Oncological hyperthermia: working exposure assessment to RF field Simona Valbonesi 1* , Marina Barbiroli 2 , Mario Frullone 1 , Ermanno Papotti 3 , Silvia Vaccari 3 , and Andrea Vanore 4 1 Consorzio Elettra 2000, Pontecchio Marconi, Italy, 2 Department of Electronics, Computer Sciences and Systems – DEIS – University of Bologna, Bologna, Italy, 3 Health Physics Department, University of Parma, Parma, Italy, 4 Prevention and Protection Office – ASL 1, Massa Carrara, Italy *Corresponding author e-mail: simona@mail.elettra2000.it Introduction Hypertermia is a cancer treatment used to support traditional therapy which consist in selectively administer heat through a RF field (13.56 MHz) in order to raise up deep tumor temperature to 42-45°C. Similar to all other irradiation methods, RF fields exposure is not restricted to the target region; scattered fields can lead to potential over exposure of nerby persons, in particular medical staff and nurses [1]. In this paper we evaluated the professional exposure to RF field within Oncological hyperthermia environment. Measurements and evalutations performed have shown that, in condition of maximum exposure Directive 2004/40/EC [2] action values for electric field and limbs induced current can be overrated. The same happens for limits if we consider whole body SAR, while for SAR localised at limbs the limit is exceeded only if we consider SAR 10 applied to a portion of muscolar tissue. Materials and Methods Measurements and evaluations heve been performed on a EHY 2000 Hot-OncoTherm medical equipment installed within Oncologic Dept. of Massa Carrara Hospital. The test protocol involved the measurement of electric field (E) levels and induced current at limbs in different points within the treatment room, starting from the applicator’s centre on a 10 cm step diagonal until the room exit door and in conditions of maximum exposure (larger plate applicator at 150 W). We studied electic field and induced current patterns (at 10-110-150-190 cm from the floor) and we evaluated whole body SAR and SAR 10 localised at limbs taking into account anisotropies due to tissues differences. At the specific frequency thermal effects are predominant [3,4]; the biological effect are correlated with the absorbed power density, or in an equivalent way, with the current density: P J σ = (1) Where σ is the electric conductivity and depends on the amount of water contained in biological tissues, on cellular architecture and on RF applied signal frequency. The dosimetric evaluation have been performed by calculating the SAR, which expresses the power absorbed per unit mass: ρ σ 2 2 E SAR= (2) both ρ and σ depend on the intrinsic characteristics of the biological tissue. We used (2) to evaluate whole body SAR by approximating the whole human body to a a high water content tissue, such as muscle tissue; this kind of approximation leads to a SAR maximization. The frequency depending values of σ were extrapolated using the interactive form developed by IFAC CNR [5] on the basis of the parametric model for biological tissues dielectric properties calculation developed by Gabriel [6,7]. Localized SAR calculation was performed by applying (2) to a limb model based on a series of concentric cylinders composed in the order by: red bone marrow, spongious bone and muscolar tissue.