Marta Cremonesi | Theragnostic Imaging

Rethinking Dosimetry: A European Perspective

Thu, 22 May 2025 00:00:00 +0000

Radiopharmaceutical therapy (RPT) is entering a new era of personalization, driven by advances in molecular imaging, radiopharmaceutical development, and a growing body of clinical evidence linking absorbed dose to treatment outcomes. Although external-beam radiotherapy has long integrated dosimetry into standard practice, RPT historically relied on fixed radiopharmaceutical activities and absorbed dose-effect relationships adapted from external-beam radiotherapy, often without accounting for the unique pharmacokinetics, absorbed dose rate dynamics, and biologic responses of systemically administered radiopharmaceuticals. As RPT expands into earlier disease stages, at which patients have longer life expectancies and better performance status, the role of dosimetry in optimizing treatment is becoming increasingly evident. However, despite growing recognition of its benefits, the implementation of dosimetry in clinical practice remains limited, partly because of a self-reinforcing cycle in which the lack of routine dosimetry limits clinical evidence, which in turn hinders its broader adoption. Breaking this cycle is essential to advancing RPT and ensuring that evaluation of dosimetry is based on clinical merit rather than logistic constraints. This article examines the current landscape of RPT dosimetry, highlighting key challenges and opportunities from a European perspective and aiming to foster a more factual and constructive discussion on the topic. We discuss the fundamental differences between dosimetry-driven treatment planning and posttherapy absorbed dose verification, emphasizing the latter as a practical entry point for clinical adoption. We underscore the need for harmonized standards, improved imaging resolution, and tailored absorbed dose-effect relationships that reflect the heterogeneity of RPT delivery and the complexity of tumor and organ responses. The paper also addresses regulatory, infrastructural, and resource barriers to RPT dosimetry implementation and highlights ongoing European initiatives to strengthen frameworks, enhance stakeholder collaboration, and integrate absorbed dose biomarkers into authorization processes and clinical decision-making. By rethinking dosimetry and promoting standardized, evidence-based approaches, the field can advance beyond fixed-activity protocols toward truly individualized RPT. However, achieving clinically feasible integration of dosimetry into routine practice requires structured efforts to generate high-quality clinical evidence and improve accessibility. Ultimately, reliable, patient-centered dosimetry has the potential to enhance therapeutic efficacy, manage toxicity more effectively, and support the long-term evolution of RPT as a cornerstone of precision oncology.

Do we need dosimetry for the optimization of theranostics in CNS tumors?

Mon, 09 Dec 2024 00:00:00 +0000

Radiopharmaceutical theranostic treatments have grown exponentially worldwide, and internal dosimetry has attracted attention and resources. Despite some similarities with chemotherapy, radiopharmaceutical treatments are essentially radiotherapy treatments, as the release of radiation into tissues is the determinant of the observed clinical effects. Therefore, absorbed dose calculations are key to explaining dose-effect correlations and individualizing radiopharmaceutical treatments. The present article introduces the basic principles of internal dosimetry and provides an overview of available loco-regional and systemic radiopharmaceutical treatments for central nervous system (CNS) tumors. The specific characteristics of dosimetry as applied to these treatments are highlighted, along with their limitations and most relevant results. Dosimetry is performed with higher precision and better reproducibility than in the past, and dosimetric data should be systematically collected, as treatment planning and verification may help exploit the full potential of theranostic of CNS tumors.

EANM guidance document: dosimetry for first-in-human studies and early phase clinical trials

Mon, 01 Apr 2024 00:00:00 +0000

The numbers of diagnostic and therapeutic nuclear medicine agents under investigation are rapidly increasing. Both novel emitters and novel carrier molecules require careful selection of measurement procedures. This document provides guidance relevant to dosimetry for first-in human and early phase clinical trials of such novel agents. The guideline includes a short introduction to different emitters and carrier molecules, followed by recommendations on the methods for activity measurement, pharmacokinetic analyses, as well as absorbed dose calculations and uncertainty analyses. The optimal use of preclinical information and studies involving diagnostic analogues is discussed. Good practice reporting is emphasised, and relevant dosimetry parameters and method descriptions to be included are listed. Three examples of first-in-human dosimetry studies, both for diagnostic tracers and radionuclide therapies, are given.

