ESTRO 2023 - Abstract Book

S402

Sunday 14 May 2023

ESTRO 2023

all sequences, including vendor provided T1 and T2 weighted (W) images, were assessed using visual grading analysis (VGA) by 3 independent observers (2 Radiographers, 1 Oncologist). Results of phase 1 informed the positioning choice for phase 2. Sequences were also optimised. Phase 2 recruited 5 patients to undergo 2 scans in the same position, with the questionnaire and VGA repeated. Reproducibility of positioning was evaluated by an automatic bone (sternum, ribs, anterior-lateral chest wall) match of the 2 scans in Monaco (v5.40.01, Elekta AB, Sweden). Results Phase 1 participants, independent of vac-bag status, reported identical comfort scores at the start of the scan (27.5%). At the end of the scan, levels of discomfort were greater in the non vac-bag cohort than with the vac-bag (82.5% vs 52.5%). Paraesthesia in the arms, with pain in the shoulders was reported by 60% of participants without the vac-bag. VGA signified overall structure visibility was greater (very clear/clear) without the vac-bag compared to with (64.38% vs 56.48%). All participants preferred the vac-bag (Fig 1), which was selected for phase 2. Sequence parameters were modified to retain signal-to-noise ratio and spatial resolution (Table 1). Phase 2 patients reported a higher comfort level than the volunteers with the vac-bag indicating good tolerability. Paraesthesia in the hands with no other pain was described by 40% of patients. VGA determined overall conspicuity was better on the T1W sequence than T2W (58.3% vs 45%). Reproducibility of positioning was satisfactory, with overall mean displacements of -0.29, 0.57 and 0.50cm in the right-left, superior-inferior and antero-posterior directions respectively.

Conclusion The addition of the vac-bag provided participants with greater comfort and acceptable reproducibility, with little compromise to image quality. The tissue weighting selected for APBI daily online image registration is T1W. Work continues to investigate the dosimetric implication of this positioning.