The Impact of Bioabsorbable 3D Fiducial Marker on Radiation Dosimetry and Cosmesis in Early Stage Breast Cancer

Purpose/Objective(s)

In women with early-stage breast cancer, lumpectomy and breast radiation achieve comparable cancer control as mastectomy. After whole breast irradiation (WBI), a lumpectomy cavity directed supplemental dose ("boost') reduces ipsilateral breast recurrences yet can be associated with worse cosmesis. Moreover, identifying the lumpectomy cavity precisely is a practical challenge in radiation treatment planning. We hypothesized that the 3D marker would reduce Lumpectomy Gross volume (GTV) and clinical target volumes (CTV) and improve cosmesis.

Materials/Methods

After IRB approval, 248 charts of women with a pathological ductal carcinoma in situ or invasive carcinoma treated with post lumpectomy WBI between January 2016 and December 2017 were reviewed. All cases had delineation of gross lumpectomy volume (GTV), clinical (CTV) and planning (PTV) target volumes and as well Breast CTV and PTV for standard RT planning. Every case met dose goals and OAR constraints for approval. Pathological lumpectomy volume (PLV) was calculated from specimen dimensions in the gross portion of the pathology report. Median follow up is 27.33 months (range 4.1 – 45 months). Data was analyzed using linear regression to predict the clinical and dosimetric variables associated with target volumes and cosmetic outcomes.

Results

The mean age was 57.8 years. Twelve women (4.8%) underwent oncoplastic lumpectomy, 237 (95.2%) underwent lumpectomy only. Sixteen (6.27%) received neoadjuvant chemotherapy. Mean lumpectomy GTV was 31.45ml with the use of surgical clips (n = 99), 23.59 cm3 with the use of 3D Marker (n = 58), and 16.8 cm3 without any demarcation (n = 98) (P = 0.0001) and highly correlated with PLV (P = < 0.0001.) PLV was significantly associated with individual surgeon after adjustment for surgical marker used and overall pathological stage (P < 0.05). Surgical marker was not associated with PLV on univariate or multivariate analysis. Individual surgeons predicted the use of a surgical marker during surgery (P < 0.0001). Overall Breast cosmesis was Excellent/Good (EG) in242 (98%) and in 233 (93.3%) women at 6- and 12-months, respectively. A 3D marker was not associated with breast cosmesis; however, a negative association with Breast PTV Eval Structure Volume (P < 0.04) was observed after adjustment for surgeon, marker, overall pathologic stage, breast and boost dose, age at radiation, PLV and lump GTV.

Conclusion

In this analysis, the presence of a 3D marker significantly increases the size of a lumpectomy GTV compared to no demarcation and less than surgical clips. The lack of demarcation is worrisome for potential marginal misses – especially for partial breast irradiation. The usage of clips and/or 3D marker is strongly associated with the individual surgeon. The marker used did not influence cosmetic outcome but very few patients had less than EXC-good outcomes. A collaboration between radiation oncologists and surgeons may lead to increased usage of markers and improved lumpectomy delineation.