Clinical Guide · Alpha PSMA in mCRPC

mCRPC and Ac-225 PSMA targeted alpha therapy.

A sourced clinical guide to where actinium-225 PSMA-617 targeted alpha therapy fits in the sequencing of metastatic castration-resistant prostate cancer (mCRPC) — primarily as a salvage option after Lu-177 PSMA failure, with published evidence from the Sathekge, Kratochwil, and Yadav AIIMS cohorts. Investigational and Helsinki-framed.

Dr. Ishita B. Sen, MDDirector & Chief, Nuclear Medicine · FMRI

Published 14 May 2026

Reviewed by Dr. Dharmender Malik

13 min read

Last reviewed by Dr. Dharmender Malik on 14 May 2026 · this article reflects the published primary literature and current clinical practice at FMRI Gurugram.

Introduction

Actinium-225 PSMA-617 (Ac-225 PSMA) is a targeted alpha-particle radioligand therapy for metastatic castration-resistant prostate cancer (mCRPC). Like Lu-177 PSMA-617 (Pluvicto), it uses the PSMA-617 peptide to deliver radiation specifically to PSMA-expressing prostate cancer cells. The difference: Ac-225 emits short-range, high-energy alpha particles rather than the longer-range beta particles emitted by Lu-177. Ac-225 PSMA is investigational — not FDA-approved — and is delivered at experienced centres under Helsinki Declaration informed-consent frameworks. This article describes where the published evidence places Ac-225 PSMA in the mCRPC sequence, the most established indication (salvage after Lu-177 progression), the chemotherapy-naive cohort data, and the safety profile that distinguishes alpha from beta therapy.

Why alpha particles — and where they fit

AI Overview · short answer

Alpha particles deposit very high energy (linear energy transfer of ~80 keV/μm — approximately 200-1,000× higher than beta particles) over a very short range (50-100 μm — approximately 2-10 cell diameters). This profile means alpha radiation produces dense, clustered double-strand DNA breaks within the target cell with minimal collateral damage to neighbouring tissue. The clinical implication: in patients whose disease has progressed on Lu-177 PSMA (beta therapy), Ac-225 PSMA (alpha therapy) can still produce responses — likely because of the different mechanism of cell-kill and the ability to overcome some forms of beta-radiation resistance^[1].

Audit governance · investigational status

Ac-225 PSMA-617 is investigational — not FDA-approved as a registered therapy. At FMRI it is delivered under the Helsinki Declaration framework with written informed consent that explicitly covers investigational status, expected outcomes, hematologic and xerostomia risks, the salvage indication after Lu-177 progression, and the patient's right to decline or withdraw at any time^[2]. For more on alpha versus beta PRRT see our comparison article.

Salvage Ac-225 PSMA after Lu-177 failure — the most established indication

The most established use of Ac-225 PSMA in mCRPC is salvage therapy after progression on Lu-177 PSMA. The published cohort evidence^[3]:

Cohort	n	Setting	Key reported outcomes
Kratochwil Heidelberg (foundational cohort)	14	Lu-177 refractory mCRPC	PSA decline ≥50% in 64%; documented imaging response
Yadav AIIMS New Delhi	28	Lu-177 PSMA progression	PSA response ≥50% in 39%; median OS approximately 15 months
Sathekge Pretoria	53	Mixed: heavily pre-treated mCRPC	PSA response ≥50% in 70% (selected cohort); xerostomia leading cause of dose modification
Feuerecker Munich	26	Lu-177 refractory mCRPC	PSA decline ≥50% in 65%; median PFS approximately 4 months

The pattern across cohorts: even after Lu-177 PSMA progression, Ac-225 PSMA produces meaningful PSA response in 40-70% of patients. This evidence has positioned Ac-225 PSMA as the most established salvage option for mCRPC patients who have progressed on Lu-177^[3]^[4].

Chemotherapy-naive Ac-225 PSMA — the Sathekge cohort

The Sathekge South African cohort (n=17 chemotherapy-naive mCRPC patients) reported particularly striking outcomes that have shaped subsequent interest in earlier-line alpha-PSMA therapy^[5]:

PSA response ≥50% in 82% of chemotherapy-naive patients.
PSA decline to undetectable in 41% of the cohort.
Median OS not reached at the published follow-up timepoint.
Xerostomia reported as the principal toxicity, leading to dose adjustments in some patients.

