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

PURPOSE

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

On the use of solid 133Ba sources as surrogate for liquid 131I in SPECT/CT calibration: a European multi-centre evaluation

INTRODUCTION

Commissioning, calibration, and quality control procedures for nuclear medicine imaging systems are typically performed using hollow containers filled with radionuclide solutions. This leads to multiple sources of uncertainty, many of which can be overcome by using traceable, sealed, long-lived surrogate sources containing a radionuclide of comparable energies and emission probabilities. This study presents the results of a quantitative SPECT/CT imaging comparison exercise performed within the MRTDosimetry consortium to assess the feasibility of using 133Ba as a surrogate for 131I imaging.

MATERIALS AND METHODS

Two sets of four traceable 133Ba sources were produced at two National Metrology Institutes and encapsulated in 3D-printed cylinders (volume range 1.68-107.4 mL). Corresponding hollow cylinders to be filled with liquid 131I and a mounting baseplate for repeatable positioning within a Jaszczak phantom were also produced. A quantitative SPECT/CT imaging comparison exercise was conducted between seven members of the consortium (eight SPECT/CT systems from two major vendors) based on a standardised protocol. Each site had to perform three measurements with the two sets of 133Ba sources and liquid 131I.

RESULTS

As anticipated, the 131I pseudo-image calibration factors (cps/MBq) were higher than those for 133Ba for all reconstructions and systems. A site-specific cross-calibration reduced the performance differences between both radionuclides with respect to a cross-calibration based on the ratio of emission probabilities from a median of 12-1.5%. The site-specific cross-calibration method also showed agreement between 133Ba and 131I for all cylinder volumes, which highlights the potential use of 133Ba sources to calculate recovery coefficients for partial volume correction.

CONCLUSION

This comparison exercise demonstrated that traceable solid 133Ba sources can be used as surrogate for liquid 131I imaging. The use of solid surrogate sources could solve the radiation protection problem inherent in the preparation of phantoms with 131I liquid activity solutions as well as reduce the measurement uncertainties in the activity. This is particularly relevant for stability measurements, which have to be carried out at regular intervals.

Quantitative validation of Monte Carlo SPECT simulation: application to a Mediso AnyScan GATE simulation

BACKGROUND

Monte Carlo (MC) simulations are used in nuclear medicine imaging as they provide unparalleled insight into processes that are not directly experimentally measurable, such as scatter and attenuation in an acquisition. Whilst MC is often used to provide a 'ground-truth', this is only the case if the simulation is fully validated against experimental data. This work presents a quantitative validation for a MC simulation of a single-photon emission computed tomography (SPECT) system.

METHODS

An MC simulation model of the Mediso AnyScan SCP SPECT system installed at the UK National Physical Laboratory was developed in the GATE (Geant4 Application for Tomographic Emission) toolkit. Components of the detector head and two collimator configurations were modelled according to technical specifications and physical measurements. Experimental detection efficiency measurements were collected for a range of energies, permitting an energy-dependent intrinsic camera efficiency correction function to be determined and applied to the simulation on an event-by-event basis. Experimental data were collected in a range of geometries with [Formula: see text]Tc for comparison to simulation. The procedure was then repeated with [Formula: see text]Lu to determine how the validation extended to another isotope and set of collimators.

RESULTS

The simulation's spatial resolution, sensitivity, energy spectra and the projection images were compared with experimental measurements. The simulation and experimental uncertainties were determined and propagated to all calculations, permitting the quantitative agreement between simulated and experimental SPECT acquisitions to be determined. Statistical agreement was seen in sinograms and projection images of both [Formula: see text]Tc and [Formula: see text]Lu data. Average simulated and experimental sensitivity ratios of ([Formula: see text]) were seen for emission and scatter windows of [Formula: see text]Tc, and ([Formula: see text]) and ([Formula: see text]) for the 113 and 208 keV emissions of [Formula: see text]Lu, respectively.

CONCLUSIONS

MC simulations will always be an approximation of a physical system and the level of agreement should be assessed. A validation method is presented to quantify the level of agreement between a simulation model and a physical SPECT system.

Development of a validation imaging dataset for Molecular Radiotherapy dosimetry multicenter intercomparison exercises based on anthropomorphic phantoms

Validation of a Molecular Radiotherapy (MRT) dosimetry system requires imaging data for which an accompanying "ground truth" pharmacokinetic model and absorbed dose calculation are known.

METHODS

We present a methodology for production of a validation dataset for image based ¹⁷⁷Lu dotatate dosimetry calculations. A pharmacokinetic model is presented with activity concentrations corresponding to common imaging timepoints. Anthropomorphic 3D printed phantoms, corresponding to the organs at risk, have been developed to provide SPECT/CT and Whole Body imaging with known organ activities corresponding to common clinical timepoints.

RESULTS

Results for the accuracy of phantom filling reproduce the activity concentrations from the pharmacokinetic model for all timepoints and organs within measurement uncertainties, with a mean deviation of 0.6(8)%. The imaging dataset, ancillary data and phantoms designs are provided as a source of well characterized input data for the validation of clinical MRT dosimetry systems.

CONCLUSIONS

The combination of pharmacokinetic modelling with the use of anthropomorphic 3D printed phantoms are a promising procedure to provide data for the validation of Molecular Radiotherapy Dosimetry systems, allowing multicentre comparisons.

