Abstract
The aim of this study was to investigate quantitatively the dosimetric factors that increase the risk of clinical complications of rib fractures or chest wall pain after stereotactic body radiation therapy (SBRT) to the lung. The correlations of clinical complications with standard-uptake values (SUV) and FDG-PET activity distributions from post-treatment PET-imaging were studied. Mean and maximum doses from treatment plans, FDG-PET activity values on post-SBRT PET scans and the presence of clinical complications were determined in fifteen patients undergoing 16 SBRT treatments for lung cancer. SBRT treatments were delivered in 3 to 5 fractions using 5 to 7 fields to prescription doses in the range from 39.0 to 60.0 Gy. The dose and FDG-PET activity values were extracted from regions of interest in the chest wall that matched anatomically. Quantitative evaluation of the correlation between dose deposition and FDG-PET activity was performed by calculating the Pearson correlation coefficient using pixel-by-pixel analysis of dose and FDG-PET activity maps in selected regions of interest associated with clinical complications. Overall, three of fifteen patients developed rib fractures with chest wall pain, and two patients developed pain symptoms without fracture. The mean dose to the rib cage in patients with fractures was 37.53 Gy compared to 33.35 Gy in patients without fractures. Increased chest wall activity as determined by FDG-uptake was noted in patients who developed rib fractures. Enhanced activity from PET-images correlated strongly with high doses deposited to the chest wall which could be predicted by a linear relationship. The local enhanced activity was associated with the development of clinical complications such as chest wall inflammation and rib fracture. This study demonstrates that rib fractures and chest wall pain can occur after SBRT treatments to the lung and is associated with increased activity on subsequent PET scans. The FDG-PET activity provides a useful parameter that can be used clinically to predict chest wall complication in lung patients.