Quiz 1 Material Flashcards
What is the goal of Planning?
Develop a plan that delivers a therapeutic dose of RT to tumour cells while limiting the dose to surrounding normal tissue
What are the challenges of planning?
- Targets are at depth
- Targets have complex shapes
- Targets are surrounded by healthy tissue
What are some of the factors that are considered during the Simulation process?
Positioning
Immobilization
Type of data acquired
External contour
Reference markers (BBs, etc)
What are the prescription parameters?
Volumes (GTV, CTV, PTV)
Prescription doses
OAR constraints
Anatomy
Homogeneity
DVH analysis
Radiation Physics factors:
ISL
PDD/TPR
Attenuation
Backscatter
Penumbra
Inhomogeneity
Tumour dose/Given dose/ MUs
Isodose charts
Beam weighting
Normalization
PDD Changes with Energy, Field size, Depth and SSD
What is a non coplanar beam arrangement?
Angled couch to prevent the overlapping of beams at the center to prevent overdosing
List 5 Treatment/Machine Parameters for treatment planning
- MLCs
- Wedges
- Shielding
- Fluence modulation
- IGRT
What was historically used for TBI treatment?
Cobalt
What is the standard field size for TBI?
40 x 40cm
What is the normal SSD for TBI?
355cm
Name 3 positioning options for TBI
- Supine
- Lateral decubitus
- Bolus coffin
List 2 reasons for knowing patient geometry
- For lateral patient measurements for compensator fabrication
- For off-axis distance measurements for planning (OARs)
What is the “beam spoiler” and what does it do?
A large plastic screen placed between linac and patient. Makes scattered electrons deposit energy at shallow depths
Formular for TBI dosimetry:
What is the length of the plastic sheet used in TBI set up ?
60cm
List the 7 spots where TLDs are placed for TBI
- Umbillicus
- Head
- Neck
- Axilla
- Shoulders
- Pelvis
- Knees
Which two spots for the TLD placements in TBI do not have a dose buildup?
- Axilla
- Knees
What are the two main concerns of TBI IMRT?
- Does not make it attack circulating leukemia cells
- Increased dose rate (lung, liver, kidney toxicity)
What is the patient set up for CCMBs supine VMAT + APPA technique for TBI?
- Supine, arms by side, legs flat and close together
- Vac-loc bag with marks for bolus and hand placement
- Thermo-shell Head and Neck
- Use of repurposed treatment couch with rotating bearing
NB: Dose to the small bowel and kidneys with this technique is significantly reduced
What is the use of scar wire in the sim process?
- For boost treatment volumes
- For bolus placement
What margin is given for breast borders to account for scatter?
5cm
What device is used to track patient’s breathing during DIBH?
RPM cube
(Real Time Position Management)
What is the main technique for DIBH breast treatment?
Field-based technique
What are the main OARs for DIBH treatment?
- Lung
- Heart
- Liver
- Thyroid
- Brachial plexus
- Contralateral breast
How many lobes is the breast tissue divided into?
15-20 lobes
What is the RT definition of breast tissue for simulation purposes?
Medial - midline over the sternum
Lateral - mid-axillary line
Superior - inferior aspect of the head of the clavicle
Inferior - 2cm below the inframammary fold
LADCA =
Left Anterior Descending Coronary Artery
What is the main rationale for using half-beam block?
To eliminate divergence into the lung
T or F. For half beam block, the posterior jaw is closed
True
What energy is preferred in breast treatment plans?
4 to 6 MV
T or F. In breast treatment, we do not want skin sparing
True
What is the CCMB normalization point for breast treatment planning?
Point A:
1. Midfield superior and inferior
2. Mid-plane medial/lateral
3. At least 1cm from lung
4. At least 2.5cm from shielding
NB: Norm point should never fall in bone or lung
What is the standard dose/fractionation for breast treatment?
What about hypo?
5000/25 or 4256/16
Hypo: 2600/5
What is the dose/fractionation for Partial Breast Irradiation?
2700/5
Name 3 challenges of tangent planning for breast treatment
- Variability in tissue thickness
- Lack of scatter from lung tissue
- Hotspots (especially in patients with larger separation?
Which nodes receive approximately 85% of lymphatic drainage from all quadrants?
Axillary nodes
Parameters for 3-field Supraclav nodes:
- Borders:
Superior - to thyroid cartilage; avoid skin flash
Inferior - matching tangent superior border
Medial - midline/avoid vertebral bodies
Lateral - coracoid process - Shielding for spinal cord
- Gantry angled approx. 10 degrees from the cord
Parameters for 4-field Supraclavicular and Axillary nodes:
- All axillary nodes should be treated
- Same borders as 3-field but borders are half-beam blocked inferiorly and lateral is 2-3cm lateral to humeral head
T or F. For 3/4 field breast - tangents, the collimator is rotated
False
What is the photon “bouquet”?
Boost plan that is non-coplanar 4-5 beam arrangement that is meant to minimize exit dose.
T or F. IMRT use is discouraged for whole breast.
True
NB: IMRT can be used in cases of “unusual anatomy”
What is the wide tangents?
When the medial edge is extended approx. 3cm to contralateral side to include that internal mammary nodes
NB: increased dose to lung and contralateral breast
What is the margin for lumpectomy cavity?
1.5 - 2.5cm
Name three techniques for breath hold monitoring
- Active Breathing Control (ABC)
- Visual monitoring (Identify system)
- Infrared camera
Name some of the advantages of treating patients in prone position
- Improved homogeneity
- Decreased lung dose
- Reduce field separation for patients with pendulous breasts
T or F. We use PBI to treat node negative disease only
True
