Nuclear medicine (only RT relevant applications) and PET Flashcards

1
Q

What are the indications which lead to a bone scan?

A

Staging of a cancer known to metastasis
Investigate bone pain in cancer
Investigate treatment response
Loosening/infection of a joint replacement

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2
Q

What is a typical protocol for a bone scan?

A

Inject with 600MBq of Tc-99m HDP
Image 2-3 hours later
Image the whole body with LEHR collimators

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3
Q

What is a typical protocol for a parathyroid SPECT scan?

A

Inject 800MBq of Tc-99m MIBI
Static image at 10mins and 2hrs
SPECT at 2hrs
Perform low dose CT

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4
Q

In bone scans what uptake would suggest tumourous disease?

A

Single sided uptake, away from joints and other known areas of degenerative uptake

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5
Q

What are the two PET tracers used for oncology purposes?

A

F-18 FDG

Fluorothymidine (FLT) - used for assessing tumour response

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6
Q

Why is exact attenuation correction possible for PET?

A

The attenuation along a known line of response is independent of the position of the emission along that line

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7
Q

Why use quantification?

A

Lesion characterisation
Response assessment
Data reduction in trials and statistical analysis
Dose optimisation
Testing drug targetting
RT target identification - gives functional target volumes

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8
Q

What is the equation for the standard uptake value?

A

SUV = Activity concentration/(Injected dose/body weight)

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9
Q

What are the three measures of body weight and why would each be used?

A

Body mass - most common
Lean body mass - more consistent across range of body habitus for FDG but more complex to measure
Body surface area - tallies with some dosing regimes

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10
Q

What are the three measures of activity concentration?

A

SUVmax
SUVmean
SUVpeak - the hottest mean value in a small given volume

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11
Q

What is the correction to the SUV equation for the existing blood glucose level?

A

Gluc(mmol/l)/5(mmol/l)

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12
Q

What are the common errors when calculating the SUV and what are their effects?

A

Incorrect cross-calibration between dose calibrator and scanner - systematic error equal to the relative cross calibration
Residual activities in administration system unaccounted for - lower net administration than used to calculate SUV so get lower SUV
Incorrect decay correction - incorrect SUV
Tissued injection - incorrect SUV

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13
Q

What are the technical considerations for the SUV calculation and what effect do they have?

A

Aquisition parameters - affect SNR, get upward bias with low SNR
Image reconstruction - affect convergance, partial voluming effects are worse when convergance is insufficient
ROI strategy - type and size of ROI can change SUV
Normalisation factor and glucose factor used - BSA, BM, and LBM are not comparable, need to use glucose factor for accuracy
Contrast agents - produces attenuation map errors so can effect SUV values

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14
Q

What are the patient factors that need to be considered for SUV calculations and what effect do they have?

A

Blood glucose level - can reduce uptake if high
Uptake period - different point on uptake curve therefore different SUV
Patient comfort - FDG uptake in muscle and brown fat higher due to discomfort
Inflammation - false positively increased SUV
Patient motion/breathing - causes mismatch of attenuation correction, may also smear out counts so get lower SUV

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15
Q

What SUV calculation did the PERCIST trial use and why?

A

SUV peak and lean body mass

Gave hottest SUL for the baseline and follow-up lesions

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16
Q

What were the four PERCIST classifications?

A

Total metabolic response - can’t distinguish lesion at baseline from bloodpool at follow-up
Partial metabolic response - drop in SUL >30% and at least 0.8 in absolute terms
Stable metabolic disease - no change
Progressive metabolic disease - increase in SUL>30% and of at least 0.8 in absolute terms

17
Q

Why use compartmental models?

A

Derived kinetic parameters may more closely describe pathophysiology

18
Q

What corrections are needed to calculate the activity concentration?

A
Randoms correction
Normalisation
Dead time correction
Scatter correction
Attenuation correction
PET scanner calibration
19
Q

What is the cause of ‘randoms’ and what is the equation to estimate the rate of randoms per second?

A

Two uncorrelated single detection events happen within sufficient temporal activity to fall within trues detection window
Cij = 2.tau.ri.rj

20
Q

What are causes of the variable sensitivities which normalisation accounts for?

A
Axial data summing and 'mashing'
Detector efficiency
Geometric and solid angle effects
Time window alignment
Structural alignment
Septa
21
Q

How is direct normalisation achieved?

A

Illuminate all possible lines of response with a positron source
Analytical correction is made for non-uniform radial illumination
Normalisation coefficients including all effects are taken to be inversely proportional to the counts acquired in each LOR

22
Q

What are the issues with direct normalisation?

A

Long acquisition times needed for good quality normalisation matrix
Needs excellent uniformity
Quantity and distribution of scatter is rarely comparable to that of a patient