Modelling SPECT auto-contouring acquisitions for 177Lu & 131I molecular radiotherapy using new developments in Geant4/GATE

PURPOSE

Monte Carlo modelling of SPECT imaging in Molecular Radiotherapy can improve activity quantification. Until now, SPECT modelling with GATE only considered circular orbit (CO) acquisitions. This cannot reproduce auto-contour acquisitions, where the detector head moves close to the patient to improve image resolution. The aim of this work is to develop and validate an auto-contouring step-and-shoot acquisition mode for GATE SPECT modelling.

METHODS

¹⁷⁷Lu and ¹³¹I SPECT experimental acquisitions performed on a Siemens Symbia T2 and GE Discovery 670 gamma camera, respectively, were modelled. SPECT projections were obtained for a cylindrical Jaszczak phantom and a lung and spine phantom. Detector head parameters (radial positions and acquisition angles) were extracted from the experimental projections to model the non-circular orbit (NCO) detector motion. The gamma camera model was validated against the experimental projections obtained with the cylindrical Jaszczak (¹⁷⁷Lu) and lung and spine phantom (¹³¹I). Then, ¹⁷⁷Lu and ¹³¹I CO and NCO SPECT projections were simulated to validate the impact of explicit NCO modelling on simulated projections.

RESULTS

Experimental and simulated SPECT images were compared using the gamma index, and were in good agreement with gamma index passing rate (GIPR) and gamma_avg of 96.27%, 0.242 (¹⁷⁷Lu) and 92.89%, 0.36 (¹³¹I). Then, simulated ¹⁷⁷Lu and ¹³¹I CO and NCO SPECT projections were compared. The GIPR, gamma_avg between the two gamma camera motions was 99.85%, 0.108 for ¹⁷⁷Lu and 75.58%, 0.6 for ¹³¹I.

CONCLUSION

This work thereby justifies the need for auto-contouring modelling for isotopes with high septal penetration.

Overview of commercial treatment planning systems for targeted radionuclide therapy

INTRODUCTION

Targeted Radionuclide Therapy (TRT) is a branch of cancer medicine dealing with the therapeutic use of radioisotopes associated with biological vectors accumulating in the tumors/targets, indicated as Molecular Radiotherapy (MRT), or directly injected into the arteries that supply blood to liver tumour vasculature, indicated as Selective RT (SRT). The aim of this work is to offer a panoramic view on the increasing number of commercially-available TRT treatment planning systems (TPSs).

MATERIALS AND METHODS

A questionnaire was sent to manufacturers' representatives. Academic software were not considered. Questions were grouped as follows: general information, clinical workflow, calibration procedure, image processing/reconstruction, image registration and segmentation tools, time-activity curve (TAC) fitting and absorbed dose calculation.

RESULTS

All software reported have CE-marking. TPSs were divided between SRT-dedicated software [4] and MRT [5] dosimetry software. In SRT, since no kinetic process is involved, absorbed dose calculation does not require TAC fitting, and image registration is not fully developed in all TPS. All software requires a radionuclide-specific calibration. In SRT, a relative image calibration can be obtained by scaling the counts to a known activity. Automated VOI contouring and rigid/deformable propagation between different acquisitions time-points is implemented in most TPSs, although DICOM export is rare. Different TAC fits are available depending on the number of time-points. Voxel S-value and Local deposition methods are the most frequent dosimetric approaches; dose-voxel kernel convolution and semi-Monte Carlo method are also available.

CONCLUSIONS

Available TPSs allows performing personalized dosimetry in clinical practice. Individual variations in methodology/algorithms must be considered in the standardisation/harmonization processes.

The internal dosimetry user group position statement on molecular radiotherapy

The Internal Dosimetry User Group (IDUG) is an independent, non-profit group of medical professionals dedicated to the promotion of dosimetry in molecular radiotherapy (www.IDUG.org.uk). The Ionising Radiation (Medical Exposure) Regulations 2017, IR(ME)R, stipulate a requirement for optimisation and verification of molecular radiotherapy treatments, ensuring doses to non-target organs are as low as reasonably practicable. For many molecular radiotherapy treatments currently undertaken within the UK, this requirement is not being fully met. The growth of this field is such that we risk digressing further from IR(ME)R compliance potentially delivering suboptimal therapies that are not in the best interest of our patients. For this purpose, IDUG proposes ten points of action to aid in the successful implementation of this legislation. We urge stakeholders to support these proposals and ensure national provision is sufficient to meet the criteria necessary for compliance, and for the future advancement of molecular radiotherapy within the UK.

A multicentre and multi-national evaluation of the accuracy of quantitative Lu-177 SPECT/CT imaging performed within the MRTDosimetry project

PURPOSE

Patient-specific dosimetry is required to ensure the safety of molecular radiotherapy and to predict response. Dosimetry involves several steps, the first of which is the determination of the activity of the radiopharmaceutical taken up by an organ/lesion over time. As uncertainties propagate along each of the subsequent steps (integration of the time-activity curve, absorbed dose calculation), establishing a reliable activity quantification is essential. The MRTDosimetry project was a European initiative to bring together expertise in metrology and nuclear medicine research, with one main goal of standardizing quantitative 177Lu SPECT/CT imaging based on a calibration protocol developed and tested in a multicentre inter-comparison. This study presents the setup and results of this comparison exercise.

