Volumetric modulated arc therapy versus conventional intensity modulated radiation therapy for stereotactic spine radiotherapy: A planning study and early clinical data

Background and purpose

Outcomes for selected patients with spinal metastases may be improved by dose escalation using stereotactic body radiation therapy (SBRT). As target geometry is complex, we compared SBRT plans using volumetric modulated arc radiotherapy (RapidArc®, RA) and conventional intensity-modulated radiotherapy (IMRT).

Materials and methods

RA and IMRT plans to deliver a fraction of 16 Gy to at least 90% of planning target volume (PTV) were compared for PTV coverage, normal organ sparing and estimated delivery times. Group 1 consisted of PTVs to only vertebral body (n = 3), while group 2 had PTVs encompassing the entire vertebra (n = 4). Finally, RA delivery parameters in four patients were assessed.

Results

Both techniques delivered 16 Gy to a mean of 95% and 85% of the PTV in groups 1 and 2, respectively. Spinal cord sparing was comparable; mean V_{10-partial cord} for RA and IMRT in group 1 was 3.6%, and was 9.4% versus 11.5%, respectively, in group 2. Estimated mean treatment times for RA with 2-3 arcs and IMRT were comparable. Clinical RA beam-on times ranged from 11 to 15.4 min.

Conclusions

Both RA and conventional IMRT plans deliver high quality vertebral SBRT, but plan quality was poorer when the PTV consisted of the entire vertebra.