Targeted Radionuclide Therapies: Lu-177, Ra-223, Y-90 & Radioimmunotherapy

ABMP Medical Health Physics Exam

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1 Radiation Detection Instrumentation

Ionization Chambers & Geiger-Mueller Counters Scintillation Detectors, Photomultipliers & Gamma Spectroscopy Liquid Scintillation & Gamma Counting Systems: Well Counters & Thyroid Probes Personnel Dosimeters & Electronic Radiation Monitors Neutron Detection & Emergency Field Instrumentation

2 Laboratory Design & Contamination Control

Radiopharmaceutical Laboratory Design & USP <825> Standards Ventilation Systems, Fume Hoods & Contamination Engineering

3 Radiation Protection Standards & Dose Limits

Federal Regulatory Framework & Advisory Authorities Federal Guidance Documents: NRC Regulatory Guides, NUREGs, EPA & FDA Guidance Occupational & Public Dose Limits and ALARA Principles Radiobiological Basis of Limits & Risk Communication

4 Medical Licensing, Written Directives & Security

NRC Form 313 Authorizations, RSO Responsibilities & Written Directives Medical Event Reporting & 10 CFR 37 Category 1/2 Source Security

5 Diagnostic Radiology Structural Shielding

Diagnostic Shielding Methodology: NCRP Report 147 Modality Shielding: Radiography, Fluoroscopy & CT Facilities

6 Megavoltage Therapy Vault & Facility Shielding

Megavoltage Vault Primary & Secondary Barriers: NCRP Report 151 Therapy Maze Design, Photoneutrons & Shielded Doors PET/CT & Nuclear Medicine Facility Shielding (AAPM TG-108)

7 Radiation Oncology Quality Management & Safety

External Beam QA & Dosimetry Calibration Protocols Brachytherapy Safety, Inventory Control & Leak Testing

8 Radiation Oncology Emergency Procedures & TPS QA

Treatment Planning System (TPS) QA & Patient Verification Radiation Oncology Emergency Procedures: HDR Stuck Sources & Linac Failures Medical Events, Incident Investigation & Joint Commission Requirements in Radiation Oncology

9 Diagnostic Imaging Safety & Fluoroscopy Management

Diagnostic X-ray & Fluoroscopy Safety Interventional Fluoroscopy Dose Management & NCRP Report 168

10 CT Optimization, MQSA & Diagnostic Accreditation

Computed Tomography Dosimetry & Protocol Optimization Mammography Quality Standards Act (MQSA) & Mammography Physics Diagnostic Imaging Quality Management, Accreditation & Regulatory Oversight

11 Nuclear Medicine Radiopharmacy & Unsealed Therapy

Radiopharmaceutical QC & Radionuclide Calibrators Unsealed Source Therapy: I-131 Protocols & Patient Release Criteria

12 Targeted Radionuclide Therapy, Decontamination & RAM Transport

Targeted Radionuclide Therapies: Lu-177, Ra-223, Y-90 & Radioimmunotherapy Contamination Surveys, Spill Response & Personnel Decontamination Radioactive Waste Disposal & US DOT Transport Regulations

13 Radiobiology & Radiation Risk Assessment

Cellular Radiobiology, DNA Damage & Dose-Response Models Prenatal Radiation Risks & Population Exposures

14 Non-Ionizing Radiation Safety: Lasers & MRI

Healthcare Laser Safety: ANSI Z136.1 & Z136.3 MRI Safety, Facility Design & Bioeffects

Targeted Radionuclide Therapies: Lu-177, Ra-223, Y-90 & Radioimmunotherapy

Key Takeaways Explain This Topic AI

Lu-177 (6.65 d) emits betas of up to 498 keV (mean 133 keV) for therapy and 113 and 208 keV gammas for imaging; Lu-177 dotatate is given with a lysine and arginine infusion to reduce kidney dose.

