Performance of Multiple Conformity, Homogeneity and Dose Gradient Indices in SRS and SBRT Treatment Planning of the Spinal, Pelvic and Lung Lesions
R Bassalow1*, A Sabbas1, J Chang1, B Parashar1, G Wernicke1, K Chao2, (1) NewYork Presbyterian Hospital/ Weill Cornell Medical College, New York, NY, (2) NewYork Presbyterian Hospital\Weill Cornell Medical College and Columbia Un, New York, NYSU-E-T-702 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: Presently, various forms of quality indices (QI) are used to compare and evaluate stereotactic treatment plans with no single QI accepted as universal. In this work we evaluate and compare the performance of 11 previously reported QI: 5 conformity (CI), 5 homogeneity (HI), and 1 dose gradient (DGI) indices as a function of target size, site, and mode of treatment. A novel unified quality function (UQF) which combines conformity, homogeneity and dose gradient is presented and investigated.
Methods: 27 spine SRS, 8 pelvic SBRT and 34 lung SBRT cases were analyzed using an in-house wxPython program which imports treatment plan data and calculates various quality indices, dose volume tables, displays 3D dose/CT images, cumulative and differential DVHs.
Results: Mean spine, pelvis and lung coverages were 0.91, 0.93, 0.85 respectively. Mean maximum target dose was best for pelvis (108%), followed by the lung (115%) and the spine (118%). Mean minimum target dose was best for the lung (95%), followed by pelvis (94%) and spine (88%). Mean DGI were 4.6, 5.2 and 7.54 for the pelvis, spine and lung. UQF scores the best for pelvis (0.2), followed by spine (0.28) and the lung (0.42). IMRT spine plans had better mean coverages (0.94), and lower maximum target dose (114%), while VMAT plans had better minimum target dose (89%).
Conclusion: Mean CI, HI and DGI show various sensitivities to the treatment site, size and the delivery type (VMAT or IMRT). All CI except coverage show large variations with volume < 130 cc while all 5 HI show little dependence on the PTV volume. DGI values fall sharply for the lung (from 15 to 6) and spine (from 10 to 5) as the PTV increases to about 100 cc, while pelvic DGI stays about 5 for all PTV sizes.