Abstract
Background: Magnetic resonance image-guided radiation therapy (MR-IGRT) promises more precise and effective radiation treatments compared to conventional IGRT by using real-time on-board MR imaging. Under the influence of a magnetic field, however, secondary electrons exiting a surface can be forced in a circular path and re-enter the medium, resulting in dose increase at a beam-exit surface, called the electron return effect (ERE). The purpose of the study is to compare the exit skin dose computed by Monte Carlo dose calculation with measurements using an adult anthropomorphic phantom and to measure the effect of skin dose reduction by adding 1 cm-thick bolus. Method: The plan was compared with measurements using an adult anthropomorphic phantom combined with radiochromic films and thermoluminescent dosimeters. We also measured the skin dose reduction by adding 1 cm-thick bolus on the frontal surface of the phantom. Results: We found that 1 cm-thick bolus reduced the skin dose by up to 20% both in measurements and calculations. The plan was found to overestimate the measured skin dose by about 10% and there was no significant difference in the bolus effect between the breast skin and the skin (without breast attachment) doses. Conclusion: In conclusion, we confirmed the ERE effect on the anthropomorphic phantom under the magnetic field and the exit skin dose reduction by adding a bolus. Skin dose measurements using anthropomorphic phantom may be helpful to evaluate more realistic skin dose and the bolus effect in the magnetic field.
Highlights
Magnetic resonance image-guided radiation therapy (MRIGRT) promises more precise and effective radiation treatments compared to conventional IGRT by using real-time on-board MR imaging
The plan was found to overestimate the measured skin dose by about 10% and there was no significant difference in the bolus effect between the breast skin and the skin doses
We investigated the skin dose reduction by adding 1 cm-thick bolus on the frontal surface of the phantoms irradiated by the PA beam
Summary
Magnetic resonance image-guided radiation therapy (MRIGRT) promises more precise and effective radiation treatments compared to conventional IGRT by using real-time on-board MR imaging. Under the influence of a magnetic field, secondary electrons exiting a surface can be forced in a circular path and re-enter the medium, resulting in dose increase at a beam-exit surface, called the electron return effect (ERE). Conclusion: In conclusion, we confirmed the ERE effect on the anthropomorphic phantom under the magnetic field and the exit skin dose reduction by adding a bolus. It is reported that under the influence of a magnetic field, secondary electrons exiting a surface can be directed in a circular path and re-entering the medium, resulting in dose increase at a beam-exit surface, called the electron return effect (ERE) [1] [2] [3] [4]. It is important to measure the skin dose increase by the ERE and its reduction by a bolus using physical anthropomorphic phantoms, in more realistic radiotherapy condition
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