Small Linear Accelerators (LINAC) for IORT:
Intra Operative Radiation Therapy (IORT) is a technique based on the delivery of a high dose of ionizing radiation directly to the tumor location, and immediately after tumor ablation, as part of the surgical operation. The radiation is directed locally to the tumor site while reducing the exposure of other surrounding healthy tissue. IORT can be used as the unique radiotherapy treatment or being associated with later radiotherapy sessions using external beams. A single application (single dose) of radiation therapy using IORT with electrons has been shown to give many advantages both for the patient and for the facility, for the following reasons: a) The higher irradiation precision excludes the surrounding tissues from the radiation beam, thus reducing the damage of the healthy tissues; b) The overall exposure to radiation is reduced with consequent elimination of the 5-6 weeks of external radiation therapy, thus eliminating the waiting time and reducing the long waiting lists; c) The effect of a single high dose has a higher radiobiological efficiency compared to the same dose fractionated in the conventional way. Finally, the application of direct irradiation, the visual precision obtained and the limiting of the effective operational site performed during the surgical treatment enables an increasing local control of the disease. IORT can be performed with the common linac, generally used for conventional radiotherapy, by means of special adapters, but this procedure requires the transport of the patient from the operating theatre to the radiation bunker where the treatment is performed, with a consequent decrease of total operating time and risk of virus infection (this is the traditional way in which the therapy has been done). In the last few years, the availability of small, mobile electron linear accelerators (with energies ranging between 3 and 12 MeV), have allowed the installation of sterile radiation systems directly in operating theatres, with a consequent simplification of the required procedures. The modern linear accelerators designed for IORT treatment are conceived to be directly used in an operating theatre. The accelerator is mounted on a mobile arm which supports the handling and control of the radiating head. Beam collimation is performed with different diameter Perspex cylindrical collimators. Three commercial models of IORT are currently available in the world and one of them, NOVAC 7, has been developed in collaboration between ENEA and HITESYS (today called NRT, New Radiant Technology, www.newrt.com). The NOVAC 7 system, has been commercially available since 1997, and has an auto-focusing radiating structure, magnetic lens free system and an applicators geometry which does not require dispersion filters. Both these characteristics allow the use of the NOVAC 7 directly in the operating room without changing its structure and without the necessity of particular shielding. IORT: Clinical experiences The major objective of IORT is to increase the therapeutic index between the local control of the tumor and the tolerance of the surrounding healthy tissues, by means of a better definition of the target volume and the dislocation or shielding of the organs at risk, during the surgical treatment. This technique is used for the treatment of several diseases: stomach, pancreas, rectal and gynecological tumors, soft tissue sarcoma and, most recently, also for the conservative therapy of breast cancer. The increasing number of Italian centers making use of IORT has promoted an interest in the definition of a policy for the programs of Guaranteed Quality, in order to facilitate the use of such a 'special' technique, according to the best premises of inter-comparison and verification of results. The definition of such a policy has been coordinated by the Istituto Superiore della Sanità (ISS) and collected in a document ISTISAN (Istisan 03/10). In parallel, the requirements for the definition of clinical use of IORT have been defined, in order to prescribe it, according to the rules based on evidence (Evidence Based Medicine, EBM). The complexity of all diseases for which the use of IORT requires confirmation through medical studies, has been also defined. The AIRO approved on 3/12/2004 the consent from the centers, for the use of IORT for the following diseases: • Locally advanced neoplasias of rectal |
