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Proton Beam Therapy

Proton Therapy Basics

Proton beam therapy (PBT) is a U.S. FDA approved technology that delivers external beam radiation with positively charged atomic particles to tumors. Due to its unique radiation dose deposition properties, PBT delivers radiation to tumors while reducing radiation exposure to surrounding normal tissues. This confers a clinical advantage for some patients compared to conventional X- ray (photon) treatment.

Proton Therapy Center

Our physicians are UW Medicine Department of Radiation Oncology faculty and have trained and worked at some of the best proton therapy centers nationwide, including Harvard, MD Anderson, University of Pennsylvania and Loma Linda.

The Seattle Cancer Care Alliance Proton Therapy Center is equipped with the most advanced cutting-edge proton therapy technology available, a highly skilled medical professional team, and provides a supportive environment for exceptional and personalized patient care, multiple clinical trials and latest research-based cancer therapies.

Children and Proton Therapy

Proton therapy is a particularly important treatment option for children because their higher vulnerability to the effects of any radiation. Children can experience more serious short-term toxicity and more long-term side effects, such as developmental and growth delays, solid organ damage and new malignancies. Proton therapy may minimize these risks.

Second Malignancies

As powerful a tool as radiation is for the treatment of cancer, radiation exposure to normal tissues can cause secondary cancers. In fact, for some cancers, such as retinoblastoma, the most likely cause of death after radiotherapy is from a second malignancy. The Massachusetts General Hospital recently reported long-term outcome on their retinoblastoma patients treated with protons, showing significant reduction in second malignancies with protons.

Role of Proton therapy by Cancer Site

Cancer Type
Clinical Rationale for Consideration of Protons

Base-of-Skull, Spine

Proton therapy “wraps” the radiation dose distribution around the spinal cord, keeping dose levels within tolerance while treating the tumor to a considerably higher dose than can be delivered by standard X-ray radiotherapy.

Rutz HP; et al. Int.J. Radiat. Oncol. Biol. Phys. 2007;67(2):512-520.

· Glioma
· Meningioma
· Chordoma
· Chondrosarcoma
· Ependymoma

Radiation doses to normal brain tissue can be significantly decreased by using proton therapy rather than X-ray radiation treatment. This can decrease long-term risks of neurocognitive decline, pituitary dysfunction, hearing loss, and secondary malignancies. In certain cases, such as craniospinal irradiation, it can also decrease acute side effects of radiotherapy.

Merchant TE; et al. Pediatr Blood Cancer 2008;51:110-117. PMID: 18306274

Brown AP; et al. Int J Radiat Oncol Biol Phys 2013;86:277-284.

Breast Cancer

Normal tissues such as the heart, lung and contralateral breast receive significantly lower radiation dose with the use of proton therapy. This is particularly the case with locally advanced breast cancers. In many cases with X-ray treatment, the prescribed dose to target regions (chest wall, breast, lymph nodes) is compromised to meet dose constraints to surrounding, normal organs.

MacDonald SM et al. Int J Radiat Oncol Biol Phys. 2013 Jul 1;86(3):484-90.

MacDonald SM et al. Radiat Oncol. 2013 Mar 24;8:71.

Fagundes MA et al. Int J Radiat Oncol Biol Phys. 2013 Supplement;87(2S):S245.

Gastrointestinal Cancers
· Esophagus
· Pancreas
· Liver
· Rectum
· Anus

Combined modality treatment of many GI cancers often carries significant toxicities. Preliminary data suggest that protons may reduce severe GI side effects and complications related to chemoradiotherapy. Data in primary liver cancers demonstrate protons may allow for safe radiation dose escalation with a shortened course of radiation and without the need for concurrent chemotherapy.

Lin SH et al. Int J Radiat Oncol Biol Phys. 2013 Jul 1;83(3):e345-51

Nichols RC et al. Acta Oncol. 2013 Apr;52(3):498- 505

Mizumoto M et al. Int J Radiat Oncol Biol Phys. 2011 Nov 15;81(4):1039-45

Head and Neck

Protons may offer substantial reduction in dose delivery to normal tissue structures resulting in a lower risk of significant side effects such as blindness, dry eye and dry mouth, and secondary malignancies

Steneker M; et al. Radiotherapy and Oncology 2006;80:263-267.

