Single-Dose Radiation Found Effective for Prostate Cancer

by Jessica Hall

Normally, when you hear iridium, you may think of the satellite constellation. But the uses of this exotic element are not limited to digital entertainment. Iridium also has isotopes that are useful in cancer treatment — and especially in prostate cancer treatment. The results of a two-year study from Europe have come in, concerning the use of iridium-192 in single-dose radiation therapy for prostate cancer. The treatment is called HDR (high dose rate) brachytherapy. And the outcomes are encouraging.

Here’s how it works: HDR brachytherapy involves using ultrasound to guide the precise positioning of catheters, while the patient is under spinal or general anesthetic. Then a measured dose of iridium-192 is delivered via the catheters to the affected area of the prostate, avoiding other structures such as the bladder and the bowel, so that they deliver as much of the dose as possible, precisely to the target region. Such a treatment would happen on an outpatient basis — it takes about half an hour.

In a two-year study of 45 patients who had low- to moderate-risk prostate tumors of 60cc or less, HDR iridium brachytherapy was so well-tolerated that none of the patients experienced “grade 3” (severe) side effects. At follow-up appointments six months post-treatment, 77 percent of patients said they were “extremely satisfied” with their treatment and quality of life, and 23 percent said they were “very satisfied.”

These results were presented at a recent conference of the cancer research body ESTRO. Dr. Alfonso Gomez-Iturriaga, who presented the research, told the conference, “Our study demonstrates that patients do not suffer higher toxicity or a worse quality of life than might be expected with other methods of delivering radiation treatment. In fact, patients are very satisfied with this single outpatient treatment, which they find convenient and which allows them to return rapidly to normal activities.”

“It is too early to say that this strategy can be used outside the trial setting,” he continued, “but it seems quite clear that the toxicity and impact on quality of life are very low. Longer follow-up for at least five years is needed to demonstrate definite cancer control.”

The dose makes the poison

This study has implications beyond just the success of this specific isotope in this specific procedure. Recall Paracelsus’ statement that the dose makes the poison. Giving the same quantitative dose of radiation in a single dose, versus over a long period of time, can be more acutely toxic; by way of example, the same 10-Gy dose that can cause hair loss to be permanent if given all at once can spare those follicles if delivered over a period of months or years. But this research involved doses of 19 Gy. Encouraging indeed.

We’ve recently written about another form of brachytherapy that uses tiny, tiny implants to avoid the pass-through damage that a radiation therapy beam can do to tissue “in the way.” But where that places a solid and durable implant in tissue, this cather-delivery technique is closer to a wash or a local infusion. HDR brachytherapy also contrasts in another way with the tiny radiotherapeutic implants we wrote about earlier. Those implants deliver a low dose of radiation over a long period of time, where these are quick but higher-dose. It’s sort of the other side of the radioactivity coin.

No method of treatment is without its drawbacks. And the choice of what therapy to use is between a patient and their doctor. Nevertheless, there do exist differences between the HDR and LDR application modalities. “The precise control over dose delivery inherent in HDR brachytherapy is not readily achievable with low-dose rate (LDR) brachytherapy because of several factors: movement of the radioactive seeds away from the target site, swelling of the prostate after the implant and uncertain dose delivery outside the prostate, which can all contribute to less than optimal dose distributions,” explained Dr. Gomez-Iturriaga.

“With LDR brachytherapy, the actual dose distribution achieved is not known until the post plan quality assurance is completed, several weeks after the treatment. In contrast, with HDR brachytherapy, what you plan to treat is exactly what is actually administered.”

Now read: What is gene therapy?


Originally published at www.extremetech.com on June 22, 2017.

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