Author(s)

Hideharu Miura^1*, Shuichi Ozawa^1,2, Shintaro Tsuda¹, Masahiro Hayata¹, Kiyoshi Yamada¹, Yasushi Nagata^1,2

¹Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan.
²Department of Radiation Oncology, Institute of Biomedical & Health Science, Hiroshima University, Hiroshima, Japan.

The stability of delivery of low monitor unit (MU) setting is important especially for step-and-shoot intensity-modulated radiotherapy (IMRT), because the nature of the technique is inherent to repeat beam on/off according to the number of the segments. This study evaluates the dose linearity and profile flatness/symmetry under low MU settings for Vero4DRT, a new linear-accelerator based irradiation system that currently implements step-and-shoot IMRT. To evaluate the dose linearity and flatness/symmetry, the point doses and beam profiles were measured as functions of MU and dose rates. The accuracy of dose delivery depended on the dose rate. Under all dose rates, the dose was linear within 1% above 5 MU and within 2% above 3 MU. The beam symmetry was degraded in-line compared with crossline, although both profiles were symmetric within 2% at all dose settings. The profile flatness was also within 2% above 5 MU at any dose rate and showed no significant variation among the low MU settings. To ensure stable beam delivery without increasing the treatment time of Vero4DRT, we recommend a delivery of 5 MU per segment at a dose rate of 500 MU/min.

Vero4DRT, Step-and-Shoot IMRT, Low Monitor Unit, Beam Characteristic

Miura, H. , Ozawa, S. , Tsuda, S. , Hayata, M. , Yamada, K. and Nagata, Y. (2015) Beam Characteristics at Low Dose Monitor Unit Settings for Vero4DRT. International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 4, 284-289. doi: 10.4236/ijmpcero.2015.44034.