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Radiotherapy Equipment

Radiotherapy Equipment

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Radiotherapy Equipment

  1. 1. ZMT 335 122/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak RADIOTHERAPY & NUC MEDICINE
  2. 2. TOPIC 5 & 6 Radiotherapy Equipment 222/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak
  3. 3. OBJECTIVE 322/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak To understand the design and functionality of the equipment To review physics and technology of external beam radiotherapy equipment
  4. 4. 5.0 External Beam Equipment 5.1 Low-energy Machines 5.1.1 Superficial Equipment 5.1.2 Orthovoltage Units 5.2 Telecurie Units 5.2.1 Cs-131 5.2.2 Cobalt – 60 Unit 5.3 Linear accelerator (LINAC) 422/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak
  5. 5. 5.0 External Beam Equipment 522/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak
  6. 6. Therapeutic x-ray equipment • 10 kVp - 150 kVp (superficial); • 150 kVp - 400 kVp (orthovoltage/ deep) Radioactive sources ( γ ray equipment) • Cobalt 60 & Cesium 137 MV accelerators for X and electron therapy • Linear accelerator 6 5.0 External Beam Equipment
  7. 7. 5.1 Low-energy Machines 5.1.1 Superficial Equipment 5.1.2 Orthovoltage Units 722/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak
  8. 8. • 10-15 kVp • Treatment of inflammatory disorders (Langerhans’ cells), Bowen’s disease, patchystage mycosis fungoides, herpes simplex 1.Grenz rays • Superficial skin lesions • Endocavitary treatments for curative intent (rectal) 2.Contact therapy 5.1 Low-energy Machines •Low-energy machines: Uses x-rays generated at voltages up to 500kVp
  9. 9. • 50-150 kVp • Skin cancer and tumors no deeper than 0.5 cm 3.Superficial equipment • 150-500 kVp • Skin, mouth, and cervical carcinoma • Experience limitation in the treatment of lesions deeper than 2 to 3 cm. 4.Orthovoltage machines 5.1 Low-energy Machines
  10. 10. “conventional” X Ray tube with electrons accelerated by an electric field filtration important Stationary anode (in contrast to diagnostic tubes which have a rotating anode to allow for a smaller focal spot) Part 5, lecture 2: Equipment - superficial, telecurie 10 5.1 Superficial / Orthovoltage equipment5.1 Low-energy Machines
  11. 11. 5.1 Superficial / Orthovoltage equipment Can not reach deep-seated tumors with an adequate dosage of radiation Do not spare skin and normal tissues. LIMITATIONS OF LOW ENERGY MACHINES 5.1 Low-energy Machines
  12. 12. Part 5, lecture 2: Equipment - superficial, telecurie 12 5.1 Superficial / Orthovoltage equipment 50 to 150kVp small skin lesions maximum applicator size typically < 7cm typical FSD < 30cm beam quality measured in HVL aluminium (0.5 to 8mm) Superficial 150 to 500kVp applicators or diaphragm skin lesions, bone metastases FSD 30 to 60cm beam quality in HVL copper (0.2 to 5mm) Orthovoltage 5.1 Low-energy Machines
  13. 13. 5.1.1 Superficial Equipment 1322/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak
  14. 14. Part 5, lecture 2: Equipment - superficial, telecurie 14 Superficial X Ray tube (Philips RT 100) • Manufacturers picture... X Ray tube Cooling water Target Applicator/ collimator 5.1.1 Superficial Equipment5.1.1 Superficial Equipment
  15. 15. Part 5, lecture 2: Equipment - superficial, telecurie 15 X-ray tube ApplicatorFilter 5.1.1 Superficial Equipment
  16. 16. X-ray produced at 50-150 kV Varying thickness of filtration (usually 1-6 mm Al) are added to harden the beam to a desire degree Superficial treatment are usually given with the help of applicators or cones attachable to the diaphragm of the machine SSD range 15 to 20 cm 5.1.1 Superficial Equipment
  17. 17. 17 Superficial x-ray equipment (cont) • Dose is highly dependent on source-skin distance, filtration and applicator area. 5.1.1 Superficial Equipment 15 cm FSD cones 25cm FSD cones
  18. 18. 5.1.1 Superficial Equipment5.1.1 Superficial Equipment Usually operated at 5-8 mA Beyond this depth, the dose drop-off is too severe to deliver adequate depth dose without considerable overdosing of the skin surface Useful for irradiating tumor confined to about 5 mm depth (~90% depth dose)
