Intensity-Modulated Radiotherapy for Breast Cancer: Advances in Whole and Partial Breast Treatment

Intensity-modulated radiotherapy (IMRT) can improve dose distributions through the treated breast and also reduce radiation doses to adjacent normal tissues including the contralateral breast, heart and lung with appropriate planning. Analyses demonstrate that the quality of radiation dose distribution does affect clinical results, and that outcomes are enhanced through improved planning and dose delivery methods. To achieve these results, it is essential to carefully define tissue volumes for treatment or avoidance, select technologies that can potentially conform fields to those volumes, use comprehensive planning methods, and assess their results in terms of objective dose constraints. IMRT can also be used to boost the region of tumor excision concurrently with whole breast treatment, an approach now being evaluated in on-going clinical studies. Partial breast irradiation (PBI) has been proposed as an alternative to irradiation of the entire breast for early-stage breast cancer patients undergoing breast conservation treatment. Numerous single institution phase II studies have demonstrated promising results, and the American Society of Radiation Oncology (ASTRO) has defined a suitable group of low-risk patients for PBI treatment off protocol at this time. IMRT has been proposed as an alternative to 3D conformal radiotherapy (3DCRT) for external beam PBI to improve the dose conformality to target volumes and the sparing of normal tissues. There are an increasing number of institutions evaluating and using IMRT instead of 3DCRT for PBI because of the potential treatment advantages for the breast cancer patient.