Breast IMRT: new tools leading to new vision.

In this issue, Vicini et al. (1) describe their experience implementing a comprehensive CT-based system for treatment planning and delivery for breast cancer. It is an elegant system that incorporates 3D treatment planning and IMRT delivery using a static, field-in-field technique for the routine irradiation of early-stage breast cancer patients undergoing conservation therapy. Their approach was impressive in achieving the stated goals of (1) optimizing whole breast radiation dose homogeneity, (2) avoiding unnecessary normal tissue irradiation, and (3) standardizing target volume coverage while not significantly increasing the amount of time required to plan or treat these patients. Because they could achieve uniform coverage of the target volume with treatment times equivalent to conventional wedged-tangent treatment techniques, they foresee the widespread implementation of this technology with minimal imposition on clinic resources and time constraints. Indeed, even their median planning time for the dosimetric calculation of the optimal multileaf collimator segments—at 45 min—is not significantly different from that required for more conventional techniques. The most profound consequence of these findings may not merely be the easy ability to implement a new technology but the impact that this new technology will have on its users—those of us who care for women with breast cancer. In December 2000, at The University of Texas M. D. Anderson Cancer Center, we, too, began using a similar system of IMRT for the planning and treatment of the intact breast. It took us some time to work out the mechanics of a planning process that could be used on a large-scale basis, but the plans were truly elegant and reproducible and this encouraged us to continue. We also found that the treatments were relatively straightforward to deliver after the initial validation process. My colleagues and I have the impression that the short-term effects of breast irradiation are improved, and this is currently being analyzed. However, the most important impact of this change has been on us—how we think about the breast and the operative bed as targets, in the designing of fields to encompass those targets, and a standardization of the dosimetric and dose-prescribing process. Let me explain. I am writing this editorial in June, having just returned from the American Board of Radiology oral examinations and the Radiation Therapy Oncology Group semiannual meeting. One of the opportunities afforded an examiner at the American Board of Radiology oral examinations is the opportunity to quickly sample technical details about the treatment approaches taught in our various training programs, using a qualified examinee’s responses. The following weekend at the Radiation Therapy Oncology Group meeting, I assisted Dr. Beryl McCormick as she reviewed simulation films and treatment plans for patients receiving breast irradiation on the ductal carcinoma-in-situ clinical trial (Radiation Therapy Oncology Group 98-04). This, too, provided me a broad and rapid, if not scientifically rigorous, sampling of current treatment techniques throughout the United States for the intact breast. First, it is my impression that the approach to treatment planning for the intact breast remains largely mechanistic and arbitrary, with little consideration of the unique circumstances of this specific tumor in each individual patient. The placement of field borders continues to be based primarily on relatively insignificant surface anatomic features, even when CT findings or tumor bed locations suggest these field borders be modified. All but the most confident and experienced radiation oncologists find it difficult to tailor the breast tangent fields to the individual patient’s circumstances and anatomy. Second, there are substantial variations in the dose actually delivered to the breast because of variations in the location of the prescription isodose line—anywhere from just off the deep field edge (even if this is in the lung) to halfway through the field (possibly near the surface of the breast). One of the consequences of this phenomenon is that the 45 Gy delivered in Boston may be almost identical to the 50 Gy delivered in Houston. Thus, even though we talk to one another as if we mutually understand what “breast irradiation” means, there may be surprising variations in how a patient is actually treated from center to center.