Lantheus-affiliated entities disclose a 17.3% beneficial ownership position in Radiopharm Theranostics via shares and options, reported on a passive Schedule 13G basis.
Radiopharm Theranostics Ltd (RADX) is reported to have a significant shareholder group led by Lantheus Omega, LLC, together with Lantheus Medical Imaging, Inc. and Lantheus Holdings, Inc., which collectively beneficially own 792,958,513 Ordinary Shares, or 17.3% of the class. This stake includes (i) 149,625,180 shares issued on August 23, 2024, (ii) 133,333,333 shares issued on January 20, 2025, (iii) 255,000,000 shares issued on December 9, 2025 and (iv) options to purchase 255,000,000 shares at an exercise price of AUD$0.039 per share expiring on October 31, 2027.
The reporting group has no sole voting or dispositive power but may be deemed to share voting and dispositive power over all 792,958,513 shares held of record by Lantheus Omega, LLC. They state that they no longer beneficially own more than 20% of Radiopharm’s outstanding Ordinary Shares and that they do not hold the securities with the purpose or effect of changing or influencing control of the company, changing their reporting posture from a Schedule 13D to a Schedule 13G.
Positive
None.
Negative
None.
Key Figures
Beneficial ownership:792,958,513 Ordinary SharesPercent of class:17.3%Ordinary Shares issued August 23, 2024:149,625,180 shares+5 more
8 metrics
Beneficial ownership792,958,513 Ordinary SharesOwned by Lantheus Omega, LLC and affiliates as of the Schedule 13G
Percent of class17.3%Radiopharm Ordinary Shares beneficially owned including options
Ordinary Shares issued August 23, 2024149,625,180 sharesIssued to Lantheus Omega, LLC
Ordinary Shares issued January 20, 2025133,333,333 sharesIssued to Lantheus Omega, LLC
Ordinary Shares issued December 9, 2025255,000,000 sharesDecember Issuance to Lantheus Omega, LLC
Options held255,000,000 underlying sharesOptions to purchase Radiopharm Ordinary Shares held by Lantheus Omega, LLC
Option exercise priceAUD$0.039 per shareExercise price for options expiring October 31, 2027
Shares outstanding baseline3,928,709,960 + 408,839,531 sharesOrdinary Shares reported outstanding as of July 28, 2026 and August 3, 2026 used to compute ownership percentage
Key Terms
beneficially owned, dispositive power, Schedule 13D, Schedule 13G, +2 more
6 terms
beneficially ownedfinancial
"Aggregate amount beneficially owned consists of (i) 149,625,180 Ordinary Shares"
Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.
dispositive powerfinancial
"Shared Dispositive Power 792,958,513.00"
Dispositive power is the authority to decide the final outcome of an asset, legal claim, contract, or corporate action — in effect the power to dispose of or resolve something. For investors it matters because whoever holds that authority can determine who gets paid, who controls an asset or vote, and how risks and returns are allocated; think of it like holding the key that lets you lock in the winner or loser in a deal.
Schedule 13Dregulatory
"The Reporting Persons previously filed a Schedule 13D (the "Schedule 13D")"
A Schedule 13D is a legal document that investors file with regulators when they buy a large enough stake in a company to potentially influence its management or decisions. It provides details about the investor’s intention, ownership stake, and plans, helping other investors understand who is gaining control and what their motives might be.
Schedule 13Gregulatory
"As such, this is deemed to amend the Schedule 13D."
A Schedule 13G is a formal document that investors file with the government when they acquire a large ownership stake in a company, usually for investment purposes rather than control. It helps keep the public informed about who owns significant parts of a company's shares, which can influence how the company is managed and how investors make decisions. Filing this schedule is important for transparency and understanding the ownership landscape of publicly traded companies.
Rule 13d-1(k)regulatory
"pursuant to Rule 13d-1(k) promulgated by the (the "SEC")"
Ordinary Sharesfinancial
"Ordinary Shares, no par value per share"
Ordinary shares are a type of ownership stake in a company, giving shareholders a right to participate in the company’s profits and decision-making through voting. They are similar to owning a piece of a business, and their value can rise or fall based on the company's performance. Investors buy ordinary shares to potentially earn dividends and benefit from the company's growth over time.
FAQ
How much of Radiopharm Theranostics (RADX) do the Lantheus entities beneficially own?
