Radiation Dose: Part II

How do we convert DAP to Effective Dose?

Understanding radiation dose in Angiography & Intervention is important knowledge for our professional practice and patient care. It is however, often overlooked and misunderstood.

DAP is related to the stochastic effects which has potential to induce cancer and other cellular mutations. AK is related to the deterministic effects and can be used to determine the risk of skin erythema (>2 Gy) or skin epilation (>5 Gy) for example. AK is equivalent to the Peak Skin Dose (PSD) or Skin Equivalent Dose (SED).

DAP can be used to determine the overall radiation risk from a particular procedure or intervention by converting this to the radiological protection form of measurement, with Effective Dose (ED). Effective dose sums up the number of different exposures into a single measurement that reflects overall risk to radiation-induced injury.

By referring to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and the Global Survey on Medical Exposure: A User Manual, factors for estimating effective dose from image-guided interventional procedures are provided.

It is important to have your DAP value converted into Gy.cm^2 and to use to the given Dose Conversion Coefficient (DCEE) [mSv.(Gy.cm^2)^-1]. The product of the DAP and the DCCE is the Effective Dose for the interventional procedure.

For example, a DAP value of 10.5 Gy.cm^2 for a uterine artery embolization procedure, multiplied by the DCCE for pelvic artery embolization at 0.26 mSv.(Gy.cm^2)^-1, gives an Effective Dose of 2.73 mSv. According to the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA), one chest x-ray is 0.06 mSv and one chest CT is 5 mSv. For this single UAE procedure, this would be less than one chest CT scan and more than 45 PA and Lateral chest x-rays.

Summary of Ionizing Radiation and Effects on Humans:

Dose range up to 10 mSv has no direct evidence of human health effects
10 - 1000 mSv has no early effects, but increased incidence of certain cancers in exposed populations at higher doses
1000 - 10000 mSv induces radiation sickness (risk of death), and an increased incidence of certain cancers in exposed populations
> 10000 mSv is fatal

Source: UNSCEAR's Global Survey of Radiation Exposure [UNSCEAR survey]

“There is no safe dose of radiation since radiation is cumulative. Harm in the form of excess human cancer occurs at all doses of ionizing radiation, down to the lowest conceivable dose and dose rate.”

- John Gofman