Gamma to X-Ray Transition

[ccollins]

My company is considering the transition from Gamma to X-Ray irradiation modalities. I understand that a dose experiment is necessary to transfer the sterilization dose but is the Max Dose stability transferrable without repeating the study or can we do some minimal verification testing in lieu of a full blow stability study? We will be sterilizing at the same dose on the x-ray irradiator.

Thanks.

 

[planB]

Per the ISO 11137 series, the irradiation modalities gamma, e-beam and x.ray are considered transferable and governed by the equivalent, transferable physical principles. Thus, "dose is dose is dose": as long as you do not change the dose (range), you get the same output, including stability. So your plan to limit verification of stability to a minimum seems reasonable to me.

HTH,

 

[Randy]

Pretty much dose-dose-dose ( Energy source (type of radiation) taking into consideration Time/Shielding/Distance = dose (Absorbed, Equivalent, Effective).

Bit more to it than the above of course.

 

[Ronen E]

Per the ISO 11137 series, the irradiation modalities gamma, e-beam and x.ray are considered transferable and governed by the equivalent, transferable physical principles. Thus, "dose is dose is dose": as long as you do not change the dose (range), you get the same output, including stability. So your plan to limit verification of stability to a minimum seems reasonable to me.

HTH,

(I don't have a copy of the current published standard)

How does wavelength play into the equivalence?

Gamma and X-ray radiation differ in their physical sources (inside/outside the atom nucleus), but in terms of their effect on a target, they are similar in essence - EM waves (or photons = packets of energy). Aren't they?... The main difference is in wavelength - Gamma radiation has a shorter wavelength compared with X-ray. Does the standard relate to the energy delivered per unit volume? If it does, doesn't wavelength have additional effects, other than energy density / rate of delivery?

 

[ccollins]

(I don't have a copy of the current published standard)

How does wavelength play into the equivalence?

Gamma and X-ray radiation differ in their physical sources (inside/outside the atom nucleus), but in terms of their effect on a target, they are similar in essence - EM waves (or photons = packets of energy). Aren't they?... The main difference is in wavelength - Gamma radiation has a shorter wavelength compared with X-ray. Does the standard relate to the energy delivered per unit volume? If it does, doesn't wavelength have additional effects, other than energy density / rate of delivery?

11137-1 does not speak to wave length differences in regards to transference of dose:
8.4 Transference of maximum acceptable, verification or sterilization dose between radiation sources
8.4.1 Transference of maximum acceptable dose
In transferring a maximum acceptable dose to a radiation source different from that on which the dose was
originally established, an assessment shall be made demonstrating that differences in irradiation conditions of
the two radiation sources do not affect the validity of the dose. The assessment shall be documented and the
outcome shall be recorded (see 4.1.2)

Most of the guidance that I can find points to the dose rate and temperature as factors for consideration. Gamma to Xray represents a decrease in temperature and an increased dose rate (less exposure time) therefore the risk factors that impact material stability would seem to decrease overall? It seems to me there is a basis for justification/not repeating max dose study with a risk assessment and supporting literature evidence but I wonder how investigators/auditors would view this?

 

[Ed Panek]

In the Navy, they told us the 3 radioactive cookie stories. You have three cookies, one is gamma-emitting, the next is alpha-emitting and then beta-emitting.

You can put the alpha cookie in a paper bag and be mostly safe
Put the Beta cookie in a lead container
You eat the gamma cookie since gamma rays dont interact with the human body much.

I suspect that this is proper. For example, the polonium that killed Litvinenko was an alpha emitter that destroyed the cell lining of his stomach and intestines.

 

[Ronen E]

In the Navy, they told us the 3 radioactive cookie stories. You have three cookies, one is gamma-emitting, the next is alpha-emitting and then beta-emitting.

You can put the alpha cookie in a paper bag and be mostly safe
Put the Beta cookie in a lead container
You eat the gamma cookie since gamma rays dont interact with the human body much.

I suspect that this is proper. For example, the polonium that killed Litvinenko was an alpha emitter that destroyed the cell lining of his stomach and intestines.

Alpha radiation (particles) is mostly harmless - at least in the "normal" (external exposure) sense.
Beta radiation (electrons) can be blocked by thin layers of many materials (e.g. aluminum foil).
It's the Gamma radiation (no mass particles) that requires thick layers of lead to stop. It definitely interacts with organic tissues, and it can be extremely harmful. The correct bit is that it PASSES THROUGH the human body almost unaffected (because it's so powerful), but it's very naïve to assume it does no harm on the way.

 

[Ronen E]

11137-1 does not speak to wave length differences in regards to transference of dose:
8.4 Transference of maximum acceptable, verification or sterilization dose between radiation sources
8.4.1 Transference of maximum acceptable dose
In transferring a maximum acceptable dose to a radiation source different from that on which the dose was
originally established, an assessment shall be made demonstrating that differences in irradiation conditions of
the two radiation sources do not affect the validity of the dose. The assessment shall be documented and the
outcome shall be recorded (see 4.1.2)

Most of the guidance that I can find points to the dose rate and temperature as factors for consideration. Gamma to Xray represents a decrease in temperature and an increased dose rate (less exposure time) therefore the risk factors that impact material stability would seem to decrease overall? It seems to me there is a basis for justification/not repeating max dose study with a risk assessment and supporting literature evidence but I wonder how investigators/auditors would view this?

Thanks for sharing your knowledge!

The sentence "Gamma to Xray represents a decrease in temperature and an increased dose rate (less exposure time)" does not make sense to me, though. All other things being equal (total dose etc.), I would expect a lower resultant temperature to correlate with a LOWER dose rate (i.e. a longer exposure required). In general, an X ray wave carries less energy per unit time (delivers less power) than a Gamma wave at the same amplitude - due to wavelength. The shorter the wavelength, the higher the energy the EM radiation carries.

The only explanation I can think of for a lower resultant temperature and at the same time a higher dose rate would be that X ray is somehow more lethal to microorganisms, but this is purely speculative (imaginary?) - as far as I know the case is actually the opposite (Gamma is more lethal). I'd be very curios to learn the true explanation.

 

[Randy]

In the Navy, they told us the 3 radioactive cookie stories. You have three cookies, one is gamma-emitting, the next is alpha-emitting and then beta-emitting.

You can put the alpha cookie in a paper bag and be mostly safe
Put the Beta cookie in a lead container
You eat the gamma cookie since gamma rays dont interact with the human body much.

I suspect that this is proper. For example, the polonium that killed Litvinenko was an alpha emitter that destroyed the cell lining of his stomach and intestines.

I think you've got it twisted Ed, I'd much rather have a basket of Alpha compared to Beta or Gamma........Gamma will fry you and Beta won't do you any good. That's why I don't worry one bit about standing next to 6-10 tons of Depleted Uranium (U-235) but I wouldn't want to get with 100 ft of the same amount of Plutonium

 

[Ed Panek]

(1) You have three cookies. One emits alpha radiation, one emits beta radiation and one emits gamma radiation. You have to eat one, put another in your pocket and put a third into a lead box. Which do you put where? Explain. : askscience (reddit.com)

PhysicsLAB: Radioactive Cookies

Document3 (umn.edu)