PV QA 4 - Poster Viewing Q&A 4
Purpose/Objective(s): At breast conserving surgery (BCS), surgical clips are often placed in the tumor bed to mark the extent of the surgical cavity and to assist with radiation treatment planning (RTP). However, clip utilization, placement position, and number of clips used is variable, calling into question their reliability as fiducials. Recently, a bioabsorbable device (BD) with an imbedded array of titanium clips has become commercially available in various sizes that is sutured into the cavity following BCS. We hypothesized that using the BD for RTP will result in better localization and smaller target volumes; specifically for lumpectomy (gross tumor volume) GTV and thereby, minimize the boost volume and reduce toxicity.
Materials/Methods: The BD became available at our institution 1/2016. Eligible cases received post BCS WBI from 1/2016-12/2017 using 3D conformal radiation therapy (3DCRT) in the prone position. The following targets were routinely delineated at RTP: lump GTV, lump CTV, lump PTVeval, breast CTV, and breast PTVeval. Patients received 40-50 Gy to the breastPTVeval, 2-2.7 Gy fractions and 70% received a boost to the LumpPTVeval of 8-16 Gy in 2 Gy fractions. Descriptive statistics for variables were done and Wilcoxon signed-rank test was used to compare the median cc LumpGTV between groups.
Results: We identified 358 eligible cases (71 DCIS, 231 stage I, 55 stage II, 1 stage III) of women that received prone WBI during the study period; 177 (49.4%) right and 181 (50.6%) left-sided. The median BreastPTV is 1106 cc (IQR=763-1493 cc) and LumpGTV is 18.1 cc (IQR=11-30.1 cc). A BD was placed at BCS for 69 (19.3%) and the median LumpGTV is 15.9 cc (IQR=10.0-30.6 cc). Surgical clips were present in 149 (41.6%) and LumpGTV median is 21.9 cc (IQR=15.4-39.6 cc). No markers were present for 140 (39.1%) and median LumpGTV is 14.8 cc (IQR=8.1-22.9 cc). When compared, the median BD LumpGTV trends smaller than all others combined, 18.9 cc (IQR=11.1-29.4 cc) (p=0.08); is larger than those with clips (p=0.006) and not significantly different to those with no marker (p=0.845). The median LumpGTV for no marker was significantly smaller when compared to those with clips (p=0.0005).
Conclusion: Median LumpGTV volumes in patients with BD trended towards smaller when compared to all others and significantly smaller than patients who had surgical clips present for RTP. This may reflect the placement of the BD within the cavity or variability in clip placement around the cavity. Median LumpGTV in patients without a marker compared to those with clips was significantly smaller, concerning for possibly missing parts of the tumor cavity on RTP due to lack of easy visualization. BD use could potentially improve therapeutic ratio by facilitating visibility of the cavity and its localization for RTP. Future studies include evaluation of cosmesis and radiation toxicity with BD.
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