Intro to Brachy Flashcards
What is the definition of Brachytherapy?
A ‘near treatment’ - sealed sources placed close to, in contact with, or inside the volume of tissue to be treated
It can also include miniaturised electronic radiation sources
Why is Brachytherapy used?
Gives high dose to the target volume with rapid inverse square law fall off
Low integral dose
Can optimise by adjusting source dwell positions and dwell times
Gives the same dose to the CTV whilst reducing the OAR doses
Sources move with the target
No external beams passing through normal tissue
Radiobiology can be better as fewer fractions can be used and there is greater conformality
When is Brachytherapy used?
Post surgery to irradiate any remaining clonogenic cells
As a boost for EBRT
Monotherapy where EBRT and surgery aren’t available
What are the disadvantages of using Brachytherapy?
Invasive surgery - time consuming, need lots of resources
Geometric misplacement results in poor coverage due to rapid fall off of dose
Large volumes (>5cm) lose the inverse square law advantage
Need specific radiation protection and security requirements
What are the 4 pieces of legislation around Brachytherapy?
Sealed sources registration permit
HASS
ARSAC
EURATOM
What is the Sealed Source Registration Permit required by?
Environmental Permitting Regulations 2016 - England and Wales
Radioactive Substances Act 1993 - Scotland
What does the Sealed Sources Registration Permit application include?
Sources held, how they are stored, how they are used
Need to reapply if adding sources or changing premises
Includes HASS form
What is HASS?
High Activity Sealed Sources Directive 2005
What are the aims of HASS?
To prevent exposure of workers and the public to radiation arising from inadequate control of high activity sealed radioactive sources
To harmonise controls in place
Set out specific requirements for control
Which sources require a HASS form?
Those with an activity at the time of fabrication of > 1/100 x A1 value in IAEA regs for safe transport of radioactive materials
What is needed to get a HASS permit?
Prior authorisation for any practice involving HASS
Demonstrate adequate management arrangements
Adequate provision, financially or otherwise, made for safe management of HASS when they become disused
Responsibilities, training, equipment, and emergency procedures
Record keeping by users and competent authorities
Security arrangements in liaison with local counter terrorist security
What is required in a HASS site security plan?
Posts and responsibilities Specifications of competence (job descriptions) Details of information and training Operating procedures Outline of maintenance Emergency procedures
What does the level of security at a HASS site depend on?
isotope and activity - specified in table produced by National Counter Terrorism Security Office and National Security Advice Centre
What does a level 1 site require?
Security plan
Ability and options to upgrade security
Information security plan
Personnel background checks
What does a level 2 site require?
Sources protected by 1 physical security measure
What does a level 3 site require?
2 physical security measures, intruder alarm with either a local or police response
What does a level 4 site require?
The same as level 3 but with the intruder alarm externally monitored and the response must be from the police
What are the requirements for obtaining an ARSAC licence?
For an oncologist to prescribe Brachy treatments
Must demonstrate the Oncologist’s qualifications, experience, the source type to be used, and scientific support
Needs to be renewed every 5 years
What is EURATOM?
Permission from the Environment Agency to ship sources between EU member states
Requires form detailing the sender and receipt of sources and the quantity per shipment
Renewed every 3 years
What factors are considered when deciding on a Brachytherapy source?
Photon energy spectrum - 0.2-0.4MeV ideal
Charged particle emissions - avoid except pure beta emitters
Source size - small
Specific activity - high=small source
Half life - depends on use
Source strength
Decay scheme - are daughter elements radioactive
Physical form
What is the average photon energy from Ra-226?
0.83MeV
How was Ra-226 available?
Needles loaded into gold cells - 1cm long, 1mm diameter encased in platinum to prevent leakage, prevent alpha/beta particles escaping, provide strength and rigidity
What are the advantages of using Ra-226?
Long half life
Lots of experience using it
What are the disadvantages of using Ra-226?
Gaseous recay product, Ra-222, which is radioactive
Low specific activity
Bulky source
High energy beta emissions - needs heavy screening to avoid necrosis
High energy photons - needs shielding
