Proton Beam Therapy Basics

• As explained by Devanshi Dinesh Mayani and reviewed by J Oncol Pharm Pract., proton beam therapy is an advancement in the treatment of various types of cancer and is a precise form of radiotherapy. The therapy "uses a beam of protons to target the cancer cells and destroys them. It scores high on precision and effectiveness when compared to other conventional cancer treatments like surgery, chemotherapy and x-ray radiotherapy. Proton beam therapy destroys the cancerous cells without harming the healthy cells, thus it considerably reduces the side-effects that accompany conventional cancer treatments."
• The abstract to his PubMed.gov report continues, "Supporters say the technology allows physicians to treat a broad spectrum of cancers with few adverse effects, while more precisely targeting tumor cells with higher doses of radiation. Detractors say proton beam therapy is hugely expensive and has not been shown to be superior to conventional radiation treatment. With proton beam therapy, physicians use a cyclotron to accelerate protons and fire them directly into tumor cells with submillimeter precision. Because healthy tissue is largely spared, oncologists can, in theory, deliver much higher doses of radiation, while improving local control and reducing the risk for recurrence and morbidities."
• The Mayo Clinic describes the therapy as an alternative to traditional radiation therapy and declares, "More radiation, with less risk". They detail how "traditional X-ray treatment delivers radiation to everything in its path", but proton therapy is more precise as "it uses the positively charged particles in an atom (protons) that release their energy within the target: the tumor. There is small amount of entrance radiation, but virtually none travels beyond the tumor. Because proton beams can be much more finely controlled, specialists can safely deliver higher doses of radiation to tumors."
• The Mayo Clinic offers proton beam therapy at their locations in Arizona and Minnesota by 37 of their oncology doctors.
• MD Anderson details the differences between traditional radiation therapies and proton beam therapy. They explain, "Standard radiation therapy has evolved and improved over the years and is effective in controlling many cancers. However, because X-ray beams are composed of primary photons and secondary electrons, they deposit their energy along the path of the beam, to the targeted tumor and beyond, and deliver radiation to healthy tissues before and after the tumor site. This radiation “exit dose” may cause health issues later because it can damage the normal tissue or organs near the tumor or area of concern."
• The difference with proton therapy lies in its ability to focus on smaller areas and only the cancerous cells, with very little spill over into adjacent healthy cells. "The advantage of proton therapy (also called proton beam therapy) is that the physician can control where the proton releases the bulk of its cancer-fighting energy. As the protons move through the body, they slow down and interact with electrons, and release energy. The point where the highest energy release occurs is the “Bragg peak.” A physician can designate the Bragg peak’s location, causing the most damage to the targeted tumor cells. A proton beam conforms to the shape and depth of a tumor, while sparing healthy tissues and organs."
• In addition, MD Anderson has improved on the technology through its pencil beam tech. They explain, "The team at MD Anderson Proton Therapy Center continues to expand ways to use proton therapy to benefit patients and pioneered pencil beam proton therapy, also called scanning beam, and intensity modulated proton therapy (IMPT)."
• MD Anderson's "pencil beam technology and IMPT build on the benefits of 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 tumor 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."
• "The Johns Hopkins Proton Therapy Center in Washington, D.C., is one of the largest and most advanced centers in the U.S., with three treatment rooms and more than 30 specialists." They state, "Proton therapy is a highly precise radiation treatment for tumors. It focuses more radiation on the tumor and less on the surrounding healthy tissue. This is particularly important for children, who may suffer lasting side effects from traditional cancer treatments."
• The Washington Post explained, "Proton therapy uses beams of protons, charged subatomic particles that can be controlled with magnets. A small amount of radiation is deposited on the way into the body, most goes directly into the tumor and none passes through the other side. That means, for instance, that radiation aimed at a tumor in one side of the brain wouldn’t harm the healthy side. And a beam aimed at a spinal tumor wouldn’t reach the heart or lungs behind it."

