Novel Assessment of Renal Motion in Children as Measured via Four-Dimensional Computed Tomography

Abstract

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.

Methods for image guided and intensity modulated radiation therapy in high-risk abdominal neuroblastoma

“…Multiple respiratory traces were obtained and reconstructed through 8 respiratory phases. These 8 phases were exported to the Siemens multi-modality workstation for evaluation by InSpace software [4]. …”

“…For the actual treatment plan (IMRT_phys), we used an ITV surrounding the CTV and accounting for physiologic organ motion of 1 mm radially and inferiorly and 4 mm superiorly. Although no class solution works for all cases, a near-class solution was found suitable for each of these 8 cases on the basis of individual review of 4DCT data and estimation of renal motion in these uniformly young children [4]. In each patient, the adjacent renal organs served as surrogates to estimate the tumor bed/target motion due to the retroperitoneal/adrenal primary location of each tumor bed.…”

“…In this study, we describe the implementation of IGRT-based IMRT in the pediatric abdomen; this process accounts for physiologic motion and setup error and is based on established prospective work at our institution [3, 4]. Additionally, ICRU 62–compliant IMRT volumes were compared to conventional target volumes and used to quantify the reduction in the dose delivered to various normal tissues.…”

A Review of Kidney Motion under Free, Deep and Forced-Shallow Breathing Conditions: Implications for Stereotactic Ablative Body Radiotherapy Treatment

“…Pai Panandiker et al (42) analyzed kidney motion data for children undergoing anesthesia (2-8 years of age) and showed that kidney motion for this age group was less than 2 mm for both the right and left kidneys. The older age group (9-18 years of age), not under general anesthesia, showed mean motion of 3.9 and 3.07 mm for the right and left kidneys respectively.…”

Motion Correction Options in PET/MRI

“…Only the abdominal motion of the diaphragm was moderately correlated with that of the kidney (23). However, even this potential surrogate was demonstrated to be unreliable in predicting the kidney position in pediatric patients (24). Interestingly, the same study demonstrated that the amount of motion in the cranio-caudal direction increases with age, while the motion in the lateral direction increases with height.…”