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CSH076 > QA of specialised techniques > Flashcards

QA of specialised techniques Flashcards

1
Q

Quality Assurance: Definition

A

Refers to systematic program designed to ensure that the performance of equipment, procedures and processes involved in RT meets defined standards of safety, accuracy and consistency

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2
Q

Key Elements of QA in RT

A

Consistency

Safety

Reliability

Accuracy

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3
Q

General Components of QA in RT

A

Administrative Policies
* Define the roles and responsibilities of the staff, including the RO, physicists, RTs and dosimetrists
* Protocols include frequency

Quality Control

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4
Q

QA for Brachytherapy

A
  1. Source Calibration
    * After every source exchange, the physicist checks the source strength (with ionisation chambers and electrometers)
  • Ensure the activity matches the TPS
  1. Applicator QA
    * All clinical applicators need to be comprehensively QA’d prior to clinical use
  • Physicist must determine that the source can travel accurately to intended locations within the applicators
  • Must also confirm that the total treatment length (applicator plus transfer tube) coincides with the planned one
  1. Ionisation Chamber and Electrometer
    * Checks are conducted by physicists to verify reproducibility, sensitivity, and linearity of the instrument (must be documented at least annually)
  • Ionisation chamber and electrometer must be calibrated at least every 2 years at the ADCL facility
  • Constancy of the ionisation chamber and electrometer used for calibrating the HDR source must be checked upon receipt, after repair and prior to each use.

Plan: RTs do QA, independent dose calc check by RO, MP, AAPM manual calculation form check by MP

Treatment: pre and post treatment survey, physicists/RTs use the survey meter to ensure that source has returned home

Physicists check source strength and complete a form with total dwell time and activity

After treatment planning:

Before each application, check source strength and check that it matches values

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5
Q

Brachytherapy Emergency Procedures

A

Steps:
1. Press emergency stop button
2. MP enters room with dose meter
3. If radiation is detected by survey meter, turn hand crank till it blocks
4. If dose meter is still beeping, RO needs to enter room and remove applicators from patient
5. Put applicators in a container
6. RTs get patient out to a safe area
7. All staff leave the room, close door and alarm
8. Survey all staff and patient
9. Call engineers

*Emergency procedures are vital in cases of equipment or source misplacement

  • Ensures the source can be retrieved safely and the patient is protected from unnecessary radiation exposure
  • In cases where the applicator collides with the transfer tube or the equipment malfunctions, the emergency stop button should be pressed, and the source should be manually retrieved using specific emergency tools
  • Post-treatment survey is conducted to confirm that the source has returned to its safe position and no radioactive material remains with the patient –> maintain patient safety before they leave the treatment room
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6
Q

SRS/SRT: Definition

A

SRS –> single, high dose radiation treatment

SRT –> delivers high dose radiation in multiple fractions

Both target small areas with high degree of precision

Due to high precision required, stringent QA procedures are required

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7
Q

SRS/SRT QA Goals

A

Target Localisation
* Ensure that the target area is correctly identified and positioned during each treatment session

Mechanical Isocentre Accuracy
* Essential to verify that the mechanical isocentre (gantry, collimator, and couch axes) aligns with the radiation isocentre
* Typical tolerance = < 1mm

Dosimetry
* Phantom tests are used to verify the planned dose distribution matches the actual delivered dose

Image Guidance System
* Ensures the patient positioning aligns with the treatment plan before each session

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8
Q

SRS/SRT: QA of Radiation Isocentre

A

Radiation Isocentre
* The point in space where radiation beams intersect when the gantry is rotated during beam-on

QA Process:
1. Radiation isocentre is typically identified by exposing film dosimeters to multiple exposures with slit-like fields

  1. Collimator, gantry or couch is then rotated, and the field is re-exposed
  2. Performing this test on multiple angles for each collimator, gantry, or couch allows the determination of the isocentre and the error in its positioning
  3. Typically, the radiation isocentre is kept within the 1mm movement in all planes
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9
Q

SRS/SRT QA: Wintson Lutz Test

A

Used to verify that the radiation isocentre aligns with the mechanical isocentre

Procedure
1. Small metallic ball is placed at the machine’s isocentre defined by the room lasers of the treatment room

