Abstract
4110
Introduction: Dosimetry for treatment planning and verification of radiopharmaceutical therapies (RPT) can help enable personalized cancer treatments. However, performing patient-specific dosimetry can be challenging due to its time-consuming process especially in departments with limited resources or over-extended workloads. Historically, the different steps of the dosimetry workflow have been performed mostly by the medical physicists. Segmentation (the most time-consuming part of the workflow) usually involves the medical physicists and nuclear medicine (NM) physicians. The aim of this work was to explore a role for the nuclear medicine technologists (NMT) in the dosimetry process to facilitate routine implementation of dosimetry for RPT.
Methods: To ensure that quantitative images are accurate, it is important for the NMTs to learn and gain experience with equipment calibration for dosimetry. For this, NMTs have been shadowing the medical physicists when performing equipment calibration (dose calibrator, gamma counter, SPECT/CT scanners) at our institution. Moreover, the NMTs have assisted in preparing sources for those calibration procedures. It's essential that NMTs understand the effect of patient positioning and scanned field of view on dosimetry calculations, in particular for multi-timepoint imaging. In addition, NMTs will complete case report forms and send image datasets to a central database. When patient blood samples are required (e.g. for bone marrow dosimetry), the NMTs will collect the samples at pre-defined time points and assay them on a calibrated gamma counter for analysis by the medical physicists.
The NMTs have received training by NM physicians to identify organs and tumors to participate in the segmentation step of the dosimetry workflow. To simplify this process, physicists have built workflows in MIM (MIM Software, USA) that automatically load, register and display the diagnostic (i.e. PET/CT, MRI, CT) and therapy SPECT/CT images. The NMTs performs segmentation using semi-automatic algorithms and thresholding values recommended by the physicists that generate volumes of interests (VOIs) for healthy organs (e.g. kidneys, salivary glands, spleen, liver, whole body, vertebrae) and tumours. Once the segmentation is complete and stored in the patient database, NM physicians reviews and adjusts VOIs as required for accuracy and completeness. The medical physicists then create the time-activity curves, perform fitting to determine the time-integrated activity, and complete the dosimetry calculations. Results could potentially be used to modify and personalize subsequent cycle injections. The suggested workflow has been tested with the image datasets available from the 177Lu SNMMI dosimetry challenge.
Results: Shadowing the medical physicist in calibration procedures has made the NMTs more aware about the importance of using the correct dose calibrator number when assaying the radiopharmaceutical. Further, the importance of accurate, quantitative post-therapy imaging has been underlined. The centralized database, including the blood sampling and gamma counter assay, will ensure that all the required information for dosimetry calculations (including injected activity and time of injection) is easily accessible. The image processing workflow and training received from the NM physicians allowed NMTs to accurately delineate organs and tumors with few corrections required.
Conclusions: Education and appropriate training have been key to integrate our NMTs in the dosimetry workflow. NMTs have become aware of the importance of calibration and quantitative imaging and are now capable of detecting issues early in the process. NMTs can play an important role in optimizing resources and accuracy for future implementation of routine dose assessments for RPT in the clinical environment.