METHODS

The inter-comparison included nine SPECT/CT systems. Each site performed a set of three measurements with the same setup (system, acquisition and reconstruction): (1) Determination of an image calibration for conversion from counts to activity concentration (large cylinder phantom), (2) determination of recovery coefficients for partial volume correction (IEC NEMA PET body phantom with sphere inserts), (3) validation of the established quantitative imaging setup using a 3D printed two-organ phantom (ICRP110-based kidney and spleen). In contrast to previous efforts, traceability of the activity measurement was required for each participant, and all participants were asked to calculate uncertainties for their SPECT-based activities.

RESULTS

Similar combinations of imaging system and reconstruction lead to similar image calibration factors. The activity ratio results of the anthropomorphic phantom validation demonstrate significant harmonization of quantitative imaging performance between the sites with all sites falling within one standard deviation of the mean values for all inserts. Activity recovery was underestimated for total kidney, spleen, and kidney cortex, while it was overestimated for the medulla.

CONCLUSION

This international comparison exercise demonstrates that harmonization of quantitative SPECT/CT is feasible when following very specific instructions of a dedicated calibration protocol, as developed within the MRTDosimetry project. While quantitative imaging performance demonstrates significant harmonization, an over- and underestimation of the activity recovery highlights the limitations of any partial volume correction in the presence of spill-in and spill-out between two adjacent volumes of interests.

An open source heterogeneous 3D printed mouse phantom utilising a novel bone representative thermoplastic

The lack of rigorous quality standards in pre-clinical radiation dosimetry has renewed interest in the development of anthropomorphic phantoms. Using 3D printing customisable phantoms can be created to assess all parts of pre-clinical radiation research: planning, image guidance and treatment delivery. We present the full methodology, including material development and printing designs, for the production of a high spatial resolution, anatomically realistic heterogeneous small animal phantom. A methodology for creating and validating tissue equivalent materials is presented. The technique is demonstrated through the development of a bone-equivalent material. This material is used together with a soft-tissue mimicking ABS plastic filament to reproduce the corresponding structure geometries captured from a CT scan of a nude mouse. Air gaps are used to represent the lungs. Phantom validation was performed through comparison of the geometry and x-ray attenuation of CT images of the phantom and animal images. A 6.6% difference in the attenuation of the bone-equivalent material compared to the reference standard in softer beams (0.5 mm Cu HVL) rapidly decreases as the beam is hardened. CT imaging shows accurate (sub-millimetre) reproduction of the skeleton (Distance-To-Agreement 0.5 mm ± 0.4 mm) and body surface (0.7 mm ± 0.5 mm). Histograms of the voxel intensity profile of the phantom demonstrate suitable similarity to those of both the original mouse image and that of a different animal. We present an approach for the efficient production of an anthropomorphic phantom suitable for the quality assurance of pre-clinical radiotherapy. Our design and full methodology are provided as open source to encourage the pre-clinical radiobiology community to adopt a common QA standard.

Standardised quantitative radioiodine SPECT/CT Imaging for multicentre dosimetry trials in molecular radiotherapy

The SEL-I-METRY trial (EudraCT No 2015-002269-47) is the first multicentre trial to investigate the role of 123I and 131I SPECT/CT-based tumour dosimetry to predict response to radioiodine therapy. Standardised dosimetry methodology is essential to provide a robust evidence-base for absorbed dose-response thresholds for molecular radiotherapy (MRT). In this paper a practical standardised protocol is used to establish the first network of centres with consistent methods of radioiodine activity quantification. Nine SPECT/CT systems at eight centres were set-up for quantitative radioiodine imaging. The dead-time of the systems was characterised for up to 2.8 GBq 131I. Volume dependent calibration factors were measured on centrally reconstructed images of 123I and 131I in six (0.8-196 ml) cylinders. Validation of image quantification using these calibration factors was performed on three systems, by imaging a 3D-printed phantom mimicking a patient's activity distribution. The percentage differences between the activities measured in the SPECT/CT image and those measured by the radionuclide calibrator were calculated. Additionally uncertainties on the SPECT/CT-based activities were calculated to indicate the limit on the quantitative accuracy of this method. For systems set-up to image high 131I count rates, the count rate versus activity did not peak below 2.8 GBq and fit a non-paralysable model. The dead-times and volume-dependent calibration factors were comparable between systems of the same model and crystal thickness. Therefore a global calibration curve could be fitted to each. The errors on the validation phantom activities' were comparable to the measurement uncertainties derived from uncertainty analysis, at 10% and 16% on average for 123I and 131I respectively in a 5 cm sphere. In conclusion, the dead-time and calibration factors varied between centres, with different models of system. However, global calibration factors may be applied to the same system model with the same crystal thickness, to simplify set-up of future multi-centre MRT studies.

Vascular Redistribution for SIRT—A Quantitative Assessment of Treatment Success and Long-Term Analysis of Recurrence and Survival Outcomes

Aim Flow redistribution is not uncommonly performed as a treatment strategy to optimize delivery of radioembolization particles to the liver. We quantitatively evaluated the effect of vessel embolization to promote flow redistribution when performing selective internal radiation therapy (SIRT) for liver metastases, and assessed long-term outcomes of treatment.

