Protons are hydrogen atoms whose electrons have been removed. Proton beam radiotherapy uses a special machine called a cyclotron to energize protons. Protons are extracted from the cyclotron and directed with magnetic fields to the tumor. How deeply the radiation penetrates is calculated based on the tumor's location. Protons lose only a small amount of energy when they enter the body. Their remaining energy is released when they reach the tumor, delivering the most effective dose of radiation. Proton beams have no exit dose unlike conventional radiation therapy.
- What is proton therapy and how is it used?
 Protons are atoms that carry a positive charge. Just as x-rays are used to treat both benign and malignant tumors, a beam of protons can be used to irradiate tumors in the same way. There is no difference in the biological effects of protons versus photons (x-rays). Physically, protons release most of their energy when they hit the tumor and deliver no exit dose beyond the tumor boundary, unlike photons. Therefore, the dose of radiation conforms to the tumor better and there is less damage to healthy tissue. As a result, the treating physician (a radiation oncologist) can potentially give an even greater dose to the tumor while minimizing unwanted side effects. This is especially important when treating children, because it reduces radiation to growing and developing tissues.
Proton therapy is being used to treat tumors in these areas of the body with encouraging early results:
- Lung
- Prostate
- Brain
- Spinal or vertebral body tumors
- Skull base sarcomas
- Pediatric brain tumors
- Head and neck
- Eye melanomas
Protocols are being developed to explore the use of protons in other parts of the body.
- Who will be involved in this procedure?
Proton beam therapy requires a treatment team, including a radiation oncologist, radiation physicist, dosimetrist, immobilization specialist, radiation therapist, and nurse. The radiation oncologist is a specially trained physician who evaluates the patient and determines the appropriate therapy, specific area for treatment, and radiation dose. Working together, the radiation oncologist, radiation physicist, dosimetrist and radiation therapist establish the best way to deliver the prescribed dose. The radiation physicist and the dosimetrist then make detailed treatment calculations. Radiation therapists are specially trained technologists who perform the daily radiation treatments. Imaging studies are very important in delivering this treatment and a diagnostic radiologist is often involved with planning, too. Radiation therapy nurses are team members who tend to your day-to-day concerns and help to manage the side effects of the treatment.
- What equipment is used?
Proton beam therapy uses a special machine called a cyclotron or a synchrotron to generate and accelerate protons. The protons leave the machine and are steered by magnets toward the tumor. Other pieces of equipment are used to modify the range of the protons, shape of the beam, and to compensate for organ location.
- Who operates the equipment?
 With backgrounds in mechanical, electrical, software, hardware and controls, specialized operators maintain, upgrade and repair the cyclotron or synchrotron and radiation delivery system. They are also present in the facility's main control room during treatments in order to monitor the performance of the radiation delivery system.
- Is there any special preparation needed for the procedure?
Before a patient begins proton therapy, there are a few preparation steps. First, the patient will be fitted for an immobilization device to put his or her body in the exact same position for each therapy treatment. The device used will depend upon the location of the tumor. Patients with a tumor below the neck will have a full-body mold made of foam liners surrounded by rigid plastic shells. Patients with a tumor in the eye, brain or head will be fitted with a custom-made mask.
Once the immobilization device is constructed, patients will often undergo computed tomography (CT) or magnetic resonance imaging (MRI) scanning to create a 3-D reconstruction of the tumor to define its boundaries with the surrounding normal structures. The patient wears the device during the CT scan so that it can be taken into account for treatment planning. Sometimes a CT or MRI scan is done prior to mask-fitting. In the case of eye melanoma patients with tantalum rings sutured, simple x-rays may be taken to image the rings' placement.
The radiation oncologist uses a computer to trace the tumor and the surrounding normal tissues. Physicists and dosimetrists create a treatment plan on the computer that outlines a single or multiple proton beams entering at various angles. They use this to calculate the radiation dose that the tumor will receive. After the physician reviews this plan, it is transferred to automated machines that make the special devices, apertures and tissue-compensating filters that will be used during therapy. All of these devices are calibrated by the physics support staff before the patient's first treatment to ensure that the planning and fabrication have been done correctly.