Ra-223 delivers about 95% of its 28.2 MeV decay energy as alpha particles with ranges below 100 µm; about 63% of the activity has left the body within 7 days, mainly through the intestine, so fecal contamination is the main safety issue.

Y-90 is a pure beta emitter (E_max 2.28 MeV); it is shielded first with at least 1 cm of acrylic and then lead to limit bremsstrahlung, and Tc-99m MAA lung shunt imaging keeps lung dose below 30 Gy per treatment and 50 Gy cumulatively for glass microspheres.

Y-90 ibritumomab tiuxetan (Zevalin) is given at 14.8 MBq/kg (0.4 mCi/kg), or 11.1 MBq/kg with platelets of 100,000–149,000/mm³, after rituximab, never exceeding 1,184 MBq (32 mCi).

Lutathera and Pluvicto are each given as 7.4 GBq (200 mCi) doses, every 8 weeks for 4 doses and every 6 weeks for up to 6 doses, respectively; Xofigo is 55 kBq/kg every 4 weeks for 6 injections.

Last updated: October 2026

Targeted Radionuclide Therapies & Contamination Decontamination

Targeted radionuclide therapy (TRT) has revolutionized clinical oncology by delivering cytotoxic particulate radiation directly to cellular tumor targets while sparing normal anatomical structures. In contrast to conventional external beam radiotherapy or sealed source brachytherapy, TRT administers unsealed radiopharmaceuticals that circulate systemically or locoregionally. This introduces complex health physics challenges: managing high-energy beta emitters and alpha-emitting decay cascades, mitigating organ-specific radiotoxicities, engineering specialized radiation shielding, executing sensitive contamination monitoring, and establishing rapid-response spill decontamination protocols.

Targeted Beta & Alpha Therapeutics: Physical Decay & Dosimetric Characteristics

The clinical efficacy and radiation protection profile of therapeutic radiopharmaceuticals depend directly on their nuclear decay topology, particulate range, linear energy transfer (LET), and physiological clearance pathways.

Radionuclide Physical Half-Life ( T 1 / 2 T_{1/2} T 1/2 ​ ) Primary Decay Mode & Energies Mean / Max Range in Soft Tissue Clinical Indications Critical Organs & Toxicities Primary Radiation Shielding

Lutetium-177 ( 177 Lu ^{177}\text{Lu} 177 Lu ) 6.65 days 6.65\text{ days} 6.65 days ( 159.6 hr 159.6\text{ hr} 159.6 hr ) β − \beta^- β − ( E β , max ⁡ = 498 keV E_{\beta,\max} = 498\text{ keV} E β , m a x ​ = 498 keV , E ˉ β = 133 keV \bar{E}_\beta = 133\text{ keV} E ˉ β ​ = 133 keV ); γ \gamma γ ( 113 keV 113\text{ keV} 113 keV [ 6.2 % 6.2\% 6.2% ], 208 keV 208\text{ keV} 208 keV [ 10.4 % 10.4\% 10.4% ]) Mean: 0.67 mm 0.67\text{ mm} 0.67 mm ; Max: 1.8 mm 1.8\text{ mm} 1.8 mm GEP-NETs ( 177 Lu ^{177}\text{Lu} 177 Lu -Dotatate); mCRPC ( 177 Lu ^{177}\text{Lu} 177 Lu -PSMA-617) Bone marrow (myelosuppression); Kidneys (proximal tubular reabsorption) Lead or tungsten ( 2 – 5 mm 2\text{--}5\text{ mm} 2 – 5 mm ); secondary low- Z Z Z lining

