Evaluation of multi-institutional end-to-end testing for post-operative spine stereotactic body radiation therapy

Post-operative spine stereotactic body radiation therapy (SBRT) represents a significant challenge as there are many restrictions on beam geometry to avoid metal hardware as it surrounds the target volume. In this study, an international multi-institutional end-to-end test using an in-house spine phantom was developed and executed. The aim was to evaluate the impact of titanium spine hardware on planned and delivered dose for post-operative spine SBRT.

Five centers performed simulation, planning and irradiation of the spine phantom, with/without titanium metal hardware (MB/B), following our pre-specified protocol. The doses were calculated using the centers' treatment planning system (TPS) and measured with radiophotoluminescent glass dosimeters (RPLDs) embedded within each phantom.

The dose differences between the RPLD measured and calculated doses in the target region were within ± 5% for both phantoms studied. Differences greater than 5% were observed for the spinal cord and the out-of-the target regions due to steeper dose gradient regions that are created in these plans. Dose measurements within ± 3% were observed between RPLDs that were embedded in MB and B inserts. For the spinal cord and the out-of-target regions surrounded by metal hardware, the dose measured using RPLDs was within 3% different near the titanium screws compared to the dose measured near only the metal rods.

We have successfully performed the first multi-institutional end-to-end dose analysis using an in-house phantom built specifically for post-operative spine SBRT. The differences observed between the measured and planned doses in the presence of metal hardware were clinically insignificant.