The dynamic tumor bed: volumetric changes in the lumpectomy cavity during breast-conserving therapy.
OBJECTIVE
To characterize the magnitude of volume change in the postoperative tumor bed before and during radiotherapy, and to identify any factors associated with large volumetric change.


METHODS
Thirty-six consecutive patients with early-stage or preinvasive breast cancer underwent breast-conserving therapy at our institution between June 2006 and October 2007. Computed tomography (CT) scans of the breast were obtained shortly after surgery, before the start of radiotherapy (RT) for treatment planning, and, if applicable, before the tumor bed boost. Postoperative changes, seroma, and surgical clips were used to define the tumor bed through consensus agreement of 3 observers (B.P., D.I., and J.L.). Multiple variables were examined for correlation with volumetric change.


RESULTS
Between the first and last scan obtained (median time, 7.2 weeks), the tumor bed volume decreased at least 20% in 86% of patients (n = 31) and at least 50% in 64% of patients (n = 23). From the postoperative scan to the planning scan (median time, 3 weeks), the tumor bed volume decreased by an average of 49.9%, or approximately 2.1% per postoperative day. From planning scan to boost scan (median interval, 7 weeks), the median tumor bed volume decreased by 44.6%, at an average rate of 0.95% per postoperative day. No single factor was significantly associated with a change in tumor bed volume greater than 20%.


CONCLUSIONS
The average postlumpectomy cavity undergoes dramatic volumetric change after surgery and continues this change during RT. The rate of change is inversely proportional to the duration from surgery. In this study no factors studied predicted large volumetric change.
Prendergast
Brendan
B
Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL 32610-0385, USA.
Indelicato
Daniel J
DJ
Grobmyer
Stephen R
SR
Saito
Anneyuko I
AI
Lightsey
Judith L
JL
Snead
Felicia E
FE
Morris
Christopher G
CG
Copeland
Edward M
EM
Mendenhall
Nancy P
NP
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy / Q000601:surgery*; D005260:Female; D006801:Humans; D015412:Mastectomy, Segmental; D008875:Middle Aged; D015588:Observer Variation; D012074:Remission Induction; D049291:Seroma / Q000000981:diagnostic imaging; D013525:Surgical Instruments; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden / Q000528:radiation effects