Radium-223 ( 223 Ra ^{223}\text{Ra} 223 Ra ) 11.43 days 11.43\text{ days} 11.43 days ( 274.3 hr 274.3\text{ hr} 274.3 hr ) 4 α 4\alpha 4 α cascade ( 28.2 MeV 28.2\text{ MeV} 28.2 MeV total decay energy, 95.3 % 95.3\% 95.3% α \alpha α , 3.6 % 3.6\% 3.6% β − \beta^- β − , 1.1 % 1.1\% 1.1% γ \gamma γ ) Range: < 100 μ m < 100\,\mu\text{m} < 100 μ m ( 2 – 10 cell diameters 2\text{--}10\text{ cell diameters} 2 – 10 cell diameters ) Bone metastases in mCRPC ( 223 RaCl 2 ^{223}\text{RaCl}_2 223 RaCl 2 ​ , Xofigo) Bone marrow (mild neutropenia/thrombocytopenia); Gut mucosa Standard syringe shield / lead vial pig (external hazard minimal)

Yttrium-90 ( 90 Y ^{90}\text{Y} 90 Y ) 64.1 hours 64.1\text{ hours} 64.1 hours ( 2.67 days 2.67\text{ days} 2.67 days ) Pure β − \beta^- β − ( E β , max ⁡ = 2.28 MeV E_{\beta,\max} = 2.28\text{ MeV} E β , m a x ​ = 2.28 MeV , E ˉ β = 0.93 MeV \bar{E}_\beta = 0.93\text{ MeV} E ˉ β ​ = 0.93 MeV ); no primary γ \gamma γ Mean: 2.5 mm 2.5\text{ mm} 2.5 mm ; Max: 11.0 mm 11.0\text{ mm} 11.0 mm Unresectable HCC & liver metastases (TheraSphere, SIR-Spheres) Liver parenchyma; Lungs (radiation pneumonitis via arteriovenous shunting) Transparent acrylic / Lucite ( ≥ 10 mm \ge 10\text{ mm} ≥ 10 mm ); outer lead foil for Bremsstrahlung

Lutetium-177: Theranostic Mechanics & Nephroprotection

Lutetium-177 ( 177 Lu ^{177}\text{Lu} 177 Lu ) is the prototypical "theranostic" radionuclide. Its moderate-energy beta emission ( E β , max ⁡ = 498 keV E_{\beta,\max} = 498\text{ keV} E β , m a x ​ = 498 keV ) provides local soft-tissue crossfire irradiation over a path length of ∼ 1.8 mm \sim 1.8\text{ mm} ∼ 1.8 mm , sufficient to sterilize microscopic metastatic clusters while minimizing collateral marrow toxicity. Simultaneously, its co-emitted gamma photons at 113 keV 113\text{ keV} 113 keV ( 6.2 % 6.2\% 6.2% ) and 208 keV 208\text{ keV} 208 keV ( 10.4 % 10.4\% 10.4% ) closely mirror the imaging photopeaks of standard diagnostic single-photon emission computed tomography (SPECT), enabling direct planar scintigraphy, quantitative pharmacokinetic clearance mapping, and patient-specific internal dosimetry. 71 177 Lu → β − ( 100 % ) 72 177 Hf ∗ 72 177 Hf ∗ → γ 72 177 Hf + γ ( 113 keV , 208 keV ) \begin{aligned}

{}^{177}_{71}\text{Lu} &\xrightarrow{\beta^- (100\%)} {}^{177}_{72}\text{Hf}^* \\

{}^{177}_{72}\text{Hf}^* &\xrightarrow{\gamma} {}^{177}_{72}\text{Hf} + \gamma\, (113\text{ keV}, 208\text{ keV})

\end{aligned} 71 177 ​ Lu 72 177 ​ Hf ∗ ​ β − ( 100% ) ​ 72 177 ​ Hf ∗ γ ​ 72 177 ​ Hf + γ ( 113 keV , 208 keV ) ​

Renal Radiotoxicity & Amino Acid Co-Infusion

Peptide receptor radionuclide therapy (PRRT) agents such as 177 Lu ^{177}\text{Lu} 177 Lu -DOTA-TATE and small-molecule PSMA ligands such as 177 Lu ^{177}\text{Lu} 177 Lu -PSMA-617 are excreted mainly in urine, much of it within the first day or two. Because these radiolabeled peptides filter freely across the renal glomerulus, they are actively reabsorbed by the endocytic multi-ligand receptor complex (megalin and cubilin) in the brush border of the proximal renal tubules. Unmitigated, the intracellular accumulation of 177 Lu ^{177}\text{Lu} 177 Lu delivers massive, dose-limiting localized beta irradiation to the renal cortex, inducing delayed radiation nephropathy, tubular atrophy, and progressive renal failure.

