Program Information

Position Verification in Breast Cancer Radiotherapy Using Tantalum Clips in the Lumpectomy Cavity

J van Santvoort*, M Van der Drift , J Kuipers , M Mast , J Van Egmond , H Struikmans , Haaglanden Medical Center, The Hague, Netherlands

Presentations

SU-E-J-201 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To find out whether tantalum surgical clips can be used for on-line position verification in treatment of the lumpectomy cavity (LC) in breast cancer patients. Tantalum is a high density metal that could be visible on Electronic Portal Images (EPIs) and be an affordable alternative to gold markers. Clips are considered more representative for the LC position than nearby bony structures.

Methods: In twelve patients the surgeon had placed 2 to 5 tantalum clips in the LC. The AP and lateral fields used for portal imaging, were adapted. In doing so, both bony structures and tantalum clips were visible on EPIs. The following analyses were performed:
1. Image degradation, with respect to delineating the CTV, of the axial CT slices by artefacts because of the tantalum clips was evaluated by a radiation oncologist;
2. The visibility of the tantalum clips on the EPIs was evaluated by four radiation therapists (RTTs);
3. Bony anatomy and tantalum clip matches were performed on the same images independently by two observers.

Results:
1. Delineation of the CTV by the radiation oncologist was not hampered by CT image artefacts because of the clips.
2. The mean score for visibility of the clips on the EPIs, analysed by the four RTTs, was 5.6 on a scale of 10 (range 3.9 - 8.0).
3. In total 12 patients with 16 fractions each were analysed. The differences between clip match and bone match are significant with a mean vector length of 5.2 mm (SD 1.9 mm) for the difference.

Conclusion: Results of matches on tantalum clips as compared to matches on bony structures differ substantially. Therefore clip matches can result in smaller CTV to PTV margins than bone matches. Visibility of the clips on EPIs is sufficient, so they can be an alternative to gold markers.

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