Accelerated partial breast irradiation (APBI) is a potentially attractive way to significantly reduce the duration of time a patient spends on an RT treatment course. The vast majority of in-breast cancer recurrences occur in the same quadrant as the primary tumor, whereas non-tumor bed recurrences and new primaries in the contralateral breast occur with similar frequency in irradiated and nonirradiated patients, suggesting that the primary efficacy of RT in early-stage disease is due to the eradication of residual disease in the region of the tumor bed.3,15–18 The majority of tumors may therefore be controlled by RT delivered only to the region of the tumor bed, sparing the remainder of the breast. APBI options include interstitial catheter-based brachytherapy, endocavitary brachytherapy, threedimensional (3-D) conformal RT and intra-operative RT (IORT).19–21 This article will focus on the two IORT options currently being investigated—partial mastectomy followed by IORT and vice versa.
IORT Delivered Following a Partial Mastectomy
Veronesi et al. were the first to report IORT to treat the excised tumor bed with a single dose of RT delivered in the operating room (OR).22,23 Briefly, their technique is as follows.A standard sentinel node procedure is performed followed by a standard quadrantectomy down to the pectoralis major fascia with at least 1cm of grossly tumor-free surgical margins. The breast parenchyma is then detached from the overlying skin as well as the underlying pectoralis muscle for 3–4cm. An aluminum-lead disk is then positioned on the surface of the pectoralis muscle to prevent irradiation of the chest wall. The breast parenchyma is temporarily re-approximated over the metal disk and the thickness of the breast tissue is measured with a ruler at multiple locations. The average thickness is then used to calculate the radiation dose. Single fraction radiation is performed with a mobile, linear accelerator (LINAC). The irradiation tube is placed directly onto the re-approximated breast tissue with the skin protected by a moist gauze. Following irradiation, the metal disk is removed and definitive surgical closure is completed.
Two hundred and thirty-seven patients with clinical T1, N0 breast cancers were treated with a quadrantectomy and axillary sentinel node procedure.23 With a median follow-up of 19 months, four (1.7%) patients developed mild or severe posttreatment breast fibrosis. Furthermore, three (1.4%) patients have developed an ipsilateral breast cancer and two (1%) patients have developed a contralateral breast cancer.23 With short-term follow-up, IORT appears to have an acceptable cosmetic result, but longer follow-up is necessary before conclusions regarding efficacy can be made.