Feasibility of using interpolated contours of targets and organs at risk in intensity‐modulated radiation therapy treatment planning for advanced‐stage nasopharyngeal carcinoma

To assess the dosimetric effect of using interpolated contours in planning intensity‐modulated radiation therapy (IMRT) for advanced T‐stage nasopharyngeal carcinoma. The present study focused on T3–T4 tumours where the proximity of targets to neurological organs poses a stringent test on the feasibility of such an approach. Contours of targets and organs were delineated on CT images of 2.5‐mm interval and a reference IMRT plan was generated. An investigative (INV) IMRT plan was then generated with the same planning protocol, but based on interpolated contours that replaced deleted contours on alternate slices. The reference and INV plans were compared. Regarding target coverage, all targets in the INV plans met the acceptance criteria except for the PTV in one case. Regarding organs, the mean dose to 1% volume of the brainstem and spinal cord in the INV plans were kept below their dose limits. No significant differences in the mean doses to others organs were found. Satisfactory target coverage and protection of critical organs to a degree similar to full‐scale contouring could be achieved with use of interpolated contours. The saving in manpower time for contouring is expected to significantly improve the throughput of the IMRT planning process.     

Lung function abnormalities at 6 months of age after neonatal intensive care.

Respiratory function was studied in 46 preterm infants (median gestational age 28 weeks) at 6 months of age. Respiratory function was assessed by measurement of thoracic gas volume, airways resistance (from which specific conductance was calculated), and functional residual capacity. To determine the effect of the duration of neonatal intermittent positive pressure ventilation (IPPV) on respiratory function, the infants'' results were divided into three groups: group A, no IPPV; group B, IPPV for less than seven days; and group C, IPPV for more than seven days. Measurements of thoracic gas volume and functional residual capacity were similar to published reference ranges and there were no significant differences between the three groups. Measurements of airways resistance and specific conductance were higher than published reference ranges (mean airways resistance of group A, 34 cm H2O/l/sec; B, 34.1 cm H2O/l/sec, and C, 30.4 cm H2O/l/sec) but there was no significant difference between the three groups. The 95% confidence intervals of the difference of the means between groups A and B were -6.94 to 6.73 cm H2O/l/sec and between groups A and C -3.8 to 11.0 cm H2O/l/sec. Our results suggest that factors other than neonatal ventilation may be more important in the pathogenesis of chronic lung function abnormalities in preterm infants.     

Randomised controlled trial of two methods of weaning from high frequency positive pressure ventilation.

Forty preterm infants suffering from respiratory distress syndrome were entered into a randomised controlled trial to assess the importance of the length of inspiratory time during weaning from high frequency positive pressure ventilation (HFPPV). Two weaning regimes were compared: in one (group A) inspiratory time was limited to 0.5 seconds throughout weaning, in the other (group B) ventilator rate was reduced by increasing both inspiratory and expiratory time (inspiration:expiration ratio constant) until inspiratory time reached 1.0 seconds. At ventilator rates of 20 and 40 breaths/minute an acute comparison was made in all 40 infants of the two inspiratory times; despite the lower mean airway pressure associated with the shorter inspiratory time blood gases were maintained. There was no difference in the incidence of pneumothoraces or need for reventilation between the two regimens but infants in group A had a shorter duration of weaning. We conclude limitation of inspiratory time to 0.5 seconds during weaning from HFPPV is advantageous to preterm infants with respiratory distress syndrome.     

Acute deteriorations in neonatal chronic lung disease

Preterm infants with chronic lung disease (CLD) have frequent respiratory relapses. The aim of this study was to assess the aetiology of such deteriorations and in particular the proportion due to viral infections. During the study period 118 preterm infants with birth weight <1500g were consecutively admitted to the neonatal intensive care unit; 22 (18.6%) developed CLD. At the onset of all respiratory deteriorations, infants were examined for the presence of patent ductus arteriosus, apnoea or aspiration; they were also carefully screened for both viral and bacterial infection. The 22 infants had a total of 74 episodes of respiratory deterioration; median 3 per baby (range 1–8). Two episodes were associated with patent ductus arteriosus, 18 with apnoea and 5 with aspiration. Infection was suspected or proven in association with all other episodes. On ten occasions the infants had positive blood cultures and on a further eight, bacteria were isolated only from the endotracheal or nasopharyngeal secretions. On the remaining 31 occasions, 27 associated with chest X-ray film abnormalities, infection was suspected, but no bacteria isolated. Viral infections were identified in association with 8 (11%) of these episodes. We conclude viral infection should be considered as a cause of otherwise unexplained respiratory deteriorations in infants with neonatal CLD.     

Longitudinal assessment of infant lung function following pregnancies complicated by prolonged and preterm rupture of the membranes

Serial measurements of functional residual capacity (FRC) were made in 22 infants (median gestational age at delivery 32 weeks, range 25–40) during the first 2 years of life. All infants had been delivered from pregnancies complicated by prolonged and preterm rupture of the membranes (PPROM) of at least 1 week in duration. The onset of membrane rupture was at a median of 26 weeks (range 15–32) with a median duration of 5.5 weeks (range 1–21). The mean FRC at all postnatal ages studied: 25 ml/kg at 6 and 12 months and 24ml/kg at 18 and 24 months did not differ significantly from the control population (mean 24ml/kg). There was, however, a wider scatter of results in the study population: four infants born very preterm consistently had FRC results above the 95% confidence limits of the controls but only two infants had FRCs consistently below this range. These results suggest PPROM may not be an invariable association of abnormal antenatal lung growth.     

Synchronous intermittent mandatory ventilation modes compared with patient triggered ventilation during weaning.

The efficacy of combining rate and pressure reduction during weaning by synchronous intermittent mandatory ventilation (SIMV) were compared with weaning by patient triggered ventilation (PTV) (pressure reduction alone) in two randomised trials. Regardless of ventilation mode, pressure was reduced to the same level according to the size of the infant. In the first trial, the SIMV rate was also reduced progressively to a minimum of 20 breaths/minute, and in the second to five breaths/minute. Forty premature infants aged 15 days of age or less were randomly allocated into each trial. No significant differences were found in the first trial between ventilation modes in either the duration of weaning or the number of infants in whom weaning failed. In the second trial, the duration of weaning was shorter by PTV than by SIMV (median 24 hours, range 7-432 v 50 hours, range 12-500; p < 0.05); weaning failed in two infants in the PTV group and in five in the SIMV group. It is concluded that weaning by a combination of pressure and rate reduction, such as can be achieved during SIMV, offers no significant advantage over pressure reduction alone.     

Patient triggered ventilation in premature neonates.

Patient triggered ventilation using oesophageal pressure changes was assessed in eight premature neonates. Respiratory activity was reliably recorded and positive pressure inflation occurred synchronously with inspiration. Peristalsis resulted in only minimal interference. During patient triggered ventilation, inflating volume and oxygenation increased significantly compared with periods of conventional ventilation.     

Immediate effects of albumin infusion in ill premature neonates.

Ten normotensive premature infants with idiopathic respiratory distress syndrome, and albumin concentrations of less than 30 g/l were given 5 ml/kg of 20% salt poor albumin by infusion. Concentrations measured six hours after infusion had increased significantly and these were associated with significant reduction in weight and improvement in urine output.