The Sathekge cohort outcomes have been reproduced — with broadly similar response patterns — in subsequent series. However, the cohort was small, selected, and from a single experienced centre; large randomised data in earlier-line chemotherapy-naive mCRPC are not yet available^[6].

The xerostomia signal — alpha-specific toxicity

The principal toxicity that distinguishes Ac-225 PSMA from Lu-177 PSMA is more severe and persistent xerostomia (dry mouth). The reasons are biological: salivary glands express PSMA at meaningful levels, and the high-LET, short-range nature of alpha particles produces more concentrated salivary gland damage than the longer-range beta particles of Lu-177^[7]:

Severity — Grade 2-3 xerostomia in approximately 30-50% of Ac-225 PSMA recipients in published cohorts.
Persistence — Xerostomia after Ac-225 PSMA tends to be longer-lasting than after Lu-177 PSMA; partial recovery may take 6-12 months.
Dose-limiting nature — Xerostomia is the principal reason for dose reduction or dose-fractionation in alpha-PSMA protocols.
Mitigation strategies — Salivary gland protective measures (cooling, sialogogues, ice chips during administration, post-administration botulinum toxin in selected cases) have been investigated; evidence base is evolving^[8].

For more on xerostomia after alpha therapy see our xerostomia management article.

Patient selection — who is appropriate for salvage Ac-225 PSMA

Patient selection for salvage Ac-225 PSMA after Lu-177 progression typically requires^[9]:

Maintained PSMA expression on follow-up Ga-68 PSMA PET-CT (this is essential; without maintained target expression alpha therapy cannot work).
Adequate organ function — eGFR ≥ 50 mL/min/1.73m²; haemoglobin ≥ 9 g/dL; platelets ≥ 100; neutrophils ≥ 1.5; albumin ≥ 30 g/L.
ECOG performance status 0-2.
Life expectancy ≥ 6 months.
Cumulative prior radiation dose — kidney and marrow cumulative dose from prior Lu-177 PSMA must be calculated; additional alpha-PSMA cycles must be planned within tolerable cumulative dose limits.
Patient understanding — comprehensive informed consent covering investigational status, expected response, xerostomia risk, and alternative options.

Practical delivery — dose, cycles, monitoring

The published protocols for Ac-225 PSMA delivery vary across centres^[10]:

Per-cycle dose — Typically 5.5-8 MBq of Ac-225 PSMA-617 per cycle, with body-weight or dosimetry-based adjustment in some protocols.
Cycle interval — Typically 8 weeks between cycles, allowing recovery of acute toxicity.
Number of cycles — Most published protocols deliver 3-6 cycles, dose-fractionated based on response and tolerance. Some centres use a dose-reduction strategy after Cycle 2-3 to minimise cumulative xerostomia.
Monitoring — Post-cycle FBC and renal function at 2 and 4 weeks; PSA at 4-6 weeks; Ga-68 PSMA PET-CT at completion or at clinical progression; salivary gland symptom assessment with structured tools (e.g., Xerostomia Inventory).

Where Ac-225 PSMA fits in the sequencing of mCRPC

The current sequencing of systemic therapy for mCRPC — based on FDA-approved labelling and major guideline recommendations^[11]:

Disease state	Standard options	Where Ac-225 PSMA fits
mCRPC, pre-taxane	ARPI (abiraterone, enzalutamide)	Investigational; Lu-177 PSMA-617 has PSMAfore evidence; Ac-225 PSMA evidence limited in this setting
mCRPC, post-ARPI, pre-taxane	Taxane (docetaxel); Lu-177 PSMA-617 (off-label in some jurisdictions)	Investigational; Sathekge chemotherapy-naive cohort relevant; specific patient-by-patient discussion
mCRPC, post-taxane, Lu-177 PSMA-naive	Lu-177 PSMA-617 (Pluvicto, FDA-approved); cabazitaxel	Investigational; some centres consider Ac-225 PSMA as alternative when Lu-177 PSMA contraindicated
mCRPC, post-Lu-177 PSMA progression	Limited established options; cabazitaxel if not received; clinical trials	Most established investigational use; salvage Ac-225 PSMA evidence base (Kratochwil, Yadav, Sathekge, Feuerecker cohorts)

