Recent Clinical Study Compares Proton Therapy and IMRT for Prostate Cancer Treatment in Younger Men

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Improvements in treatment technologies consistently push the medical community to assess the potential benefits, risks, and costs. As proton therapy becomes more accessible, studies will be used to evaluate the most broadly beneficial ways to use the limited resource.

A 2018 report, published in the Journal of Clinical Oncology, authored by Hubert Y. Pan et al., compared the toxicities and costs of treating prostate cancer with IMRT (x-ray) or proton therapy1. The authors evaluated a slightly different population than typically reviewed in prostate cancer studies. They focused on patients who were 65 years old or younger and had commercial insurance coverage. The study yielded some interesting results, but as with most clinical papers, it needs some points of reference and context to understand.

Proton therapy was associated with lower urinary toxicity (side effects) and better erectile function at 2 years versus IMRT (an advanced form of x-ray/photon therapy).  The authors report proton therapy was associated with a positive difference across multiple domains of urinary toxicity including incontinence, stricture, and bleeding.  This urinary benefit was seen in both the short term and the long term. This indicates there is an ongoing, lasting benefit for those treated with proton therapy.

The proton therapy patients in this study did have a 5% higher occurrence of bowel toxicity at two years which was limited mainly to rectal bleeding. There is some important context needed to understand this outcome. Rectal bleeding is a known possible complication of proton therapy, but it can be part of the healing process of the anterior rectal wall. It usually gets better on its own or resolves with medication.

To put this in perspective, in a well-respected study from the University of Florida, only 8 men out of more than 1,300 prostate patients, required referral to a GI specialist to treat the rectal wall2. This UF study also showed that proton patients had less rectal pain with bowel movement and a lower rate of bowel urgency than those treated with IMRT.

The clinical evidence showing the advantages of proton therapy continues to accumulate. It will be increasingly important to place the data presented in these studies within the context of our existing knowledge base. The biggest take away of this study may be that younger men treated with proton therapy had decreased urinary and erectile side effects compared with those treated with an advanced form of x-ray therapy. Quantifying the value of that difference to patients may not be as straight forward.

  1. Hubert Y. Pan, Jing Jiang, Karen E. Hoffman, et al (2018). Comparative Toxicities and Cost of Intensity-Modulated Radiotherapy, Proton Radiation, and Stereotactic Body Radiotherapy Among Younger Men with Prostate Cancer. Journal of Clinical Oncology, 36:18, 1823-1830. DOI: 10.1200/JCO.2017.75.5371
  2. Bryant, Curtis et al. (2016). Five-Year Biochemical Results, Toxicity, and Patient-Reported Quality of Life After Delivery of Dose-Escalated Image Guided Proton Therapy for Prostate Cancer. International Journal of Radiation Oncology • Biology • Physics, Volume 95, Issue 1, 422 – 434. DOI: https://doi.org/10.1016/j.ijrobp.2016.02.038