Perceptions of Healthcare Professionals

•  Justin E. Bekelman, Andrea Denicoff, and Jeffrey Buchsbaum argue in favor of the therapy. They reason, "Compared with photon (eg, x-ray) therapies, such as intensity-modulated radiation therapy, proton therapy reduces or eliminates lower radiation dose to normal tissue, possibly either enhancing effectiveness, reducing toxicity, or both." However, they caution "Proton therapy has greater physical and biologic uncertainties than photon-based treatments."
• Jeffrey Buchsbaum, of the NCI, "pointed out that a major concern in proton therapy is the unanticipated severe toxicities that may be attributable to higher RBE at the distal and lateral beam edges."
• The Washington Post quotes executives from MedStar Georgetown Sibley, and others, stating experts "generally agree that proton therapy’s greatest potential is in treating children, particularly those with brain and eye tumors. The therapy can be administered at higher doses than conventional radiation and causes fewer long-term side effects." However, experts also "acknowledge that research has yet to demonstrate that the treatment is better than conventional therapy for other cancers, such as prostate, even though many hospitals want to use proton therapy to treat that disease."
• Daniel J. Indelicato, Julie A. Bradley, Eric S. Sandler, Philipp R. Aldana, Amy Sapp, Jennifer E. Gains, Adrian Crellin, and Ronny L. Rotondo concluded in their study, "In this cohort of British children referred overseas for proton therapy, disease control does not appear compromised, toxicity is acceptable, and improvement in long‐term function is anticipated in survivors owing to the reduced brain exposure afforded by proton therapy."
• In a paper titled, "Proton Beam Therapy for the Treatment of Cancer in Children and Adults: A Health Technology Assessment" and published in NCBI, the following questions are asked: "What ethical issues are known in cancer treatment, and how might the availability of PBT influence these issues? What new ethical issues are raised by the use of PBT in cancer treatment? In particular, what issues are raised by the need to travel out of country for treatment? If PBT therapy is installed and implemented more widely in Canada, how should it be provided to best address the identified issues?"
• The authors conclude, "In cancer care, clinical benefits tend to include outcomes like overall survival, disease-specific survival, local or regional recurrence, and the management of side effects. The clinical effectiveness review of the evidence has shown that, to date, the evidence for PBT is based on the results of low-quality studies. Further, within that evidence, it is not clear that PBT offers clinical benefits compared with existing therapies; in some cases, PBT led to worse clinical outcomes.21 Readers are advised to refer to the Clinical Review section for an authoritative summary on the clinical benefits of PBT that have been outlined in the literature. Careful consideration about whether to increase access to a technology is required if the technology can provide only marginal clinical benefit."
• In a John Hopkins Hospital video, "Dr Bill Nelson speaks with Dr Matt Ladra, the Director of Pediatric Oncology at Sibley Memorial Hospital in Washington DC, about using radiation and proton therapy to treat children with cancer. In this preview, Dr Ladra explains the advantages proton therapy offers children by limiting the side effects often caused by traditional radiation treatments."
• In another John Hopkins video, "Kimmel Cancer Center Director Dr Bill Nelson talks to Dr Ted DeWeese, the Center’s Director of the Department of Radiation Oncology and Molecular Radiation Sciences, about the advances in radiation therapy and how treatments are becoming more refined and targeted. In the Fall of 2019 at proton therapy center that will come online at Sibley Memorial Hospital in Washington DC., DeWeese explains the precision of proton therapy and how it can be used to deal with specific types of harder to treat cancers."
• Yet another study by the University of Pennsylvania School of Medicine declares, "Proton therapy leads to significantly lower risk of side effects severe enough to lead to unplanned hospitalizations for cancer patients when compared with traditional radiation, while cure rates between the two groups are almost identical."
• A different study looked at patient perceptions. A study titled, "Improved long‐term patient‐reported health and well‐being outcomes of early‐stage breast cancer treated with partial breast proton therapy" by Sandra L. Teichman et al., concluded, "Patients’ responses suggest that PBPT is associated with improved overall QoL compared to standard whole breast treatment. These self‐perceptions are reported by patients who are 5‐10 years post‐treatment, and that PBPT may enhance QoL in a multitude of interrelated ways."