Proton radiation therapy is used to treat any cancer or disease that can be treated with conventional radiation therapy. Since the John M. Slater Proton Treatment Center opened, proton therapy has treated a growing list of cancerous and non-cancerous problems.
Proton radiation therapy is a local treatment that has few side effects. It is excellent for treating cancers or other diseases that are limited to one place within the patient’s body. Proton therapy cannot be used to cure systemic cancers such as leukemia, for example, or for cancers that have spread widely to other areas in the body. It may be used, however, to relieve symptoms arising from localized metastases.
While proton treatment is used for a variety of common cancers, Loma Linda University Medical Center (LLUMC) is constantly working to expand the list of conditions treated with protons.
Acoustic neuromas are benign tumors that involve the eighth cranial nerve and they affect our hearing. With traditional radiosurgery, more than 50 percent of patients may experience a significant loss of hearing over time. This is because the large, single doses of radiosurgery can cause tissue damage to surrounding tissue.
At LLUMC’s Proton Treatment Center this problem can be avoided by using fractionation of radiation treatment. This process involves the division of the total radiation dose into smaller doses, which are delivered over a longer period so as to reduce the damage to healthy cells. This not only minimizes side effects, but also makes the treatment more effective. Consequently the proton radiation therapy can achieve a high rate of tumor control while minimizing the hearing loss associated with other forms of therapy.
Chordomas and Chondrosarcomas
Chordomas and chondrosarcomas are tumors of the brain stem, spinal cord and central nervous system tissue. Proton radiation therapy has long been used to treat these tumors because it can deliver a high dose without damaging healthy brain or spinal cord tissues.
These slow-growing tumors develop from the protective linings of the brain and spinal cord, which are called meninges. Meningiomas are almost always noncancerous (benign), but they can be difficult to remove because of their location. Proton radiation therapy’s precision makes it ideal for treating these tumors.
Proton radiation therapy is used for meningiomas to deliver a high dose of radiation in a few treatments. Long-term results show that proton therapy for benign meningiomas yields excellent results with minimal side effects.
Arteriovenous Malformations (AVMs)
Arteriovenous malformations (AVMs) are defects of the circulatory system that are thought to arise during embryonic or fetal development or else soon after birth. AVMs are comprised of snarled tangles of arteries and veins. Proton radiation has been used successfully for many years to treat AMVs and success rates in the three years following treatment approach 80 to 85 percent for small AVMs.
Isolated Brain Metastases
Proton radiation therapy is used to relieve symptoms from isolated brain metastases. A high dose of radiation can be delivered in a few treatments, reducing symptoms and improving quality of life.
These tumors occur in the pituitary gland, which is sometimes called the “master” gland of the endocrine system because it controls the functions of the other endocrine glands. Currently, microsurgery is the treatment of choice in managing this disease. Success rates with surgery in microadenomas (tumors less than 1 cm in diameter) range from 70 to 90 percent, but are much lower for larger tumors.
Pituitary adenomas typically need additional treatment after surgery to cure or prevent recurrence. Radiation with photons and charged particles, such as protons or helium ions, has been used successfully in the past. More recently, pituitary adenomas have been treated with stereotactic radiotherapeutic approaches such as single-dose radiosurgery with the "gamma knife" or linear accelerator.
At LLUMC proton beams have been used for focal irradiation of pituitary adenomas since 1990. LLUMC has pursued high-precision fractionated radiation therapy – the division of radiation doses over a period of time -- as opposed to single-dose radiosurgery. This may be a more reasonable approach in cases where the target volume is larger than 1 cm and the tumor is adjacent to vital structures.
Uveal melanomas, which are also called choroidal melanomas, are malignant tumors of the eye. Historically, these tumors have been treated by the complete removal of the eye. However, precise forms of radiation treatment such as proton beam therapy have been used to minimize the need for removal.
Protons have been used to treat uveal melanomas since the mid-1970s. Reports reveal control rates greater than 95 percent, with long-term survival consistent with survival rates for patients who have had their diseased eyes removed. Most proton patients have retained useful vision in their treated eyes. Results indicate that proton radiation is useful for medium and large tumors as well as smaller lesions.
Carcinoma of the nasopharynx is typically treated with radiation therapy alone. Local control rates for T3 lesions range from 60-85 percent. The corresponding rate is 45-70 percent for T4 tumors. Treatment-related complications can be severe because of the high doses received by critical structures surrounding the nasopharynx. These include:
• endocrine complications secondary to hypothalmic or pituitary dysfunction
• cranial nerve injuries
One can increase the total dose to the primary tumor while shortening the overall treatment time by using the improved properties of proton radiation treatment. Proton treatment:
• increases local control of primary tumors
• reduces treatment-related side effects seen with conventional radiation
• is suitable for re-treatment of recurrent tumors
Patients treated for locally advanced oropharynx cancer usually receive combined surgery and postoperative photon radiation, or in some selected cases, radiation alone. Unfortunately, with either treatment approach a significantly high incidence of post-treatment morbidity has been reported. Severe treatment-related complications have been reported in up to 50 percent of long-term survivors. While greater doses of radiation are associated with improved levels of control, it also results in an increased complication rate. This is partly related to the large volume that is taken to a high dose using conventional radiation.
Proton treatment increases the total dose to the tumor while decreasing the dose to surrounding normal tissues. At LLUMC, protons are used in conjunction with conventional photon irradiation, with noted improvements in disease control and reduced morbidity.
Early Lung Cancer (medically inoperable)
When lung cancer is caught at an early stage, it is curable with surgery in more than 50 percent of cases. Standard treatment is surgical removal of the tumor and possibly of the entire lung. Some patients with severe heart or lung disease are unable to undergo such an operation. Traditionally, these patients have been offered conventional radiotherapy, with published results being inferior to those of surgery.
LLUMC uses proton beam radiation for such patients in an effort to increase the dose delivered to the tumor while minimizing the damage to the surrounding normal heart and lung. Computed tomography studies show that proton radiation is able to help restrict the volume of normal lung tissue damaged by radiation. Preliminary clinical results suggest that this treatment yields good rates of local tumor control and minimizes lung injury.