The use of plane parallel ionization chambers with electron beams with high dose per pulse entails dose uncertainties due to the overestimation of the ion recombination factor, k, up to 20% if conventional dosimetric protocols are used. In this work MD-55-2 radiochromic films have been used as reference dosimeters to obtain dose to water per pulse DGAF(w) values for three Novac7 (Hitesys) electron beams of E0 = 5.8 MeV. However, the beam calibration by MD-55-2 films is time consuming and the use of plane parallel chambers is fundamental for a periodic quality control procedure. Three plane parallel chambers have been used and the general formula for the k determination has been tested using the calibration doses, DGAF(w). In particular, consistent ion recombination factors ksat(V0) (with the ion chamber polarized at V0), that follow the Boag theory, have been estimated at different dose per pulse values for the three plane parallel ionization chambers. This means that at present any ion chamber needs a specific ksat (V0) determination by using a reference dosimeter for which the response is independent of the dose rate. An accurate determination of ksat(V0), using a reference quality beam, can be used to determine the dose to water per pulse for electron beams of different quality and geometrical configuration.

Our data confirm that neutron exposure levels around the new dedicated IORT accelerator are very low. Mobile shielding panels can be used to reduce x-ray levels to below regulatory levels without necessarily providing permanent shielding in the operating room.

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To solve logistic problems in the method of transporting the anesthetized patient from the surgical theater to the radiation department, a new linear accelerator, named Novac7, was developed in order to enable its use in the operating room.In this paper some interesting features concerning the practice of a Novac7 unit, in the conventional way of irradiation, are presented: (1) preliminary study of medical and nursing staff radioprotection is evaluated; (2) measurements of beam intensity reproducibility have been performed; (3) isodose distributions, carried out by a radiation field analyzer using diodes and water phantom, and beam dosimetry carried out by gafchromic MD55 films in acrylic phantom to solve problems due to the high-dose-rate output of the machine are described. Materials and MethodsNovac7 is a new compact medical linear accelerator, produced by Hitesys SpA. The accelerator is designed to produce an electron beam of 9 MeV maximum nominal energy, with a maximum beam current of 3 mA.