Скачать презентацию Diamond Detectors for Medical Dosimetry CARAT Workshop 13 Скачать презентацию Diamond Detectors for Medical Dosimetry CARAT Workshop 13

075f41e62f405c354dfe9832153c4b12.ppt

  • Количество слайдов: 24

Diamond Detectors for Medical Dosimetry CARAT Workshop, 13– 15 December 2010 Jan U. Würfel, Diamond Detectors for Medical Dosimetry CARAT Workshop, 13– 15 December 2010 Jan U. Würfel, PTW-Freiburg, jan. [email protected] de

Outline 4 Quick introduction to PTW 4 What a Diamond detector is used for Outline 4 Quick introduction to PTW 4 What a Diamond detector is used for 4 Some PTW test criteria for diamond dosemeters

Quick introduction to PTW Company Profile 4 PTW-Freiburg Gmb. H (1922) PTW-New York Corporation Quick introduction to PTW Company Profile 4 PTW-Freiburg Gmb. H (1922) PTW-New York Corporation (1995) PTW-France SARL (2001) PTW-Asia Pacific Limited (2004) PTW-Latin America LTDA (2005) PTW-Beijing Limited (2007) PTW-UK Limited (2008) K&S Associates, Inc. (2009) Sales, consolidated: 39. 6 million € Employees: approx. 260 4 More than 60 distributors worldwide 4 ISO 9001 and ISO 13485 certified

Quick introduction to PTW Employees 4 Freiburg 4 Non-permanent 4 Subsidiaries 205 9 47 Quick introduction to PTW Employees 4 Freiburg 4 Non-permanent 4 Subsidiaries 205 9 47 4 Total 261

Quick introduction to PTW Calibration Laboratories 4 PTW-Freiburg Secondary Standard Dosimetry Laboratory (SSDL) Accredited Quick introduction to PTW Calibration Laboratories 4 PTW-Freiburg Secondary Standard Dosimetry Laboratory (SSDL) Accredited by PTB since 1979 Member of DKD and IAEA network 12, 000 Chamber calibrations per year 4 K&S Associates Accredited Dosimetry Calibration Laboratory (ADCL) Accredited by AAPM since 1982 1, 500 Chamber calibrations per year

Quick introduction to PTW Consolidated Turnover Quick introduction to PTW Consolidated Turnover

Quick introduction to PTW Product Overview Electrometers X-Ray Test Tools Ionization Chambers OEM Components Quick introduction to PTW Product Overview Electrometers X-Ray Test Tools Ionization Chambers OEM Components Detector Arrays Water Phantoms Calibration Benches Application Software

What a Diamond detector is used for Outline 4 Quick introduction to PTW 4 What a Diamond detector is used for Outline 4 Quick introduction to PTW 4 What a Diamond detector is used for 4 Some PTW test criteria for diamond dosemeters

What a Diamond detector is used for Measurements in Water 4 Propagation and interaction What a Diamond detector is used for Measurements in Water 4 Propagation and interaction of photons in water is very similar to human tissue Measurements in radiation therapy are performed in real or artificial (plastic) water 4 The quantity we are looking for is: How much energy per mass is deposited in water by the radiation? Name: Absorbed Dose to water, Dw Unit: 1 J/kg = 1 Gy

What a Diamond detector is used for What Are We Actually Measuring? 4 Only What a Diamond detector is used for What Are We Actually Measuring? 4 Only very few photon interactions 4 The interacting photon transfers energy to an electron 4 The dose is deposited by these (“secondary”) electrons Processes for this photon energy transfer in radiation therapy beams: Photoelectric effect Compton effect Pair production low energy high energy 500 ke. V 25 Me. V

What a Diamond detector is used for Unfortunately. . . 4 Our detector is What a Diamond detector is used for Unfortunately. . . 4 Our detector is not made out of water 4 Photoelectric effect: mass attenuation coefficient ~ Z³ A detector with Z > Zwater will over-respond to scattered (low-energy) radiation. 4 This is called (bad) energy response 4 In large treatment fields (> 10 x 10 cm²) silicon detectors (Z = 14) over-respond by several %.