Implementation of dosimetry for molecular radiotherapy; results from a European survey

Mon, 01 Jan 2024 00:00:00 +0000

The use of molecular radiotherapy (MRT) has been rapidly evolving over the last years. The aim of this study was to assess the current implementation of dosimetry for MRTs in Europe. A web-based questionnaire was open for treating centres between April and June 2022, and focused on 2020-2022. Questions addressed the application of 16 different MRTs, the availability and involvement of medical physicists, software used, quality assurance, as well as the target regions for dosimetry, whether treatment planning and/or verification were performed, and the dosimetric methods used. A total of 173 responses suitable for analysis was received from centres performing MRT, geographically distributed over 27 European countries. Of these, 146 centres (84 %) indicated to perform some form of dosimetry, and 97 % of these centres had a medical physicist available and almost always involved in dosimetry. The most common MRTs were ¹³¹I-based treatments for thyroid diseases and thyroid cancer, and [²²³Ra]RaCl₂ for bone metastases. The implementation of dosimetry varied widely between therapies, from almost all centres performing dosimetry-based planning for microsphere treatments to none for some of the less common treatments (like ³²P sodium-phosphate for myeloproliferative disease and [⁸⁹Sr]SrCl₂ for bone metastases). Over the last years, implementation of dosimetry, both for pre-therapeutic treatment planning and post-therapy absorbed dose verification, increased for several treatments, especially for microsphere treatments. For other treatments that have moved from research to clinical routine, the use of dosimetry decreased in recent years. However, there are still large differences both across and within countries.

Time-Activity data fitting in molecular Radiotherapy: Methodology and pitfalls

Mon, 01 Jan 2024 00:00:00 +0000

Absorbed radiation doses are essential in assessing the effects, e.g. safety and efficacy, of radiopharmaceutical therapy (RPT). Patient-specific absorbed dose calculations in the target or the organ at risk require multiple inputs. These include the number of disintegrations in the organ, i.e. the time-integrated activities (TIAs) of the organs, as well as other parameters describing the process of radiation energy deposition in the target tissue (i.e. mean energy per disintegration, radiation dose constants, etc). TIAs are then estimated by incorporating the area under the radiopharmaceutical’s time-activity curve (TAC), which can be obtained by quantitative measurements of the biokinetics in the patient (typically based on imaging data such as planar scintigraphy, SPECT/CT, PET/CT, or blood and urine samples). The process of TAC determination/calculation for RPT generally depends on the user, e.g., the chosen number and schedule of measured time points, the selection of the fit function, the error model for the data and the fit algorithm. These decisions can strongly affect the final TIA values and thus the accuracy of calculated absorbed doses. Despite the high clinical importance of the TIA values, there is currently no consensus on processing time-activity data or even a clear understanding of the influence of uncertainties and variations in personalised RPT dosimetry related to user-dependent TAC calculation. As a first step towards minimising site-dependent variability in RPT dosimetry, this work provides an overview of quality assurance and uncertainty management considerations of the TIA estimation.

Correction to: EANM enabling guide: how to improve the accessibility of clinical dosimetry

Tue, 01 Aug 2023 00:00:00 +0000

No abstract available

Results from an EANM survey on time estimates and personnel responsible for main tasks in molecular radiotherapy dosimetry

Sat, 01 Jul 2023 00:00:00 +0000

No abstract available

EANM enabling guide: how to improve the accessibility of clinical dosimetry

Thu, 01 Jun 2023 00:00:00 +0000

Dosimetry can be a useful tool for personalization of molecular radiotherapy (MRT) procedures, enabling the continuous development of theranostic concepts. However, the additional resource requirements are often seen as a barrier to implementation. This guide discusses the requirements for dosimetry and demonstrates how a dosimetry regimen can be tailored to the available facilities of a centre. The aim is to help centres wishing to initiate a dosimetry service but may not have the experience or resources of some of the more established therapy and dosimetry centres. The multidisciplinary approach and different personnel requirements are discussed and key equipment reviewed example protocols demonstrating these factors are given in the supplementary material for the main therapies carried out in nuclear medicine, including [¹³¹I]-NaI for benign thyroid disorders, [¹⁷⁷Lu]-DOTATATE and ¹³¹I-mIBG for neuroendocrine tumours and [⁹⁰Y]-microspheres for unresectable hepatic carcinoma.