Intrafractional motion in stereotactic body radiotherapy of spinal metastases utilizing cone beam computed tomography image guidance

Jørund Graadal Svestad; Christina Ramberg; Birgitte Skar; Taran Paulsen Hellebust

doi:10.1016/j.phro.2019.10.001

Intrafractional motion in stereotactic body radiotherapy of spinal metastases utilizing cone beam computed tomography image guidance

Phys Imaging Radiat Oncol. 2019 Nov 2:12:1-6. doi: 10.1016/j.phro.2019.10.001. eCollection 2019 Oct.

Authors

Jørund Graadal Svestad¹, Christina Ramberg¹, Birgitte Skar², Taran Paulsen Hellebust^{1

3}

Affiliations

¹ Department of Medical Physics, Oslo University Hospital, Oslo, Norway.
² Department of Oncology, Oslo University Hospital, Oslo, Norway.
³ Department of Physics, University of Oslo, Oslo, Norway.

Abstract

Background and purpose: Spine stereotactic body radiotherapy (SBRT) requires a high degree of accuracy due to steep dose gradients close to the spinal cord. This study aimed to (1) evaluate intrafractional motion in spine SBRT utilizing flattening filter free (FFF) beam delivery and cone beam computed tomography (CBCT) image guidance and (2) evaluate if adding another CBCT acquisition and corrections prior to treatment improves the overall position accuracy.

Materials and methods: Intrafractional motion was retrospectively analyzed for 78 fractions in 54 patients. All patients were immobilized with an evacuated cushion. Before treatment, a CBCT was acquired, a bony fusion with the planning CT was performed and translational and rotational errors were corrected. For 30 of the patients (39 fractions) acquisition of another CBCT and corrections were performed before treatment. A post treatment CBCT was acquired for all patients, and translational and rotational errors measured by fusion of the post treatment CBCT with the planning CT were recorded to calculate means and standard deviations (SDs).

Results: The positional errors were significantly smaller in 4 out of 6 error values in the patient group treated with verification CBCT. In this group, translational and rotational SDs ranged from 0.5 to 0.6 mm and 0.3°, respectively. Corresponding values in the group treated without verification CBCT were 0.7-1.0 mm and 0.4-0.7°.

Conclusion: With proper CBCT image guidance, patient immobilization and FFF-beam delivery, one can obtain very high patient position accuracy in spine SBRT. Inclusion of a verification CBCT prior to treatment increases the overall position accuracy.

Keywords: Cone beam computed tomography; Flattening filter free; Image guided radiotherapy; Intrafractional motion; Spine; Stereotactic body radiotherapy.