Localisation of Tumor Bed and Its Impact on Dosimetry for Tumor Bed Boost Irradiation in Patients Treated With Breast Conserving Surgery Using Different Techniques

Introduction:

For patients with early stage invasive disease, surgery can either be a breast conserving resection of the primary tumor or a mastectomy. Several randomized prospective clinical trials have indicated that breast conserving surgery with whole breast radiation provides long term outcomes equivalent to those of mastectomy. The goal of breast conserving surgery is to remove the primary tumor with surgical margins that are free from invasive or in-situ disease. A secondary goal is to provide the best possible cosmetic outcome without retraction, nipple displacement, or excess volume loss from the procedure. For some women with larger breasts, oncoplastic surgery can be used in which local tissue rearrangements are performed at the time of surgical resection to maintain optimal breast aesthetics

Radiation is essential component of breast conserving therapy. The use of RT improved recurrence free, breast cancer specific survival and overall survival in both patients with negative and positive axillary lymph nodes in the most recent meta-analysis of Early Breast Cancer Trialists Collaborative Group(EBCTCG)5 which included trials begun before 2000.It included data from 42080 patients with breast cancer treated in 78 clinical trials that investigated loco regional treatments between 1952 and 1995.Among those patients were 7311 patients treated in 10 trials comparing radiation vs no radiation after breast conserving surgery and 9933 patients treated in 25 trials comparing radiation vs no radiation after modified radical mastectomy. In the trials that investigated radiation as a component of breast conserving therapy, radiation was shown to reduce the risk of local recurrence by two thirds and to improve the absolute 15 year overall survival rate by 6% (41% versus 35%).Similarly for patients with positive lymph nodes treated with modified radical mastectomy, radiation reduced the risk of loco-regional recurrence rate by 21% at 15 years(29% versus 8%), which was associated with a 5% decrease in the 15 year breast cancer mortality rate (60% versus 55%).A more recent update of the analyses continues to demonstrate loco-regional and survival advantages for radiation therapy

Even if surgical margins are negative after BCS, 30-40% risk of microscopic tumor cells in tumor bed. Most recurrences (65-80%) are located in vicinity of tumor bed as shown in EORTC6 trial and NSABP-06 trial. It is therefore important to ensure the tumor bed lies well inside the treatment volume encompassed by tangential fields to whole breast and subsequent tumor bed boost. There is also a pathological basis for giving boost to tumor bed-residual tumor foci have been reported in 1-2 cm in around 20-25% patients/ histopathological specimens.

The EORTC 22881-108827 trial studied the effect of addition of a boost dose on the primary tumor bed after lumpectomy in breast conserving treatment for breast cancer.It was found that 47% of local recurrences were in primary tumor bed, at 10 years, the cumulative incidence of local recurrence was 10.2% versus 6.2% for the 0 Grays and the 16 Grays boost groups (p< 0.0001).