The bottom line

Ac-225 PSMA-617 targeted alpha therapy is investigational — not FDA-approved — and is delivered at experienced centres under Helsinki Declaration informed-consent frameworks^[2].
The most established indication is salvage therapy after Lu-177 PSMA progression. Published cohorts (Kratochwil, Yadav AIIMS, Sathekge, Feuerecker) report PSA response ≥50% in 40-70% of patients in this setting^[3]^[4].
The chemotherapy-naive cohort data from Sathekge (n=17) reported PSA response ≥50% in 82% and undetectable PSA in 41% — striking outcomes that have not yet been reproduced in larger randomised settings^[5].
The principal alpha-specific toxicity is more severe and persistent xerostomia. Grade 2-3 xerostomia is reported in 30-50% of patients; dose-fractionation and salivary gland protective strategies are evolving^[7].
Patient selection requires maintained PSMA expression on Ga-68 PSMA PET-CT, adequate organ function, careful cumulative dose calculation from prior Lu-177 PSMA, and detailed informed consent.

Important

This article describes investigational Ac-225 PSMA-617 therapy. Individual decisions about salvage alpha-PSMA require detailed multidisciplinary review of disease state, prior treatments, PSMA imaging, organ function, and treatment goals — and must include comprehensive informed consent covering investigational status and expected outcomes.

"The conversation I have most often with mCRPC patients who have progressed on Lu-177 PSMA is — 'is there still a targeted option?' For most patients with maintained PSMA expression on Ga-68 PSMA PET-CT, the answer is yes: investigational Ac-225 PSMA can still produce meaningful response. The published cohort data — Kratochwil Heidelberg, Yadav AIIMS, Sathekge Pretoria, Feuerecker Munich — give us 40-70% PSA response in the Lu-177-refractory salvage setting. The trade-off is xerostomia, which is more severe and more persistent than with Lu-177. The decision is always individual, always Helsinki-framed, and always made in multidisciplinary review."

Dr. Ishita B. Sen, MD · Director & Chief, Nuclear Medicine, FMRI

Ac-225 PSMA evaluation · salvage-line consult

For mCRPC patients who have progressed on Lu-177 PSMA, our nuclear medicine team can review your current Ga-68 PSMA PET-CT, cumulative prior dose, and organ function to discuss whether investigational Ac-225 PSMA-617 is appropriate for your case — under Helsinki Declaration informed-consent framework.

Salvage Ac-225 PSMA consult · WhatsApp +91 8800 988936

For patients & referring clinicians

Frequently asked questions

Q01 What is Ac-225 PSMA-617?

Ac-225 PSMA-617 is a targeted alpha-particle radioligand therapy for prostate cancer. The radioisotope actinium-225 is attached to PSMA-617, the same prostate-cancer-targeting peptide used in Lu-177 PSMA-617 (Pluvicto). When infused, the radioligand binds PSMA receptors on prostate cancer cells and delivers high-energy, short-range alpha particles to those cells, producing concentrated DNA damage with minimal effect on neighbouring healthy tissue [1].

Q02 Is Ac-225 PSMA approved for prostate cancer?

No — Ac-225 PSMA-617 is investigational and not currently approved by FDA, EMA, or other major regulators for prostate cancer or any other indication. It is delivered at experienced centres under Helsinki Declaration informed-consent frameworks for patients meeting specific criteria, primarily as salvage therapy after Lu-177 PSMA progression [2].

Q03 What is the difference between Ac-225 PSMA and Lu-177 PSMA?

Both use the same PSMA-617 targeting peptide but different radioisotopes. Lu-177 emits longer-range (1-2 mm) beta particles; Ac-225 emits very short-range (50-100 μm) high-energy alpha particles. Alpha particles produce more concentrated DNA damage with denser double-strand breaks. The clinical implication: in patients who progress on Lu-177 PSMA (beta), Ac-225 PSMA (alpha) can still produce meaningful responses because of the different mechanism of action [1].

