TG53 Flashcards
what is TG53 on?
QA of treatment planning
7 QA concepts regarding TPS
-acceptance testing and specs
-testing of non-dosimetric aspects
-testing of dosimetric aspects
-routine QA testing
-QA of clinical use of TP throughout planning and treatment process
-computer systems
-vendor and user responsibilities for QA and vendor support
8 parts of treatment planning process
- patient positioning and immobilization
- image acquisition and input
- anatomy definition
- beam/source technique
5.dose calculations
6.plan evaluation
7.plan implementation
8.plan review
sources of uncertainties in treatment planning
-patient localization
-imaging
-definition of anatomy
-establish beam geometry
-dose calculation
-dose display and plan evaluation
-plan implementation
2D TPS
-no CT data, only manual contour input
-only allows axial beams
-no blocks or compensators
-2D algorithm
error in PTV creation for traditional vs 3D TPS
0.5-10 cm
vs
0.3 cm
error in dose in penumbra for 2D vs 3D TPS
2-5 mm vs 1-5 mm
error in dose to norm pt in blocked field for 2D vs 3D
10% vs 2%
error for dose under block in 2D vs 3D TPS
> 100% vs 2 %
-traditional system cannot handle blocks
error for dose in central axis slice, central 80% of beam, for 2D vs 3D TPS
1% for both
does it make sense to write a spec requiring 2% TPS dose accuracy?
This is much too broad a statement.Where? Under what circumstances? With what input beamdata? In addition, satisfaction of specifications usually should not be dependent on clinic-specific beam data since a vendor typically cannot test or verify the quality of an indi-vidual clinic’s data
-have to make the spec testable..
3 categories for items suitable for spec
-computer hardware
-software features and functions
-benchmark tests
what is benchmark test
Performance on benchmark tests indi-cates the accuracy of the dose calculation algorithm un-der very specific circumstances with specific beam data.Calculation times can also be measured
why do we test parameters used to determine things like pixel size, slice thickness, orientation?
Vendor and scanner-specific file formats and conventionscan cause very specific geometrical errors when convertedfor RTP system
3 ways bolus may be used
Definition of external bolus on the surface of the pa-tient.* Modification of the CT-based electron densities in acertain region of the patient~e.g., to edit out the effectsof contrast material!.* Introduction of bolus material into sinuses or other bodycavities
tests regarding boluses
-density in bolus is correct value
-tools read the correct density in bolus
-verify it is accounted for in dose calculation
-verify bolus is displayed properly
beam parameters regarding beam geometry
- isocenter location and table position* gantry angle* table angle* collimator angle
beam parameters regarding field definition
- source-collimator distance* source-tray distance* source-MLC distance* collimator settings~symmetric or asymmetric!* aperture definition, block shape, MLC settings* electron applicators* skin collimation
how often should tests on system readout conventions and motion descriptions be completed?
Verify the accuracy of this information at the commissioning of the RTP system and at each major software update
ex: beam diverges away from source, hot spot for wedge is under toe,
what are DVHs prone to?
grid alignment errors
tests on algorithm
-regions to be calculated
-grid definition- dose is invalide if grid is changed, inerpolation between point, uniform or non-unifrom grid space
-how are density corrections stored and documented
-functionality of reading stored info
-rules for recalculation when changes are made- is only affected beam re-calculated?
-verify default algorithm is appropriate
where are NTCP and TCP used in TPS
-sometimes models are used to help evaluate competing treatment plans
issues with coordinate systems and scale conventions
issues when TPS are not the same as that used by department
a dose calc test for brachy that is different than EBRT
Brachytherapy source arrangements consist of indi-vidual sources, but they are often grouped as strings,trajectories, or applicators. One should confirm that pa-rameter changes which should affect an entire group ofsources are correctly made.
common issues with commissioning TPS
-input data- does TPS reproduce input data
-does algorithm work correctly
-calculation verification (between TPS and measured data)
-applicability and limits of TPS
-dose verification over range of clinical usage
methods for obtaining a self-consistent data set
-use same equipment and procedures for similar measurements
-use reference chamber (or integration mode for small field)
-use same measurement session for related data
-periodically repeat vase measurement to monitor consistency of machine output and measuring system
most common method of inputing data into PTS
direct transfer from computer controlled water scanning system
what info should be included in water scanning sofware file?
