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CSB094 - RT Planning 4 > Wk 11 - Brachytherapy > Flashcards

Wk 11 - Brachytherapy Flashcards

1
Q

low dose rate (LDR)

A

0.4-2Gy/h

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2
Q

medium dose rate (MDR)

A

2-12Gy/h

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3
Q

high dose rate (HDR) gy/h

A

> 12Gy/h

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4
Q

half life of 226 radium

A

1600 years

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5
Q

half life of 60 Cobalt

A

5.26 years

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5
Q

half life of 137 Caesium

A

30 years

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5
Q

half life of 192 iridium

A

74 days

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5
Q

half life of 125 iodine

A

59.5 days

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6
Q

advantages of HDR

A
  • 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
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7
Q

disadvantages of HDR

A
  • 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
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8
Q

brachy workflow

A
  1. implantation
  2. image acquisition
  3. catheters
  4. targets and OAR delineation
  5. treatment planning and optimisation
  6. quality control
  7. treatment delivery
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9
Q

high risk CTV

A

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

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10
Q

intermediate risk CTV

A

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

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11
Q

low risk CTV

A

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

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12
Q

interdigitated scheduling + EBRT and HDR fractionation for cervix

A

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

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13
Q

pre-treatment imaging

A

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

14
Q

brachy imaging for each insertion

A

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

15
Q

post-treatment imaging

A
  • evaluate tumour response and toxicity
16
Q

What is the clinical use of ultrasound in brachytherapy?

A
  • 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
17
Q

Advantages of MR images

A
  • excellent soft tissue differentiation - CTV can be located
  • use to define target structures and OAR
18
Q

inter and intrafraction variation

A
  • may be significant
  • may cause deviation from prescribed dose
  • more significant for HDR as the number of fractions is higher than LDR
19
Q

prostate HDR advantages

A
  • image guided needle placement
  • optimised dose distribution
  • organ motion minimised
  • radiobiological advantage
  • remote afterloading
  • single reusable source
20
Q

what are some acute clinical issues for prostate HDR

A
  • template/catheter movement
  • haematrurial/clot retention
  • perineal discomfort and back discomfort
  • infection risks
  • DVT prophylacxis
  • defaecation
21
Q

management for template/catheter movement

A

minimise movement of patient/bed rest

22
Q

management of haematrurial/clot retention

A

continuous bladder irrigation

23
Q

management of perineal discomfort and back discomfort

A

analgesics

24
Q

management of infection risk

A

prophylactic antibiotics

25
Q

management of DVT prophylaxis

A

stockings/heparin

26
Q

management of defaecation

A

low residue diet prior to and during admission

27
Q

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

A

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.

28
Q

disadvantages of MRI images

A
  • smaller aperture size, which may not accomodate all patient sizes
  • small FOV - external body of the patient is not visualised
29
Q

Define what a tumoricidal dose is

A

The amount of radiation given in order to control the cancer

30
Q

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

A

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

31
Q

limitations of MR images in brachy

A
  • smaller aperture size, which may not accomodate all patient sizes
  • small FOV - external body of the patient is not visualised
32
Q

interfraction and intrafraction motion

A
  • 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
33
Q

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

A

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

CSB094 - RT Planning 4 (9 decks)

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