What Is Proton Therapy?
- What Is Proton Therapy?
- Frequently Asked Questions
- Am I A Candidate for Proton Therapy?
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New technologies are significantly reducing the cost of proton beam therapy, making it more widely available. It differs from standard radiation in method and results. To learn more about how this cutting-edge treatment process works, view our illustrated guide to understanding proton therapy.
It is easy to understand why proton beam therapy is so effective. Proton therapy delivers higher doses of radiation to the targeted area, spares healthy tissue and avoids critical structures. Our proton therapy team uses state-of-the-art beam delivery systems, patient imaging and treatment planning systems, and patient immobilization and setup techniques.
Advantages of proton beam radiation therapy include:
- Minimizing the entrance dose of radiation before it reaches the tumor;
- Eliminate the exit dose of radiation past the tumor; and
- Sparing normal tissue, organs and previously irradiated tissue.
What's the difference between proton radiation and traditional X-ray radiation?
Traditional X-ray radiation affects everything in its path, so doctors often limit the radiation dose to minimize damage to critical organs. X-rays also continue to pass through the body after reaching the tumor, affecting the healthy cells beyond it.
With the precision of proton beam radiation therapy, we can provide a lower dose of radiation to healthy tissues. This advantage allows higher doses to be delivered to the tumor with a lower risk of hurting healthy cells.
Conditions that may be appropriate for proton therapy include:
- Brain tumors and inoperable brain lesions.
- Pediatric tumors (to reduce the risk of secondary malignancies and to avoid the irradiation of growth plates).
- Tumors near the eye.
- Tumors next to the spinal cord or brain stem.
- Prostate cancer (to spare the rectum and bladder).
- Treatment of recurrent tumors that may have previously received radiation treatment.
Medical Information on the Doses and Treatment Plans for Some of the Conditions Treated with Proton Beam Radiation Therapy
Prostate cancer is typically treated with opposed lateral beams (right and left laterals) that overlap on the anatomical midline. The prostate gland is next to the anterior rectal wall and inferior to the bladder, and beam cross sections are chosen to meet dose constraints to these structures.
As in the figure to the right, the 7524 cGy isodose line contacts the anterior rectal wall but the 3000 cGy isodose line is removed from the posterior rectal wall.
Typical prescribed radiation doses for prostate cancer are 5040 cGy in 28 fractions to the prostate gland and seminal vesicles, with an additional 2880 cGy in 16 fractions to the prostate gland while sparing the bladder and anterior rectal wall to constraints. The total dose delivered is 7920 cGy in 44 fractions. The DVH constraints on the anterior rectal wall are <30 percent to 7740 cGy and <10 percent to 7020 cGy. The bladder constraint is <20 percent to 6000 cGy.
Based on 7524 cGy (95 percent of the prescription dose of 7920 cGy), the prostate gland is typically treated at the 100 percent level, while the prostate gland plus margin is typically treated at the >97 percent level.
Compared to treatment plans for prostate cancer radiated with IMRT (intensity-modulated radiation therapy), proton therapy provides a more uniform dose distribution (no hot spots), significantly lower dose to normal tissue (lower integral dose) and greater sparing of the rectum.
Clival chordomas are located near critical structures including your optic nerves and optic chiasm, the brain stem, the spinal cord and various bone-air interfaces.
Therapeutic doses are high, 7740 cGy, while tolerance doses to critical structures are significantly lower:
- Brain stem 5400/6200 cGy (center/surface)
- Spinal cord 5040/5500 cGy (center/surface)
- Optic nerves 4500-5400 cGy (point)
- Optic chiasm 4500-5400 cGy (point)
- Globes (eyes) <4500 cGy (point)
- Lens of eye <1000 cGy (point)
The lower integral dose achieved with proton therapy is crucial to maintain an acceptable dose level to these critical structures surrounding the treatment site.
Before you have treatment for a clival chordoma, we fit you for immobilization devices (a plastic mask and body mold). These custom-made devices help to keep your head still and in the exact position necessary for proton therapy.
Orbital Atypical Meningioma
In this example, the tumor is enveloping the right optic nerve and is pushing against the right eye. The goal in this plan is to treat the tumor and spare the eye, optic nerve, optic chiasm and brain stem. A highly conformal treatment plan was developed using a three-field technique.
The patient is immobilized on a carbon fiber table using their custom immobilization devices. This system, along with fiducial markers surgically placed in the skull, facilitates daily positioning with ±1.0 mm accuracy. Orthogonal X-ray images are used to determine the setup position, and small day-to-day variations are compensated with the robotic positioning system.
An orbital atypical meningioma is a challenging tumor to deliver radiation to because of its closeness to the optic nerve and eye. We want to avoid those structures receiving unnecessary radiation. You may have fiducial markers placed in your skull to help the treatment team position your radiation dose during every treatment session. During a treatment session, you are immobilized on a carbon fiber table, and we take orthogonal X-rays to verify your positioning and the equipment setup. The approach we use is to deliver proton beams from three fields.
Depending on their age, treatment site and temperament, younger patients may require daily anesthesia (with laryngeal airway mask) to avoid movement during treatment.
As demonstrated in the Dose Volume Histogram (above) , the chiasm, brain stem and contralateral optic apparatus receive no dose, yet 97 percent of the tumor volume receives at least 5640 cGy (95 percent of the prescribed dose).