-file name in water tank system and TPS
-date of measrurement
-beam energy, field size etc
-3D coordinate system of water tank and its relation to TPS coordinates
-scan parameters (direction, depth, mode)
what is distance map?
shows distance between particular isodose lnes in calculated and measured distributions
data comparison methods
1-D lines
tables of differences
2-D lines
colorwash dose displays
dose difference displays
DVH analysis
distance maps
accuracy achievable for different aspects of RT, per Cunningham
2.5% - beam calibration
3-4% relative dose calc
3-4% beam delivery
5% overall
different parts of beam that should be analyzed separately (don’t combine low dose gradient with high)
-inner beam
-penumbrl region
-outside region
-buildup region
-central axis
-absolute dose at beam normalization point
typical acceptable dose error in build-up region
20-50%
daily TPS process QA checks
error log
change log - keep log of hardware or software changes
weekly TPS process QA checks
-digitizer accuracy
-hardcopy output- ex scaling for plotter
-computer files- verify integrity with checksums
-review clinical planning (errors, problems etc)
monthly TPS process QA checks
CT data input accuracy into TPS
review all problems
Review current configuration and status of all RTP system software,hardware, and data files
annual TPS process QA checks
-dose calculations: agreement between measured and calculated
-data and input/output devices
-critical software tools like BEV generation, DVH calculations
when might you check beam parametrization for TPS?
-machine changes or problems
most important part of TPS QA program
NOT dosimetry tests
-design and implementation of a clinical planning/delivery process that incorporates QA elements to comprehensively check all aspects of the planning and delivery for each pa-tient and each plan
how many software errors are theer?
1 in every 100-1000 lines of code
what does treatment plan review consist of?
The physician and a second treatment planner/physicist should review the plan, including alltreatment parameters, before implementation.
what does MU review consist of?
Monitor unit calculations should be reviewed by a second physicist, preferably before treatment starts, but certainly before the third fraction or 10% of the dose has been delivered
SSD checks
SD to the central axis of each treatment field should be measured during simulation and periodically during treatment and compared to that used in the treatment plan.
External beam plan implementation review
check:
-all parameters transferred to machine properly
-portal images can verify patient position and blocks
-check for collisions
Brachytherapy plan implementation review
confirm before the brachytherapy sources are placed into the patient that all source and plan information was correctly transferred from treatment plan to the treatment documentation or patient chart
.* Dose calculations and prescription should be verified as accurate and appropriate before treatment begins.
* Confirmation of source location and loading, if possible, should be performed as soon after loading as possible.
frequency of backups
daily: incermemental backups of all new or altered files
weekly: backups of all treatment plan related files
monthly: backup of entire system
suggested vendor documentation for version upgrades
-list of bugs fixed
-implications of the fixes
-new features
-components that work differently than before
-suggestion for tests the user can perform
-relevant results from beta testing
-how to convert old patients into new formats
-list of know bugs and limits
open field data is acquired for what fields?
square fields, standard SSD
square fields, extended SSD
rectangular fields
test for patient shape effects
oblique incidence
surface irregularity
tangential geometry
square phantom - Compare measurements with beam centered on phantom and with beam off-center and flashing off one edge.
brachy TPS considerations
-source library (up to date)
-source strength and decay
-check each alogorithm against independent computer calculations oand published reference data
brachy single source tests for TPS
-isotropic dose distribution
-anisotropic factors
-geometry fators
-shielding effects
global system tests in brachy
test the overall behavior of thesystem, including source input, identification of sources fromthe source library, source arrangement, dose calculation, andevaluation of the dose distribution. The procedure for each ofthese system tests should follow, as closely as possible, thenormal procedures used in the clinic.
