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. 2016 May 8;17(3):14-24.
doi: 10.1120/jacmp.v17i3.5611.

Comparison of surface matching and target matching for image-guided pelvic radiation therapy for both supine and prone patient positions

Hui Zhao  1 , Brian Wang, Vikren Sarkar, Prema Rassiah-Szegedi, Y Jessica Huang, Martin Szegedi, Long Huang, Victor Gonzalez, Bill Salter
Affiliations

Comparison of surface matching and target matching for image-guided pelvic radiation therapy for both supine and prone patient positions

Hui Zhao et al. J Appl Clin Med Phys. .

Abstract

We investigate the difference between surface matching and target matching for pelvic radiation image guidance. The uniqueness of our study is that all patients have multiple CT-on-rails (CTOR) scans to compare to corresponding AlignRT images. Ten patients receiving pelvic radiation were enrolled in this study. Two simulation CT scans were performed in supine and prone positions for each patient. Body surface contours were generated in treatment planning system and exported to AlignRT to serve as reference images. During treatment day, the patient was aligned to treatment isocenter with room lasers, and then scanned with both CTOR and AlignRT. Image-guidance shifts were calculated for both modalities by com-parison to the simulation CT and the differences between them were analyzed for both supine and prone positions, respectively. These procedures were performed for each patient once per week for five weeks. The difference of patient displace-ment between AlignRT and CTOR was analyzed. For supine position, five patients had an average difference of displacement between AlignRT and CTOR along any direction (vertical, longitudinal, and lateral) greater than 0.5 cm, and one patient greater than 1 cm. Four patients had a maximum difference greater than 1 cm. For prone position, seven patients had an average difference greater than 0.5 cm, and three patients greater than 1 cm. Nine patients had a maximum difference greater than 1 cm. The difference of displacement between AlignRT and CTOR was greater for the prone position than for the supine position. For the patients studied here, surface matching does not appear to be an advisable image-guidance approach for pelvic radiation therapy for patients with either supine or prone position. There appears to be a potential for large alignment discrepancies (up to 2.25 cm) between surface matching and target matching.

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Figures

Figure 1
Figure 1
Snapshots of AlignRT real‐time surface tracking for supine position setup. The purple images were body surface contours automatically generated from corresponding simulation CT images. The green images were the real‐time tracking data, which were superimposed on the CT body contours to show the level of agreement. The range of the green image was preset as region of interest.
Figure 2
Figure 2
(Top row) AlignRT shifts along the vertical, longitudinal, and lateral directions from patient's tattoo aligned with linac isocenter lasers for all 10 patients over five‐week treatment. The figure on the left is for supine patient position, and the figure on the right is for prone patient position. (Middle row) CTOR shifts along the vertical, longitudinal, and lateral directions from patient's tattoo aligned with linac isocenter lasers. (Bottom row) AlignRT and CTOR shifts along the vertical, longitudinal, and lateral directions from patient's tattoo aligned with linac isocenter lasers. For each patient, the left group data are the AlignRT shifts, and the right group data are the CTOR shifts.
Figure 3
Figure 3
Comparison of simulation CT and CTOR after image registration for Patient #4 (supine), the fourth week of treatment. Images shown are the axial, sagittal, and frontal CT images for simulation CT (a), CTOR (b) and a blend view of simulation CT and CTOR after image registration (c).
Figure 4
Figure 4
Comparison of simulation CT and CTOR after image registration for Patient #4 (prone), the fourth week of treatment. Images shown are the axial, sagittal, and frontal CT images for simulation CT (a), CTOR (b) and a blend view of simulation CT and CTOR after image registration (c).
Figure 5
Figure 5
Comparison of simulation CT and CTOR after image registration for Patient #10 (prone), the third week of treatment. Images shown are the axial, sagittal, and frontal CT images for simulation CT (a), CTOR (b) and a blend view of simulation CT and CTOR after image registration (c).
Figure 6
Figure 6
Comparison of simulation CT and CTOR after image registration for Patient #10 (supine), the third week of treatment. Images shown are the axial, sagittal, and frontal CT images for simulation CT (a), CTOR (b) and a blend view of simulation CT and CTOR after image registration (c).
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