A solution for dosimetry and quality assurance in IMRT and hadrontherapy: the pixel ionization chamber. S. Amerio a, S. Belletti b, A. Boriano c, R. Cirio d, S. Coda a, M. Donetti e,d, B. Ghedi b, A. Luparia d, E. Madon f, F. Marchetto d, U. Nastasi a, C. Peroni d,C.J. Sanz Freire d,g, E. Trevisiol f, A. Urgesi f a Servizio di Fisica Sanitaria, Ospedale S. Giovanni A.S., V. Cavour 31, I Torino b Servizio di Fisica Sanitaria, Spedali Civili di Brescia, P.le Ospedale 1, I Brescia c ASP, V.le Settimio Severo 65, I Torino d University and INFN of Torino, V. Giuria 1, I Torino e TERA Foundation, V. Puccini 11, I Novara f OIRM S. Anna, V. Baiardi 43, I Torino f partially supported by IBA, Ion Beam Application, Louven la-Neuve, Belgium

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 2 Introduction In Intensity Modulated Radiation Therapy (IMRT) techniques like step and shoot, sliding window, dynamic wedge and in hadrontherapy with scanning beam the delivered dose in the treated volume is not just function of the space but also of the time. An instrument useful in dose measurements has to be fast, reproducible and able to measure in several points. We have developed, built and tested a fast ionization chamber segmented in pixels that measures the dose in a plane which can help the physicist in the dose measurements and in quality assurance. The outline of the talk is the following detector design read out electronics data acquisition test performed results

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 3 Detector design parallel plate ionization chamber anode segmented in 1024 square pixels pixel dimension = 7.5 X 7.5 mm 2 sensitive area = 24 X 24 cm 2 cathode made of aluminized mylar foil total dimension = 64 X 64 X 3 cm 3 front end electronics, placed around the chamber, perform the analog to digital conversion

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 4 Detector design Thin version When used like monitor chamber the detector has to be thin to minimize the effects on the beam energy and shape. For this configuration, anode and cathode are glued to frames in order to assure the mechanical rigidity and the gap thickness. Water equivalent thickness < 1 mm.

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 5 Detector design Thick version When used in plastic phantom the detector can be thick. With photon or electron beam air gap has to be minimized. Anode and cathode are glued to a plastic slab, which is a grid of 1024 holes. Each hole can be considered as an independent sensitive volume.

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 6 Read out electronics The read out electronics is housed next to the electrodes. We developed a Very Large Scale Integration (VLSI) chip. Every chip has 64 channels that convert the collected charge in digital output. The name of the last version is TERA05

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 7 Read out electronics TERA05 characteristics Very Large Scale Integration i  f conversion output  Q int 100 fC<charge quantum<800 fC f max = 5 MHz  I max = 4  A 64 channels 16 bit wide counters multiplexed digital output three-state output no dead time max read out = 10 MHz

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 8 Read out electronics Recycling Integrator architecture.

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 9 Read out electronics The excellent linearity over a large range is due to recycling integrator architecture. Q C = 600 fC 10 pA < I < 2  A Linearity better than 0.3 % Q C = 100 fC 20 pA < I < 0.6  A Linearity better than 0.7 %

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 10 Read out electronics Charge quantum have been measured over different chips in order to evaluate the spread of the value. Results show an RMS  1 % I = nA 26 chips

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 11 Read out electronics I = nA Qc = 600 fC 24 ºC < T < 27 ºC 1 month 6 measures Charge quantum reproducibility has been measured.

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 12 Data acquisition connection by twisted pair flat cables (100 m max) max rate transfer = 1 MHz = 2 Mb/s read out transfer time = 1 ms PCI DAQ card LabVIEW software cheap solution easy to handle Slow data acquisition

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 13 Data acquisition connection by twisted pair flat cables (100 m max) max rate transfer = 10 MHz = 40 Mb/s read out transfer time = 50  s read out cycle total time = 500  s (FIFO operation + data transfer) real time operation system expensive solution Fast data acquisition

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 14 Hadron beam test voxels GSI - Darmstadt - Germany Beam characteristics raster-scan delivery system 270 MeV/u, C +6, 8.8 mm (FWHM) fast data acquisition system data acquisition synchronized with raster-scan Aims spatial resolution homogeneity of response

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 15 Hadron beam test Spatial resolution  < 0.2 mm Spatial resolution pixel dimensions = 7.5 × 7.5 mm 2 beam dimension = 8.8 mm (FWHM) counts per voxel  10 3

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 16 Hadron beam test Response homogeneity before calibration  = 2.0 % after calibration  = 1.1 % 18 × 18 cm 2 uniform field The calibration accounts for the different gain of each channel (gas gap variations and electronics)

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 17 Photon beam S. Giovanni A.S. and S. Anna hospitals – Torino Quality Assurance Aims Measurements reproducibility Depth dose profile measurements and comparison to reference ion chamber (Farmer) results Profile measurements In such measurements there aren’t DAQ time constraints. Anyway the system can measure the delivered dose in real time.

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 18 Photon beam Several measures have been performed to evaluate the reproducibility. After a pre-irradiation reproducibility is better than 1% 100 MU per irradiation field bigger than sensitive volume

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 19 Photon beam Depth dose profiles have been measured for different photon energy. We use a Farmer ion chamber in a plastic phantom to compare the results. An excellent agreement has been found for every photon energy.

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 20 Photon beam Profile comparison with a water phantom have been performed. Field 10 X 10 cm 2 Depth 10 cm Field 20 X 20 cm 2 Depth 10 cm

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 21 Photon beam IMRT measurements Dynamic wedge case: Moving each side of the collimator with different speed one obtains a wedge shape of the dose At the end of the treatment one has to check the delivered dose in different points The pixel ion chamber can measure precisely the 2D dose in 1024 points.

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 22 Photon beam Delivered dose in function of timeTotal dose delivered The pixel ion chamber has a fast read out. Every 1ms (slow DAQ system) a complete read out can be performed. It is possible to monitor the 2D dose in real time. Dynamic multi leaves collimator (DMLC) case: independent leaves can be moved to shape the beam field one needs to check as a function of time the 2D delivered dose IMRT measurements

Villa Olmo, Como October 7 th International Conference on Advanced Technology and Particle Physics 23 Conclusions We developed and tested a pixel ionization chamber that can be used to measure and monitor the treatment in IMRT and hadrontherapy. Its time resolution allows to perform 2D dose measurements in real time. Two prototypes have been built in order to use the same technique both as monitor chamber and to perform relative dose measurements. Future development: By stacking several chambers 3D measurements can be obtained.