Phase II Protocol of Proton Therapy for Partial Breast Irradiation in Early Stage Breast Cancer

Current standard of care for early stage breast cancer is mastectomy or breast conserving therapy with whole breast irradiation following lumpectomy. However, studies of breast cancer recurrence have demonstrated the majority of tumors to recur in or adjacent to the original tumor site. The question has thus been raised as to whether radiation to the whole breast is necessary or justified. Limiting radiation to the area of the original tumor may reduce acute and long-term skin and organ toxicities while making radiation therapy more convenient and less expensive. Several clinical trials are underway comparing partial breast irradiation (PBI) to whole breast irradiation. Numerous centers are offering partial breast irradiation outside of clinical trials as well, despite the lack of long-term safety and efficacy data on PBI. Available PBI methods include brachytherapy, in which catheters or balloons are surgically inserted to deliver radiation therapy to the lumpectomy cavity, and conventional external beam radiation therapy, or EBRT. External beam photon therapy is attractive for its non-invasive nature and ability to deliver a more homogenous dose distribution compared to brachytherapy, however it also delivers a greater radiation dose to surrounding normal breast tissue.Proton therapy has the capacity to provide the same advantages as photon EBRT while minimizing dose to normal surrounding tissue. Clinical data on PBI with protons is minimal, however, leaving many questions unanswered. The impetus behind this protocol is to address these gaps by further investigating the feasibility, safety, and efficacy of proton therapy for partial breast irradiation.