  19. 19. 5.1.1 Superficial Equipment • Short focus to skin distance (FSD) and hence high output and large influence of inverse square law • Calibration difficult due to strong dose gradient i.e. dose fall off and electron contamination Issues with Superficial radiotherapy
  20. 20. 5.1.2 Orthovoltage Units 2022/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak
  21. 21. Uses conventional X-ray tube Energy range 150- 500 kV X-rays Mostly used around 250 - 300 kVp Applicators are used in superficial therapy Treatment depths of around 20 mm Penetration sufficient for palliative treatment of bone lesions relatively close to the surface (ribs, spinal cord) 5.1.2 Orthovoltage Units5.1.2 Orthovoltage Units
  22. 22. 5.1.2 Orthovoltage Units 5.1.2 Orthovoltage Units • Higher dose to bone - photoelectric absorption • Maximum dose on the surface hence higher skin dose • Treatment to a depth of only a few centimeters possible • Low energy, hence high scattered radiation and larger penumbra Disadvantages Of Deep X-ray
  23. 23. 5.2 Telecurie Units 5.2.1 Cs-131 5.2.2 Cobalt – 60 Unit 2322/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak
  24. 24. Part 5, lecture 2: Equipment - superficial, telecurie 24 5.2 Telecurie Units Features of a Teletherapy Source high energy gamma ray emission high specific air kerma rate constant simple means of production Low cost high specific activity long half- life
  25. 25. Part 5, lecture 2: Equipment - superficial, telecurie 25 5.2.1 137-Cs 137-Cs Photon energy 0.66MeV Relatively large source to relatively low specific activity Medium FSD (around 60cm) No isocentric mounting - similar to orthovoltage equipment in set-up Not sold anymore and should not be in use
  26. 26. 5.2.2 Cobalt – 60 Unit 5.2.2.1 Properties 5.2.2.2 Application 5.2.2.3 Production 5.2.2.4 Source 5.2.2.5 Activity 5.2.2.6 Half-Life 5.2.2.7 Shielding 5.2.2.8 Penumbra 5.2.2.9 Dose Maximum 5.2.2.10 Equipment 5.2.2.10 Cobalt – 60 Equipment 5.2.2.11 Annual dose to staff 5.2.2.12 Gamma Knife 2622/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak
  27. 27. Part VII.14.3 : Radiation Sources in Teletherapy Slide 28 Natural Cobalt (59Co) COBALT - Kobald, from the German for goblin or evil spirit. Discovered in 1735. Brittle hard metal similar to iron and nickel. Found in minerals and meteorites. Salts and glass oxides are deep blue in colour. 5.2.2 Cobalt – 60 Unit
  28. 28. 5.2.2 Cobalt – 60 Unit ORTHOVOLTAGE UNIT 150-500 KV x-rays Maximum dose on the skin Treatment to a depth of few centimeters Higher absorption by bone non uniform dose distribution Higher side scatter hence larger penumbra Telecobalt Unit 1.25 MeV ‫ﻻ‬ Photon Maximum dose at depth of 5 mm Relatively uniform dose absorption Higher penetration deep seated tumours Relatively uniform distribution More of forward scatter, lesser penumbra Mostly isocentric unit 5.2.2 Cobalt – 60 Unit
  29. 29. 5.2.2 Cobalt – 60 Unit Linear Accelerator 4 to 21 MV photon beams Maximum dose at higher depth with energy No radioactive source Radiation only when the source is switched is ON Uniform dose absorption 1mm source – nearly point source Small Penumbra Electron beam of various energies possible Telecobalt Unit 1.25 MeV ‫ﻻ‬ Photon Maximum dose at depth of 5 mm Source to be changed every 4 to 5 years Leakage radiation present even while the beam is off Relatively uniform distribution 1-2 cm source diameter Larger penumbra Gamma Photon only 5.2.2 Cobalt – 60 Unit
  30. 30. 31 Introduced in the 1950’s, being replaced by linacs. The first practical radiation therapy treatment unit to provide a significant dose below the skin surface and simultaneously spare the skin the harsh effects of earlier methods. Still used in developing countries: simpler design, cost, little tech support. 5.2.2 Cobalt – 60 Unit
  31. 31. 32 Photon energy around 1.25MeV Specific activity large enough for FSD of 80cm or even 100cm Therefore, isocentric set-up possible Constantly emit radiation 60Co source must be shielded in a protective housing (source head). source head is a steel shell filled with lead (may be up to 2 ft in diameter PROPERTIES 5.2.2.1 Properties
  32. 32. 33 5.2.2 Cobalt – 60 Unit 5.2.2.2 Application APPLICATION To treat cancers of the head and neck area, breast, spine, and extremities Areas just below the skin surface Ideal in treating lymph nodes.
