Beam Characteristics at Low Dose Monitor Unit Settings for Vero4DRT

Abstract

The stability of delivery of low monitor unit (MU) setting is important especially for step-andshoot 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.

Analyzing the characteristics of 6 MV photon beam at low monitor unit settings

“…Reena et al .,[ 7 ] Bhangle et al .,[ 8 ] and Miura et al . [ 13 ] recommended ≥4 MU, <5 MU, and 5 MU, respectively. Our results showed that the treatment delivered with <3 MU settings can result in an error in dose delivery.…”

“…Several researchers have reported the characteristics of low MU such as stability, linearity, flatness, symmetry, and reproducibility for various linear accelerators from Elekta, Siemens, and Varian. [ 4 5 6 7 8 9 10 11 12 13 ] Different results were reported for the same make of the linear accelerator, which revealed that the characteristics of the beam differ between the machines.…”

Dataset for Beam Commissioning of the Vero4DRT System

“…of the MLC for MHI-TM2000 using a well-commissioned 6-MV photon beam, EDR2 films, and water-equivalent phantoms [5]. Miura et al reported the dose linearity and profile flatness/symmetry under low-MU settings of Vero4DRT under low-MU settings [10]. Because the Novalis system likewise supports only iPlan RT, dosimetric characteristics of the Novalis may serve as a reference [11].…”