A Novel Approach to Evaluate the Prostate Pelvis Lymph Node Setup Margin
Abstract
Purpose
Current techniques for assessing setup margins in prostate and PLN radiation treatments rely on manual, time-consuming workflows. A novel automated workflow approach was developed to evaluate three clinical sites with different immobilization methods.
Methods
A total of 30 patients, ten from each site, were randomly selected. Each site used different immobilization
Methods
a foot strap, an alpha cradle from the knee to the feet, and a vacuum bag from the pelvis to the feet. One planning CT and 7 CBCTs for each patient were imported into MIM software. A MIM automated workflow was developed to automate the process. Rigid registration was performed between the CBCT and CT, aligning the pelvic bones. The PLN structure was copied from CT to CBCT and expanded to 15 structures with an increased margin ranging from 1mm to 15mm. The CBCT was manually shifted to align with the fiducials, and the PLN structure was copied to the CBCT again, which intersected with the 15 expansion structures. The intersection volume of less than 0.1 cc was defined as full PLN coverage in this study. The smallest margin corresponding to the intersection volumes greater than 0.1 cc was recorded for each CBCT. The margins were analyzed for each patient and each site using the Mann-Whiteney U to evaluate the difference between each site.
Results
The smallest margin required to cover PLN varies among patients, ranging from 2.9±1.4mm to 10.1±2.5mm. The mean and standard deviation of the margins are 5.5±2.3mm, 5.7±3.1mm, and 5.5±2.5mm, respectively, for three sites. P-value is 0.8713, 0.9899, and 0.858 between foot strap and vacuum bag, foot strap and alpha cradle, vacuum bag and alpha cradle, respectively.
Conclusion
This novel approach revealed that PLN setup margins vary significantly among patients, but there is no statistical difference between the different immobilization methods.