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Patient Alignment Using TomoTherapy MV-Topograms: Clinical Assessment at Three TumorSites

L Yang

L Yang*, D Low , P Lee , R Chin , P Beron , A Raldow , M Steinberg , X Qi , UCLA, Los Angeles, CA


TU-C3-GePD-JT-2 (Tuesday, August 1, 2017) 10:30 AM - 11:00 AM Room: Joint Imaging-Therapy ePoster Theater

Purpose: To evaluate the potential of using megavoltage (MV)-topograms for patient setup by comparing against clinical MVCT-based positioning in three clinical sites.

Methods: MV-topogram based alignment has potential for replacing MVCT in TomoTherapy patient setups, reducing both imaging time and dose. Eighteen patients with mesothelioma (4), head-and-neck (HN) cancer (5) and pelvis cancer (9) enrolled in an ongoing IRB-approved clinical trial were analyzed at our institute. Ninety-two anteroposterior (AP) and lateral (LAT) MV-topograms were acquired on weekly basis using our previously established topogram protocols.Offline commercial automated fusion was employed for the HN and pelvic patients. Manual alignment was conducted for the mesothelioma cases, aligning using the carina. The MVCT and topogram-based shifts were compared. Least-squares linear fits were conducted between topogram-measured and MVCT-measured shifts to show correspondence between the two techniques. MVCT and MV-topogram doses were measured using an ion-chamber in a 28 cm diameter cylindrical water-equivalent phantom at depths between 1-14cm. Imaging times were also recorded.

Results: The slopes and root-mean-squared-error (RMSE) in millimeters for mesothelioma cases were (1.16, 0.97), (0.91, 2.01) and (0.96, 3.49) for lateral (LAT), longitudinal (LONG) and vertical (VERT) directions, for HN cases were (0.73, 1.19), (0.79, 1.60) and (1.18, 1.46), and for pelvis cases (0.61, 2.56), (0.94, 2.09) and (0.74, 1.93), respectively. The RMSE represents that shifts using MV-Topograms could be predicted using MVCT shifts to within the respective range for mesothelioma, HN and pelvis cases. Dose ratio between MVCT and MV-Topogram ranged from 14.7 to 26.9 for depths between 1 cm and 14 cm, respectively. On average, time required to acquire 38 cm long MVCT scans were five times longer than a pair of 50 cm long MV-Topograms.

Conclusion: MV-topograms shifts provided equivalent clinical performance to MVCT for multiple anatomic sites. MV-topograms also delivered less dose and took less time to acquire.

Funding Support, Disclosures, and Conflict of Interest: This study has been supported by a grant from Accuray Inc.

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