Materials and Methods One hundred and fifty-eight SIRT procedures over an 8-year period were retrospectively reviewed. Twenty-three patients who underwent partial/whole embolization of the left hepatic artery were compared to a control group of 18 patients who did not receive any hepatic embolization as part of their work up. Counts were measured for each patient on both the post-99mTcMAA injection, and the post-90Y microspheres injection imaging. Recurrence and survival rates were also measured.

Results A statistically significant shift in the right:left ratio between planning and treatment procedures was seen in patients who had vessel embolization in favor of the embolized lobe (p = 0.014). There was no significant difference in the time to recurrence in the embolized lobes versus the nonembolized lobes. No significant difference in overall survival was detected between the two cohorts.

Conclusion To facilitate safe whole liver treatment, it is sometimes necessary to partially or completely occlude main or accessory hepatic arteries. This study shows that the success of flow redistribution strategies can be quantitatively measured, and there is no adverse impact on time to recurrence or overall survival outcomes.

Improving molecular radiotherapy dosimetry using anthropomorphic calibration

The optimised delivery of Molecular Radiotherapy requires individualised calculation of absorbed dose to both targeted lesions and neighbouring healthy tissue. To achieve this, accurate quantification of the activity distribution in the patient by external detection is vital.

METHODS

This work extends specific anatomy-related calibration to true organ shapes. A set of patient-specific 3D printed organ inserts based on a diagnostic CT scan was produced, comprising the liver, spleen and both kidneys. The inserts were used to calculate patient-specific calibration factors for ¹⁷⁷Lu. These calibration factors were compared with previously reported calibration factors for corresponding organ models based on the Cristy and Eckerman phantom series and for a comparably sized sphere. Monte Carlo calculations of the patient-specific radiation dose were performed for comparison with current clinical dosimetry methods for these data.

RESULTS

Patient-specific calibration factors are shown to be dependent on the volume, shape and position of the organ containing activity with a corresponding impact on the calculation of the dose to the patient. The impact of organ morphology on calculated dose is reduced when the dominant contributor to dose is beta particles. This is due to the small range of beta particles in tissue. Overestimations of recovered activity and hence dose of up to 135% are observed.

CONCLUSION

For accurate quantification to be performed calibration factors accounting for organ size, shape and position must be used. Such quantification is vital if accurate, patient-specific dosimetry is to be achieved.

Inter-comparison of quantitative imaging of lutetium-177 (177Lu) in European hospitals

BACKGROUND

This inter-comparison exercise was performed to demonstrate the variability of quantitative SPECT/CT imaging for lutetium-177 (177Lu) in current clinical practice. Our aim was to assess the feasibility of using international inter-comparison exercises as a means to ensure consistency between clinical sites whilst enabling the sites to use their own choice of quantitative imaging protocols, specific to their systems. Dual-compartment concentric spherical sources of accurately known activity concentrations were prepared and sent to seven European clinical sites. The site staff were not aware of the true volumes or activity within the sources-they performed SPECT/CT imaging of the source, positioned within a water-filled phantom, using their own choice of parameters and reported their estimate of the activities within the source.

RESULTS

The volumes reported by the participants for the inner section of the source were all within 29% of the true value and within 60% of the true value for the outer section. The activities reported by the participants for the inner section of the source were all within 20% of the true value, whilst those reported for the outer section were up to 83% different to the true value.

CONCLUSIONS

A variety of calibration and segmentation methods were used by the participants for this exercise which demonstrated the variability of quantitative imaging across clinical sites. This paper presents a method to assess consistency between sites using different calibration and segmentation methods.

Abstract P1-14-06: Selective internal radiation therapy (SIRT) with Yttrium-90 resin microspheres and FOLFOX/5FU chemotherapy in pre-treated breast cancer patients with liver metastases: A retrospective analysis of response rates, times to progression and survival of patients treated in Manchester UK between 2010 and 2016

Background:

SIRT is a globally licensed technique of Radio-Embolization (RE) of hepatic tumors via intra-arterial infusion of β-particle emitting Yttrium-90 (Y-90) radio-labelled microspheres. It increases response rates and hepatic time to progression in metastatic colorectal cancer when used in combination with 5FU/Oxaliplatin (FOLFOX) chemotherapy with acceptable toxicity profile. FOLFOX gives a radio-sensitizing effect and also controls disease outside the liver. Breast cancer liver metastases (BCLM) patients often have extra-hepatic disease and respond to multiple lines of systemic therapy and SIRT is infrequently used.

Methods and patients

Between 2010 and 2016 we treated 25 BCLM patients with Y-90 SIRT.

Receptor status: 20 ER+ve/HER-2 -ve, 3 ER-ve/HER-2 +ve, 2 triple -ve.

Eleven patients had liver only disease with 14 also having known extra-hepatic disease. Average number of previous lines of therapy in metastatic setting: chemotherapy = 2.4; endocrine = 1. Sixty-four % patients had prior Capecitabine (n=16); 12% platinum (n=3, all Carboplatin). Twenty patients received chemotherapy with SIRT: 17 had modified FOLFOX6 (Oxaliplatin/bolus 5FU day1, infusional 5FU day 1-3 (46 hrs); 3 patients had Modified de Gramont style 5FU alone. Five patients had no chemotherapy.

