When it comes to treating prostate cancer (PCa) with radiation, there’s a new kid on the block. Conventional external beam radiation therapy (EBRT) has been routinely performed for more than half a century. EBRT targets the whole gland. It is considered a safe and effective alternative to surgical gland removal (radical prostatectomy). Since its original form, it has continued to evolve.

There are two types of subatomic particles used for PCa radiation: photons and protons. Traditional radiation uses photons (lower photon doses are used for x-rays). The problem with photons is difficulty focusing and controlling them. They can travel deeply into the body but scatter some radiation along their path, and they continue beyond the target into healthy tissue. Conventional EBRT for PCa can have damaging side effects for the bladder, colon, rectum, and nerves that control erections; these effects may occur gradually over time, causing late onset side effects and secondary cancers.

In order to reduce radiation side effect risks while improving effectiveness, delivery systems with better focus have been developed. Thus, you may have heard of 3-D conformal radiation, intensity modulated radiation therapy (IMRT) and stereotactic body radiation therapy (SBRT). These have fewer late onset side effects, but the search for something even better has led to proton beam therapy.

Protons have different physics properties than photons so they deposit the majority of their energy in the targeted tumor, with only a small exposure beyond the target. Photon therapy seems to reduce damage to surrounding tissues, but there’s an economic problem. It’s very costly to build a specialized facility, so it’s not widely available. Furthermore, insurers have lately begun resisting reimbursing for the procedure. This is because it costs more than conventional radiation but has not been demonstrated to offer cancer results. While proton beam is excellent for things like pediatric brain tumors, such cancers are relatively infrequent—while PCa is the most common tumor cancer in men. Proton centers need to treat numerous PCa cases, but If insurance won’t cover it. the center can’t repay loans needed for construction and set-up. It appears that proton beam for PCa has an uncertain future.

Carbon ion radiation

Enter carbon ion radiation therapy (CIRT)! Unlike photons, protons and electrons, ions are entire atoms or molecules, so they are heavier than subatomic particles. According to Frontiers in Oncology, “The therapeutic use of heavy ions, such as carbon, has gained significant interest due to advantageous physical and radiobiologic properties compared to photon based therapy. By taking advantage of these unique properties, carbon ion radiotherapy may allow dose escalation to tumors while reducing radiation dose to adjacent normal tissues.” Similar to proton therapy, the peak of the lethal energy dose is released in the target. However, CIRT’s transfer of carbon ion energy is more direct and efficient than proton energy, so it packs a more powerful punch to the DNA of cancer cells with less effect on neighboring tissues.

Most PCa patients have not yet heard much about CIRT because it didn’t start gaining ground until after 2000. Pioneering research in CIRT came from Japan starting in 1994, where their National Institute of Radiological Sciences conducted two dose-escalation studies from 1995-2000.^[i] In 2003, Japan’s Ministry of Health, Labor and Welfare approved the treatment for prostate cancer. Since then, Japan and Germany have been leaders in testing CIRT against an amazing range of cancers such as head and neck tumors, cancers of the lung, pancreas, bowel, breast, skin, etc.

CIRT for Prostate Cancer

A 2016 Japanese multicenter study reported on 2157 PCa patients who were treated with CIRT. Here is a summary of their results:

	Low-risk	Intermediate-risk	High-risk
Number of patients	263 (12%)	679 (31%)	1215 (56%)
5-year biochemical disease free	92%	89%	92%
5-year cancer-specific survival	100%	100%	99%
Overall survival (any other cause)	100%	99%	96%

There were low rates of side effects. Short term followup revealed 58% incidence of low-to-moderate increase in urinary frequency that resolved fairly quickly after treatment. Low-to-moderate late onset side effects were less than 5%, with no severe side effects reported for either short or longer term followup. While these results are encouraging, more studies with PCa are needed.

Perhaps the biggest obstacle to research is the small number of international centers offering CIRT. As of this writing, there are 13 centers in Japan, China and Europe; in March 2020, the Mayo Clinic (Jacksonville, FL) announced plans to construct the first CIRT facility in North America.

So, stay tuned. If CIRT has not yet appeared on the prostate cancer radar screen in the U.S., it won’t be long before doctors and patients with PCa or many other types of cancer will be hearing about it as its track record grows.

NOTE: This content is solely for purposes of information and does not substitute for diagnostic or medical advice. Talk to your doctor if you are experiencing pelvic pain, or have any other health concerns or questions of a personal medical nature.

References

[i] Ishikawa H, Tsuji H, Kamada T, Akakura K, Suzuki H, Shimazaki J, Tsujii H; Working Group for Genitourinary Tumors. Carbon-ion radiation therapy for prostate cancer. Int J Urol. 2012 Apr;19(4):296-305