Hypofractionated stereotactic body radiation therapy (SBRT) for limited hepatic metastases
The records of 69 patients with 174 metastatic liver lesions treated with SBRT between April 2001 and October 2004 were reviewed. The most common primary tumors were colorectal (n = 20), breast (n = 16), pancreas (n = 9), and lung (n = 5). The mean number of lesions treated per patient was 2.5 (range, 1–6). The longest diameter of the lesions ranged in size from 0.6 to 12.2 cm (median, 2.7 cm). Dose per fraction ranged from 2 Gy to 6 Gy, with a median total dose of 48 Gy (range, 30–55 Gy). Dose was prescribed to the 100% isodose line (IDL), with the 80% IDL covering the gross tumor volume with a minimum margin of 7 mm.
Treatment planning was performed using the BrainScan treatment planning system. The gross target volume was contoured on a biphasic contrast treatment planning computerized tomography (CT) scan. Additional imaging studies, such as magnetic resonance imaging and positron emission tomography, were frequently fused with the planning CT scan for more accurate delineation of the gross target volume. No margin was added for the clinical target volume, but a minimum of 10 mm was added to the craniocaudal margin and 7 mm was added to the other margins for the planning target volume. We have previously shown that this allows for 2 standard deviations of motion to be covered.
Treatment was prescribed to the 100% isodose line, with the 80% isodose line covering the planning target volume. The radiation was delivered using conformal arcs or multiple fixed coplanar beams. The dose per fraction and total dose were determined using the dose volume histogram of organs at risk, with a preferred schedule of 50 Gy in 5 Gy fractions over 2 weeks.
liver was defined as the volume of liver not involved by gross
tumor (total liver volume) and was
mandated at >1,000 cm3.
The normal tissue constraints for the liver were based on the
level of preexisting but nonmalignant hepatic disease. For
patients with no preexisting macronodular sclerosis or history
of liver failure or hepatitis, the dose to
60% of the liver volume
was not to exceed 30 Gy, and, for those patients with a history
of hepatitis or cirrhosis, the dose to 70% of the volume was not
to exceed 27 Gy.
The median follow up was 14.5 months. Sixty patients were evaluable for response based on an abdominal computed tomography scan obtained at a minimum of 3 months after completion of SBRT. The actuarial overall infield local control rate of the irradiated lesions was 76% and 57% at 10 and 20 months, respectively. The median overall survival time was 14.5 months. The progression-free survival rate was 46% and 24% at 6 and 12 months, respectively. None of the patients developed Grade 3 or higher toxicity.
Hypofractionated SBRT provides excellent local control with minimal side effects in selected patients with limited hepatic metastases.