Employ of a new device for intra-operative radiotherapy of intracranial tumours

Background. This paper presents the operating experience acquired during 18 months of use of the Photon Radiosurgery System manufactured by Photo-electron Corp. as an intra-operative radiation therapy device. The device is based on a miniature x-ray source that delivers low energy x-rays from the tip of a 3.2 nun thick needlelike probe. The interstitial stereotactic employ of the source has already been reported, while there is no evidence of the open-field intra-operative use in the literature. Method. Open field intra-operative radiation therapy (IORT) is possible inserting the probe into spherical applicators with diameters ranging from 1.5 to 5 cm. The applicators are made to fit the surgical cavity in order to provide uniform distance between the x-ray source and the tumour bed, Delivery of the prescribed dose takes typically 10 to 45 minutes. Radiation characteristics of the source were measured by means of ionization chambers and radiochromic films positioned in a water phantom. Operating procedures aimed at quality assurance and radiation safety were developed. IORT was administered to 14 patients affected by malignant intracranial tumours. Doses from 10 to 15 Gy at 5 mm depth from the tumour bed were delivered after tumour removal. Findings. This preliminary experience does not afford any clinical evidence of IORT efficacy for intracranial lesions; it permits one however to state the feasibility and safety of the procedure. Interpretation, This system could favour a rapid and significant increase of the experience of intra-operative irradiation in the treatment of CNS tumours. A role in the treatment of extracranial neoplasms can be also foreseen but needs to be more extensively investigated.