Brachytherapy The use of radioactive sources in close proximity to the target area for radiotherapy

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1 Brachytherapy The use of radioactive sources in close proximity to the target area for radiotherapy Interstitial Seven 192-Ir wires Interstitial implant for breast radiotherapy

2 Intracavitary Three 137-Cs sources Intracavitary gynecological implant

3 Brachytherapy overview Brachytherapy uses encapsulated radioactive sources to deliver a high dose to tissues near the source brachys (Greek) = short (distance) Inverse square law determines most of the dose distribution

4 Brachytherapy Characterized by strong dose gradients Many different techniques and sources available Implants are highly customized for individual patients

5 Brachytherapy Use of radioactive materials in direct contact with patients - more radiation safety issues than in external beam radiotherapy Less than 10% of radiotherapy patients are treated with brachytherpay Per patient treated the number of accidents in brachytherapy is considerably higher than in EBT

6 Contents Brachytherapy Sources and equipment Brachytherapy techniques

7 Brachytherapy Sources and Equipment Objectives To understand the concept of sealed source To know the most common isotopes used for brachytherapy To be familiar with general rules for source handling and testing To be aware of differences between permanent implants, low (LDR) and high dose rate (HDR) applications To understand the basic fundamentals of brachytherapy equipment design.

8 1. Sealed sources IAEA BSS glossary: Radioactive material that is a) permanently sealed in a capsule or b) closely bound and in a solid form. In other words: the activity is fixed to its carrier and contamination of the environment is not possible as long as the source is intact Have an activity which can be derived from a calibration certificate and the half life of the isotope (nothing is lost) MUST be checked for integrity regularly - a good means of doing this is by wipe tests

9 Sealed and unsealed sources in radiotherapy Both are used to treat cancer Sealed sources are used for EBT and Brachytherapy - the Brachytherapy sources are discussed here Unsealed sources may be used for systemic treatments (Nuclear Medicine) as: 131-I for thyroid treatment 89-Sr and 153-Sm for treatment of bone metastasis.

10 2. The ideal source in Brachytherapy What do you think one would expect from and ideal Brachytherapy source? Clinical usefulness determined by Half life = the time after which half of the original activity is still present in the source Specific activity = activity per gram of material. The higher the smaller a source of a particular activity can be made Radiation energy determines the range of radiation in tissue (AND the requirements for shielding)

11 The Ideal Brachytherapy source Pure gamma emitter - betas or alphas are too short in range and result in very high doses to small volumes around the source Medium gamma energy high enough to treat the target with homogenous dose low enough to avoid normal tissues and reduce shielding requirements High specific activity suitable also for high dose rate applications small

12 The Ideal Brachytherapy source Stable daughter product For مؤقتtemporary implants: long half life allows economical re-use of sources For permanent implants: medium half life

13 3. Real brachytherapy Sources A variety of source types and isotopes are currently in use They differ for different applications because of half life, size (specific activity) and radiation energy When deciding on a source one must also keep the shielding requirements in mind.

Brachytherapy Sources Radionuclide Half-life Photon Energy (MeV) Half-value Layer (mm lead) 226 Ra 1600 years 0.047-2.45 (0.83 ave) 8.0 222 Rn 3.83 days 0.047-2.45 (0.83 ave) 8.0 60 Co 5.

14 Brachytherapy Sources Radionuclide Half-life Photon Energy (MeV) Half-value Layer (mm lead) 226 Ra 1600 years (0.83 ave) Rn 3.83 days (0.83 ave) Co 5.26 years 1.17, Cs 30.0 years Ir 74.2 days (0.38 ave) Au 2.7 days I 60.2 days ave Pd 17.0 days ave 0.008

15 Brachytherapy sources The first isotope used clinically was radium around 1903 However, radium and radon have only historical importance - they should not be used in a modern radiotherapy department

16 Brachytherapy sources Because: wide energy spectrum leading to high dose close to the source and still high dose around the patient - shielding difficult Radon, the daughter product of radium, is a noble gas which is very difficult to contain - contamination risk The long half life means disposal is very difficult

17 Popular sources: 137-Cs Cesium 137 Main substitute for radium Mostly used in gynecological applications Long half life of 30 years ---> decay correction necessary every 6 months Sources are expensive and must be replaced every 10 to 15 years

18 Popular sources: 192-Ir Iridium 192 Many different forms available Most important source for HDR applications Medium half life (75 days) - decay correction necessary for each treatment Needs to be replaced every 3 to 4 months to maintain effective activity and therefore an acceptable treatment time

19 Popular sources: 192-Ir Iridium 192 High specific activity - therefore even high activity sources can be miniaturized essential for HDR applications A bit easier to shield than 137-Cs - because the gamma energies of 192-Ir range from 136 to 1062keV (effective energy around 350keV)

