[Intl_DxMedPhys] Sanity Check Needed for Pb-212 HVL

Thu Apr 16 17:58:02 EDT 2026

Hi,

If it helps, I have attached a graph of the PB212 and daughter activities over 24hrs (using the WISE uranium website). So, t=0 is freshly produced Pb212. A transient equilibrium state is reached after about 8-9hrs, with all daughters appearing to 'decay' then with the same half-life as Pb212.

But the point to watch is that due to half-life ratios, the Bateman equations give the first daughter (Bi208) activity as 110% that of Pb212 , despite the decay value being 100%. This in turn leads to higher activities for Tl208 and Po212 of 40% and 71% respectively.

As noted , the main gamma emission of concern for shielding from Tl208 is the 2.6MeV gamma , in 100% of the Tl208 decays. Calculations of shielding might need  the appropriate activity of Tl208 , in relation to the PB212 activity, so this might help.

Regards

Bill Thomson

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From: Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces+bill.thomson=nhs.net at lists.osu.edu> on behalf of Gretchen Raterman Bell via Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list at lists.osu.edu>
Sent: 16 April 2026 21:02
To: Gretchen Raterman Bell via Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list at lists.osu.edu>
Subject: Re: [Intl_DxMedPhys] Sanity Check Needed for Pb-212 HVL

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UPDATE: I made a rookie error. Dr. Reagan Dugan pointed out that the Smith/Stabin table only provides HVL data for that isotope and not the daughter products. Gretchen R. Bell, M. S. , DABR Diagnostic Imaging Physicist Ochsner Medical Center (504)842-8506
UPDATE:  I made a rookie error.  Dr. Reagan Dugan pointed out that the Smith/Stabin table only provides HVL data for that isotope and not the daughter products.

Gretchen R. Bell, M.S., DABR
Diagnostic Imaging Physicist
Ochsner Medical Center
(504)842-8506

On Thu, Apr 16, 2026 at 2:59 PM Gretchen Raterman Bell <gretchen.raterman at gmail.com<mailto:gretchen.raterman at gmail.com>> wrote:
Thank you for pointing that out!  I'll update the group.  Someone else sent me a Canadian paper that states 11.2 for 1st HVL and 15.2 for 2nd.  So all this makes more sense!!

Gretchen R. Bell, M.S., DABR
Diagnostic Imaging Physicist
Ochsner Medical Center
(504)842-8506

On Thu, Apr 16, 2026 at 2:55 PM Reagan Dugan <rdugan1102 at gmail.com<mailto:rdugan1102 at gmail.com>> wrote:
Hi Gretchen,

If I'm reading the Stabin paper correctly, they didn't combine emissions from parent/daughter, so that HVL for Pb-212 would only be accounting for the Pb-212 gamma emissions (238  keV mostly). If you scroll down the list a bit to Tl-208, the HVL is 15.5 mm, which makes more sense to me given the number of emissions and energies.

I haven't had to do shielding designs for alpha emitters yet, but I'd probably base the design off the Tl-208 data since those are the primary gammas used for imaging. Trying to account for the entire decay chain will probably require monte carlo simulations and another task group. I'd also double check to make sure you use the correct half life for Tl-208 since there's equilibrium issues at play.

For our clinical trials here we've just been using one of our pluvicto rooms in PET which were shielded for F18 before any of the theranostics stuff took off. We haven't gone through the math yet, but I think we're operating under the assumption that the workload for the trials is so low that the existing shielding is fine. For newer rooms we've just been assuming a full workload of Lu-177 therapies using the TG-313 archer coefficients.

If you end up working through the math for the alpha emitters, I'd love to see what you come up with if you're willing to share.

Good luck!

Reagan Dugan, PhD

Imaging Physics Resident

Department of Radiology

The University of Chicago Medicine

5841 S. Maryland Ave. | MC 2026 | Room M-529

Chicago, Il 60637

Office: 773-702-1220

On Thu, Apr 16, 2026 at 2:14 PM Gretchen Raterman Bell via Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list at lists.osu.edu<mailto:intl_dxmedphys_wd_osu_list at lists.osu.edu>> wrote:
Greetings! I am dipping my toe into shielding requirements for theranostics.   One of the hot new isotopes of course is Pb-212.   I had looked at its decay chain a while back and saw a rather high-yield MeV emission from its daughter Tl-208 and
Greetings!

I am dipping my toe into shielding requirements for theranostics.  One of the hot new isotopes of course is Pb-212.  I had looked at its decay chain a while back and saw a rather high-yield MeV emission from its daughter Tl-208 and figured we could forget about a reasonable amount of lead.  We'd have to use time and distance.  HOWEVER today, I thought to look at the Smith and Stabin paper that lists 1000+ isotopes with their gamma rate factors and HVL, etc. data.  Pb-212 is listed as having an HVL of only 0.756 mm Pb, which is about 1/7th the HVL they list for F-18!  I understand that F-18 is almost 100% positron decay, but I still find this difference in HVL incredible.

Before going down a wild rabbit hole, I figured I'd probe the list for any other insights into Pb-212.  We are starting a clinical trial soon using it, and I've been tasked with writing up a Radiation Safety SOP.  In addition, we are doing a reno of one of our NM departments, and they would like to add dedicated theranostic injection rooms... so trying to see what kind of lead to put in the walls.  (It's truly an impossible task, but I'm giving it my "college try.")

Many, many thank yous in advance.

Gretchen R. Bell, M.S., DABR
Diagnostic Imaging Physicist
Ochsner Medical Center
(504)842-8506

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