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Evaluation of SpaceOAR Gel Stability and Its Rectum Dose Sparing Compared to Rectum Balloon During Proton Therapy of Prostate Cancer Patients

H Singh

H Singh1*, J Taylor1 , T Twyford1 , M Chacko1 , Y Zheng2 , (1) Procure Proton Therapy Center, Oklahoma City, OK,(2) Atlantic Health System, Morristown, NJ


WE-RAM1-GePD-T-4 (Wednesday, August 2, 2017) 9:30 AM - 10:00 AM Room: Therapy ePoster Lounge

Purpose: To evaluate the stability of SpaceOAR gel during the treatment course and its rectum dose sparing compared to the use of rectum balloon for prostate cancer patients in proton therapy.

Methods: This study includes eight patients, four each with SpaceOAR gel and rectum balloon. All patients were implanted with three Visicoilâ„¢ fiducial markers, CT simulated in supine position with full bladder and 1.25 mm slice thickness, and treated using uniform scanning proton therapy (USPT). For patients with SpaceOAR gel, MRI was performed for better visibility of the gel. Both prostate and SV were treated with a dose of 79.2 CGE in 44 fractions. A uniform margin of 5mm from CTV was used. For patients with rectum balloon, dose to both prostate and SV was scaled to 79.2 CGE from either 45 or 54 CGE for comparison purpose. 3mm posterior & 5mm elsewhere margins were used. The stability of SpaceOAR was evaluated by comparing the MRI in the last week of treatment with the initial MRI. In addition, weekly quality assurance CT scans were performed for patients with SpaceOAR. Dose volume histograms were compared to evaluate target coverage and normal tissue sparing.

Results: PTV coverage was similar for both SpaceOAR gel and rectum balloon techniques. The most notable difference was observed in rectum dose. The percentage of volume of rectum receiving 81, 75, 65, 50 and 40 CGE were 0.01, 2.67, 6.78, 12.25 and 15.90% for SpaceOAR patients; and 0.58, 10.38, 16.54, 22.89 and 27.06% for rectum balloon. No change in SpaceOAR was observed on the QA MRI compared to the initial scan.

Conclusion: SpaceOAR gel remained stable during the course of the treatment and allowed better dose sparing in rectum compared to the use of rectum balloon for patients receiving USPT.

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