An analysis of dose reduction and the level of image quality attained by iDOSE

Radiotherapy services in Ireland have undergone extensive changes in terms of number and complexity of equipment installed in both public and private institutes in recent years. The latest addition to the ever growing number of sophisticated equipment was the unveiling of the CyberKnife facility at the Hermitage Medical Clinic. Due to planning restrictions the new facility had to be contained in the existing hospital’s blueprint with the only available location being an unused CT simulation room. The room design would be different from conventional radiotherapy bunkers due to the fact that the CyberKnife can fire an unfiltered beam in any direction except the roof (restriction of 220 above the horizontal). Therefore all walls must be primary barriers with the roof designed to protect against the large leakage radiation resulting from the high MUs used during the treatments. Space consideration indicated that concrete alone could not be used to restrict the radiation beam to acceptable limits. To this end a combination of steel, lead, normal and heavy concrete were used to meet the dose constraints established by the Irish licensing authorities. Novel designs to protect against ground shine and from primary and leakage radiation emerging under the direct shielding door had to be developed. Also many of the difficulties encountered during the design and conversion of the CT simulation room will be addressed.