The Lantheus-affiliated entities beneficially own 792,958,513 Ordinary Shares of Radiopharm Theranostics Ltd, representing 17.3% of the outstanding Ordinary Shares when including shares issuable upon exercise of options.
What securities do the Lantheus entities hold in RADX and when were they issued?
They hold 149,625,180 Ordinary Shares issued August 23, 2024, 133,333,333 shares issued January 20, 2025, 255,000,000 shares issued December 9, 2025, plus options to purchase 255,000,000 additional Ordinary Shares issued December 9, 2025.
What are the key terms of the options held by the Lantheus entities in RADX?
The Lantheus entities hold options to purchase 255,000,000 Ordinary Shares of Radiopharm at an exercise price of AUD$0.039 per share, with an expiration date of October 31, 2027.
Do the Lantheus entities seek to influence control of Radiopharm Theranostics (RADX)?
They state that, as of the date of the Schedule 13G, they do not hold the securities with the purpose or effect of changing or influencing control of Radiopharm Theranostics Ltd.
Why did the Lantheus entities move from a Schedule 13D to a Schedule 13G for RADX?
They previously reported on a Schedule 13D but now report on a Schedule 13G because they no longer beneficially own more than 20% of Radiopharm’s outstanding Ordinary Shares and report the holdings on a passive basis.
What share count was used to calculate the 17.3% ownership in RADX?
The 17.3% figure is based on 3,928,709,960 Ordinary Shares outstanding as of July 28, 2026, plus 408,839,531 additional Ordinary Shares outstanding as of August 3, 2026, and 255,000,000 shares issuable upon conversion of the options.
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 13G
UNDER THE SECURITIES EXCHANGE ACT OF 1934
Radiopharm Theranostics Limited
(Name of Issuer)
Ordinary Shares, no par value per share
(Title of Class of Securities)
Q79455103
(CUSIP Number)
07/28/2026
(Date of Event Which Requires Filing of this Statement)
Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
Rule 13d-1(b)
Rule 13d-1(c)
Rule 13d-1(d)
schemaVersion:
SCHEDULE 13G
CUSIP Number(s):
Q79455103
1
Names of Reporting Persons
Lantheus Omega, LLC
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
792,958,513.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
792,958,513.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
792,958,513.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
17.3 %
12
Type of Reporting Person (See Instructions)
OO
Comment for Type of Reporting Person: Aggregate amount beneficially owned consists of (i) 149,625,180 ordinary shares, no par value ("Ordinary Shares"), of the Issuer (as defined below) issued to Lantheus Omega, LLC on August 23, 2024, (ii) 133,333,333 Ordinary Shares issued to Lantheus Omega, LLC on January 20, 2025, (iii) 255,000,000 Ordinary Shares issued to Lantheus Omega, LLC on December 9, 2025 (the "December Issuance") and (iv) options to purchase 255,000,000 Ordinary Shares issued to Lantheus Omega, LLC on December 9, 2025 in connection with the December Issuance, with an exercise price of AUD$0.039 per share and expiring on October 31, 2027 (the "Options").
Lantheus Medical Imaging, Inc. is the sole member of Lantheus Omega, LLC and a wholly-owned subsidiary of Lantheus Holdings, Inc. Lantheus Holdings, Inc., Lantheus Medical Imaging, Inc. and Lantheus Omega, LLC may each be deemed to have shared voting and dispositive power over all of the shares of Common Stock held by Lantheus Omega, LLC.
Percent of class represented by amount in Row (11) is based on 3,928,709,960 Ordinary Shares of the Issuer reported to be outstanding by the Issuer as of July 28, 2026 in the Issuer's prospectus filed pursuant to Rule 424(b)(5) on July 27, 2026, 408,839,531 additional Ordinary Shares reported to be outstanding by the Issuer as of August 3, 2026 in the Issuer's Notice of Extraordinary General Meeting and Proxy Form filed with the Issuer's 6-K on August 13, 2026, and the 255,000,000 Ordinary Shares issuable upon conversion of the Options.
SCHEDULE 13G
CUSIP Number(s):
Q79455103
1
Names of Reporting Persons
Lantheus Medical Imaging, Inc.
