ABSTRACT
The 3D-CT planning allows dosimetric evaluation of the breast not just in a single plane but at all levels. Achieving a homogeneous dose distribution in the breast is challenging because its contour changes in both craniocaudal and sagittal
planes. To compensate for the changing contour of the breast, wedge-shaped beam attenuators are positioned in the radiation fi eld, thus attenuating the beam from a minimum along the chest wall to a maximum in the subareolar region. They compensate for the diminishing tissue volume from the chest wall to the apex of the breast by differentially reducing the intensity of the beam from the chest wall to the nipple-areola complex. Wedges compensate for dose heterogeneity in two dimensions (2D), normally optimized in the central plane of the breast. While 2D planning can achieve excellent dose homogeneity along the central axis of the breast, dose homogeneity is poorer in the upper and lower regions resulting in marked “hot spots” in areas of the breast away from the central axis (11). Tangential beam plans can be optimized to ensure that signifi cant volumes of the breast do not exceed 105% of the prescribed dose. IMRT in which the X-ray beam is dynamically collimated to modifi ed its infl uence, allows the dose to be “painted” to the breast/chest wall and peripheral lymphatics while minimizing the passage of unwanted dose to critical adjacent structures. IMRT attenuates the radiation beam differentially in multiple planes, improving homogeneity throughout the breast. The “fi eld-infi eld” technique [also called “fi eld in fi eld forward planned intensity-modulated radiotherapy (FiF-IMRT)] enables areas of suboptimal dose homogeneity to be improved, reducing “hot spots” such as the inframammary fold and the thin area of the breast close to the nipple-areola complex (11,12). In a comparison of dosimetry in 201 breast cancer patients treated with FiF-IMRT and 131 patients treated with a standard wedged 3D technique for postoperative treatment of wholebreast (according to breast size and supraclavicular node irradiation) homogeneity of dose distribution signifi cantly improved with forward IMRT, irrespective of breast size or supraclavicular nodal irradiation (13). Scattered dose to the contralateral breast is also reduced with FiF-IMRT techniques (14). In a randomized trial comparing acute breast toxicity after conventional 3D CT planning with IMRT in 358 patients with early breast cancer treated by BCS and whole-breast irradiation, moist desquamation and breast pain were signifi cantly less with IMRT and associated with improved quality of life and better dose homogeneity compared with standard RT (15). Longer term follow-up will be needed to see if late radiation changes such as breast fi brosis are also reduced by IMRT. This seems likely since a United Kingdom (UK) randomized trial comparing 2D wedges to 3D IMRT showed at fi ve years a signifi cant improvement in the breast appearance (16). Another advantage of the improved dose homogeneity of IMRT is that it may diminish the risk of breast fi brosis and impaired cosmesis from large fraction sizes used in accelerated whole-breast
axilla (pN0), the equivalent risk reductions were from 31% to 15.6%, absolute reduction in recurrence of 15.4% (95% CI 13.2-17.6, 2p = <0.00001), and an absolute reduction in mortality of 3.3% from 20.5% to 17.2%. There were far fewer women with pathologically involved axillary nodes (pN1) (1050) in whom the 10-year risk reduction was higher at 21.2% (95% CI 14.5-27.9, 2p = <0.00001) from 63.7% to 42.5% with an 8.5% reduction in 15-year breast cancer mortality (95% CI 1.8-15.2, 2p = 0.01) from 51.3% to 42.8%. The 10-year risks of any recurrence varied with age, tumor size, grade, ER status, use of tamoxifen, and extent of surgery as shown in Figure 41.1. While the proportional reduction in any recurrence is the same for younger and older women, the absolute reduction in risk is substantially lower for women over the age of 70, although the older group is much less represented. This is largely due to historical exclusion of patients over the age of 70 in many trials. The most marked reduction in recurrence after RT was achieved in ER-positive patients not receiving tamoxifen. The differences in risk of breast cancer mortality according to reduction in fi rst recurrence for different risk groups according to pathological nodal status are shown in Figure 41.2. Patients with pN0 disease were ascribed a 10-year absolute reduction in risk of recurrence (large, intermediate, and lower) based on their characteristics and features of the trial in which they participated.
