Radiopharmaceuticals - Board Review Summary

PART I - FOUNDATIONS: THERANOSTICS, ISOTOPES, AND CURRENT LANDSCAPE

Core Management Paradigm

Question	Board-style answer	Why it matters
Is there a target?	Use target-specific imaging before therapy: PSMA PET for Lu-PSMA, SSTR imaging for Lu-DOTATATE, iobenguane avidity for I-131 MIBG.	No target means no useful radiopharmaceutical for that pathway.
Is there target-negative disease?	Look for discordant biology such as FDG-positive / PSMA-negative progression or rapidly growing target-negative lesions.	Target-negative disease is one of the most important reasons RPT fails.
Is the patient safe for treatment?	Check marrow, renal, hepatic, hydration, prior EBRT, prior chemo, and diffuse marrow tumor burden.	Most serious toxicities are predictable from reserve and organ dose.
Is there an urgent local problem?	Cord compression, unstable bone, focal neurologic deficit, obstruction, bleeding, or a dominant painful lesion usually needs surgery and/or EBRT first.	Systemic target therapy is not a substitute for urgent local control.
Is this approved-use or trial-frontier?	Separate current standards from moving-frontier trials such as PSMAddition, UpFrontPSMA, LUNAR, and alpha-emitter strategies.	Boards often test the difference between "promising" and "standard."

Core Definition

Targeted radionuclide therapy delivers radiation systemically through a radiolabeled molecule, peptide, antibody, particle, or microparticle that naturally accumulates in, or is designed to target, tumor. The central board principle is that the therapeutic effect comes from absorbed radiation dose, not from the carrier molecule itself.

Theranostics

Radiopharmaceuticals fit a theranostic model: the same target can be used for diagnosis, treatment selection, dosimetry, response assessment, and therapy. This is the conceptual shift to memorize: imaging is not just staging; it can select, guide, and evaluate systemic radiation therapy.

Alpha vs Beta vs Beta-Auger Emitters

Property	Alpha emitters	Beta emitters	Dual beta-Auger (next-gen)
Examples	Ac-225, Th-227, Pb-212, Ra-223	I-131, Y-90, Lu-177, Sr-89, Sm-153	Tb-161
Physics advantage	High LET, dense double-strand DNA damage, less dependence on oxygenation	Cross-fire effect and broader dose deposition	Beta + abundant Auger / conversion electrons deliver concentrated nm-μm radiation
Path-length advantage	Very short path length, often cell-scale	Millimeter-scale path length, useful for heterogeneous uptake	Theoretical edge against micrometastases and single cells
Key drawback	Dose heterogeneity, daughter-decay toxicity, difficult imaging and dosimetry	Lower LET and more normal-tissue spill than alpha emitters	First-in-human only; long-term toxicity profile not yet established

Major Clinical Agents to Know

Agent	Main disease	Particle / decay	Target / mechanism	Board takeaway
I-131 sodium iodide	Differentiated thyroid cancer	Beta emitter with gamma emission	Elemental iodine uptake through NIS	Historic proof that systemic targeted RT can improve survival.
Y-90 microspheres	HCC and selected liver-dominant disease	Pure beta emitter	Intra-arterial radioembolization	Locoregional radiopharma; dosimetry and arterial mapping are central.
I-131 MIBG	PPGL; selected pediatric NB contexts	Beta emitter with gamma emission	Norepinephrine-transporter targeting	Rare but testable theranostic platform with scan selection and thyroid blockade.
Radium-223	Bone-metastatic mCRPC	Alpha emitter	Bone-seeking calcium mimetic	Improves OS in symptomatic bone-metastatic mCRPC without known visceral disease.
Lu-177 DOTATATE	SSTR-positive GEP-NET	Beta emitter with gamma emission	Radiolabeled somatostatin analog	Core PRRT platform for SSTR-positive GEP-NETs.
Lu-177 PSMA-617	PSMA-positive prostate cancer	Beta emitter with gamma emission	PSMA-targeted radioligand therapy	Core therapy in mCRPC; moving earlier through trials.
Ac-225 PSMA	PSMA-positive mCRPC (investigational)	Alpha emitter	PSMA-targeted alpha therapy (TAT)	Effective post-Lu-177 progression; xerostomia is dose-limiting.
Tb-161 PSMA	PSMA-positive mCRPC (investigational)	Beta-Auger emitter	PSMA-targeted beta + Auger therapy	First-in-human signals favorable activity and tolerability; theoretical advantage against micrometastases.

