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Validation of Electron Monte Carlo(eMC) Algorithm in Heterogenous Conditions Using Imatrixx 2D Array Chamber Detectors

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A Ananda Giri Babu

A Ananda Giri Babu1*, K M Ganesh2, B Durga Prasad1, K Krishna Murthy1, K Kaviarasu 1, (1)Krishna Institute Of Medical Sciences, Secunderabad, Andhra Pradesh, (2) Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka,

SU-E-T-14 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
To validate the eMC dose calculation algorithm in eclipse TPS in various heterogeneous conditions using Imatrixx chamber 2D-array system, by comparing the dose planes.

Methods:
Clinac-iX Linear Accelerator with 6,9,12,16 and 20MeV electron energies with 6x6,10x10,15x15 and 20x20 electron applicators and Eclipse TPS eMC algorithm is used in this study. Dose planes are calculated with different heterogeneous media like SP-34(solid water) slabs, Gel Bolus, Perspex and airgap placing them on Imatrixx. In TPS, Calculation grid size was kept 0.15 and 3D-Gaussian smoothing done. All calculations are normalized to 100% and the plans are delivered on Imatrixx heterogeneous setup for measurements. Initially, Imatrixx is calibrated for all electron energies with SP-34 slabs as per protocol of Omnipro-IMRT software and it is verified for homogenous medium. For all heterogeneous setup,1cm thickness of heterogeneity in study was kept above the Imatrixx surface and on top to heterogeneity, 1cm SP-34 slab was kept facing the beam entry. Hence detector array plane was at 2.3cm depth from the surface and all dose plane comparisons are made at this depth. Since 6MeV beam will not contribute higher dose at this depth, setup changed only for 6MeV as 5mm SP34 and 5mm heterogeneous medium and dose plane at 1.3cm depth is studied.

Results:
For 9 and 12MeV all the applicators and all the heterogeneous media the pass percentage between TPS and measured is above 96% even for 1% & 1mm Gamma Criteria. For 16 and 20MeV, smaller applicators (6x6 and 10x10), Perspex gave less pass percentage for 2% & 2mm and others passed well. For 6MeV , near applicator edges fail points were more , hence pass percentage is less.

Conclusion:
Hence above 9MeV accuracy of eMC is good with all heterogeneities and 6MeV should be evaluated carefully in clinical plans.



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