Study Confirms Tissue Sparing Advantage of Proton Beam Radiotherapy
Tuesday, May 08, 2007
A report published in a recent issue of the Cancer Journal (March/April 2007, volume 13, no. 2, pp. 114-118) by physicians in the departments of radiation medicine and surgical oncology at Loma Linda University Medical Center (LLUMC) described development of a breast immobilization system and clinical technique to deliver partial breast irradiation with a proton beam, and also to compare dose distributions using proton therapy and conformal x-rays. Twenty patients were reported, each of whom had a lumpectomy to excise the primary cancer mass in the breast. The initial objective of the work was to establish a method of providing reproducible breast immobilization and eliminating respiratory motion. This was accomplished by devising a treatment brassiere, supplemented with the patient placed a cylindrical shell with the upper and lower body supported and immobilized with foam bead cushions and expandable foam. A treatment planning CT scan was followed by outlining the lumpectomy cavity on the CT and developing a clinical target volume by adding 1 cm in all dimensions around the cavity, for proton treatment. Radiation oncologists used two to four proton beams to deliver 40 cobalt Gray equivalents (CGE) in 10 daily fractions of 4 CGE, with several fields treated each day. No patient's treatment had to be interrupted for any reason. The procedure was well tolerated; patients reported no significant discomfort during treatment and acute toxicity was limited to occasional mild radiation dermatitis, which cleared upon cessation of treatment. Other patients are being treated similarly and analyses of long-term toxicity, local control, and survival are ongoing.
The study also compared proton and x-ray treatment plans. The investigators used dose-volume histogram (DVH) analyses to determine the volumes of normal breast tissue and skin treated with each technique. Proton plans were compared with two methods of photon partial breast irradiation, including reduced tangential fields and five-field conformal techniques. DVH analyses revealed that the use of proton beams provided a significant reduction in doses to the ipsilateral breast and skin while eliminating doses to the heart and lung tissues. The results led the investigators to conclude that protons can provide substantial normal tissue protection compared with the use of conformal x-rays when used for partial breast treatment. This confirms the experience that LLUMC researchers have observed with proton treatment of other cancers and disease processes. Research in this area will continue, and investigators expect the role of proton radiation therapy in breast cancer to expand in the future.