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Efficiency and Efficacy of Intensity Modulated Treatments On a Prototype Linear Accelerator

T Netherton

T Netherton*, Y Li , P Nitsch , P Balter , S Gao , M Muruganandham , S Shaitelman , R McCarroll , S Frank , S Hahn , A Klopp , L Court , The University of Texas MD Anderson Cancer Center, Houston, TX


MO-F-FS1-3 (Monday, July 31, 2017) 4:30 PM - 6:00 PM Room: Four Seasons 1

Purpose: We investigated the performance and quality of treatments delivered on a prototype linac with a 6MV flattening-filter-free beam. The prototype linac has a gantry speed of 6 rpm and MLCs with 1cm wide leaves and a maximum speed of 5.0cm/s.

Methods: Dynamic IMRT and VMAT plans were created and delivered for head and neck, prostate, whole brain, breast, pelvis, and lung. Treatments that are typically planned using 3DCRT were planned with 2-4 field IMRT. Plans were compared with clinically treated plans and verified with patient-specific QA (95% pixels passing 3%/3mm) using portal dosimetry and a diode array. Treatment time, modulation (MU/cGY), and imaging time (CBCT and orthogonal) were recorded.

Results: Resulting treatment plans met clinical target coverage and normal tissue constraints for all sites. The treatment plans were generally not as homogeneous as the clinically treated plans; VMAT plans required more arcs (average=4 arcs) and modulation than VMAT on conventional linacs. All patient-specific QA passed the given criteria. Average beam delivery times per patient were 1.3 minutes (2-4 field novel IMRT) vs. 1.4 minutes (conventional linac 3DCRT), 2.6 minutes (≥5 field novel IMRT) vs. 2.9-3.5 minutes (conventional dynamic and step-and-shoot IMRT), and 1.9 minutes (4-arc novel VMAT) vs. 2.5 minutes (conventional linac VMAT). The average beam modulation for the prototype linac was 2.9 MU/cGy (2-4 field IMRT), 6.2 MU/cGy (≥5 field IMRT) and 3.6 MU/cGy (4-arcVMAT). IGRT times including reconstruction for partial-CBCT and MV-MV orthogonal were 22s and 13s (prototype linac) vs. 33s and 62s (conventional linac), respectively.

Conclusion: Performance and treatment plan quality for the prototype linac are comparable with those for a conventional linac. Additionally, our results suggest that even though this linac requires more modulation than a conventional linac, a modest increase in throughput for radiotherapy is seen given the decrease in imaging and mechanical time.

Funding Support, Disclosures, and Conflict of Interest: Funded by Varian Medical Systems

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