Sir-spheres were inserted on day 2 of FOLFOX with the 5FU infusion pump continuing to day 3. Further 2-weekly FOLFOX chemo cycles were at clinician's discretion: average number delivered 3.8. Four patients had the liver treated in two halves, approximately 6 weeks apart. One patient received SIRT only to half the liver. Patients were imaged with PET-CT/CT before and 2-3 months after SIRT. Retrospective case note review was performed and data correlated to evaluate tumor response (RR); hepatic and extra hepatic progression free survival (HPFS and EHPFS) and overall survival (OS). Accurate toxicity data was not recorded.

Results

Hepatic CT response rates: PR 56% (n=14), SD 28% (n=7) and PD 16% (n=4). Hepatic PET response rates: CR 32% (n=8), PR 40% (n=10), SD 12% (n=3), PD 16%(n=4). (Overall PET liver disease control rate = 84%).

Eight patients (32%) had extra-hepatic PD at first assessment. Of them, 4 had PR, 2 SD and 2 PD in the liver at that assessment. Two HER-2 +ve patients had brain metastases as first sign of PD within 75 days, an area not previously screened. Of 16 pre-treated with Capecitabine, liver CT response rates: 62.5% PR, 18.75% SD (n=10,3). Post SIRT/FOLFOX, average number of therapy lines: 2 for chemo and 0.75 for endocrine, with 8 patients still alive at time of censoring.

Median OS: 766 HPFS: 210 days (CI 140-286). Median EHPFS in patients with extra-hepatic disease: 152 days (CI 96-636).

Conclusions

SIRT with FOLFOX in previously treated BCLM patients produces high response rates, excellent tumor control and time to progression in the liver with good overall survival. It does not seem to decrease the ability to give further lines of chemotherapy and can be considered as an option for breast cancer patients with liver metastases.

Citation Format: Wilson G, Mullamitha S, Bentley D, Bell J, Mullan D, Carter L, Chittalia A, Howell S, Laasch H-U, Westwood T, Jeans S, Tipping J, Ryder D, Farquharson F, Arumugam P, Sheen A, Rajashanker B, Armstrong A, Misra V, Manoharan P, Lawrance J. Selective internal radiation therapy (SIRT) with Yttrium-90 resin microspheres and FOLFOX/5FU chemotherapy in pre-treated breast cancer patients with liver metastases: A retrospective analysis of response rates, times to progression and survival of patients treated in Manchester UK between 2010 and 2016 [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-14-06.

Variations in the practice of molecular radiotherapy and implementation of dosimetry: results from a European survey

BACKGROUND

Currently, the implementation of dosimetry in molecular radiotherapy (MRT) is not well investigated, and in view of the Council Directive (2013/59/Euratom), there is a need to understand the current availability of dosimetry-based MRT in clinical practice and research studies. The aim of this study was to assess the current practice of MRT and dosimetry across European countries.

METHODS

An electronic questionnaire was distributed to European countries. This addressed 18 explicitly considered therapies, and for each therapy, a similar set of questions were included. Questions covered the number of patients and treatments during 2015, involvement of medical specialties and medical physicists, implementation of absorbed dose planning, post-therapy imaging and dosimetry, and the basis of therapy prescription.

RESULTS

Responses were obtained from 26 countries and 208 hospitals, administering in total 42,853 treatments. The most common therapies were 131I-NaI for benign thyroid diseases and thyroid ablation of adults. The involvement of a medical physicist (mean over all 18 therapies) was reported to be either minority or never by 32% of the responders. The percentage of responders that reported that dosimetry was included on an always/majority basis differed between the therapies and showed a median value of 36%. The highest percentages were obtained for 177Lu-PSMA therapy (100%), 90Y microspheres of glass (84%) and resin (82%), 131I-mIBG for neuroblastoma (59%), and 131I-NaI for benign thyroid diseases (54%). The majority of therapies were prescribed based on fixed-activity protocols. The highest number of absorbed-dose based prescriptions were reported for 90Y microsphere treatments in the liver (64% and 96% of responses for resin and glass, respectively), 131I-NaI treatment of benign thyroid diseases (38% of responses), and for 131I-mIBG treatment of neuroblastoma (18% of responses).

CONCLUSIONS

There is a wide variation in MRT practice across Europe and for different therapies, including the extent of medical-physicist involvement and the implementation of dosimetry-guided treatments.

Dosimetry-based treatment planning for molecular radiotherapy: a summary of the 2017 report from the Internal Dosimetry Task Force

BACKGROUND

The European directive on basic safety standards (Council directive 2013/59 Euratom) mandates dosimetry-based treatment planning for radiopharmaceutical therapies. The directive comes into operation February 2018, and the aim of a report produced by the Internal Dosimetry Task Force of the European Association of Nuclear Medicine is to address this aspect of the directive. A summary of the report is presented.

RESULTS

A brief review of five of the most common therapy procedures is included in the current text, focused on the potential to perform patient-specific dosimetry. In the full report, 11 different therapeutic procedures are included, allowing additional considerations of effectiveness, references to specific literature on quantitative imaging and dosimetry, and existing evidence for absorbed dose-effect correlations for each treatment. Individualized treatment planning with tracer diagnostics and verification of the absorbed doses delivered following therapy is found to be scientifically feasible for almost all procedures investigated, using quantitative imaging and/or external monitoring. Translation of this directive into clinical practice will have significant implications for resource requirements.

