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

Abstract

IntroductionTo 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.MethodsTwenty‐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.ResultsThe 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.

Monitoring deep inspiration breath hold for left‐sided localized breast cancer radiotherapy with an in‐house developed laser distance meter system

“…that portal images underestimate the actual bony anatomy setup in breast cancer patients by 20%–50% in comparison to cone beam computed tomography (CBCT), whereas Batumalai et al. did not find any difference between the two imaging techniques 34, 35…”

Survey of image‐guided radiotherapy use in Australia

“…This is not surprising as EPI is reported to be adequate for breast RT, especially for techniques that are robust against setup uncertainties (e.g. simple tangential beams) . Most kV EPI was used in lung and gastrointestinal cancers possibly because kV EPI offers better image quality and lower imaging dose compared to MV EPI.…”

“…simple tangential beams). 22,23 Most kV EPI was used in lung and gastrointestinal cancers possibly because kV EPI offers better image quality and lower imaging dose compared to MV EPI. kV CBCT was mostly used in lung and H&N cancers as 3D visual of soft tissue anatomy are crucial for these sites.…”

AlignRT® and Catalyst™ in whole‐breast radiotherapy with DIBH: Is IGRT still needed?

“…The advantage of DIBH over FB in reducing the dose to the heart depends on BHL reproducibility during treatment . In breast‐only (N0) RT using DIBH, tangential images can be considered as the most important estimator for the accuracy of the actual treatment delivery if tangential beams are used . In previous studies, good inter‐fractional accuracy has been achieved in N0 DIBH with margins of 5–6 mm .…”