In the treatment of cancer, radiation therapy works by attacking a cancer cell’s DNA, inhibiting growth and reproduction. While advancements in targeting have made the delivery of photon radiation more exact, it can damage nearby healthy tissue and organs. X-rays deposit their energy on the way to, and then beyond, its target, necessitating administration of entry and exit doses.[1] This additional exposure can cause substantial side effects for patients.
Proton therapy, conversely, leaves healthy tissue undisturbed.[2] This distinct advantage comes from the unique behavior of protons as they move through the body. Demonstrated on the Bragg Curve, protons reach a peak near the end of their path. The absorbed dose of radiation increases very gradually with greater depth, rising to its peak when the protons are stopped. Highly charged protons deliver a treatment dose more directly into targeted tissue and tumors than X-rays. In clinical applications, proton therapy can be administered to a precise depth within a patient’s body, to a site as small as a few millimeters in diameter — leaving healthy cells unaffected.[3]
The Bragg Peak
Note: Spread-Out Bragg Peak (SOBP) is defined as the extended uniform dose region in depth formed by the optimal stacking of multiple depth dose curves of pristine peaks of different energies.
In head and neck cancers specifically, proton therapy significantly reduces unnecessary radiation exposure to the spinal cord, auditory canal, and thyroid. By reducing exposure to these critical organs, patients experience less long-term complications and a reduction in the expense of long-term follow-up care following radiation therapy treatment.[4]
Interested in learning more about treating certain head and neck cancers with proton therapy? Download our whitepaper.
References
[1] Newhauser WD, Zhang R. The physics of proton therapy. Physics in Medicine and Biology. 2015 60(8).
[2] Zhang X, Li Y, et. al. Intensity-Modulated Proton Therapy Reduces the Dose to Normal Tissue Compared With Intensity-Modulated Radiation Therapy or Passive Scattering Proton Therapy and Enables Individualized Radical Radiotherapy for Extensive Stage IIIB Non-Small-Cell Lung Cancer: A Virtual Clinical Study. Int J Radiat Oncol Biol Phys. 2010 June 77(2):357-66.
[3] Welsh J, Gomez D, et. al. Intensity-modulated proton therapy further reduces normal tissue exposure during definitive therapy for locally advanced distal esophageal tumors: A dosimetric study. Int J Radiat Oncol Biol Phys. 2011 81(5): 1336–1342.
[4] Diwanji TP, Mohindra P, et. al. Advances in radiotherapy techniques and delivery for non-small cell lung cancer: benefits of intensity-modulated radiation therapy, proton therapy, and stereotactic body radiation therapy. Transl Lung Cancer Res. 2017 Apr;6(2):131-147.
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