Localisation procedures Flashcards
Breast
Check for:
- showing cancer diagnosis
- referral from the Dr
- anatomical site and laterality
- prescription if contrast required
- consent form
- pregnancy status
Immobilisation:
- Bring the patient into the room and ID them. Position the patient on the breast board.
- This should be tilted so that the sternum is parallel to the couch top which enables planning to be done without having to twist the collimators to move lung out of the field.
- Arms should be positioned above the head to bring them out of the field - patients who struggle to maintain this arm position may have a vac bag for extra support. - Patients with moveable breasts require further immobilisation in order to obtain adequate inf and lateral coverage. The patient may be put into a bra to immobilise the breasts and bring them ant and sup. In other hospitals patients may be treated prone.
Set up:
- Straighten the patient using SSN and TOX.
- Localise the breast tissue by finding SSN for sup edge, 1cm below tissue for inf and lateral edges, and midline for medial edge.
- Lateral PMs and an ant PM are marked on with radio-opaque markers.
- If treatment is for left-breast DIBH may be used, so breathing coaching is required. Ensure there is 0.5-1cm chest movement. 2 scans will be taken instead of 1, with 1 in FB and 1 in DIBH. Patients must be able to hold breath for 30 seconds, not have COPD, vac bag or tilt of 15
- If there is an SCF field ensure the chin is lifted to keep it out of the field. CT is used for planning.
CT Scan:
- An AP topogram is acquired first to assess scanning limits.
- Scan levels for 2 field are 5cm sup to shoulders/lung apices to 5cm inf of breast tissue (marked on with wire). For 3 field scan levels are columella to 5cm inf of breast tissue.
- The scan is then acquired with 3mm slice thickness every 3mm and sent to VSIM for planning, where OARs are outlined and beams are put on.
- CT exposure is documented with scan levels and dose.
PMs are tattooed.
Prostate/Pelvis
Check for:
- histology showing cancer diagnosis
- referral from the Dr
- anatomical site and laterality
- prescription if contrast required
- consent form
- pregnancy status
Preparation:
- Prior to the scan some centres will insert fiducials to localise the prostate for treatment.
- Before being seen the patient must empty their rectum, to reduce variation in prostate position
- fill their bladder (350ml/45mins), to push the dome of the bladder and small bowel out of the field.
Immobilisation:
- Bring the patient into the room and ID them.
- Perform an ultrasound scan to check the bladder is within tolerance (200-300ml). If not, ask them to drink some more and wait 15 mins. If still not fill they will have to come back another day having hydrated.
- The patient is positioned on the lower limb immobilisation - head rest, knee support to prevent pelvic tilt, and adjustable foot support with hands on chest.
Set up:
- Straighten the patient using SSN, TOX and ROP.
- An anterior marker is placed 5cm sup to ROP and laterals in line.
CT Scan:
- AP topogram is taken first with control slices to check straightness and marker visibility. Control slices check rectum size in the AP direction at the level of the pubic symph, 2cm above pubic symph and one other point, which should be <4.5cm. If too large patient may need to take an enema/dietary advice.
- Main scan is then taken with slice thickness of 2.5mm every 3mm
- scan levels are from the top of iliac crests to 7cm inf to lesser trochanters. If nodes are included then go from the bottom of L3 as sup edge.
- If there is nodal involvement the Dr may prescribe contrast to be given during the scan. We use 100ml Omnipaque which enters the bloodstream and highlights the vessels to contrast against the nodes. - Dose received, scan levels and number of slices are recorded and the scan is exported to Eclipse for planning.
The markers are tattooed on the patient.
Thorax
Check for:
- histology showing cancer diagnosis
- referral from the Dr
- anatomical site and laterality
- prescription if contrast required
- consent form
- pregnancy status
Immobilisation:
- Bring the patient into the room and ID them.
- Position the patient on the thoracic board with arms above the head for increased choice of beam arrangement for better target coverage and OAR sparing.
- If the patient cannot maintain this position a vac bag may be used for additional support.
- There are adjustable hand grips and height position, head rest and foot support.
Set up:
- Straighten the patient using SSN and TOX.
- Markers are placed anteriorly in close proximity to the tumour with laterals in line.
- If 4DCT is to be used an RPM box is placed on the xiphoid process and respiratory coaching may be given if a specific breathing pattern is required for the scan. Lung usually will have FB, but liver/pancreas patients may be scanned in EEBH as this is the position the organ is in most of the time.
CT scan:
- Localisation is performed using CT.
- An AP topogram is taken first to check for straightness and marker visibility.
- Scan levels are selected. For lung this is 5cm sup to lung apices to 5cm inf of diaphragm.
- The main scan is then taken - if nodal involvement contrast is injected at this point.
- CT slice thicknesses are 3mm every 3mm.
- Dose received, scan levels and number of slices are recorded and the scan is exported to Eclipse for planning.
The markers are tattooed on the patient.
