Dosimetric commissioning and quality assurance of scanned ion beams at the Italian National Center for Oncological Hadrontherapy.
OBJECTIVE
To describe the dosimetric commissioning and quality assurance (QA) of the actively scanned proton and carbon ion beams at the Italian National Center for Oncological Hadrontherapy.


METHODS
The laterally integrated depth-dose-distributions (IDDs) were acquired with the PTW Peakfinder, a variable depth water column, equipped with two Bragg peak ionization chambers. fluka Monte Carlo code was used to generate the energy libraries, the IDDs in water, and the fragment spectra for carbon beams. EBT3 films were used for spot size measurements, beam position over the scan field, and homogeneity in 2D-fields. Beam monitor calibration was performed in terms of number of particles per monitor unit using both a Farmer-type and an Advanced Markus ionization chamber. The beam position at the isocenter, beam monitor calibration curve, dose constancy in the center of the spread-out-Bragg-peak, dose homogeneity in 2D-fields, beam energy, spot size, and spot position over the scan field are all checked on a daily basis for both protons and carbon ions and on all beam lines.


RESULTS
The simulated IDDs showed an excellent agreement with the measured experimental curves. The measured full width at half maximum (FWHM) of the pencil beam in air at the isocenter was energy-dependent for both particle species: in particular, for protons, the spot size ranged from 0.7 to 2.2 cm. For carbon ions, two sets of spot size are available: FWHM ranged from 0.4 to 0.8 cm (for the smaller spot size) and from 0.8 to 1.1 cm (for the larger one). The spot position was accurate to within ± 1 mm over the whole 20 × 20 cm(2) scan field; homogeneity in a uniform squared field was within ± 5% for both particle types at any energy. QA results exceeding tolerance levels were rarely found. In the reporting period, the machine downtime was around 6%, of which 4.5% was due to planned maintenance shutdowns.


CONCLUSIONS
After successful dosimetric beam commissioning, quality assurance measurements performed during a 24-month period show very stable beam characteristics, which are therefore suitable for performing safe and accurate patient treatments.
Fondazione CNAO, strada Campeggi 53, Pavia 27100, Italy.
Alfredo
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Mirandola
Fondazione CNAO, strada Campeggi 53, Pavia 27100, Italy.
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Molinelli
Fondazione CNAO, strada Campeggi 53, Pavia 27100, Italy.
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Vilches Freixas
Fondazione CNAO, strada Campeggi 53, Pavia 27100, Italy.
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Mairani
Fondazione CNAO, strada Campeggi 53, Pavia 27100, Italy.
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Gallio
Fondazione CNAO, strada Campeggi 53, Pavia 27100, Italy.
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Panizza
Fondazione CNAO, strada Campeggi 53, Pavia 27100, Italy.
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Russo
Fondazione CNAO, strada Campeggi 53, Pavia 27100, Italy.
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Ciocca
INFN, Torino 10125, Italy and Fondazione CNAO, strada Campeggi 53, Pavia 27100, Italy.
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Donetti
INFN-Dipartimento di Fisica, Università degli Studi di Pavia, Via U. Bassi 6, Pavia 27100, Italy and Fondazione CNAO, strada Campeggi 53, Pavia 27100, Italy.
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Magro
INFN, Torino 10125, Italy.
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Giordanengo
Fondazione CNAO, strada Campeggi 53, Pavia 27100, Italy and Radiotherapy Division, European Institute of Oncology, Via Ripamonti 435, Milano 20141, Italy.
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Orecchia
D002138:Calibration; D063193:Heavy Ion Radiotherapy / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D009010:Monte Carlo Method; D009369:Neoplasms / Q000532:radiotherapy*; D019047:Phantoms, Imaging; D061766:Proton Therapy / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D011785:Quality Assurance, Health Care; D011874:Radiometry; D011879:Radiotherapy Dosage