Radiotherapy Planning FRCR CO2A Flashcards
1
Q
Why is it important to understand basic techniques of radiotherapy planning?
A
These techniques help in developing complex plans and are used by the Physics Department for checking calculations before treatment.
2
Q
What are the stages of radiotherapy planning?
A
- Patient preparation, position, and immobilisation. 2. Localisation method. 3. Definition of target volumes and organs at risk. 4. Radiotherapy technique. 5. Prescription. 6. Verification.
3
Q
What is the significance of patient position and immobilisation in radiotherapy?
A
Accurate delivery of radiotherapy is crucial, and proper positioning ensures effective treatment while maintaining patient comfort.
4
Q
What are some commonly used immobilisation devices?
A
- Simple supports (head, knee, ankle). 2. Chest board. 3. Vacuum bags. 4. Vacuum-formed shells. 5. Complete fixation devices like stereotactic frames.
5
Q
What is the role of imaging in radiotherapy planning?
A
Imaging is essential for delineating gross tumour volume (GTV), clinical target volume (CTV), planning target volume (PTV), and outlining critical structures.
6
Q
What is a CT simulator?
A
A CT simulator is a wide-bore CT scanner used for 3D conformal planning, providing precise imaging and positioning information.
7
Q
What are the definitions of GTV, CTV, and PTV?
A
GTV is the demonstrable tumour. CTV includes GTV and suspected subclinical tumour. PTV is CTV plus margins for uncertainties.
8
Q
What is the purpose of defining organs at risk (OARs) in radiotherapy?
A
OARs are critical normal structures sensitive to radiation, and their delineation is essential to avoid exceeding tolerance doses.
9
Q
What is the difference between serial and parallel organs in terms of radiation sensitivity?
A
Serial organs are highly sensitive; damage to any part can affect function. Parallel organs’ function depends on the volume irradiated.
10
Q
What is the planning organ at risk volume (PRV)?
A
PRV is the OAR with a margin added to account for movements and uncertainties in set-up.
11
Q
What is the effect of radiation on serial organs?
A
The function of serial organs may be seriously affected if even a small portion is irradiated above a tolerance dose.
12
Q
How does radiation affect parallel organs?
A
The effect of radiation on the function of parallel organs is more dependent on the volume irradiated.
13
Q
Why is treatment planning important for serial organs?
A
The accuracy of treatment planning and delivery are important to ensure that tolerance is not exceeded.
14
Q
What is a Planning Organ at Risk Volume (PRV)?
A
A margin must be added to the Planning Target Volume (PTV) to create the PRV.
15
Q
What is beam divergence?
A
The width of the radiation beam increases linearly with distance from the treatment head.
16
Q
What is beam penumbra?
A
At the edge of the radiation beam, the dose reduces over the distance of some millimetres. The penumbra is the distance between the 80% and 20% isodoses.
17
Q
What is percentage depth dose?
A
The dose is expressed as a percentage of the maximum dose deposited by the beam, occurring at a depth dmax.
18
Q
What causes build-up of dose below the skin surface?
A
With mega-voltage beams, secondary electrons travel primarily in a forward direction, causing dose build-up before dmax is reached.
19
Q
What is the tissue phantom ratio (TPR)?
A
TPR or tissue maximum ratio (TMR) is used instead of percentage depth dose in some centres for isocentric calculations.
20
Q
How does the radial profile of a megavoltage beam change?
A
The radial profile changes with depth due to differential hardening across the beam, which may result in an asymmetric profile.
21
Q
What happens to the beam as the distance from the treatment machine increases?
A
The cross-sectional area of the beam increases due to divergence, while the intensity decreases according to the inverse-square law.
22
Q
How does field size affect radiation dose?
A
As the field size increases, the central axis receives more radiation per monitor unit due to increased scatter.
23
Q
What is a typical use for a single beam in radiotherapy?
A
A single beam is used for superficial tumours such as skin cancers or for tumours not at or near the midplane.
24
Q
What is the purpose of opposing beams?