21 Popular sources: 125-I Very low energy - therefore shielding is easy and radiation from an implant is easily absorbed in the patient: permanent implants are possible Mostly used in the form of seeds

22 125-I seeds Many different designs

23 125-I seeds Design aims and features: sealed source non-toxic tissue compatible encapsulation isotropic dose distribution radio-opaque for localization Mentor

24 X-ray visibility of 125-I seeds

25 Other isotopes used for seeds Palladium 103 Half Life = 17 days - dose rate about 2.5 times larger than for 125-I Energy = 22 kev TVL lead = 0.05mm Gold 198 Half Life = 2.7 days - short enough to let activity decay in the patient Energy = 412 kev TVL lead = around 8mm

26 Brachytherapy Sources A variety of source shapes and forms: pellets = balls of approximately 3 mm diameter seeds = small cylinders about 1 mm diameter and 4 mm length needles = between 15 and 45 mm active length tubes = about 14 mm length, used for gynaecological implants hairpins = shaped as hairpins, approximately 60 mm active length wire = any length, usually customised in the hospital - inactive ends may be added HDR sources = high activity miniature cylinder sources approximately 1mm diameter, 10mm length

Source form examples Seeds (discussed before): small containers for activity usually 125-I, 103-Pd or 198-Au for permanent implant such as prostate cancer Needles and hairpins:

27 Source form examples Seeds (discussed before): small containers for activity usually 125-I, 103-Pd or 198-Au for permanent implant such as prostate cancer Needles and hairpins: Scale in mm for life implants in the operating theatre - activity is directly introduced in the target region of the patient usually 192-Ir for temporary implants eg. of the tongue

28 Source form: 192-Ir wire Used for LDR interstitial implants Cut to appropriate length prior to implant to suit individual patient Cutting using manual technique or cutter...

29 Source form 192-Ir wires 192-Ir wire: activity between 0.5 and 10mCi per cm used for interstitial implants low to medium dose rate can be cut from 50 cm long coils to the desired length for a particular patient Length measurement Movement controls Shielding Wire cutter

30 Source form example 192-Ir wire: activity between 0.5 and 10mCi per cm used for interstitial implants low to medium dose rate can be cut from 50 cm long coils to the desired length for a particular patient Length measurement Movement controls Shielding Wire cutter

31 Question: Why would people use 198-Au for brachytherapy?

32 Some clues for an answer Key features of 198-Au are: small sources (seed) short half life (2.7 days) inert material photon energy 412keV Therefore, ideal for permanent implant

33 Brachytherapy Brachytherapy installations cover direct source loading 137-Cs sources for gynaecological applications (radium should not be used) permanent seed implants (gold or 125-I) surface applicators (moulds, 125-I, strontium and ruthenium plaques manual afterloading (137-Cs, 192-Ir) automatic afterloading (LDR, PDR and HDR)

34 Brachytherapy Highly customized treatment techniques - each patient is treated differently Techniques depend on Disease site and stage Operator/clinician Technology/equipment available Many of the points covered for External Beam installations also apply to Brachytherapy installations, particularly for automatic afterloading systems

35 Preparation of sources for brachytherapy Choosing the correct sources is an important part of the implant optimization This is applicable for situations when: there are several different sources available (eg 137-Cs source with slightly different length and activity for gynecological implants) sources are ordered and customized for an individual patient (eg. 192-Ir wire)

36 Require a pre-implant plan...

37 Choosing the correct sources Prepare a plan for a particular implant following the prescription Select appropriate sources If existing sources are to be used select sources from the safe and place in transport container Document what is done source safe shielding

38 Interstitial implants For LDR usually use 192-Ir wire (compare part VI) Optimization is possible as the length of the wire can be adjusted for a particular implant

39 HDR sources No preparation necessary Ensure source calibration optimized plan

40 Implant techniques Permanent implants patient discharged with implant in place Temporary implants implant removed before patient is discharged Here particular emphasis on radiation protection issues in medical exposures

41 Permanent Implants: Radiation protection issues Implant of activity in theatre: Radiation protection of staff from a variety of professional backgrounds - radiation safety training is essential RSO or physicist should be present Source transport always necessary Potential of lost sources

42 Problems with handling activity in the operating theatre The time to place the sources in the best possible locations is typically limited Work behind shields or with other protective equipment may prolong procedure and result in sub-optimal access to the patient

43 Working behind shields

44 Permanent Implants: Radiation protection issues Patients are discharged with radioactive sources in place: lost sources exposure of others issues with accidents to the patient, other medical procedures, death, autopsies and cremation - compare part XV of the course

45 Temporary implants Mostly done in afterloading technique Radiation safety issues for staff: Source handling and preparation Exposure of nursing staff in manual afterloading Radiation safety issues for patients: Source placement and removal