CONCLUSIONS

Molecular radiotherapy is undergoing a significant expansion, and the groundwork for dosimetry-based treatment planning is already in place. The mandated individualization is likely to improve the effectiveness of the treatments, although must be adequately resourced.

Organ-specific SPECT activity calibration using 3D printed phantoms for molecular radiotherapy dosimetry

Background

Patient-specific absorbed dose calculations for molecular radiotherapy require accurate activity quantification. This is commonly derived from Single-Photon Emission Computed Tomography (SPECT) imaging using a calibration factor relating detected counts to known activity in a phantom insert.

Methods

A series of phantom inserts, based on the mathematical models underlying many clinical dosimetry calculations, have been produced using 3D printing techniques. SPECT/CT data for the phantom inserts has been used to calculate new organ-specific calibration factors for ^99mTc and ¹⁷⁷Lu. The measured calibration factors are compared to predicted values from calculations using a Gaussian kernel.

Results

Measured SPECT calibration factors for 3D printed organs display a clear dependence on organ shape for ^99mTc and ¹⁷⁷Lu. The observed variation in calibration factor is reproduced using Gaussian kernel-based calculation over two orders of magnitude change in insert volume for ^99mTc and ¹⁷⁷Lu. These new organ-specific calibration factors show a 24, 11 and 8 % reduction in absorbed dose for the liver, spleen and kidneys, respectively.

Conclusions

Non-spherical calibration factors from 3D printed phantom inserts can significantly improve the accuracy of whole organ activity quantification for molecular radiotherapy, providing a crucial step towards individualised activity quantification and patient-specific dosimetry. 3D printed inserts are found to provide a cost effective and efficient way for clinical centres to access more realistic phantom data.

Short duration immunochemotherapy followed by radioimmunotherapy consolidation is effective and well tolerated in relapsed follicular lymphoma: 5-year results from a UK National Cancer Research Institute Lymphoma Group study

We report a phase II study to evaluate the efficacy and toxicity of abbreviated immunochemotherapy followed by (90) Y Ibritumomab tiuxetan ((90) Y-IT) in patients with recurrent follicular lymphoma. Of the 52 patients enrolled, 50 were treated with three cycles of R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisolone) or R-CVP (rituximab, cyclophosphamide, vincristine, prednisolone), followed by (90) Y-IT regimen (15 MBq/kg, maximum 1200 MBq) preceded by two infusions of 250 mg/m(2) rituximab. The overall response rate was 98% with complete response (CR) 30% and partial response (PR) 68%. 18 patients with a PR following chemotherapy improved to a CR following (90) Y-IT: a conversion rate of 40%. Seven patients with PR following (90) Y-IT subsequently improved to a CR 12-18 months later, leading to an overall CR rate of 44%. With a median follow-up of 5 years, median progression-free survival was 23·1 months and overall survival was 77·5% at 5 years. High trough serum rituximab levels (median 112 μg/ml; range 52-241) were attained after four doses of rituximab, prior to (90) Y-IT; this was not found to influence response rates. The treatment was well tolerated with few (13·5%) grade 3 or 4 infective episodes and manageable haematological toxicity. Abbreviated immunochemotherapy followed by (90) Y-IT is an effective and well-tolerated treatment in recurrent follicular lymphoma patients previously exposed to rituximab.

TRIAL REGISTRATION

clinicaltrials.gov identifier: NCT00637832.

Fractionated 90Y-Ibritumomab Tiuxetan Radioimmunotherapy As an Initial Therapy of Follicular Lymphoma: An International Phase II Study in Patients Requiring Treatment According to GELF/BNLI Criteria

Purpose

We report an international, multicenter phase II trial to evaluate the efficacy and toxicity of fractionated 90Y-ibritumomab tiuxetan (90Y-IT) as initial therapy of follicular lymphoma (FL).

Patients and Methods

A total of 74 patients, with a median age of 61 years (range, 28 to 80 years), were recruited requiring initial therapy by Groupe d'Etude des Lymphomes Folliculaires (GELF)/British National Lymphoma Investigation (BNLI) criteria. Among them, 78% had stage III-IV disease, 32% intermediate, and 44% high-risk (according to FL International Prognostic Index). Treatment consisted of two doses of 90Y-IT (11.1 MBq/kg) administered 8 to 12 weeks apart. Patients with more than 20% lymphoma infiltration of bone marrow (BM) received one infusion per week for 4 consecutive weeks of rituximab (375 mg/m2) and proceeded to fractionated radioimmunotherapy (RIT) only if a repeat BM biopsy demonstrated clearing of lymphoma to less than 20% involvement. The primary end point was end of treatment response of the intention-to-treat population. Secondary objectives were safety and progression-free survival (PFS).

Results

Initial overall response rate (ORR) was 94.4% (68 of 72 patients) with combined complete response (CR/CRu) of 58.3% (42 of 72 patients). Nine patients subsequently improved response making an ORR of 95.8% (69 of 72 patients) and CR/CRu of 69.4% (50 of 72 patients). At a median follow-up of 3.1 years (range, 0.2 to 5.2 years) estimated 3-year PFS is 58%, treatment-free survival 66%, and overall survival 95%. Median PFS is 40.2 months. Thirty patients have experienced disease progression and 24 have required further treatment. The treatment was well tolerated with few (2.8%) grade 3 or 4 infectious episodes or adverse events and manageable hematologic toxicity.

