Abstract
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.
Highlights
Several linear-accelerator-based irradiation techniques, such as intensity-modulated radiation therapy (IMRT), stereotactic radiotherapy and conformal arc radiotherapy, deliver a highly accurate dose to the target volumeHow to cite this paper: Miura, H., Ozawa, S., Tsuda, S., Hayata, M., Yamada, K. and Nagata, Y. (2015) Beam Characteristics at Low Dose Monitor Unit Settings for Vero4DRT
As dynamic MLC (DMLC) and volumetric modulated radiotherapy (VMAT) are unavailable in the current commercial version of Vero4DRT, the system should be operated in the step-and-shoot IMRT mode
The dosimetric variation was higher under low than under high monitor unit (MU) settings, and the linearity was poor under the lowest setting (1 MU)
Summary
Several linear-accelerator-based irradiation techniques, such as intensity-modulated radiation therapy (IMRT), stereotactic radiotherapy and conformal arc radiotherapy, deliver a highly accurate dose to the target volumeHow to cite this paper: Miura, H., Ozawa, S., Tsuda, S., Hayata, M., Yamada, K. and Nagata, Y. (2015) Beam Characteristics at Low Dose Monitor Unit Settings for Vero4DRT. Several linear-accelerator-based irradiation techniques, such as intensity-modulated radiation therapy (IMRT), stereotactic radiotherapy and conformal arc radiotherapy, deliver a highly accurate dose to the target volume. (2015) Beam Characteristics at Low Dose Monitor Unit Settings for Vero4DRT. IMRT is typically categorized into dynamic MLC (DMLC) mode (referred to as sliding window) [1] and static MLC (SMLC) mode (referred to as step-and-shoot) [2]. As DMLC and VMAT are unavailable in the current commercial version of Vero4DRT, the system should be operated in the step-and-shoot IMRT mode. In previous reports, when step-and-shoot IMRT was implemented with several low monitor units (MUs) per segment at high dose rates, the dosimetric errors were large [9]-[14]. By determining the uncertainty in the actual dose at low MUs, we can deliver the target dose to within ±5% for better tumor control [15]
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