Cancer imaging Flashcards
What are the uses of imaging in cancer?
- Diagnosis - many tumours have characteristic appearances, CT/USS can be used to guide biopsies
- Staging - need to know anatomical extent of the disease, CT standard but MRI for bone and soft tissue lesions
- Response assessment - can help define response to treatment (along with clinical status and tumour markers), can accurately measure changes in dimension
- Follow-up and surveillance - only useful in some cancers (e.g. testicular), where asymptomatic relapse has been shown to affect clinical outcome
- Screening - mammogram for breast cancer
What system is used to measure response to treatment via imaging?
RECIST system
Complete response - no disease detectable radiologically
Partial response - all lesions have shrunk by at least 30%, but disease still present
Stable disease - less than 20% increase in size or less than 30% decrease in size
Progressive disease - new lesions or lesions that have increased in size by more than 20%
A woman’s lung tumour has increased by 5% on imaging, what would her response be classified as?
Stable disease
A man’s nodule had shrunk by 25% on imaging, what would his response be classified as?
Stable disease
A woman’s nodules have mostly decreased by 35%, however some only by 15%, what class is she?
Stable disease - all lesions need to have shrunk by at least 30% to have partial response
Describe the basic principles of CT
Data are acquired using a rotating X-ray tube and opposing detectors, housed in a fixed gantry with computed reconstruction of axial cross-sectional images
When must an oral contrast medium be administered with CT?
To outline the GI tract - can demonstrate intra-luminal pathology or bowel obstruction, avoids misinterpretation of the bowel loops as mass lesions
What is IV contrast medium used for with CT?
To delineate vascular structures, and to demonstrate tumour enhancement thus increasing lesion detection - especially in the liver
Standard contrast is nephrotoxic and should be avoided in patient’s with known renal impairment
What are the two biggest concerns with CT?
- Radiation - radiation exposure has a risk of inducing malignancies, one additional cancer per 1000 CT (people are followed up for many years)
- Pregnancy in women of child-bearing age
What tissues does MRI image, and what cancers is it now gold-standard for?
MRI produces images of high soft tissue contrast in any cross-sectional plane
Gold standard imaging for neurospinal, rectal, prostate, and MSK tumours
Describe one big contra-indication for MRI?
Metal objects - pacemakers, implantable cardiac defribillators. Also some metabolic foreign bodies - vascular clips, surgical staples, metallic shards following trauma
Most ortho joint replacements try to use non-ferrous materials so these patient’s can still have MRI
Describe the basics of ultrasound and it’s advantages
The reflection of high-frequency sound waves at soft tissue interfaces generates the ultrasound image
Has no ionising radiation, so is safe, widely available and inexpensive
Describe some uses of ultrasound in oncology
- Detecting metastases in solid abdominal organs
- Duplex and doppler USS can be used to assess tumour blood flow
- Real-time guidance of biopsy and therapeutic interventional procedures
NOT GOOD for measuring treatment response
Describe the basics of nuclear medicine
Radioisotope-labelled pharmaceuticals are administered, and their distribution is measure by y-camera detection of emitted photons
Isotopes can be given orally or IV
Which nuclear scan is the principle detection investigation for skeletal metastases?
Bone scintography