Conclusion

Fractionated RIT using 90Y-IT is an effective initial treatment for advanced-stage FL in patients with higher tumor burden requiring treatment.

Comparisons of dosimetric approaches for fractionated radioimmunotherapy of non-Hodgkin lymphoma

AIM

The aim of this study was to compare different dosimetric approaches on therapy naïve patients enrolled in a multicentre fractionated radioimmunotherapy trial, to determine which methodological approach correlates with bone marrow toxicity.

METHODS

Twenty-height non-Hodgkin lymphoma patients were treated with one or two fractions of 90Y-Ibritumomab-Tiuxetan (11.1 MBq/kg) 8 to 12 weeks apart in four different institutions. Quantitative imaging with 111In-Ibritumomab-Tiuxetan (185 MBq) was performed at 0, 1, 4 and 7 days after infusion, starting two weeks before the therapeutic administration. A whole-body (WB) CT scan was also acquired prior to the 111In-Ibritumomab injection, for attenuation correction purposes and was segmented to derive patient-specific organ masses. All dosimetry processing was centralized in a single institution. The first method (M_2D) was based on geometric mean WB scans, corrected for attenuation, scatter and organs superposition. The second method (M_2.5D) was based on the computed assisted matrix inversion approach and used segmented CT scans. The third method (M_3D) used iterative reconstruction of tomographic scans, corrected for attenuation, scatter and collimator response. Absorbed doses were estimated for lungs, liver, kidneys and spleen using MIRD S values adjusted for organ masses. Bone marrow (BM) absorbed doses were evaluated according to imaging methods (3) and compared to blood-based approaches.

RESULTS

For some patients, organ masses such as liver or spleen significantly differed from male/female reference masses, whereas lungs and kidneys masses were relatively constant. Except for lungs, absorbed doses estimated by M_2D were higher than those from M_2.5D and these, in turn, were higher that those calculated from M_3D (Wilcoxon P<8.6e-4). Median organ absorbed dose estimates were equivalent for both fractions except for the spleen. In fact, spleen absorbed doses for the second fraction were lower than those for the first fraction, regardless of the approach. Possible explanations are that patient spleen masses were kept constant for analysis of both fractions and/or that spleen uptake was lowered after the first fraction. Estimation of BM absorbed doses from blood sampling was unable to predict platelet toxicity, but image-based methods performed better. Additionally, for most organs, the absorbed dose delivered by the first fraction could predict that delivered by the second fraction.

CONCLUSION

These results confirm that different acquisition/processing protocols will lead to statistically different absorbed doses. Additionally, image-based dosimetric approaches are needed in order to correlate absorbed dose to bone marrow toxicity.

A retrospective analysis of selective internal radiation therapy (SIRT) with yttrium-90 microspheres in patients with unresectable hepatic malignancies

AIM

To evaluate the efficacy and safety of selective internal radiation therapy (SIRT).

MATERIALS AND METHODS

A retrospective analysis was undertaken of all patients who underwent SIRT at a single institution. Diagnostic and therapeutic angiograms, computed tomography (CT) images, positron-emission tomography (PET) images, and planar isotope images were analysed. The response to SIRT was analysed using radiological data and tumour markers. Overall survival, complications, and side effects of SIRT were also analysed.

RESULTS

The initial 12 patients were included on an intention-to-treat basis, between 21/09/2005 and 07/05/2008. All patients had advanced disease and multiple prior courses of chemotherapy. One patient did not receive yttrium-90 due to complex vascular anatomy; the remaining 11 patients underwent 13 SIRT treatment episodes following work-up angiography. A response was seen using PET in 80% of patients. Using CT, the response of the tumour to therapy in the treated hepatic segments demonstrated a 20% partial response, stable disease in 50%, and progressive disease in 30%. Estimated median survival was 229 days, with 64% of patients still alive at the time of writing. No major complications were observed, although 82% of patients experienced side-effects following SIRT, mainly nausea, vomiting, and abdominal pain.

CONCLUSIONS

There have been no complications in the 12 SIRT patients. Tumour response was seen in four out of five patients who underwent PET. Objective CT response rates were mixed and are perhaps partially explained by advanced disease and limitations of using measurements to assess response. This complex and potentially hazardous service has been successfully and safely established.

Breast disease and undergraduate medical education: a randomized trial to assess the effect of a home study module on medical student performance

BACKGROUND

This study sought to demonstrate the effectiveness of a home study module (HSM) on student performance at a large urban medical school.

METHOD

Second-year students were randomized to receive: 1) a HSM in addition to regular teaching of clinical breast examination or, 2) the regular teaching alone. The HSM included adult learning principles, problem-based learning, and practice guidelines. Students completed a pretest, a post-test, and course evaluation. The pre- and post-tests examined students' knowledge and comfort levels.

RESULTS

Of 176 students, 136 agreed to participate and 127 completed both pre- and post-tests. Baseline pretest indicated no significant difference between the intervention and control groups. Post-test showed that students receiving the HSM gained significantly more knowledge than had the control group, and their comfort levels shifted nonsignificantly more. Student evaluations indicated perceived value of the HSM.