A
Opposing beams are used for palliative treatments or for sites with relatively small separation, such as head and neck.
25
What are external tissue compensators used for?
They are used when the external contour of the patient is irregular around the central axis of the beam.
26
What is the benefit of combinations of beams in radical treatments?
They spare adjacent normal tissues in sites such as the chest, pelvis, and brain.
27
Why is beam weighting important?
Beam weighting allows adjustment of the relative proportion of dose delivered to the tumour from each beam.
28
What factors influence the choice of beam directions in conventional planning?
The treatment intent and the locations of the Planning Target Volume (PTV) and Organs at Risk (OARs) influence beam direction choices.
29
What is a two-phase technique in radiotherapy?
It combines different beam approaches to prevent tolerance doses from being exceeded.
30
How can treatment plans be improved?
Using non-coplanar beams can improve dose distribution in the PTV and reduce dose to organs at risk.
31
What is the significance of non-coplanar beams?
They can be achieved easily by rotating the table and gantry, improving treatment outcomes.
32
33
What influences the shape of the treated volume in radiotherapy?
The directions of the beams
## Footnote
The shape is identified by tracing the edges of the beams, assuming a balanced dose distribution.
34
What is likely to be the location of the global hot spot in a balanced multi-beam treatment?
Close to the centre of the treated volume
35
What are the two situations where wedges are used in radiotherapy?
* As a tissue compensator for a sloping external surface
* To even out the dose when two or more beams intersect
36
How does surface obliquity affect isodoses?
Causes isodoses to tilt in the same directions as the surface
37
What is the purpose of a tissue compensator in radiotherapy?
To correct for dose gradients caused by surface obliquity
38
What key factors must be understood for patient calculations in radiotherapy?
* Percentage depth dose (PDD) or tissue maximum ratio (TMR)
* Inverse-square law
* Wedge factor
* Field size (output) factor
* Accessory factors (e.g. trays)
39
What does DVH stand for in radiotherapy planning?
Dose-Volume Histogram
40
What is the ICRU reference point used for in radiotherapy?
To report doses based on clinically relevant and representative points in the PTV
41
What are the criteria for selecting the ICRU reference point?
* Clinically relevant and representative of the dose throughout the PTV
* Easy to define clearly
* Accurate determination of dose
* Located in a region without a steep dose gradient
42
What happens to dose penetration when beams pass through organs of different densities?
Changes in penetration can occur, affecting dose delivery
43
What is a significant challenge when planning treatments involving high-density materials?
Artificial hips can create planning issues due to artifacts on CT imaging
44
What is the goal when treating organs at risk (OAR) in radiotherapy?
To minimize high doses to normal tissue while effectively treating the tumor
45
What is the purpose of verification in radiotherapy?
To ensure the treatment delivered matches the planned treatment
46
What can cause differences between planned and delivered treatment?
Set-up errors and internal movements during treatment
47
What technique can improve the accuracy of treatment set-up?
Implanted markers, such as gold grains
48
What is the purpose of using half-beam blocking or couch rotations?
To minimize dose variations at junctions between adjacent beams
49
What does TLD stand for in the context of in vivo dosimetry?
Thermoluminescence dosimetry
50
What is essential for treating patients safely in radiotherapy?
Technical quality and quality assurance of the clinical process
51
What is the significance of Quality Assurance in Radiation Therapy (QART)?
To ensure overall control of activities in the radiotherapy department
52
What does the complexity of manual treatments in radiotherapy lead to?
Increased treatment errors
53
What is a major challenge with modern 3D treatment planning systems?
Ensuring the validity of the data used in treatment planning
54
What does modern 3D treatment planning systems provide?
A wealth of information such as the density of internal body organs and DVHs
## Footnote
DVH stands for Dose-Volume Histogram
55
What is the importance of quality assurance (QA) in 3D treatment planning?
To ensure that the data are valid and to avoid errors
## Footnote
QA is critical for patient safety and treatment efficacy
56
What is 'TG53'?
