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Efficacy of Dose Reconstruction Algorithm for Non Coplanar Beams in Octavius 4D System

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M Manavalan

M Muthukumaran1*, D Manigandan2 , Vikraman3 , V Murali4 , Ganapathy Krishnan5 , S Chitra6 , K Kanakavel7 , (1) Apollo Speciality Hospitals, Chennai(2) Fortis Cancer Institute, Mohali, Punjab, (3) The Brunei Cancer Center, Brunei Darussalam, (4) Apollo Speciality Hospitals, Chennai (5) Apollo Speciality Hospitals, Chennai (6) Apollo Speciality Hospitals, Chennai (7) PTW Dosimetry India Ltd, Chennai.


SU-I-GPD-T-269 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To check the efficacy of dose reconstruction algorithm for non co-planar beams in Octavius 3D Dosimetry system.

Methods: Twenty Rapidarc patients with different treatment sites with non co-planar beams were taken for the study. Octavius 4D phantom, 1000 SRS detector and PTW Verisoft software were used for the study.In Octavius 4D dose is reconstructed throughout the phantom from the measured data using the PDD values which is inputted during commissioning of Octavius system. For plans with non co-planar beams measurement is done with planar phantom orientation(with couch 0) and while reconstructing dose, couch angle is specified in the software. The measurement is done for planar and non co-planar beams and saved separately. Dose is reconstructed for planar and non co-planar beams as per the plan. Additionally while reconstructing the dose for non co-planar beams different couch angles in steps of 2 degrees were intentionally introduced and dose is reconstructed throughout the volume. Each of this measured/reconstructed dose is compared with TPS calculated dose.

Results: Gamma analysis is done with 3%DD and 3mm DTA with local and suppress dose of 5% for various combinations of non co-planar reconstructed doses. 2D, 3D and volume gamma were analysed for axial, coronal and sagital planes. The 3D gamma was giving better results than 2D gamma for reconstructed non co-planar beams. 2D and 3D gamma pass in sagital and coronal planes were always less than that for axial planes. Till 4 degrees, manually introduced error in couch angle does not have drastic impact on gamma results.

Conclusion: The 3D dose reconstruction for non co-planar beams is accurate enough to be used clinically. Small error in the order of 1 to 2 degrees in the couch angle does not have much impact on the gamma results.

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