Program Information
Dosimetric Comparison of a LINAC Fallback Plan Generated From Tomotherapy System
C Yang*, Y Chen , Monmouth Medical Center, Long Branch, NJ
Presentations
SU-E-T-303 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: Quantitatively evaluate the Multi Criteria Optimization (MCO) based MLC step and shoot (sMLC) fallback plan derived from Tomotherapy of multiple lesions lung SBRT
Methods: Inter-comparison of various IMRT planning systems tends to be difficult due to the vendor-specific functionalities. The methodology of defining dose constraints and beam geometries is challenging. Raysearch™ planning system offers an alternative replanning to deliver same intensity map from Tomotherapy without modifying original fluence. This intuitive comparison comes from the final fluence map converted without any embedded system dependent dose optimization. This planner independent approach could be utilized to study the merits of individual machines. The term “fallback” was utilized to (A) transfer plans in among treatment delivery systems; (B) maintain acceptable plan qualities; and (C) minimize the biological dose impact due to machine breakdown. The Tomotherapy specific DICOM RT dose and plan are retrieved into Raystation’s pre-defined sMLC protocol. Based on specific machine characteristics, same fluence maps were converted to generate equivalent deliverable segments (Fig.1). Therefore, the treatment plans were evaluated among two planning tools, Tomotherapy and MCO based sMLC delivery plans.
Results: By converting the fluence map with the pre-defined machine characteristics, the 9-fields fallback plan has similar ITV coverage compared to the original Tomotherapy plan. ITV average doses, the D95 consisted of 0.9% variation. The total lung doses of fallback plan drifted from 17.4% to 30.5% which represents the limitations of the static beam delivery. D2 of fallback spinal cord increased from 22.4% to 36.4% but still within tolerances (Fig.2). Ipsilateral lung changed from 11.0% to 22.6%. Low dose region between ITVs presented increased dose to the normal lung tissues (Fig.3).
Conclusion: Acceptable fallback plan for Tomotherapy SBRT has similar ITVs coverage, but lack of the normal tissues avoidance due to the limitation of geometrical factors to reduce doses in between ITVs.
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