Utility of a 3-Dimensional Bioabsorbable Marker for the Planning of Prone Breast Irradiation

Abstract

A 3-dimensional bioabsorbable marker (3-DM) can be implanted at the site of a lumpectomy during breast conserving surgery for delineation of the tumor site and to create a scaffolding for tissue rearrangement to improve aesthetic outcomes. The device provides a fixed, radio-opaque target for lumpectomy cavity boost or partial breast volumes. Prior studies have demonstrated that a 3-DM device reduces cavity volumes in patients treated in the supine position, potentially reducing short and long term toxicities. The goal of this study is to determine the impact of a 3-DM device on treatment planning in patients positioned prone for adjuvant radiation. A retrospective review was conducted of patients treated at a single institution between 1/2017 and 1/2019. All patients receiving adjuvant radiation in the prone position were identified. Lumpectomy cavity volumes (CTV) had been delineated at the time of treatment planning in all patients. For patients without a 3-DM in place, the CTV was defined using the operative report, pre-treatment imaging, surgical clips, and seroma. For patients with a 3-DM in place, the CTV was delineated as the device itself as a marker of the lumpectomy site. The t-test was used for statistical comparisons between groups. A total of 23 pTis-pT2N0 females with breast cancer were identified who had been treated in the prone position. Eleven patients had a 3-DM device in place, and 12 had no 3-DM in place. Patients with a 3-DM had a mean tumor size of 1.7 cm compared to 2.1 cm in the group without a 3-DM (p=0.43). The mean CTV volume in patients with a 3-DM device in place was 10.77 cc (Range: 5.47-23.86 cc) compared to 27.29 cc (Range: 5.10 – 64.64 cc) without a 3-DM in place, (p=.001). Of the 12 patients without a 3-DM, 5 patients (41.7 %) required re-simulation in the supine position for boost planning to allow improved access to the lumpectomy cavity and to reduce normal tissue doses. None of the patients with a 3-DM in place required repeat CT simulation. In patients with a 3-DM, mean lumpectomy CTV volume was reduced by approximately 60% in prone-positioned patients receiving adjuvant breast irradiation. Repeat simulation for repositioning of prone patients into the supine position to improve dosimetric parameters was avoided in all patients with a 3-DM.