RESUMO
PURPOSE: The goal of this work was to evaluate measured vs. calculated surface dose as a function of PTV-to-skin proximity and calculation matrix oxel size, determine effects on plan quality, and provide parameters and levels of uncertainty for clinical use. METHODS: A right-sided CTV with the lateral border 5mm from the surface was delineated on the CT data of a head and neck phantom. A 5mm PTV was generated except laterally where distances of 0-5mm were used. A 7-field IMRT plan was generated using the Eclipse TPS. Optimization was performed where 95% of the PTV receives the prescription dose using a matrix size of 2mm3 . Dose calculations were repeated for grid sizes of 1, 3 and 5mm3 . For each plan nine point dose values were obtained just inside the phantom surface, corresponding to a 2cm2 grid near the central target region. Nine ultra-thin TLDs were placed on the phantom surface corresponding to the grid. Measured and calculated dose values were compared. Conformality, homogeneity and target coverage were compared. RESULTS: Surface dose is over-estimated by the TPS by 21 and 8% for 5 and 3mm3 voxels, respectively and accurately predicted for 2mm3 voxels. A voxel size of 1mm3 results in underestimation of 13%. Conformality improves with increasing PTV to skin distance and a CI of unity results for grid sizes of 1-3mm3 between 4 and 4.5mm. Hot spot decreases as the PTV moves away from the surface and falls below 110% at 4mm. Underdosage worsens as the PTV approaches the skin. CONCLUSIONS: For decreasing PTV-to-skin distance with this TPS, isodose conformality decreases, 'hot spot' increases, and target coverage degrades. Surface dose is accurately predicted for a 2mm3 voxel size, while choosing a finer or coarser grid results in underestimation or overestimation, respectively. All of the above appear to hold for VMAT.
RESUMO
A prospective longitudinal study assessed the effects of intraventricular hemorrhage (IVH) and socioeconomic status on the perceptual, cognitive, and neurologic status of preterm infants at 5 years of age. The preterm group consisted of infants with no IVH, grade I to II IVH, and grade III to IV IVH; a control group of normal term infants was also studied. Outcome was evaluated at 3, 4, and 5 years of age. Twenty-four percent of infants with grade III to IV IVH had abnormal neurologic diagnoses at 5 years of age. Correlations of predictor variables including IVH status, latency of visual evoked response, days of hospitalization, and socioeconomic status with 5-year neurologic outcome indicated that IVH status and visual evoked response at 1, 2, and 3 years continued to have an effect on neurologic outcome, but socioeconomic status and days of hospitalization did not; socioeconomic status did have a significant effect on the McCarthy cognitive scores but not on the perceptual scores at 5 years. Multiple regression analyses revealed that duration of hospitalization (reflecting neonatal morbidity), visual evoked response, and socioeconomic status all have independent effects on the cognitive index, whereas only duration of hospitalization has an independent effect on the perceptual index. These data support the concept that a complex interaction of biologic and environmental risk factors determines the degree of recovery from IVH by high-risk preterm infants.