I-131 Therapy for Thyroid Cancer

I-131 therapy for differentiated thyroid cancer is the oral administration of beta-emitting iodine-131 after thyroidectomy to ablate the thyroid remnant, treat presumed microscopic disease, or treat known structural and metastatic disease — with administered activities that range from about 1.11 GBq (30 mCi) for low-risk remnant ablation up to several GBq for higher-risk and metastatic settings. The treatment exploits the thyroid's natural iodine avidity, and the same radionuclide that delivers the therapeutic dose also produces imageable photons for a post-therapy scan. This guide covers the nuclear-medicine physics: how the three treatment intents differ, when to choose fixed activities versus dosimetry, how patients are prepared, what the post-therapy whole-body scan and SPECT/CT add, and how effective half-life and MIRD dosimetry govern both efficacy and safety.

Introduction

Iodine-131 was among the first radionuclides used therapeutically, and radioiodine ablation of differentiated thyroid cancer (DTC) remains one of the most established and most physics-rich therapies in nuclear medicine. The premise is elegant: differentiated papillary and follicular thyroid cells retain the sodium-iodide symporter that normal thyroid uses to concentrate iodine, so an oral capsule of radioactive iodide is trafficked selectively into the very cells you want to destroy. The short-range beta particles then deposit nearly all of their energy within a few millimeters, sparing surrounding tissue.

What makes I-131 therapy interesting from a medical-physics standpoint is that the apparent simplicity hides several consequential decisions: how much activity, fixed or dosimetry-guided, withdrawal or recombinant TSH, and when to image. Each has a physics answer grounded in iodine kinetics, MIRD dosimetry, effective half-life, and quantitative imaging.

This article focuses on the nuclear-medicine physics for physicists, residents, RSOs, and clinicians who want the quantitative reasoning behind the protocol. The downstream patient-release calculations — the dose-to-others limits that govern when a treated patient can go home — are covered separately in our patient release after radiopharmaceutical therapy guide; here we reference but do not duplicate them. DRPS provides this analysis as part of its PET/CT and nuclear medicine physics support.

Topic Explanation

The radionuclide and the target

Iodine-131 has a physical half-life of about 8.02 days and decays by beta-minus emission to xenon-131, with a principal gamma photon at 364 keV that makes it both therapeutic and imageable. The beta particles (maximum energy near 606 keV, mean energy roughly 190 keV) have a mean tissue range on the order of a fraction of a millimeter to a couple of millimeters and carry the therapeutic dose. The 364 keV gamma — emitted in roughly 81% of decays — is what allows post-therapy scintigraphy, but it also drives the external dose rate and the shielding and patient-release considerations.

The molecular target is the sodium-iodide symporter (NIS), expressed on normal thyroid follicular cells and retained, to varying degrees, on differentiated tumor cells. Because uptake depends on functioning NIS and on a high circulating TSH level to upregulate it, both patient preparation (raising TSH) and tumor differentiation determine whether therapy will work. Poorly differentiated and dedifferentiated tumors lose iodine avidity and become radioiodine-refractory.

Three treatment intents

The single most important conceptual distinction in modern DTC management is that "radioiodine therapy" is not one thing — it is three different interventions with different goals and different activities. Following the framework articulated in the contemporary literature ²:

Remnant ablation targets the benign normal-thyroid tissue left behind after total or near-total thyroidectomy. The goal is to eliminate residual normal thyroid so that serum thyroglobulin becomes a clean tumor marker and follow-up imaging is interpretable. This is the lowest-activity setting.
Adjuvant treatment targets presumed but unproven microscopic disease in intermediate- to high-risk patients. There is no visible target; the rationale is to sterilize occult microscopic foci and reduce recurrence. This warrants an activity greater than remnant ablation ².
Treatment of known disease targets macroscopic structural disease — residual neck tumor, nodal metastases, or distant (lung, bone) metastases. This uses the highest activities and is the setting where individualized dosimetry has the strongest rationale.

The 2015 American Thyroid Association (ATA) guidelines tie the choice of intent and activity to a recurrence-risk stratification (low, intermediate, high) and have steadily de-escalated radioiodine use in low-risk disease ¹.

Key Technical Principles

Administered activity by intent

Administered activities span roughly an order of magnitude across the three intents, from about 1.11 GBq (30 mCi) for low-risk remnant ablation to 5.55 GBq (150 mCi) or more for higher-risk adjuvant and known-disease settings, with dosimetry-defined ceilings beyond that. The table below summarizes the typical ranges; every figure should be anchored to the cited guideline and individualized to the patient.