Current Standard vs Trial Frontier

Agent	Current practical standard / label anchor	Moving-frontier signal
Xofigo / Ra-223	mCRPC with symptomatic bone metastases and no known visceral metastatic disease; 55 kBq/kg q4wk x6.	PEACE-3 now shows final OS benefit for enzalutamide + Ra-223, but bone-protective therapy and patient selection are mandatory.
Lutathera / Lu-177 DOTATATE	Adult and pediatric age ≥12 with SSTR-positive GEP-NET; 7.4 GBq q8wk x4. NCCN category 1 for progressive, octreotide-refractory GI NETs with intact SSTR expression.	NETTER-2 moves PRRT into first-line treatment for higher grade well-differentiated GEP-NET.
Pluvicto / Lu-177 PSMA-617	PSMA-positive mCRPC after ARPI therapy, either after taxane or when appropriate to delay taxane; 7.4 GBq q6wk x6.	PSMAddition, UpFrontPSMA, and LUNAR move PSMA-RLT into hormone-sensitive disease; WARMTH Act (Ac-225) and VIOLET-161Tb push isotope physics.
Azedra / I-131 MIBG	Iobenguane-scan-positive unresectable, locally advanced, or metastatic PPGL requiring systemic therapy; use can be limited by program availability.	Useful for boards because it demonstrates theranostic selection, dosimetric dosing, and thyroid blockade.
Y-90 microspheres	Liver-directed radioembolization for selected HCC and liver-dominant tumors after mapping angiography and lung-shunt assessment.	Modern Y-90 is increasingly dosimetry-driven rather than empiric activity driven.

Classic Platform Quick Hits

Platform	Selection / workflow	High-yield toxicity or safety point
Differentiated thyroid I-131	NIS-dependent iodine avidity; used after thyroidectomy in selected intermediate/high-risk disease and for iodine-avid metastatic disease.	Pregnancy is contraindicated; salivary glands, marrow, and radiation isolation counseling matter.
I-131 MIBG / Azedra	Requires iobenguane scan-positive PPGL; dosimetric dose precedes therapeutic dosing.	Thyroid blockade is mandatory; monitor marrow, blood pressure, renal function, hypothyroidism, and pneumonitis.
I-131 MIBG / pediatric NB	MIBG avidity is common in high-risk NB; I-123 MIBG is diagnostic, and I-131 MIBG is therapeutic in selected high-risk or relapsed settings.	Know the Curie-score concept and that persistent MIBG-avid metastatic sites can drive local RT decisions.
Y-90 radioembolization	Mapping angiography, extrahepatic-flow prevention, lung-shunt evaluation, and liver/tumor dose planning are core steps.	Watch for GI ulceration, radiation pneumonitis, biliary injury, and radioembolization-induced liver disease.
Sr-89 / Sm-153 bone palliation	Older beta-emitting bone-seeking agents for painful osteoblastic metastases.	Pain palliation without the OS signal that distinguishes Ra-223 in mCRPC.

PART II - RADIUM-223

Indication and Practical Identity

Radium-223 dichloride is a bone-seeking alpha-emitting calcium mimetic approved for castration-resistant prostate cancer with symptomatic bone metastases and no known visceral metastatic disease. It is not simply a pain drug: in the right bone-metastatic mCRPC population, it improves survival and delays skeletal events.

ALSYMPCA

ALSYMPCA randomized 921 men with mCRPC, castrate testosterone, and at least 2 bone metastases to 6 injections of Ra-223 every 4 weeks vs placebo. The historical activity was reported as 50 kBq/kg; the current label-equivalent dose is 55 kBq/kg after NIST calibration standardization. Median OS improved from 11.3 to 14.9 months, median time to first skeletal event improved from 9.8 to 15.6 months, and time to alkaline phosphatase rise improved from 3.8 to 7.4 months. The study was stopped early for efficacy.

Radium-223 Management Paradigm

Clinical question	Board-style answer
Best candidate	mCRPC with symptomatic bone metastases, adequate marrow reserve, and no known visceral metastases.
Soft-tissue / visceral disease	Do not expect Ra-223 to control visceral disease; choose systemic therapy or focal RT as appropriate.
Bone health	Use bone-protective agents when combining with androgen-axis therapy; dental evaluation can be a practical bottleneck.
Response assessment	PSA and bone scan can mislead; alkaline phosphatase and symptom/skeletal-event trajectory are more informative, but imperfect.
Local symptom flare or impending event	Use EBRT or surgery for focal instability, cord compression, or dominant pain; Ra-223 is systemic bone-targeted treatment.

What to Monitor

Parameter	Practical point
Main toxicity concern	Marrow suppression; check CBC before each dose.
Common non-hematologic issues	Nausea, vomiting, constipation, diarrhea, peripheral edema; drug is cleared through liver/bile so stool is radioactive.
Pretreatment counts	ANC ≥1.5 x 10^9/L, platelets ≥100 x 10^9/L, Hgb ≥10 g/dL for first dose.
Subsequent-dose counts	ANC ≥1.0 x 10^9/L, platelets ≥50 x 10^9/L, Hgb ≥8 g/dL.
Hepatic labs	Typical threshold: bilirubin ≤1.5 x ULN and AST/ALT ≤2.5 x ULN.

