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Name the 3 methods of junctioning:
- 1) Angulation
- 2) Half beam block
- 3) Asymmetric jaws
How are asymmetric jaws used to junction, and what are the advantages?
- - Produces two non-divergent beam edges that can be matched without angling the couch, gantry, or collimators
- - Almost all junctioning done using mono-isocentric technique
- - The beam central axes are at the junction
- - Accurate, reliable, quick, and easy to perform
Describe the dose distribution at the junction
- - 100% total isodose due to the sum of the two 50% isodose lines which follow the geometric beam edge
- - The two adjacent beams must be matched within a fraction of a mm for the dosimetry to be correct; in reality, precise to 1-2mm
- - There is some inaccuracy built into junctional treatment technique, due to set up limitations/inaccuracies, pt movement, variation of position within mask etc.
How do we manage the dose inaccuracy/inhomogeneity at the junction region?
- - Moving/feathered junctions which "blur" the region of dose uncertainty
- - Using several junctions (usually 3) which are alternated for different fractions during the course of tx
What are some of the advantages of MRI over CT for brain cancer?
- 1) Superior soft tissue delineation, especially in CNS structures
- 2) Superior definition of oedema in brain tumours
- 3) More sensitive than CT in detecting abnormalities
What are some of the symptoms of brain cancer?
- - Nausea
- - Vomiting
- - Headaches
- - Seizures (in 50%)
- - Mental changes
- - Unilateral weakness
- - Specific symptoms related to the tumour location
- - Increased ICP
- - Visual problems
- - Changes in coordination
- - Clumsy walk
- - Weakness in limbs
- - Tireness
What are some of the symptoms of H&N cancer?
- Oral cavity: swelling or an ulcer that fails to heal
- Oropharynx: painful swallowing, referred otalgia
- Nasopharynx: bloody discharge, difficulty hearing, respiratory or auditory dysfunction
- Larynx: hoarsness andstridor
- Hypopharynx: dysphagia, painful neck node
- Nasal/sinuses: obstruction, discharge, facial pain, local swelling
What is involved in the diagnostic process for H&N cancer?
- Physical examination is very important including location, number and size of nodes that are hard, >1cm, non-tender and raised this can often suggest the site of the primary tumour.
- Laryngoscopy, & fiberoptic endoscopy
- Biopsy on all suspicious lesions to determine a precursor for a benign condition or to evaluate the predominant malignant growth pattern (grading).
- Fine needle aspiration biopsy (FNAB) is performed on neck masses.
- Blood test: anti-EBV antibody titers- immunoglobulin G & A are fairly specific to NPC and may aid in the diagnosis of cervical node cancer with an unknown primary cancer.
- X-rays of the skull, sinuses and soft tissue
- For symptomatic patients a barium swallow, along with chest films and bone scans to rule out metastases.
- PET for an unknown primary
- For staging: CT or MRI of the H & N, a chest x-ray (lung mets) and routine blood counts and serum chemistries.
- Combined PET/CT to precisely define loco-regional spread and to detect distant metastases.
- CT useful in deep invasion, to determine bone invasion and for regional lymph node assessment.
- MRI useful to assess muscle invasion with retromolar trigone lesions
- PET most useful with locally advanced disease, sensitivity and specificity of about 90% for nodal staging limitation of identifying early stage tumours
- CT & MRI can identify up to 50% of primary tumours that show no clinical evidence of tumour on physical examination.
- Tumours that are not identified using CT or MRI are detected with a stand alone PET (no CT fusion)
- Stand alone PET has a detection of 25% for localising undetected tumours with these other imaging modalities and an endoscopy examination.
- Fusion studies with CT are expected to produce a higher detection rate and should be performed instead of MRI or CT & before endoscopy.
What is involved in the diagnostic process for brain cancer?
- Physical examination general, importantly hearing
- Neurological workup including mental status, intellectual function, coordination skills, balance & reflexes
- Vision exam: opthalmoscopy which is a check for papilledema (oedema of the optic nerve)
- Information from other people on the patients i.e. personality changes or changes in behaviour
- X-ray may show changes in skull
- CT with contrast shows tumour extension, grade & growth pattern
- MRI with contrast (Gadolinium) to differentiate between oedema and the tumour & detect surface seeding (essential)
- PET differentiates necrosis from malignancy brain tumours have an increased glucose metabolism which is highlighted.
- Stereotactic biopsy not so common
- Cerebral angiography for surgical planning to study the intrinsic blood supply
- Surgery usually supplies the histological diagnosis
- No standard grading system.
