3236 - Hyaluronic Acid Rectal Spacer in Locally Recurrent Prostate Cancer with Prior Radiation Receiving SBRT: A Report on Feasibility, Safety and Toxicity

L. N. McLean¹, N. Nair², S. J. Poiset³, J. W. DiNome⁴, A. C. Mueller⁵, and M. J. Greenberg⁶; ¹Department of Radiation Oncology, Sidney Kimmel Medical College of Thomas Jefferson University, Philadelphia, PA, ²Department of Radiation Oncology, Sidney Kimmel Medical College & Cancer Center of Thomas Jefferson University, Philadelphia, PA, ³Department of Radiation Oncology, Sidney Kimmel Cancer Center of Thomas Jefferson University, Philadelphia, PA, ⁴Department of Radiation Oncology, Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, PA, ⁵Department of Radiation Oncology, Sidney Kimmel Medical College & Cancer Center at Thomas Jefferson University, Philadelpha, PA, ⁶Department of Radiation Oncology, Sidney Kimmel Medical College & Cancer Center at Thomas Jefferson University, Philadelphia, PA

Purpose/Objective(s): Hyaluronic acid (HA) injected between the prostate and rectum is commonly used in patients undergoing definitive external beam radiotherapy EBRT for prostate cancer given its ease of custom administration, favorable dosimetric advantages, and lower rates of gastrointestinal (GI) toxicity. Here we report novel use of HA in patients undergoing repeat local therapy with stereotactic body radiotherapy (SBRT). Materials/

Methods: 22 patients at a single institution were identified with recurrent prostate cancer localized to the prostate, seminal vesicles, and/or prostate fossa with prior local therapy including EBRT, brachytherapy, or cryoablation +/- prostatectomy. Patients underwent HA injection into the perirectal space +/- fiducial marker insertion prior to SBRT for 35 Gy in 5 fractions. 17 patients were treated with daily MR-guidance SBRT. HA safety, separation, ease of placement, and treatment toxicity were assessed.
Results: Prior radiation was completed over 5 years ago in 80% of patients. 8 patients underwent prior EBRT alone, 6 prostatectomies with postoperative EBRT, 5 brachytherapy, 1 EBRT with salvage cryotherapy, and 1 cryotherapy alone. To place the HA, all patients received local anesthetic with no procedure taking greater than 30 minutes. HA was able to be placed with 100% success rate and no adverse events. No saline dissection was used. The mean minimum GTV-rectum separation was 8.7 (± 5.6) mm. The mean GTV was 6.5 cm³ (± 6). The implant was rated as adequately separating the recurrence in 86.4% of cases. All patients subsequently completed their re-irradiation with 35Gy in 5 fractions. There was one case of grade 1 GI toxicity related to pretreatment bowel preparation managed with probiotics. There were no cases of acute grade 3+ urinary toxicity, and 1 case of late grade 3 hemorrhagic cystitis which the patient had experienced during initial definitive EBRT. The mean Dmax, D30%[Gy], and D60%[Gy] were 22.7 Gy (± 6.8), 6.8 Gy (±3.0), and 3.0 Gy (± 2.2), respectively.
Conclusion: Injection of HA in patients undergoing retreatment with SBRT for locally recurrent prostate cancer is safe and feasible and should be considered in select patients.