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A New Clinical Workflow for Dose Accumulation of Spine SBRT in RayStation

M.J. Vaccarelli1, S.P. Krafft1, T.M.Briere1, S. Svensson2, E.Y. Han1 (1) MD Anderson Cancer Center, Houston, TX, (2) RaySearch Laboratories AB, Stockholm, SE

Presentations

(Saturday, 3/26/2022)   [Central Time (GMT-5)]

Purpose: To illustrate a new dose accumulation workflow in RayStation 10B for fractionated spine stereotactic radiosurgery (SSRS).

Methods: Two clinical SSRS plans were retrospectively selected and examined with the suggested dose accumulation workflow as follows. The sequence consisted of importing pre-treatment CBCT’s into RayStation, maintaining the treatment position alignment (TPA) determined at delivery. A corrected CBCT was generated to achieve improved image quality. A hybrid deformable image registration (DIR) was created between the corrected CBCT and planning CT for dose accumulation. The GTV, CTV and spinal cord were rigidly copied over to the corrected CBCT, while other soft tissues such as the esophagus and pharynx were mapped from the DIR. The RayStation 10B dose tracking module was then utilized to calculate fractional doses from the TPA, which was deformed to the planning CT for accumulated delivered dose.

Results: Close agreement between the accumulated delivered dose and the planned reference dose was found for D95%, average dose and D1cc for GTV and CTV with less than a 1.9% difference on average. Accumulated delivered dose for the spinal cord in case A and B, respectively, was greater than the reference plan by an absolute difference of 100 cGy (6.9%) and 90 cGy (8.4%) for D1cc and 202 cGy (13.5%) and 214 cGy (18.2%) for Dmax. The pharynx had absolute differences of 171 cGy (11.8%) in D1cc and 347 cGy (23.9%) in Dmax. The esophagus had an absolute deviation of 2 cGy (.1%) and 1 cGy (.5%), respectively.

Conclusion: Delivered dose accumulation is feasible in the SSRS setting. Close agreement between the accumulated delivered dose and the planned reference dose for targets confirms robust program protocols in patient immobilization and imaging standards at our institution.

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