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Comparison of Sparing Rectal Tissue in Stereotactic Ablative Radiation Therapy (SABR) in Prostate Cancer for Injectable Spacer Gel and Rectal Balloon

N Hassan Rezaeian

N Hassan Rezaeian*, R Jones , N Desai , R Hannan , X Jia , M Folkert , The University of Texas Southwestern Medical Center, Dallas, TX


SU-I-GPD-T-373 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Quantitative evaluation of dosimetric capabilities and limitations of an absorbable, injectable spacer gel versus an endorectal balloon immobilizer in stereotactic ablative radiation therapy (SABR) for prostate cancer.

Methods: Patient cohorts for this study are selected from ongoing prospective trails at our institution for prostate cancer under SABR protocols using endorectal balloon immobilizer and injectable spacer gel to achieve lower dose to rectum. Volumetric data for the prostate, bladder, and rectum were obtained for both cohorts from plans, as were the dosimetric parameters.

Results: The fairness of our study is verified by the statistical analysis of the volumetric parameters (prostate volumes, planning target volumes, and others), BMI, and maximum doses to the bladder and the prostate for two patient cohorts were not significantly different. Statistical comparison of dose to 33% of the rectal circumference, absolute volume of rectum receiving 30Gy and 40Gy, and maximum dose to the rectum shows a significant advantage of using injectable spacer gel. Our statistical analysis does not show any significance improvement of the cohorts using injectable spacer gel for both doses to 50% of the rectal circumference and volume of the rectum receiving 40Gy.

Conclusion: The analysis of the patients enrolled on two consecutive prospective trials of SABR for prostate cancer at our institution suggests the patients were participated in the injectable spacer gel trial outperformed the endorectal balloon immobilizer patients in the majority of the examined rectal sparing parameters. The rectal balloon immobilizer technique does not indicate any advantage in rectal sparing in any measures. The direct comparison in this study recommends the implementation of the injectable spacer gel between the rectum and prostate for in prostate cancer patients under SABR procedure.

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