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S. Amerio a , S. Belletti b , A. Boriano c , R. Cirio d , S. Coda a , M. Donetti e,d ,

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 ,

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S. Amerio a , S. Belletti b , A. Boriano c , R. Cirio d , S. Coda a , M. Donetti e,d ,

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  1. A solution for dosimetry and quality assurance in IMRT and hadrontherapy: the pixel ionization chamber. S. Amerioa, S. Bellettib, A. Borianoc, R. Ciriod, S. Codaa, M. Donettie,d, B. Ghedib, A. Lupariad, E. Madonf, F. Marchettod, U. Nastasia, C. Peronid,C.J. Sanz Freired,g, E. Trevisiolf, A. Urgesif a Servizio di Fisica Sanitaria, Ospedale S. Giovanni A.S., V. Cavour 31, I-10123 Torino b Servizio di Fisica Sanitaria, Spedali Civili di Brescia, P.le Ospedale 1, I-25123 Brescia c ASP, V.le Settimio Severo 65, I-10133 Torino d University and INFN of Torino, V. Giuria 1, I-10125 Torino e TERA Foundation, V. Puccini 11, I-28100 Novara f OIRM S. Anna, V. Baiardi 43, I-10126 Torino f partially supported by IBA, Ion Beam Application, Louven la-Neuve, Belgium

  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 7thInternational 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 mm2 sensitive area = 24 X 24 cm2 cathode made of aluminized mylar foil total dimension = 64 X 64 X 3 cm3 front end electronics, placed around the chamber, perform the analog to digital conversion 7thInternational 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. 7thInternational 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. 7thInternational 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 7thInternational Conference on Advanced Technology and Particle Physics

  7. Read out electronics • TERA05 characteristics • Very Large Scale Integration • if conversion • output  Qint • 100 fC<charge quantum<800 fC • fmax= 5 MHz  Imax= 4 A • 64 channels • 16 bit wide counters • multiplexed digital output • three-state output • no dead time • max read out = 10 MHz 7thInternational Conference on Advanced Technology and Particle Physics

  8. Read out electronics Recycling Integrator architecture. 7thInternational Conference on Advanced Technology and Particle Physics

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

  10. Read out electronics I = 49.96 nA 26 chips Charge quantum have been measured over different chips in order to evaluate the spread of the value. Results show an RMS  1 % 7thInternational Conference on Advanced Technology and Particle Physics

  11. Read out electronics Charge quantum reproducibility has been measured. I = 49.96 nA Qc = 600 fC 24 ºC < T < 27 ºC 1 month 6 measures 7thInternational Conference on Advanced Technology and Particle Physics

  12. Data acquisition Slow 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 7thInternational Conference on Advanced Technology and Particle Physics

  13. Data acquisition Fast 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 7thInternational Conference on Advanced Technology and Particle Physics

  14. Hadron beam test voxels GSI - Darmstadt - Germany • Aims • spatial resolution • homogeneity of response • 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 7thInternational Conference on Advanced Technology and Particle Physics

  15. Hadron beam test Spatial resolution pixel dimensions = 7.5 × 7.5 mm2 beam dimension = 8.8 mm (FWHM) counts per voxel  103 Spatial resolution  < 0.2 mm 7thInternational Conference on Advanced Technology and Particle Physics

  16. Hadron beam test Response homogeneity The calibration accounts for the different gain of each channel (gas gap variations and electronics) 18 × 18 cm2 uniform field before calibration  = 2.0 % after calibration  = 1.1 % 7thInternational 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. 7thInternational 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 7thInternational 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. 7thInternational Conference on Advanced Technology and Particle Physics

  20. Photon beam Profile comparison with a water phantom have been performed. Field 20 X 20 cm2 Depth 10 cm Field 10 X 10 cm2 Depth 10 cm 7thInternational 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. 7thInternational Conference on Advanced Technology and Particle Physics

  22. Photon beam IMRT measurements • 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 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. Delivered dose in function of time Total dose delivered 7thInternational 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. 7thInternational Conference on Advanced Technology and Particle Physics

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