Fiducial-free real-time image-guided robotic radiosurgery for tumors of the sacrum/pelvis

Abstract 

Background and purpose

Radiosurgery is a non-invasive treatment for many spinal tumors. Sacral radiosurgery, however, requires invasive fiducial marker insertion to target and track the tumor’s position. We present preliminary clinical results and phantom accuracy measurements of sacral radiosurgery using fiducial-free alignment based on vertebral anatomy distant to tumor location.

Materials and methods

Fifty-one lesions in 38 patients were treated using fiducial-free spinal tracking of the L5 vertebra. An anthropomorphic phantom was used for accuracy measurements of this approach. Dose planning was based on 1.0mm computer tomography slices using inverse treatment planning.

Results

Tracked targets were up to 17cm from the treated tumor. Phantom tests produced an overall mean targeting error of 1.43mm (±0.47mm). Patient median follow-up was 12.7months. Local tumor control was 95%. Treatment doses were 12–25Gy with a median prescription isodose of 65% (40–70%) and tumor volumes between 1.3 and 152.8cc. No short-term adverse events were noted during the follow-up period.

Conclusions

Fiducial-free tracking of the lower lumbar vertebrae is a feasible, accurate, and reliable tool for radiosurgery of sacral and pelvic tumors. It is a valuable novel alternative to surgical procedures and conventional fractionated radiation therapy for these challenging cases.

Keywords: Bony pelvis, Cyberknife, Radiosurgery, Spine, Fiducial-free registration