To reduce kidney dose from 177 Lu ^{177}\text{Lu} 177 Lu -dotatate, the Lutathera label calls for an intravenous infusion of an amino acid solution containing L-lysine ( 2.5 % 2.5\% 2.5% ) and L-arginine ( 2.5 % 2.5\% 2.5% ) started before and continued during and after the dose. (Amino acid infusion is not part of the 177 Lu ^{177}\text{Lu} 177 Lu -PSMA-617 regimen.) The positively charged basic side chains competitively saturate the anionic binding sites of megalin and cubilin in the proximal tubules, blocking peptide reabsorption and forcing the radiopharmaceutical into the collecting ducts for bladder evacuation. Co-infusion reduces the kidney absorbed dose by roughly 40 % 40\% 40% to 50 % 50\% 50% , allowing the standard cumulative regimen of 29.6 GBq 29.6\text{ GBq} 29.6 GBq ( 800 mCi 800\text{ mCi} 800 mCi ) in four doses.

Radium-223: Targeted Alpha Emitter Dynamics & Excretion Hazard

Radium-223 dichloride ( 223 RaCl 2 ^{223}\text{RaCl}_2 223 RaCl 2 ​ ) is an unsealed targeted alpha therapy approved for castration-resistant prostate cancer with symptomatic osteoblastic bone metastases. As an alkaline earth metal, the divalent cation Ra 2 + \text{Ra}^{2+} Ra 2 + acts as a biological mimetic of calcium ( Ca 2 + \text{Ca}^{2+} Ca 2 + ) . Following intravenous injection, 223 Ra ^{223}\text{Ra} 223 Ra rapidly clears from systemic circulation and forms complexes with bone mineral hydroxyapatite ( [ Ca 10 ( PO 4 ) 6 ( OH ) 2 ] [\text{Ca}_{10}(\text{PO}_4)_6(\text{OH})_2] [ Ca 10 ​ ( PO 4 ​ ) 6 ​ ( OH ) 2 ​ ] ) specifically at regions of active osteoblastic osteogenesis surrounding metastatic lesions.

The Alpha Decay Cascade

Upon incorporation into the bone matrix, 223 Ra ^{223}\text{Ra} 223 Ra initiates a decay cascade releasing four high-energy alpha particles across five daughter transitions before reaching stable lead-207 ( 207 Pb ^{207}\text{Pb} 207 Pb ): 88 223 Ra → α ( 5.72 MeV , 11.43 d ) 86 219 Rn → α ( 6.82 MeV , 3.96 s ) 84 215 Po → α ( 7.39 MeV , 1.78 ms ) 82 211 Pb 82 211 Pb → β − ( 1.37 MeV , 36.1 min ) 83 211 Bi → α ( 6.62 MeV , 2.14 min ) 81 207 Tl → β − ( 1.42 MeV , 4.77 min ) 82 207 Pb (stable) \begin{aligned}

{}^{223}_{88}\text{Ra} &\xrightarrow{\alpha\, (5.72\text{ MeV}, 11.43\text{ d})} {}^{219}_{86}\text{Rn} \xrightarrow{\alpha\, (6.82\text{ MeV}, 3.96\text{ s})} {}^{215}_{84}\text{Po} \xrightarrow{\alpha\, (7.39\text{ MeV}, 1.78\text{ ms})} {}^{211}_{82}\text{Pb} \\

