Feasibility of Patient Quality Assurance Method Based on Log File and Onboard Detector in Helical Tomotherapy Technique

Ghazal  Etemadi; Ahmad  Mostaar; Payam  Azadeh; Niloofar Yousefi  Moteghaed

doi:10.18502/fbt.v13i2.21939

Ghazal Etemadi Department of Medical Physics and Biomedical Engineering, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Ahmad Mostaar Department of Medical Physics and Biomedical Engineering, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Payam Azadeh Department of Radiation Oncology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Niloofar Yousefi Moteghaed Department of Medical Physics and Biomedical Engineering, Shahid Beheshti University of Medical Sciences, Tehran, Iran

DOI: https://doi.org/10.18502/fbt.v13i2.21939

Keywords: Tomotherapy; Patient-Specific Quality Assurance; Prostate Cancer; Log File; Onboard Detector; Delivery Analysis Software.

Abstract

Purpose: The phantom-less Patient-Specific Quality Assurance (PSQA) for Intensity‐Modulated Radiotherapy (IMRT) plan verification has been exploited recently. This study aimed to evaluate the feasibility of PSQA based on log files and onboard detectors for prostate patients in helical tomotherapy.

Materials and Methods: For 15 prostate patients, the Quality Assurance (QA) of the helical tomotherapy plan was performed using the Delta4 phantom and Cheese phantom to evaluate the spatial dose distribution and point dose, respectively. These parameters were also reconstructed by Delivery Analysis (DA) software using measured Leaf Open Times (LOTs). Gamma analysis and relative dose difference were used to compare the measured and reconstructed doses with the calculated values. Then, using the relative discrepancy, the log file and onboard detector data were compared to the expected data to assess machine performance.

Results: The mean relative dose difference was within 1.3% among the measurement, reconstruction, and calculation. Statistical analysis and p-value results indicated that there was no statistically significant difference in the dose difference between the DA-based and conventional QA methods. The gamma values for the DA-based QA method were similar to the measurement QA method for the criteria 3%/3mm, 3%/2mm, 2%/3mm, 2%/2mm, 2%/1mm, and 1%/1mm. However, the gamma values for the criteria 3%/1mm, 1%/3mm, and 1%/2mm were comparable. The mean percentage difference in LOTs was 0.07%, with most discrepancies occurring in very low and some high LOTs. The relative difference between the log file and expected data was lower than 2.30% for the couch speed, couch movement, monitor unit, and gantry rotation per minute.

Conclusion: The DA software is an efficient alternative to measurement-based PSQA methods. However, the accuracy of the DA software requires further investigation for gamma analysis with strict criteria. The very low and high LOTs may lead to the dose discrepancy. The tomotherapy machine can accurately implement the planned parameters.