46 Afterloading Manual The sources are placed manually usually by a physicist The sources are removed only at the end of treatment Remote The sources are driven from an intermediate safe into the implant using a machine ( afterloader ) The sources are withdrawn every time someone enters the room

47 Afterloading advantages No rush to place the sources in theatre - more time to optimize the implant Treatment is verified and planned prior to delivery Significant advantage in terms of radiation safety (in particular if a remote afterloader is used)

48 Use of lead shield reduces scatter to the patient

49 High Dose Rate Brachytherapy Most modern brachytherapy is delivered using HDR Reasons? Outpatient procedure Optimization possible

50 HDR brachytherapy In the past possible using 60-Co pellets Today, virtually all HDR brachytherapy is delivered using a 192-Ir stepping source Source moves step by step through the applicator - the dwell times in different locations determine the dose distribution

51 HDR unit interface

52 4. Brachytherapy equipment Design considerations often similar to external beam therapy Nucletron

53 Remote Afterloading Equipment The most complex pieces of equipment in brachyhterapy Low dose rate units High dose rate units Many important design consideration in IEC standard

54 Low dose rate brachytherapy Selectron for gynecological brachytherapy 137-Cs pellets pushed into the applicators using compressed air Location of active and inactive pellets can be chosen by the operator to optimize the source loading for an individual patient Shown are 6 channels - the red lights indicate the location of an active source Nucletron

55 Other features No computer required Two independent timers Optical indication of source locations Permanent record through printout Key to avoid unauthorized use

56 HDR brachytherapy units Must be located in a bunker Have multiple channels to allow the same source to drive into many catheters/needles MDS Nordion

57 Nucletron HDR unit control Emergency off button Keypad Printout = permanent record Display Key Key for source out Memory card for transfer of the dwell positions for the treatment of a particular patient - labeled

58 Catheters are indexed to avoid mixing them up Transfer catheters are locked into place during treatment - green light indicates the catheters in use

59 Regular maintenance is required Source drive must be working within specified accuracy (typically 1-2mm) Emergency buttons must work Manual retraction of the source in case of power failure must work

60 Regular maintenance is required Maintenance work should follow manufacturers recommendations All modifications MUST be documented A physicists should be notified to perform appropriate tests

61 LDR and HDR units are not all... Other brachytherapy equipment: PDR (pulsed dose rate) units Seed implant equipment Endovascular brachytherapy

62 LDR and HDR units are not all... Other brachytherapy equipment: PDR units - similar to HDR Seed implant equipment - discussed in more detail in the second lecture of part VI Endovascular brachytherapy

63 Typical Radiation Levels Selectron LDR (Cs-137) Cervix insertion 10 pellets of 15 mci/seed = 150 mci 20 mr/h at 1m 0.2 msv/h 5 days for 1 msv (Background) this is inside the room! microselectron HDR (Ir-192) turned ON! 10 Ci source = mci 4700 mr/h at 1m 47 msv/h 1.3 minutes for 1 msv (Background) door interlock ensures that no-one is in room

64 Brachytherapy Techniques 1. Clinical brachytherapy applications 2. Implant techniques and applicators 3. Delivery modes and equipment

65 Brachytherapy Very flexible radiotherapy delivery Source position determines treatment success Depends on operator skill and experience In principle the ultimate conformal radiotherapy Highly individualized for each patient Typically an inpatient procedure as opposed to external beam radiotherapy which is usually administered in an outpatient setting

66 Clinical brachytherapy

67 History Brachytherapy has been one of the earliest forms of radiotherapy After discovery of radium by M Curie, radium was used for brachytherapy already late 19th century There is a wide range of applications - this versatility has been one of the most important features of brachytherapy

68 Today Many different techniques and a large variety of equipment Less than 10% of radiotherapy patients receive brachytherapy Use depends very much on training and skill of clinicians and access to operating theatre

69 A brachytherapy patient Typically localized cancer Often relatively small tumor Often good performance status (must tolerate the operation) Sometimes pre-irradiated with external beam radiotherapy (EBT) Often treated with combination brachytherapy and EBT

70 1. Clinical brachytherapy applications A. Surface moulds B. Intracavitary (gynaecological, bronchus,..) C. Interstitial (Breast, Tongue, Sarcomas, )

71 A. Surface moulds Treatment of superficial lesions with radioactive sources in close contact with the skin Hand A mould for the back of a hand including shielding designed to protect the patient during treatment Catheters for source transfer

73 Surface mould advantages Fast dose fall off in tissues Can conform the activity to any surface Flaps available

74 B. Intracavitary implants Introduction of radioactivity using an applicator placed in a body cavity Gynaecological implants Bronchus Oesophagus Rectum

75 Gynaecological implants Most common brachytherapy application - cervix cancer Many different applicators Either as monotherapy or in addition to external beam brachytherapy as a boost