{}^{211}_{82}\text{Pb} &\xrightarrow{\beta^-\, (1.37\text{ MeV}, 36.1\text{ min})} {}^{211}_{83}\text{Bi} \xrightarrow{\alpha\, (6.62\text{ MeV}, 2.14\text{ min})} {}^{207}_{81}\text{Tl} \xrightarrow{\beta^-\, (1.42\text{ MeV}, 4.77\text{ min})} {}^{207}_{82}\text{Pb}\text{ (stable)}

\end{aligned} 88 223 ​ Ra 82 211 ​ Pb ​ α ( 5.72 MeV , 11.43 d ) ​ 86 219 ​ Rn α ( 6.82 MeV , 3.96 s ) ​ 84 215 ​ Po α ( 7.39 MeV , 1.78 ms ) ​ 82 211 ​ Pb β − ( 1.37 MeV , 36.1 min ) ​ 83 211 ​ Bi α ( 6.62 MeV , 2.14 min ) ​ 81 207 ​ Tl β − ( 1.42 MeV , 4.77 min ) ​ 82 207 ​ Pb (stable) ​

About 95.3 % 95.3\% 95.3% of the total decay energy ( 28.2 MeV 28.2\text{ MeV} 28.2 MeV ) is emitted as high-LET alpha radiation ( ∼ 80 keV / μ m \sim 80\text{ keV}/\mu\text{m} ∼ 80 keV / μ m ). The path length of these alpha particles is less than 100 μ m 100\,\mu\text{m} 100 μ m (only 2 to 10 2\text{ to } 10 2 to 10 cell diameters). This high local ionization density produces complex, unrepairable double-strand DNA cluster breaks in adjacent tumor cells and osteoclasts, while sparing the adjacent hematopoietically active bone marrow stroma located further away. Consequently, severe myelosuppression is rare compared to broad-spectrum beta therapies.

Radiation Protection & Excretion Profile

External Exposure : Photons carry only about 1.1 % 1.1\% 1.1% of the decay energy (low-yield gammas such as 154 keV 154\text{ keV} 154 keV and 269 keV 269\text{ keV} 269 keV ). With the label dose of 55 kBq/kg 55\text{ kBq/kg} 55 kBq/kg (about 4 MBq 4\text{ MBq} 4 MBq , 0.1 mCi 0.1\text{ mCi} 0.1 mCi , for a 75 kg patient), the external dose rate is very low, and patients can be released immediately under 10 CFR 35.75.

Internal Contamination Hazard : The Xofigo label reports that excretion is mainly through the intestine: about 13 % 13\% 13% of the activity appears in feces and about 2 % 2\% 2% in urine within 48 hours, and about 63 % 63\% 63% has been excreted from the body within 7 days (decay corrected), with no evidence of hepatobiliary excretion; the drug is thought to pass into the gut by secretion through the intestinal wall. The health physics operational hazard is almost exclusively related to internal alpha contamination via fecal cross-contamination. Patient instructions must emphasize rigorous fecal hygiene: double-flushing toilets, using dedicated bathroom facilities, wearing disposable gloves to handle soiled clothing, and laundering contaminated linens separately.

Yttrium-90 Microspheres: Bremsstrahlung Physics & Radioembolization Dosimetry

Selective internal radiation therapy (SIRT), or transcatheter arterial radioembolization (TARE), treats unresectable hepatocellular carcinoma (HCC) and hepatic colorectal metastases using Yttrium-90 ( 90 Y ^{90}\text{Y} 90 Y ) microspheres. Two commercial formulations dominate clinical practice: non-biodegradable glass microspheres (TheraSphere, 20 – 30 μ m 20\text{--}30\,\mu\text{m} 20 – 30 μ m diameter, high specific activity ∼ 2 , 500 Bq \sim 2,500\text{ Bq} ∼ 2 , 500 Bq /sphere) and biocompatible resin microspheres (SIR-Spheres, 20 – 60 μ m 20\text{--}60\,\mu\text{m} 20 – 60 μ m diameter, lower specific activity ∼ 50 Bq \sim 50\text{ Bq} ∼ 50 Bq /sphere). Microspheres are delivered via transfemoral catheterization directly into the hepatic arterial branches feeding the hypervascular tumor.

