Radiotherapy and the Effects on Tissues Flashcards
What are the aims of radiotherapy
To achieve local tumour control by delivering a radical curative dose of radiation to the tumour, whilst keeping the dose to the neighbouring normal tissues as low as possible
What does dose limit mean?
Normal tissues have a radiation dose tolerance limit beyond which the probability of normal tissue complication increases
- RT curative for localised disease but dose limited by both acute and late side effects
What is the RT process
- Immobilisation/planning CT scan
- Target volume
- depending on primary site, TMN stage, likelihood of occult nodal disease, pattern of spread, histological prognostic factors (margins, ECS, grade) - Radiation doses
- 4-6MV photons
- Increasing dose increases probability of tumour control and risk of radiation-induced normal tissue damage
- Dose limited by organs at risk (OAR)
- Curative dose: 70Gy in 35 daily fractions
- Prophylactic dose: 50Gy in 25 daily fractions
- Post-op dose: 60-64Gy in 30-32 daily fractions
Risks of RT
- Potential increase in local recurrence
- Multiple fields => increased volume of tissue receiving low dose of radiation… potential changes in toxicity patterns
- Increased risk of secondary malignancies
How do you make radiotherapy more effective
- Increasing accuracy of delivery
- Increasing dose delivered
- Concomitant chemotherapy
What is hypofractionation
- Larger doses per fraction to a total lower dose
- Reduced overall tx time
What is hyperfractionation
- Smaller dose per fraction: reduced late morbidity
- Higher total dose over same time: increased tumour control
What is accelerated RT
- Rationale: proliferation during FT leads to tumour repopulation and local failure
- Shorter overall time, >1 tx/day: reduce opportunity for repopulation and improve local control
What does normal tissue tolerance depend on
- Total volume irradiated
- fractionation schedule: size of each fraction, number of fraction, duration of tx
- Previous surgery
- Co-morbidities and co-exisiting problems (smoking, drinking)
What are the clinical features of acute toxicity
- Occurs in rapid turnover tissues
- Symptoms begin 2-3 weeks from start of tx
- Reversible: settle within 4-6 weeks of completion of tx
- Present to some degree in all pts
- Severity does not predict for late toxicity
- Skin: erythema, dry/moist desquamation, necrosis, hair loss
- Mucous membranes: loss of taste/metallic taste, dry mouth, dysphagia, Mucositis (patchy/confluent)
What is the pathogenesis of mucositis
Initiation/vascular phase (inflammation)
=> Epithelial phase (apoptosis and tissue damage)
=> signalling/up regulation phase
=> ulcerative phase (provides environment for invasion of bacteria)
=> healing phase
Types of mucositis
- RT induced mucositis affects any mucosal surface exposed (lips to cervical oesophagus) 3-12 weeks
- Chemotherapy induced mucositis (stomatitis or oral mucositis) involves anterior oral cavity) - less severe
- Concurrent chemotherapy with RT. shortens the onset and exacerbates the severity
Associated symptoms of acute toxicity
- Mouth soreness and pain (can affect speech and swallowing)
- dysphagia (can reduce oral intake - dehydration/weightloss)
- Odynophagia (pain in chest on swallowing)
- Loss or altered taste
- Excessive secretions that may lead to gagging
- Nausea and vomiting
- Loss of appetite
- Fatigue
- Xerostomia - which can lead to mucositis
How can oral hygiene help manage acute toxicity
- Does not prevent mucositis
- Reduces risk of infection and late effects
- Dental assessment pre-RT should be carried out
- Cleaning sponges can be given if brushing intolerable
- Dentures cleaned after meals and soaked overnight
- Avoid flossing if platelets low
- Avoid smoking/drinking
- Use of baby soft toothbrush
How can mouthwashes help manage acute toxicity
- Saline rinses
- Difflam mouthwash/spray
- Avoid all mw containing alcohol except difflam, CHX, cocaine
