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

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Presentation on theme: "Radiation Protection in Radiotherapy Part 5 Properties and safety of radiotherapy sources and equipment used for external beam radiotherapy IAEA Training."— Presentation transcript:

1 Radiation Protection in Radiotherapy Part 5 Properties and safety of radiotherapy sources and equipment used for external beam radiotherapy IAEA Training Material on Radiation Protection in 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 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques3 External Beam Radiotherapy patient tumour Beam 3 Beam 2 Beam 1

4 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques4 External Beam Therapy (EBT) l Non-invasive l Target localization important and beam placement may be tricky l Usually multiple beams to place target in the focus of all beams patient Single beam Three coplanar beam Multiple non- coplanar beams

5 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques5 External Beam Radiotherapy l More than 90% of all radiotherapy patients are treated using EBT l Most of these are treated using X Rays ranging from 20keV to 20MeV in peak-energy l 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

6 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques6 Objectives l To become familiar with different radiation types used for external beam radiotherapy l To understand the function of different equipment used for EBT delivery l To appreciate the implications of different treatment units and their design l To be familiar with auxiliary equipment required and used for EBT l To understand the measures used in this equipment to ensure radiation safety

7 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques7 Contents l Lecture 1: Radiation types and techniques l Lecture 2: Equipment and safe design

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

9 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques9 Objectives l To be familiar with different radiation types used in EBT l To appreciate the technical needs to make these radiation types applicable to radiotherapy l To understand common external beam radiotherapy techniques

10 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques10 Contents 1. External Beam Radiotherapy process 2. Radiation qualities in use 3. Delivery techniques 4. Prescription and reporting 5. Special procedures

11 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques11 1. EBT process

12 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques12 EBT process: Use of radiation

13 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques13 Note on the role of diagnosis l The responsibility of clinicians l Without appropriate diagnosis the justification of the treatment is doubtful l Diagnosis is important for target design and the dose required for cure or palliation

14 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques14 Note on the role of simulation l Simulator is often used twice in the radiotherapy process n Patient data acquisition - target localization, contours, outlines n Verification - can the plan be put into practice? Acquisition of reference images for verification l Simulator may be replaced by other diagnostic equipment or virtual simulation

15 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques15 Simulator l Important to mimic isocentric treatment environment l 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 l Other functions (isocentricity) can then be mimicked on the treatment unit

16 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques16 Virtual simulation l All aspects of simulator work are performed on a 3D data set of the patient l This requires high quality 3D CT data of the patient in treatment position l Verification can be performed using digitally reconstructed radiographs (DRRs)

17 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques17 CT Simulation (Thanks to ADAC) Marking the Patient already during CT

18 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques18 Virtual Simulation 3D Model of the patient and the Treatment Devices

19 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques19 Digitally Reconstructed Radiographs as reference image for verification View and print DRRs for all planned fields: Improved confidence for planning and reference for verification

20 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques20 Note on the role of treatment planning l Links prescription to reality l The ‘center piece’ of radiotherapy l Becomes more and more sophisticated and complex l Extensive discussion in part 10

21 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques21 2. External beam radiotherapy (EBT) treatment approaches l Superficial X Rays l Orthovoltage X Rays l Telecurie units l Megavoltage X Rays l Electrons l Heavy charged particles l Others

22 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques22 External beam radiotherapy (EBT) treatment approaches l Superficial X Rays l Orthovoltage X Rays l Telecurie units l Megavoltage X Rays l Electrons l Heavy charged particles l Others +40 to 120kVp +150 to 400kVp +137-Cs and 60-Co +Linear accelerators +Protons from cyclotron, C, Ar,... +Neutrons, pions

23 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques23 Photon percentage depth dose comparison for photon beams Superficial beam Orthovoltage beam

24 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques24 Superficial radiotherapy l 50 to 120kVp - similar to diagnostic X Ray qualities l Low penetration l Limited to skin lesions treated with single beam l Typically small field sizes l Applicators required to collimate beam on patient’s skin l Short distance between X Ray focus and skin

25 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques25 Superficial radiotherapy Philips RT 100

26 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques26 Superficial radiotherapy issues l Due to short FSD high output and large influence of inverse square law l Calibration difficult (strong dose gradient, electron contamination) l Dose determined by a timer - on/off effects must be considered l Photon beams may be contaminated with electrons from the applicator

27 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques27 Orthovoltage radiotherapy l 150 - 400kVp l Penetration sufficient for palliative treatment of bone lesions relatively close to the surface (ribs, spinal cord) l Largely replaced by other treatment modalities