Yttrium-90 decays with a half-life of 64.1 hours 64.1\text{ hours} 64.1 hours via pure beta emission ( E β , max ⁡ = 2.28 MeV E_{\beta,\max} = 2.28\text{ MeV} E β , m a x ​ = 2.28 MeV , mean E β = 0.93 MeV E_\beta = 0.93\text{ MeV} E β ​ = 0.93 MeV ) directly to the ground state of zirconium-90 ( 90 Zr ^{90}\text{Zr} 90 Zr ):

39 90 Y → β − ( 100 % ) 40 90 Zr + ν ˉ e ( E β , max ⁡ = 2.28 MeV ) {}^{90}_{39}\text{Y} \xrightarrow{\beta^- (100\%)} {}^{90}_{40}\text{Zr} + \bar{\nu}_e \quad (E_{\beta,\max} = 2.28\text{ MeV}) 39 90 ​ Y β − ( 100% ) ​ 40 90 ​ Zr + ν ˉ e ​ ( E β , m a x ​ = 2.28 MeV )

Bremsstrahlung Generation & Shielding Engineering

When high-energy beta particles decelerate in the Coulomb field of atomic nuclei, they lose energy via radiative collisions, producing a continuous spectrum of bremsstrahlung X-rays . The radiative stopping power and fractional kinetic energy converted into bremsstrahlung ( f rad f_{\text{rad}} f rad ​ ) are proportional to the atomic number ( Z Z Z ) of the absorber and the maximum beta kinetic energy ( E β , max ⁡ E_{\beta,\max} E β , m a x ​ in MeV \text{MeV} MeV ):

f rad ≈ 3.5 × 10 − 4 × Z × E β , max ⁡ f_{\text{rad}} \approx 3.5 \times 10^{-4} \times Z \times E_{\beta,\max} f rad ​ ≈ 3.5 × 1 0 − 4 × Z × E β , m a x ​

Consider the contrast between shielding 90 Y ^{90}\text{Y} 90 Y ( E β , max ⁡ = 2.28 MeV E_{\beta,\max} = 2.28\text{ MeV} E β , m a x ​ = 2.28 MeV ) with elemental lead ( Z = 82 Z = 82 Z = 82 ) versus transparent acrylic/polymethyl methacrylate (PMMA, Z eff ≈ 6.5 Z_{\text{eff}} \approx 6.5 Z eff ​ ≈ 6.5 ):

Lead ( Z = 82 Z = 82 Z = 82 ) : f rad ≈ 3.5 × 10 − 4 × 82 × 2.28 ≈ 0.0654 f_{\text{rad}} \approx 3.5 \times 10^{-4} \times 82 \times 2.28 \approx 0.0654 f rad ​ ≈ 3.5 × 1 0 − 4 × 82 × 2.28 ≈ 0.0654 ( 6.54 % 6.54\% 6.54% of beta energy converted to bremsstrahlung).

Acrylic ( Z eff = 6.5 Z_{\text{eff}} = 6.5 Z eff ​ = 6.5 ) : f rad ≈ 3.5 × 10 − 4 × 6.5 × 2.28 ≈ 0.0052 f_{\text{rad}} \approx 3.5 \times 10^{-4} \times 6.5 \times 2.28 \approx 0.0052 f rad ​ ≈ 3.5 × 1 0 − 4 × 6.5 × 2.28 ≈ 0.0052 ( 0.52 % 0.52\% 0.52% converted to bremsstrahlung, a > 12 × > 12\times > 12 × reduction).

