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Radiation Protection in Radiotherapy

Radiation Protection in Radiotherapy. IAEA Training Material on Radiation Protection in Radiotherapy. Part 5 Properties and safety of radiotherapy sources and equipment used for external beam radiotherapy. IAEA Safety Series 120, Safety Fundamentals (1996).

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Radiation Protection in Radiotherapy

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  1. Radiation Protection inRadiotherapy IAEA Training Material on Radiation Protection in Radiotherapy Part 5 Properties and safety of radiotherapy sources and equipment used for external beam radiotherapy

  2. IAEA Safety Series 120, Safety Fundamentals (1996) Source: “Anything that may cause radiation exposure… an X-ray unit may be a source …”

  3. External Beam Radiotherapy Beam 2 Beam 3 Beam 1 tumour patient Part 5, lecture 1: Radiation types and techniques

  4. External Beam Therapy (EBT) • Non-invasive • Target localization important and beam placement may be tricky • Usually multiple beams to place target in the focus of all beams Multiple non- coplanar beams Single beam Three coplanar beam patient Part 5, lecture 1: Radiation types and techniques

  5. External Beam Radiotherapy • More than 90% of all radiotherapy patients are treated using EBT • Most of these are treated using X Rays ranging from 20keV to 20MeV in peak-energy • Other EBT treatment options include telecurie units (60-Co and 137-Cs), electrons from linear accelerators and accelerators for heavy charged particles such as protons Part 5, lecture 1: Radiation types and techniques

  6. Objectives • To become familiar with different radiation types used for external beam radiotherapy • To understand the function of different equipment used for EBT delivery • To appreciate the implications of different treatment units and their design • To be familiar with auxiliary equipment required and used for EBT • To understand the measures used in this equipment to ensure radiation safety Part 5, lecture 1: Radiation types and techniques

  7. Contents • Lecture 1: Radiation types and techniques • Lecture 2: Equipment and safe design Part 5, lecture 1: Radiation types and techniques

  8. Radiation Protection inRadiotherapy IAEA Training Material on Radiation Protection in Radiotherapy Part 5 External Beam RT Lecture 1: Radiation types and techniques

  9. Objectives • To be familiar with different radiation types used in EBT • To appreciate the technical needs to make these radiation types applicable to radiotherapy • To understand common external beam radiotherapy techniques Part 5, lecture 1: Radiation types and techniques

  10. Contents 1. External Beam Radiotherapy process 2. Radiation qualities in use 3. Delivery techniques 4. Prescription and reporting 5. Special procedures Part 5, lecture 1: Radiation types and techniques

  11. 1. EBT process Part 5, lecture 1: Radiation types and techniques

  12. EBT process:Use of radiation Part 5, lecture 1: Radiation types and techniques

  13. Note on the role of diagnosis • The responsibility of clinicians • Without appropriate diagnosis the justification of the treatment is doubtful • Diagnosis is important for target design and the dose required for cure or palliation Part 5, lecture 1: Radiation types and techniques

  14. Note on the role of simulation • Simulator is often used twice in the radiotherapy process • Patient data acquisition - target localization, contours, outlines • Verification - can the plan be put into practice? Acquisition of reference images for verification • Simulator may be replaced by other diagnostic equipment or virtual simulation Part 5, lecture 1: Radiation types and techniques

  15. Important to mimic isocentric treatment environment However, some functions can be replaced by other diagnostic X Ray units provided the location of the X Ray field can be marked on the patient unambiguously Other functions (isocentricity) can then be mimicked on the treatment unit Simulator Part 5, lecture 1: Radiation types and techniques

  16. Virtual simulation • All aspects of simulator work are performed on a 3D data set of the patient • This requires high quality 3D CT data of the patient in treatment position • Verification can be performed using digitally reconstructed radiographs (DRRs) Part 5, lecture 1: Radiation types and techniques

  17. CT Simulation (Thanks to ADAC) Marking the Patient already during CT Part 5, lecture 1: Radiation types and techniques

  18. Virtual Simulation 3D Model of the patient and the Treatment Devices Part 5, lecture 1: Radiation types and techniques

  19. Digitally Reconstructed Radiographs as reference image for verification View and print DRRs for all planned fields: Improved confidence for planning and reference for verification Part 5, lecture 1: Radiation types and techniques

  20. Note on the role of treatment planning • Links prescription to reality • The ‘center piece’ of radiotherapy • Becomes more and more sophisticated and complex • Extensive discussion in part 10 Part 5, lecture 1: Radiation types and techniques

  21. 2. External beam radiotherapy (EBT) treatment approaches • Superficial X Rays • Orthovoltage X Rays • Telecurie units • Megavoltage X Rays • Electrons • Heavy charged particles • Others Part 5, lecture 1: Radiation types and techniques

  22. Superficial X Rays Orthovoltage X Rays Telecurie units Megavoltage X Rays Electrons Heavy charged particles Others 40 to 120kVp 150 to 400kVp 137-Cs and 60-Co Linear accelerators Linear accelerators Protons from cyclotron, C, Ar, ... Neutrons, pions External beam radiotherapy (EBT) treatment approaches Part 5, lecture 1: Radiation types and techniques

  23. Photon percentage depth dose comparison for photon beams Superficial beam Orthovoltage beam Part 5, lecture 1: Radiation types and techniques

