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Establishing inherent uncertainty in the shifts determined by volumetric imaging

Published online by Cambridge University Press:  18 April 2017

Upendra Kumar Giri  and
Anirudh Pradhan
Upendra Kumar Giri*
Affiliation:
Department of Radiation Oncology, Fortis Memorial Research Institute, Gurgaon-122002, Haryana, India Department of Physics, Institute of Applied Sciences & Humanities, GLA University, Mathura-281406, Uttar Pradesh, India
Anirudh Pradhan
Affiliation:
Department of Mathematics, Institute of Applied Sciences & Humanities, GLA University, Mathura-281406, Uttar Pradesh, India
*
Correspondence to: Upendra Kumar Giri, Department of Radiation Oncology, Fortis Memorial Research Institute, Opposite to Huda City Metro Station, Gurgaon, Haryana 122002, India. Tel: +9196 5077 8852. E-mail: upendragiribhu@gmail.com
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Abstract

Objective

This study was conducted for establishing inherent uncertainty in the shift determination by X-ray volumetric imaging (XVI) and calculating margins due to this inherent uncertainty using van Herk formula.

Material and methods

The study was performed on the XVI which was cone-beam computed tomography integrated with the Elekta AxesseTM linear accelerator machine having six degree of freedom enabled HexaPOD couch. Penta-Guide phantom was used for inherent translational and rotational shift determination by repeated imaging. The process was repeated 20 times a day without moving the phantom for 30 consecutive working days. The measured shifts were used for margins calculation using van Herk formula.

Results

The mean standard deviations were calculated as 0·05, 0·05, 0·06 mm in the three translational (x, y and z) and 0·05°, 0·05°, 0·05° in the three rotational axes (about x, y, z). Paired sample t-test was performed between the mean values of translational shifts (x, y, z) and rotational shifts. The systematic errors were found to be 0·03, 0·04 and 0·03 mm while the random errors were 0·05, 0·06 and 0·06 mm in the lateral, cranio-caudal and anterio-posterior directions, respectively. For the rotational shifts, the systematic errors were 0·02, 0·03 and 0·03 and the random errors were 0·06, 0·05 and 0·05 in the pitch, roll and yaw directions, respectively.

Conclusion

Our study concluded that there was an inherent uncertainty associated with the XVI tools, on the basis of these six-dimensional shifts, margins were calculated and recorded as a baseline for the quality assurance (QA) programme for XVI imaging tools by checking its reproducibility once in a year or after any major maintenance in hardware or upgradation in software. Although the shift determined was of the order of submillimetre order, still that shift had great significance for the image quality control of the XVI tools. Every departments practicing quality radiotherapy with such imaging tools should establish their own baseline value of inherent shifts and margins during the commissioning and must use an important QA protocol for the tools.

Keywords

image-guided radiotherapyquality assuranceX-ray volumetric imaging
Type
Original Articles
Information
Journal of Radiotherapy in Practice , Volume 16 , Issue 3 , September 2017 , pp. 258 - 264
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Copyright
© Cambridge University Press 2017 

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