Intent	Typical empiric activity	Rationale / evidence	Dosimetry role
Remnant ablation (low risk)	~1.11 GBq (30 mCi) ¹	ATA favors low activity; HiLo RCT showed 1.1 GBq non-inferior to 3.7 GBq ³	Minimal; fixed activity standard
Adjuvant (intermediate / high risk)	~3.7 GBq (100 mCi), up to ~5.55 GBq (150 mCi) ^{1, 2}	Activity should exceed remnant-ablation activity; optimal value debated ^{2, 4}	Selective
Known structural / nodal disease	~3.7–5.55 GBq (100–150 mCi) ¹	Macroscopic target; higher activity for bulkier disease	Increasingly considered
Distant metastatic disease	~5.55–7.4 GBq (150–200 mCi) empiric	Highest empiric activities	Strongest rationale for blood/lesion dosimetry

For low-risk remnant ablation, the evidence base is unusually firm. The randomized HiLo trial (438 patients) compared 1.1 GBq with 3.7 GBq, each crossed with rhTSH or withdrawal, and found ablation success rates of 85.0% versus 88.9% — within the non-inferiority margin — while the low-activity arm had fewer adverse events and far fewer prolonged hospitalizations ³. A separate retrospective comparison in intermediate-to-high-risk patients found no significant overall difference between 1.11 GBq and 2.96–3.7 GBq, though high-dose therapy trended better specifically in the high-risk subgroup ⁴. The recurring theme: lower activities suffice for low-risk ablation, while the optimal activity for adjuvant and known-disease treatment remains genuinely unsettled ².

Effective half-life and patient retention

The radiation dose delivered by I-131 depends not on the physical half-life alone but on the effective half-life, which combines physical decay with biological clearance. This is the quantity that governs both tumor dose and the whole-body retention that drives patient-release timing. The relationship is:

\frac{1}{T _{eff}} = \frac{1}{T _{phys}} + \frac{1}{T _{bio}}

equivalently, in terms of decay constants, $λ_{eff} = λ_{phys} + λ_{bio}$ . Consider a normal thyroid remnant, where iodine is organified and retained for a long time — say a biological half-life of $T_{bio} = 60$ days against the physical $T_{phys} = 8.02$ days:

T_{eff} = \frac{T _{phys} \cdot T _{bio}}{T _{phys} + T _{bio}} = \frac{8.02 \times 60}{8.02 + 60} \approx 7.1 days

Because biological retention is long, the effective half-life sits close to the physical value. By contrast, iodine that is not trapped clears renally with a biological half-life of hours, so whole-body (blood-pool) clearance is dominated by biology in the first day or two and by physical decay thereafter. This split behavior — fast non-thyroidal clearance, slow thyroidal retention — is exactly what dosimetry models must capture, and it is why a single retention measurement at the wrong time can mislead.

MIRD dosimetry and the blood-dose constraint

The MIRD schema computes mean absorbed dose to a target as the time-integrated activity in each source region multiplied by the appropriate S value, and in I-131 thyroid therapy it is applied both to maximize lesion dose and to cap the dose to blood as a surrogate for bone marrow. The general MIRD expression is:

D (r_{T}) = r_{S} \sum \tilde{A} (r_{S}) \cdot S (r_{T} \leftarrow r_{S})

where $D (r_{T})$ is the mean absorbed dose to target region $r_{T}$ , $\tilde{A} (r_{S})$ is the time-integrated activity (total number of decays) in source region $r_{S}$ , and $S (r_{T} \leftarrow r_{S})$ is the absorbed dose to the target per decay in the source. The time-integrated activity is the area under the time–activity curve, obtained by serial measurements (blood samples, whole-body counts, or quantitative imaging) and integration.

Two complementary dosimetry philosophies exist:

Lesion dosimetry aims to confirm that a tumor or remnant will receive a tumoricidal absorbed dose. A frequently cited heuristic from the older literature is that remnant ablation tends to succeed when the remnant receives on the order of a few hundred gray, and gross tumor a lower threshold; lesion-dose estimates per unit administered activity vary widely across patients ⁹.
Blood (bone-marrow) dosimetry caps the activity so that the dose-limiting organ — red marrow, surrogated by blood — is not overdosed. The classic Benua–Leeper maximum-tolerable-activity framework limits the absorbed dose to blood to 2 Gy (200 cGy), with additional retention constraints of no more than 4.44 GBq (120 mCi) whole-body retention at 48 hours, reduced to no more than 2.96 GBq (80 mCi) at 48 hours in the presence of diffuse pulmonary metastases to avoid radiation pneumonitis and pulmonary fibrosis ⁹. These limits are reaffirmed in modern dosimetry practice and contemporary procedure standards.