'TG53' is an important document produced by the AAPM Radiation Therapy Committee that describes all the tests to be considered when commissioning a treatment planning system
## Footnote
AAPM stands for American Association of Physicists in Medicine
57
What can cause errors when using DVHs in 3D planning?
Errors can occur due to a low number of dose points or high dose gradients within a volume
## Footnote
Incorrect DVH usage can lead to inaccurate treatment assessments
58
What is the expected dose behavior under MLCs?
The dose is expected to increase due to leaf penetration and interleaf leakage
## Footnote
MLC stands for Multi-Leaf Collimator
59
What are the three principles for critical analysis of treatment plans?
* Homogenous dose to the PTV
* Organs at risk
* Other normal tissues
60
What is the consequence of not achieving homogenous dose to the PTV?
The highest dose in the PTV is usually considerably less than the +7% maximum described in ICRU 50
## Footnote
ICRU 50 refers to the International Commission on Radiation Units and Measurements publication
61
What is the significance of the dose fall-off in normal tissue?
The high dose volume in the PTV should fall off rapidly in normal tissue to minimize damage
## Footnote
This is crucial for protecting surrounding healthy tissues during treatment
62
What are the two examples of plans requiring improvement in radical radiotherapy for carcinoma of the larynx?
* Example (a): Two lateral beams with non-ideal PTV dose homogeneity
* Example (b): Use of small-angled wedged beams as tissue compensators
63
What is the solution for the PTV dose being outside the lateral margins in prostate treatment?
Make the anterior beam narrower
## Footnote
This adjustment helps achieve better dose coverage
64
What is the difference in isodose shape between electron beams and photon beams?
Electron beam isodoses have a homogeneous dose distribution close to the surface and a rapid fall-off at depth, unlike photon beams
## Footnote
This property makes electron beams ideal for superficial tumors
65
What are the care considerations when using electron beams?
* High-dose treatment isodoses tend to pinch in
* Low-dose isodoses tend to spread out
* A bolus is often required to increase surface dose
66
Define brachytherapy.
Radiation treatment given by placing a radioactive source near or in the target, usually a malignant tumor
## Footnote
Brachytherapy allows for high dose delivery while sparing normal tissues
67
What are the types of brachytherapy treatments based on the position of the radioactive source?
* Interstitial
* Intracavitary
* Intraluminal
* Intravascular
* Surface applications
68
What are the classifications of radiation dose rates according to ICRU report?
* Low dose rate (LDR): 0.4–2 Gy/h
* Medium dose rate (MDR): 2–12 Gy/h
* High dose rate (HDR): > 12 Gy/h
69
What is the Paris system in brachytherapy?
A method based on experience in the use of iridium-192 wires, which includes specific rules for source configuration and dose calculation
## Footnote
The Paris system ensures uniformity and accuracy in brachytherapy treatments
70
What is the formula for calculating the basal dose rate in brachytherapy?
The basal dose rate is calculated in the central plane of the implant and is the arithmetic mean of the local minimum dose rates.
71
What is the reference dose rate in brachytherapy?
The reference dose rate is calculated as 85% of the basal dose rate and is used for the tumour prescription and calculation time of the implant.
72
What is the reference isodose in brachytherapy?
The isodose surface that corresponds to the reference dose rate and must encompass the PTV.
73
What is the treated volume in brachytherapy?
The volume enclosed in the reference isodose.
74
What is the Manchester interstitial system also known as?
The Paterson–Parker system.
75
What types of configurations does the Manchester interstitial system govern?
Planar implants, volume implants, and moulds.
76
What is the applicator configuration for treating cervical cancer in the Manchester system?
A central uterine tube and two vaginal ovoids.
77
Where is point A located in the Manchester system for cervical cancer treatment?
2 cm lateral to the centre of the uterine canal and 2 cm above the lateral vaginal fornices.
78
Where is point B located in the Manchester system?
5 cm lateral to the midline at the level of point A.
79
What organization specified additional reference points for brachytherapy?
ICRU 38.
80
What are the four defined levels of image-guided brachytherapy?
