Proton Therapy

Apollo Proton Cancer Centre signs its 25th alliance globally and its 1st in eastern India with Belle Vue Clinic, Kolkata, Group of MP Birla.
Preetha Reddy HARSHAD REDDY

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What is Proton Therapy?

Proton therapy is a radiation therapy that uses tiny particles called protons. Protons are excellent cell killers, but because of the way protons deliver their energy, proton therapy does not damage as much healthy tissue as much as photon therapy. Therefore, a higher dose of radiation can be targeted at the tumour without affecting many normal healthy cells.

What is Proton Therapy?

Proton therapy can be effective in treating many types of tumours, including tumours of the brain, head and neck, central nervous system, lung, prostate and gastrointestinal system. Proton therapy is often the preferred option for treating solid tumours in children because protons can be controlled precisely so there is less radiation of normal tissues, helping prevent serious complications and lessening the chance of secondary tumours. Proton beam therapy is the preferred standard for many tumours including:

  •  Ocular tumours, including intraocular melanomas
  •  Tumours that approach or are located at the base of skull such as Chordoma and Chondrosarcomas
  •  Spine tumours – Primary or metastatic
  •  Hepatocellular cancer
  •  Paediatric solid tumours – primary or benign tumours in children
  •  Brain and spinal cord tumours – Malignant and benign
  •  Advanced and/or unrespectable head and neck cancers such as Cancers of the paranasal sinuses and other accessory sinuses; e.g. adenoid cystic carcinomaAdvanced Nasopharyngeal cancer and Advanced cancer of the buccal mucosa
  •  Retroperitoneal sarcomas
  •  Re-irradiation cases- where radiation is being considered for the second or third time to the same site

The above sites have sufficient evidence available currently that there is a definite benefit in using proton therapy. However, many other cancers may also have a benefit when proton therapy is used, especially when compared to conventional X-ray therapy. These include:

  •  Oesophageal cancers
  •  Breast Cancer
  •  Oropharynx Cancer
  •  Salivary Gland cancers
  •  Lung Cancer
  •  Prostate Cancer
  •  Sarcomas
  •  Tumours in the base of the skull

Proton Therapy for Lung Cancer

Proton therapy for lung cancer treatment is one of the many exciting developments in the field. Despite best advances with photon therapy such as IMRT, IGRT, Cyberknife, Helical tomotherapy, the doses received by heart and lungs sometimes remain prohibitive. Even if the dose is within the thresholds, there is significant cardiopulmonary toxicity leading to significant morbidity (upto 80%) and even mortality (up to 5%). Proton therapy because of its unique physical and biological properties can deliver significantly lower doses to critical structures such as healthy lung as well as heart thereby limiting the collateral damage.

Why should you choose Proton Therapy for Prostate Cancer?

Proton therapy is one of the most effective forms of treatment for prostate cancer. Proton therapy may be used as the only treatment or can be combined with hormonal therapy or after other treatments, such as surgery, to manage cancer that has recurred or is at high risk of recurrence.

Because it involves significantly less radiation exposure to normal tissues, proton therapy lowers the risk of side effects and secondary radiation-induced cancers. Proton therapy has an excellent record of success, providing long-term disease control and survival rates equivalent to other treatments, including surgery.

What is the success rate of Proton Therapy?

Proton therapy is at least as effective as conventional radiation therapy, but with fewer side effects. In some cases, proton therapy is not only the best but also the only option. It has been proven to be successful in curing or controlling many cancers when used appropriately. Success after radiation therapy depends on the type and stage of cancer treated. In certain cancers like chordomas, brain tumours or liver cancers, control rates with proton therapy can be as high as 85-90%.

What is Proton Therapy used for?

Proton beam therapy (PBT) is an advanced form of radiotherapy, with radiation treatment delivered by accelerated proton beams rather than X-rays. A proton beam delivers some radiation to healthy tissue in reaching the tumour but very little radiation beyond the edge of the tumour being treated. This means PBT is able to treat cancers just as effectively but delivers less radiation to other healthy parts of the body which surround the tumour.

What is the Physics of Proton Therapy?

The best way to understand how proton therapy works is to take a look at the physics and engineering inside the proton accelerator, or the cyclotron/synchrotron, and the beam delivery system.

