Eye Plaque Brachytherapy Radiation Safety

Q: What is eye plaque brachytherapy?

Eye plaque brachytherapy is a form of manual brachytherapy that treats intraocular tumors — most commonly uveal (choroidal) melanoma — by surgically suturing a small, curved radioactive plaque onto the outside of the eye (the sclera) directly over the tumor. The plaque holds sealed radioactive sources, usually iodine-125 seeds in the United States, and delivers a high, localized dose to the tumor over several days. It is then surgically removed. The plaque has a gold-alloy backing that shields radiation away from healthy tissue and the surrounding environment, making it a directional source.

Q: Which radionuclides are used in eye plaques?

In the United States, iodine-125 is the most common, following the Collaborative Ocular Melanoma Study. Palladium-103 is also used; it emits even lower-energy photons. In Europe, ruthenium-106/rhodium-106 beta plaques are common for thinner tumors. The choice affects the dose distribution, the depth of penetration, and the radiation-safety profile, but all three are sealed sources regulated as byproduct material.

Q: Is eye plaque brachytherapy an inpatient or outpatient procedure?

It depends on the dose rate and the release calculation. Because iodine-125 and palladium-103 emit low-energy photons and the gold backing shields most of the emission, external exposure to others is low, and many patients can be released under 10 CFR 35.75 with written instructions and a shielding eye patch. Whether a patient is released or kept as an inpatient is a documented radiation-safety decision, not an automatic one.

Q: How much radiation dose does the tumor receive?

The prescription is to the tumor apex. A commonly used prescription is 85 Gy at 5 mm depth in a homogeneous-medium calculation, though accounting for the gold-alloy backing and insert reduces the actual delivered dose at that depth. The plaque stays in place for several days — typically around 5 to 7 — with the exact duration set by the source strength and the dose-rate calculation.

Q: What happens if a source is dislodged or a medical event occurs?

Emergency equipment — a shielded container and long-handled forceps — must be available to recover a dislodged source, which is then placed in the shielded container and secured. If the delivered dose differs from the written directive beyond regulatory thresholds, or the wrong site or source is used, it may be a reportable medical event under 10 CFR 35.3045, requiring notification of the NRC or Agreement State, the referring physician, and the patient.

Eye plaque brachytherapy treats an intraocular tumor by sewing a radioactive plaque onto the outside of the eye, directly over the tumor, and leaving it in place for several days. It is one of the most elegant radiation-safety problems in medicine: the gold-alloy plaque is engineered to aim a steep dose at the tumor while shielding healthy tissue and the outside world, which is exactly why a program can treat these patients safely — provided the written directive, dosimetry, surveys, source accountability, and release decisions are done correctly under NRC Part 35. ^{1, 2}

Uveal melanoma is the most common primary intraocular malignancy in adults, and eye-sparing plaque brachytherapy has become a standard alternative to removing the eye. The Collaborative Ocular Melanoma Study (COMS) established that for medium-sized choroidal melanomas, iodine-125 plaque brachytherapy produces mortality rates no different from enucleation, which is why the eye-sparing approach is now routine and why iodine-125 became the dominant isotope in North America. ^{3, 4}

This guide explains how eye plaques work, the radionuclides and dosimetry involved, and — most importantly for a health physics audience — the radiation-safety program that surrounds a case: the written directive, source handling and surveys, the release decision, emergency response, and the regulatory framework. DRPS supports facilities with this work through radiation safety officer consulting, radioactive material license support, and medical physicist consulting across Florida, Maryland, Virginia, Washington DC, California, Nevada, and our other service areas.

Introduction

An eye plaque is a small, dish-shaped device, typically 10–22 mm across, with a gold-alloy shell that holds sealed radioactive sources on its concave (eye-facing) side. The surgeon localizes the tumor, sutures the plaque to the sclera over it, and leaves it for a calculated number of days to deliver the prescribed dose. A second operation removes it. Because the sources sit in a gold cup, radiation is directed into the eye and the gold backing absorbs most of the emission in every other direction — the plaque is a deliberately directional source. ^{1, 2}

That directionality is the heart of the radiation-safety story. It concentrates dose where it is wanted, spares the opposite side of the eye and the orbit as much as geometry allows, and dramatically reduces external exposure to staff, family, and the public. It is also why the dosimetry is demanding: the dose gradient is extremely steep, critical structures (fovea, optic disc, lens) are millimeters from the source, and small geometric errors translate into large dose differences. ¹

This article treats the plaque as what it is from a health physics standpoint: a licensed, sealed byproduct-material source implanted in a patient under the manual-brachytherapy rules, with all of the accountability, survey, dosimetry, and release obligations that implies.