- How is the procedure performed?
The procedure is performed on an outpatient basis. The average course of treatment is usually five to seven weeks, but rarely it may last only a few days. The length of each treatment will vary depending upon the tumor type and stage. The delivery of the proton beam to the patient lasts only about a minute, although the total time spent in the treatment room will be longer (about 15-20 minutes) for positioning and adjustments to the equipment settings.
For daily treatments, the patient enters the treatment room and is fitted with his or her personal immobilization device. The patient is positioned with the aid of laser sights to within a half-centimeter accuracy. The radiation therapist then takes several low-energy diagnostic radiographs (x-rays) or digital /images to insure proper alignment. This process is repeated before each treatment. In some cases a fan beam CT system will be used to image the target before each treatment.
Special apertures and filters that are made for each patient are loaded into the beam line. A computer may be used to scan and verify the individual bar codes on these devices. Once positioning and treatment parameters are verified, the radiation oncologist and technologists step out into a control room located next to the treatment room and begin the treatment. After the prescribed radiation dose has been delivered, the computer shuts off the proton beam and the technologists re-enter the room to assist the patient in removing the mask or immobilization device.
- What will I feel during and after the procedure?
You should not feel any pain or discomfort from the proton beam. Afterward, there may be some side effects, although these are less frequent and usually less intense than with standard radiation therapy with x-rays, because there is much less healthy tissue that is injured. Other factors that may influence how well you feel after treatment are how big a dose you are given and whether you are also getting chemotherapy at the same time. Common side effects include temporary hair loss and skin reactions in the direct path of the radiation and fatigue, especially when a large area is being treated.
Side effects of radiation treatment include problems that occur as a result of the treatment itself as well as from radiation damage to healthy cells in the treatment area.
The number and severity of side effects you experience will depend on the type of radiation and dosage you receive and the part of your body being treated. You should talk to your doctor and nurse about any side effects you experience so they can help you manage them.
Radiation therapy can cause early and late side effects. Early side effects occur during or immediately after treatment and are typically gone within a few weeks. Common early side effects of radiation therapy include tiredness or fatigue and skin problems. Skin in the treatment area may become more sensitive, red, irritated, or swollen. Other skin changes include dryness, itching, peeling and blistering.
Depending on the area being treated, other early side effects may include:
- hair loss in the treatment area
- mouth problems and difficulty swallowing
- eating and digestion problems
- diarrhea
- nausea and vomiting
- headaches
- soreness and swelling in the treatment area
- urinary and bladder changes
Late side effects, which are rare, occur months or years following treatment and are often permanent. They include:
- brain changes
- spinal cord changes
- lung changes
- kidney changes
- colon and rectal changes
- infertility
- joint changes
- lymphedema
- mouth changes
- secondary cancer
There is a slight risk of developing cancer from radiation therapy. Following radiation treatment for cancer, you should be checked on a regular basis by your radiation oncologist for recurring and new cancers.
Using techniques such as proton therapy, imaging specialists are maximizing the cancer-destroying capabilities of radiation treatment while minimizing its effect on healthy tissues and organs and the side effects of the treatment itself.
Proton therapy FAQs
What are protons?
Protons are positively charged particles – the nucleus of the hydrogen atom. In radiotherapy they enter the human body at a pre-selected energy level and continue in a straight line up to a precisely calculated depth. While moving, they release energy with little radiation damage effects. Toward the end of their trajectory they slow down, coming to rest at the Bragg peak (called after the physicist of that name), where they release most of their energy and damage the cells. Behind the Bragg peak the dose reduces to nil after a few millimeters. This physical profile is the reason for using protons in radiotherapy. It permits deep-seated tumors to be treated without overshooting the mark.
How does proton therapy work?
Proton radiotherapy works by ionizing tissue molecules, which damages the cell nucleus, the surrounding membrane and other components, and thereby inhibits cell growth. Cell division is interrupted or the cell dies.
