Quality assurance device for four‐dimensional IMRT or SBRT and respiratory gating using patient‐specific intrafraction motion kernels

Abstract

Emerging technologies such as four‐dimensional computed tomography (4D CT) and implanted beacons are expected to allow clinicians to accurately model intrafraction motion and to quantitatively estimate internal target volumes (ITVs) for radiation therapy involving moving targets. In the case of intensity‐modulated (IMRT) and stereotactic body radiation therapy (SBRT) delivery, clinicians must consider the interplay between the temporal nature of the modulation and the target motion within the ITV. A need exists for a 4D IMRT/SBRT quality assurance (QA) device that can incorporate and analyze customized intrafraction motion as it relates to dose delivery and respiratory gating. We built a 4D IMRT/SBRT prototype device and entered (X, Y, Z)(T) coordinates representing a motion kernel into a software application that transformed the kernel into beam‐specific two‐dimensional (2D) motion “projections,”previewed the motion in real time, anddrove a precision X–Y motorized device that had, atop it, a mounted planar IMRT QA measurement device. The detectors that intersected the target in the beam's‐eye‐view of any single phase of the breathing cycle (a small subset of all the detectors) were defined as “target detectors” to be analyzed for dose uniformity between multiple fractions. Data regarding the use of this device to quantify dose variation fraction‐to‐fraction resulting from target motion (for several delivery modalities and with and without gating) have been recently published. A combined software and hardware solution for patient‐customized 4D IMRT/ SBRT QA is an effective tool for assessing IMRT delivery under conditions of intrafraction motion. The 4D IMRT QA device accurately reproduced the projected motion kernels for all beam's‐eye‐view motion kernels. This device has been proved to• effectively quantify the degradation in dose uniformity resulting from a moving target within a static planning target volume, and• integrate with a commercial respiratory gating system to ensure that the system is working effectively.Such a device is discussed as a potential tool to optimize the gating duty cycle to maximize delivery efficiency while minimizing dose variability.PACS numbers: 87.50.Gi, 87.53.Dq, 87.53.Kn, 87.53.Mr, 87.53.Tf, 87.56.Fc, 87.58.Sp

Motion as a perturbation: Measurement-guided dose estimates to moving patient voxels during modulated arc deliveries

“…With the motion in either the X or Z direction, the SDD changes in a similar fashion as a function of the gantry angle. This is important because the motion table available for this work (MotionSim, Sun Nuclear Corp, Melbourne, FL) 9 can move the phantom only in the XY (coronal) plane.…”

“…The table motion must be synchronized with the beam start time so that the virtual motion kernel in the software would reflect the physical one. It was accomplished by using the breath hold gating feature of the accelerator and the gating simulator of the motion table, 9 as was described by Court et al 8 The gating simulator was programmed to first produce a periodic up and down (Z) 1.5 cm motion of the reflector block to establish a pattern required to initialize the accelerator gating routine (Fig. 2).…”

“…[6][7][8] Therefore, this motion may need to be incorporated into patient dose reconstruction, particularly in the case of hypofractionated delivery, where the interplay effect is not likely to be washed out by averaging of 20-30 fractions. 6 Typically, measurement-based investigations of the dose to a moving target involve a dosimeter mounted on a physical motion stage, with a paper from Nelms et al 9 serving as one such example (though using time resolved-data from a stationary planar array convolved with a motion kernel has also been reported for interplay evaluation 8 ). Even with electronic dosimetry arrays, the physical motion table experiments are delicate and time-consuming, particularly if the data for a number of fractions and/or motion phases are collected.…”

Motion as perturbation. II. Development of the method for dosimetric analysis of motion effects with fixed-gantry IMRT

“…The MC2 was mounted atop of the MotionSim 2D (IEC XY) computer-controlled motion stage (Sun Nuclear). 7 The motion trajectory programmed into the motion stage is shown in Fig. 1.…”

Implementation of a lung radiosurgery program: Technical considerations and quality assurance in an Australian institution

“…Guidelines for the delivery of stereotactic lung radiotherapy have been produced in the context of multi‐institutional randomised phase III trials 3,4 . However, to date, there is only limited literature regarding the use of patient‐specific respiratory patterns in the phantom dosimetry of stereotactic body radiotherapy (SBRT) plans 5,6 …”