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ETHZ-METAS-PSI Project: Dosimetry for Scanned Proton Therapy Beams with Water Calorimetry

Understand the importance of dosimetry in proton therapy & the use of water calorimetry to directly measure dose. Learn principles, challenges, & verification methods. Explore the benefits and limitations of water calorimetry.

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ETHZ-METAS-PSI Project: Dosimetry for Scanned Proton Therapy Beams with Water Calorimetry

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  1. ETHZ-METAS-PSI Project:Dosimetry forScanned Proton Therapy Beams with Water Calorimetry Solange Gagnebin, Damian Twerenbold Sektion Thermometrie und Ionisierende StrahlungBundesamt für Metrologie METAS3003 Bern-Wabern Eros Pedroni, David Meer, Silvan Zenklusen, Christian BulaPaul Scherrer Institut, Proton Radiation Therapy Centre, 5232 Villingen

  2. Why Dosimetry is so important? DOSE dose † † does not destroy tumors harmful for the patient Dose healing of the patient

  3. ETHZ - METAS - PSI Project: Goal Realizing a water calorimeterto determine directly the dose in scannedproton therapy beam at PSI Gantry 2.

  4. Plan of the presentation • Principles of Water Calorimetry • Dosimetry with ionizing chambers • Conclusion and Perspectives

  5. Water Calorimetry: Basic Principles very simple principle: radiation : specific heat capacity of water (very well known, since 1930‘s) absorbed-dose-to-water [Gy = 1 J/kg] at position x Dose-to-water : main advantage: direct determination of dose-to-water

  6. METAS Water Calorimeter for Protons water calorimeter in water phantom sealed water vessel thermistor 250 mm thermistor bead (metal oxide NTC)

  7. Schematic scanned proton dose profile in the vessel of the water calorimeter

  8. Proton Dosimetry : Results 2008

  9. Problem: Water Calorimetry needs a lot of statistics (1) J. Medin, C. K. Ross, N. V. Klassen, H. Palmans, E. Grussel, J.-E. Grindborg, Phys. Med. Biol. 51 (2006) 1503-1521.

  10. Nevertheless: Dosimetry has to be SI unit traceable IAEA-TRS-398 protocol: Calibration factor of the ionizing chambers calculated correction factors kQ Co60 radiation and water calorimeter Verification with indirect method using ionizing chambers only.

  11. Beam Dosimetry: Ionizing chamber beam qualities and ionizing chamber dependentonthe calibration factor MU: monitor units water tank

  12. measured Determination of the calibration factor kQ factor determines the transition from Co-60 to the user‘s beam quality Co-60 beam

  13. Experimental verification of factor Measurements in July 2009 DW drops when performing relative measurements measured at METAS Co-60 with ionizing chamber measured at PSI proton beam with ionizing chamber For the same dose: Journal of the ICRU, Vol. 7, No 2, Report 78, Oxford University Press, 2007.

  14. Conclusion and Perspectives • First results show good agreement between calculated dose-to-water as determined by ionizing chamber and measured with water calorimeter • However, Water Calorimetry needs a lot of statistics • An alternative is to verify the calibration factors of ionizing chambers with an indirect method • => Measurements at PSI Gantry 2 • July 2009: Dosimetry with Ionizing Chambers to verify the correction factor kQ

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