In comparison with the photons used in conventional radiotherapy, protons have certain physical advantages. They release their maximum dose – which attacks the tumor cells – right at the end of their trajectory. The point where they stop is called the Bragg peak. Their speed (or energy) is calculated so that this point occurs at a precisely selected spot within the tumor. No radiation is deposited in the healthy tissue behind the tumor. The dose released in healthy tissue on the way to the tumor is considerably less than with photon therapy. Therefore, on the one hand the sparing of healthy tissue is optimal, and on the other a significantly higher radiation dose can be released precisely within the tumor.
What tumors can best be treated with proton therapy?
Proton therapy is best used where high dose to the tumor and maximum precision is required. If the medical indications favor lower dose and wide-area radiotherapy, proton treatment may bring no distinct advantage. In case of doubt, a comparative therapy plan can be drawn up, and a decision for proton or photon therapy made on the basis of the calculated dose distributions.
What results has proton therapy achieved? What are the chances of a cure?
Protons have been used in medical therapy since 1954, when patients were first irradiated with these positively charged particles in Berkeley, California. Since then more than 50'000 people have been treated at various centers worldwide, mostly for tumors of the eye (choroid melanomas), brain, skull base, spine and pelvis. Impressive success has been achieved with eye tumors, with a local tumor control rate exceeding 98% after five years, and there has been a similarly striking increase from 40% to more than 80% in the control rate for chondrosarcomas and more than 65% for chordomas of the skull base. These results reinforce the thesis that precise placing of the radiation dose, along with the significantly higher radiation that can thereby be released inside the tumor, enable growth to be halted in even relatively radiation-resistant tumors, or permit them to be destroyed altogether, without damage to surrounding tissue.
It is on the basis of these successes that the spot-scanning technique and compact gantry at SHANGHAI have been developed and built. As facilities spread for treating tumors that cannot be adequately subjected to conventional radiotherapy, we may expect from all these sources an increase in the indications for proton-beam treatment.
What are the side effects?
Side effects are divided into acute and long-term effects. They depend both on the condition of the organs concerned and on the radiation dose to which they are exposed. Radiation has its effects where the dose is deposited. For example, hair loss will only occur when the skull is irradiated, and temporary inflammation and discomfort will generally arise after radiotherapy affecting the mucous membrane of the bladder or rectum, but as a rule this lasts only a few weeks.
If you need radiotherapy, you will be informed in detail about possible side-effects. As protons generally release little radiation in healthy tissue, side effects are minimal and can be treated. Acute effects occur during or immediately after treatment and generally last only a few weeks. Long-term effects can occur months or even years after treatment has ended, and are frequently permanent. They then as a rule need regular treatment and may seriously affect a patient's overall well being. For this reason great trouble is taken when planning a therapy to avoid radiation of healthy organs – nerves, skin, brain tissue etc. Protons are ideally suited to this task, and the rate of long-term complications after proton therapy is low.
Will I feel anything during the therapy?
Proton therapy is painless and does not burn. Patients feel nothing during treatment. There are rare situations when specific sensory centers in the brain are irradiated, which can lead to temporary stimulation during treatment, causing e.g. light flashes or scent sensations.
How long does the therapy last?
A course of radiotherapy usually lasts several weeks, with a relatively large number of small individual doses given, until the total dose necessary to destroy the tumor is reached. As a rule this takes 25-37 days of treatment. At SHANGHAI we currently calculate 4 to 5 days of treatment per week, so a course of therapy lasts from 5 to 9 weeks. On each treatment day the therapy lasts about half an hour, most of which time is taken up with the exact positioning of the body so that the tumor can be irradiated with optimally spearing out the surrounding tissue. The proton irradiation itself only lasts a few minutes.
Where do patients stay during the therapy?
Proton therapy is predominantly an out-patient treatment worldwide. Our patients live in the apartment nearby for the duration of the treatment. China Medical Tourism Inc. will help arrange accommodation, including patients accompanied by a relative or friend.
How do patients arrange treatment at SHANGHAI?
As a rule patients are referred by their specialist clinic or physician, but in a number of cases relatives, friends or the patient themselves make the initial contact. We always take time to discuss the patient's individual situation, and if proton therapy is indicated, the treatment will take place in consultation with the patient's own doctors.
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