Radiation Safety Pearls

Ra-223 has a half-life of about 11.4 days. After administration, blood, urine, and stool are radioactive, with stool the most practical issue.
Counsel on gloves for contaminated fluids/laundry, closed-lid toilet flushing, separate washing of stained clothes, and airport radiation sensor detection. There are generally no major routine contact restrictions, but avoid prolonged close contact such as holding a small child in the lap for long periods. No routine post-treatment imaging is used.

ERA-223 and PEACE-3

Trial	Schema	Main result	Takeaway
ERA-223	Abiraterone/prednisone +/- Ra-223	No improvement in symptomatic skeletal EFS; fractures 29% vs 11%.	Do not give abiraterone and Ra-223 concurrently.
PEACE-3	Enzalutamide +/- Ra-223 in first-line mCRPC with bone metastases	rPFS 19.4 vs 16.4 mo; final OS 38.2 vs 32.6 mo, HR 0.76.	Combination is active, but bone-protective therapy and careful selection are required.

PART III - LU-177 DOTATATE

Indication and Mechanism

Lu-177 DOTATATE is a beta-emitting radiolabeled somatostatin analog indicated for adult and pediatric patients age ≥12 with SSTR-positive GEP-NETs, including foregut, midgut, and hindgut NETs. It binds somatostatin receptors, is internalized, and then delivers beta radiation to the tumor and nearby cells; the accompanying gamma emission also enables post-therapy imaging and dosimetry. Lu-177 DOTATATE is the only NCCN category 1 recommendation for progressive, octreotide-refractory GI NETs with intact SSTR expression on Ga-68 DOTATATE imaging.

Management Paradigm + Dose Anchors

Decision point	Practical answer
Required imaging	Confirm SSTR-positive disease on SSTR imaging; SSTR-negative or poorly differentiated NEC biology should push away from PRRT.
Classic standard setting	Progressive well-differentiated SSTR-positive midgut NET after somatostatin analog therapy: NETTER-1.
Earlier-line setting	Newly diagnosed advanced well-differentiated higher grade 2 or grade 3 GEP-NET with SSTR expression: NETTER-2.
Standard course	7.4 GBq q8 weeks x4, with octreotide LAR 30 mg after each treatment dose.
Renal protection	Lysine/arginine amino acid infusion plus antiemetics; nausea often comes from the amino acids rather than the radioligand itself.

NETTER-1

NETTER-1 randomized 229 patients with advanced, well-differentiated, progressive SSTR-positive midgut NETs to Lu-177 DOTATATE 7.4 GBq every 8 weeks x4 plus octreotide LAR 30 mg vs high-dose octreotide LAR 60 mg every 4 weeks. PFS HR was 0.18, 20-month PFS was 65.2% vs 10.8%, and ORR was 18% vs 3%. Median OS was 48.0 vs 36.3 months, not statistically significant but clinically favorable. This established Lutathera as a standard PRRT platform.

NETTER-2

NETTER-2 moved PRRT earlier. In 226 patients with newly diagnosed advanced SSTR-positive, well-differentiated, higher grade 2-3 GEP-NETs, Lu-177 DOTATATE 7.4 GBq every 8 weeks x4 plus octreotide LAR 30 mg significantly improved median PFS from 8.5 to 22.8 months (HR 0.276) and improved ORR from 9.3% to 43.0%. This is the first phase III trial showing first-line radioligand benefit in a metastatic solid tumor setting.

NETTER-1 vs NETTER-2

Feature	NETTER-1	NETTER-2
Tumor group	Midgut NET only	All GEP-NETs
Grade	Grade 1-2	Higher grade 2 and well-differentiated grade 3
Line of therapy	Post-SSA progression	First line
PFS HR	0.18	0.276
ORR	18%	43%

Administration Pearl

Standard course is 4 doses every 8 weeks.
L-lysine / L-arginine amino acid infusion starts 30 minutes before therapy and continues during and for at least 3 hours after to help protect kidneys. Long-acting octreotide 30 mg IM is typically given 4-24 hours after each Lutathera dose and then continued on schedule. Avoid long-acting SSA within about 4 weeks before therapy when feasible; short-acting octreotide can be used for symptoms but is usually stopped 24 hours before treatment.

Toxicity / Monitoring Pearls

Issue	What to remember
Marrow	Check CBC before each cycle; prior chemotherapy, diffuse marrow disease, and prior large-field RT increase cytopenia risk.
Kidney	Renal dose is why amino acids matter; monitor creatinine / clearance and hydrate.
Liver	Monitor LFTs, especially with bulky liver disease or prior liver-directed therapy.
Hormonal syndrome	Carcinoid crisis is uncommon but board-testable; coordinate somatostatin analog management.
Late risks	MDS / AML are rare but real long-term risks after PRRT.

PART IV - LU-177 PSMA-617 AND RELATED PSMA-RLT STRATEGIES

Current Pluvicto Paradigm

Pluvicto is Lu-177 PSMA-617 / lutetium Lu 177 vipivotide tetraxetan, a beta-emitting PSMA-targeted radioligand. Current U.S. use includes adults with PSMA-positive mCRPC after ARPI therapy who either already received taxane-based chemotherapy or are considered appropriate to delay taxane-based chemotherapy. This bridges the original VISION post-taxane evidence base and the PSMAfore taxane-naive expansion.

