Detection of secondary particles from 12 C fragmentation in an anthropomorphic phantom for SOBP position monitoring M. Vanstalle 1 , C. La Tessa 1 , C. Schuy 1 , A. Sarti 2 , L. Piersanti 2 , V. Patera 2 , A. Sciubba 2 , and M. Durante 1,3 1 GSI, Darmstadt, Germany; 2 Universit` a di Roma La Sapienza, Roma, Italy; 3 TUD, Darmstadt, Germany The real time monitoring of the Spread-Out-Bragg-Peak (SOBP) position represents one of the major concerns in modern ion therapy as it would allow a direct check of the patient alignment in combination with the treatment plan- ning delivered. A possible method to achieve this goal is to exploit the fragmentation of the primary ions in the patient, correlating the production of secondary particles with the tumor position. Results have already been obtained with prompt gammas [1] but no data are available so far for sec- ondary charged particles. A first experiment was performed at GSI in cave M with carbon ions. The goal of this mea- surement was to study the relation between the SOBP lo- cation and the yield of secondary particles (ions, neutrons and gammas) as a function of their angular distribution. Material and methods The experimental setup is similar to the one described in [2]. The carbon ions beam was impinging on an anthro- pomorphic RANDO phantom according to different con- figurations of irradiation: • a spot irradiation with a monoenergetic pencil beam of 200 MeV/u stopped at the center of the phantom head; • a 3D irradiation for treating a 2x5x7.6 cm 3 volume placed at the center of the phantom head; • a 3D irradiation for treating a C-shaped volume placed at the center of the phantom head and having a length of 7.8 cm along the beam direction and a height of 2 cm. All irradiations were performed under full treatment conditions. A scheme of the experimental apparatus is shown in Figs. 1 and 2. The primary ions outgoing from the exit window were monitored with a 2 mm plastic scin- tillator (start counter). On the upper and left arm, two drift chambers were placed to reconstruct the trajectories of secondary charged particles. Two ΔE - E telescopes composed of a plastic scintillator (VETO) for measuring the energy loss (ΔE) and a barium fluoride (BaF 2 ) to de- termine the residual energy (E) were placed on the upper arm, behind the chamber, and on the right arm, behind a lead collimator (1 mm aperture pointing at the center of the SOBP). On the left arm, a plastic scintillator was placed upstream of the drift chamber while a LYSO scintillator was positioned downstream. Both lateral arms could be rotated around he head to allow the study of the produc- tion of secondary particles as a function of the angle. The data acquisition system was triggered when a coincidence between the start counter and either one of the BaF 2 or the LYSO occurred. Particle identification will be possi- ble thanks to Time-Of-Flight (TOF) measurement between the start counter and the BaF 2 or LYSO detectors as well as from 2-dimensional ΔE - E plots. Furthermore, the sig- nals of the BaF 2 s were integrated over a short (70 ns) and a long (2 μs) gate to apply the technique of pulse shaping. 62.5 18.4 2 0.2 BaF2'(crystal) BaF2(crystal) VETO Chamber LYSO (crystal only) 45 13 47.5 1.5 Phantom Collimator 16 2 30 114.5 19 3.6 12 14 1 3.6 x 5 cm2 4.5 x 4.5 cm (window) 2 5 x 10 cm (iron blocks) 2 5.6 x 5.6 cm (window) 2 Figure 1: Scheme of experimental setup, lateral view. Beam 22 48.5 5 START 0.1 Figure 2: Scheme of experimental setup, top view. Prospects The data analysis is still in progress. The first step is to identify the peak of the prompt γ in the TOF spectrum for the time calibration. Monte Carlo simulations of the full setup will be carry out to estimate the geometry acceptance and compare the number of tracks measured with the ex- pected values. References [1] M. Testa, M. Bajard, M. Chevallier et al., Radiat. Environ. Biophys. 49(3):337-43 (2010). [2] K. Gunzert-Marx, H. Iwase, D. Schardt et al., New J. Phys. 10:1-21 (2008). GSI SCIENTIFIC REPORT 2011 CANCER-47 531