SU‐E‐P‐37: Helical Tomotherapy to LINAC Plan Conversion Utilizing RayStation Fallback Planning

Abstract

Purpose:RayStation Fallback (RSF) plan was developed to switch patient's treatment from Helical Tomotherapy (HT) to Varian TrueBeam. Helical Tomotherapy plans were compared with the corresponding RSF plans by looking at the following dosimetric parameters: PTV coverage (Dmean and D95), Paddick conformity index (CI), uniformity index (UI=(D98‐D2)/Drx) and organ‐at‐risk (OAR) doses.Methods:Five patients with five tumor sites including larynx, head and neck, esophagus, lung, and prostate previously treated with HT were re‐planned using RSF treatment planning station(TPS) to best match the HT treatment plans. IMRT technique with nine fields 6 MV X‐ray beams and a static multi‐leaf collimator (MLC) were used for RSF plans without any additional attempt to further optimize the RSF plans.Results:A physician evaluated and confirmed the clinical acceptability of the RSF plans. Both HT and RSF plans gave comparable PTV coverage with a maximum percentage difference for D95 of 0.7%. HT plans had a better CIs ranging from 2%–15% higher conformity compared to RSF plans. HT plans also had better UIs for all tumor sites except the esophagus. The UIs were 1.6% to 8.9% lower for HT plans compared to RSF plans. Both HT and RSF plans gave comparable and acceptable OAR doses. However, the integral dose was 1%–15% higher for HT plans compared to RSF plans.Conclusion:RSF plans were simple and fast to generate. In the study cases of 5 various tumor sites, RSF efficiently created clinically acceptable plans without further optimization. However, further optimization for any IMRT plan can be done if clinically warranted. The absolute differences in CI and UI were small between RSF and HT plans.