Q04 When is Ac-225 PSMA used?

The most established use of Ac-225 PSMA is as salvage therapy after progression on Lu-177 PSMA-617. Published cohorts report PSA response ≥50% in 40-70% of patients in this setting (Kratochwil, Yadav AIIMS, Sathekge, Feuerecker) [3][4]. Some centres also consider Ac-225 PSMA in earlier disease states (chemotherapy-naive mCRPC) where the Sathekge cohort showed striking response, but evidence at earlier lines is limited [5].

Q05 What are the main side effects of Ac-225 PSMA?

The principal alpha-specific toxicity is more severe and persistent xerostomia (dry mouth) than seen with Lu-177 PSMA. Grade 2-3 xerostomia is reported in 30-50% of patients. Other side effects include fatigue, cytopenia (lower than Lu-177 in most cohorts), and rare renal toxicity. Xerostomia is the principal reason for dose reduction in alpha-PSMA protocols [7][8].

Q06 How is the xerostomia after Ac-225 PSMA managed?

Strategies include: salivary gland cooling during administration (limited evidence); dose-fractionation (reducing per-cycle dose, extending intervals); sialogogues (pilocarpine, cevimeline); intensive oral hygiene; saliva substitutes; in selected refractory cases, intra-glandular botulinum toxin has been investigated. The evidence base for xerostomia mitigation is evolving; published response varies. Our xerostomia management article provides detailed guidance [8].

Q07 How many cycles of Ac-225 PSMA are typical?

Most published protocols deliver 3-6 cycles of Ac-225 PSMA-617 at 8-week intervals. Per-cycle dose is typically 5.5-8 MBq, with body-weight or dosimetry-based adjustment. Some centres use dose-reduction strategies after Cycles 2-3 to minimise cumulative xerostomia. The exact protocol depends on the centre's experience, the patient's tolerance, and observed response [10].

Q08 Can Ac-225 PSMA cure mCRPC?

Ac-225 PSMA is not a curative therapy for mCRPC. The realistic goal is meaningful response (PSA decline, imaging response, symptom improvement) and extended progression-free interval. Some patients achieve very deep responses (undetectable PSA) but durable cure is not the documented outcome. The published cohort data show median PFS of 4-6 months in the Lu-177-refractory salvage setting, with selected patients achieving longer responses [3][4].

Q09 Where is Ac-225 PSMA available in India?

Ac-225 PSMA-617 is available at a small number of Indian tertiary centres with active alpha-radiopharmaceutical programmes, including AIIMS New Delhi (Yadav, Bal, Ballal published series), FMRI Gurugram, and a few others. Delivery requires the centre to have AERB licensure for alpha-emitter handling, qualified personnel, comprehensive informed consent frameworks, and integrated multidisciplinary review [4].

Q10 What labs are needed before Ac-225 PSMA?

Standard pre-treatment workup: recent Ga-68 PSMA PET-CT confirming maintained PSMA expression; full blood count; urea/electrolytes/creatinine with eGFR; liver function tests; PSA; cumulative prior PRRT dose calculation; ECOG performance status documentation; baseline salivary gland function assessment; multidisciplinary review documenting indication. Some centres add Tc-99m DMSA for detailed renal function [9].

Q11 Can Ac-225 PSMA be combined with other prostate cancer treatments?

Combinations with ARPI (abiraterone, enzalutamide), PARP inhibitors, and other agents are being investigated in trials. Outside trials, most experienced centres deliver Ac-225 PSMA alongside continued ADT (the patient remains on hormonal therapy throughout); some allow continuation of ARPI. Concurrent docetaxel is not standard. Specific combination decisions require multidisciplinary discussion of evidence and patient-specific factors [11].

Q12 How do I know if I am a candidate for Ac-225 PSMA at FMRI?

Candidacy review at FMRI requires: recent Ga-68 PSMA PET-CT confirming maintained PSMA expression in known disease; documented prior treatment trajectory (including Lu-177 PSMA cycles and response); current organ function; recent imaging for cumulative dose calculation; multidisciplinary case review documenting indication and alternative options. WhatsApp +91 8800 988936 to begin a confidential review.

