Surgical Clips In Breast Tumor Cavity Photon Boosts: Impact On Ctv Size, And Utility In Image Verification Using Non-Orthogonal Kv Imaging

Surgical clips are important in guiding the delineation of the tumor cavity CTV in adjuvant breast irradiation[i]. They also serve as markers for accurate image verification. With the advent of IMRT and potential to deliver simultaneous integrated boost treatment, accurate image verification has become a more pertinent issue. In addition, the size of the boost CTV can have long term implications with regards to breast lymphedema, fibrosis and overall cosmetic outcome. We compared the CTV sizes of patients with clips and without clips. We report on 60 patients receiving adjuvant breast irradiation with a photon boost to the tumor cavity using non-orthogonal kv imaging, matching to surgical clips for image verification. 60 patients received sequential photon boosts as part of adjuvant breast radiation therapy. Non-orthogonal kV images were acquired as described by Willis et al[ii] on fraction one and two of the boost. Image matching was based on the pectoral clip or chest wall, if clips were not present, with 5mm tolerance. If tolerance was exceeded, the necessary shift in all directions was applied, and imaging was performed on subsequent fractions. The mean PTV breast volume was 1027cm3 (range 371.7cm3 - 2574.6cm3) and the mean CTV boost volume was 23.9cm3 (range 3.1cm3-136.9cm3). 21 patients did not have surgical clips, and 39 did. The mean CTV volume of patients with clips was 28.2cm3, which was significantly larger than the mean CTV volume of patients without clips, (17.4cm3) (p < 0.04). Of the patients with clips, 36% required shifts on the first image. Of the patients without clips, 15.8% required shifts on the first image. Patients requiring at least one move had a significantly larger mean CTV (32.9cm3) compared to patients not requiring a move (17.3 cm3) (p < 0.005). Non-orthogonal kv-imaging matching to surgical clips or chest wall provides an accurate and efficient means of image verification. The use of clips in the delineation of tumor bed boost CTVs provides greater accuracy in identifying the tumor bed, but results in significantly larger CTVs. We postulate that this may result in increased late toxicity. Daily use of image verification, with 0mm tolerance may allow revision of PTV expansions and hence mitigate the potential impact of larger CTVs.