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A Prospective 4π Radiotherapy Clinical Trial in Recurrent Glioblastoma Multiforme (GBM) Patients

V Yu

V Yu*, A Landers , K Woods , D Nguyen , M Cao , R Chin , T Kaprealian , K Sheng , UCLA School of Medicine, Los Angeles, CA


SU-K-FS1-3 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: Four Seasons 1

Purpose: To evaluate the feasibility, safety, delivery efficiency, dosimetric benefits, and patient comfort in the clinical implementation of 4π radiotherapy.

Methods: Eleven patients with recurrent GBM were recruited for the trial. 4π plans integrating beam orientation and fluence-map optimization were created with an in-house column generation algorithm. The collision-free beam solution space throughout the 4π steradian was determined using a computer-aided-design surface model of the Varian TrueBeam system and a human subject. Twenty beams were optimized for each case and imported into Eclipse for intensity modulated radiation therapy (IMRT) planning. Beam orientations with neighboring couch kicks were merged for increased delivery efficiency, generating plans with an average of 16 beam orientations. Volumetric modulated arc therapy (VMAT) plans with 3-4 arcs were also generated for each case, and the plan achieving superior tradeoff between dosimetric quality and delivery efficiency was selected for treatment. Patient comfort was evaluated through survey collection after every fraction. Multiple 2D X-ray images were obtained to measure intrafractional motion.

Results: 9 out of 11 patients were treated with 4π. Mean and maximum OAR doses were equal or significantly lower (p<0.05) compared with VMAT. Particularly substantial average brainstem mean dose reductions of 32.9% enabled treatments that would otherwise not satisfy safe dose constraints with VMAT. One patient was not treated because neither plan met the dosimetric criteria,and the other was treated with VMAT due to undemanding dosimetry that resulted in a comparable VMAT plan with higher delivery efficiency. Treatments were well-tolerated, with an average patient comfort score of 8.6/10. Intrafractional motion was <1.5mm for all delivered fractions and the average delivery time was 35 minutes.

Conclusion: The feasibility, safety, and dosimetric benefits of 4π radiotherapy have been clinically demonstrated with a prospective clinical trial. These results pave the way for 4π implementation in many more clinically challenging cases.  

Funding Support, Disclosures, and Conflict of Interest: DOE DE-SC0017057, NIH R44CA183390, NIH R01CA188300, NIH R43CA183390, NIH U19AI067769

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