Radiation survey around a Liac mobile electron linear accelerator for intraoperative radiation therapy.
The aim of this study was to perform a detailed analysis of the air kerma values around a Liac mobile linear accelerator working in a conventional operating room (OR) for IORT. The Liac delivers electron beams at 4, 6, 8 and 10 MeV. A radiation survey to determine photon leakage and scatter consisted of air kerma measurements on a spherical surface of 1.5 m radius, centered on the titanium exit window of the accelerating structure. Measurements were taken using a 30 cm3 calibrated cylindrical ion chamber in three orthogonal planes, at the maximum electron energy. For each point, 10 Gy was delivered. At selected points, the quality of x-ray radiation was determined by using lead sheets, and measurements were performed for all energies to investigate the energy dependence of stray radiation. The photon scatter contribution from the metallic internal patient-shielding in IORT, used to protect normal tissues underlying the target, was also evaluated. At seven locations outside the OR, the air kerma values derived from in-room measurements were compared to measurements directly performed using a survey meter. The results, for a delivered dose of 10 Gy, showed that the air kerma values ranged from approximately 6 microGy (upper and rear sides of the Liac) to 320 microGy (lateral to beam stopper) in the two orthogonal vertical planes, while values lower than 18 microGy were found in the horizontal plane. At 10 MeV, transmission behind 1 cm lead shield was found to be 42%. The use of internal shielding appeared to increase the photon scatter only slightly. Air kerma values outside the OR were generally lower than 1 mGy for an annual workload of 200 patients. Thus, the Liac can safely work in a conventional OR, while the need for additional shielding mainly depends on patient workload. Our data can be useful for centers planning to implement an IORT program using a mobile linear accelerator, permitting radiation safety personnel to estimate in advance the shielding required for a particular workload.
Ciocca
Mario
M
Unit of Medical Physics, European Institute of Oncology, Milano, Italy.
Pedroli
Guido
G
Unit of Medical Physics, European Institute of Oncology, Milano, Italy.
Orecchia
Roberto
R
Division of Radiation Oncology, European Institute of Oncology, Milano, Italy.|Faculty of Medicine, Università degli Studi di Milano, Milano, Italy.
Guido
Andrea
A
Division of Radiation Oncology, European Institute of Oncology, Milano, Italy.
Cattani
Federica
F
Unit of Medical Physics, European Institute of Oncology, Milano, Italy.
Cambria
Raffaella
R
Unit of Medical Physics, European Institute of Oncology, Milano, Italy.
Veronesi
Umberto
U
Scientific Direction, European Institute of Oncology, Milano, Italy.
D001943:Breast Neoplasms / Q000532:radiotherapy / Q000601:surgery; D002138:Calibration; D003131:Combined Modality Therapy; D005260:Female; D006801:Humans; D007432:Intraoperative Period; D010315:Particle Accelerators / Q000592:standards; D011829:Radiation Dosage; D011834:Radiation Monitoring; D011835:Radiation Protection; D011878:Radiotherapy / Q000295:instrumentation*; D011879:Radiotherapy Dosage