PSMA-RLT Patient Selection

Selection step	Why it matters
PSMA PET positivity	Required for treatment selection; approved PSMA PET products are used to confirm target expression.
Discordant disease check	FDG-positive / PSMA-negative or clinically aggressive target-negative disease predicts poor RLT control and may need another strategy.
Marrow reserve	Diffuse bone metastases, prior taxane, prior Ra-223, prior EBRT, and low baseline counts increase cytopenia risk.
Renal / salivary toxicity	Hydration and frequent voiding reduce bladder dose; dry mouth and renal lab changes are practical toxicities.
Focal progression	Heterogeneous oligoprogression can be treated with EBRT/SBRT while continuing or sequencing RLT in selected cases.

NCCN / VISION Exclusion Criteria: 177Lu-PSMA-617 is not recommended in patients with dominant PSMA-negative lesions. A lesion is considered PSMA-negative if its uptake is ≤ liver background and it meets size criteria: solid organ metastases ≥ 1.0 cm or lymph nodes ≥ 2.5 cm in short axis. FDG-avid/PSMA-negative mismatch lesions suggest an aggressive variant biology that predicts poor response, often making alternatives like cabazitaxel more appropriate.

VISION: Post-Taxane mCRPC

VISION randomized 831 patients with PSMA-positive mCRPC who had progressed after ARPI and taxane therapy to Lu-177 PSMA-617 7.4 GBq every 6 weeks x6 plus SOC vs SOC alone. Median OS improved from 11.3 to 15.3 months, and image-based PFS improved from 3.4 to 8.7 months. Grade 3+ toxicity was higher (53% vs 38%), but QOL was not adversely affected.

PSMAfore: Taxane-Naive mCRPC

PSMAfore tested Lu-177 PSMA-617 7.4 GBq every 6 weeks x6 against a change in ARPI in taxane-naive mCRPC after ARPI progression. FDA-reported rPFS improved from 5.6 to 9.3 months (HR 0.41), while OS was not statistically significant, in part with substantial crossover. This supports using Pluvicto before taxane in selected patients where taxane delay is appropriate.

Lu-PSMA Hematologic Dose Modification

Hematologic toxicity from Lu-177 PSMA-617 is cumulative, predictable, and manageable with proactive monitoring and dose modification.

20% dose reduction for grade 2-3 thrombocytopenia or grade 3-4 anemia/neutropenia.
Treatment delays up to 4 weeks for count recovery are acceptable.
Plan for 6 total cycles with flexibility based on count recovery, tumor response, and patient-specific factors.
Higher risk in patients with diffuse marrow disease, prior taxane, prior Ra-223, or prior wide-field RT.

TheraP and ENZA-P

Trial	Comparator	Main result	Takeaway
TheraP	Cabazitaxel vs Lu-PSMA-617	PSA response 66% vs 37%; grade 3-4 AEs 33% vs 53%.	Strong phase II support for Lu-PSMA vs cabazitaxel in selected mCRPC.
ENZA-P	Enzalutamide +/- adaptive Lu-PSMA-617	PSA-PFS 13 vs 8 months; grade 3+ toxicity similar.	Upfront combination strategy is promising in taxane-naive mCRPC.

Moving Earlier: PSMAddition, UpFrontPSMA, and LUNAR

Trial	Population	Main result	Current interpretation
PSMAddition	PSMA-positive mHSPC, phase III	rPFS HR 0.72; PSA nadir <0.2 at 48 weeks 87.4% vs 74.9%; OS not yet significant at interim analysis.	First phase III targeted RLT trial in hormone-sensitive metastatic prostate cancer, but not a current universal label-standard.
UpFrontPSMA	De novo high-volume mHSPC, phase II (n=130). Required PSMA-avid disease on Ga-68 PSMA-11 PET-CT with no major FDG-PSMA discordance.	Sequential Lu-PSMA 7.5 GBq x2 q6wk → docetaxel 75 mg/m² x6 q3wk vs docetaxel alone. Undetectable PSA at 48 weeks 41% vs 16% (OR 3.88). PSA-PFS HR 0.43; rPFS HR 0.45; ORR 66% vs 37%.	First randomized trial of Lu-PSMA in mHSPC; only 2 cycles (not 6 as in VISION) added to standard docetaxel/ADT.
LUNAR	Oligorecurrent hormone-sensitive prostate cancer	PFS 17.6 vs 7.4 months, HR 0.37; hormone-therapy-free survival 24.3 vs 14.1 months.	Proof of concept that PSMA-RLT + SBRT can treat visible and occult disease together; future-direction rather than routine standard.

