Radiation protection measurements around a 12 MeV mobile dedicated IORT accelerator

Antonella Soriani, Giuseppe Felici, Mario Fantini, Massimiliano Paolucci, Oscar Borla, Giovanna Evangelisti, Marcello Benassi, Lidia Strigari

Research output: Contribution to journalArticlepeer-review

Abstract

Purpose: The aim of this study is to investigate radioprotection issues that must be addressed when dedicated accelerators for intraoperative radiotherapy (IORT) are used in operating rooms. Recently, a new version of a mobile IORT accelerator (LIAC Sordina SpA, Italy) with 12 MeV electron beam has been implemented. This energy is necessary in some specific pathology treatments to allow a better coverage of thick lesions. At an electron energy of 10 MeV, leakage and scattered x-ray radiation (stray radiation) coming from the accelerator device and patient must be considered. If the energy is greater than 10 MeV, the x-ray component will increase; however, the most meaningful change should be the addition of neutron background. Therefore, radiation exposure of personnel during the IORT procedure needs to be carefully evaluated. Methods: In this study, stray x-ray radiation was measured and characterized in a series of spherical projections by means of an ion chamber survey meter. To simulate the patient during all measurements, a polymethylmethacrylate (PMMA) slab phantom with volume 30×30×15 cm3 and density 1.19 g/ cm3 was used. The PMMA phantom was placed along the central axis of the beam in order to absorb the electron beams and the tenth value layer (TVL) and half value layer (HVL) of scattered radiation (at 0°, 90°, and 180° scattering angles) were also measured at 1 m of distance from the phantom center. Neutron measurements were performed using passive bubble dosimeters and a neutron probe, specially designed to evaluate ambient dose equivalent H (10). Results: The x-ray equivalent dose measured at 1 m along the beam axis at 12 MeV was 260 μSv/Gy. The value measured at 1 m at 90° scattering angle was 25 μSv/Gy. The HVL and TVL values were 1.1 and 3.5 cm of lead at 0°, and 0.4 and 1 cm at 90°, respectively. The highest equivalent dose of fast neutrons was found to be at the surface of the phantom on the central beam axis (2.9±0.6 μSv/Gy), while a lower value was observed below the phantom (1.6±0.3 μSv/Gy). The neutron dose equivalent at 90° scattering angle and on the floor plane on the beam axis below the beam stopper was negligible. Conclusions: 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.

Original languageEnglish
Pages (from-to)995-1003
Number of pages9
JournalMedical Physics
Volume37
Issue number3
DOIs
Publication statusPublished - 2010

Keywords

  • Electron beams
  • IORT
  • Linear accelerators
  • Neutron contamination
  • Radiation protection

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging

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