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11 Radiation Protection for X-Ray Technologists Linacs, radioactive substances and all the rest John Saunderson Consultant Physicist / Radiation Protection Adviser

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2 Beam energy - kV or MV? mid = 9% mid = 77%

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3 Kilovoltage X-ray good for imaging good for radiotherapy near skin surface Megavoltage X-ray deep therapy imaging poor, but possible for verification

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4 Filament (heats up on prep.) Target kV + - Electron production in the X-ray tube Applied voltage chosen to give correct velocity to the electrons mA Voltage to arc 1 m air at STP = 3.4 MV

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5 How to get megavoltage energy photons? Normal X-ray tube? - insulation needed too thick, arcing, etc. 2-MeV Van de Graaff accelerator Van de Graaff generator

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6 Normal X-ray tube? - insulation needed too thick, arcing, etc. Van de Graaff generator Radioactive sources - Co-60 (1.2 MeV gamma rays) How to get megavoltage energy photons?

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7 Linear Accelerator (linac) Klystron or magnetron microwaves electrons

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9 CL6

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10 Typical dose rates Fluoroscopy entrance dose rate < 50 mGy/min > 40 minutes to erythema threshold > 3 min to annual hand dose limit Linac entrance dose rate > 2.4 Gy/min < 1 minute to erythema threshold < 4 seconds to annual hand dose limit

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11 MV electrons / X-ray photons

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13 MV electrons / X-ray photons Photon or electron energy Electron rangeX-ray transmission 6 MeV3 g/cm 2 = 2.6 mm Pb or = 30 mm H 2 O 10% 55 mm Pb 1% 110 mm Pb 15 MeV10 g/cm 2 = 8.8 mm Pb or = 74 mm H 2 O 10% 57 mm Pb 1% 114 mm Pb

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15 Hull & East Yorks. CL1 & CL2

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17 Tenth Value Layers / mm MaterialDensityZ eff 80kVp x15MVx Concrete2.412.5 (?) 17.4 mm432 mm Water1.07.4278 mm620 mm Lead11.4820.2 mm56 mm Iron7.9261.0 mm108 mm Tungsten19.374 Uranium18.9592 i.e. @ 80 kVp, 1 mm lead 90 mm concrete @ 15 MVx, 1 mm lead 8 mm concrete (lead 5 x density of concrete)

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18 Neutron Production Binding energy (BE) of neutrons 7-20 MeV (mostly)

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19 Pb 207 B 10

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20 Very little neutron production below 10MVx MVxGy n / Gy X 100.003% 15-180.010% 20-250.030% Neutron Production Binding energy (BE) of neutrons 7-20 MeV (mostly) Probability increases with (E X BE) up to (2 x BE)

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21 Neutron Shielding TVL neutrons ~ 400 cm lead (thermal) < 31cm concrete for medical linacs < 10 cm polythene (TVL for 15MVx is 43.2 cm)

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22 Hull & East Yorks. CL1 & CL2

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23 Neutron Activation

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24 Neutron Activation Products Port 1 m

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25 Neutron Activation Products (2) Half lives Aluminium 2.5 minutes Bed end 9.2 minutes Linac head 8.4 minutes Plasterboard, water, Perspex no activity detected

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27 Why 7.5 Sv/h ? Today Post 2000, 6 mSv is unclassified person effective dose limit 6mS/y / (7.5 Sv/h x 7.5h/d) = 100 d/y Originally 7.5 Sv/h x 8 h/d x 5 d/wk x 50 wk/y = 15mSv Pre 1/1/2000, 15 mSv was unclassified person effective dose limit

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29 Why 75 Sv/h ? Remember Dose limit not like a speed limit Optimisation Keep doses A s L ow A s R easonably A chievable Follow local rules. 75 Sv/h x 8 h/d x 5 d/wk x 50 wk/y = 150mSv/y Eye dose limit = 150 mSv/y Skin dose limit = 500 mSv/y

