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Physics 632 > Week 3 Quality Assurance > Flashcards

Week 3 Quality Assurance Flashcards

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1
Q

quality assurance

A

Program that is designed to control and maintain the standard of quality set for that program
Rad Onc: set of policies and procedures to maintain quality of patient care
set collectively by the profession

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2
Q

Dosimetric Accurary

A

+/- 5%: equipment calibration, treatment planning, patient setup
Errors: random and systematic,
Ion chamber uncertainty 1.5%
Estimated overall machine calibration uncertainty 2.5%

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3
Q

Acceptance testing required

A

New piece of equipment- linac, sim, brachy sources

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4
Q

Linac Acceptance testing

A

Radiation survey-does not exceed permissable doses, formal: head leakage, area survey, interloks, warning lights, emergency switches
jaw symmetry (error less than 1mm)
coincidence: collimator axis, light beam axis, cross hairs
light field with xray beam–+/-2mm, 1% on the side
Mechanical iso: collimater, rotate with rod attached, noting distance of rod to iso= tol 2mm diameter circle
Gantry rotation: same rod, with ring, rotate 360, not displacement, tol +/- 1mm

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5
Q

Acceptance: radiation isocenter collimator

A

collimator: place film on couch, open 1 set of coll wide, other small slit, rotate coll, do 6-7 exposures, repeat for opposite jaws with new film. intersection tolerance 2mm diameter circle

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6
Q

Acceptance: radiation iso treatment table

A

film on table, open small split in lower jaws, rotate couch, multiple exposures. tol 2mm diameter circle at intersection

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7
Q

Acceptance: radiation iso Gantry

A

film on table perpendicular, slit opening, 12 exposures at 30 degree intervals, 2mm circle

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8
Q

Acceptance: multiple beam alignment check

A

more than 1 beam
causes: focal spot displacement, assymmetry of col jaws, displacement in coll or gantry rotation
Split field test

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9
Q

Acceptance: MLCs

A

TG40
Projected leaf width at iso: film
Cal of leaf positions: film at iso with buildup, expose up to 8 fields, matchlines every 5cm
Leaf travel: max range of leaf travel in both directions
transmission: intra and interleaf, and beneath jaws/leaves
leakage: leakage when mlc leaves closed, check w ion chamber or film
Field shaping: series of irregularly shaped fields
IMRT additional tests

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10
Q

Acceptence Electrons: Energy

A

Depth dose distribution: practical method of specifying clinical beam energy
CAX curve is measured with ion chamber in a water phantom and compared to published data to specify the energy
10 x 10 cm field size, 100cm SSD, and 10cm depth

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11
Q

Acceptence Electrons:Field Flatness

A

Traditional definition: the transverse variation of dose relative to the CAX over the central 80% of the field size at 10cm depth plane perpendicular to the CAX
Tolerance: ± 3%
Flattening filter & penumbra

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12
Q

Acceptence Electrons: Field symmetry

A

Beam profiles for flatness can be used here

Tolerance: 2% at any pair of points situated symmetrically with respect to the CAX

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13
Q

Acceptance: wedge

A

10 x 10 field
Tolerance: ± 2 degrees of values specified
The angle between the isodose curve and the line perpendicular to the central axis at a specified depth (often 10cm).
Side Note: Wedge Angle = (180o – hinge angle)/2

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14
Q

Acceptance: Conventional Sim

A

Geometric and special accuracies
Performance evaluation of the x-ray generator and the associated imaging system
If used for mimicking the LINAC, then geometric accuracy should be comparable

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15
Q

Acceptance: CT sim

A

Accuracy of image from the CT scanner
Alignment of simulation hardware
Lasers
Couch alignment under typical load conditions
Accuracy of target localization & accuracy of DRRs
+/- 5HUs for daily tolerance

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16
Q

Acceptance: brachy

A

.Source Identity:Check physical length, diameter, serial number, and color-coding of all sources
.Source Uniformity & Symmetry
Autoradiograph: distribution of activity & active length
.Source Calibration: Individually calibrated to check source strength
Well-type ionization chamber
National Institute of Standards & Technology (NIST)
Tolerance: ± 5%
.Applicator Evaluation
Applicators hold sources in specific geometry and some have shielding
Orthogonal radiographs
Dummy sources
Shields compared to vendor’s drawings
Mechanical function (source loading and removal)
.Interstitial Sources
Needles (Cs-137)
Sources tested the same as intracavitary
Short-lived sources (seeds, wires, or seed loaded ribbons) can be tested by visual check from behind a leaded glass window

