(Saturday, 4/7/2018)
Room: Foyer
Purpose: TG – 119 provides a set of IMRT commissioning tests to assist with inter-clinic quality standards in Intensity Modulated Radiation Therapy. Outcomes from TG –119 were based on Step and Shoot IMRT plans using only 6 MV beams. Modern IMRT has evolved toward Volumetric Modulated Arc Therapy and can incorporate a wide range of energies. The purpose of this work is to compare plans between multiple linacs to the established data using multiple energies with both IMRT and VMAT.
Methods: The plans were created on the Pinnacle3 treatment planning system using Varian Novalis Tx and Elekta VersaHD linear accelerator models. All plans meet the dose constraints as designated within TG – 119. Treatments were recalculated to be delivered to the PTW Octavius4D phantom for measurement. The Gamma passing rate was determined using PTW Verisoft.
Results: MultiTarget gamma index pass rates within 3%/3mm were 95.7% for 6 MV IMRT and 97.4% for 6 MV VMAT. The prostate plans passed with 95.6% for 6 MV IMRT, 98.3% for 6 MV VMAT, 95.0% for 10 MV IMRT, and 98.4% for 10 MV VMAT. VMAT plans within Pinnacle3 allowed for more homogeneous distribution within the target (smaller cold and hot spots) and reduced overall dose to organs at risk.
Conclusion: VMAT plans produced similar desired treatment results to IMRT plans with gamma passing at a slightly higher rate. 6 and 10 MV were able to create similar plans for the phantom tested and show no significant difference in gamma passing rate. It is important to verify that VMAT accuracy is as acceptable as that of previous IMRT plans. This work allows for the development of more accurate IMRT delivery and verification of current quality assurance standards within the clinic.
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