  1. Machine delivers beams from multiple gantry, collimator and couch angles
  2. Metallic balls is imaged using film or EPID
  3. Distance between the centre of the ball shadow and the radiation field is measured to reveal isocentre movements
    * Deviations should be less than 1mm to ensure treatment accuracy
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10
Q

Gamma Knife Overview

A

Used for SRS treatments, particularly for small complex brain lesions

Uses multiple cobalt-60 sources to deliver radiation to the target area with extreme position

QA for Gamma Knife includes routine checks for the machine’s dose output, source strength, and safety systems

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11
Q

Daily QA for Gamma Knife

A

Daily checks:
* Functionality of the unit on a short test run
* Checking the daily decayed estimate of standard
* Absorbed dose rate computed by the TPS

Output Verification (Elekta Gamma Knife Perfexion)
* Diode test tool (consisting of 4 diodes) measures output during a 4 min exposure for comparison against pre-computed profiles

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12
Q

Gamma Knife: Weekly QA

A

Check functionality of emergency alarms and interlocks

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13
Q

Gamma Knife: Monthly QA

A

Regulatory agencies require an output measurement be performed by a ‘spot check’
* result should be within 1-2% of that predicted by the last annual measurement

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14
Q

Gamma Knife: Monthly QA: Spot Check

A

Simplified and quick output measurement of the machines radiation delivery

  1. Position the phantom on the treatment couch (in alignment with the isocentre)
  2. Ensure dosimeter or ion chamber is properly calibrated and positioned within the phantom, at the machine’s isocentre
  3. Run a predefined QA treatment plan (typically delivers a fixed radiation dose to the iso)
  4. Check dose output measures on dosimeter to reference values from the last annual calibration
  5. Record the dose values in the QA log for documentation and future comparison
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15
Q

Gamma Knife: Dosimetry QA

A
  • Dosimetry Phantom is used to accurately measure absorbed dose and dose ate in Leksell Gamma Knife
  • Three adapters for measuring with ionisation chamber or other detectors are included
  • The dosimetry phantom can also be used to verify dose 3D distributions by means of film dosimetry
  • Dose distribution position is defined by accurately positioning the films in the phantom using two rods
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16
Q

Tomotherapy QA: Guidelines

A

AAPM TG 148:

Attention should be the accuracy of laser localisation, geometric distortions and the concordance of imaging, treatment delivery, and laser position

17
Q

Tomotherapy: Daily QA

A

Beam Output:
1. Common phantoms used (TomoDose or ArcCheck)

  1. Verify alignment of phantom with machine isocentre with a MVCT
  2. Run a pre-configured Daily QA plan stored in the TPS –> used to verify both beam output and beam uniformity
  3. Embedded ionisation chambers or diodes record the radiation dose
  4. Beam flatness and symmetry will also be assessed
  5. Document results in daily QA log

MVCT Image Quality Consistency:
1. Catphan or Image Quality Phantom is used (contain different objects like spheres, grids and inserts)
* Assess contrast, spatial resolution and uniformity

  1. Perform an MVCT scan
  2. Acquired data is reconstructed into a 3D image data set
  3. Assess Imaging Parameters
    Contrast Resolution
    * Ability to identify contrast inserts representing materials of differing densities

Spatial Resolution
* Assess line pair patterns used to represent different frequencies

Noise Levels
* Measure the SD of CT numbers in a homogenous region

Uniformity
* Select multiple ROIs across the phantoms homgenous region

Geometric Accuracy
* Assess known geometric structures in the phantom (e.g., grids) and verify their dimensions in the reconstruction

18
Q

Halcyon: What is IBA my QA Halo and it’s Benefits.