17
Q

Acceptance: Remote Afterloader

A 
\+Source Positioning
Radiograph of dummy & autoradiograph of sources
Position Tolerance: ± 1mm
\+Source Calibration
=Well ionization chamber
LDR sources
HDR sources –must be able to measure large currents
=Cylindrical ion chamber
LDR & HDR sources
Farmer-type, using free-air geometry
Must have appropriate build-up cap
18
Q

Commissioning

A

Most equipment ready after acceptance testing, but some need additional data before using with patient treatments
LINAC- calibrated, beam data
Treatment Planning Computer- isodose lines
Once all the beam data is acquired and in the treatment planning system, the machine is commissioned for clinical use

19
Q

Linac Commissioning: Central Axis Depth Dose Tables

A

PDD & TPR/TMR
Manually interpolation
Tolerance ± 2% (preferably ± 1%) of manually measured & computer generated

20
Q

Linac Commissioning: Isodose Curves

A

Central Tolerance: ± 2% (up to about 1cm from field edge)

Penumbra region Tolerance: 2mm (between 90% & 20% ISL)

21
Q

Linac Commissioning: MU calculations

A

MU- deliver a certain dose at a point of depth on the CAX

Number of dosimetric quantities have to be measured

22
Q

Linac Commissioning: MLC

A 
Transmission
Average leaf and interleaf < 2%
CAX Depth Dose
Spot-checked to show agreement
Penumbra
Dose distribution profiles of MLC-generated fields and conventional collimators should be compared
23
Q

Treatment planning commisioning: Hardware

A

Accuracy and linearity of input digitizers, output plotters & printers

24
Q

Treatment planning commisioning: Software

A

Accuracy of dose distribution

25
Q

Treatment planning commisioning: Algorithm verification

A

Accuracy, precision, limitations & special features

26
Q

Treatment planning commisioning: brachytherapy software

A

Testing of linear source and seeds
Dose distributions
Strength, filtration, tissue attenuation, source anisotrophy

27
Q

Periodic Quality Assurance

A

Maintain system within it’s acceptable limits
Tests similar to acceptance testing on a regular basis
LINAC
AAPM TG-40 & AAPM TG-142
Must log QA measurements
Procedure for variations

28
Q

Linac Tolerances:

A

TG- 142: Tables 17.8 A,B,C (Daily, Monthly, Annual)
AAPM Task Group 50: Table 17.9 (MLC)
Refer to Khan to study these

29
Q

Treatment planning algorithms

A

Based on physics of radiation interactions within tissue
Complex- so uses simplifications for speed
Uncertainties
Monte Carlo is the gold standard
Provided by manufacturer

Require basic radiation data
Specific to each energy & each machine in a department

Patient-Specific Information
CT, MRI
Dose calculations are usually performed for each beam independently, then summed

30
Q

Treatment planning process: Patient Data

A

CT
Patient positioned to identically to the eventual treatment
Data must be transferred correctly into the TPS
Conversions of CT numbers to electron densities must be correct (phantom with known electron densities)

31
Q

Treatment planning process: Display of Patient Data

A

Manipulate display, slices, reconstruction of images

32
Q

Treatment planning process: Display of Beam-Related Information

A

Field size, beam direction, collimator rotation

Field shape: jaws, MLCs, auto surround

33
Q

Treatment planning process: Dose Calculation and Display

A

Accuracy of the geometric correctness of isodose lines are difficult to assess

34
Q

Treatment planning process: Output

A

Printing the plan, distribution, magnification

35
Q

Measurements: In Vivo

A

Measurements on or in the patient with the patient in treatment position
TLD, OSL, diode or MOSFET devices
Used when there is concern about critical structures (eyes, gonads, or a fetus)
Or for coverage

36
Q

Measurements: In Vitro

A

Measurements on a special-purpose or anthropomorphic phantoms
Helpful in new treatment techniques
Uses TLD’s or OSL in the phantom that has humanlike tissue densities and composition (Rando)
Agreement should be 3-4%, since dose delivery to the patients should be ≤ 5%

Physics 632 (7 decks)

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