Purpose Abdominal intensity-modulated radiation therapy and proton therapy require quantification of target and organ motion to optimize localization and treatment. Although addressed in adults, there is no available literature on this issue in pediatric patients. We assessed physiologic renal motion in pediatric patients. Methods and Materials Twenty free-breathing pediatric patients at a median age of 8 years (range, 2-18 years) with intra-abdominal tumors underwent computed tomography (CT) simulation and 4-dimensional CT (4DCT) acquisition (slice thickness, 3 mm). Kidneys and diaphragms were contoured during 8 phases of respiration to estimate center of mass motion. We quantified center of kidney mass mobility vectors in 3 dimensions: anterior-posterior (A-P), medial-lateral (M-L), and superior-inferior (S-I). Results Kidney motion decreases linearly with decreasing age and height. The 95% confidence interval for the averaged minima and maxima of renal motion in children younger than 9 years was 5 to 9 mm in the M-L direction, 4 to 11 mm in the A-P direction, and 12 to 25 mm in the S-I dimension for both kidneys. In children older than 9 years, the same confidence interval reveals a widening range of motion that was 5 to 16 mm in the M-L direction, 6 to 17 mm in the A-P direction, and 21 to 52 mm in the S-I direction. Although not statistically significant, renal motion correlated with diaphragm motion in older patients. The correlation between diaphragm motion and BMI was borderline (r = 0.52, p = 0.0816) in younger patients. Conclusions Renal motion is age and height dependent. Measuring diaphragmatic motion alone does not reliably quantify pediatric renal motion. Renal motion in young children ranges from 5 to 25 mm in orientation-specific directions. The vectors of motion range from 5 to 52 mm in older children. These preliminary data represent novel analyses of pediatric intra-abdominal organ motion.

Purpose While evaluations of FDG PET-CT in adult patients with NPC have documented advantages and disadvantages of the technique compared with conventional imaging, to our knowledge, no such studies have been performed with pediatric patients. In this investigation, we studied the utility of FDG PET-CT in children with NPC. Methods Eighteen children with biopsy-proven NPC who underwent FDG PET-CT and MRI were studied (total 38 pairs of imagings). All baseline and follow-up FDG PET-CT and MRI studies were independently reviewed for restaging of disease. Results The concordance between FDG PET-CT and MRI in T, N, and overall staging was 29%, 64%, and 43%, respectively. Compared with MRI, FDG PET-CT yielded lower T and overall staging and showed less cervical and retropharyngeal lymphadenopathy. The concordance between follow-up FDG PET-CT and MRI was 79% overall and 100% 9 months after therapy. In patients who achieved complete remission, FDG PET-CT showed disease clearance 3-6 months earlier than MRI. There were no false positive or false negative FDG PET-CT scans during follow-up. Conclusions FDG PET-CT may underestimate tumor extent and regional lymphadenopathy compared with MRI at the time of diagnosis, but it helps to detect metastasis and clarify ambiguous findings. FDG PET-CT is sensitive and specific for follow-up and enables earlier determination of disease remission. FDG PET-CT is a valuable imaging modality for the evaluation of and monitoring NPC in pediatric patients.

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