ANALYSIS OF CLINICAL COMPLICATION DATA FOR RADIATION HEPATITIS USING A PARALLEL ARCHITECTURE MODEL

Purpose: The detailed knowledge of dose volume distributions available from the three-dimensional (3D) conformal radiation treatment of tumo rs in the liver (reported elsewhere) offers new opportunities to quant ify the effect of volume on the probability of producing radiation hep atitis, We aim to test a new parallel architecture model of normal tis sue complication probability (NTCP) with these data, Methods and Mater ials: Complication data and dose volume histograms from a total of 93 patients with normal liver function, treated on a prospective protocol with 3D conformal radiation therapy and intraarterial hepatic fluorod eoxyuridine, were analyzed with a new parallel architecture model. Pat ient treatment felt into six categories differing in doses delivered a nd volumes irradiated, By modeling the radiosensitivity of liver subun its, we are able to use dose volume histograms to calculate the fracti on of the liver damaged in each patient, A complication results if thi s fraction exceeds the patient's functional reserve. To determine the patient distribution of functional reserves and the subunit radiosensi tivity, the maximum likelihood method was used to fit the observed com plication data, Results: The parallel model fit the complication data well, although uncertainties on the functional reserve distribution an d subunit radiosensitivity are highly correlated. Conclusion: The obse rved radiation hepatitis complications show a threshold effect that ca n be described well with a parallel architecture model, However, addit ional independent studies are required to better determine the paramet ers defining the functional reserve distribution and subunit radiosens itivity.