PMID- 29537642 OWN - NLM STAT- MEDLINE DCOM- 20180823 LR - 20180823 IS - 2473-4209 (Electronic) IS - 0094-2405 (Linking) VI - 45 IP - 5 DP - 2018 May TI - Characterization of a multilayer ionization chamber prototype for fast verification of relative depth ionization curves and spread-out-Bragg-peaks in light ion beam therapy. PG - 2266-2277 LID - 10.1002/mp.12866 [doi] AB - PURPOSE: To dosimetrically characterize a multilayer ionization chamber (MLIC) prototype for quality assurance (QA) of pristine integral ionization curves (ICs) and spread-out-Bragg-peaks (SOBPs) for scanning light ion beams. METHODS: QUBE (De.Tec.Tor., Torino, Italy) is a modular detector designed for QA in particle therapy (PT). Its main module is a MLIC detector, able to evaluate particle beam relative depth ionization distributions at different beam energies and modulations. The charge collecting electrodes are made of aluminum, for a nominal water equivalent thickness (WET) of ~75 mm. The detector prototype was calibrated by acquiring the signals in the initial plateau region of a pristine BP and in terms of WET. Successively, it was characterized in terms of repeatability response, linearity, short-term stability and dose rate dependence. Beam-induced measurements of activation in terms of ambient dose equivalent rate were also performed. To increase the detector coarse native spatial resolution (~2.3 mm), several consecutive acquisitions with a set of certified 0.175-mm-thick PMMA sheets (Goodfellow, Cambridge Limited, UK), placed in front of the QUBE mylar entrance window, were performed. The ICs/SOBPs were achieved as the result of the sum of the set of measurements, made up of a one-by-one PMMA layer acquisition. The newly obtained detector spatial resolution allowed the experimental measurements to be properly comparable against the reference curves acquired in water with the PTW Peakfinder. Furthermore, QUBE detector was modeled in the FLUKA Monte Carlo (MC) code following the technical design details and ICs/SOBPs were calculated. RESULTS: Measurements showed a high repeatability: mean relative standard deviation within +/-0.5% for all channels and both particle types. Moreover, the detector response was linear with dose (R(2) > 0.998) and independent on the dose rate. The mean deviation over the channel-by-channel readout respect to the reference beam flux (100%) was equal to 0.7% (1.9%) for the 50% (20%) beam flux level. The short-term stability of the gain calibration was very satisfying for both particle types: the channel mean relative standard deviation was within +/-1% for all the acquisitions performed at different times. The ICs obtained with the MLIC QUBE at improved resolution satisfactorily matched both the MC simulations and the reference curves acquired with Peakfinder. Deviations from the reference values in terms of BP position, peak width and distal fall-off were submillimetric for both particle types in the whole investigated energy range. For modulated SOBPs, a submillimetric deviation was found when comparing both experimental MLIC QUBE data against the reference values and MC calculations. The relative dose deviations for the experimental MLIC QUBE acquisitions, with respect to Peakfinder data, ranged from ~1% to ~3.5%. Maximum value of 14.1 muSv/h was measured in contact with QUBE entrance window soon after a long irradiation with carbon ions. CONCLUSION: MLIC QUBE appears to be a promising detector for accurately measuring pristine ICs and SOBPs. A simple procedure to improve the intrinsic spatial resolution of the detector is proposed. Being the detector very accurate, precise, fast responding, and easy to handle, it is therefore well suited for daily checks in PT. CI - (c) 2018 American Association of Physicists in Medicine. FAU - Mirandola, Alfredo AU - Mirandola A AD - Centro Nazionale di Adroterapia Oncologica (CNAO Foundation), Pavia, 27100, Italy. FAU - Magro, Giuseppe AU - Magro G AD - Centro Nazionale di Adroterapia Oncologica (CNAO Foundation), Pavia, 27100, Italy. AD - Universita degli Studi di Milano, Milano, 20100, Italy. FAU - Lavagno, Marco AU - Lavagno M AD - De.Tec.Tor. S.r.l., Torino, 10144, Italy. FAU - Mairani, Andrea AU - Mairani A AD - Centro Nazionale di Adroterapia Oncologica (CNAO Foundation), Pavia, 27100, Italy. AD - Heidelberg Ion Beam Therapy Center (HIT), Heidelberg, 69121, Germany. FAU - Molinelli, Silvia AU - Molinelli S AD - Centro Nazionale di Adroterapia Oncologica (CNAO Foundation), Pavia, 27100, Italy. FAU - Russo, Stefania AU - Russo S AD - Centro Nazionale di Adroterapia Oncologica (CNAO Foundation), Pavia, 27100, Italy. FAU - Mastella, Edoardo AU - Mastella E AD - Centro Nazionale di Adroterapia Oncologica (CNAO Foundation), Pavia, 27100, Italy. FAU - Vai, Alessandro AU - Vai A AD - Centro Nazionale di Adroterapia Oncologica (CNAO Foundation), Pavia, 27100, Italy. FAU - Maestri, Davide AU - Maestri D AD - Centro Nazionale di Adroterapia Oncologica (CNAO Foundation), Pavia, 27100, Italy. AD - Universita degli Studi di Milano, Milano, 20100, Italy. FAU - La Rosa, Vanessa AU - La Rosa V AD - De.Tec.Tor. S.r.l., Torino, 10144, Italy. FAU - Ciocca, Mario AU - Ciocca M AD - Centro Nazionale di Adroterapia Oncologica (CNAO Foundation), Pavia, 27100, Italy. LA - eng PT - Journal Article DEP - 20180406 PL - United States TA - Med Phys JT - Medical physics JID - 0425746 SB - IM MH - *Heavy Ion Radiotherapy MH - Monte Carlo Method MH - Radiometry/*instrumentation MH - Radiotherapy Dosage OTO - NOTNLM OT - MLIC OT - QA OT - ion beam therapy EDAT- 2018/03/15 06:00 MHDA- 2018/08/24 06:00 CRDT- 2018/03/15 06:00 PHST- 2017/10/17 00:00 [received] PHST- 2018/02/22 00:00 [revised] PHST- 2018/03/03 00:00 [accepted] PHST- 2018/03/15 06:00 [pubmed] PHST- 2018/08/24 06:00 [medline] PHST- 2018/03/15 06:00 [entrez] AID - 10.1002/mp.12866 [doi] PST - ppublish SO - Med Phys. 2018 May;45(5):2266-2277. doi: 10.1002/mp.12866. Epub 2018 Apr 6.