Radiation dose

Question 1

radiation effects pregnancy

Answer 1

stochastic effect - teratogenesis, no threshold hold, chance events, increase chance with dose but not severity
non stochastic / deterministic - carcinogenesis, mutations,
absorbed dose more than 0.5mGy needs justification
carcinogenesis no dose threshold or gestational age limit

Question 2

teratogenic effect pregnancy risk period

Answer 2

Teratogenic effects are cumulative with increasing dose and require a threshold dose (< 50 mGy are considered as safe) and depend on the gestation age (minimum risk prior to 8th week and after the 23rd week

Question 3

CT vs MRI for stones in pregnancy

paper of increased diagnostic accuracy

Answer 3

For the detection of urolithiasis during pregnancy, low-dose CT is associated with a higher positive predictive value (95.8%), compared to MRI (80%) and US (77%).

As per White et al., low-dose CT offers improved diagnostic accuracy that can avoid negative interventions such as ureteroscopy.

Question 4

IVU dose vs VMUG

Answer 4

The radiation dose for IVU is comparable to that for voiding cysto-urethrography (0.33 mSV)

Question 5

10mSv cancer risk

Answer 5

1/1000 risk cancer expsorure, 1 in 2000 develop fatal cancer

Question 6

pregnancy American college of O+G
risk of teratogenesis threshold dose of deterministic effect
dose related to stochastic carcinogenic effect
increased risk to background of leukaemia

Answer 6

<50mSV no risk of anomoly, growth restricture

risk of carcinogenesis unclear, 10-20mSV may increase leukaemia x 2 over BG rate of 1 in 30000

Question 7

radiation dose dexa scan

background radiation dose

Answer 7

0. 4 microsieverts = 4 bananas
1. 4 microsieverts = 0.004 millisieverts

background radiation dose 0.3mSv per month or around 3 mSV per year

Question 8

pet vs spect
type of radiation detectors
how pet scans works

Answer 8

The main difference between SPECT and PET scans is the type of radiotracers used.
While SPECT scans measure gamma rays, the decay of the radiotracers used with PET scans produce small particles called positrons. A positron is a particle with roughly the same mass as an electron but oppositely charged. These react with electrons in the body and when these two particles combine they annihilate each other. This annihilation produces a small amount of energy in the form of two photons that shoot off in opposite directions. The detectors in the PET scanner measure these photons and use this information to create images of internal organs.

Question 9

use of PET CT in seminoma

paper of sens and spec for seminoma and FDG PET

Answer 9

> 3cm
santis et al
sesitivity 80%, spec 100% for F-FDG PET

Question 10

deterministic effects vs stochastic effects radiation

Answer 10

Stochastic effects of ionising radiation are chance events, with the probability of the effect increasing with dose, but the severity of the effect is independent of the dose received. Stochastic effects are assumed to have no threshold.

Deterministic effects (or tissue reactions) of ionising radiation are related directly to the absorbed radiation dose and the severity of the effect increases as the dose increases. A deterministic effect typically has a threshold (of the order of magnitude of 0.1 Gy or higher) below which the effect does not occur. Deterministic effects are based on tissue damage.