UpFrontPSMA dual-tracer pearl: the trial used both PSMA-PET and FDG-PET to select patients with high-volume PSMA-avid disease and no major discordance. FDG-positive / PSMA-negative disease identifies more aggressive, potentially neuroendocrine-differentiated tumors less likely to respond to PSMA-RLT. Dual-tracer imaging is increasingly important in patient selection across PSMA-RLT trials.

LUNAR pearl: this was the first randomized trial of PSMA-targeted radioligand therapy in hormone-sensitive oligorecurrent prostate cancer. It is an important "where the field is going" study rather than a current universal standard.

Beyond Lu-177: Alpha and Beta-Auger Emitter Strategies

Trial / agent	Physics / mechanism	Key findings	Takeaway
WARMTH Act (Sathekge 2024) Ac-225-PSMA-617	Alpha emitter with 4 alpha particles in decay chain; RBE ~4.2x higher than Lu-177-PSMA. Effective even in oxygen-poor microenvironments.	Largest cohort: 488 patients, 7 international centers. Dose 8 MBq IV q8 weeks. Xerostomia is dose-limiting: 68% after 1 cycle, 100% after ≥8 cycles, though only 11 patients discontinued for xerostomia. Hematologic: any-grade anemia 81%, leukopenia 44%, thrombocytopenia 54%; grade ≥3 toxicity relatively low.	Effective post-Lu-177 progression but salivary gland toxicity remains the main limitation of PSMA-targeted alpha therapy (TAT).
VIOLET-161Tb (Buteau 2025) Tb-161-PSMA-I&T	Dual beta-Auger emitter. Half-life 6.89 days (similar to Lu-177's 6.65). Beta + abundant Auger / conversion electrons deposit concentrated radiation over nm-μm distances — theoretical edge against single cells and micrometastases.	First-in-human phase I/II (n=30, mCRPC post-taxane + ARPI). 7.4 GBq per cycle. No dose-limiting toxicities; only 7% grade 3-4 AEs. PSA50 70%, PSA90 40%; PSA-PFS 9.0 months; rPFS 11.1 months. Preclinical: 2.4x higher tumor-absorbed dose vs Lu-177-PSMA-617 with improved therapeutic index.	Encouraging early signal for next-generation isotope; uses logistics similar to Lu-177. Phase III data not yet available.

Retreatment / Sequencing

Retrospective studies such as RALU, REALITY, and extended-therapy series suggest that rechallenge or additional Lu-PSMA can be feasible in selected patients, with the main risks being myelosuppression and renal function decline. This remains individualized rather than a fixed standard. Lu-PSMA after Ra-223 can be feasible when marrow reserve allows. Sequencing of Lu-PSMA → Ac-225 after progression is an active area of investigation.

PART V - I-131 MIBG, Y-90, AND OLDER / SPECIALIZED PLATFORMS

I-131 MIBG / Azedra

Feature	Practical point
Main approved niche	Age ≥12 with iobenguane-scan-positive, unresectable, locally advanced, or metastatic PPGL requiring systemic anticancer therapy.
Workflow	Dosimetric dose first, then up to 2 therapeutic doses adjusted by dosimetry and weight, at least 90 days apart.
Therapeutic dose anchor	18,500 MBq if >62.5 kg, or 296 MBq/kg if ≤62.5 kg.
Thyroid blockade	Start inorganic iodine at least 24 hours before each dose and continue after treatment per protocol.
Toxicities	Marrow suppression, hypertension, nausea/vomiting, fatigue, hypothyroidism, pneumonitis, and rare MDS/AML.

Y-90 Radioembolization

Y-90 radioembolization is not systemic RLT in the same way as Lu-PSMA or Lu-DOTATATE. It is catheter-directed liver RT that exploits hepatic arterial tumor supply. The board workflow is: mapping angiography, protect extrahepatic flow, Tc-99m MAA / lung-shunt assessment, activity and liver/tumor dosimetry, treatment delivery, then response/toxicity surveillance.

Y-90 concept	Board-review pearl
Tumor supply	HCC is often mostly arterial; normal liver gets substantial portal venous flow.
Physics	Y-90 is a pure beta emitter with half-life about 2.7 days and millimeter-to-centimeter beta range.
Dosimetry	Modern Y-90 is increasingly personalized; DOSISPHERE-01 supports tumor-dose-driven planning in selected HCC.
Toxicity	GI ulceration from nontarget delivery, radiation pneumonitis from lung shunt, biliary injury, liver failure, and radioembolization-induced liver disease.
EBRT comparison	Y-90 is intra-arterial and lobar/segmental; EBRT is anatomy-based and often better for vascular invasion, nonarterial target geometry, or extrahepatic local problems.

Older Bone-Targeted Beta Emitters

Sr-89 and Sm-153 are older bone-seeking beta emitters used for painful multifocal osteoblastic metastases. They can palliate pain but do not carry the mCRPC OS evidence that distinguishes Ra-223. Their use has declined as EBRT, systemic therapy, Ra-223, and Lu-PSMA have evolved.