A simplified blood-dose model treats the blood self-dose and the whole-body (penetrating photon) contribution separately. The classic Benua formulation estimates blood absorbed dose as a sum of a beta term proportional to the integral of blood activity concentration and a gamma term proportional to whole-body residence time, normalized by patient mass. In practice a physicist samples blood and counts whole-body retention at several time points (for example, 2, 24, 48, 72, and 96 hours), fits clearance curves, and computes the maximum administrable activity that keeps the projected blood dose at or below 2 Gy. A dosimetry study in metastatic DTC reported a mean red-marrow absorbed dose near 0.5 Gy per 100 mCi (about 0.5 Gy/3.7 GBq) using a blood-surrogate model — illustrating that the historical empiric ceiling of 250 mCi (9.25 GBq) can, in some patients, approach the 2 Gy marrow constraint ¹⁰. That same study found marrow dose was slightly higher after thyroid hormone withdrawal than after rhTSH stimulation, a kinetic difference with real dosimetric consequences ¹⁰.

Fixed-activity versus dosimetry-guided dosing

This is the central methodological choice, and it parallels the same debate in Lu-177 theranostics dosimetry:

Fixed (empiric) activity assigns a standard activity by risk category — 1.11 GBq for low-risk ablation, higher fixed activities for adjuvant and known disease. It is simple, fast, requires no serial sampling, and is supported by strong randomized data in the low-risk setting ³.
Dosimetry-guided activity individualizes the prescription, either to deliver a target tumor dose (lesion dosimetry) or to avoid exceeding the 2 Gy blood limit (blood/marrow dosimetry). Its rationale is strongest in young patients, those with extensive metastatic disease, those requiring repeated treatments, and any case where an empiric high activity might breach the marrow ceiling ^{9, 10}.

No regulation or guideline mandates dosimetry for routine ablation. The honest position, mirrored across radiopharmaceutical therapy, is that dosimetry is scientifically sound and valuable for advanced and individualized cases, but unproven to improve outcomes versus fixed activity in low-risk disease.

Clinical Impact

Patient preparation: raising TSH and depleting cold iodine

Effective I-131 uptake requires high TSH to upregulate the symporter and a low body iodine pool so the radioiodine is not diluted by stable iodine — achieved by TSH stimulation plus a low-iodine diet. TSH elevation is accomplished one of two ways:

Thyroid hormone withdrawal (THW) stops levothyroxine (often with a liothyronine bridge) long enough to render the patient hypothyroid, driving endogenous TSH above the commonly cited target of roughly 30 mIU/L. It is inexpensive but produces weeks of hypothyroid symptoms.
Recombinant human TSH (rhTSH, Thyrogen) is given as two intramuscular injections on consecutive days, stimulating uptake while the patient remains euthyroid on levothyroxine.

The physics-relevant point is that the two methods change iodine kinetics, not just comfort. Randomized data (HiLo) and a meta-analysis of seven randomized trials (1,535 patients) found comparable ablation success between rhTSH and withdrawal, with rhTSH giving better quality of life at the time of treatment ^{3, 5}. Crucially for radiation safety, rhTSH preparation generally produces faster whole-body clearance and lower whole-body absorbed dose than withdrawal, because a euthyroid patient clears non-thyroidal iodine through the kidneys more rapidly than a hypothyroid one — a difference that propagates into both marrow dose and patient-release timing ^{5, 10}.

A low-iodine diet, typically for one to two weeks before therapy, depletes the stable-iodine pool so that administered radioiodine is preferentially trapped. Recent iodinated CT contrast and amiodarone are important confounders that can block uptake for weeks to months and must be screened for.

The post-therapy scan: free, high-quality, and management-changing

Because the therapeutic activity is orders of magnitude larger than a diagnostic tracer dose, a post-therapy whole-body scan acquired several days after administration yields excellent count statistics, and adding SPECT/CT routinely improves lesion localization and changes staging. The post-therapy scan is typically performed 2–7 days after administration, when background has cleared and target-to-background contrast is high.

