A comparison between conventional radiotherapy and proton beam therapy

Conventional Radiotherapy

Conventional radiation therapy utilizes high energy waves in order to kill cancer cells and prevent their division. The high energy waves used, are photons in the form of x-rays, that work through altering the DNA of our cells. This then leads to an inability of cell division. When we want to use radiotherapy, we first make an exact 3D model of the tumor and its surrounding area. This model then helps us to determine the best and most direct path for the waves, so that they are passing the least possible amount of normal tissues, on their way towards the tumor. The common goal of doctors using radiotherapy is maximizing the damage to cancer cells while minimizing damage to normal cells.

Radiotherapy is effective because fast growing cells, such as cancer cells, are more sensitive to radiation therapy and less likely to recover from its effects afterwards, than normal cells are. Radiation therapy is often combined with surgery and chemotherapy by the virtue of radiotherapy alone not being capable of destroying all cancer cells in larger tumors and therefore additional methods being needed to assist the treatment.

This kind of therapy has many advantages, that include death of large proportions of cancer cells and a painless treatment delivered from the outside of the body. On the other side however, it has also some disadvantages. These include damage to surrounding tissues, the failure to kill cancer cells that are not visible on imaging scans, the long duration of the treatment over monthly periods and the inability to treat tumors in sensitive tissues. However, most of these side effects vanish after the course of the treatment is finished. The only real problem remaining is the impotence of treating tumors surrounded by sensitive tissues. Examples for these tissues would include eyes and the brain.

Proton Beam Therapy

Proton beam therapy is a kind of radiation therapy, with the main difference between conventional radiotherapy and proton beam therapy being the usage of protons instead of photons. Proton beam therapy uses a machine called synchrotron to speed up the protons and beam them into the tumor. The produced speed then determines the energy level and distance of travel of the protons. After leaving the synchrotron, magnets direct the protons towards the tumor. This progress is possible due to protons being relatively heavy particles, especially compared to the in conventional radiotherapy used photons that have no mass. The positive charge of the protons attracts the negatively charged electrons, that are orbiting around atoms. This attraction then pulls the electrons out of their orbit, a progress called ionization. Ionization changes the characteristics of the atoms and consequently the ones of the molecules, damaging the DNA of the cells.

When the protons are moving at high speed, ionization is minimized and when they are moving at low speeds, ionization is maximized. This effect is due to attraction being less severe when the attracting particles persist at higher relative speeds in relation to each other. As the protons advance through the body, they slow down and release energy. The point where the most energy is released and protons interfere the most with the electrons is called the Bragg peak. This position can be exactly calculated using the properties of protons and electrons. Due to most of the beam’s energy being released at this point, the beam stops here.

In conventional radiotherapy, the rays don’t stop after passing through the tumor and therefore continue to damage healthy tissues. This, as a result of exact calculations, achieved preciseness of the proton beams, makes this therapy especially useful in critical areas, that are surrounded by sensitive tissues. As already mentioned above, these areas include for instance the brain and the eyes.

Some of the advantages of proton beam therapy, are the preciseness and the painless treatment. Additionally, it might deliver 60% less radiation to healthy tissues and cause therefore less severe side effects than conventional radiation therapy. This then leads to proton beam therapy may allowing a higher radiation dose due to the reduced damage to the surroundings and hence destroy more of one’s cancer cells. The disadvantages are the enormous cost of the treatment, the scarcity of cancer centers offering this therapy, due to the usage of highly specialized devises, and the inconvenience connected with the long duration of the treatment. Another significant disadvantage is, that proton beam therapy only treats certain types of cancer efficiently. It is the most efficient at threatening solid, well defined and localized tumors. Treating tumors that have spread is less efficient due to the precise proton beams, that would not be able to hit the whole area of a spread tumor. Currently, proton beam therapy is usually reserved for people with rare types of cancer, located in critical areas. This is roughly one in one thousand cancer patients.

Conclusion

Both conventional radiotherapy and proton beam therapy are pretty similar with the main difference being the preciseness of the treatment. This accomplished accuracy could play a great role in treating critical tumor areas or children, whose bodies are still developing and therefore would face more severe and long-lasting effects from healthy cell damage. The crucial bottom line that we have to consider when choosing patients for proton beam therapy is that it cannot be used efficiently for the treatment of all tumors and that it is very costly. Therefore, it may be beneficial to keep conventional radiation therapy as the norm and take proton beam therapy as the exception. Furthermore, momentarily “for most patients […], there’s no strong evidence that proton beam radiotherapy is ‘better’ at curing cancer” (Dr. Adrian Crellin, NHS United Kingdom). This concludes that after current knowledge, using proton beam therapy for threatening tumors in non-critical areas will just be more expensive than conventional radiation therapy without many additional advantages.

References

American Society of Clinical Oncology. (2016, Dezember). Proton Therapy. Retrieved January 21, 2018, from ASCO – Cancer.Net: https://www.cancer.net/navigating-cancer-care/how-cancer-treated/radiation-therapy/proton-therapy

NHS. (2014, September 3). What is proton beam therapy? Retrieved January 21, 2018, from NHS: https://www.nhs.uk/news/cancer/what-is-proton-beam-therapy/

Seattle Cancer Care Alliance. (n.d.). Questions and Answers About Proton Therapy. Retrieved January 21, 2018, from Seattle Cancer Care Alliance: https://www.seattlecca.org/treatments/proton-therapy/questions-and-answers-about-proton-therapy

Smith, E. (2015, July 16). Proton beam therapy: where are we now? Retrieved January 21, 2018, from Cancer Research UK: http://scienceblog.cancerresearchuk.org/2015/07/16/proton-beam-therapy-where-are-we-now/

The National Association for Proton Therapy. (n.d.). HOW IT WORKS. Retrieved January 21, 2018, from Proton Therapy: http://www.proton-therapy.org/howit.htm

WHY IS PROTON THERAPY A PREFERABLE OPTION, AND WHAT IS THE BRAGG PEAK? (n.d.). Retrieved January 21, 2018, from Proton Therapy Today: http://www.proton-therapy-today.com/what-is-proton-therapy/why-is-proton-therapy-a-preferable-option-and-what-is-the-bragg-peak/

Winship Cancer Institute. (n.d.). Radiation Therapy. Retrieved January 21, 2018, from CancerQuest: https://www.cancerquest.org/patients/treatments/radiation-therapy

 

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