neck tumor Proton particles do not deposit exit dose, so proton therapy can spare normal tissues far from the tumor. This is particularly useful for head and neck tumors because of the anatomic constraints found in nearly all cancers in this region. The dosimetric advantage unique to proton therapy translates into toxicity reduction. For recurrent head and neck cancer requiring reirradiation, proton therapy is able to maximize a focused dose of radiation to the tumor while minimizing dose to surrounding tissues, hence a minimal acute toxicity profile, even in patients who got multiple prior courses of radiotherapy. Left-side breast cancer When breast cancer — especially in the left breast — is treated with conventional radiation, the lung and heart, which are near the left breast, are particularly susceptible to photon radiation damage. Such damage can eventually cause lung problems (e.g. lung cancer) or various heart problems. Depending on location of the tumor, damage can also occur to the esophagus, or to the chest wall (which can potentially lead to leukemia). One recent study showed that proton therapy has low toxicity to nearby healthy tissues and similar rates of disease control compared with conventional radiation. Other researchers found that proton pencil beam scanning techniques can reduce both the mean heart dose and the internal mammary node dose to essentially zero. Small studies have found that, compared to conventional photon radiation, proton therapy delivers minimal toxic dose to healthy tissues and specifically decreased dose to the heart and lung. Large-scale trials are underway to examine other potential benefits of proton therapy to treat breast cancer. Lymphoma Though chemotherapy is the main treatment for lymphoma, consolidative radiation is often used in Hodgkin lymphoma and aggressive non-Hodgkin lymphoma, while definitive treatment with radiation alone is used in a small fraction of lymphoma patients. Unfortunately, treatment-related toxicities caused by chemotherapy agents and radiation exposure to healthy tissues are major concerns for lymphoma survivors. Advanced radiation therapy technologies such as proton therapy may offer significant and clinically relevant advantages such as sparing important organs at risk and decreasing the risk for late normal tissue damage while still achieving the primary goal of disease control. This is especially important for lymphoma patients who are being treated with curative intent and have long life expectancy following therapy. Prostate cancer In prostate cancer cases, the issue is less clear. Some published studies found a reduction in long term rectal