PURPOSE: Delineation of gross @entity5 volumes (GTVs) is important for stereotactic body radiotherapy (SBRT). However, @entity5 volume changes during treatment response. Here, we have investigated @entity5 volume changes and movement during SBRT for @entity2 , as a means of examining the need for adaptive radiation therapy (ART). METHODS: Fifteen @entity5 in 15 @entity1 with @entity2 were treated with SBRT (total dose: 60 Gy in 4 fractions). GTVs were obtained from cone-beam computed tomography scans (CBCT1-4) taken before each of the 4 fractions was administered. GTVs were delineated and measured by radiation oncologists using a treatment planning system. Variance in the @entity5 position was assessed between the planning CT and the CBCT images. To investigate the dosimetric effects of @entity5 volume changes, planning CT and CBCT4 treatment plans were compared using the conformity index (CI), homogeneity index (HI), and Paddick's index (PCI). RESULTS: The GTV on CBCT1 was employed as a baseline for comparisons. GTV had decreased by a mean of 20.4% (range: 0.7% to 47.2%) on CBCT4. Most @entity1 had smaller GTVs on CBCT4 than on CBCT1. The interfractional shifts of the @entity5 position between the planning CT and CBCT1-4 were as follows: right-left, -0.4 to 1.3 mm; anterior-posterior, -0.8 to 0.5 mm; and superiorinferior, -0.9 to 1.1 mm. Indices for plans from the planning CT and CBCT4 were as follows: CI = 0.94  0.02 and 1.11  0.03; HI= 1.1  0.02 and 1.10  0.03; and PCI = 1.35  0.16 and 1.11  0.02, respectively. CONCLUSION: CI, HI, and PCI did not differ between the planning CT and CBCTs. However, daily CBCT revealed a significant decrease in the GTV during lung SBRT. Furthermore, there was an obvious interfractional shift in @entity5 position. Using ART could potentially lead to a reduced GTV margin and improved regional @entity5 control for @entity2 @entity1 with significantly decreased GTV.

SU-E-J-179: Assessment of Tumor Volume Change and Movement During Stereotactic Body Radiotherapy (SBRT) for XXXX : Is Adaptive Radiation Therapy (ART) Necessary?

@entity5 :: ('MESH:D009369', 'Disease') :: ['tumor', 'tumors'] @entity1 :: ('9606', 'Species') :: ['patients'] @entity2 :: ('MESH:D008175', 'Disease') :: ['lung cancer']
@entity2 :: (MESH:D008175,Disease) :: ['Lung Cancer']
