Brachytherapy Authorization and Inspection of Radiation Sources in

Brachytherapy

Authorization and Inspection of Radiation Sources in Radiotherapy Objective Module 2. 2 To become familiar with the sealed sources, devices and ancillary equipment used in brachytherapy. 2

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Contents • • • Radioactive sources Afterloading devices (HDR and LDR) Implants (permanent and temporary) Intravascular brachytherapy (IVB) Other techniques (e. g. eye applicators) Brachytherapy treatment planning 3

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 “Ideal” Brachytherapy Source The ideal brachytherapy source would be: • a pure gamma emitter with an energy suitable for the intended treatment site; q with a high specific activity; and q suitable for high dose rate applications. • physically small; • for temporary implants, a long half life; q to allow economical re-use of sources 10 mm • for permanent implants, a medium half life. 4

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Brachytherapy • Very flexible radiotherapy delivery • The source position determines the success of the treatment • In principle, it is the ultimate ‘conformal’ radiotherapy • Highly individualized • Dependent on operator skill and experience Conformal radiotherapy describes the attempt to conform the treatment volume as closely as possible to the actual target volume thereby sparing the surrounding normal tissue as much as possible. In general, the normal radiation safety considerations will also apply to conformal radiotherapy. 5

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Manual brachytherapy In manual brachytherapy several types of treatments are available, including: • Interstitial treatment of cancer • Intra-cavity treatment of cancer • Eye plaque implants • Topical application 6

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Manual brachytherapy 7

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Interstitial Treatments The following sources are routinely used: • 137 Cs and 60 Co as sealed sources in needles and applicator cells; • 192 Ir • 198 Au, 125 I as seeds or wires encased in nylon ribbons; and 103 Pd as sealed sources in seeds. 8

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Intra-cavity treatments The following sources are routinely used: • 137 Cs • 90 Sr and 60 Co as sealed sources in needles and applicator cells. as a sealed source in an applicator for the treatment of superficial eye conditions. 9

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Eye plaques • The eye plaque consists of a curved, soft plastic insert that has a series of grooves molded into the rear convex surface to hold the radioactive seeds. • Because the plaque is placed in the orbit of the eye over the tumor site and sutured to the sclera, this is considered interstitial, not topical / surface treatment. 10

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Topical (surface) treatments The following sources are routinely used: • 90 Sr • 137 Cs as a sealed source in an applicator for treatment of superficial eye conditions. and 60 Co as sealed sources in needles and applicator cells. 11

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 History Surface applicator with irregular distribution of radium on the applicator surface. (Murdoch, Brussels 1933) 12

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Surface Moulds Treatment of superficial lesions with radioactive sources in close contact with the skin. A mould for the back of a hand including shielding designed to protect the patient during treatment. 13

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Surface Moulds (cont) Treatment of superficial lesions with radioactive sources in close contact with the skin. Mould for the treatment of squamous cell carcinoma of the forehead. Catheters for source placement. 14

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Surface Moulds (cont) Advantages • Fast dose fall-off in tissues due to the inverse square law • Can conform the activity to any surface 15

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Brachytherapy Applicators 16

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Afterloading devices (HDR and LDR) HDR – high dose rate / LDR – low dose rate • Afterloading techniques are those in which non-radioactive applicators or guide tubes are initially placed in the patient and the radioactive sources are later loaded into these applicators • Depending on the manufacturer and model, remote afterloaders typically employ 192 Ir, 60 Co or 137 Cs sources 17

Authorization and Inspection of Radiation Sources in Radiotherapy HDR and LDR devices Module 2. 2 • HDR units typically have a single source with activities ranging from ~180 GBq to ~740 GBq. • LDR units may have single or multiple sources with activities of ~370 MBq to ~550 MBq. • Because of the higher activities involved, the shielding requirements for HDR are greater than LDR units. • HDR devices typically step the single source through a series of dwell positions while a LDR device does not reposition its multiple source string. • HDR employs shorter irradiation time at higher dose rates than LDR treatment. 18

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 HDR brachytherapy • Treatments are usually fractionated (e. g. 6 fractions of 6 Gy each); • Either the patient has a new implant each time or stays in hospital for bi-daily treatments; • The time between treatments should be >6 hours to allow normal tissue to undertake some recovery. 19

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 HDR brachytherapy 20

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 HDR brachytherapy (cont) Catheters are indexed to avoid mixing them up. Transfer catheters are locked into place during treatment - green light indicates the catheters that are in use. 21

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Intravascular brachytherapy • This technology uses radioactive catheters, pellets, and stents to treat coronary and peripheral vascular problems. • The radioactive source can be ion implanted, plated, or encapsulated in a sealed source device attached to a guide wire used in the angioplasty procedure. • The radioactive device can be either permanently implanted or removed via the guide wire following treatment of the affected vessel wall. 22

Authorization and Inspection of Radiation Sources in Radiotherapy HDR Planning • • Module 2. 2 Optimization procedure needs extensive checking. How are dwell times transferred to the treatment unit? Where is the source strength correction applied? How is transfer time modeled? 23

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Tests for brachytherapy sources The following should be done on receipt of sources and documented. • Physical / chemical form • Source encapsulation, wipe test • Radionuclide distribution and uniformity: q autoradiograph q uniformity of activity amongst seeds q visual inspection of seeds in ribbons 24

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 Tests for brachytherapy sources (cont) Calibration • Ideally, the calibration of all sources should be checked on • • receipt However, for a large number of short lived sources a sample check (~10%) may be satisfactory Document results Suggested calibration tolerances: q mean of batch: 3% q deviation from mean: 5% Review manufacturer’s documentation for tolerances 25

Authorization and Inspection of Radiation Sources in Radiotherapy Source accountability Module 2. 2 Sources must: • be stored securely to prevent unauthorized access • be audited regularly to confirm the source inventory in compliance with the requirements of the Regulatory Body 26

Authorization and Inspection of Radiation Sources in Radiotherapy Source accountability Module 2. 2 Source inventory records should identify: • The radionuclides and source activities; • The location and description of sources; • Disposal details (including permanent implants in patients). 27

Authorization and Inspection of Radiation Sources in Radiotherapy Module 2. 2 References • Johns H E and Cunningham J R 1983 The Physics of Radiology, 4 th edition (Springfield: C Thomas). • Khan F M 1994 The Physics of Radiation Therapy, 2 nd edition • • (Williams & Wilkins, Baltimore). Williams J R and Thwaites D I 1993 Radiotherapy Physics in Practice (Oxford: Oxford University Press). International Commission on Radiation Units and Measurements. Determination of dose equivalent resulting from external sources, ICRU report 39, Bethesda: ICRU; 1985. • International Commission on Radiation Units and Measurements ICRU 55, Bethesda. Prescribing, recording, and reporting interstitial brachytherapy, 1993. 28