Describe the three roles that MRI has in the diagnostic workup of brain cancer.
- 1) Diagnosis and staging
- 2) RT treatment planning - tumour volume definition, image fusion, image registration
- 3) Post RT evaluation: compare pre/post MRI to evaluate tumour response to treatment
Describe image fusion and its aims in RT.
Image fusion is the process of combining information from 2 or more images into a single composite image that is more informative and more suitable for visual perception. It aims to provide an improved view of the GTV, oedema, and surrounding anatomy.
What are some limitations of MRI registration?
- The PT head position may different between the MRI/CT. Some anatomy may not match perfectly; a "best fit" match is needed.
- Less number of MRI images are acquired.
- MRI cannot be used alone for treatment planning due to lack of electron density information.
Name some of the communication issues you may encounter with your patient. How would you deal with them?
- - Anxiety
- - Medical jargon
- - Side effects of surgery and dental work
- - Multiple sclerosis
- - Language barriers
- - Deaf/blindness
Name the OAR and their tolerances in brain treatment (7)
- - Eye (orbit): 45 Gy
- - Eye (lens): 5 Gy
- - Optic nerve: 50 Gy
- - Optic chiasm: 50 Gy
- - Brainstem: 54 Gy
- - Pituitary gland: 40gy
- - Spinal cord: 45 Gy
Name the OAR and their tolerances in H&N treatment (7)
- - Eye (orbit): 45Gy
- - Eye (lens): 5 Gy
- - Optic nerve: 50 Gy
- - Optic chiasm: 50 Gy
- - Brainstem: 54 Gy
- - Parotid gland: Mean in 1 gland 26 Gy, 50% to one gland 30 Gy
- - Spinal cord: 45 Gy
Which OAR must be considered especially for paediatric CNS treatment? What are their tolerances?
Pituitary and hypothalamus. Tolerance depends on the age of the child.
At what dose to the pituitary can problems with growth occur in paeds?
Describe the three phases of H&N treatment, their treatment sites, beam energy and prescription.
- P1: Laterals to upper neck - 40Gy/20# - 6MV
- P1: AP lower ASN - 50 Gy/25# - 6MV
- P2: Laterals to upper neck offcord - 10Gy/5# - 6MV
- P2: Lt upper neck post neck - 10Gy/5# - 9MeV
- P2: Rt upper neck post neck - 10Gy/5# - 9MeV
- P3: Laterals to upper neck boost (primary site) - 10Gy/5# - 6MV
What is shielded in the P1 laterals to upper neck fields?
- Oral cavity - ant sup corner
- Base of skull - post sup corner
What is shielded in the P1 AP lower field?
- Spinal cord - midline
- Trachea and oesophagus
- Apex of lungs - bilateral corners inf to clavicle
What is shielded in the P2 upper neck offcord?
- Oral cavity - ant sup corner, same as oncord
- Base of skull and spinal cord
- * it is a shrinking field and smaller than oncord field *
What is the point of the P2 Post Neck Electron (PNE) laterals?
To avoid overdosing of the spinal cord which has a tolerance of 45 Gy, but boosts the posterior neck nodes.
What is shielded in the P3 upper neck boost laterals?
- Oral cavity - ant sup corner, more than oncord/offcord fields
- Base of skull & spinal cord - same as offcord field
- * shrinking field: smallest of upper neck fields *
Name some of the side effects of H&N treatment and how to manage them
- Management of loss of taste:
- Partial loss of taste (hypogeusia), complete loss of taste (ageusia)
- Varies greatly in patients anything that helps the patient continue to eat is useful e.g. using plastic utensils if foods have a metallic taste
- Encourage patients to identify and consume foods longer to allow more contact of the food with taste buds
- Scheduling meal times and sticking to them if there is no desire to eat is important
- Management of xerostomia:
- This is acute radiation injury to the salivary glands may be permanent
- Likely to occur at 1000-2000cGy can result in a 50-60% reduction in saliva after only 1-2 weeks on tmt.
- Can result in pain, cough, ulceration, taste disturbance, dry mouth, difficulty swallowing and thick, tenacious, ropey or nonexistent saliva
- Aim of management is to maintain adequate nutritional intake with minimal weight loss
- Tmt includes anti-fungals such as Fungilin lozenges or Nilstat to prevent infection, analgesia (introduced as early as possible) for the pain, maintenance of adequate nutritional intake with minimal weight loss.
