Abstract
Several investigators have pointed out that electron and neutron contamination from high‐energy photon beams are clinically important. The aim of this study is to assess electron and neutron contamination production by various prostheses in a high‐energy photon beam of a medical linac. A 15 MV Siemens PRIMUS linac was simulated by MCNPX Monte Carlo (MC) code and the results of percentage depth dose (PDD) and dose profile values were compared with the measured data. Electron and neutron contaminations were calculated on the beam's central axis for Co‐Cr‐Mo, stainless steel, Ti‐alloy, and Ti hip prostheses through MC simulations. Dose increase factor (DIF) was calculated as the ratio of electron (neutron) dose at a point for 10×10 cm2 field size in presence of prosthesis to that at the same point in absence of prosthesis. DIF was estimated at different depths in a water phantom. Our MC‐calculated PDD and dose profile data are in good agreement with the corresponding measured values. Maximum dose increase factor for electron contamination for Co‐Cr‐Mo, stainless steel, Ti‐alloy, and Ti prostheses were equal to 1.18, 1.16, 1.16, and 1.14, respectively. The corresponding values for neutron contamination were respectively equal to: 184.55, 137.33, 40.66, and 43.17. Titanium‐based prostheses are recommended for the orthopedic practice of hip junction replacement. When treatment planning for a patient with hip prosthesis is performed for a high‐energy photon beam, attempt should be made to ensure that the prosthesis is not exposed to primary photons.PACS numbers: 87.56.bd, 87.55.kh, 87.55.Gh
Highlights
The number of patients with hip prosthesis undergoing pelvic irradiation in radiotherapy is growing.[1]
A schematic diagram illustrating the components of the Siemens PRIMUS linac head (15 MV photon energy) is presented in Fig. 1.(8) In our model, we have incorporated the main components in the beam path
As it was mentioned in the previous section, comparisons of the simulation and measurement data were based on gamma function calculations
Summary
The number of patients with hip prosthesis undergoing pelvic irradiation in radiotherapy is growing.[1] According to the report of Task Group No 63 (TG-63) of American Association of Physicists in Medicine (AAPM), between 1% and 4% of radiotherapy patients have prosthetic devices which could affect the predetermined value of the dose that they would receive. This Task Group was formed to identify the problems caused by the presence of high-Z prosthesis material in radiation therapy in the megavoltage photon energy range.[1]. The treatment aim is not to irradiate the skin, the amount of skin dose must be taken into account when establishing the treatment criteria.[6]
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