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.

In carbon ion radiotherapy there is an urgent clinical need to develop objective tools for the conversion of relative biological effectiveness (RBE)-weighted doses based on different models. In this work we introduce a clinically oriented method to compare NIRS-based and LEM-based GyE systems, minimizing differences in physical dose distributions between treatment plans. Carbon ion plans were optimized on target volumes of cubic and spherical shapes, for RBE-weighted dose prescription levels ranging from 3.6 to 4.4 GyE. Plans were calculated for target sizes from 4 to 12 cm defining three beam geometries: single beam, opposed beam and orthogonal beam configurations. The two treatment planning systems currently employed in clinical practice were used, providing the NIRS-based and LEM-based GyE calculations. Physical dose distributions of NIRS-based and LEM-based treatment plans were compared. LEM-based prescription doses that minimize differences in physical dose distributions between the two systems were found. These doses were compared with the mean RBE-weighted dose obtained with a Monte Carlo code (FLUKA) interfaced with LEM I. In the investigated dose range, LEM-based RBE-weighted prescription doses, that minimize differences with NIRS plans, should be higher than NIRS reported prescription doses. The optimal dose depends on target size, shape and position, number of beams and dose level. The opposed beam configuration resulted in the smallest average prescription dose difference (0.45 ± 0.09 GyE). The second approach of recalculating NIRS RBE-weighted dose with a Monte Carlo code interfaced with LEM resulted in no significant difference with the results obtained from the planning study. The delivery of a voxel by voxel iso-effective plan, if different RBE models are employed, is not feasible; it is however possible to minimize differences in a treatment plan with the simple approach presented here. Dose prescription ultimately represents a clinical task under the responsibility of the radiation oncologist, the presented analysis intends to be a quantitative and objective way to assist the clinical decision.

During one year of clinical activity at the Italian National Center for Oncological Hadron Therapy 31 patients were treated with actively scanned proton beams. Results of patient-specific quality assurance procedures are presented here which assess the accuracy of a three-dimensional dose verification technique with the simultaneous use of multiple small-volume ionization chambers. To investigate critical cases of major deviations between treatment planning system (TPS) calculated and measured data points, a Monte Carlo (MC) simulation tool was implemented for plan verification in water. Starting from MC results, the impact of dose calculation, dose delivery and measurement set-up uncertainties on plan verification results was analyzed. All resulting patient-specific quality checks were within the acceptance threshold, which was set at 5% for both mean deviation between measured and calculated doses and standard deviation. The mean deviation between TPS dose calculation and measurement was less than ±3% in 86% of the cases. When all three sources of uncertainty were accounted for, simulated data sets showed a high level of agreement, with mean and maximum absolute deviation lower than 2.5% and 5%, respectively.

Purpose: This paper describes the system for the dose delivery 15 currently used at the Centro Nazionale di Adroterapia Oncologica (CNAO) for ion pencil beam scanning radiotherapy. Methods

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