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Using Varian Eclipse as An Independent MU Check for MRI-Guided Radiation Therapy

J Yang*, P Zhang, N Tyagi, P Godoy Scripes, J Mechalakos, A Li, D Lovelock, S Lim, Memorial Sloan-Kettering Cancer Center, New York, NY

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To investigate the feasibility of adopting a commercial treatment planning system(TPS) as an independent MU (IMU) check for both offline reference and online adaptive plans for MRI guided radiotherapy.


Methods: The beam and multi-leaf collimator models of the 7 MV FFF 1.5T Elekta Unity MR Linac in Monte Carlo based Monaco TPS (MTPS) was used as the standard reference to construct a 7 MV FFF beam in Eclipse TPS (ETPS) using the AAA algorithm. The MLC dosimetric leaf gap of the beam in ETPS was determined by matching the dose distribution of ETPS generated IMRT plans to MTPS, with the B-field induced shift modeled by isocenter shift. The plans were automatically adjusted for different SAD between the two systems. For independent check, the treatment plans, developed in MTPS were transferred to ETPS and dose was recalculated using AAA. A 2D gamma analysis of the ETPS and MTPS dose distribution on a BEV parallel plane was performed for each beam. MTPS dose distribution was shifted laterally by 2mm during gamma analysis to account for the magnetic effect. The Eclipse dose for posterior beams was corrected for both the Unity couch as well as the posterior MR coil attenuation. Five prostate cases with five reference plans and four online adaptive plans and three liver reference plans were evaluated.


Results: For prostate cases, the average per-beam gamma (4%/4mm) pass rate for a plan was between 99.2% and 100% with the lowest per-beam gamma pass rate at 98.4%. For the liver cases, the average pass rate was between 98.6 and 99.9% with the lowest at 96.2%. The time for the process was within 5 minutes.


Conclusion: Eclipse TPS can provide an efficient way to perform IMU check for Monaco offline reference and online adaptive plans.

Download ePoster [PDF]

Keywords

Quality Assurance, Image-guided Therapy

Taxonomy

TH- External Beam- Photons: Quality Assurance - IMRT/VMAT

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