Topic Explanation

The radionuclides

Three radionuclides dominate eye plaque brachytherapy, and they behave very differently:

Radionuclide	Emission used	Principal energy	Half-life	Typical use	Key radiation-safety feature
Iodine-125	Low-energy photons	~27–35 keV	~59.4 days	Standard in the U.S. (COMS); medium choroidal melanoma	Easily shielded; gold backing and thin lead stop most emission ^{1, 9}
Palladium-103	Low-energy photons	~20–23 keV	~17 days	Alternative photon plaque; steeper tissue falloff	Even more readily absorbed in tissue than I-125 ^{1, 9}
Ruthenium-106 / Rh-106	Beta particles	Rh-106 beta up to ~3.5 MeV	~374 days	Common in Europe for thinner tumors	Beta source — different shielding and handling; thin silver window ^{9, 10}

Iodine-125 and palladium-103 are photon emitters whose low energies make them simultaneously effective (sharp dose falloff spares distant structures) and easy to shield. Ruthenium-106 is fundamentally different: it is a beta plaque, where the therapeutic dose comes from high-energy beta particles emitted by its short-lived daughter rhodium-106. Beta shielding and handling considerations differ from photons, and the delicate silver entrance window of a Ru-106 plaque must not be scratched. ^{9, 10}

Why the gold backing matters

The gold-alloy backing does two jobs. Clinically, it reflects and absorbs radiation so the dose is delivered into the eye rather than out through the orbit. From a radiation-safety perspective, it is the primary shield: iodine-125's 27–35 keV photons are attenuated strongly by even a fraction of a millimeter of gold or lead, so the plaque exports relatively little dose to the room. This is why a procedure that implants tens of thousands of becquerels of sealed activity into a patient can often be managed on an outpatient basis. ^{1, 2}

The procedure and the sources

Eye plaques use sealed sources — iodine-125 "seeds" in seed-guides or carriers, or a sealed Ru-106 foil — loaded into reusable or custom plaque shells. The sources are calibrated, the plaque is loaded and verified, it is implanted, dwell time is tracked against the dose plan, and the plaque is removed and returned to inventory. Each of those steps is a radiation-safety control point: calibration, accountability, survey, and (for reusable hardware) leak testing. ^{1, 6}

Key Technical Principles

Dose calculation and the TG-43 formalism

Eye plaque dose calculations use the AAPM TG-43 brachytherapy dosimetry formalism. The two-dimensional dose-rate equation for a line source is:

\dot{D} (r, θ) = S_{K} Λ \frac{G _{L} ( r , θ )}{G _{L} ( r _{0} , θ _{0} )} g_{L} (r) F (r, θ)

where $S_{K}$ is the air-kerma strength, $Λ$ is the dose-rate constant, $G_{L}$ is the geometry function, $g_{L} (r)$ is the radial dose function, and $F (r, θ)$ is the anisotropy function. The reference point is $r_{0} = 1$ cm, $θ_{0} = 9 0^{\circ}$ . ⁵

TG-129 — the joint AAPM/ABS task group report on eye plaque dosimetry — showed that standard homogeneous-water calculations overestimate the delivered dose because they ignore the gold-alloy backing and the Silastic seed carrier. For COMS-design plaques, a prescription of 85 Gy at 5 mm depth in a homogeneous medium actually delivers about 75 Gy (iodine-125) and 69 Gy (palladium-103) at that depth once plaque heterogeneities are accounted for — differences exceeding 10%. In the interim, TG-129 recommends calculating with the line-source approximation and the 2D TG-43U1 formalism in homogeneous water while reporting a concurrent heterogeneity-corrected estimate. ^{1, 5}

The prescription and treatment time

The prescription is to the tumor apex (its highest point above the sclera). A commonly used prescription is 85 Gy at the apex. Because the source decays during the implant, the delivered dose is the time integral of the dose rate. For a source with initial apex dose rate $\dot{D}_{0}$ and decay constant $λ$ , the dose delivered over implant time $T$ is:

D = \dot{D}_{0} \frac{1 - e ^{- λ T}}{λ}

Worked example

Suppose an iodine-125 plaque has an initial apex dose rate of $\dot{D}_{0} = 0.70$ Gy/h and the prescription is $D = 85$ Gy. Iodine-125 has a half-life of 59.4 days, so:

λ = \frac{ln 2}{59.4 d} = \frac{0.693}{1426 h} \approx 4.86 \times 1 0^{- 4} h^{- 1}

Solving $85 = 0.70 \cdot (1 - e^{- λ T}) / λ$ for $T$ gives approximately 125 hours, or about 5.2 days. If decay were ignored, the estimate would be $85/0.70 \approx 121$ hours (5.1 days); the decay correction adds only a few hours because the 59.4-day half-life is long relative to a five-day implant. The practical point is that the plaque stays in place for a specific, calculated number of days — typically around 5 to 7 — and the radiation-safety plan has to cover that entire interval, not just the two operations. ^{1, 5}

The steep gradient

Because these are low-energy photon (or beta) sources, dose falls off very rapidly with distance. That is clinically desirable — it spares the opposite retina and optic nerve — but it means geometric accuracy is everything. A one-millimeter error in plaque placement or in apex height can change the apex dose by a clinically meaningful amount, which is why localization, plaque selection, and verification are treated as part of the safety program, not just the clinical workflow. ^{1, 2}

Clinical Impact

Eye plaque brachytherapy exists because it saves eyes without costing lives. The COMS medium-tumor trial randomized more than 1,300 patients between iodine-125 plaque brachytherapy and enucleation and found no difference in mortality for up to 12 years — establishing plaque brachytherapy as an eye- and vision-sparing standard of care for medium choroidal melanoma. ^{3, 4}

The American Brachytherapy Society consensus guidelines add the clinical boundaries that shape a safe program: plaque brachytherapy is best performed in subspecialty centers with the right surgical and physics expertise; most iris, ciliary body, and choroidal melanomas can be treated this way; but tumors with gross orbital extension, blind painful eyes, and eyes with no light perception are not suitable. Only selected retinoblastomas are eligible. Quality assurance, plaque construction, and dosimetry should follow the 2012 AAPM/ABS (TG-129) recommendations. ^{1, 2}

For the patient, the trade is a few days with a radioactive plaque sutured to the eye — usually with a shielding patch — against the alternative of losing the eye. For the facility, the clinical benefit only materializes if the radiation-safety program is sound: the right dose to the right apex, verified sources, documented surveys, and a defensible release or confinement decision. The clinical and safety sides are inseparable here because the same geometric precision that makes the treatment effective is what keeps dose off the wrong structures and out of the room. ^{1, 2}

Practical Optimization Tips

A defensible eye plaque program runs the same radiation-safety sequence every case.

1. Lock down the written directive

A signed written directive is required before and after implantation. Before implantation it specifies the treatment site, the radionuclide, and the dose; after implantation it records the sources, total source strength, and treatment duration or total dose. Revisions must be dated and signed by the authorized user. This is the document the entire case is checked against. ⁶

2. Calibrate and account for every source

Source strength (air-kerma strength) must be verified by the qualified medical physicist against the manufacturer's certificate, and every source must be inventoried in and out. A seed count before implantation and after removal is a non-negotiable accountability step. ^{1, 6}

3. Survey at placement and at removal

Perform radiation surveys when the plaque is placed and when it is removed, document dose rates, and confirm the plaque (and every seed) is recovered. The removal survey is what proves no source was left behind. ⁶

4. Keep emergency equipment at the bedside

A shielded container and long-handled forceps must be available wherever the patient is during the implant, so a dislodged plaque or source can be recovered and secured immediately. ⁶

5. Make the release decision explicitly

Decide and document whether the patient is released under 10 CFR 35.75 or kept as an inpatient, based on the dose-rate calculation and the likely dose to others. For iodine-125 and palladium-103 with the gold backing, release with written instructions and a shielding eye patch is common — but it is a calculated, documented decision. ^{6, 7}

6. Leak-test reusable hardware

Reusable plaque shells and non-seed sealed sources (for example Ru-106 plaques) are subject to leak testing on the required schedule; document results and remove any leaking source from service. ⁶

Common pitfalls to avoid

Treating release as automatic. It is a documented calculation, not a default.
Skipping the removal survey/seed count. This is how a retained source becomes a reportable event.
Ignoring plaque heterogeneity in dose reporting. Homogeneous-water calculations overestimate delivered dose; report a heterogeneity-corrected estimate alongside. ¹
Handling a Ru-106 plaque like a photon seed. Beta sources have different shielding and a fragile window. ¹⁰
Weak source accountability. Every seed in and every seed out, documented.