  33. 33. 34 5.2.2 Cobalt – 60 Unit 5.2.2.3 Production of Cobalt – 60 1 • Cobalt: produced in nuclear reactors by the irradiation of neutrons of the common stable form of 59Co. 2 • The 59Co nucleus absorbs a neutron in the reactor and becomes 60Co. 3 • Radioactive 60Co produces a useful therapy beam when it undergoes beta decay
  34. 34. 35 5.2.2 Cobalt – 60 Unit 5.2.2.3 Production of Cobalt – 60 4 • The nucleus emits a beta particle and then two photons, 1.17 MeV and 1.33 MeV for an effective energy of 1.25 MeV 5 • 60Co  60Ni+ + B- + neutrino (v) + gamma rays 6 • Radioactive 60Co emits radiation in the form of high energy gamma rays in an effort to return to its more stable state.
  35. 35. 36 5.2.2 Cobalt – 60 Unit5.2.2.4 Cobalt – 60 Source Of the close to 300 natural nuclides and over 3000 artificially produced radionuclides, only four meet the teletherapy source requirements (Co-60, Cs-137, Eu-152, and Ra-226) and only cobalt-60 is actually used in practice.
  36. 36. 37 5.2.2 Cobalt – 60 Unit5.2.2.4 Cobalt – 60 Source • 1 to 3 centimetersDiameter of a 60Co source • Encased in multiple layers of welded metal to prevent contamination of the environment and to absorb β- particles produced by the decay process. Source Form: Pellets of radioactive 60Co • Smaller source with less penumbra for the same beam intensity • Less hazard of contamination should a source ever become exposed to the environment. Source Form: 60Co fused into a solid cylinder
  37. 37. Part VII.14.3 : Radiation Sources in Teletherapy Slide 38 How does a teletherapy Cobalt source look? 3500 pellets; 275 Ci/g; 7700 Ci 5.2.2.4 Cobalt – 60 Source
  38. 38. Part VII.14.3 : Radiation Sources in Teletherapy Slide 39 Cobalt source – how does it look? 5.2.2.4 Cobalt – 60 Source
  39. 39. 40 5.2.2 Cobalt – 60 Unit5.2.2.5 Cobalt – 60 Activity SI unit: Curies (Ci) 3.7 x 1010 Becquerel (Bq) 1 Bq = 1 disintegration per second also defined in rhm units (roentgens per hour at 1 meter) Most sources have an activity of 750-9000 Ci, typically 3000-9000 Ci used in radiation therapy
  40. 40. 41 •Half-life: the time necessary for a radioactive material to decay to half or 50% of its original intensity. • Requires a correction factor for this decay of about 1% per month in all treatment calculations. • Source must be replaced at about five year intervals. •The half-life of 60Co is 5.26 years. 5.2.2 Cobalt – 60 Unit5.2.2.6 Cobalt – 60 Half-Life
  41. 41. 42 5.2.2 Cobalt – 60 Unit5.2.2.7 Cobalt – 60 Shielding Cerrobend (Lipowitz metal): Lower melting point than Pb, cheaper 50% Bismuth 26.7% Lead 13.3% tin 10% Cadmium (a toxic metal can get into bloodstream Density ratio of Cerrobend to Lead: 1.2 cm Cerrobend to 1 cm lead. 5 HVL is needed to reduce intensity A thickness of 7.2 cm of Cerrobend needed, 6 cm lead.