28 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques28 Orthovoltage Equipment (150 - 400 kVp) l Depth dose dramatically affected by the FSD FSD 6cm, HVL 6.8mm Cu FSD 30cm, HVL 4.4mm Cu

29 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques29 Orthovoltage patient set-up l Like for superficial irradiation units the beam is set- up with cones directly on the patient’s skin

30 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques30 Megavoltage radiotherapy l 60-Cobalt (energy 1.25MeV) l Linear accelerators (4 to 25MVp) l Skin sparing in photon beams l Typical focus to skin distance 80 to 100cm l Isocentrically mounted

31 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques31 Photon percentage depth dose comparison l PHOTONS l ELECTRONS

32 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques32 Typical locations of tumor and normal tissues l PHOTONS l ELECTRONS

33 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques33 Build-up effect Result of the forward direction of secondary electrons - they deposit energy down stream from the original interaction point

34 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques34 Build-up effect l Clinically important as all radiation beams in external radiotherapy go through the skin l Is reduced in large field sizes and oblique incidence and when trays are placed in the beam l Can be avoided by the use of bolus on the patient if skin or scar shall be treated

35 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques35 Isocentric set-up

36 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques36 Isocentric set-up l Result of the large FSDs possible with modern equipment l 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

37 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques37 Common photon treatment techniques l Two parallel opposed fields n lung n breast n head and neck

38 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques38 Common photon treatment techniques l Four field ‘box’ n cervix n prostate

39 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques39 Isocentric or not? l 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.

40 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques40 Photon beam modification l Blocks l Wedges l Compensators

41 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques41 Shielding blocks l Beam shaping l Conform the high dose region to the target n Fixed blocks n Customized blocks made from low melting alloy (LMA) l Partially replaced now by Multi Leaf Collimator (MLC) Siemens MLC Customized shielding block

42 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques42 Physical wedge

43 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques43 Wedges l One dimensional dose modification l Different realizations l Now often a dynamic wedge

44 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques44 Use of wedges l Wedged pair l Three field techniques patient Isodose lines patientTypical isodose lines

45 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques45 Compensators l Physical compensators n lead sheets n brass blocks n customized milling l Intensity modulation n multiple static fields n arcs n dynamic MLC

46 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques46 Intensity modulation l Can be shown to allow optimization of the dose distribution l Make dose in the target homogenous l Minimize dose outside the target l Different techniques n physical compensators n intensity modulation using multileaf collimators

47 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques47 Intensity Modulation l Achieved using a Multi Leaf Collimator (MLC) l The field shape can be altered n either step-by-step or n dynamically while dose is delivered MLC pattern 1 MLC pattern 3 MLC pattern 2 Intensity map

48 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques48 Dynamic treatment techniques l Arcs l Dynamic wedge l Dynamic MLC á increasing complexity with increasing flexibility in dose delivery. Verification becomes essential patient

49 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques49 Electron radiotherapy l Finite range l Rapid dose fall off

50 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques50 Characteristics of an electron beam RpRp d max 50 0 10 20 30 40 60 70 80 90 100 0123456789101112 Depth (cm) %DD R 100 R 50 Surface dose Therapeutic range x-ray component

51 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques51 Electron beam isodoses (20MeV) Watch ‘bulging’ of isodoses at depth Watch dose increase (115%!) due to oblique incidence

52 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques52 Other issues with electron beams Dose distribution significantly affected by surface contour changes - this must be considered when using bolus to shape dose distribution at depth.

53 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques53 Inhomogeneities affect the dose distribution Air cavity Monte Carlo Calculations

54 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques54 Use of electrons l Skin lesions l Scar boosting l Avoidance of deep lying sensitive structures (e.g. spinal cord)

55 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques55 More issues with the use of electrons for radiotherapy l Computer prediction of dose distribution more difficult l Small fields difficult to predict l Dosimetry somewhat more difficult than in photons due to strong dose gradients and variation of electron energy with depth

56 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques56 Other radiation types l Neutrons n Complex radiobiology n Complex interactions n Potential advantages for hypoxic and radioresistant tumors n Not widely used l Protons - probably the most promising other radiation type

57 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques57 Comparison to other radiation types

58 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques58 Potential Advantage of Proton radiotherapy: dose sparing before and behind the target due to Bragg peak

59 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques59

60 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques60 X Rays versus protons

61 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques61 4. Prescription and reporting l Prescription is the responsibility of individual clinicians, depending on the patient’s condition, equipment available, experience and training. l The prescription should follow protocols which are established by professional organizations and modified and adopted by radiotherapy departments. l The prescription must be informed - as far as possible - by clinical evidence