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
792,958,513.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
792,958,513.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
792,958,513.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
17.3 %
12
Type of Reporting Person (See Instructions)
CO
Comment for Type of Reporting Person: Aggregate amount beneficially owned consists of (i) 149,625,180 Ordinary Shares issued to Lantheus Omega, LLC on August 23, 2024, (ii) 133,333,333 Ordinary Shares issued to Lantheus Omega, LLC on January 20, 2025, (iii) 255,000,000 Ordinary Shares issued to Lantheus Omega, LLC on December 9, 2025 and (iv) options to purchase 255,000,000 Ordinary Shares issued to Lantheus Omega, LLC on December 9, 2025 in connection with the December Issuance, with an exercise price of AUD$0.039 per share and expiring on October 31, 2027.
Lantheus Medical Imaging, Inc. is the sole member of Lantheus Omega, LLC and a wholly-owned subsidiary of Lantheus Holdings, Inc. Lantheus Holdings, Inc., Lantheus Medical Imaging, Inc. and Lantheus Omega, LLC may each be deemed to have shared voting and dispositive power over all of the shares of Common Stock held by Lantheus Omega, LLC.
Percent of class represented by amount in Row (11) is based on 3,928,709,960 Ordinary Shares of the Issuer reported to be outstanding by the Issuer as of July 28, 2026 in the Issuer's prospectus filed pursuant to Rule 424(b)(5) on July 27, 2026, 408,839,531 additional Ordinary Shares reported to be outstanding by the Issuer as of August 3, 2026 in the Issuer's Notice of Extraordinary General Meeting and Proxy Form filed with the Issuer's 6-K on August 13, 2026, and the 255,000,000 Ordinary Shares issuable upon conversion of the Options.
SCHEDULE 13G
CUSIP Number(s):
Q79455103
1
Names of Reporting Persons
Lantheus Holdings, Inc.
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
792,958,513.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
792,958,513.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
792,958,513.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
17.3 %
12
Type of Reporting Person (See Instructions)
CO
Comment for Type of Reporting Person: Aggregate amount beneficially owned consists of (i) 149,625,180 Ordinary Shares issued to Lantheus Omega, LLC on August 23, 2024, (ii) 133,333,333 Ordinary Shares issued to Lantheus Omega, LLC on January 20, 2025, (iii) 255,000,000 Ordinary Shares issued to Lantheus Omega, LLC on December 9, 2025 and (iv) options to purchase 255,000,000 Ordinary Shares issued to Lantheus Omega, LLC on December 9, 2025 in connection with the December Issuance, with an exercise price of AUD$0.039 per share and expiring on October 31, 2027.
Lantheus Medical Imaging, Inc. is the sole member of Lantheus Omega, LLC and a wholly-owned subsidiary of Lantheus Holdings, Inc. Lantheus Holdings, Inc., Lantheus Medical Imaging, Inc. and Lantheus Omega, LLC may each be deemed to have shared voting and dispositive power over all of the shares of Common Stock held by Lantheus Omega, LLC.
Percent of class represented by amount in Row (11) is based on 3,928,709,960 Ordinary Shares of the Issuer reported to be outstanding by the Issuer as of July 28, 2026 in the Issuer's prospectus filed pursuant to Rule 424(b)(5) on July 27, 2026, 408,839,531 additional Ordinary Shares reported to be outstanding by the Issuer as of August 3, 2026 in the Issuer's Notice of Extraordinary General Meeting and Proxy Form filed with the Issuer's 6-K on August 13, 2026, and the 255,000,000 Ordinary Shares issuable upon conversion of the Options.
This Statement on Schedule 13G (this "Statement") is being jointly filed by (i) Lantheus Omega, LLC, (ii) Lantheus Medical Imaging, Inc. and (iii) Lantheus Holdings, Inc. (collectively, the "Reporting Persons") pursuant to Rule 13d-1(k) promulgated by the Securities and Exchange Commission (the "SEC") pursuant to Section 13 of the Securities Exchange Act of 1934, as amended.
The Reporting Persons have entered into a Joint Filing Agreement, dated September 4, 2026, a copy of which is attached as Exhibit 99.1 to this Statement, pursuant to which the Reporting Persons have agreed to file this Statement jointly in accordance with the provisions of Rule 13d-1(k)(1) under the Act.
