Title. Study of the Dose Delivery System inaccuracies and their impact on the dose distribution during the first years of the CNAO clinical activity. (Max 160 characters, spaces included)
Authors. A. Vignati1, M. A. Hosseini2, A. Attili1, M. Donetti3, S. Giordanengo1, L. F. Guarachi4, F. Marchetto1, F.
Mas Milian5, A. Mirandola3, S. Molinelli3, V. Monaco1,4, G. Russo6, R. Sacchi1,4, M. Varasteh Anvar4, R. Cirio1,4. 1 Istituto Nazionale di Fisica Nucleare, Torino, Italy
2 Ionizing and Non-ionizing Radiation Protection Research Center (INIRPRC), Shiraz University of Medical
Sciences (SUMS), Shiraz, Iran.
3 Centro Nazionale di Adroterapia Oncologica (CNAO), Pavia, Italy 4 Università degli studi di Torino, Torino, Italy
5 Universidade Estadual de Santa Cruz, CNPq Fellow, Bahia, Brazil 6 Internet-Simulation Evaluation Envision (I-SEE) s.r.l., Torino, Italy
Abstract (max 2000 ch)
Introduction. The Italian hadrontherapy center (CNAO) uses actively scanned proton and carbon-ion beams to treat tumors, and is equipped with a Dose Delivery System (DDS) to monitor and guide the beams to the patient. This work aims at evaluating the impact of the DDS inaccuracies on the dose distribution of patients treated at CNAO, through a retrospective analysis of the data collected during the delivery (D) and their comparison with the planning (P).
Materials and Methods. The DDS delivers the dose in spots according to the P, each spot being defined by the number of particles, the beam position and energy. The same quantities are measured by the DDS during the D, and saved in the LOG files. The absolute difference between D- and P-spot positions at the reference plane at the isocenter, and the relative difference between the P- and D-number of particles were assessed. Then, the P- and D-spot quantities were used as inputs of a Forward Planning program, which computes the dose of a treatment configuration, based on the patient anatomy and the beams set-up. The obtained P- and D-dose maps were compared through the Gamma-Index, which measures the discrepancy between two dose distributions, in terms of spatial distance and dose difference.
Results. 61 patients (01/2012-04/2013) were studied. 98% of the spots showed position deviations less than 1.5 mm, and differences in number of particles less than 2.5%. The P- and D-dose maps were compared for 5 patients, representing time periods with different accuracy level of the DDS. Even in the worst case, more than 98% of points passed the (3%, 3 mm) Gamma-index criteria.
Conclusions. The accuracy of the CNAO DDS was evaluated in terms of deviation of the spot position and number of particles between P- and D-spots. Variations in the position accuracy were correlated with fine tunings of the accelerator. The influence of the observed deviations on the dose distribution was found to be negligible.