Regulatory Considerations

Eye plaque brachytherapy is manual brachytherapy using sealed byproduct material, governed by NRC 10 CFR Part 35 Subpart F or the equivalent Agreement State program. The plaque's sealed sources, the written-directive requirement, the authorized-user structure, and the medical-event rules all apply.

10 CFR Part 35, Subpart F — Manual Brachytherapy. Covers use of sources, safety instructions, safety precautions, source calibration, and the requirement to recover and account for sources. The written-directive and authorized-user provisions apply to every case. ⁶
10 CFR 35.75 — Release of individuals. Permits release of a patient containing implanted sources if the total effective dose equivalent to any other individual is not likely to exceed 5 mSv (0.5 rem), with record-keeping and, where applicable, written instructions. Eye plaque patients are frequently releasable because of the low-energy, gold-shielded sources. ^{6, 7}
10 CFR 35.3045 — Medical event reporting. A delivered dose that differs from the written directive beyond regulatory thresholds, or a wrong site, wrong source, or wrong patient, is a reportable medical event requiring notification of the NRC or Agreement State, the referring physician, and the patient. ⁶
10 CFR Part 20 — Standards for Protection Against Radiation. Sets occupational and public dose limits and the ALARA framework for staff handling sources and for the areas where the implanted patient is cared for. ⁷
NRC NUREG-1556, Volume 9. Program-specific licensing guidance for medical use, including expectations for sealed-source programs, surveys, and emergency procedures. ⁸
Dosimetry standards (AAPM TG-129 and TG-43U1; ICRU Report 72). Define the dose-calculation formalism and the beta/low-energy-photon dosimetry that underpin a defensible dose plan. ^{1, 5, 10}

The safety precautions of Subpart F (for example, 10 CFR 35.415) apply primarily when a patient cannot be released under 35.75 — so for a released outpatient eye plaque case, the emphasis shifts to the release instructions, the surveys, and source accountability rather than inpatient confinement. Of the states DRPS serves, radioactive material is regulated directly by the NRC in Washington, DC and Delaware and by the Agreement State program in Florida, Maryland, Virginia, California, Nevada, Pennsylvania, New York, and New Jersey; the licensee must confirm which authority issues and inspects its license. For related programs, see our guides to prostate seed brachytherapy radiation safety, HDR brachytherapy remote afterloader safety, and medical event reporting under 35.3045.

Frequently Asked Questions (FAQs)

What is eye plaque brachytherapy?

It is a manual brachytherapy that treats intraocular tumors — most commonly uveal (choroidal) melanoma — by suturing a small, curved radioactive plaque onto the sclera over the tumor. The plaque holds sealed sources (usually iodine-125 seeds in the U.S.), delivers a high localized dose over several days, and is then surgically removed. Its gold-alloy backing makes it a directional source. ^{1, 2}

Which radionuclides are used in eye plaques?

Iodine-125 is most common in the United States (following COMS). Palladium-103 emits even lower-energy photons. In Europe, ruthenium-106/rhodium-106 beta plaques are common for thinner tumors. All three are sealed sources regulated as byproduct material. ^{1, 9}

Is eye plaque brachytherapy an inpatient or outpatient procedure?

It depends on the dose-rate calculation. Because iodine-125 and palladium-103 emit low-energy photons and the gold backing shields most emission, external exposure to others is low, and many patients can be released under 10 CFR 35.75 with written instructions and a shielding eye patch. The release-versus-confinement choice is a documented radiation-safety decision. ^{6, 7}

What radiation-safety steps are required for an eye plaque case?

A signed written directive before and after implantation, source calibration and dosimetry by a qualified medical physicist, source accountability and inventory, surveys at placement and removal, emergency procedures and shielded equipment for a dislodged source, a release or confinement decision, and leak testing of reusable hardware — the Subpart F manual-brachytherapy requirements plus license conditions. ⁶

How much radiation dose does the tumor receive?

The prescription is to the tumor apex, commonly 85 Gy at 5 mm depth in a homogeneous-medium calculation; accounting for the gold backing and insert reduces the actual delivered dose at that depth. The plaque stays in place for several days, typically around 5 to 7, set by the source strength and dose-rate calculation. ^{1, 5}

What happens if a source is dislodged or a medical event occurs?