Planar whole-body imaging alone is often ambiguous: a focus in the lower neck could be remnant or nodal metastasis; a chest focus could be lung metastasis or physiologic activity. SPECT/CT resolves these. In a prospective study of 365 DTC patients, SPECT/CT correctly characterized uptake in 82 of 100 patients whose planar scans were equivocal, reclassified nodal or distant metastases in 22 of those 100, and changed the TNM stage in 13 — concluding that SPECT/CT affects therapy decision-making and patient management ⁶. Pediatric and young-adult series show similar incremental value, with management change in roughly 7% of cases ⁷. For the underlying acquisition and quality-control considerations, see our SPECT/CT quality control guidance.

The same gamma camera and quantitative methods used here connect directly to other nuclear-medicine measurements; the pretherapy uptake question is covered in thyroid uptake measurement.

Practical Optimization Tips

For a facility running or building an I-131 DTC therapy program:

1. Match activity to intent, not habit

Confirm whether the case is remnant ablation, adjuvant, or known disease before choosing an activity. Defaulting every low-risk ablation to 3.7 GBq when 1.11 GBq is non-inferior adds unnecessary dose, hospitalization, and release delay ^{1, 3}.

2. Verify preparation before dosing

Document a TSH above the target threshold (for withdrawal) or a completed rhTSH course, confirm low-iodine-diet compliance, and screen for recent iodinated contrast, amiodarone, and pregnancy. Uptake-blocking confounders waste the entire treatment.

3. Reserve dosimetry for where it pays

Apply blood/marrow dosimetry when an empiric activity could approach the 2 Gy blood limit or the 48-hour retention ceilings — extensive metastatic disease, diffuse lung metastases, repeat treatment, renal impairment, and pediatric patients ^{9, 10}. For routine low-risk ablation, fixed activity is appropriate.

4. Always acquire post-therapy SPECT/CT

Treat the post-therapy scan as a staging study, not an afterthought. Add SPECT/CT of the neck and chest to every planar whole-body scan; the incremental staging and management value is well documented ^{6, 7}.

5. Standardize quantitative methods

If you do dosimetry, lock in the calibration, energy window (364 keV photopeak), scatter and attenuation correction, and the blood-sampling and whole-body-counting schedule, and keep them constant so serial and cross-cycle comparisons remain valid.

Common pitfalls

Over-treating low-risk patients with high empiric activities the evidence does not support.
Skipping confounder screening, especially recent CT contrast, and getting a failed uptake.
Relying on planar imaging alone and mis-staging equivocal foci.
Ignoring the withdrawal-versus-rhTSH kinetic difference when projecting marrow dose and release timing.
Treating the 2 Gy blood limit and 48-hour retention ceilings as optional in metastatic and pulmonary disease.

Regulatory Considerations

In the United States, I-131 is byproduct material whose therapeutic use requires a written directive and is governed by NRC 10 CFR Part 35 (or the equivalent Agreement State program), with patient release handled under a separate framework that this article references but does not duplicate. Therapeutic administration of I-131 falls under 10 CFR 35.300, "Use of unsealed byproduct material for which a written directive is required," with authorized-user training requirements in 10 CFR 35.390 and, for parenteral administration, 10 CFR 35.396. A signed written directive specifying the radiopharmaceutical, activity, and route is required before administration, and the facility's radioactive material license and the radiation safety officer's program must support the use.

Patient release after therapy is governed by 10 CFR 35.75 and detailed in NRC Regulatory Guide 8.39, "Release of Patients Administered Radioactive Material" (Revision 1, April 2020), which implements the 5 mSv (0.5 rem) dose-to-others criterion and the instructions-to-patient and breastfeeding requirements. The release calculation — which depends directly on the effective half-life and retained activity discussed above — is treated fully in our patient release after radiopharmaceutical therapy guide and is not repeated here. Contamination control and waste handling after therapy are covered in radioactive waste management in nuclear medicine.

DRPS supports facilities across Florida, Maryland, Virginia, Washington DC, California, Nevada, Pennsylvania, New York, New Jersey, and Delaware. For I-131 as byproduct material, Florida, Maryland, Virginia, California, Nevada, Pennsylvania, New York, and New Jersey are NRC Agreement States that administer their own equivalent programs, while Washington DC and Delaware are regulated directly by the NRC as non-Agreement jurisdictions. Programs standing up therapy services should coordinate licensing through radioactive material license support.

Frequently Asked Questions (FAQs)

What is I-131 therapy for thyroid cancer?

