A phase I radiation dose escalation of stereotactic body radiotherapy for malignant lung tumors

Abstract

Objectives: This Phase I study determines the maximum tolerated dose (MTD) of stereotactic body radiotherapy (SBRT) for lung tumors. Methods: Eli- gible patients had biopsy proven cancer with a maxi- mum tumor size ≤ 5 cm. Total doses were escalated from 40 to 48, then to 56 Gy, delivered in 4 equal fractions administered 2 to 3 times per week on an IRB approved protocol. SBRT was administered us- ing 5 to 9 fixed beam arrangements with CT loca- lization. Internal target volumes (ITV) were based on breath hold scans or 4D CT simulation. The planning target volume (PTV) was defined as the ITV with a uniform 5 mm expansion. Dose limiting toxicity (DLT) was defined as any grade 3 or higher toxicity using the Radiation Therapy Oncology Group (RTOG) common toxicity criteria (CTC). Results: Between April 2004 and February 2008, 18 patients received the prescribed treatment (40 Gy n = 6, 48 Gy n = 7, 56 Gy n = 5). Seventeen of 18 patients had non-small cell lung cancer (1 with rectal cancer), four of whom were treated for an oligometastasis. The median age of the patients was 68, while the median Karnofsky performance status was 90. The mean tumor size was 2.6 cm (range 0.9 to 4.5 cm). One grade 3 pulmonary event occurred (at 48 Gy dose level) immediately following treatment with the onset of fever and shortness of breath that responded to antibiotics. No other DLTs occurred. Conclusions: SBRT utilizing patient specific target volumes without gating appears safe. The maximum tolerated dose was not reached.