INTERPRETATION

Student performance can be enhanced and comfort levels increased by providing a critical core of knowledge in the form of a HSM. This approach may be applicable to other important subjects.

Value of unstructured time (breaks) during formal continuing medical education events

BACKGROUND

Unstructured time (breaks) at formal continuing medical education (CME) events is nonaccredited in some jurisdictions. Program participants, however, perceive this time as valuable to their learning. The purpose of this research was to determine what activities occur during unstructured time in formal CME events and how these activities impact learning for physicians.

METHODS

A qualitative method based on grounded theory was used to determine themes of behavior. Both individual and focus group interviews were conducted. Data were analyzed and coded into themes, which were then further explored and validated by the use of a questionnaire survey.

RESULTS

One hundred ninety-seven family physicians were involved in the study. Several activities related to the enhancement of learning were identified and grouped into themes. There were few differences in the ranking of importance between the themes identified, nor were differences determined based on gender or type of CME in which the break occurred.

FINDINGS

The results suggest that unstructured time (breaks) should be included in formal CME events to help physician learners integrate new material, solve individual practice problems, and make new meaning out of their experience. The interaction between colleagues that occurs as a result of the provision of breaks is perceived as crucial in aiding the process of applying knowledge to practice.

Family physicians' knowledge of malignant melanoma

BACKGROUND

The incidence and mortality of melanoma have been increasing during the past two decades. Melanoma is relatively easy to detect and, when diagnosed early, is curable.

OBJECTIVE

Our purpose was to assess the baseline knowledge of malignant melanoma among family practitioners and to identify their preferred method of learning new information about the skin.

METHODS

The design was a randomized survey by mailed questionnaire.

RESULTS

More than 50% of physicians stated they lacked confidence in being able to recognize melanoma. Family physicians were well informed on factors affecting prognosis, but knowledge deficits were identified on history, physical examination, and risk factors. The most effective method of learning new information about the skin was hands-on teaching demonstration.

CONCLUSION

Many family physicians are not confident in their ability to recognize melanoma, and knowledge deficits were identified. In addition, some important risk factors were not well recognized. Thus, those at highest risk may not be receiving education on early detection that may help decrease the incidence and mortality of melanoma.

Using faculty and student perceptions of group dynamics to develop recommendations for PBL training

BACKGROUND

In training faculty as tutors for problem-based learning (PBL), certain aspects (domains) of teaching methodology are highlighted in the medical education literature. These are content, cognitive processing, and group dynamics. The authors contend that the amounts of attention given to these domains in faculty and student development have not been equal and that group dynamics needs further attention.

METHOD

In March 1993 the authors conducted a time-lapse study that involved 27 first-year students and three faculty in three PBL groups at the University of Toronto Faculty of Medicine. The purpose of the study was to determine faculty and student perceptions and knowledge of effective group dynamics, and to develop recommendations for student and faculty training. A qualitative approach was used that combined projective questions, post-tutorial questionnaires, and live and videotaped observations.

RESULTS

Observations and analysis of the data revealed a generally low awareness of effective group dynamics and the absence of a mechanism for reflection that could help groups analyze and learn from their behaviors. The results also revealed a discrepancy between self-reported behavior and observed behavior. For example, the students and faculty perceived their groups as generally "working well as a team," but observers noted that several aspects of group productivity (such as the articulation of goals and planning for future sessions) were not addressed.

CONCLUSION

The authors recommend that medical schools develop comprehensive training programs to teach group members to evaluate group performance and engage in open discussion of effective and ineffective behaviors.

Shifting students and faculty to a PBL curriculum: attitudes changed and lessons learned

BACKGROUND

The University of Toronto Faculty of Medicine is implementing a new undergraduate curriculum that emphasizes active, self-directed learning. The aims of this study were to (1) evaluate shifts in students' attitudes after initial direct experience with problem-based learning (PBL), (2) describe faculty experiences, and (3) develop guidelines for further implementation of PBL.

METHOD

Questionnaires were administered at the beginning of the first PBL session and at the close of the last session (five weeks later) to the 250 second-year students in 1992-93 and to their 15 faculty tutors. Quantitative data were analyzed using multivariate analysis of variance and univariate tests. Open-ended questions were categorized based on common patterns that emerged.

RESULTS

Of the 250 students, 196 (78%) responded to the pretest, and 207 (83%) responded to the posttest. There was a statistically significant shift in the students' perceptions from pretest to posttest in agreeing that PBL is more effective than traditional teaching methods (increasing from 38% to 52%). The students rated traditional methods as better for knowledge acquisition, whereas PBL methods were rated better for improving teamwork and doctor-patient relationships. At pretest, the most common themes concerned a perceived danger that PBL would result in knowledge gaps, reinforce the wrong information, and make inefficient use of valuable time. Perceived advantages of PBL included that it is more stimulating and enjoyable, and it teaches students how to learn rather than to memorize. At posttest, there was an increase in favorable comments by the students. Virtually all of the attitudes expressed by the students were shared by the faculty. In addition, at pretest the faculty were anxious about the perceived lack of structure in PBL.

CONCLUSION

Direct experience with PBL led to more favorable attitudes among the students and faculty. Recommendations are suggested for other schools and programs seeking to implement PBL curricula.