If high-activity 90 Y ^{90}\text{Y} 90 Y vials ( > 10 GBq > 10\text{ GBq} > 10 GBq ) are placed directly inside an unlined lead shield, high-energy betas striking the high- Z Z Z lead nuclei produce an intense flux of penetrating bremsstrahlung photons, sharply increasing extremity and whole-body exposure. Consequently, the primary engineering rule for high-energy beta shielding requires a two-layer composite shield : an inner layer of low- Z Z Z acrylic (Lucite or Plexiglas) of thickness exceeding the maximum beta range in PMMA (minimum ≥ 10 to 12 mm \ge 10\text{ to } 12\text{ mm} ≥ 10 to 12 mm ) to absorb all primary electrons with minimal radiative loss, surrounded by an outer secondary shell of thin lead ( 2 to 3 mm 2\text{ to } 3\text{ mm} 2 to 3 mm ) to attenuate the residual low-yield bremsstrahlung.

Pre-Treatment Workup: Lung Shunt Fraction (LSF)

Hepatic malignancies often establish pathological arteriovenous shunts that bypass the hepatic sinusoids, diverting arterial blood into the hepatic veins, inferior vena cava, and pulmonary capillary bed. Microspheres escaping through these shunts lodge in pulmonary capillaries, causing radiation pneumonitis. Prior to 90 Y ^{90}\text{Y} 90 Y therapy, an interventional radiologist infuses 150 to 200 MBq 150\text{ to } 200\text{ MBq} 150 to 200 MBq ( 4 to 5 mCi 4\text{ to } 5\text{ mCi} 4 to 5 mCi ) of technetium-99m macroaggregated albumin ( 99 m Tc ^{99\text{m}}\text{Tc} 99 m Tc -MAA, particle size 10 – 90 μ m 10\text{--}90\,\mu\text{m} 10 – 90 μ m ) into the target hepatic artery. Planar gamma camera or SPECT/CT imaging calculates the Lung Shunt Fraction (LSF) :

LSF = C lung C lung + C liver \text{LSF} = \frac{C_{\text{lung}}}{C_{\text{lung}} + C_{\text{liver}}} LSF = C lung ​ + C liver ​ C lung ​ ​

where C lung C_{\text{lung}} C lung ​ and C liver C_{\text{liver}} C liver ​ represent the geometric mean counts in the pulmonary and hepatic regions of interest, corrected for background and tissue attenuation. Under standard MIRD schema, assuming uniform distribution across a standard 1.0 kg 1.0\text{ kg} 1.0 kg lung mass ( M lung M_{\text{lung}} M lung ​ ), the absorbed dose delivered to the lungs ( D lung D_{\text{lung}} D lung ​ ) from an administered activity A admin A_{\text{admin}} A admin ​ (in GBq \text{GBq} GBq ) is:

D lung ( Gy ) = A admin ( GBq ) × LSF × 50 J/GBq M lung ( kg ) D_{\text{lung}} (\text{Gy}) = \frac{A_{\text{admin}} (\text{GBq}) \times \text{LSF} \times 50\text{ J/GBq}}{M_{\text{lung}} (\text{kg})} D lung ​ ( Gy ) = M lung ​ ( kg ) A admin ​ ( GBq ) × LSF × 50 J/GBq ​

(Note: Complete decay of 1 GBq 1\text{ GBq} 1 GBq of 90 Y ^{90}\text{Y} 90 Y yields A ~ = 10 9 Bq × ( 64.1 × 3600 s ) / ln ⁡ ( 2 ) = 3.33 × 10 14 disintegrations \tilde{A} = 10^9\text{ Bq} \times (64.1 \times 3600\text{ s}) / \ln(2) = 3.33 \times 10^{14}\text{ disintegrations} A ~ = 1 0 9 Bq × ( 64.1 × 3600 s ) / ln ( 2 ) = 3.33 × 1 0 14 disintegrations , which at E ˉ β = 0.93 MeV = 1.49 × 10 − 13 J \bar{E}_\beta = 0.93\text{ MeV} = 1.49 \times 10^{-13}\text{ J} E ˉ β ​ = 0.93 MeV = 1.49 × 1 0 − 13 J equals ≈ 50 Joules \approx 50\text{ Joules} ≈ 50 Joules ).

