Brachytherapy

Question 1

What is BT used for?

Answer 1

Cervical cancer (HPV)
Prostate cancer

Question 2

Why can’t we use EBRT for cervical cancer?

Answer 2

• 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

Question 3

What are the types of BT

Answer 3

LDR 0.4-2Gy per/hr
MDR 2-12 Gy per/hr
HDR >12 Gy per/hr

Question 4

What are the advantages of HDR compared to LDR?

Answer 4

Outpatient treatment'
Dose optimisation (Adaptive RT)
Reduced RT exposure to staff
More stable positioning
Smaller applicators
Smaller treatment time

Question 5

What are the disadvantages of HDR compared to LDR

Answer 5

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

Question 6

What is high risk CTV?

Answer 6

High Risk CTV - major risk of local recurrence - residual macroscopic tumour at time of BT (smaller than at time of diagnosis) •

Question 7

What is intermediate risk CTV ?

Answer 7

major risk of local recurrence - initial macroscopic tumour at time of diagnosis

Question 8

What is low risk CTV?

Answer 8

potential microscopic tumour spread - treated with surgery and/or external beam radiotherapy but not brachytherapy

Question 9

What is the scheduling of EBRT and BT?

Answer 9

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

Question 10

What is the EBRT prescription?

Answer 10

45 in 25# Pelvis+/- 5.4 in 3 PSW, +/- PA Lns +chemo

Question 11

What is the HDR BT prescription?

Answer 11

30Gy in 5# or 28 Gy in 4# 2 a week

Question 12

What is the purpose of pre treatment imaging?

Answer 12

• Evaluate tumour
• Determine treatment modality
• Determine optimum treatment volume & dose
(PET, MRI, CT)

Question 13

What is the prpose of brachytherapy insertion imaging?

Answer 13

• Evaluate tumour response,
• Verification of applicator position
• Define HRCTV, IRCTV and OAR 
• Adaptive radiation therapy

(MRI, CT, US)

Question 14

What is the purpose of post treatment imaging?

Answer 14

• Evaluate tumour response & toxicity

Question 15

What is the most optimal imaging modality?

Answer 15

• 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.

Question 16

What is the intrafraction and infra fraction variation?

Answer 16

• 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

Question 17

factors associated with BT?

Answer 17

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

Question 18

Advantages of Prostate HDR?

Answer 18

Image guided needle placement
Optimised dose distribution
Organ motion minimised
Radiobiological advantage
remote afterloading
single reusuable source

Question 19

Acute clinical issues for prostate HDR?

Answer 19

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)