Stereotactic radiotherapy for pulmonary oligometastases: a systematic review

Hypofractionated stereotactic body radiotherapy (SBRT) is an emerging noninvasive technique for the treatment of oligometastatic cancer. The use of small numbers of large doses, should in theory, achieve high rates of local control. The aim of this literature review is to critically assess the use of SBRT for the treatment of pulmonary metastases as judged by its effect on local control, survival, and toxicity.

A systematic literature search was performed. Both single fraction stereotactic radiosurgery (SRS) and hypofractionated radiotherapy (SBRT) were considered individually. Thirteen institutions reported results regarding SBRT and seven institutions regarding SRS (a total of 29 publications). Outcomes, techniques, radiobiology, and the scientific rigor of the reported studies were analyzed.

A wide range of techniques, doses, and dose fractionation schedules were found. Three hundred thirty-four patients with 564 targets were reported in the SBRT series. The 2-year weighted local control was 77.9%. The corresponding 2-year weighted overall survival was 53.7%, with a 4% rate of grade 3 or higher radiation toxicities. One hundred fifty-four patients with 174 targets were treated in the SRS series. The 2-year weighted local control was 78.6%. The corresponding weighted 2-year overall survival was 50.3%, with 2.6% rate of grade 3 or higher toxicities.

There was insufficient evidence to recommend a consensus view for optimal tumor parameters, dose fractionation, and technical delivery of treatment. This indicates the need for further prospective studies. However, high local control rates that could potentially lead to a survival benefit justifies the consideration of stereotactic radiotherapy for patients with limited pulmonary oligometastases.