Investigation of the feasibility of a simple method for verifying the motion of a binary multileaf collimator synchronized with the rotation of the gantry for helical tomotherapy

Abstract

In this paper, we suggest a new method for verifying the motion of a binary multileaf collimator (MLC) in helical tomotherapy. For this we used a combination of a cylindrical scintillator and a general‐purpose camcorder. The camcorder records the light from the scintillator following photon irradiation, which we use to track the motion of the binary MLC. The purpose of this study is to demonstrate the feasibility of this method as a binary MLC quality assurance (QA) tool. First, the verification was performed using a simple binary MLC pattern with a constant leaf open time; secondly, verification using the binary MLC pattern used in a clinical setting was also performed. Sinograms of simple binary MLC patterns, in which leaves that were open were detected as “open” from the measured light, define the sensitivity which, in this case, was 1.000. On the other hand, the specificity, which gives the fraction of closed leaves detected as “closed”, was 0.919. The leaf open error identified by our method was −1.3±7.5%. The 68.6% of observed leaves were performed within ± 3% relative error. The leaf open error was expressed by the relative errors calculated on the sinogram. In the clinical binary MLC pattern, the sensitivity and specificity were 0.994 and 0.997, respectively. The measurement could be performed with −3.4±8.0% leaf open error. The 77.5% of observed leaves were performed within ± 3% relative error. With this method, we can easily verify the motion of the binary MLC, and the measurement unit developed was found to be an effective QA tool.PACS numbers: 87.56.Fc, 87.56.nk

Development of a novel delivery quality assurance system based on simultaneous verification of dose distribution and binary multi-leaf collimator opening in helical tomotherapy

“…Our results showed a LOT error of − 3.9 ± 7.8% in the reconstructed sinogram compared with the TPS. This outcome is consistent with the − 3.4 ± 8.0% accuracy reported in a previous study by Hashimoto et al [ 19 ]. In a previous study, we demonstrated the feasibility of measuring binary MLC movements using a PS and a general-purpose camcorder.…”

“…Investigation of the characteristics of the scintillation light detected by our system is necessary to measure MLC opening. Based on the procedure of Hashimoto et al [ 19 ], we investigated the relationship between the scintillation light and LOT. The irradiation field was 10 cm (25–40th leaves opened), and the LOT varied from 29.41 to 294.12 ms for a gantry angle of 0°.…”

“…The PS is made using a water-equivalent material and affords the advantages of a linear dose response; it can be used as a phantom and can be easily fabricated into any shape. Hashimoto et al [ 19 ] measured a binary multi-leaf collimator (MLC) operation using a PS and a general-purpose camcorder. Their study demonstrated the feasibility of using a simple device to measure complex instrumentation in HT.…”

Measurement and correction of leaf open times in helical tomotherapy

“…Methods for the verification of MLC LOTs have been investigated by many authors, some of whom used independent devices, 6 whereas others used the MVCT detector to allow for in vivo dose calculation based on dose reconstruction in the presence of the patient. [7][8][9][10][11][12] We present a QA procedure that involves applying a simple method to measure LOTs with no attenuation between the MLC and the MVCT detector.…”

Reconstruction of the treatment area by use of sinogram in helical tomotherapy

“…This system also allows one to acquire the delivery sinogram during the actual treatment. The sinogram has often been used in the treatment verification [ 12 , 13 ], and one can come up with the visualization of treatment area from the sinogram. For conventional linear accelerators, in fact, CT reconstruction with portal images during rotational treatment such as a volumetric modulated arc therapy (VMAT) has been successfully performed [ 14 , 15 ].…”