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  4. Investigating a Dynamic Dose Rate Approach for Rotating Gamma Ray Systems

Investigating a Dynamic Dose Rate Approach for Rotating Gamma Ray Systems

A Eldib1*, B Nguyen2 , J Li3 , G Mora4 , O Chibani1 , M Abdelgawad5 , L Chen1 , C Ma1 , (1) Fox Chase Cancer Center, Philadelphia, PA, USA (2) Prowess Inc., Concord, CA, USA (3)OUR United Corporation, Xian, China, (4) Universidade de Lisboa, Codex, Lisboa, Portugal, (5) Biophysics branch, Physics Department, faculty of science, Al-Azhar University, Cairo, Egypt

Presentations

(Wednesday, 7/17/2019) 10:00 AM - 10:30 AM

Room: Exhibit Hall | Forum 7

Purpose: A novel rotating gamma ray system has been developed for intra- and extra-cranial stereotactic radiotherapy. In this study, we are proposing a simple method for dynamic dose rate delivery that can overcome machine design limitations. In this work, we evaluate the added dosimetric benefits of the new method to the treatment planning process.

Methods: The new SRS/SRT system (CybeRay, OUR United RT Group, Xian, China) consists of a ring gantry and a focusing treatment head with 13 cobalt-60 sources. Each radiation shot delivers a specific dose based on the optimization results (RTpro-Prowess, Concord, CA), which are controlled by the gantry rotations/speed. The lowest attainable gantry speed is 6min/rotation while the highest speed is 1min/rotation. These limitations impose restrictions to the planning process. One method to improve plan optimization is to remove these limitations. We implemented an approach for dynamic dose rate delivery that does not violate the gantry speed limits. For a shot of large dose, we allowed the gantry to rotate with the lowest speed through multiple arcs. To deliver a shot with a lower dose, shots were split into sectors with radiation beams turned off at equal intervals with gantry rotating with maximum speed.

Results: Treatment plans generated for different body sites of 10 patients were evaluated based on isodose distributions and dose volume histograms. It was shown that removing the speed limits resulted in better plans. The use of our dynamic dose rate delivery method improved the plan deliverability allowing dose prescription at desired isodose values. The number of shots used ranged from 4 to 30 shots dictated by the size and shape of the target. The mean value for PTV coverage was 96.9%.

Conclusion: The proposed approach improved the planning system searching abilities for optimal plans and extended the CybeRay capabilities.

Keywords

Treatment Planning, Rotational Therapy, Stereotactic Radiosurgery

Taxonomy

TH- External beam- photons: dose computation engines- deterministic

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