Interim analysis of a prospective phase I/II trial of SBRT for liver metastases

Abstract

Stereotactic Body Radiation Therapy (SBRT) is a potent means of systemic cytoreductive therapy for selected patients with metastatic cancer. We here report an interim analysis of a prospective Phase I/II study of SBRT for liver metastases. Eligible patients with liver metastases met these criteria: (1) maximum tumor diameter < 6 cm; (2) ≤3 discrete lesions; (3) treatment planning confirmed ≥ 700 cm3 of normal liver receives ≤15Gy. The gross tumor volume (GTV) was expanded 5–10 mm to yield the planning target volume, which received 60 Gy in 3 fractions of SBRT over 3–14 days in the Phase II component of the trial. As of July, 2006, 36 patients have been enrolled: 18 in Phase I, 18 in Phase II. The median age was 58 years (range 27–91); the M:F ratio was 20:16. The most common primary sites were lung (n = 10), colorectal (n = 9), and breast (n = 4). Among 21 pts with ≥ 6 months post-SBRT follow-up (median 19 months, range 6–29), one instance of SBRT-related grade 3 toxicity occurred in subcutaneous tissue superficial to the liver. No grade IV toxicity occurred. For 28 discrete lesions treated (median GTV 14 cm3, range 1–98) the 18 month actuarial local control estimate is 93%. This interim analysis indicates that a very high rate of durable in-field tumor control can be safely achieved with SBRT to 1–3 liver lesions as administered in this protocol, to a prescription dose of 60 Gy in 3 fractions.