ABSTRACT
In order to assign appropriate planning target volume [PTV] margins, each centre should measure the patient positioning deviations for their set-up techniques. At the Royal Marsden Hospital, UK, a conformal shell [cast] system is used when a stereotactic frame is not suitable. In this paper, we report on a series of measurements with the aim of obtaining the systematic and random components of positioning error when using the above-mentioned shell system. The verification protocol was based on orthogonal pairs of anterior-posterior and lateral electronic portal images [EPIs] used to check the isocentre position. The isocentre verification results of paediatric patients were analysed. A practical [off-line] patient set-up correction strategy had been used with the aim of reducing systematic errors. The verification protocol involved EPI acquisition on the first three fractions and then on a weekly basis. Additional images were taken if an isocentre movement was applied based on a 3 mm tolerance for a consistent 1D discrepancy. Four patients required isocentre corrections ranging between 2 mm and 4 mm. Following the offline corrections, the residual systematic errors in each direction were within 0.5 mm while the 1D random variation was about 1.0 mm. The head fixation system in conjunction with the correction strategy successfully kept the random and systematic positioning errors within an acceptable level well within the 3 mm tolerance. The measured components of positioning error can be used to define appropriate PTV margins
ABSTRACT
A method is described for surface mapping of the S - T segment elevation seen in myocardial infracts which eliminates the drawbacks of methods in current use. The latter include the lack of satisfactory contact between electrode and chest wall, the- difficulty in reproducing initial points of contact at follow up studies, and the time consuming nature of these elaborate techniques. The method described was clinically applied in the evaluation of normal S - T segment elevation in normal subjects to establish whether there was any degree of variability in recordings obtained four times a day. The technique was then used to record the S- T segment behaviour, when this was elevated in patients with anterior myocardial infarcts, to determine whether this could be correlated with the evolution of the clinical picture. The new method is shown to be useful in close monitoring of such patients and may show a value in determining prognosis