76 Gynecological applicators Different design - all Nucletron

77 Vaginal applicators Single source line Different diameters and length Gammamed - on the right with shielding Nucletron

78 Bronchus implants Often palliative to open air ways Usually HDR brachytherapy Most often single catheter, however also dual catheter possible

79 Dual catheter bronchus implant Catheter placement via bronchoscope Bifurcation may create complex dosimetry

80 C. Interstitial implants Implant of needles or flexible catheters directly in the target area Breast Head and Neck Sarcomas Requires surgery - often major

81 Interstitial implants - tongue implant Catheter loop tongue tongue Button

82 Breast implants Typically a boost Often utilizes templates to improve source positioning Catheters or needles

83 2. Implant techniques and applicators Permanent implants patient discharged with implant in place Temporary implants implant removed before patient is discharged from hospital

84 Source requirement for permanent implants Low energy gammas or betas to minimize radiation levels outside of the patient (125-I is a good isotope) May be short-lived to reduce dose with time (198-Au is a good isotope) More details on most common 125-I prostate implants in section 4A of the lecture

85 Temporary implants Implant of activity in theatre Manual afterloading Remote afterloading

86 3. Delivery modes and equipment Low Dose Rate (LDR) Medium Dose Rate High Dose Rate (HDR) Pulsed Dose Rate (PDR)

87 Delivery modes - different classifications are in use Low Dose Rate Medium Dose Rate High Dose Rate Pulsed Dose Rate < 1Gy/hour around 0.5Gy/hour > 1Gy/hour not often used >10Gy/hour pulses of around 1Gy/hour

88 Low dose rate brachytherapy The only type of brachytherapy possible with manual afterloading Most clinical experience available for LDR brachytherapy Performed with remote afterloaders using 137-Cs or 192-Ir

89 Low dose rate brachytherapy Selectron for gynecological brachytherapy 137-Cs pellets pushed into the applicators using compressed air 6 channels for up to two parallel treatments Nucletron

90 Simple design No computer required Two independent timers Optical indication of source locations Permanent record through printout Key to avoid unauthorized use

91 Treatment process Implant of applicator (typically in the operating theatre) Verification of applicator positioning using diagnostic X-rays (eg radiotherapy simulator)

92 Treatment planning Most commercial treatment planning systems have a module suitable for brachytherapy planning: Choosing best source configuration Calculate dose distribution Determine time required to give desired dose at prescription points Record dose to critical structures

93 Treatment planning of different brachytherapy implants

94 High Dose Rate Brachytherapy Most modern brachytherapy is delivered using HDR Reasons? Outpatient procedure Optimization possible

95 HDR brachytherapy In the past possible using 60-Co pellets Today, virtually all HDR brachytherapy is delivered using a 192-Ir stepping source Source moves step by step through the applicator - the dwell times in different locations determine the dose distribution

96 HDR 192-Ir source Source length 5mm, diameter 0.6mm Activity: around 10Ci From presentation by Pia et al

97 Optimization of dose distribution adjusting the dwell times of the source in an applicator Nucletron

98 HDR brachytherapy procedure Implant of applicators, catheters or needles in theatre For prostate implants as shown here use transrectal ultrasound guidance

99 HDR brachytherapy procedure Localization using diagnostic X-rays HDR prostate implant: Simulator image Scout image for CT scan

100 Treatment planning Definition of the desired dose distribution (usually using many points) Computer optimization of the dwell positions and times for the treatment

101 Treatment Transfer of date to treatment unit Connecting patient Treat... Gammamed Nucletron

102 HDR unit interface

103 HDR brachytherapy Usually fractionated (eg. 6 fractions of 6Gy) Either patient has new implant each time or stays in hospital for bi-daily treatments Time between treatments should be >6hours to allow normal tissue to repair all damage

104 HDR units: different designs available

105 Catheters are indexed to avoid mixing them up Transfer catheters are locked into place during treatment - green light indicates the catheters in use

106 HDR systems Can be moved eg between different facilities or into theatre for intraoperative work

107 Pulsed dose rate Unit has a similar design as HDR, however the activity is smaller (around 1Ci instead of 10Ci) Stepping source operation - same optimization possible as in HDR Treatment over same time as LDR treatment to mimic favorable radiobiology In-patient treatment: hospitalization required Source steps out for about 10 minutes per hour and then retracts. Repeats this every hour to deliver minifractions ( pulses ) of about 1Gy

108 Feras Mansour Jargon فراس منصور جرغون IAEA Training Course: Radiation Protection in Radiotherapy slide 109

Brachytherapy an Overview

Brachytherapy an Overview Yakov Pipman, D Sc North Shore LIJ Health System Monterrey, Nov30-Dec1, 2007 Brachytherapy A procedure in therapeutic radiology that involves the irradiation of a target with