What is radiotherapy - how is it delivered, what effect does it have on cancer?
Strongly targeted rays of ionising radiation
Destroys or inactivates cancer Disrupts cell division Invisible, silent + pain free
Delivered by a linear accelerator - delivering high energy, short wavelength x rays
Electrons vs photons
Photons = high energy x ray treatments = penetrate deep. Cause DNA damage
Electrons = used for skin tumours
What is a differential cell kill?
Kills more cancer cells than healthy cells Due to cancer cells having ineffective DNA repair pathways
Units of measurement + dose
Delivered as series of small doses (fractions)
What is IMRT?
Intensity modulated radiotherapy
Given continuously as it moves in arc around the patient - delivered quicker + greater accuracy
What is VMAT?
Volumetric modulated arc therapy - type of IMRT
Protects more healthy tissue MLC movement throughout beam delivery so head can move around (patient not fixed)
What is MLC?
Multi leaf collimator Part of RT machine, helps to shape beam of radiation
What is the margin for setting up?
Extra margin added due to tumour moving slightly
Treatment schedule for category A cancers
5 days a week throughout treatment as can't give cancer cells time to regenerate
What is the toxicity skin reaction in RT?
Eventually causes fibrosis Borders are defined
Side effects of RT
Long term urinary frequency + urgency due to bladder fibrosis
Bronchitis/ pneumonitis (can occur 4 weeks - 6 months post treatment)
Grading for radiation dermatitis
Grade 1 = faint erythema, dry desquamation 2 = moderate erythema, moist desquamation, confined to skin folds 3 = moist desquamation other than skin folds 4 = skin necrosis or ulceration 5 = death
RT in prostate pts - requirements, SE
Need to have a full bladder, empty bowels
SE: skin reaction, fatigue, diarrhoea, tenesmus, cystitis, urinary frequency
RT in head and neck cancer - SE
Worst SE - intensive mouth care needed
Held in place by thermoplastic shells
SE: skin reaction, fatigue, mouth soreness, difficulty swallowing, voice changes, hair loss, tinnitus Long term risk of tooth decay, hearing changes, difficulty swallowing + xerostomia (dry mouth)
What is brachytherapy + what are the types?
Inserting radioactive material into affected area
intracavity = into body cavity eg uterus
intrastitial = into target eg prostate
What cancers use brachytherapy?
Prostate, cervical + womb, head and neck
What is the skin sparing effect?
X rays penetrate deep into body tissue, sparing overlying skin Reduces skin toxicity reactions
Which cancers are more radio sensitive?
Seminoma Hodgkins disease
Which cancers are radio resistant?
Why is concurrent chemo helpful?
Acts as radiosensitiser
What is the radiotherapy pathway?
Immobilisation CT scan
Disease delineation by oncologist
Treatment plan developed
Pt has daily treatments
Review + monitoring
What is the most common type of RT used?
External beam - 3D conformal RT Treatment based on 3D shape of their tumour
What is the GTV, CTV + PTV?
GTV = gross tumour volume CTV = clinical target volume (margin has been added) PTV = Planning target volume (added margin due to patient + tumour movement)
Long term toxicity effects of RT
Lung fibrosis, skin atrophy + infertility
What are radioisotopes + what is it commonly used for?
Unstable form of chemical element
Emits radiation when it decays
Commonly used is radiactive iodine I-131 - used in thyroid cancer
What is stereotactic RT?
Delivered using VMAT technique
Image guided radiotherapy
works for small + well defined tumours
Large dose of RT given in small number of large fractions