What a Diamond detector is used for What Happens at High Energies? 4 At What a Diamond detector is used for What Happens at High Energies? 4 At high energies (> 1 Me. V), the electron stopping power ratio (detector / water) is the important quantity

What a Diamond detector is used for What’s so Special about a Diamond Detector? What a Diamond detector is used for What’s so Special about a Diamond Detector? The perfect detector is infinitesimally small and made out of water Type of detector Size for same response @ Low energy @ High energy Air filled ionisation chamber 1 excellent not perfect but corrections available Diode 1000 x smaller bad good Diamond 1000 x smaller good

What a Diamond detector is used for Only One Type of Diamond on the What a Diamond detector is used for Only One Type of Diamond on the Market 4 The PTW diamond detector is the only usable diamond detector on the market 4 It’s a natural diamond 4 Limited resources (smaller than the market need) 4 Quite expensive

What a Diamond detector is used for This is what a diamond detector is What a Diamond detector is used for This is what a diamond detector is used for Linac g Profile PDD

What a Diamond detector is used for Diamond “Quality” Depends on its intended Use What a Diamond detector is used for Diamond “Quality” Depends on its intended Use 4 A diamond detector may react very fast to a single particle event but very slow to high-flux radiation therapy photons (mean flux density roughly 1010 1/(cm²s)) 4 Reaction to 30 ke. V X-rays can be completely different from reaction to 1 Me. V gamma radiation. This includes response, priming (= pumping), and speed of response

Some PTW test criteria for diamond dosemeters Outline 4 Quick introduction to PTW 4 Some PTW test criteria for diamond dosemeters Outline 4 Quick introduction to PTW 4 What a Diamond detector is used for 4 Some PTW test criteria for diamond dosemeters

Some PTW test criteria for diamond dosemeters Priming (Pumping) 4 Natural diamond, Co-60, 6. Some PTW test criteria for diamond dosemeters Priming (Pumping) 4 Natural diamond, Co-60, 6. 77 m. Gy/s 4 Dose for priming: when final signal ± 0. 5 % is reached 4 Here: 5 Gy

Some PTW test criteria for diamond dosemeters Speed of Response 4 Reaction to beam-on Some PTW test criteria for diamond dosemeters Speed of Response 4 Reaction to beam-on and -off: 4 Signal rise: 99 % reached within 2 s 4 Signal drop: 1 % reached within 2 s

Some PTW test criteria for diamond dosemeters Signal to Dark Current Ratio (SDR) 4 Some PTW test criteria for diamond dosemeters Signal to Dark Current Ratio (SDR) 4 NOT the same as Signal to noise ratio (SNR) SDR_2 s SDR_1 min 4 SDR_2 s 100 4 SDR_1 min 1000

Some PTW test criteria for diamond dosemeters Why is the Speed of Response so Some PTW test criteria for diamond dosemeters Why is the Speed of Response so Important? A slow speed can lead to tilted shoulders in profile measurements scan direction

Some PTW test criteria for diamond dosemeters Radiation Hardness? 4 Diamond is less sensitive Some PTW test criteria for diamond dosemeters Radiation Hardness? 4 Diamond is less sensitive to radiation damage than silicon 4 But is it fully radiation resistant to 25 MV Linac radiation?

Some PTW test criteria for diamond dosemeters Re-Priming Effect 4 For artificial diamond dosemeters Some PTW test criteria for diamond dosemeters Re-Priming Effect 4 For artificial diamond dosemeters it can happen that after a break of a few minutes, re-priming is necessary 4 This can lead to tilted shoulders 4 Re-priming dose after 3 min pause should be below 100 m. Gy

The End Thank You for Your Attention The End Thank You for Your Attention