For glass microspheres (TheraSphere), the lung absorbed dose should not exceed 30 Gy 30\text{ Gy} 30 Gy in a single administration or 50 Gy 50\text{ Gy} 50 Gy cumulatively . For resin microspheres (SIR-Spheres), treatment is generally not given when the lung shunt fraction exceeds 20 % 20\% 20% , and the activity is reduced for intermediate shunt fractions.

Radioimmunotherapy and Other Targeted Agents

Radioimmunotherapy (RIT) attaches a therapeutic radionuclide to a monoclonal antibody. The model US agent is 90 Y ^{90}\text{Y} 90 Y -ibritumomab tiuxetan (Zevalin) , an anti-CD20 antibody for B-cell non-Hodgkin lymphoma. Its label regimen is:

Day 1 : rituximab 250 mg/m 2 250\text{ mg/m}^2 250 mg/m 2 infusion (to clear circulating B cells and improve biodistribution).

Day 7, 8, or 9 : a second rituximab 250 mg/m 2 250\text{ mg/m}^2 250 mg/m 2 infusion, then within 4 hours 90 Y ^{90}\text{Y} 90 Y -Zevalin at 14.8 MBq/kg 14.8\text{ MBq/kg} 14.8 MBq/kg ( 0.4 mCi/kg 0.4\text{ mCi/kg} 0.4 mCi/kg ) if platelets are at least 150,000 / mm 3 150{,}000/\text{mm}^3 150 , 000/ mm 3 , or 11.1 MBq/kg 11.1\text{ MBq/kg} 11.1 MBq/kg ( 0.3 mCi/kg 0.3\text{ mCi/kg} 0.3 mCi/kg ) for relapsed or refractory patients with platelets of 100,000 100{,}000 100 , 000 – 149,000 / mm 3 149{,}000/\text{mm}^3 149 , 000/ mm 3 ; patients below 100,000 100{,}000 100 , 000 are not treated.

Maximum : 1,184 MBq 1{,}184\text{ MBq} 1 , 184 MBq ( 32 mCi 32\text{ mCi} 32 mCi ) regardless of body weight.

Because 90 Y ^{90}\text{Y} 90 Y is a pure beta emitter, the radiation safety issues are the same as for microspheres: acrylic syringe shields, bremsstrahlung awareness, and attention to contamination. The dose-limiting toxicity is myelosuppression, which is why the activity is scaled to platelet count. The 131 I ^{131}\text{I} 131 I -labeled antibody tositumomab (Bexxar) was withdrawn from the US market in 2014.

Other approved regimens a health physicist should recognize:

Agent Typical Regimen Main Radiation Safety Points

177 Lu ^{177}\text{Lu} 177 Lu -dotatate (Lutathera) 7.4 GBq 7.4\text{ GBq} 7.4 GBq ( 200 mCi 200\text{ mCi} 200 mCi ) every 8 weeks, 4 doses, with lysine/arginine infusion Urine contamination; gamma emissions allow imaging and need modest shielding

177 Lu ^{177}\text{Lu} 177 Lu -vipivotide tetraxetan (Pluvicto) 7.4 GBq 7.4\text{ GBq} 7.4 GBq ( 200 mCi 200\text{ mCi} 200 mCi ) every 6 weeks, up to 6 doses Renal excretion; salivary and kidney uptake

223 Ra ^{223}\text{Ra} 223 Ra dichloride (Xofigo) 55 kBq/kg 55\text{ kBq/kg} 55 kBq/kg every 4 weeks, 6 injections Alpha contamination control; fecal excretion

90 Y ^{90}\text{Y} 90 Y microspheres Activity planned from liver and lung dosimetry Bremsstrahlung; lung shunt limits

131 I ^{131}\text{I} 131 I sodium iodide Hundreds of MBq to several GBq Penetrating 364 keV gammas; volatility; patient release

Each of these therapies needs a written directive under 10 CFR 35.40, and the activity is verified before administration under 35.63.