Using the axillary vein & artery to validate metrics for high tangents within the POSNOC trial
Roeum Butt,
United Kingdom
PD-0321
Abstract
Using the axillary vein & artery to validate metrics for high tangents within the POSNOC trial
Authors: Roeum Butt1, Rushil Patel1, Chloe Brooks1, Gareth Jackson1, David Dodwell2, Elizabeth Miles1, Amit Goyal3
1National Radiotherapy Trials Quality Assurance Group, Mount Vernon Cancer Centre , Radiotherapy Physics, London, United Kingdom; 2Oxford University Hospital, Oncology, Oxford, United Kingdom; 3Royal Derby Hospital, Oncoplastic Breast Surgery , London, United Kingdom
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Purpose or Objective
The purpose of this study was to validate the use of simple anatomical bony landmarks to define high tangents in breast radiotherapy for the UK-ANZ POSNOC (ISRCTN54765244) randomised trial of axillary treatment in women with early stage breast cancer. A comprehensive radiotherapy quality assurance (QA) programme was implemented for the trial. As part of this QA process the patients randomised to the ‘no axillary treatment’ arm were monitored for high tangent use.
Material and Methods
Anatomical bony landmarks used for this study are the base of clavicle (BOC) and head of humerus (HH). Simple descriptive metrics; cranial, caudal and proximal positioning of the superior tangent border in relation to the BOC were recorded in addition to a measurement from the inferior most extent of the HH to the superior aspect of the tangents. The ACOSOG Z0011 trial defined high tangents as superior tangent border ≤2 cm from humeral head. The axillary vein & artery (AX) were outlined according to the 2016 ESTRO consensus guideline on target volume delineation for elective radiation therapy for early stage breast cancer (figure 1). A binomial logistic regression analysis was used to measure the reliability of the results seen and robustness for the metrics used when accounting for amount of AX within the field.
Results
BOC metric, HH measurements and AX outlining was completed for 119 patients.
Use of high tangents was confirmed if any of the tangential field overlapped with the AX volume. The cranial (p<0.003) & caudal (p<0.010) metrics were good predictors for defining high tangents, however proximal (p<0.214) was not significant.
The results also suggest that distance from HH is a good predictor (figure 2) for the amount of AX within the field p<0.001.
The logistic regression model accuracy was 90%.
Conclusion
The study suggests that for the POSNOC trial, the position of the superior border of the tangential fields, relative to BOC, can be used as a time efficient QA tool for defining high tangents. This simple approach can be used for future trials as part of the radiotherapy QA programme. The distance from HH can be used to predict amount of AX within the field which may suggest unintentional treatment of the axillary lymph nodes.
Further work may still be required to investigate the robustness of these metrics and to ensure their reliability for future radiotherapy trials QA.