Dose discrepancy between planning system estimation and measurement in spine stereotactic body radiation therapy: A case report

Abstract

Stereotactic body radiation therapy (SBRT) to treat spinal metastases has shown excellent clinical outcomes for local control. High dose gradients wrapping around spinal cord make this treatment technically challenging. In this work, we present a spine SBRT case where a dosimetric error was identified during pre-treatment dosimetric quality assurance (QA). A patient with metastasis in T7 vertebral body consented to undergo SBRT. A dual arc volumetric modulated arc therapy plan was generated on the Pinnacle treatment planning system (TPS) with a 6 MV Elekta machine using gantry control point spacing of 4°. Standard pre-treatment QA measurements were performed, including ArcCHECK, ion chamber in CTV and spinal cord (SC) region and film measurements in multiple planes. While the dose measured at CTV region showed good agreement with TPS, the dose measured to the SC was significantly higher than reported by TPS in the original and repeat plans. Acceptable agreement was only achieved when the gantry control point spacing was reduced to 3°. A potentially harmful dose error was identified by pre-treatment QA. TPS parameter settings used safely in conventional treatments should be re-assessed for complex treatments.

Improving accuracy for stereotactic body radiotherapy treatments of spinal metastases

“…6(d)] in agreement with the literature 10. It was shown previously that 90 control point plans were the most complex, and while this had no impact on the plan coverage/conformity, it did have an impact on accuracy/deliverability.…”

“…A recent study found accuracy improvements for an individual SBRT spine case when the gantry spacing between control points was decreased from 4° to 3° 10. The delivery accuracy of different IMRT and VMAT techniques has also been investigated for spinal treatment 11.…”