Citations & references

All clinical numbers above are sourced from the primary literature listed below. Every reference links to the open journal page or the FDA archive — open in a new tab to verify.

[1] Sgouros G, Bodei L, McDevitt MR, et al. Radiopharmaceutical therapy in cancer: clinical advances and challenges. Nat Rev Drug Discov. 2020;19(9):589-608. View source ↗

[2] World Medical Association. Declaration of Helsinki — Ethical Principles for Medical Research Involving Human Subjects. JAMA. 2013;310(20):2191-2194. View source ↗

[3] Kratochwil C, Bruchertseifer F, Rathke H, et al. Targeted alpha-therapy of metastatic castration-resistant prostate cancer with ²²⁵Ac-PSMA-617: dosimetry estimate and empiric dose finding. J Nucl Med. 2017;58(10):1624-1631. View source ↗

[4] Yadav MP, Ballal S, Sahoo RK, et al. ²²⁵Ac-PSMA-617 in mCRPC after failure of Lu-177 PSMA-617: Indian institutional experience. Eur J Nucl Med Mol Imaging. 2024. View source ↗

[5] Sathekge M, Bruchertseifer F, Knoesen O, et al. ²²⁵Ac-PSMA-617 in chemotherapy-naive patients with advanced prostate cancer. Eur J Nucl Med Mol Imaging. 2019;46(1):129-138. View source ↗

[6] Sathekge M, Bruchertseifer F, Vorster M, et al. Predictors of overall and disease-free survival in mCRPC receiving ²²⁵Ac-PSMA-617. J Nucl Med. 2020;61(1):62-69. View source ↗

[7] Kratochwil C, Apostolidis L, Rathke H, et al. Dosing ²²⁵Ac-PSMA-617 in mCRPC: practical considerations and toxicity profile. Eur J Nucl Med Mol Imaging. 2021;48(5):1543-1550. View source ↗

[8] Rathke H, Kratochwil C, Hohenberger R, et al. Salivary gland protection in ²²⁵Ac-PSMA-617 radioligand therapy. J Nucl Med. 2019;60(11):1631-1632. View source ↗

[9] Hofman MS, Iravani A, Nzenza T, et al. Targeted radionuclide therapy for prostate cancer: A clinical perspective. Eur Urol. 2022;82(2):149-158. View source ↗

[10] Feuerecker B, Tauber R, Knorr K, et al. Activity and adverse events of ²²⁵Ac-PSMA-617 in advanced mCRPC after failure of Lu-177 PSMA. Eur Urol. 2021;79(3):343-350. View source ↗

[11] National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Prostate Cancer (Version 4.2024). View source ↗

[12] European Association of Urology. EAU Guidelines on Prostate Cancer. 2024 Update. View source ↗

[13] Sartor O, de Bono J, Chi KN, et al. Lutetium-177-PSMA-617 for Metastatic Castration-Resistant Prostate Cancer (VISION). N Engl J Med. 2021;385(12):1091-1103. View source ↗

[14] Hofman MS, Emmett L, Sandhu S, et al. [¹⁷⁷Lu]Lu-PSMA-617 versus cabazitaxel in mCRPC (TheraP). Lancet. 2021;397(10276):797-804. View source ↗

[15] Hofman MS, Buteau JP, Sandhu S, et al. Final overall survival in the TheraP trial. Lancet Oncol. 2024;25(1):99-107. View source ↗

[16] Morris MJ, Castellano D, Herrmann K, et al. ¹⁷⁷Lu-PSMA-617 versus a change of ARPI for taxane-naive patients with progressive mCRPC (PSMAfore). Lancet. 2024. View source ↗

[17] Calais J, Czernin J, Cao M, et al. ⁶⁸Ga-PSMA-11 PET/CT mapping of prostate cancer biochemical recurrence after radical prostatectomy. J Nucl Med. 2018;59(4):576-585. View source ↗

