Brachytherapy Flashcards
What is BT used for?
Cervical cancer (HPV) Prostate cancer
Why can’t we use EBRT for cervical cancer?
- Cervical cancer is controllable if enough radiation dose is delivered
- It is not possible to deliver the amount of radiation necessary by EBRT alone due to patient morbidity & high toxicity
- Therefore, it is necessary for cervical cancer to receive both EBRT and BT to ensure a tumouricidal dose
- Limiting factors include the size of the target volume, proximity of organs at risk (OAR) and toxicity for the patient
What are the types of BT
LDR 0.4-2Gy per/hr
MDR 2-12 Gy per/hr
HDR >12 Gy per/hr
What are the advantages of HDR compared to LDR?
Outpatient treatment' Dose optimisation (Adaptive RT) Reduced RT exposure to staff More stable positioning Smaller applicators Smaller treatment time
What are the disadvantages of HDR compared to LDR
More complex treatment and planning techniques’
Compressed time frame for planning
Larger potential for error
Potential for high radiation dose to staff and patient with source failure
What is high risk CTV?
High Risk CTV - major risk of local recurrence - residual macroscopic tumour at time of BT (smaller than at time of diagnosis) •
What is intermediate risk CTV ?
major risk of local recurrence - initial macroscopic tumour at time of diagnosis
What is low risk CTV?
potential microscopic tumour spread - treated with surgery and/or external beam radiotherapy but not brachytherapy
What is the scheduling of EBRT and BT?
Week 1-4 EBRT
Week 5 M, W, T EBRT T,F HDR
Week 6 M, W EBRT TF HDR BT
Week 7 HDR BT Tues
What is the EBRT prescription?
45 in 25# Pelvis+/- 5.4 in 3 PSW, +/- PA Lns +chemo
What is the HDR BT prescription?
30Gy in 5# or 28 Gy in 4# 2 a week
What is the purpose of pre treatment imaging?
• Evaluate tumour
• Determine treatment modality
• Determine optimum treatment volume & dose
(PET, MRI, CT)
What is the prpose of brachytherapy insertion imaging?
- Evaluate tumour response,
- Verification of applicator position
- Define HRCTV, IRCTV and OAR
- Adaptive radiation therapy
(MRI, CT, US)
What is the purpose of post treatment imaging?
• Evaluate tumour response & toxicity
What is the most optimal imaging modality?
• Useful to use a combination of two or more methods
• Use CT/US to localise applicators and MR to outline target volumes and OAR
• Recommendation from EMBRACE Study:Use MRI and CT for every fraction
OAR.
What is the intrafraction and infra fraction variation?
- May be significant
- May cause deviation from prescribed dose
- More significant for HDR as the number of fractions is higher than for LDR
- Steep dose gradient around the applicators
- Tumour shrinkage and normal tissue fibrosis may occur over the total length of time that HDR is delivered
factors associated with BT?
HDR BT is needed to achieve appropriate tumouricidal dose
dose limiting organ bladder not so much rectum
need to have good imaging
need to accomodate variances in patient anatomy
Advantages of Prostate HDR?
Image guided needle placement Optimised dose distribution Organ motion minimised Radiobiological advantage remote afterloading single reusuable source
Acute clinical issues for prostate HDR?
Template/catheter movement
Haematuria/clot retention (continous bladder irrigation)
Perineal discomfort and back pain (Analgesics)
Infection risk (Prophylactic antibiotics)
DVT prophylaxis (stockings, Heparin)
Defaecation (Low residue diet)