Shielded emergency equipment must be available to recover a dislodged source and secure it. If the delivered dose differs from the written directive beyond regulatory thresholds, or the wrong site or source is used, it may be a reportable medical event under 10 CFR 35.3045, requiring notification of the NRC or Agreement State, the referring physician, and the patient. ⁶

Key Takeaways

The plaque is a directional sealed source. The gold-alloy backing aims dose into the eye and shields everything else, which is what makes the procedure safe to manage. ^{1, 2}
Isotope choice matters. Iodine-125 (U.S. standard), palladium-103, and ruthenium-106 differ in emission type, energy, and shielding — and Ru-106 is a beta source handled differently. ^{1, 9, 10}
Dosimetry is unforgiving. The dose gradient is steep and critical structures are millimeters away; homogeneous calculations overestimate delivered dose, so report heterogeneity-corrected values. ^{1, 5}
The prescription is to the apex, commonly 85 Gy, delivered over a calculated implant of several days. ¹
Radiation safety is a fixed sequence. Written directive, calibration, accountability, surveys at placement and removal, emergency equipment, and a documented release decision. ⁶
It is manual brachytherapy under Part 35. Subpart F, 35.75 release, and 35.3045 medical-event reporting all apply. ^{6, 7}

Conclusion

Eye plaque brachytherapy is a case study in how good engineering makes radiation safety tractable: a gold-shielded, directional source that puts a steep, high dose on an intraocular tumor while keeping dose off the rest of the eye and out of the room. That design is what allows many patients to be treated and released safely. But the design only works inside a disciplined program — a signed written directive, verified source strength, strict accountability, surveys at placement and removal, emergency equipment at the bedside, and a documented release decision under 10 CFR 35.75. The clinical evidence from COMS makes the case for treating; the radiation-safety program is what makes it defensible. A board-certified medical physicist and the radiation safety officer own that program together. ^{1, 3, 6}

How DRPS Can Help

Diagnostic Radiation Physics Services helps facilities build and defend sealed-source and brachytherapy radiation-safety programs. Our work includes radiation safety officer consulting, radioactive material license support and amendments for manual brachytherapy, written-directive and medical-event procedures, source accountability and leak-testing programs, survey and release-decision documentation, and radiation safety training for staff.

DRPS supports facilities across our service locations, including Florida, Maryland, Virginia, Washington DC, California, Nevada, New York, Pennsylvania, New Jersey, and Delaware. Whether you are adding an eye plaque service or preparing for inspection, a documented program is what turns a complex sealed-source procedure into a routine, defensible one.

Related Resources

References

Chiu-Tsao ST, Astrahan MA, Finger PT, et al. Dosimetry of 125I and 103Pd COMS eye plaques for intraocular tumors: report of Task Group 129 by the AAPM and ABS. Med Phys. 2012;39(10):6161-6184. doi:10.1118/1.4749933. PubMed
American Brachytherapy Society – Ophthalmic Oncology Task Force. The American Brachytherapy Society consensus guidelines for plaque brachytherapy of uveal melanoma and retinoblastoma. Brachytherapy. 2014;13(1):1-14. doi:10.1016/j.brachy.2013.11.008. PubMed
Straatsma BR, Fine SL, Earle JD, et al. Enucleation versus plaque irradiation for choroidal melanoma. Ophthalmology. 1988;95(7):1000-1004. doi:10.1016/s0161-6420(88)33086-1. PubMed
Robertson DM. Changing concepts in the management of choroidal melanoma. Am J Ophthalmol. 2003;136(1):161-170. doi:10.1016/s0002-9394(03)00265-4. PubMed
Rivard MJ, Coursey BM, DeWerd LA, et al. Update of AAPM Task Group No. 43 Report: a revised AAPM protocol for brachytherapy dose calculations. Med Phys. 2004;31(3):633-674. doi:10.1118/1.1646040. PubMed
U.S. Nuclear Regulatory Commission. 10 CFR Part 35: Medical Use of Byproduct Material (Subpart F — Manual Brachytherapy; §§35.40, 35.75, 35.415, 35.3045). nrc.gov
U.S. Nuclear Regulatory Commission. 10 CFR Part 20: Standards for Protection Against Radiation. nrc.gov
U.S. Nuclear Regulatory Commission. NUREG-1556, Volume 9, Revision 3: Consolidated Guidance About Materials Licenses — Program-Specific Guidance About Medical Use Licenses. nrc.gov
National Nuclear Data Center, Brookhaven National Laboratory. Decay data for I-125, Pd-103, and Ru-106/Rh-106. nndc.bnl.gov
International Commission on Radiation Units and Measurements. ICRU Report 72: Dosimetry of Beta Rays and Low-Energy Photons for Brachytherapy with Sealed Sources. Bethesda, MD: ICRU; 2004. icru.org