[18] Kratochwil C, Haberkorn U, Giesel FL. ²²⁵Ac-PSMA-617 for treatment of mCRPC: clinical experience from a single center. Semin Nucl Med. 2020;50(2):133-140. View source ↗

[19] Heck MM, Tauber R, Schwaiger S, et al. Treatment outcome, toxicity, and predictive factors for ¹⁷⁷Lu-PSMA-I&T in mCRPC. Eur Urol. 2019;75(6):920-926. View source ↗

[20] Iravani A, Violet J, Azad A, et al. Lutetium-177 PSMA therapy: practical aspects, dosimetry, and outcomes. Theranostics. 2020;10(20):8854-8866. View source ↗

[21] Sgouros G, Roeske JC, McDevitt MR, et al. MIRD Pamphlet No. 22: radiobiology and dosimetry of alpha-particle emitters for targeted radionuclide therapy. J Nucl Med. 2010;51(2):311-328. View source ↗

[22] Pommé S, Marouli M, Suliman G, et al. Measurement of ²²⁵Ac for medical applications. Appl Radiat Isot. 2012;70(9):1561-1566. View source ↗

[23] Apostolidis L, Yadav MP, Rathke H, et al. Tumour heterogeneity and PSMA expression in mCRPC: implications for radionuclide therapy. Eur J Nucl Med Mol Imaging. 2022;49(9):3194-3204. View source ↗

[24] de Bono JS, Logothetis CJ, Molina A, et al. Abiraterone and increased survival in metastatic prostate cancer (COU-AA-301). N Engl J Med. 2011;364(21):1995-2005. View source ↗

[25] Scher HI, Fizazi K, Saad F, et al. Increased survival with enzalutamide in prostate cancer after chemotherapy (AFFIRM). N Engl J Med. 2012;367(13):1187-1197. View source ↗

[26] de Bono JS, Oudard S, Ozguroglu M, et al. Prednisone plus cabazitaxel or mitoxantrone for mCRPC progressing after docetaxel (TROPIC). Lancet. 2010;376(9747):1147-1154. View source ↗

[27] Tagawa ST, Vallabhajosula S, Christos PJ, et al. Phase I/II study of fractionated dose ¹⁷⁷Lu-J591 anti-PSMA antibody. Cancer. 2019;125(15):2561-2569. View source ↗

[28] Ballal S, Yadav MP, Bal C, et al. Concomitant ¹⁷⁷Lu-DOTATATE and capecitabine therapy and updated outcomes of ²²⁵Ac-DOTATATE. Eur J Nucl Med Mol Imaging. 2020;47(4):934-946. View source ↗

[29] Hennrich U, Eder M. ¹⁷⁷Lu-PSMA-617 (Pluvicto): The First FDA-Approved Radiotherapeutical for Treatment of Prostate Cancer. Pharmaceuticals (Basel). 2022;15(10):1292. View source ↗

[30] Khreish F, Ebert N, Ries M, et al. ²²⁵Ac-PSMA-617/¹⁷⁷Lu-PSMA-617 tandem therapy of mCRPC: pilot experience. Eur J Nucl Med Mol Imaging. 2020;47(3):721-728. View source ↗

[31] Rosar F, Hau F, Bartholomä M, et al. Molecular imaging and biochemical response assessment after a single cycle of ²²⁵Ac-PSMA-617/¹⁷⁷Lu-PSMA-617 tandem therapy in mCRPC. Theranostics. 2021;11(9):4050-4060. View source ↗

[32] Allen BJ, Singla AA, Rizvi SM, et al. Analysis of patient survival in a phase I trial of systemic targeted alpha-therapy. Immunotherapy. 2011;3(9):1041-1050. View source ↗

About the Author

Dr. Ishita B. Sen

MBBS · MD (Nuclear Medicine) · DNB · Post-doctoral Fellowship, Memorial Sloan Kettering Cancer Center, New York

Director and Chief of Nuclear Medicine at Fortis Memorial Research Institute. Co-founder of Theranostic Physicians Private Limited (TPPL). Two decades of clinical practice in PSMA imaging and PSMA-directed radioligand therapy, with one of the largest Indian institutional experiences in Lu-PSMA.

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