I-131 (radioiodine) therapy is the oral administration of iodine-131, a beta-emitting radionuclide, to destroy residual thyroid tissue or treat differentiated thyroid cancer after thyroidectomy. Iodine-avid thyroid and tumor cells concentrate the radioiodine through the sodium-iodide symporter, and the short-range beta particles deliver a high local absorbed dose while sparing surrounding tissue.

What is the difference between remnant ablation, adjuvant treatment, and treatment of known disease?

Remnant ablation targets the benign normal-thyroid remnant left after surgery and uses a low activity, typically about 1.11 GBq (30 mCi). Adjuvant treatment targets presumed microscopic disease in intermediate- to high-risk patients and uses a higher activity. Treatment of known structural or metastatic disease uses the highest activities and is the setting where individualized dosimetry matters most.

How much I-131 activity is used for remnant ablation?

For ATA low-risk patients undergoing remnant ablation, the 2015 ATA guidelines favor a low administered activity of approximately 1.11 GBq (30 mCi). Randomized data, including the HiLo trial, show that 1.1 GBq is non-inferior to 3.7 GBq (100 mCi) for successful ablation, with fewer side effects and shorter hospitalization.

What is the effective half-life of I-131 in thyroid tissue?

The effective half-life combines the 8.02-day physical half-life of I-131 with the biological clearance of iodine. For a normal thyroid remnant the biological half-life is long, so the effective half-life approaches the physical value, but for tumor and whole-body clearance it is shorter. Effective half-life is computed as 1/T_eff = 1/T_phys + 1/T_bio.

Do patients need thyroid hormone withdrawal or Thyrogen before I-131?

Both raise TSH to stimulate iodine uptake. Thyroid hormone withdrawal makes the patient temporarily hypothyroid to elevate endogenous TSH above roughly 30 mIU/L, while recombinant human TSH (rhTSH, Thyrogen) achieves stimulation without withdrawal symptoms. Randomized and meta-analytic data show comparable ablation success, with better quality of life and lower whole-body radiation exposure using rhTSH.

Why is a post-therapy whole-body scan and SPECT/CT performed after I-131?

The therapeutic activity itself produces high-quality images several days after administration. A post-therapy whole-body scan with SPECT/CT localizes iodine-avid foci, distinguishes thyroid-bed remnant from nodal or distant metastases, and frequently changes staging and management compared with planar imaging alone.

Is dosimetry required for I-131 thyroid cancer therapy?

No. Most remnant ablation and adjuvant treatment use fixed (empiric) activities, and no regulation requires patient-specific dosimetry. Dosimetry-guided approaches — lesion dosimetry to ensure tumor dose, or blood and whole-body dosimetry to cap marrow dose — are used selectively for advanced or pediatric disease and for patients where empiric activities risk exceeding safe marrow limits.

Key Takeaways

I-131 therapy is three distinct interventions — remnant ablation, adjuvant treatment, and treatment of known disease — with activities ranging from about 1.11 GBq (30 mCi) for low-risk ablation up to several GBq for higher-risk and metastatic settings ^{1, 2}.
Low-risk ablation does not need high activity. The randomized HiLo trial showed 1.1 GBq non-inferior to 3.7 GBq, with fewer adverse events ³.
Effective half-life governs dose and retention. It combines the 8.02-day physical half-life with biological clearance via 1/T_eff = 1/T_phys + 1/T_bio, approaching the physical value for retained thyroid iodine.
MIRD dosimetry serves two roles — delivering a tumoricidal lesion dose and capping blood dose at the classic Benua–Leeper limit of 2 Gy, with 4.44 GBq (120 mCi) whole-body and 2.96 GBq (80 mCi) pulmonary-metastasis retention ceilings at 48 hours ⁹.
Preparation is physics, not just comfort. rhTSH and withdrawal give comparable ablation success, but rhTSH clears faster and lowers whole-body dose; a low-iodine diet prevents stable-iodine dilution ^{5, 10}.
Post-therapy SPECT/CT changes management in a meaningful fraction of patients and should be acquired routinely ^{6, 7}.

Conclusion

I-131 therapy for differentiated thyroid cancer is a mature treatment whose quality depends on a chain of physics-grounded decisions: correctly classifying the treatment intent, choosing an activity that the evidence supports, preparing the patient so the iodine is actually trapped, deciding when dosimetry adds value, and reading the post-therapy scan as the staging study it is. The trend across the field is de-escalation in low-risk disease and individualization in advanced disease — a balance that a medical physicist is well positioned to strike.

