Evaluation of the performance of deformable image registration between planning CT and CBCT images for the pelvic region: comparison between hybrid and intensity-based DIR.

Yoshiki Takayama,Noriyuki Kadoya,Kiyokazu Sato,Ken Takeda,Keiichi Jingu,Kousei Fujiwara,Kengo Ito,Suguru Dobashi,Yuya Miyasaka,Takaya Yamamoto,Mizuki Chiba

doi:10.1093/jrr/rrw123

Abstract

This study aimed to evaluate the performance of the hybrid deformable image registration (DIR) method in comparison with intensity-based DIR for pelvic cone-beam computed tomography (CBCT) images, using intensity and anatomical information. Ten prostate cancer patients treated with intensity-modulated radiation therapy (IMRT) were studied. Nine or ten CBCT scans were performed for each patient. First, rigid registration was performed between the planning CT and all CBCT images using gold fiducial markers, and then DIR was performed. The Dice similarity coefficient (DSC) and center of mass (COM) displacement were used to evaluate the quantitative DIR accuracy. The average DSCs for intensity-based DIR for the prostate, rectum, bladder, and seminal vesicles were 0.84 ± 0.05, 0.75 ± 0.05, 0.69 ± 0.07 and 0.65 ± 0.11, respectively, whereas those values for hybrid DIR were 0.98 ± 0.00, 0.97 ± 0.01, 0.98 ± 0.00 and 0.94 ± 0.03, respectively (P < 0.05). The average COM displacements for intensity-based DIR for the prostate, rectum, bladder, and seminal vesicles were 2.0 ± 1.5, 3.7 ± 1.4, 7.8 ± 2.2 and 3.6 ± 1.2 mm, whereas those values for hybrid DIR were 0.1 ± 0.0, 0.3 ± 0.2, 0.2 ± 0.1 and 0.6 ± 0.6 mm, respectively (P < 0.05). These results showed that the DSC for hybrid DIR had a higher DSC value and smaller COM displacement for all structures and all patients, compared with intensity-based DIR. Thus, the accumulative dose based on hybrid DIR might be trusted as a high-precision dose estimation method that takes into account organ movement during treatment radiotherapy.

Highlights

Development of the intensity-modulated radiotherapy (IMRT) technique has enabled the tailoring of dose distributions to complex target shapes and allowed us to increase the dose to the planning target volume (PTV) and decrease the dose to organs at risk [1,2,3,4,5,6]
The average Dice similarity coefficient (DSC) for intensitybased deformable image registration (DIR) for the prostate, rectum, bladder, and seminal vesicles were 0.84 ± 0.05, 0.75 ± 0.05, 0.69 ± 0.07 and 0.65 ± 0.11, respectively, whereas those values for hybrid DIR were 0.98 ± 0.00, 0.97 ± 0.01, 0.98 ± 0.00 and 0.94 ± 0.03, respectively. These results showed that hybrid DIR had a higher DSC value than intensitybased DIR for all structures
Average center of mass (COM) displacements for intensity-based DIR for the prostate, rectum, bladder, and seminal vesicles were 3.1 ± 1.5, 4.1 ± 1.4, 7.9 ± 2.2 and 3.6 ± 1.2 mm, whereas those values for hybrid DIR were 0.1 ± 0.0, 0.3 ± 0.2, 0.2 ± 0.1 and 0.6 ± 0.6 mm, respectively (P < 0.05). These results showed that hybrid DIR had smaller COM displacements than intensity-based DIR for all structures

Summary

Introduction

Development of the intensity-modulated radiotherapy (IMRT) technique has enabled the tailoring of dose distributions to complex target shapes and allowed us to increase the dose to the planning target volume (PTV) and decrease the dose to organs at risk [1,2,3,4,5,6]. The intricate dose distribution is more susceptible to position and anatomy uncertainties of the tumor and normal tissues during the course of treatment radiotherapy [7,8,9,10]. Previous studies have shown that pelvic anatomy such as the prostate, rectum, bladder, or seminal vesicles change during the course of radiotherapy [11,12,13,14,15]. These interfraction variations in prostate IMRT cause dosimetric effects [16].

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