Genitourinary Cancer

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SU_34_2318 - Biochemical and Toxicity Outcomes Following Dose Escalated Stereotactic Body Radiation Therapy to 42.5 Gy for Prostate Cancer

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

Biochemical and Toxicity Outcomes Following Dose Escalated Stereotactic Body Radiation Therapy to 42.5 Gy for Prostate Cancer
Z. Rana1, L. Potters2, L. Lee3, and B. W. Cox2; 1Northwell Health, Lake Success, NY, 2Zucker School of Medicine at Hofstra/Northwell, Hempstead, NY, 3Department of Radiation Medicine, Zucker School of Medicine at Hofstra/Northwell, Northwell Health, Lake Success, NY

Purpose/Objective(s): Prostate cancer (CaP) has a unique radiobiology, characterized by a low a/b ratio relative to surrounding normal tissue. Consequently, a therapeutic gain could be achieved using fewer, high-dose fractions, but the optimal dose utilizing stereotactic body radiation therapy (SBRT) has yet to be identified. The purpose of this study was to report our institutional experience utilizing dose escalated SBRT to 42.5 Gy.

Materials/Methods: From June 2013 to November 2017, 98 patients (pts.) with CaP received 42.5 Gy in five fractions to the prostate and seminal vesicles without androgen deprivation therapy. Patient reported QOL was prospectively obtained from the Expanded Prostate Cancer Index Composite (EPIC) and International Prostate Symptom Score (IPSS) at baseline and intervals of every 3 months for the first two years followed by every 6 months thereafter. Common Toxicity Criteria for Adverse Events v. 4.03 data was used to grade acute and late toxicities. A PSA was obtained at each follow up.

Results: Median follow-up was 24 months (range, 3-52 months). Median PSA nadir was 0.53 ng/ml. Thirteen pts. (12%) experienced at least one PSA bounce ≥ 0.2 ng/ml. Median PSA bounce height was 0.68 ng/ml (range, 0.22-4.12 ng/ml) with a median onset and duration of 15 months and 3 months. After accounting for PSA bounce, no pts. experienced biochemical failure and prostate cancer specific survival was 100%. Actuarial overall survival was 95% as 5 patients died of causes unrelated to their CaP. There was an acute increase in EPIC and IPSS scores at 3 months followed by a return to baseline by one year. CTCAE acute grade 1 and 2 urinary toxicity occurred in 22 (22%) and 11 (11%) pts. Three pts. (3%) experienced late grade 2 urinary toxicity. One pts. (1%) experienced late grade 3 urinary obstruction requiring transurethral prostatic resection. Acute grade 1 and 2 rectal toxicity occurred in 12 (12%) and 6 (6%) pts. Late grade 1 and 2 rectal toxicity occurred in 5 (4%) and 2 (2%) patients. Grade 3 late rectal toxicity was observed in 4 (4%) patients, as three patients developed rectourethral fistula requiring diverting colostomy and one patient experienced rectal bleeding requiring transfusion and argon plasma laser ablation. All late rectal toxicities were experienced by patients with significant vasculopathies and two patients had iatrogenic manipulation of the rectum prior to development of the high-grade rectal toxicity. Of the 81 pts. who were sexually potent at baseline, 15 (19%) and 9 (11%) experienced grade 1 and 2 erectile dysfunction.

Conclusion: In a select population with localized CaP, dose escalated SBRT to 42.5 Gy was safe and effective. These findings, along with emerging data demonstrating late biochemical failures with 36.25 Gy, suggest that dose escalation may be necessary for optimal outcomes. Late rectal toxicity appears to be increased with vasculopathies and iatrogenic manipulation of the rectum after treatment. Further follow-up is needed to assess PSA freedom from recurrence and late toxicity.

Author Disclosure: Z. Rana: None. L. Potters: None. L. Lee: None. B.W. Cox: Employee; NYU.

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