Monitor units are not predictive of neutron dose for high-energy IMRT |
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Authors: | Roger A H?lg Jürgen Besserer Markus Boschung Sabine Mayer Uwe Schneider |
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Institution: | 1. Institute for Radiotherapy, Radiotherapie Hirslanden AG, Aarau, Switzerland 3. Division for Radiation Safety and Security, Paul Scherrer Institut, Villigen, Switzerland 2. Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
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Abstract: | ABSTRACT: BACKGROUND: Due to the substantial increase in beam-on time of high energy intensity-modulated radiotherapy (>10 MV) techniques to deliver the same target dose compared to conventional treatment techniques, an increased dose of scatter radiation, including neutrons, is delivered to the patient. As a consequence, an increase in second malignancies may be expected in the future with the application of intensity-modulated radiotherapy. It is commonly assumed that the neutron dose equivalent scales with the number of monitor units. METHODS: Measurements of neutron dose equivalent were performed for an open and an intensity-modulated field at four positions: inside and outside of the treatment field at 0.2 cm and 15 cm depth, respectively. RESULTS: It was shown that the neutron dose equivalent, which a patient receives during an intensity-modulated radiotherapy treatment, does not scale with the ratio of applied monitor units relative to an open field irradiation. Outside the treatment volume at larger depth 35% less neutron dose equivalent is delivered than expected. CONCLUSIONS: The predicted increase of second cancer induction rates from intensity-modulated treatment techniques can be overestimated when the neutron dose is simply scaled with monitor units. |
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