Accuracy of PRIMO validated against a reference dosimetry dataset for Varian clinical linear accelerators Juan Francisco Calvo Ortega1, David Sánchez Artuñedo2 and Marcelino Hermida López2
[email protected]
Servicio de Radioterapia. Hospital Quirón (Barcelona) 2 Servicio de Física y Protección Radiológica. Hospital Universitario Vall d’Hebron (Barcelona) 1
Introduction The parameters that characterize the initial electron beam in the simulation of a clinical linac, mainly the initial energy and the focal spot size, largely influence on the simulated dose distributions.
The users of a Monte Carlo code for simulation transport must match the simulated dose distributions to measurements and this is achieved usually in a lengthy iterative process, by tuning the simulation parameters and comparing the simulated with the measured dose distributions.
To reduce the time needed for this tuning process, PRIMO suggests default values of the initial beam parameters for each nominal energy of the available linac models.
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Objective To investigate the suitability of PRIMO default beam parameters by comparing:
• a published dataset based on measurements on large series of linacs
• dosimetric data obtained from PRIMO simulations
We focused on dosimetric data of 6 MV photon beams from Varian Clinac 2100 linacs with a Millennium 120 MLC.
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Methods: IROC-H dosimetry dataset
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Methods: IROC-H measurement setup SSD = 100 cm, reference field: 10 x 10 cm2
PDD for
6×6 10×10 20×20
cm2 fields at z =
Jaw output factors for
6×6 10×10 15×15 20×20 30×30
5 10 15 20
cm
cm2 fields at z=10 cm (converted to dmax)
Off-axis ratios for 40×40 cm2 field at dmax
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Methods: IROC-H measurement setup
Output factors for
2×2 3×3 4×4 6×6
cm2 fields at z = 10 cm
SBRT-style output factors
IMRT-style output factors
10×10
10×10
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Methods: IROC-H linac classification
Kerns et al. (2016)
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Methods: IROC-H data 6 MV PDD at 5, 10, 15, and 20 cm
Norm. To dmax 10×10 cm2
Kerns et al. (2016)
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Methods: IROC-H data 6 MV PDD at 5, 10, 15, and 20 cm.
10×10 cm2
Kerns et al. (2016)
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Methods: PRIMO simulations PRIMO v. 0.3.1.1363 (beta, Apr 1, 2017) Clinac 2100, 6 MV photon beam Phase-space file: 450 × 106 histories E = 5.4 MeV, EFWHM = 0, focal spot FWHM = 0, beam divergence = 0 Default transport parameters
MLC Millennium 120
Water phantom 40.2 x 40.2 x 40.2 cm3 Voxel size 0.2 x 0.2 x 0.2 cm3 DPM
Splitting factor: 170 Accuracy of PRIMO validated against a reference dosimetry dataset
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Results: PDD 6x6
Accuracy of PRIMO validated against a reference dosimetry dataset
10x10
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20x20
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Results: off-axis ratio of 40x40 cm2 field
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Results: jaw output factors at dmax
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Results: small-field output factors IMRT-style
SBRT-style
10×10 Accuracy of PRIMO validated against a reference dosimetry dataset
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Conclusions PRIMO default initial beam parameters for 6 MV photon beams from Varian Clinac 2100 linacs allows obtaining dose distributions in a water phantom which agree within 2%-3% with a database of measured dosimetric data from a large series of linacs of the same model.
First step in the validation of PRIMO for independent verification of radiotherapy plans computed by a commercial treatment planning system.
Future work: • MLC evaluation for dynamic treatments (DLG)
• IMRT and VMAT clinical plans evaluation
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