Comparison of setup accuracy of three different image assessment methods for tangential breast radiotherapy. Issue 4 (31st May 2016)

• Record Type: Journal Article
• Authors: Batumalai, Vikneswary; Phan, Penny; Choong, Callie; Holloway, Lois; Delaney, Geoff P.
• Is Part Of: Journal of medical radiation sciences. Volume 63:Issue 4(2016:Dec.)
• Page Start: 224
• Page End: 231
• Publication Date: 2016-05-31
• Subjects: Breast cancer -- cone‐beam computed tomography (CBCT) -- electronic portal image (EPI) -- radiotherapy -- setup errors; Radiology, Medical -- Periodicals; Radiology, Medical -- Australia -- Periodicals; Radiology, Medical -- New Zealand -- Periodicals; Radiotherapy -- Periodicals; Diagnostic imaging -- Periodicals; 616
• DOI: 10.1002/jmrs.180
• Languages: English
• ISSNs: 2051-3895

Abstract

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 ( Σ V = 3.7 mm, Σ U = 2.8 mm and σ V = 2.9 mm, σ U = 2.5) and CBCT‐B ( Σ V = 3.5 mm, Σ U = 3.4 mm and σ V = 2.8 mm, σ U = 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. Abstract : This study investigates the differences in setup errors measured with simulated electronic portal image (EPI), cone‐beam computed tomography (CBCT) bony matching and CBCT soft tissue matching in patients undergoing tangential breast radiotherapy (RT). The study's main finding was that there were no significant differences in setup errors that would make one modality to be considered superior over the other. This finding emphasises that CBCT is not justified for the routine setup of tangential breast RT and EPI should remain the standard of care.