  42. 42. 46 • Penumbra: the area at the edge of the radiation beam at which the dose rate changes rapidly as a function of distance from the beam axis.5.2.2 Cobalt – 60 Unit5.2.2.8 Penumbra 1 • Describes the edge of the field having full radiation intensity for the beam compared with the area at which the intensity falls to 0. 2 • The larger the source size, the larger the penumbra 3 • Larger field sizes are necessary to cover the same amount of tissue adequately compared to the linac. 4 • Geometric penumbra typically wide because source diameter is large (>2cm)
  43. 43. Part 5, lecture 2: Equipment - superficial, telecurie 48 5.2.2 Cobalt – 60 Unit5.2.2.8 Penumbra
  44. 44. 49 5.2.2 Cobalt – 60 Unit5.2.2.8 Penumbra The transmission penumbra can be reduced by using satellite collimators, penumbra trimmers or trimmer bars Trimmers are metal bars that attenuate the edge of the beam providing a sharper field edge. It Should be placed no closer than 15 cm from the patients skin to reduced electron contamination (increased skin dose) by metal devices. Provides enough distance for the secondary electrons produced by the trimmer bars to lose sufficient energy REDUCING PENUMBRA
  45. 45. 52 5.2.2 Cobalt – 60 Unit5.2.2.9 Dose Maximum Dose maximum (Dmax): when a greater percentage of dose occurs below the skin surface Dmax is the depth of maximum buildup, in which 100% of the dose is deposited For 60Co, Dmax occurs at 0.5 cm below the skin surface.
  46. 46. Part 5, lecture 2: Equipment - superficial, telecurie 53 • Source head and transfer mechanism 5.2.2.10 Cobalt – 60 Equipment
  47. 47. Part 5, lecture 2: Equipment - superficial, telecurie 54 5.2.2.10 Cobalt – 60 Equipment • shield against the primary cobalt-60 beam Primary barriers • shield against leakage radiation and radiation scattered from the patient Secondary barriers Typical cobalt-60 teletherapy installation:
  48. 48. 55 11. Beam On/Beam Off 5.2.2 Cobalt – 60 Unit5.2.2.10 Cobalt – 60 Equipment • Turning the beam on requires physically exposing the source either by moving it into position or by removing shields around the source. Turning the beam • the compressor generates air pressure by pushing the source horizontally into position over the collimator opening. Air pressure: • the motor rotates a wheel 180 degrees by placing the source over the collimator opening. Rotating wheel:
  49. 49. Part 5, lecture 2: Equipment - superficial, telecurie 56 5.2.2.10 Cobalt – 60 Equipment
  50. 50. Part 5, lecture 2: Equipment - superficial, telecurie 57 Picture of a Co source change 5.2.2.10 Cobalt – 60 Equipment
  51. 51. Part 5, lecture 2: Equipment - superficial, telecurie 58 •Assume: • 200 days, 8hours per day working time per year • 10% of this time in treatment room • 3 Gy h-1 typical dose averaged over all locations of the staff member in the treatment room •Dose = 200 x 8 x 0.1 x 3 Gy •  0.5mGy/year (half of dose limit for general public) 5.2.2 Cobalt – 60 Unit5.2.2.11 Annual dose to staff
  52. 52. 5.2.2 Cobalt – 60 Unit5.2.2.12 GAMMA KNIFE Therefore it is also known as the stereotactic surgery Patient wears a specialized helmet that is surgically fixed to their skull (brain tumor remains stationary at target point of the gamma rays) It is placed in a circular array in a heavily shielded assembly Aims gamma radiation through a target point in the patient's brain. Contains 201 cobalt-60 sources of approximately 30 curies each
  53. 53. 60 Patient positioning collimator 5.2.2 Cobalt – 60 Unit5.2.2.12 GAMMA KNIFE
  54. 54. Part 5, lecture 2: Equipment - superficial, telecurie 62 5.2.2.12 GAMMA KNIFE

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