An Investigation into the Variability of Breast Tangent Setups Using the Portal Imaging Process

This study set out to examine the imaging schedule for a specific group of patients, that is, those receiving the two-field tangent technique for breast cancer treatment at our centre. This group makes up a large percentage of our workload. The departmental policy on imaging for breast tangent patients at the time the study was conducted stated that one image be taken on either the medial or lateral tangent field on the first day of treatment. The majority of images were taken pre-treatment (the current policy has been updated to specify pre-treatment images) and if a setup discrepancy was noted adjustments were made and another image taken. The study consisted of eighteen patients who attended the centre for treatment and who were prescribed a tangent technique. Eligible patients were identified from the appointment scheduling system. Consent to participate was given at the time of the patients planning appointment. The study was reviewed by the Research Ethics Board at our affiliated hospital and was supported by the breast site group at the centre. There was no exclusion criterion. 133 images were taken during the course of this study. The lung volume was measured at three specific points with the measuring tools available from the software programme. The results demonstrated that for the majority of patients (94%) the setup variability does not warrant a change to the current imaging protocol. Data from one patient (6%), however, suggested that for some patients there may be a need for a more comprehensive imaging schedule. The variability of setup for these patients was unpredictable. This group of patients would require further investigation and discussion within the site group at our centre.