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Comparative Study
. 2016 Dec;63(4):224-231.
doi: 10.1002/jmrs.180. Epub 2016 May 31.

Comparison of setup accuracy of three different image assessment methods for tangential breast radiotherapy

Vikneswary Batumalai  1   2   3 , Penny Phan  1 , Callie Choong  1 , Lois Holloway  1   2   3   4   5 , Geoff P Delaney  1   2   3   6
Affiliations
Comparative Study

Comparison of setup accuracy of three different image assessment methods for tangential breast radiotherapy

Vikneswary Batumalai et al. J Med Radiat Sci. 2016 Dec.

Abstract

Introduction: To compare the differences in setup errors measured with electronic portal image (EPI) and cone-beam computed tomography (CBCT) in patients undergoing tangential breast radiotherapy (RT). Relationship between setup errors, body mass index (BMI) and breast size was assessed.

Methods: Twenty-five patients undergoing postoperative RT to the breast were consented for this study. Weekly CBCT scans were acquired and retrospectively registered to the planning CT in three dimensions, first using bony anatomy for bony registration (CBCT-B) and again using breast tissue outline for soft tissue registration (CBCT-S). Digitally reconstructed radiographs (DRR) generated from CBCT to simulate EPI were compared to the planning DRR using bony anatomy in the V (parallel to the cranio-caudal axis) and U (perpendicular to V) planes. The systematic (Σ) and random (σ) errors were calculated and correlated with BMI and breast size.

Results: The systematic and random errors for EPI (ΣV = 3.7 mm, ΣU = 2.8 mm and σV = 2.9 mm, σU = 2.5) and CBCT-B (ΣV = 3.5 mm, ΣU = 3.4 mm and σV = 2.8 mm, σU = 2.8) were of similar magnitude in the V and U planes. Similarly, the differences in setup errors for CBCT-B and CBCT-S in three dimensions were less than 1 mm. Only CBCT-S setup error correlated with BMI and breast size.

Conclusions: CBCT and EPI show insignificant variation in their ability to detect setup error. These findings suggest no significant differences that would make one modality considered superior over the other and EPI should remain the standard of care for most patients. However, there is a correlation with breast size, BMI and setup error as detected by CBCT-S, justifying the use of CBCT-S for larger patients.

Keywords: Breast cancer; cone-beam computed tomography (CBCT); electronic portal image (EPI); radiotherapy; setup errors.

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Figures

Figure 1
Figure 1
Measurements taken for planning digitally reconstructed radiograph and simulated electronic portal image taken in V: cranio‐caudal distance and U: central lung distance planes.
Figure 2
Figure 2
Comparison of planning digitally reconstructed radiograph (left) with the simulated electronic portal image (right).
Figure 3
Figure 3
The percentage of errors exceeding 5 mm comparing (A) electronic portal image and cone‐beam computed tomography bone registration (CBCT‐B) in the V: cranio‐caudal distance and U: central lung distance planes, and (B) CBCT‐B and cone‐beam CT soft tissue registration (CBCT‐S) in the left–right (LR), superior–inferior and anterior–posterior directions.
Figure 4
Figure 4
Correlation between setup error and body mass index in left–right (LR), superior–inferior and anterior–posterior directions for cone‐beam computed tomography soft tissue registration.
See this image and copyright information in PMC

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