Non-interventional Observational Study of Stereotactic Body Radiotherapy (SBRT) for Oligometastatic Cancer

The investigators recently published 2 phase II trials on the use of helical tomotherapy for oligometastatic colorectal cancer [1,2]. Despite a dose increase from 40 to 50 Gy, delivered in 2 weeks time, the one-year local control was 54% only [1,2]. The high local failure rate is probably the result of geographical misses due to tumor motion and a biologically effective dose (BED) of < 100 Gy. The current study will investigate whether the one-year local control rate can be improved to 70%, using respiration correlated CT to individualize the margin needed to account for tumor motion, to avoid geographical miss, together with a Monte Carlo or collapsed cone dose calculation algorithm delivering 50 Gy to the 80% isodose, allowing higher doses in the tumor core. As the concept of an internal target volume (ITV) may result in large margins for patients displaying metastases in high mobile organs, such as liver and lung, which may lead to exposure of a relatively high dose to a large volume of normal tissue, dynamic tumor tracking by the VERO SBRT system will be applied in those patients.