Lymphoma Radioimmunotherapy Quick Hit

Y-90 ibritumomab tiuxetan and historical I-131 tositumomab are useful board-concept examples of antibody-based radioimmunotherapy in B-cell lymphoma. The practical modern takeaway is conceptual more than routine workflow: radioimmunotherapy can target CD20-positive lymphoma, but use has become uncommon.

PART VI - ACCESS, STAFFING, AND WHO SHOULD OWN RPT

Access Is a Major Clinical Problem

A major implementation priority is to expand access beyond academic centers. The geographic mismatch between where patients live and where RPT is available is a real clinical problem, and one of the main reasons radiation oncology should stay involved.

Radiation Oncology vs Nuclear Medicine

Group	Advantages	Limitations
Radiation Oncology	Community footprint, oncology referral relationships, ability to combine EBRT + RPT, dose-thinking culture, toxicity follow-up experience.	Often lacks PET/SPECT infrastructure, hot lab, radioactive bathroom, or AU-certified physicians.
Nuclear Medicine	Imaging expertise, theranostic infrastructure, direct radiopharma experience, diagnostic isotope familiarity.	Less community reach in many regions, often less longitudinal oncology toxicity management and insurance coordination, less experience with EBRT integration.

Program-Building Requirements

Minimal program ingredients:

Staffing: nuclear medicine technologist or trained RTT, nurse, APP support, financial counselor, coordinator, qualified medical physicist, and an Authorized User
Infrastructure: hot lab with dose calibrator and GM meter, dedicated administration room, RAM license, and a radioactive bathroom
Follow-up capability: lab monitoring, toxicity management, coordination with medical oncology, and transfusion support when needed

Why Radiation Oncology Belongs in the Workflow

The best framing is collaboration, not turf. Nuclear medicine often owns imaging infrastructure and radiopharmaceutical logistics; radiation oncology adds dose thinking, community access, toxicity follow-up, and the ability to combine RPT + EBRT for heterogeneous disease, urgent local problems, or consolidative treatment.

Practical Patient Counseling for Lu-PSMA-Type Therapy

Common counseling points:

Increase oral fluids and void frequently to reduce bladder dose.
Limit close contact with others for 3 days.
Sleep in a separate bedroom for 3 days.
Avoid sexual activity for 7 days.
Use contraception during therapy and for 14 weeks after the last dose.

PART VII - DOSIMETRY: THE BIG UNRESOLVED FRONTIER

Why Dosimetry Matters

EBRT is prescribed to a point or volume dose.
RPT is usually prescribed like systemic therapy, by injected activity, body weight, or surface area.
That mismatch is the core reason dosimetry remains such a hot topic.

Arguments For and Against Patient-Specific Dosimetry

Potential advantage	Potential drawback
Tumor uptake is heterogeneous across lesions and across patients.	Treatment complexity increases substantially.
Normal tissue dose also varies by patient.	Cost rises for already expensive therapies.
Injected activity could theoretically be adapted to improve therapeutic ratio.	Current fixed-activity regimens already produce major clinical benefit.
Could optimize combination RPT + EBRT plans.	Prospective trials are still needed to prove that dosimetry changes outcomes.

General Workflow

The workflow is: SPECT/CT imaging - ROI contouring - time integration - dose calculation - dose evaluation.
Post-therapy quantitative SPECT/CT is often performed about 3-5 days after administration, with camera calibration required for quantitative dosimetry. A single time point around 84-106 hours can be a practical approximation in selected workflows.

Where Dosimetry Is Most Useful Today

Scenario	Why dosimetry can change management
Heterogeneous uptake / response	Identifies lesions that may need SBRT, systemic switch, or treatment intensification.
Retreatment or extended therapy	Helps judge cumulative kidney, marrow, salivary gland, or tumor absorbed dose before giving more cycles.
Y-90 liver therapy	Personalized liver/tumor dosimetry is already clinically influential and more mature than routine Lu-PSMA dosimetry.
RPT + EBRT integration	Allows the team to think about cumulative dose to marrow, kidney, bowel, salivary glands, and overlapping targets.
Fixed-activity standard regimens	Most approved RPT is still delivered by fixed activity or weight-based activity; prospective outcome-changing dosimetry trials remain needed.

What Early Outcome Data Suggest

Several Lu-PSMA studies show that whole-body tumor absorbed dose correlates with PSA response, and in newer series also with bPFS and OS. In one real-world implementation, about half of patients undergoing dosimetry had a management change, such as adding SBRT to heterogeneous progression, consolidating residual disease, switching therapy for poor uptake, or holding treatment when response was excellent.

Exam framing: dosimetry is one of the most plausible places where radiation oncology can add unique value to radiopharmaceutical programs, but it is not yet a universally proven standard-of-care requirement.