  24. Superficial radiotherapy • 50 to 120kVp - similar to diagnostic X Ray qualities • Low penetration • Limited to skin lesions treated with single beam • Typically small field sizes • Applicators required to collimate beam on patient’s skin • Short distance between X Ray focus and skin Part 5, lecture 1: Radiation types and techniques

  25. Superficial radiotherapy Philips RT 100 Part 5, lecture 1: Radiation types and techniques

  26. Superficial radiotherapy issues • Due to short FSD high output and large influence of inverse square law • Calibration difficult (strong dose gradient, electron contamination) • Dose determined by a timer - on/off effects must be considered • Photon beams may be contaminated with electrons from the applicator Part 5, lecture 1: Radiation types and techniques

  27. Orthovoltage radiotherapy • 150 - 400kVp • Penetration sufficient for palliative treatment of bone lesions relatively close to the surface (ribs, spinal cord) • Largely replaced by other treatment modalities Part 5, lecture 1: Radiation types and techniques

  28. Orthovoltage Equipment (150 - 400 kVp) • Depth dose dramatically affected by the FSD FSD 6cm, HVL 6.8mm Cu FSD 30cm, HVL 4.4mm Cu Part 5, lecture 1: Radiation types and techniques

  29. Orthovoltage patient set-up • Like for superficial irradiation units the beam is set-up with cones directly on the patient’s skin Part 5, lecture 1: Radiation types and techniques

  30. Megavoltage radiotherapy • 60-Cobalt (energy 1.25MeV) • Linear accelerators (4 to 25MVp) • Skin sparing in photon beams • Typical focus to skin distance 80 to 100cm • Isocentrically mounted Part 5, lecture 1: Radiation types and techniques

  31. PHOTONS ELECTRONS Photon percentage depth dose comparison Part 5, lecture 1: Radiation types and techniques

  32. PHOTONS ELECTRONS Typical locations of tumor and normal tissues Part 5, lecture 1: Radiation types and techniques

  33. Build-up effectResult of the forward direction of secondary electrons - they deposit energy down stream from the original interaction point Part 5, lecture 1: Radiation types and techniques

  34. Build-up effect • Clinically important as all radiation beams in external radiotherapy go through the skin • Is reduced in large field sizes and oblique incidence and when trays are placed in the beam • Can be avoided by the use of bolus on the patient if skin or scar shall be treated Part 5, lecture 1: Radiation types and techniques

  35. Isocentric set-up Part 5, lecture 1: Radiation types and techniques

  36. Isocentric set-up • Result of the large FSDs possible with modern equipment • Places the tumour in the centre - multiple radiation beams are easily set-up to deliver radiation from many directions to the target Image from VARIAN webpage Part 5, lecture 1: Radiation types and techniques

  37. Common photon treatment techniques • Two parallel opposed fields • lung • breast • head and neck Part 5, lecture 1: Radiation types and techniques

  38. Common photon treatment techniques • Four field ‘box’ • cervix • prostate Part 5, lecture 1: Radiation types and techniques

  39. Isocentric or not? • All the beam arrangements discussed so far can be set-up with a fixed distance (e.g. 80cm) to the patient’s skin or isocentrically with a fixed distance to the centre of the target. Part 5, lecture 1: Radiation types and techniques

  40. Photon beam modification • Blocks • Wedges • Compensators Part 5, lecture 1: Radiation types and techniques

  41. Shielding blocks Customized shielding block • Beam shaping • Conform the high dose region to the target • Fixed blocks • Customized blocks made from low melting alloy (LMA) • Partially replaced now by Multi Leaf Collimator (MLC) Siemens MLC Part 5, lecture 1: Radiation types and techniques

  42. Physical wedge Part 5, lecture 1: Radiation types and techniques

  43. Wedges • One dimensional dose modification • Different realizations • Now often a dynamic wedge Part 5, lecture 1: Radiation types and techniques

  44. Use of wedges • Wedged pair • Three field techniques Isodose lines patient patient Typical isodose lines Part 5, lecture 1: Radiation types and techniques

  45. Compensators • Physical compensators • lead sheets • brass blocks • customized milling • Intensity modulation • multiple static fields • arcs • dynamic MLC Part 5, lecture 1: Radiation types and techniques

  46. Intensity modulation • Can be shown to allow optimization of the dose distribution • Make dose in the target homogenous • Minimize dose outside the target • Different techniques • physical compensators • intensity modulation using multileaf collimators Part 5, lecture 1: Radiation types and techniques

  47. Intensity Modulation MLC pattern 1 • Achieved using a Multi Leaf Collimator (MLC) • The field shape can be altered • either step-by-step or • dynamically while dose is delivered MLC pattern 2 MLC pattern 3 Intensity map Part 5, lecture 1: Radiation types and techniques

  48. Dynamic treatment techniques • Arcs • Dynamic wedge • Dynamic MLC • increasing complexity with increasing flexibility in dose delivery. Verification becomes essential patient Part 5, lecture 1: Radiation types and techniques

  49. Electron radiotherapy • Finite range • Rapid dose fall off Part 5, lecture 1: Radiation types and techniques

  50. R100 100 90 Therapeutic range Surface dose 80 70 60 R50 50 %DD 40 30 20 x-ray component 10 dmax Rp 0 0 1 2 3 4 5 6 7 8 9 10 11 12 Depth (cm) Characteristics of an electron beam Part 5, lecture 1: Radiation types and techniques

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