Program Information
Do We Need KV Imaging During CBCT Based Patient Set-Up for Abdominal Radiation Therapy?
A Gopal*, J Zhou , G Lasio , B Yi , Univ. of Maryland School Of Medicine, Baltimore, MD
Presentations
MO-RPM-GePD-J(A)-3 (Monday, July 31, 2017) 3:45 PM - 4:15 PM Room: Joint Imaging-Therapy ePoster Lounge - A
Purpose: To evaluate the role of 2D kilovoltage (kV) imaging to complement cone-beam CT (CBCT) imaging in a shift threshold based image guided radiation therapy (IGRT) strategy for abdominal radiotherapy.
Methods: A retrospective study was conducted by analyzing IGRT couch shifts for 30 patients that received pancreatic radiotherapy to evaluate the benefit of performing orthogonal kV imaging prior to CBCT imaging. A shift threshold based IGRT protocol was applied, that mandated additional CBCT verification if the applied patient shifts exceeded 3 mm to avoid intra-observer variability in CBCT registration and to confirm table shifts. For each patient, two IGRT strategies: kV + CBCT and CBCT alone, were compared and the recorded patient shifts were categorized into whether additional CBCT acquisition would have been required or not. The effectiveness of either strategy was assessed based on the likelihood of needing additional CBCT imaging for accurate patient set-up.
Results: Using CBCT alone was 3 times more likely to require an additional CBCT than KV+CBCT, for a 3 mm shift threshold (97% vs 24%). The likelihood of additional CBCT verification was significantly lower when kV+CBCT was used (21% with 5 mm threshold, 33% with 2 mm threshold), than with CBCT alone (81% with 5 mm threshold, 100% with 2 mm threshold). With CBCT alone and a 3 mm threshold, the total treatment time and overall imaging dose over the course of treatment increased by 39.8 minutes and 17.7 cGy respectively based on an average of 7 IGRT sessions per patient (73.1 cGy over 30 fractions if using daily IGRT).
Conclusion: The benefit of kV imaging to screen for gross misalignments led to more accurate CBCT based patient localization compared with using CBCT alone. The subsequently reduced need for additional CBCT verification will minimize treatment time and result in less overall patient imaging dose.
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