CROSS-CUTTING HIGH-YIELD POINTS

Theranostics integrates imaging, patient selection, dosimetry, response assessment, and therapy in one target-based workflow.
Therapeutic effect comes from absorbed dose, not from the carrier molecule.
Alpha emitters have high LET and short path length but problematic heterogeneity and harder dosimetry.
Beta emitters have lower LET but a cross-fire effect that helps with heterogeneous uptake.
Beta-Auger emitters (Tb-161) combine beta plus concentrated nm-μm Auger dose, theoretically targeting micrometastases.
I-131 is the historical proof-of-principle that systemic targeted RT can improve survival.
I-131 MIBG / Azedra is the rare PPGL theranostic platform: scan-positive disease, dosimetric dose, thyroid blockade, then therapeutic dosing.
Y-90 radioembolization is locoregional radiopharma; mapping angiography, lung-shunt assessment, and liver/tumor dosimetry are central.
Radium-223 improves OS in symptomatic bone-metastatic mCRPC without known visceral metastases and is not just a palliative drug.
ALSYMPCA numbers to know: OS 14.9 vs 11.3 months; time to skeletal event 15.6 vs 9.8 months.
Current Ra-223 label dose: 55 kBq/kg q4wk x6; older ALSYMPCA descriptions used 50 kBq/kg.
ERA-223: do not combine abiraterone and Ra-223 concurrently because fractures increased and efficacy did not improve.
PEACE-3: enzalutamide + Ra-223 improves rPFS and final OS, but bone-protective therapy and careful selection are required.
Target expression is mandatory: no PSMA, SSTR, or MIBG avidity means no target for that radiopharmaceutical.
Discordant target-negative disease: 177Lu-PSMA-617 is excluded if PSMA-negative lesions (uptake ≤ liver) meet size criteria (solid organs ≥ 1.0 cm, lymph nodes ≥ 2.5 cm). Dual-tracer PSMA + FDG imaging helps identify these aggressive clones.
Lu-177 DOTATATE is the only NCCN category 1 recommendation for progressive, octreotide-refractory GI NETs with intact SSTR expression. NETTER-1 is the classic progressive midgut dataset.
NETTER-2 moves RLT into the first-line setting for higher grade well-differentiated GEP-NETs.
Lu-177 DOTATATE administration pearl: give lysine/arginine amino acids beginning 30 minutes before and continuing for at least 3 hours after infusion.
VISION established Lu-PSMA-617 as an OS-improving therapy in post-taxane PSMA-positive mCRPC.
PSMAfore supports Lu-PSMA before taxane in selected post-ARPI mCRPC and underpins the taxane-delay label expansion.
TheraP is the memorable cabazitaxel-vs-Lu-PSMA phase II comparison.
Lu-PSMA hematologic management: 20% dose reduction for grade 2-3 thrombocytopenia or grade 3-4 anemia/neutropenia; treatment delays up to 4 weeks for count recovery.
Current Pluvicto label concept: PSMA-positive mCRPC after ARPI, either taxane-delayed or post-taxane.
PSMAddition is the first phase III targeted RLT trial in mHSPC and shows rPFS benefit, but OS and adoption are still evolving.
UpFrontPSMA is the first randomized trial of Lu-PSMA in mHSPC; 2 cycles of Lu-PSMA before docetaxel improved undetectable-PSA rate from 16% to 41%.
LUNAR is the first randomized PSMA-RLT trial in oligorecurrent hormone-sensitive prostate cancer and is a major future-direction trial.
WARMTH Act: largest Ac-225-PSMA cohort (n=488); active post-Lu-177 progression but xerostomia is dose-limiting (68% after 1 cycle, 100% after ≥8 cycles).
VIOLET-161Tb: first-in-human Tb-161-PSMA-I&T phase I/II; favorable PSA50 70% / rPFS 11.1 months with low grade 3-4 AEs.
Radiation oncology has a real role in improving access to RPT, especially in the community and in combining RPT with EBRT.
Program needs include an AU, hot lab, radioactive bathroom, trained technologists, physics support, and strong coordination infrastructure.
Dosimetry is promising but not fully validated; it may personalize activity selection and EBRT integration, but prospective trials are still needed.