  •  The proton begins its journey at the ion source. Within fractions of a second, hydrogen atoms are separated into negatively charged electrons and positively charged protons.
  •  The protons are injected via a vacuum tube into a linear accelerator and in only a few microseconds, the protons’ energy reaches 7 million electron volts.
  •  Proton beams stay in the vacuum tube as they enter the cyclotron/ synchrotron, where acceleration increases their energy to a total of 70 million to 250 million electron volts, enough to place them at any depth within the patient’s body.
  •  After leaving the synchrotron, the protons move through a beam-transport system comprised of a series of magnets that shape, focus and direct the proton beam to the appropriate treatment room.
  •  To ensure that each patient receives the prescribed treatment safely and efficiently, the facility is controlled by a network of computers and safety systems.
  •  The gantry can revolve 360 degrees, allowing the beam to be delivered at any angle.
  •  As protons come through the nozzle, a system of electromagnets placed perpendicular to each other bends each beam so that they reach the planned position within the depth of the tumour. This is called pencil-beam scanning (PBS).
  •  At Apollo Proton Cancer Centre, we have the latest PBS technology which enables us to deliver highly focused treatments to each tumour, and each tumour is treated with protons, spot- by- spot and layer-by-layer.
  •  At maximum energy, a proton beam travels 125,000 miles per second, which is equivalent to the two-thirds the speed of light. From the ion source to the patient, a proton typically travels 313,000 miles.
  •  Once the proton enters the body, it slowly increases the energy deposited in the tissue until it reaches a particular depth where it deposits almost all of its energy and comes to a halt. This effect is called Bragg’s Peak Effect. Thus, unlike an X-ray beam that passes through the entire body, the proton beam actually stops at a particular depth within the tumour. By manipulating the energy of the proton beam and the position of the spot, the tumour is treated with a high dose of radiation while the surrounding tissues are spared of radiation dose.

History of Proton Therapy

The advancements of proton technology as a treatment option for cancer began in the 1940s. The idea of using protons in medical treatment was first suggested in 1946 by physicist Robert R. Wilson, Ph.D. The first attempts to use proton radiation to treat patients began in the 1950s in nuclear physics research facilities, but applications were limited to a few areas of the body. In the late 1970s, imaging advancements coupled with the development of sophisticated computers and improved accelerator and treatment delivery technology made proton therapy more viable for routine medical applications, such as cancer treatment.

Only in recent years has it become possible to develop proton beam facilities in conjunction with established medical centres. Initially, proton therapy machines were designed so that a narrow beam of protons that emerges from the nozzle was then widened (scattered) and shaped to conform to the shape of the tumour, by custom-made accessories (collimators and compensators) which had to be mounted on the nozzle. This was called passively scattered proton therapy (PSPT). Earlier machines also had only X-rays placed perpendicular to each other to provide image guidance and so only bony anatomy could really be verified.

In addition, most of the older machines were fixed and the patient had to be rotated or positioned differently so that the beam could be directed to the tumour through various angles. However, this has now given way to Pencil Beam Scanning proton therapy (PBSPT) which is much more versatile and avoids the cumbersome and labor-intensive accessories required to deliver treatments. Also, the use of onboard image guidance and rotational gantries has made the delivery of proton therapy much more streamlined and comfortable to the patient and therapist. This has in turnmade proton therapy accessible to many more people around the world.

Pencil Beam Scanning and Intensity Modulated Proton Beam therapy (IMPT)

Pencil beam scanning technology and IMPT are the latest technology in proton therapy. With a proton beam just millimeters wide, these advanced forms of proton therapy combine precision and effectiveness, offering unmatched ability to treat a patient’s tumour and minimizing effect on a patient’s quality of life – during and after treatment. They rely on complex treatment planning systems and an intricate number of magnets to aim a narrow proton beam and essentially “paint” a radiation dose layer by layer.

Pencil beam is very effective in treating the most complex tumours, like those in the prostate, brain, eye, and cancers in children, while leaving healthy tissue and other critical areas unharmed. IMPT is best used to deliver a potent and precise dose of protons to complex or concave-shaped tumours that may be adjacent to the spinal cord or embedded head and neck or skull base, including nasal and sinus cavities, oral cavity, salivary gland, tongue, tonsils, and larynx.

Who is a candidate for Proton Therapy?

When you meet with your cancer care team, your oncologist will give you the options that will be most effective in treating your type of cancer. Together with your cancer care team, you can decide on the treatment option that’s right for you. Proton therapy will be most beneficial to:

  •  Paediatric patients
  •  Those whose tumour is very close to critical structures
  •  Those who are receiving radiation for the second or third time
  •  Those who have a long life expectancy after radiation and are at risk for second cancers to develop during their lifetime.
  •  Those with inherent conditions which predispose them to excessive toxicity or higher risk of second malignancy after radiation.

However, these are not the only patients who may benefit from proton therapy. Your radiation oncologist will discuss with you in detail the benefits of proton therapy for your particular cancer type and site.

What are the advantages of Proton Therapy?

Proton Therapy has many advantages including:

  •  Targets tumours and cancer cells with precision and minimal exit dose.
  •  Reduces overall toxicity.
  •  Reduces the probability and/or severity of short- and long-term side effects on surrounding healthy tissues and organs (e.g. reduces the likelihood of secondary tumours caused by treatment).
  •  Precisely delivers an optimal radiation dose to the tumour.
  •  Can be used to treat recurrent tumours, even in patients who have already received radiation.
  •  Improves quality of life during and after treatment.
  •  Increases the long-term, progression-free survival rates for certain types of tumours.