Pediatric Orbital Depth and Growth: A Radiographic Analysis.

BACKGROUND: Orbital reconstruction requires knowledge of orbital depth in order to prevent optic nerve injury. Numerous analyses of adult orbital dimensions have been undertaken previously in order to characterize this measurement, including skull specimen and computerized tomography studies. However, there is a paucity of information regarding the pediatric orbit. METHODS: The authors used pediatric magnetic resonance imaging (MRI) studies in order to quantify the change in orbital depth in relationship to patient age, and to develop methods to estimate and calculate orbital depth for individual pediatric patients. MRIs of the head in normal pediatric patients were reviewed retrospectively. Orbital depths were measured and correlated with age and cephalometric dimensions. In a randomly selected subgroup of patients, measurements were repeated by an independent investigator to determine interobserver reliability. RESULTS: Measurements were obtained in 72 patients ranging from 3 months to 18 years of age (mean=7.8 years). There was a significant exponential relationship between orbital depth and patient age (r=0.81, F(2,69)=143.97, P<0.001). Depth increased more rapidly in the first 6 years of life, but leveled off in the early teen years toward a horizontal asymptote of approximately 45 mm. There was also a significant relationship between orbital depth and the sum of the biparietal width plus the anterior-posterior length (r=0.72, F(2,69)=87.44, P<0.0001). There was high interobserver reliability in measurements between 2 independent investigators (r=0.79, P<0.0001). CONCLUSION: In children, orbital depth increases predictably with rising age and increasing head size. Knowledge of this growth curve and the relationship between head size and orbital depth can complement careful surgical dissection to improve safety and efficacy in pediatric orbital reconstructions.

Breast boost using noninvasive image-guided breast brachytherapy vs. external beam: a 2:1 matched-pair analysis.

BACKGROUND: To compare clinical outcomes and toxicity in patients treated with NIBB boost with those in patients treated with external beam (EB) boost. PATIENTS AND METHODS: Women with early stage breast cancer treated with WBI and NIBB boost were identified. Control subjects treated with EB boost identified as the best possible match with respect to age, stage, chemotherapy use, and fractionation were chosen for a 2:1 comparison. Acute toxicity, late toxicity, and oncologic outcomes were reviewed. The McNemar nonparametric test was used to evaluate marginal homogeneity between matched pairs. RESULTS: One hundred forty-one patients were included in the analysis: 47 patients treated with NIBB boost and 94 matched control subjects treated with EB boost (electron, n = 93) or 3-D conformal radiation (n = 1). Grade 2+ desquamation developed in 18 patients (39%) treated with NIBB boost and in 49 patients (52%) treated with EB boost (P = .07). Breast size, electron energy, and fractionation predicted for acute desquamation (P < .0001, P < .001, and P = .006). Median follow-up was 13.6 months. One patient (2%) who received NIBB had Grade 2+ skin/subcutaneous fibrosis 15 months after completion of treatment. Among those treated with EB, 9 patients (9.5%) developed Grade 2+ subcutaneous fibrosis, and 1 patient had recurrent cellulitis. There was statistically significantly less combined skin/subcutaneous toxicity in those treated with NIBB than in those treated with EB (P = .046). CONCLUSION: NIBB boost is associated with favorable short-term clinical outcomes compared with EB.

Do angles of obliquity apply to 30 degrees scattered radiation from megavoltage beams?

The angle of obliquity is used in radiation shielding calculations to account for the longer path length x rays will see when obliquely incident on the protective barrier. According to the National Council on Radiation Protection and Measurements (NCRP), use of the angle of obliquity is explicitly assumed for primary radiation, so that an angle of obliquity for secondary radiation is never addressed. However, in the example section of the latest report, it specifically recommends against using an angle of obliquity for scattered radiation. To check this assumption, the existence or not of an angle of obliquity for scattered radiation has been investigated for bremsstrahlung x-ray beams of 4, 6, 10, 15, and 18 MV and for barriers consisting of concrete, lead, and steel using a Monte Carlo approach. The MCNP Monte Carlo code, v4.2C, has been used to generate scattered radiation at 30 degrees from a water phantom and incident on a secondary barrier at the same angle relative to the normal to the barrier. The barrier thickness was increased from zero to a thickness sufficient to reduce the fluence (f4 tally) to <10(-3). A transmission curve was created for each energy-barrier material combination by normalizing to zero thickness. The results for the first tenth-value layer (TVL) in concrete (5 energies) show an average angle of obliquity of 21.7 degrees +/- 5.6 degrees , and for the first two TVLs averaged 29.7 degrees +/- 3.9 degrees . The results for the first TVL in lead (3 energies) show an average angle of obliquity of 27.7 degrees +/- 4.0 degrees , and for the first two TVLs averaged 20.5 degrees +/- 5.8 degrees . There are no data in the NCRP reports for 30 degrees scattered radiation attenuated by steel with which to make a comparison.