A

IBA myQA Halo
* Specialised solution for commissioning and QA of Varian Halcyon
* Provides efficient workflows, ensuring the commissioning of the machine is accurate and reliable

Benefits:
* Efficient Data Processing –> speeds up data collection and analysis, ensuring quick commissioning

  • High accuracy –> provides precise measurements
  • User friendly interface –> myQA software offers an intuitive interface, simplifying complex data analysis and reporting
  • Automated Reporting –> generates detailed reports, ensuring compliance with regulatory and clinical requirements
19
Q

Halcyon: Key Steps in Commissioning

A
  1. Beam Data Acquisition
    * Use IBA Blue Phantom system along with the myQA Halo software to capture all beam parameters across various field sizes
  • Data is comparted to expected baseline values for the 6MV beam to ensure consistency with the TPS
  1. Output Calibration
    * Use calibrated ionisation chamber and electrometer
    * Adjust output so that 1 MU delivers exactly 1cGy at a reference depth in a 10x10 field
  2. Beam Profile and Symmetry Checks
    * Measure flatness and symmetry using ionisation chambers and diode arrays with the IBA myQA system ,
  3. MLC Commissioning
    * Perform tests like picket-fence or MLC leaf speed tests to confirm leaf positions and movements are within tolerance
20
Q

Halcyon: Daily QA

A
  1. Beam Output Check
    * Use ionisation chamber (e.g., PTW Farmer Chamber or Sun Nuclear QA3) to measure dose output
    * Compare to expected output
    –> Tolerance: +/- 2%
  2. Mechanical System Checks
    * Visually inspect gantry, collimator and couch for signs of wear or damage
    * Verify movement to programmed positions accurately
  3. MLC Checks
    * Use picket-fence test to check alignment of the MLC leaves
    * Deliver test beam through MLC and image the result with a portal imager or a detector
  4. Imaging System QA
    * Perform a test scan with a QA phantom (e.g., Catphan phantom)
    * Assess contrast, resolution and geometric accuracy to determine image quality
  5. Laser Alignment Check
    * Verify accuracy by aligning with phantom
    * Check lasers intersect at the correct point relative to the machines iso
  6. Collision Interlock and Safety Systems Check
    * Check all emergency stop buttons and other safety interlocks to ensure they work as expected
    * Test collision avoidance system
  7. Door interlock and Radiation Monitor Check
    * Ensure door interlock and lights are functioning correctly
    * Test radiation monitor
21
Q

ACDS role

A

Annual newsletter: audit process for online adaptive development

Has been building national dataset to include the adaptive cases and is now including comparative graphs in report used for MR Linacs

22
Q

MR QA

A

ACR guidelines -> they conduct different components of QA on different days

23
Q

AAPM role in Brachy QA

A

QA program: AAPM proposing annual peer review mechnisms

Acceptance testing ->Commissioning -> calibration -> instrumentation -> tx delivery unit -> applicator QA -> Radiation safety -> routine QC tests

24
Q

AAPM 54

A

SRT QA guidelines:
Stereotactic frame

Isocentric alignment

CT image resolution

Tissue motion

MR distortion

25
Q

Brachy daily QA by RTs

A

Afterloader indicators on/off

Video cameras functional

Intercoms functional

Emergency procedures posted

Survey meter function

UPS from console function for 5min

Source retracts on battery without power

Source travel distance (cam scale) (tolerance 1mm)

Visual inspection of HDR unit

Primalert function/radiation area monitor

Time test -> time spent at each position (dwell time)

Console key test

Emergency stop on console

Emergency stop on wall (door)

Door interlock (door indicators and status lamp)

Afterloader key test -> can stop treatment

Turret lock test

Misconnected applicator

Obstuction test: not always recommended, blocks source from coming out, can cause deformation to source

Console displays, indicators and status lmp functional for all tests

Check the date/time in the computer (planning and console)

Source strength on console and table (daily changes in activity)

Visual inspection of applicators

3-channel test (If using that day)

Emergency kit inventory

Treatment console printer (functioning and paper supply)

Patients to be treated/applicator (mechnical integrity of all applicators source guide tubes and connectors)

26
Q

Applicator QA

A

Physicist must determine that the source can travel to intended locations in the applicators and must confirm that the total treatment length coincides with the planned one

27
Q

Instrumentation for brachytherapy QA

A
  • the constancy of ionisation chamber and electrometer used for calibrating the HDR sources must be checked upon receipt, after repair and prior to each use
  • ionisation chamber and electrometer must be calibrated at least every 2 years at the ADCL facility
  • sensitivity, linearity and reproducibility of the intrument must be documented at least annually
28
Q

CYBERKNIFE daily qa

A

Output
MLC qa
Flatness
Symmetry

CSH076 (11 decks)

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