An Experimental Method for the Scatter Correction of MV Images Using Scatter to Primary Ratios (SPRs)

Hosang Jeon; Dahl Park; Jayeong Lee; Jiho Nam; Wontaek Kim; Yongkan Ki; Donghyun Kim; Ju Hye Lee; Dongwon Kim

doi:10.14316/pmp.2014.25.3.143

Journal List > Prog Med Phys > v.25(3) > 1098434

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Jeon, Park, Lee, Nam, Kim, Ki, Kim, Lee, and Kim: An Experimental Method for the Scatter Correction of MV Images Using Scatter to Primary Ratios (SPRs)

Original Article

Progress in Medical Physics 2014;25(3):143-150.

Published online: 20 September 2014

DOI: https://doi.org/10.14316/pmp.2014.25.3.143

An Experimental Method for the Scatter Correction of MV Images Using Scatter to Primary Ratios (SPRs)

Hosang Jeon^∗, Dahl Park^†, Jayeong Lee^∗, Jiho Nam^∗,^‡,, Wontaek Kim^§, Yongkan Ki^†, Donghyun Kim^†, Ju Hye Lee^†, Dongwon Kim^§

^∗Department of Radiation Oncology, Pusan National University Yangsan Hospital, Yangsan, Korea

^†Department of Radiation Oncology, Pusan National University Hospital, Busan, Korea

^‡Research Institute for Convergence of Biomedical Science and Technology, Pusan National University Yangsan Hospital, Yangsan, Korea

^§Department of Radiation Oncology, Pusan National University School of Medicine, Busan, Korea

Correspondence:Jiho Nam(jihonam@hanmail.net) Tel:82-55-360-3450, Fax:82-55-360-3449

This study was supported by Research Institute for Convergence of biomedical science and technology Grant (30–2014–003), Pusan National University Yangsan Hospital

Received 3 July 2014 Revised 29 July 2014 Accepted 5 August 2014

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

In general radiotherapy, mega-voltage (MV) x-ray images are widely used as the unique method to verify radio-therapeutic fields. But, the image quality of MV images is much lower than that of kilo-voltage x-ray images due to scatter interactions. Since 1990s, studies for the scatter correction have performed with digital-based MV imaging systems. In this study, a novel method for the scatter correction is suggested using scatter to primary ratio (SPR), instead of conventional methods such as digital image processing or scatter kernel calculations. We measured two MV images with and without a solid water phantom describing a patient body with given imaging conditions, and calculated un-attenuated ratios. Then, we obtained SPR distributions for the scatter correction. For experimental validation, a line-pair (LP) phantom using several Al bars and a clinical pelvis MV image was used. As the result, scatter signals of the LP phantom image were successfully reduced so that original density distribution of the phantom was restored. Moreover, image contrast values increased after SPR correction at all ROIs of the clinical image. The mean value of increases was 48%. The SPR correction method suggested in this study has high reliability because it is based on actually measured data. Also, this method can be easily adopted in clinics without additional cost. We expected that the SPR correction can be an effective method to improve the quality of MV image guided radiotherapy.

Keywords: Scatter to primary ratio, MV image, Scatter correction, Image guided radiotherapy

References

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Fig. 1.

Pelvis image comparison of (a) kV and (b) MV imaging modalities.

Fig. 2.

Experimental conditions for (a) un-attenuated signals and (b) attenuated signals by the phantom.

Fig. 3.

(a) The comparison of horizontal SPR profiles for different phantoms having four thicknesses, and (b) a SPR map measured using the phantom with the thickness of 20 cm.

Fig. 4.

The line pair phantom images with (a) no correction and (b) SPR correction. The horizontal line profiles (see dashed lines in (a) and (b)) were compared in (c).

Fig. 5.

The comparison of (a) un-corrected and (b) corrected MV projection images of the pelvis. Five ROIs were marked on both images for the contrast evaluation.

Fig. 6.

The comparison of un-corrected and corrected histograms for (a) the line pair phantom and (b) the pelvis imag

Table 1.

The un-attenuated ratio water phantoms with four diffe os of 6MV x-ray beams for solid-erent thicknesses (calculated).

t (cm)	e^−μeff⋅^t
5	0.7374
10	0.5499
15	0.4143
20	0.3151

Table 2.

The normalized contrast values of image patches of five ROIs (Δ_C: contrast difference of no corrected and SPR corrected ROIs).

	C_ROI		Δ_C
	no correction	SPR correction	Δ_C
ROI1	0.111	0.250	0.139
ROI2	0.167	0.194	0.027
ROI3	0.132	0.139	0.007
ROI4	0.118	0.181	0.063
ROI5	0.139	0.222	0.083
Mean	0.133	0.197	0.064

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