62 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques62 Prescription and reporting l Prescription may vary within reason depending on equipment available l Reporting must be uniform - any adequately educated person must be able to understand what happened to the patient in case of: n need for a different clinician to continue treatment n re-treatment of the patient n clinical trials n potential litigation

63 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques63 Recommendations by the ICRU l International Commission on Radiation Units and Measurements l ICRU reports provide guidance on prescribing, recording and reporting

64 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques64 Target delineation l ICRU report 50

65 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques65 Definitions form ICRU 50 l Gross Tumour Volume (GTV) = clinically demonstrated tumour l Clinical Target Volume (CTV) = GTV + area at risk (e.g. potentially involved lymph nodes)

66 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques66 Definitions form ICRU 50 l Planning Target Volume (PTV) = volume planned to be treated = CTV + margin for set-up uncertainties and potential of organ movement

67 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques67 Strategies for margins l Margins are most important for clinical radiotherapy - they depend on: n organ motion - internal margin n patient set-up and beam alignment - external margin l Margins can be non-uniform but should be three dimensional l A reasonable way of thinking would be: “Choose margins so that the target is in the treated field at least 95% of the time”

68 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques68 Definitions form ICRU 50 l Treated Volume = volume that receives dose considered adequate for clinical objective l Irradiated volume = dose considered not negligible for normal tissues

69 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques69 l The concept of margins was expanded on by ICRU report 62 n Internal margin = due to organ motion n Set-up margin l The two are often combined as independent uncertainties

70 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques70 5. Special procedures l Total body irradiation l Total electron skin irradiation l Stereotactic radiosurgery

71 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques71 Total body irradiation (TBI) l Target: Bone marrow l Different techniques available n 2 lateral fields at extended FSD n AP and PA n moving of patient through the beam l Typically impossible to do a computerized treatment plan l Need many measurements

72 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques72 TBI: one possible patient position Radiation field at >3m FSD; collimator rotated

73 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques73 Issues with TBI l In vivo dosimetry essential l May need low dose rate treatment l Shielding of critical organs (e.g. lung) and thin body parts may be required n this can be only for parts of the treatment to achieve the best possible dose uniformity

74 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques74 Total electron skin irradiation l Treat all skin to very shallow depth l Different techniques available n 4 or 6 fields n rotating patient l Impossible to plan using a computer l Requires many measurements for beam characterization

75 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques75 Total Body Skin Irradiation l Multiple electron fields at extended FSD l Whole body skin as target

76 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques76 Issues with TBSI l Use low energy electrons (4 or 6MeV) l Spoiler in front of patient improves dose distribution l in vivo dosimetry required l shielding of nails and eyes l boost of some areas (e.g. under arms) may be required

77 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques77 Stereotactic procedures l Target usually brain lesions l External head frame used to ensure accurate patient positioning l Invasive or l Re-locatable

78 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques78 Image registration l Variety of systems l Many frame attachments to allow for different diagnostic modalities (MRI, CT, angiography)

79 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques79 Image registration CT scan MRI Leksell fiducial markers on both

80 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques80 Stereotactic procedures l Spatial accuracy around 1mm l High dose single fraction (e.g. for arterio-venous malformations) = stereotactic radiosurgery using an invasively mounted head frame l Multiple fractions for tumour treatment = stereotactic radiotherapy using a re-locatable head immobilisation Both systems MedTec

81 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques81 EBT verification tools l Correct location n portal films n electronic portal imaging l Correct dose n phantom measurements n in vivo dosimetry

82 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques82 EBT verification tools l Correct location n portal films n electronic portal imaging l Correct dose n phantom measurements n in vivo dosimetry l Part 10 with some comments in second lecture part 5 (now) l Parts 2 and 10

83 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques83 Summary l A wide variety of radiation qualities are available for the optimization of radiotherapy for individual patients l The choice depends on patient and availability of equipment l Given adequate understanding of radiation properties and patient requirements many highly specialized procedures have been developed to address problems in radiotherapy

84 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques84 Have we achieved the objectives? l To be familiar with different radiation types used in EBT l To appreciate the technical needs to make these radiation types applicable to radiotherapy l To understand common external beam radiotherapy techniques

85 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques85 Where to Get More Information l Part 10 relates directly to this part l References: sKarzmark, C, Nunan C and Tanabe E. Medical electron accelerators. McGraw Hill, New York, 1993. l Site visit of...

86 Any questions?

87 Question: Please put together a table comparing electron and X Rays produced by linear accelerators

88 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques88 X Rays and electrons in EBT

89 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation types and techniques89 Acknowledgments l John Drew, Westmead Hospital, Sydney l Patricia Ostwald, Newcastle Mater Hospital


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