Adaptive Radiation Therapy Planning Using Daily CBCT Image Sets in Head and Neck Cancer Treatment
Presentations
PO-GePV-T-283 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To establish a CT number to electron density table for a LINAC specific CBCT scanning protocol in order to generate adaptive plan based on the daily CBCT images.
Methods: The Gamax phantom was scanned on both CT simulator of Philips Brilliance big bore CT and CBCT of Elekta Versa HD linear accelerator. The scanning protocol on CT is 120 kVp and 80mA and 120 kVp and S20. CT to electron density curves are generated for both CT and CBCT. A treatment plan was generated on RayStation TPS version 10A using the same beam setup on the CBCT image set of a head and neck case based on two different CT to electron density curves.
Results: A VMAT plan was generated with 2 arcs, with a prescription dose of 7000 cGy delivered in 35 fractions. A difference of 8.10 %, 10.06% and 11.37% was observed between CTV, PTV, and spinal canal.
Conclusion: A significant dose difference has been observed in dose calculation using different CT to density tables. Due to scatter contribution, CBCT CT number to density table depends strongly on the scanning protocol and collimator setting. In order to calculate dose accurately on the CBCT image set, one needs to establish CBCT number to density table based on specific scanning protocol instead of using the simulator CT to density table.
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