Proton Beam Radiation Therapy (Overview)

This report provides an overview of the major clinical and operational issues related to proton beam radiation therapy and lists its various applications. Information typically found in the Evidence Basesection does not appear in this report because of the lack of appropriate data to address the key questions about comparative effectiveness. In July 2012, ECRI Institute performed a systematic search of the published literature on proton beam therapy to update the report. Our searches found no new published trials that would address our key questions.

Proprietary names: Conforma 3000; Monarch250 Proton Beam Radiation Therapy System; PROBEAT Proton Beam Therapy System (PBTS); ProBeam; PROBEAT PBTS with MGCS; PROBEAT PBTS with Discrete Spot Scanning System (DSSS); Proteus 235; Proteus One; PT Varian Proton Therapy System Generic names: charged particle radiotherapy; compact proton therapy; intensity modulated proton therapy (IMPT); medical charged-particle radiation therapy system; particle beam radiotherapy; particle beam therapy; particle irradiation; pencil-beam scanning; proton beam therapy; proton beam therapy system; proton cancer therapy radiotherapy systems; proton irradiation; proton radiotherapy; proton therapy; proton treatment; spot scanning

Proton beam radiation therapy involves directing a beam of accelerated subatomic, electrically charged particles to tumor targets. To penetrate the body, protons must be accelerated by cyclotrons and synchrotrons to attain 60% of the speed of light. Proton beam radiation therapy can be used alone or in combination with traditional photon beam radiation therapy to treat malignancies in the abdomen, central nervous system, eye, lung, head and neck, and prostate as well as some noncancerous conditions (i.e., arteriovenous malformations, circulatory system defects of the brain). The primary advantage of the use of protons over photons is decreased collateral damage to surrounding tissue. Because of the way proton energy is produced and delivered, tissue in the beam's path to the target receives only a small radiation dose, while tissue around and behind the target receives even less radiation. Avoiding collateral tissue damage is especially important when a tumor is located in or near critical structures, as is the case with tumors of the brain, eye, skull base, and spinal cord or when treating children who are more prone to radiation-induced toxicity. Further, less exposure to healthy tissue should theoretically reduce some of the untoward, acute side effects of radiation therapy, including fatigue, redness and irritation of the irradiated tissue, nausea, swelling, fistula, and secondary cancers. Proton beam therapy can be delivered by passive scattering (lateral dispersion) or spot scanning. More clinicians have begun using spot scanning, also known as pencil-beam scanning (i.e., dispersion of many points of radiation into a precise beam) to further limit the high dose to the target volume and decrease harm to normal tissue. Complications of proton beam radiation therapy can occur immediately after treatment or may not occur for several months. Acute side effects that can occur during the treatment phase include fatigue, skin reactions (redness and irritation similar to sunburn), diarrhea, nausea, hair loss, and vomiting. Secondary malignancies can occur following both photon therapy and proton therapy. Treatment typically occurs once daily for five days, up to eight weeks; dividing the total radiation dose over several treatment sessions allows for cell recovery. Patients attend pretreatment planning sessions during which they undergo computed tomography (CT) scanning to verify tumor location and fit customized immobilization devices. During treatment, patients may recline or sit upright depending on the tumor location. Also, the type of cancer determines the type of treatment room used. Gantry-beam rooms rotate the beam around the patient, whereas fixed-beam rooms direct the beam horizontally and are better suited for the treatment of eye, head, and neck malignancies. Radiation therapists apply anatomic-specific body casts, bite molds, and masks to immobilize patients and better target the proton beam. Therapists also compare treatment-planning CT images with images taken immediately before treatment begins. Certain patients may receive anesthesia. Once these steps are taken, therapists leave the treatment room and enter the system control room to direct the proton beam. Each treatment session typically lasts between 30 and 60 minutes. Patient positioning takes most of this time, while actual delivery of the proton beam lasts only about two minutes. Some patients travel hundreds of miles to undergo proton beam radiation therapy, and many patients are on waiting lists due to the scarcity of treatment centers. As of August 2012, 11 centers are operational in the United States. Facility configuration varies according to equipment type and expected patient caseload. Regardless of the design, proton beam therapy facilities are typically costly, customized, multiroom facilities that must house the following:

Development of smaller proton beam radiation therapy systems has generated a renewed interest in the technology due to the decreased space requirements and lower acquisition costs. For example, one manufacturer (Ion Beam Applications IBA S.A.; Louvain-la-Neuve, Belgium) is marketing a compact proton beam therapy system that can provide therapy in one to four treatment rooms. Another compact system expected to come online soon is the Monarch250 Proton Beam Radiation Therapy System, which occupies a moderate-size hospital treatment room. It is under development by Still River Systems (Littleton, MA, USA) and weighs approximately eight tons. The Monarch250 combines a cyclotron, treatment gantry, treatment couch, and positioning system into one comprehensive unit.

Cancer Center, Outpatient

Facilities can purchase proton beam therapy equipment from suppliers or use cyclotrons acquired from educational or research institutions. Manufacturers of proton beam...