Prog Med Phys.  2014 Sep;25(3):143-150. 10.14316/pmp.2014.25.3.143.

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

Affiliations
  • 1Department of Radiation Oncology, Pusan National University Yangsan Hospital, Yangsan, Korea. jihonam@hanmail.net
  • 2Department of Radiation Oncology, Pusan National University Hospital, Busan, Korea.
  • 3Research Institute for Convergence of Biomedical Science and Technology, Pusan National University Yangsan Hospital, Yangsan, Korea.
  • 4Department of Radiation Oncology, Pusan National University School of Medicine, Busan, Korea.

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.

Keyword

Scatter to primary ratio; MV image; Scatter correction; Image guided radiotherapy

MeSH Terms

Humans
Pelvis
Radiotherapy
Water
Water

Figure

  • 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


Reference

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