CONSOLIDATED AGENT / PHYSICS / ADMINISTRATION TABLE

Agent / isotope	Particle / decay	Half-life / range	Target / disease	Dose / schedule anchor
I-131 sodium iodide	Beta emitter with gamma emission	Half-life about 8 days; beta path roughly 2 mm	NIS / differentiated thyroid cancer	Activity individualized by risk, remnant, metastases, and practice pattern.
Y-90 microspheres	Pure beta emitter	Half-life about 2.7 days; mean beta range a few mm, max about 1 cm	Intra-arterial liver-directed therapy for selected HCC / liver-dominant disease	Activity planned by mapping angiography, lung-shunt assessment, and liver / tumor dosimetry.
I-131 MIBG / Azedra	Beta emitter with gamma emission	I-131 half-life about 8 days	Norepinephrine transporter / iobenguane-avid PPGL	Dosimetry first; therapy 18,500 MBq if >62.5 kg or 296 MBq/kg if ≤62.5 kg, up to 2 doses.
Radium-223 / Xofigo	Alpha emitter	Half-life about 11.4 days; very short alpha path length	Calcium mimetic / osteoblastic bone metastases in mCRPC without known visceral disease	Current label: 55 kBq/kg q4wk x6; historical ALSYMPCA reporting used 50 kBq/kg.
Lu-177 DOTATATE / Lutathera	Beta emitter with gamma emission	Half-life about 6.7 days; beta range about 1-2 mm	SSTR-positive GEP-NET	7.4 GBq q8wk x4; amino acids start 30 min before and continue for at least 3 h after.
Lu-177 PSMA-617 / Pluvicto	Beta emitter with gamma emission	Half-life about 6.7 days; beta range about 1-2 mm	PSMA-positive mCRPC	7.4 GBq / 200 mCi q6wk x6.
Lu-177 PSMA / UpFrontPSMA regimen	Beta emitter with gamma emission	Lu-177 half-life about 6.7 days	De novo high-volume mHSPC, sequential strategy	7.5 GBq q6wk x2 → docetaxel 75 mg/m² q3wk x6 + ADT.
Lu-177 PSMA / LUNAR (PNT2002)	Beta emitter with gamma emission	Lu-177 half-life about 6.7 days	PSMA-positive oligorecurrent hormone-sensitive prostate cancer	Investigational: 6.8 GBq x2, about 8 weeks apart, before SBRT.
Ac-225-PSMA-617	Alpha emitter; 4 alpha particles in decay chain; RBE ~4.2x vs Lu-177	Ac-225 half-life about 10 days; very short alpha path	PSMA-positive mCRPC (investigational)	8 MBq IV q8wk in WARMTH Act; xerostomia dose-limiting.
Tb-161-PSMA-I&T	Beta-Auger dual emitter	Half-life about 6.89 days; beta + concentrated nm-μm Auger	PSMA-positive mCRPC (investigational)	7.4 GBq in VIOLET phase I/II; higher activity cohort planned.
Sr-89 / Sm-153	Beta-emitting bone-seeking agents	Sr-89 longer half-life; Sm-153 shorter half-life with gamma emission	Painful osteoblastic bone metastases	Palliation platform; lacks the OS signal that distinguishes Ra-223.

KEY LANDMARK TRIALS (memorize)

Trial / anchor	Disease / setting	One-line takeaway
ALSYMPCA	Symptomatic bone-metastatic mCRPC without known visceral metastases	Radium-223 improves OS and delays skeletal events.
ERA-223	mCRPC	Abiraterone + Ra-223 increased fractures and did not help efficacy.
PEACE-3	First-line mCRPC with bone metastases	Enzalutamide + Ra-223 improves rPFS and final OS; bone protection matters.
NETTER-1	Progressive SSTR-positive midgut NET	Established Lu-177 DOTATATE as standard PRRT therapy; NCCN cat 1.
NETTER-2	First-line higher grade GEP-NET	Moved Lu-177 DOTATATE into the first-line setting with major PFS and ORR gains.
VISION	Post-taxane PSMA-positive mCRPC	Lu-177 PSMA-617 improves OS and PFS.
PSMAfore	Taxane-naive mCRPC	Pluvicto beats ARPI switch for rPFS and supports taxane-delay use.
TheraP	mCRPC, cabazitaxel comparison	Lu-PSMA improves PSA response and lowers severe toxicity vs cabazitaxel.
ENZA-P	Taxane-naive mCRPC	Upfront Pluvicto + enzalutamide improves PSA-PFS.
PSMAddition	mHSPC	First phase III targeted RLT trial in hormone-sensitive metastatic prostate cancer.
UpFrontPSMA	De novo high-volume mHSPC	First randomized Lu-PSMA + docetaxel vs docetaxel trial; 2 cycles of Lu-PSMA tripled undetectable-PSA rate at 48 weeks.
LUNAR	Oligorecurrent hormone-sensitive prostate cancer	First randomized PSMA-RLT trial in early oligometastatic hormone-sensitive disease.
WARMTH Act	Ac-225-PSMA-617 in mCRPC	Largest cohort (n=488) of PSMA-targeted alpha therapy; effective but xerostomia is dose-limiting.
VIOLET-161Tb	Tb-161-PSMA-I&T in mCRPC	First-in-human dual beta-Auger RLT; favorable activity and tolerability.
Azedra pivotal experience	Iobenguane-avid PPGL	Established high-specific-activity I-131 MIBG as a systemic option for unresectable / metastatic PPGL.
DOSISPHERE-01 / LEGACY	HCC Y-90 radioembolization	Support modern personalized Y-90 dosimetry and high local-control liver-directed therapy.
RALU / REALITY / extended Lu-PSMA series	Retreatment / rechallenge	Retreatment may be feasible, but evidence remains retrospective.
Violet / Fitzpatrick / Grkovski	Lu-PSMA dosimetry	Whole-body tumor absorbed dose correlates with response and outcomes.