Particle Beam Radiation Therapy
Particle beam radiation therapy delivers radiation by accelerating charged particles such as protons, carbon or other heavier ions.
These particle beams can carry very high energy and travel through the body with the ability to stop at a specific location (where the cancer cells are located). This important feature is utilized to destroy the tumor and spare the healthy tissues as much as possible. In the last decade, the significant radiobiological and clinical advantages of particle therapy have been quickly realized with a rising number of proton therapy centers opening in the United States and the world.
Proton therapy is the most widely used particle beam radiation therapy. Proton beams differ from photon beams mainly in the way they deposit energy in living tissue. Whereas photons (X-ray) deposit energy in small packets all along their path through tissue, protons deposit much of their energy at the end of their path (called the Bragg peak) and deposit less energy along the way. Therefore, use of protons reduces the exposure of normal tissue to radiation ultimately allowing the delivery of higher doses of radiation to a tumor with fewer side effects.
Proton therapy is painless and takes 15-45 minutes for your entire treatment visit. The penetration depth of proton beam ranges up to 38 cm in human tissues. Therefore, proton therapy can be used to treat most types of cancer, including brain, breast, eye, head and neck, lung, prostate and many other diagnoses.
Depending on how the particle beam is delivered, different devices called apertures and compensators may be used to modify the beam to improve its conformality. Recent technical advances have led to treatment with intensity modulated proton therapy (IMPT) which has similar advantages as IMRT for conventional radiation therapy without its disadvantages.
Based on the clinical outcomes in the United Stated and worldwide, the major advantages of proton therapy include:
Decrease the risk of local failure and secondary cancer, due to unnecessary radiation received by healthy tissues.
Improved quality of life during and after proton treatment. Fewer and less intense side effects should be expected. The minimized normal-tissue injury results in the potential for fewer side effects following treatment, such as nausea, vomiting, or diarrhea.
Benefits to patients with tumors located close to critical organs. Proton therapy allows the doctor to plan your treatment without exposing critical organs to radiation. Significant benefits exist for children. Proton therapy can minimize the radiation exposure to developing tissues in children with more subtle structures. After photon (X-ray) radiation therapy, children with long life expectancy have the highest risk of developing secondary cancer. According to clinical studies, proton therapy has the advantage of reducing or eliminating the early and late side effects of radiation therapy.
As of December 2012, the Particle Therapy Co-Operative Group (PTCOG) states that over 78,000 patients have benefited from proton therapy worldwide, among which 38,000 were treated in US. By January 2014, the United States has 14 operating proton therapy centers and more are under construction.
Carbon and other types of particle beams
Particles that are heavier than proton are called heavy ions, including helium, carbon, and neon. In a similar way to protons, these accelerated particles can precisely target cancer cells with a minimal dose to healthy tissue. Over 10,000 patients have been treated for cancer with heavy ion therapy, such as carbon and helium beams, mostly in Japan and Germany. Additional particle beam therapy facilities are beginning operation or are under construction worldwide.
Based on the clinical and radiobiological experiences, the characteristics of tumors most likely to benefit significantly from proton and heavy ion therapy are as follows:
Tumors with a high risk of local failure after photon (X-ray) radiation therapy
Radio-resistant tumors that do not respond positively to photon radiation therapy
Tumors involving critical normal organs that cannot afford adequate resection, or would cause loss of critical organ function after surgical resection
Tumors abutting or in very close proximity to sensitive (critical) normal structures
Efficient repair of cellular damage after conventional radiation therapy – Particle beam allows higher dose delivered to the tumors, and therefore prevent self-repair of the cancer cells
Today heavy ion radiation therapy (particles heavier than proton) is not yet available in the United States. However, advantages of particle beam radiation therapy have been quickly realized, resulting in efforts of bringing these advanced technologies to the United States, ultimately to improve cancer treatment and patient’s quality of life.