PV QA 3 - Poster Viewing Q&A 3
TU_8_3196 - Interobserver Differences in Manual SBRT Image Registration
Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3
Interobserver Differences in Manual SBRT Image Registration
M. M. Dominello1, G. Baran2, P. Paximadis3, T. Bossenberger2, R. Halford4, K. M. Masi2, A. Nalichowski2, S. R. Miller II5, M. Zaki6, N. G. Vaishampayan7, H. Beydoun5, and J. W. Burmeister2; 1Department of Oncology, Wayne State University School of Medicine, Detroit, MI, 2Karmanos Cancer Institute, Detroit, MI, 3Lakeland Care Network, St. Joseph, MI, 4William Beaumont Hospital, Royal Oak, MI, 5Department of Radiation Oncology, Wayne State University School of Medicine, Detroit, MI, 6Wayne State University School of Medicine, Detroit, MI, 7Oakwood Hospital & Medical Center, Dearborn, MI
Purpose/Objective(s): To evaluate the magnitude of inter-observer variability in pre-treatment image registration for lung SBRT patients in aggregate and within three clinical subgroups.
Materials/Methods: Retrospective image registration was performed for the first and last treatment fraction for 10 lung SBRT patients by 16 individual observers (5 physicians, 6 physicists, and 5 therapists). Registration translation values were compared within and between subgroups overall and between the first and last fractions. An equality of variance F-test was performed for the comparison of inter-fraction differences in inter-observer variability for each patient and over all registrations. In addition, the test was performed to check for differences in inter-observer variability between subgroups. For cases with true statistical differences in variance, Welch’s t-test was used to test for mean equivalency.
Results: The mean 3D displacement vector for all patients over all comparisons was 2.4 ± 1.8 mm. Three patients had mean 3D vector differences >3 mm. This cohort of patients showed a significant inter-fraction difference in variance (p-value < 0.01), increasing from first fraction to last. A significant difference in inter-observer variability was observed between physicians and physicists (p-value < 0.01) and therapists and physicists (p-value < 0.01), but not between physicians and therapists (p-value = 0.07).
Conclusion: Variability in pre-treatment image guidance represents an important treatment consideration, particularly for SBRT which employs small margins and a small number of treatment fractions. As a result of the data presented here, we have initiated weekly “registration rounds,” to familiarize all staff physicians with the target and normal anatomy for each SBRT patient and minimize inter-observer variations in image registration prior to treatment. We are currently validating image metrics to determine the best way to identify patients at high risk for this potential source of error.
Author Disclosure: M.M. Dominello: None. G. Baran: None. P. Paximadis: None. T. Bossenberger: Honoraria; ASTRO. Travel Expenses; ASTRO. R. Halford: None. K.M. Masi: None. S.R. Miller: None. M. Zaki: None. N.G. Vaishampayan: None. J.W. Burmeister: Research Grant; NIH. Board Member; SDAMPP. Chair, Radiation Oncology Physics Exam Committee; American Board of Radiology.