Wk 11 - Brachytherapy

Question 1

low dose rate (LDR)

Answer 1

0.4-2Gy/h

Question 2

medium dose rate (MDR)

Answer 2

2-12Gy/h

Question 3

high dose rate (HDR) gy/h

Answer 3

> 12Gy/h

Question 4

half life of 226 radium

Answer 4

1600 years

Question 5

half life of 60 Cobalt

Answer 5

5.26 years

Question 5

half life of 137 Caesium

Answer 5

30 years

Question 5

half life of 192 iridium

Answer 5

74 days

Question 5

half life of 125 iodine

Answer 5

59.5 days

Question 6

advantages of HDR

Answer 6

• outpatient treatment
• dose optimisation - adpative B/T planning
• reduced radiation exposure for staff under normal situations
• more stable positioning
• smaller applicators
• high dose rate = shorter treatment times

Question 7

disadvantages of HDR

Answer 7

• more complex treatment and planning techniques
• compressed time frame for planning
• greater potential for error due to much higher dose being delivered in a short timeframe
• potential for high radiation dose to staff and patient with source failure

Question 8

brachy workflow

Answer 8

1. implantation
2. image acquisition
3. catheters
4. targets and OAR delineation
5. treatment planning and optimisation
6. quality control
7. treatment delivery

Question 9

high risk CTV

Answer 9

major risk of local recurrence - residual macroscopic tumour at time of BT (smaller than at the time of diagnosis)

Question 10

intermediate risk CTV

Answer 10

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

Question 11

low risk CTV

Answer 11

potential microscopic tumour spread - treated with surgery and/or EBRT but not brachytherapy

Question 12

interdigitated scheduling + EBRT and HDR fractionation for cervix

Answer 12

give EBRT, then EBRT + HDR, then just HDR

EBRT = 45Gy in 25# to the pelvis
HDR = 30Gy in 5#, 2# per week OR 28Gy in 4#, 2# per week

Question 13

pre-treatment imaging

Answer 13

PET, CT, MRI
- evaluate tumour
- determine treatment modality
- determine optimum treatment volume and dose

Question 14

brachy imaging for each insertion

Answer 14

MRI, CT, US
- evaluate tumour response
- verification of applicator position
- define HRCTV, IRCTV and OAR
- adaptive RT

Question 15

post-treatment imaging

Answer 15

• evaluate tumour response and toxicity

Question 16

What is the clinical use of ultrasound in brachytherapy?

Answer 16

• non invasive, portable and inexpensive
• patient can be imaged during application insertion
• able to confirm applicator position and check intrauterine tandem is centres in uterine cavity
• image real time without moving the patient

Question 17

Advantages of MR images

Answer 17

• excellent soft tissue differentiation - CTV can be located
• use to define target structures and OAR

Question 18

inter and intrafraction variation

Answer 18

• may be significant
• may cause deviation from prescribed dose
• more significant for HDR as the number of fractions is higher than LDR

Question 19

prostate HDR advantages

Answer 19

• image guided needle placement
• optimised dose distribution
• organ motion minimised
• radiobiological advantage
• remote afterloading
• single reusable source

Question 20

what are some acute clinical issues for prostate HDR

Answer 20

• template/catheter movement
• haematrurial/clot retention
• perineal discomfort and back discomfort
• infection risks
• DVT prophylacxis
• defaecation

Question 21

management for template/catheter movement

Answer 21

minimise movement of patient/bed rest

Question 22

management of haematrurial/clot retention

Answer 22

continuous bladder irrigation

Question 23

management of perineal discomfort and back discomfort

Answer 23

analgesics

Question 24

management of infection risk

Answer 24

prophylactic antibiotics

Question 25

management of DVT prophylaxis

Answer 25

stockings/heparin

Question 26

management of defaecation

Answer 26

low residue diet prior to and during admission

Question 27

How and why is brachytherapy employed in the treatment of cervical cancer?

Answer 27

EBRT is not effective enough in some cases to deliver the required amount of radiation without causing high toxicity to provide a tumoricidal dose. Therefore, BT is used to increase the delivered dose.

Question 28

disadvantages of MRI images

Answer 28

- smaller aperture size, which may not accomodate all patient sizes - small FOV - external body of the patient is not visualised

Question 29

Define what a tumoricidal dose is

Answer 29

The amount of radiation given in order to control the cancer

Question 30

How and why is brachytherapy employed in the treatment of cervical cancer?

Answer 30

EBRT is not effective enough in some cases to deliver the required amount of radiation without causing high toxicity to provide a tumoricidal dose. Therefore, BT is used to increase the delivered dose

Question 31

limitations of MR images in brachy

Answer 31

- smaller aperture size, which may not accomodate all patient sizes - small FOV - external body of the patient is not visualised

Question 32

interfraction and intrafraction motion

Answer 32

- may be significant - may cause deviation from prescribed dose - more significant for HDR as the number of fractions is higher than for LDR - high dose per fraction - 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 33

What is the use of a vaginal dilator and why should patients use one?

Answer 33

From EBRT patients are at risk of vaginal adhesions, using a vaginal dilator can help reduce the occurrence as they can possibly prevent applicator insertion for BT