* Accurate verification of applicator position
* Accurate definition of normal tissue dosimetry
* Opportunity for conformal dose distributions to tumour volume and OAR
* Opportunity for dose escalation
81
What isotopes are commonly used for gynaecological brachytherapy?
* Caesium-137 for low and medium dose rate treatments
* Cobalt-60 and Iridium-192 for high dose rate treatments
82
What are indications for brachytherapy?
* Primary radical treatment
* Treatment in combination with external beam radiotherapy
* Treatment in combination with surgery
* Re-irradiation within a previously treated volume
* Palliative treatments
* Benign conditions
83
What is the most widespread use of brachytherapy in the UK?
For gynaecological cancer, head and neck cancer, and increasingly, prostate cancer.
84
What is the first practical step in the brachytherapy procedure?
The treatment is preplanned to determine the tumour volume, target volume, technique, and number/size of radiation sources required.
85
What does ICRU 58 recommend for reporting brachytherapy treatment?
To report in a standardized way, including target volume, description of sources and technique, dose prescribed, and a description of high- and low-dose volumes.
86
What allows the radiation oncologist to define the target volume in brachytherapy?
Use of cross-sectional imaging, computer planning systems, and treatment machines with moveable stepping sources
## Footnote
These technologies help in obtaining dose volume histograms and achieving optimal dose distribution.
87
What can be varied at different positions to enable dose conformity to the target volume?
Dwell times for the source
## Footnote
This variability allows for a more accurate dose distribution.
88
True or False: Optimisation can make a bad insertion good in brachytherapy.
False
## Footnote
Careful positioning of brachytherapy sources is crucial.
89
What must be drawn up to comply with current legislation in brachytherapy?
Local rules and systems of work
## Footnote
These rules include source storage, preparation, and safety protocols.
90
What should be included in the contingency plans for emergency situations in brachytherapy?
Plans for situations such as source sticking
## Footnote
Preparedness for emergencies is vital for safety.
91
What checks should be carried out upon receipt of a radiation source?
Independent measurements of the activity of the source and tests for leakage
## Footnote
These checks ensure safety and compliance.
92
Why is it important to ensure the quality of calculation methods in brachytherapy?
To ensure accuracy in treatment planning and delivery
## Footnote
Regular quality control programs are essential, especially for computerized systems.
93
What needs to be calibrated against a recognized standard in brachytherapy?
Any equipment used to measure the actual delivered dose
## Footnote
Calibration ensures the reliability of dose measurements.
94
What recent advances in technology have impacted radiotherapy?
More complex radiotherapy techniques, such as stereotactic or modulated techniques, are now routinely delivered.
95
What is the benefit of using advanced radiotherapy techniques?
They allow the radiation dose to conform closely to the planning target volume (PTV) while avoiding normal tissue.
96
What is the purpose of cranial stereotactic techniques?
To deliver advanced radiotherapy to both cranial and extracranial sites.
97
What is volumetric-modulated arc therapy (VMAT)?
An extension of IMRT where the dose is delivered while both the gantry and the MLCs are moving.
98
How does intensity-modulated radiation therapy (IMRT) differ from conventional radiotherapy?
IMRT uses beams with changing dose intensity across them.
99
What is the role of the multi-leaf collimators (MLCs) in IMRT?
They are moved during beam on time to produce appropriately modulated beams.
100
What are the two ways IMRT can be delivered?
* Step and shoot IMRT * Sliding window IMRT
101
True or False: In 'step and shoot' IMRT, the beam remains on while the MLCs move.
False
102
What does inverse treatment planning involve?
Starting with the planner defining the required dose distribution and using optimization techniques.
103
What is a dose volume histogram (DVH)?
A graphical representation of the dose distribution within the target volume and surrounding tissues.
104
What is the significance of setting dose-volume constraints in IMRT planning?
To ensure optimal coverage of the PTV and avoidance of organs at risk (OAR).
105
What is a common challenge in IMRT and VMAT planning?
They require more detailed dosimetry than conventional techniques.
106
What is the purpose of image-guided radiation therapy (IGRT)?
To ensure accurate patient set-up and treatment delivery.