Van de Water, et. al., Oncologist, 2011; 16(3): 366- 377.


Given the favorable prognosis of lymphoma (e.g. Hodgkin’s lymphoma), the current goal is to reduce treatment-related toxicity including cardiac, endocrine, and secondary malignancy risks. Preliminary data suggest that protons for mediastinal involvement are associated with similar rates of local control while delivering less dosage to the heart, lungs, breast, and total body.

Hoppe BS et al. Int J Radiat Oncol Biol Phys. 2014; 89(5):1053-1059.

Maraldo MV et al. Ann Oncol. 2013; 24:2113-2118.

Chera BS et al. Int J Radiat Oncol Biol Phys. 2009; 75(4): 1173-1180.

Ocular (Uveal) Melanoma

Protons have been used for more than 30 years to minimize eye removal and spare critical structures of the globe. Control rates are greater than 95% with long-term survival comparable to patients treated by removal of the diseased eyes. Retaining the eye provides the potential for maintaining sight (Treatment availability expected in early 2015).

Henderson, MA; et al. Technol Cancer Res Treat. 2006;5(4):411-419.

Egger E; et al. Int. J. Radiat. Oncol. Biol. Phys. 2003;55(4):867-880.

Non-small-cell Lung Cancer

Radiation induced damage to surrounding critical normal tissues is a significant cause of mortality and morbidity with X-ray treatment of lung cancer. Protons have been shown to allow safe escalation of dose to tumor with reduced dose to heart and lung, a critical determinant of survival, compared with X-rays in patients with inoperable lung cancer.

Chang, J., et. al., Cancer, 2011; 117(20): 4707- 4713.

Ghosh S; et al. Eur. J. Cardiothorac. Surg. 2003;24(6):1002-1007.


Higher doses can be delivered to improve tumor control while protecting bladder and rectum from radiation. Studies show that protons can reduce radiation exposure to the bladder by about one-third and to the rectum by about half compared to intensity-modulated radiation (IMRT). Long- term outcomes of protons demonstrate a very low risk of major bladder or rectal complications.

Vargas C; et al. Int. J. Radiat. Oncol. Biol. Phys. 2008;70(3):744-751.

Slater, JD; et al. Int. J. Radiat. Oncol. Biol. Phys. 2004;59(2):348-352.

Mendenhall et al, Int J Radiat Oncol Biol Phys. 2014 Mar 1;88(3):596-602.

· Lymphoma
· Sarcomas

Compared to standard X-ray radiation therapy and IMRT, protons can provide less radiation dose to healthy and developing tissue in a child while treating the tumor just as effectively. Protons may also reduce risks of tumors caused by radiation.

Sethi RV; et al. Cancer. 2014 Jan 1;120(1):126-33.

Merchant T; et al. Pediatr Blood Cancer 2008;51:110–117

Vega R; et al. Cancer 2013;119:4299-307

Repeat radiation of recurrent tumors
· Head and Neck
· Lung
· Sarcoma
· Gastrointestinal

Patients who have had prior radiotherapy and have localized progression of their disease may require a second course of radiation to the same or nearby region to provide control of disease. These patients are at high-risk for severe radiation injury due to the cumulative dose to normal tissues. Protons may allow for delivery of tumoricidal doses to the area of progression while sparing surrounding tissues from additional radiation dose. Preliminary studies demonstrate the utility of protons in this clinical setting.

McAvoy SA, et al. Radiother Oncol. 2013 Oct;109(1):38-44.

McDonald MW, et al; Radiat Oncol. 2013 Jan 12;8:14.

Björk-Eriksson T, Ask A, Glimelius B.; Acta Oncol. 2005;44(8):918-20.

McDonald MW, Linton OR, Shah MV.; Int J Radiat Oncol Biol Phys. 2013 Dec 1;87(5):1107-14