Abstract # 2236 A Phase II Trial of Trilogy-based Prostate SBRT: Initial Report of Favorable Acute Toxicity Outcomes

Presenter: Fernandez, Eduardo

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A total of 33 patients have been treated to date with SBRT. Protocol inclusion criteria required all of the following parameters: clinical stage T1c - T2b, PSA < 20 ng/ml, Gleason Score (GS) 7 or less, prostate volume < 60 cc, and IPSS voiding score < 18. The protocol consisted of two arms, Arm 1 for low risk patients (clinical stage T1c-T2a, PSA < 10 ng/ml, GS 6 or less), and Arm 2 for intermediate risk patients (stage T2b, or PSA > 10, or GS 7). Patients on Arm 1 were treated with SBRT alone; a total dose of 36.25 Gy was prescribed to the prostate in 5 fractions of 7.25 Gy each on an every other day schedule. Arm 2 patients received 25 fractions of Intensity Modulated Radiation Therapy (IMRT) to a dose of 45.0 Gy followed by a SBRT boost of 4 fractions of 5.5 Gy per fraction delivered on consecutive days after IMRT for a total dose of 22.0 Gy. The SBRT PTV was created by a 3-mm non-uniform expansion of the prostate volume, with the dose prescribed to the isodose line encompassing > 95% of the PTV. Organ at risk dose volume constraints were such that no rectal dose point received > 90% of the prescription dose, no urethral dose point received > 125% of the prescription dose, no bladder dose point received > 100% of the prescription dose and no femoral head dose point received > 50% of the prescription dose. The NCI CTCAE v3.0 was used to assess urinary and rectal toxicity during treatment and then at 1, 3, 6, 9, and 12 months after treatment. Acute toxicity was defined as occurring during treatment or within 30 days of treatment completion. Studied urinary toxicities included dysuria/spasms, retention, hematuria/cystitis, frequency/urgency, and incontinence. Studied rectal toxicities included diarrhea, proctitis, and hematochezia.