107
What imaging techniques are used in IGRT?
* Electronic portal imaging devices (EPIDs) * Cone beam CT (CBCT)
108
What is a significant disadvantage of EPIDs?
Poor contrast of megavoltage images limits soft tissue information.
109
What is one advantage of using VMAT over IMRT?
Faster treatment times and usually lower doses to outlined OARs.
110
What does the term 'low-dose bath' refer to in VMAT?
The distribution of lower doses outside the PTV to surrounding tissues.
111
What is a potential issue with automated optimization in treatment planning?
Mathematical algorithms may overlook intuitive considerations that a human planner would account for.
112
How are complex dose distributions achieved in modern radiotherapy?
By using inverse planning techniques and optimizing dose-volume constraints.
113
What is the clinical decision regarding a treatment plan based on?
Whether the plan meets the required constraints and is acceptable for treatment.
114
Fill in the blank: The main goal of IMRT is to produce a _______ distribution of radiation dose.
modulated
115
What is the purpose of using a dosimetric phantom in radiotherapy?
To measure each individual plan's accuracy before starting treatment.
116
Fill in the blank: The ability to 'fuse' images with the CT planning scan assists with _______ and treatment delivery.
radiotherapy planning
117
What is the expected outcome when the cost function decreases during optimization?
The plan is considered optimized and no further iterations are undertaken.
118
What is the primary benefit of kilovoltage X-rays in radiotherapy?
They provide greater contrast for generating planar images and volumetric imaging such as cone beam CT (CBCT)
## Footnote
Kilovoltage X-rays are used to enhance image quality during radiotherapy procedures.
119
What is the role of cone beam CT (CBCT) in radiotherapy?
CBCT is used to acquire a full 3D volumetric image of the patient before treatment, allowing comparison with planning CT to assess spatial accuracy
## Footnote
CBCT systems typically have a kilovoltage X-ray generator and are positioned at right angles to the therapy beam.
120
How long does it typically take to acquire and process a CBCT image?
2–3 minutes
## Footnote
This duration can lengthen the overall treatment time.
121
What are the challenges associated with imaging patients before every fraction of radiotherapy?
The cumulative additional dose, time affecting patient positioning, and the need for clear local protocols
## Footnote
These factors can complicate the implementation of IGRT.
122
What are the two imaging strategies used in IGRT?
* Online imaging
* Offline imaging
## Footnote
Online imaging involves imaging before treatment, while offline imaging calculates average patient displacement over several fractions.
123
What is a key advantage of IGRT systems, particularly those based on CBCT?
They can assess changes to patient anatomy during treatment and correct for them if necessary
## Footnote
This allows for adjustments based on significant changes in patient shape or weight.
124
What is adaptive radiotherapy?
Adaptive radiotherapy involves adapting the treatment plan during treatment due to changes in the tumor's position or size, or the patient's shape
## Footnote
This process may require repeat planning scans and can be time-consuming.
125
What is gated radiotherapy?
Gated radiotherapy switches the beam on only when the tumor is in a defined position, addressing tumor movement during treatment
## Footnote
This technique involves monitoring the patient's breathing cycle or using implanted fiducial markers.
126
What imaging modalities are commonly used in radiotherapy planning?
* CT scans
* Functional MRI
* Positron emission tomography (PET)
## Footnote
These modalities provide varying advantages such as geometric accuracy and additional functional information.
127
What is the purpose of image fusion in radiotherapy?
To merge different imaging sets into the planning system for more accurate treatment planning
## Footnote
Image fusion can be done using fixed anatomical markers or automatic systems.
128
What types of fusion methods are used in image fusion?
* Rigid fusion
* Elastic fusion
## Footnote
Rigid fusion involves movements and rotations, while elastic fusion can stretch or squash the secondary scan to match the primary image.
129
What is a potential drawback of image fusion in radiotherapy planning?
It does not provide information on the changes in doses received by the planning target volume (PTV) or organs at risk (OAR)
## Footnote
Internal movement or setup inaccuracies can affect dose delivery during treatment.
