Howard J. Halpern MD, PhD, Presenter: Consultant, Bruker Corporation

Boris Epel PhD, Abstract Co-Author: Nothing to Disclose

Gage Redler, Abstract Co-Author: Nothing to Disclose

Charles A. Pelizzari PhD, Abstract Co-Author: Research Grant, Varian Medical Systems, Inc Scientific Advisory Board, RefleXion Medical Inc

Establish a pO2-guided radiation protocol by comining prelinical electron paramagnetic resonance (EPR) pO2 images with intensity-modulated radiation therapy (IMRT).

Pulse EPR oxygen images were obtained from 9 mm FSa fibrosarcomas grown IM in the gastrocnemei of C3H mice. These images combine 1-2 torr precistion, 10 minute acqusition time and 1 mm resolution. An XRAD225Cx animal MicroCT/Radiation system delivered radiation. Radiation was delivered in two steps. First the whole tumor was given a uniform 50% tumor control dose (TCD50). Second an additional IMRT dose boost is delivered to radioresistant, hypoxic tumor regions. From possible positions of the radiation boost sphere, we chose the one that irradiates the largest fraction of tumor voxels with pO2 less than 10 torr. The sphere radius was chosen based on a Receiver Operator Characteristic (ROC) analysis. We used the fraction of irradiated hypoxic volume as the true positive fraction and the fraction of the irradiated normoxic volume as the false positive fraction in the terms of that analysis. For a control experiment, an identical radiation dose to an equal volume of normoxic regions (greater than 10 torr) was delivered. T2 MRI determined the tumor limits.

The treatment was successfully implemented on the number of animals. Image registration technique was applied to combine oxygen maps with MRI data and CT image based treatment planning. Preliminary tumor control probability will be presented.

This radiation delivery protocol opens new possibilities for efficient radiation delivery. 

pO2 is a major determinant of tumor response to radiation and chemotherapy. An oxygen-guided dose painting radiation protocol may significantly enhance the therapeutic ratio.  

Halpern, H, Epel, B, Redler, G, Pelizzari, C, Oxygen-guided Intensity Modulated Radiation Therapy.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14045609.html