimen was sought. For simplicity, we considered n-time irradiation with the same dose d per fraction (1 fraction/day).Results:We defined the proportionality factor δ for representing the dose ratio of OAR to tumor. It was found that if δ is given, the optimal value of number of fractions (n) and dose per fraction (d) can be derived from the TO plot. For example, the optimal fractionation regimen (for the surviving fraction of the tumor to be fixed at 0.001%) is n=39.6 and d=2.0 [Gy] when δ is 0.8, and n=5.5 and d=8.2 [Gy] when δ is 0.1, under the assumption that the α/β ratios of tumor and OAR are 10 and 2 respectively, and the doubling time is 10 days.Conclusions:Our investigation showed that it is possible to determine the optimal number of fractions and dose per fraction corresponding to the physical dose distribution. This concept may stipulate a new guideline for radiotherapy planning.

Sugano, Y, Mizuta, M, Takao, S, Shirato, H, Sutherland, K, Date, H, A Novel Technique for Optimizing Dose Fractionation Regimen Based on the Universal Survival Curve with Tumor Repopulation.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14045820.html