Inclusion Criteria:
1. Age between 18 and 80 years, male or female.
2. Able to understand and sign written informed consent, willing to follow pre-injection preparation requirements (adequate hydration and avoidance of high-dose riboflavin supplements), and to complete all study procedures.
3. Recurrent invasive pituitary adenoma within 6 months after surgery, without intracranial or distant metastasis. The postoperative pathological Ki-67 index of the previous pituitary tumor is ≥3%, and tumor growth cannot be controlled by standard medical therapy and radiotherapy.
4. Radiological and clinical evidence indicates residual or recurrent pituitary adenoma requiring treatment or follow-up management.
5. At least one measurable and resectable lesion suitable for correlation with PET imaging evaluation; vital signs are stable, and the participant is able to lie supine and cooperate during a 30-60 minute PET scan.
Exclusion Criteria:
1. Pregnant or planning to become pregnant, or breastfeeding women.
2. Known history of severe allergic or anaphylactoid reactions to any component of the investigational tracer (riboflavin derivatives, NOTA chelator, or formulation excipients).
3. Presence of severe or uncontrolled medical conditions (e.g., decompensated heart failure, active infection, myocardial infarction or stroke within the past 4 weeks) that, in the opinion of the investigator, make the participant unsuitable for PET imaging.
4. Concomitant severe systemic diseases such as cardiac, pulmonary, hepatic, or renal failure.
5. Pituitary adenoma patients who underwent surgery less than 4 weeks prior to enrollment or completed radiotherapy to the sellar region within the past 3 months.
6. Participation in another interventional clinical trial within the past 4 weeks, or cumulative radiation exposure from prior research procedures within the past 12 months that may exceed the ethical safety limit.
7. Severe claustrophobia unrelieved by sedation, or any other condition that would prevent completion of the PET scan.
8. Poor compliance or any factor judged by the investigator to affect the participant's safety or the quality of study data.
9. Any other condition that, in the judgment of the investigator, makes the participant unsuitable for study participation.