Head and Neck
Check for:
- histology showing cancer diagnosis
- referral from the Dr
- anatomical site and laterality
- prescription if contrast required
- consent form
- pregnancy status
Preparation:
- Before the scan the patient must have a shell made to immobilise the head and neck and ensure reproducibility of position.
- A 3 point shell is created for brain patients and a 5 point shell is created for H&N patients to ensure the shoulders are fixed as far inferiorly as possible to bring them out of the field.
- Patients being treated in the oral cavity area may also require a mouthbite to depress the tongue and bring it in or out of the field depending on treatment site. - Alternatively if 5 point shells are not used bear claws may be used instead to push the shoulders inf.
Immobilisation:
- Bring the patient into the room and ID them.
- Position the patient on the Q-fix board with arms by sides holding on to hand poles to bring the shoulders down, head rest and foot support.
- If the brain is to be scanned the head rest should have less of a slope so that the head is tipped forward to make it easier to avoid the optics and optic nerve in planning. If it is the neck that is being scanned a steeper head rest should be used to lift the chin up.
Set up:
- Straighten the patient using SSN and TOX.
- For H&N patients an anterior marker is placed 5cm inf to SSN. This is because the spinal cord will be in the field and will receive a larger dose (up to 60Gy) than brain patients whose cord will not be in the field.
- Place the shell on the patient and ensure the fit is still close.
CT scan:
- Localisation is performed using CT.
- An AP and lateral topogram are taken. The AP topogram ensures straightness and the lateral ensures there is no gap between the head and the head rest and to check for a close fit of the shell.
- Scan levels are selected with the sup from top of the shell to C5/6 inf for brain patients. For H&N go inf to carina.
- The main scan is then taken - if nodal involvement 50ml contrast is injected at this point.
- CT slice thicknesses are 1.25mm every 2mm.
- Dose received, scan levels and number of slices are recorded and the scan is exported to Eclipse for planning.
The ant marker is tattooed on the patient if present.
All procedures
Ensure the referral request form is present and complete - this should state category, diagnosis, site, laterality, prescription, other requirements (i.e. contrast), patient status (radical/palliative), as well as pregnancy status, consent form and radiology/histology confirming cancer diagnosis. ID the patient, explain procedure, check pregnancy status, and patient happy to proceed
Ensure correct anatomical area/laterality to be scanned, confirm immobilisation, scan levels/limits, ensure markers are in place
Preparation: bladder filling/bowel prep/shell/bolus
Immobilisation
Position: supine/prone, head/feet to gantry
Reference point: close to area of interest on stable anatomy
Contrast/bolus
Topogram: either AP or lateral
Scan limits: knowledge of anatomy and routes of spread, nodes/OAR to include
Review: check quality of the image, has contrast been taken up by the scan, are the bowel and bladder how we want them, air gaps with bolus
Document: record everything - PM positions, number of slices for planning, immobilisation, concomitant dose, date and time
Document immobilisation and bladder/rectum requirements
Confirm correct patient details in scanner, ensure IV prepped correctly
Scan patient
Document number of slices taken, correct labelling of images, post-scan advice
What should be included on a referral request form?
Patient details
Consultant details - contact if there is a problem, need correct Dr assigned for planning and to book them in to the correct clinic
GP details - they have the most up-to-date information on the patient; pt may need meds after treatment
Consultation date - can check for breach date
Category - certain patients will need to be hyper-fractionated on bank holidays
Diagnosis/staging/intent - need to know for slice thicknesses and will affect how they are scanned
Comorbidities: moving and handling, pace maker - need to book appts
Treatment area: for scan levels, nodes may need to be included
Any previous treatment: can re-use tattoos
Other requests: if contrast need a separate prescription, need to be cannulated, need blood results
Imaging modality: if fusion then images need to be collected from the other scanner
What is localisation?
Creating reference points and using surface anatomy to locate the tumour for alignment of radiation beams to encompass the target to be treated.
What is CT-SIM?
A verification appointment to check the correct location. It is like a linac and has a KV x-ray machine and detector that simulates the movements of a linac. Digital images or radiographs/fluoroscopy record the field borders chosen by bony landmarks. It has mostly been superseded by CT with which 4D CT can be used for motion, a topogram can be done first with low dose to get more anatomy in before taking a more detailed scan, produce tissue inhomogeneity detail, and is quicker.
What is VSIM?
The result of integrating the CT data and treatmetn software to generate images from a BEV perspective, which are equivalent to CT-SIM images. Software used to put the beams on for breast patients and move the borders around. Collimators can be rotated to adjust the amount of lung tissue in the field.
What is clinical mark-up?
Assessing and defining the treatment area by combining the following processes: visual and sensation information, palpating the region, knowledge of surface anatomy and landmarks, surgical excision sites/scars, using previous imaging/info. Commonly used for breast tangent borders and boost sites, superficial, palliative and electron treatments.
Describe 4DCT
Used for lung tumours when the tumour is near the diaphragm, breast - DIBH is a similar technique, pancreas and liver. An ITV (internal target volume) is created which takes movement into account. For treatment, we don’t gate at GSTT but take continuous scans throughout to keep assessing. EEBH aids in voluming.
