Exhibit Hall | Forum 4
Purpose: Use of SpaceOAR™ hydrogel is one of the requirements for patients undergoing prostate stereotactic body radiotherapy in our department. The SpaceOAR™ hydrogel, made of 90% water and polyethylene glycol is inserted between the prostate and rectum and pushes the rectum away thus decreasing rectal toxicity. In this study, we quantified the dosimetric benefits of the utility of the hydrogel spaceOAR™
Methods: In the case study for a clinically approved plan, we compared 5 rectal dosimetric indices namely rectal D1cc, D3cc, D90%, D80% and D50%, as used in RTOG 0938 for 3 scenarios, (1) Plan-SpaceOAR, the original plan using spaceOAR, (2)Plan-NoSpaceOAR, delivering the original plan as is and then estimating the rectal dose as if no spaceOAR™ was used (3)Plan-NoSpaceOAR-ReOptimized, the scenario with no spaceOAR™ but the plan re-optimized to meet original constraints. The same primary image was used in all 3 scenarios therefore we re-contoured the rectum in case (2) and (3) including portions of the spaceOAR™.
Results: The RTOG requirement for the rectal D1cc, D3cc, D90%, D80% and D50% are respectively ≤38.06Gy, ≤ 34.4Gy, ≤32.625Gy, ≤29Gy, and ≤18.125Gy. Plan_SpaceOAR met all requirements with rectal D1cc, D3cc, D90%, D80% and D50% as respectively 27.85 Gy, 25.25Gy, 1.8Gy, 3.5Gy, and 15.23Gy. The doses were higher in the Plan-NoSpaceOAR with the rectal D1cc, D3cc, D90%, D80% and D50% as respectively 37.11Gy, 36.12Gy, 2.28Gy, 6.23Gy, and 19.37Gy. It improved in the optimized plan, Plan-NoSpaceOAR-ReOptimized but still higher doses compared with the original plan. The rectal D1cc, D3cc, D90%, D80% and D50% were respectively 35.97Gy, 34.40Gy, 1.91Gy, 4.88Gy, and 15.11Gy.
Conclusion: We have presented a case study quantifying the dosimetric benefit of the utility of hydrogel spaceOAR™ for prostate stereotatactic body radiotherapy. More studies are needed to make a definitive conclusion as to its benefits when utilized with SBRT.
Prostate Therapy, Stereotactic Radiosurgery, Treatment Planning
TH- External Beam- Photons: treatment planning/virtual clinical studies