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Palliative Radiotherapy Simulation and Treatment in Under 10 Minutes On a Novel Linear Accelerator

P Balter

P Balter*, Y Li , T Netherton , P Nitsch , H Pan , S Gao , A Klopp , L Court , The University of Texas MD Anderson Cancer Center, Houston, TX


TH-CD-708-8 (Thursday, August 3, 2017) 10:00 AM - 12:00 PM Room: 708

Purpose: To evaluate methods for effective rapid palliation on a novel high-speed 6MV FFF only linac.

Methods: We investigated 2 strategies for palliative sim-and-treat scenarios: (1) Planning based on a diagnostic CT (“pre-planned”), (2) Applying a generic preprogrammed treatment sequence to the patient (“generic”). In both cases, plans were single-arc VMAT which would have QA done before bringing the patient to the radiotherapy clinic (pre-plan) or at the time of technique commissioning (generic). The final iso-center is set at the time of treatment using CBCT. We studied both approaches on 5 patients who received palliative radiation in our clinic.

Results: We found that the pre-planned technique gave good coverage in 4 of the 5 cases with doses within 4% (D95 97 – 104%) and with good coverage (V95 99-100%) and hotspots within 7%(98%-107%) of those in the preplan. One case showed significant difference in dose (87% of planned) due to the diagnostic scan being a deep inspiration breath-hold and the treatment area being at the level of the diaphragm. The generic technique gave good coverage (D95 98-103%, V95 97-99%) but with hotspots that ranged up to 14% higher than on the generic plan for 4 of 5 patient studied. The coverage was poor on the last patient D95=84% due to their large size, but this could be recovered by simple monitor unit scaling. This scaling, if applied to all plans, reduced the hot spots to be with 7% of expected and 13% of the prescription dose. The plans themselves were deliverable with a <5 minute imaging and beam-on-time demonstrating that a 10 minute palliative treatment is feasible on this platform.

Conclusion: We have demonstrated that we can complete palliative spine treatments patient in <10 minutes, without the need for a simulation CT. Understanding of limitations and patient selection is key.

Funding Support, Disclosures, and Conflict of Interest: The work was supported by Varian Medical Systems

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