For physicists and RSOs, the durable principles are to anchor every administered-activity figure to current guidelines, respect the 2 Gy blood limit and the 48-hour retention ceilings when activities climb, exploit the free high-quality post-therapy SPECT/CT, and hand the retention and effective-half-life data cleanly to the patient-release calculation. Done well, I-131 therapy remains one of the most effective and best-tolerated radiopharmaceutical therapies in medicine.

How DRPS Can Help

Diagnostic Radiation Physics Services supports nuclear medicine programs delivering I-131 therapy with written-directive program review, blood and whole-body dosimetry implementation, post-therapy SPECT/CT calibration and quality control, radiation-safety documentation, patient-release evaluation, and RSO program guidance aligned with NRC or Agreement State requirements and current ATA and SNMMI/EANM guidance. Whether a facility is launching radioiodine therapy or refining an existing protocol, DRPS helps translate the dosimetry and imaging literature into a defensible, documented clinical process.

DRPS supports facilities across our service locations, including Florida, Maryland, Virginia, Washington DC, California, Nevada, Pennsylvania, New York, New Jersey, and Delaware.

Related Resources

References

Haugen BR, Alexander EK, Bible KC, et al. 2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer. Thyroid. 2016;26(1):1-133. doi:10.1089/thy.2015.0020. doi.org
Juweid ME, Tulchinsky M, Mismar A, et al. Contemporary considerations in adjuvant radioiodine treatment of adults with differentiated thyroid cancer. Int J Cancer. 2020;147(9):2345-2354. doi:10.1002/ijc.33020. doi.org
Mallick U, Harmer C, Yap B, et al. Ablation with low-dose radioiodine and thyrotropin alfa in thyroid cancer (HiLo). N Engl J Med. 2012;366(18):1674-1685. doi:10.1056/NEJMoa1109589. doi.org
Iizuka Y, Katagiri T, Ogura K, Mizowaki T. Comparison between the different doses of radioactive iodine ablation prescribed in patients with intermediate-to-high-risk differentiated thyroid cancer. Ann Nucl Med. 2019;33(7):495-501. doi:10.1007/s12149-019-01357-6. doi.org
Tu J, Wang S, Huo Z, Lin Y, Li X, Wang S. Recombinant human thyrotropin-aided versus thyroid hormone withdrawal-aided radioiodine treatment for differentiated thyroid cancer after total thyroidectomy: a meta-analysis. Radiother Oncol. 2014;110(1):25-30. doi:10.1016/j.radonc.2013.12.018. doi.org
Zilioli V, Peli A, Panarotto MB, et al. Differentiated thyroid carcinoma: incremental diagnostic value of 131I SPECT/CT over planar whole body scan after radioiodine therapy. Endocrine. 2017;56(3):551-559. doi:10.1007/s12020-016-1086-3. doi.org
Jiang L, Xiang Y, Huang R, Tian R, Liu B. Clinical applications of SPECT/CT in post-ablation 131I scintigraphy in children and young adults with differentiated thyroid carcinoma. Pediatr Radiol. 2021;51(9):1724-1731. doi:10.1007/s00247-021-05039-2. doi.org
Avram AM, Giovanella L, Greenspan B, et al. SNMMI Procedure Standard/EANM Practice Guideline for Nuclear Medicine Evaluation and Therapy of Differentiated Thyroid Cancer: Abbreviated Version. J Nucl Med. 2022;63(6):15N-35N. jnm.snmjournals.org
Luster M, Clarke SE, Dietlein M, et al. Guidelines for radioiodine therapy of differentiated thyroid cancer (EANM). Eur J Nucl Med Mol Imaging. 2008;35(10):1941-1959. doi:10.1007/s00259-008-0883-1. doi.org
Abuqbeitah M, Demir M, Kabasakal L, et al. Indirect assessment of the maximum empirical activity (250 mCi) with respect to dosimetry concepts in radioiodine therapy of metastatic differentiated thyroid cancer. Nucl Med Commun. 2018;39(11):969-975. doi:10.1097/MNM.0000000000000900. doi.org
Haugen BR. Radioiodine remnant ablation: current indications and dosing regimens. Endocr Pract. 2012;18(4):604-610. doi:10.4158/EP12117.CO. doi.org
U.S. Nuclear Regulatory Commission. 10 CFR 35.300 — Use of unsealed byproduct material for which a written directive is required. Code of Federal Regulations. ecfr.gov
U.S. Nuclear Regulatory Commission. Regulatory Guide 8.39, Revision 1: Release of Patients Administered Radioactive Material. April 2020. nrc.gov