Comparison Of Normal Tissue Radiation Dose Responses For Various Regions Of The Lungs

To determine and examine the radiation dose responses for different regions of normal lung. The data from 11 patients enrolled in an IRB-approved clinical trial were analyzed to determine the normal lung dose response for varying sections of the lungs. Patients had pre- and approximately 6 months post-radiotherapy SPECT perfusion data acquired. These SPECT data were registered to the treatment planning CT and thus, the three-dimensional dose distribution. The lungs were divided into halves and thirds in the superior-inferior direction based on volume. Dose-function histograms (DFHs) were calculated for each region. These DFHs displayed the percent regional perfusion versus radiation dose. Lung perfusion is assumed to be a surrogate of that organ's function. The DFHs were then used to calculate dose response curves (DRCs) for each region. Comparisons between different lung regions' DRCs were made. DRCs for 11 patients were determined for the superior/inferior halves, and the superior/middle/inferior thirds of their normal lungs. For each DRC, a linear approximation was computed. The mean slopes for the linear DRC approximations and the corresponding standard deviations are shown in Table 1 for the defined regions. The superior and inferior halves of the lungs appear to have a similar dose response using this assessment approach. The data for thirds of the lungs show some differences, but these may be due to the limited sample size. Future studies will also examine the effects of DRC normalization as well as increasing the sample size. DRCs for various regions of normal lungs have been determined for a limited number of patients. A better understanding of radiation-induced lung injury should lead to an improvement in predicting treatment related toxicity.