The Reporting Persons previously filed a Schedule 13D (the "Schedule 13D") with the SEC on September 4, 2026 related to the Ordinary Shares held by Lantheus Omega, LLC. The Reporting Persons no longer beneficially own more than 20% of the outstanding Ordinary Shares. As of the date of filing of this Schedule 13G, the Reporting Persons do not hold the securities with the purpose or effect of changing or influencing control of the Issuer. As such, this Schedule 13G is deemed to amend the Schedule 13D.
(b)
Address or principal business office or, if none, residence:
The address of each of the Reporting Persons is 201 Burlington Road, South Building, Bedford, MA 01730.
(c)
Citizenship:
The citizenship of each of the Reporting Persons is Delaware, United States.
(d)
Title of class of securities:
Ordinary Shares, no par value per share
(e)
CUSIP Number(s):
Q79455103
Item 3.
If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)
Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)
Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)
Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)
Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)
An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)
An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)
A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)
A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)
A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)
A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution:
(k)
Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.
Ownership
(a)
Amount beneficially owned:
792,958,513 ordinary shares, no par value, of the Issuer ("Ordinary Shares"), consisting of (i) 149,625,180 Ordinary Shares issued to Lantheus Omega, LLC on August 23, 2024, (ii) 133,333,333 Ordinary Shares issued to Lantheus Omega, LLC on January 20, 2025, (iii) 255,000,000 Ordinary Shares issued to Lantheus Omega, LLC on December 9, 2025 (the "December Issuance") and (iv) options to purchase 255,000,000 Ordinary Shares issued to Lantheus Omega, LLC on December 9, 2025 in connection with the December Issuance, with an exercise price of AUD$0.039 per share and expiring on October 31, 2027 (the "Options").
(b)
Percent of class:
17.3%
The percentage of beneficial ownership stated herein and on each Reporting Person's cover page to this Schedule 13G is based on 3,928,709,960 Ordinary Shares of the Issuer reported to be outstanding by the Issuer as of July 28, 2026 in the Issuer's prospectus filed pursuant to Rule 424(b)(5) on July 27, 2026, 408,839,531 additional Ordinary Shares reported to be outstanding by the Issuer as of August 3, 2026 in the Issuer's Notice of Extraordinary General Meeting and Proxy Form filed with the Issuer's 6-K on August 13, 2026, and the 255,000,000 Ordinary Shares issuable upon conversion of the Options.
(c)
Number of shares as to which the person has:
(i) Sole power to vote or to direct the vote:
0
(ii) Shared power to vote or to direct the vote:
Each Reporting Person may be deemed to share voting power with respect to 792,958,513 Ordinary Shares, which are held of record by Lantheus Omega, LLC. Lantheus Medical Imaging, Inc. is the sole member of Lantheus Omega, LLC and a wholly-owned subsidiary of Lantheus Holdings, Inc.
(iii) Sole power to dispose or to direct the disposition of:
0
(iv) Shared power to dispose or to direct the disposition of:
Each Reporting Person may be deemed to share dispositive power with respect to 792,958,513 Ordinary Shares, which are held of record by Lantheus Omega, LLC. Lantheus Medical Imaging, Inc. is the sole member of Lantheus Omega, LLC and a wholly-owned subsidiary of Lantheus Holdings, Inc.
Item 5.
Ownership of 5 Percent or Less of a Class.
Not Applicable
Item 6.
Ownership of more than 5 Percent on Behalf of Another Person.
Not Applicable
Item 7.
Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
Not Applicable
Item 8.
Identification and Classification of Members of the Group.
Not Applicable
Item 9.
Notice of Dissolution of Group.
Not Applicable
Item 10.
Certifications:
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.
SIGNATURE
After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.
Lantheus Omega, LLC
Signature:
/s/ Eric M. Green
Name/Title:
Eric M. Green, Assistant Corporate Secretary of Lantheus Medical Imaging, Inc., its sole member
Date:
09/04/2026
Lantheus Medical Imaging, Inc.
Signature:
/s/ Eric M. Green
Name/Title:
Eric M. Green, Assistant Corporate Secretary
Date:
09/04/2026
Lantheus Holdings, Inc.
Signature:
/s/ Eric M. Green
Name/Title:
Eric M. Green, Assistant Corporate Secretary
Date:
09/04/2026
Exhibit Information
Exhibit Index
Exhibit 99.1 Joint Filing Agreement by and among the Reporting Persons as required by Rule 13d-1(k)(1).