- Other things that may help although some with little or unreliable evidence to suggest why: fresh pineapple, ice to suck, ice lollies, chewing sugar less gum, taking frequent sips of water, drinking frequently whilst eating and the use of bland, non spicy sauces and gravies as an accompaniment to dishes
- Management of mucositis (additional):
- This is acute or chronic inflammation of the mucous membrane lining the oral cavity and pharynx.
- May occur at doses ranging from 2000-3000cGy
- Can result in pharyngeal fibrosis, damage to the integrity of the mucosa and increased susceptibility to ulcers
- As for xerostomia is the last two points ^ above.
- Management of skin reactions:
- Usual management applies
- Management of a dry cough:
- Analgesia, saliva substitutes, fresh pineapple, ice to suck, ice lollies, chewing sugarless gum, taking frequent sips of water, suitable nutritional intake.
- Management of difficult swallowing:
- Generally patients to avoid hot, extremely cold, spicy acidic or citrus foods and food with hard or rough edges
- Better to consume softer foods and fluids, and frequent small meals
- Drink high protein milkshakes and other drinks such as Sustagen
- Drink small amounts often
- No smoking or drinking alcohol
- Nasogastric or PEG may be required if the patient in not maintaining adequate nutritional intake.
- Psychosocial care:
- May experience a range of effects including physical, psychosocial and financial
- Side effects experienced are probably the most severe from RT tmt
- Patients require a lot of support
- Family members and carers may also require support
- May have feelings of fear, anger, anxiety, changes to body images and perceptions of social stigma associated with the diagnosis and cancer tmt
- Support can be provided by RTs, nursing staff, oncologists, speech pathologist (esp. important for H&N patients) social workers, counsellors, psychologists, support groups and possible other patients.
- Role of dietician:
- Malnutrition is a very real side effect of H&N RT tmt.
- Approx 70% of patients will lose in excess of 5% of their pre-tmt body weight
- Important complete RT tmt without a break due to side effects
- Advise given on diet, hydration and oral intake
- Monitor changes to appetite throughout tmt ideally see the patient before they start tmt.
- Osteoradionecrosis (ORN):
- Is a severe late effect caused by previous or post-RT dental extraction. Ionising radiation promotes the decline in vascularisation and oxygen levels in tissue and consequently comprises tissue repair capabilities that are required of surgical extraction. Management of this side effect is very challenging and can result in soft tissue and bone loss and reduced quality of life. Symptoms can occur months to years after RT, which include mouth pain, jaw swelling and difficulty opening the mouth fully. Diagnosis involves imaging studies such as x-ray, CT & MRI as well as physical examination. Tmt involves antibiotics & hyperbaric oxygen therapy.
Name the short term side effects of CNS treatment
- - alopecia
- - skin reaction
- - low blood counts
- - descrease in pituitary hormones
- - GI toxicity
Name the long term side effects of CNS treatment
- - cognitive impairement
- - neuropsychological effects e.g. on emotional and social behaviour
- - cosmetics of the face (facial hair growth impaired)
- - effects on vision: blind spots, radiation retinitis, dry eyes, cataracts
- - secondary malignancies in CNS, bone, soft tissue
- - decreased height of vertebral bodies
- - hearing loss
- - possible permanent depilation
What are the three advantages offered by PET in treatment planning?
- 1) anatomical and functional information
- 2) treatment intent
- 3) evaluation of treatment outcome
What are the 5 characteristics of electron beams that make them suitable for use in a H&N technique?
- - rapid dose build up
- - rapid dose fall off
- - uniformity of dose over volume
- - energy related to depth: easy to choose appropriate depth
- - low dose to normal underlying tissue
What are the 2 factors that affect the %DD of an electron field?
The energy used: higher the energy, the more penetrating the beam. The size of the field.
How does the penumbra of a MeV beam differ from a MV photon beam?
Larger and "bulging" penumbra.
How does the penumbra of an electron field change with an increase in beam energy?
As energy increases, the penumbra decreases, and so does the ballooning.
What isodose do doctors generally prescribe electrons to?
- - 90%
- - dmax 100%
- - A specific depth
What do doctors prescribe electrons to the 90% isodose?
- Because this will provide a 'volume' of dose rather than a point dose (as with 100%)
What factors affect the elctron beam output from a linac?
- - Energy of the beam (contribution from scatter)
- - Collimator setting/cone size
- - Size of the LMA cutout
What is the main correction factor for electron calculations?
Electron beam output factor
What is the ISL formula?
ISL = (Old/New)^2
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