Anatomy‐based, patient‐specific VMAT QA using EPID or MLC log files

Abstract

In this project, we investigated the use of an electronic portal imaging device (EPID), together with the treatment planning system (TPS) and MLC log files, to determine the delivered doses to the patient and evaluate the agreement between the treatment plan and the delivered dose distribution. The QA analysis results are presented for 15 VMAT patients using the EPID measurements, the ScandiDos Delta4 dosimeter, and the beam fluence calculated from the multileaf collimator (MLC) log file. EPID fluence images were acquired in continuous acquisition mode for each of the patients and they were processed through an in‐house MATLAB program to create an opening density matrix (ODM), which was used as the input fluence for the dose calculation in the TPS (Pinnacle3). The EPID used in this study was the aSi1000 Varian on a Novalis TX linac equipped with high‐definition MLC. The actual MLC positions and gantry angles were retrieved from the MLC log files and the data were used to calculate the delivered dose distributions in Pinnacle. The resulting dose distributions were then compared against the corresponding planned dose distributions using the 3D gamma index with 3 mm/3normal% passing criteria. The ScandiDos Delta4 phantom was also used to measure a 2D dose distribution for all the 15 patients and a 2D gamma was calculated for each patient using the Delta4 software. The average 3D gamma using the EPID images was 96.1normal%±2.2normal%. The average 3D gamma using the log files was 98.7normal%±0.5normal%. The average 2D gamma from the Delta4 was 98.1normal%±2.1normal%. Our results indicate that the use of the EPID, combined with MLC log files and a TPS, is a viable method for QA of VMAT plans.PACS numbers: 87.55.Qr

Improving accuracy for stereotactic body radiotherapy treatments of spinal metastases

“…The correlation, then, between ArcCheck/film and PerFraction is of interest and has not yet been reported for any MLC log‐file‐based system for SBRT spine. Past investigations of PerFraction have been limited to its EPID dosimetry capabilities30, 31, 32 and some work has been performed on other MLC log‐file‐based systems, demonstrating good agreement between conventional QA and MLC log‐file‐based patient QA 33, 34, 35, 36. Discrepancies have been demonstrated between actual and intended MLC leaf delivery for low MU control points, with good agreement shown between MLC log‐file and diode array assessment methods 37.…”

Evaluation of machine log files/MC‐based treatment planning and delivery QA as compared to ArcCHECK QA

“…For all calculations, unless otherwise stated, particle histories were simulated to achieve 1% dosimetric variance at 70% max dose. Beam model data for the 6 MV Elekta Agility linac was acquired using IBA's Blue Phantom . Inline/crossline profiles, PDDs, and output factors were acquired for various field sizes as shown in Table III.…”

“…Beam model data for the 6 MV Elekta Agility linac was acquired using IBA's Blue Phantom. 2 Inline/crossline profiles, PDDs, and output factors were acquired for various field sizes as shown in Table III. Output factors less than 5 9 5, PDDs less than 5 9 5, and profiles less than 20 9 20 were acquired using a Sun Nuclear EDGE diode.…”

“…shows that log files can carry out IMRT QA with the same accuracy as film . Log files are also a viable method of VMAT QA for both phantom and patient geometries . However, despite its advantages, it remains debatable whether LF QA can replace conventional techniques …”

“…1 Log files are also a viable method of VMAT QA for both phantom and patient geometries. 2,3 However, despite its advantages, it remains debatable whether LF QA can replace conventional techniques. 4 The primary concern with the use of log files is that they rely upon a robust machine QA protocol.…”