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30 Half-life no more than 8 1 / 2 minutes So in hour, dose rate will be 10 times or more lower

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31 Radioactive materials Iridium-192 Used for brachytherapy in wire form 0.1-0.7 MeV beta particles absorbed by platinum coating 0.2-1.06 MeV gamma rays emitted (effective energy 0.4MeV) TVL = 12 mm Pb, 185 mm concrete

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32 Smoke detector vs Flexitron

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33 Smoke detector Americium-241 37 kBq (kilobecquerels) @10 cm 0.005 mSv/h @ 1 cm Erythema threshold in 45 years Direct skin contact 0.2 mSv/h Erythema threshold in > 1 year Hand dose limit in 1 month

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34 Flexisource 44 mGy/hour @ 100 cm 44 x 100 2 /1 2 = 440,000 mGy/h @ 1 cm 122 mGy/second @ 1 cm erythema threshold in 16 secs hand dose limit in 1.2 secs (direct skin contact 1.2 - 72 Gy/s) 400 GBq (gigabecquerels) 400 trillion gamma rays per second

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35 Radioactive Patients Patients may be radioactive if theyve been injected with or swallowed radioactive pharmaceuticals they have solid radioactive sources surgically implanted they have been involved in an accident with radioactive materials.

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36 Radioactive Decay - half life

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37 Nuclear Medicine Scan Patient injected with or swallows a radioactive pharmaceutical Gamma camera traces where that radiopharmaceutical is concentrated.

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39 Thyroid treatments with radio-iodine Hyperthyroidism / thyrotoxicosis overactive thyroid - 400 MBq Thyroid cancer must destroy all tumour - 3000 MBq c.f. thyroid scan - 0.2 MBq.

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40 Other unsealed source therapies Phosphorus-32 for polycythemia (too many red blood cells) Yttrium-90 colloid for arthritic conditions Strontium-90 for bone metastases.

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41 Brachytherapy (radioactive implants) Intracavity afterloading Iridium wire afterloading Iridium pins Iodine-125 seeds.

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42 HDR-microSelectron

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43 Iridium Implant

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44 Iodine-125 seeds in Prostate

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45 Iridium-192 Used for brachytherapy in wire form 0.1-0.7MeV beta particles absorbed by platinum coating 0.2-1.06MeV gamma rays emitted (effective energy 0.4MeV) TVL = 12mm Pb, 185mm concrete New HDR Flexitron

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46 Non-Ionising Radiations (briefly) e.g. lasers ultraviolet MRI scanners

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47 Laser Device Classes & Hazards Class 1 Class 1M Class 2 Class 2M Class 3R Class 3B Class 4 Applies to device as a whole.

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48 Class 1 no risk to eyes (including using optical viewing instruments) no risk to skin (either low power device or totally encased)

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49 Class 1M no risk to the naked eye no risk to skin

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50 Class 2 no risk to eyes for short term exposure (including using optical viewing instruments) no risk to skin (visible, so blink response protects) (may cause dazzle or flash blindness)

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51 Class 2M no risk to naked eye for short time exposure no risk to skin

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52 Class 3R low risk to eyes no risk to skin (risk for intentional intrabeam viewing only) (may be a dazzle hazard)

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53 Class 3B medium to high risk to eyes low risk to skin (aversion response protects skin, or must be focussed to such a small spot that pin-prick effect only)

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54 Class 4 high risk to eyes and skin low risk to skin (diffuse reflection may be hazardous) (possible fire hazard)

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56 Risk Assessments

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57 HEYH Trust CP137 Health & Safety at Work Policy - Lasers - Includes safety of class 3B and class 4 lasers

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58 UV Eye hazard, skin hazard Dermatology TL01 and PUVA

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59 UV treatment of psoriasis 0.0001 0.001 0.01 0.1 1 10 250275300325350375400 Wavelength / nm Relative effect Erythemaclearance of psoriasis UVA UVB UVC

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60 Relative Spectral Power of UV Therapy lamps

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62 MRI

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6430/11/0864

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65 f i n