Operational and dosimetric aspects of pediatric PET/CT

Objectives Presently, there are no standardized guidelines for pediatric PET/CT imaging techniques with respect to integrating the PET and the CT examinations. Given that children are at increased risk of adverse outcomes related to both ionizing radiation and prolonged sedation, we were particularly interested in developing a standardized PET/CT protocol that allows for the highest quality imaging, in the shortest period of time and with the lowest patient radiation exposure. Our particular focus was the elimination of unnecessary duplicate CT scanning performed in patients undergoing both diagnostic and PET/CT examinations.

Methods This educational exhibit will present a series of examples highlighting the various approaches we have undertaken to integrate the PET/CT and diagnostic CT (Dx CT) examinations within the pediatric population, taking into consideration dose optimization and scanning efficiency. By comparing CT dose data from separately performed diagnostic and attenuation correction CT (CT/AC) exams with integrated multi-series PET/CTs, our goal is to initiate a broader discussion regarding a standardized approach for integrating both diagnostic CT and PET/CT protocols into a single examination, with the goal of optimizing both image quality radiation dose, and examination time.

Results We will present the methodology we have developed at Boston Children’s Hospital for conducting PET/CT examinations, comparing patient cases before and after a recent shift in our protocol in an effort to optimize dose and improve efficiency. Prior to October 13, 2015 we acquired these multi-modality imaging sets by performing an initial whole body low-dose CT/AC exam, followed by a standard-dose diagnostic CT, as indicated, with the Dx CT limited to the area of clinical concern. We hypothesized that we could significantly reduce the patient radiation exposure, as estimated by dose length product (DLP), by instituting a multi-series CT protocol, such that a single multi-series CT exam would provide both a low-dose CT/AC in those areas not requiring a diagnostic quality CT and standard-dose Dx CT in the area of concern. These sequential CT series are then merged into a single data set, used for attenuation correction of the PET data and anatomical correlation. For example, if a diagnostic quality CT of the chest/abdomen/pelvis is required, together with a whole body PET, a single multi-series CT examination is acquired as follows: low dose CT/AC of the head/neck, followed by Dx CT of the chest/abdomen/pelvis, ending with a low-dose CT/AC of the lower extremities. Several representative examples will be presented demonstrating that merging the Dx CT and CT/AC into a single multi-series exam can yield a substantial reduction in DLP. Strategies will also be presented for overcoming challenges such as optimizing delivery of IV contrast, beam hardening, evaluation of lung nodules, and PACS system integration, as well as the challenges and opportunities that arise from integrating clinical and technologist workflows. Absorbed radiation dose will be compared in examples of size-matched patients before and after implementation of the multi-series CT protocol.

Conclusions In summary, this exhibit introduces a dose-optimized PET/CT protocol, with the goal of standardizing PET/CT imaging techniques in children, ultimately reducing unnecessary radiation exposure, decreasing the imaging time and minimizing the need for sedation and anesthesia. RESEARCH SUPPORT: This work was supported by Siemens Medical Solutions.