Soon after learning he had early stage prostate cancer, Paul Kolnik knew he wanted that cancer destroyed quickly and with as tiny disruption as feasible to his busy life as the New York City Ballet’s photographer.

So Mr. Kolnik, 65, chose a sort of radiation therapy that is raising some eyebrows in the prostate cancer field. It is much more intense than regular radiation and requires a lot less time — five sessions more than two weeks instead of 40 sessions over about two months or 28 sessions more than 5 to six weeks.

The newer therapy is surging in reputation, but no one knows whether or not it is as effective in curing prostate cancer, or how its side effects compare.

The rise of short-course radiation is an instance of the evidentiary blind spots that bedevil the therapy of prostate cancer. It is second only to lung cancer in males, striking 180,000 individuals a year. But treatments for lung cancer, and for other typical cancers like those of the breast and colon, have been evaluated in randomized clinical trials a lot more often than those for prostate cancer.

The number of men acquiring the quick, intense treatment, known as stereotactic physique radiation therapy, or S.B.R.T., much more than doubled to 1,886 in 2013 from 716 in 2007, according to the most current Medicare data. The number of guys getting standard radiation therapy fell more than that very same time period, according to Medicare, to 47,512 from 66,549.

The National Cancer Institute has just agreed to fund a clinical trial that researchers hope will settle which remedy is greater. It will randomly assign 538 guys to have either a short course of five intense radiation sessions over two weeks or 28 therapies more than 5 and a half weeks, comparing outcomes for top quality of life as well as disease-free survival.

But it will be at least eight years before the answers are in. In the meantime, guys and their physicians are left with uncertainty.

“Ideally, we want to show 5 remedies is far better,” said Dr. Rodney J. Ellis, a radiation oncologist at Case Complete Cancer Center in Cleveland and the principal investigator for the trial.

One particular cause for the dearth of data is that prostate cancer generally grows gradually, if at all, so it can take several years to see if a therapy saved lives. It is pricey and tough to comply with individuals for such a lengthy time, and the treatments given to the guys frequently adjust more than a decade, creating doctors wonder if the benefits are relevant.

Also, researchers who have tried to conduct research comparing therapies usually failed because specialists were currently convinced that the method they utilized was best and have been reluctant to assign males to other remedies. Dr. Ian Thompson of the University of Texas Wellness Science Center in San Antonio, stated he was involved with numerous clinical trials that withered for that explanation.

When clinical trials succeed, though, they can give critical info. For example, a recent one showed that hormone-blocking drugs can prolong life for guys whose prostate cancer recurs soon after surgery to get rid of the prostate.

The researchers on the new study consider recruitment will not be a major dilemma since they are comparing various courses of radiation, rather than entirely various approaches — for example, surgical removal of the prostate versus implantation of radioactive seeds in the prostate. A study to investigate these two approaches closed because investigators were in a position to enroll only 20 sufferers, Dr. Thompson mentioned.

For guys, top quality of life is usually pivotal in selecting a therapy, weighing which feasible side effects sound worse: with surgery, urinary incontinence and impotence or, with radiation, bowel problems such as diarrhea and rectal leakage, and impotence. With the shorter radiation remedy, there is also a possibility that scarring can block the urethra, an impact that might not emerge till years after the treatment.

In the absence of a broad base of solid evidence, males frequently make choices primarily based on personal preferences or on the suggestions of a trusted medical professional. Like Mr. Kolnik, some want as short a recuperation as possible and locate the newer type of radiation therapy appealing.

But prostate cancer specialists be concerned about the lack of data.

Dr. James Yu, a radiation oncologist at Yale, who will lead the high quality of life assessment for the new clinical trial, says essential unanswered concerns are, “How fast can you give it and how fast is also quick?”

Quite higher dose radiation was studied in the therapy of lung cancer, stated Dr. Anthony V. D’Amico, a radiation oncologist at Brigham and Women’s Hospital and the Dana Farber Cancer Institute in Boston. For lung cancer individuals with little tumors that are not near sensitive structures, like big blood vessels, it seems to be just as curative as surgery.

But lung cancer is simpler to treat since, with properly selected sufferers, doctors can steer clear of sensitive tissues — all the oncologist has to worry about is hitting the cancer.

Not so with prostate cancer.

“The urethra is inside the prostate and the bladder neck is actually touching to leading of the prostate,” Dr. D’Amico mentioned. Also, the rectum is directly behind the prostate. Radiation can harm those other tissues, he mentioned.

Injuries to the urethra and bladder neck may possibly not show up until five or 10 years right after the remedy, Dr. D’Amico noted. These structures can scar and close, limiting the flow of urine. It also can take years ahead of rectal scarring produces symptoms like bleeding.

A couple of years ago, Dr. Yu and his colleagues looked at Medicare information and reported that guys who had a lot more intense radiation therapy were far more most likely to have urinary problems after two years than these who had the longer-course therapy.

Dr. Yu noted that his study was not a randomized trial, the gold regular, but he mentioned the benefits had been not reassuring. Now, though, he is not so sure the intense therapy is worse.

“In my own experience, these guys have accomplished really well,” he stated. “That tells us that strategies enhanced, or the healthcare claims we evaluated had been not indicative of significant toxicity, or the way we and other folks at higher-volume centers provide radiotherapy is distinct.”

The lack of strong information bothers Dr. Daniel W. Lin, chief of urologic oncology at the University of Washington. When males ask him about the shorter radiation course, he tells them, “It almost certainly can perform but it doesn’t have lengthy-term benefits and it hasn’t been tested against common radiation.”

At centers like Sloan Kettering, doctors are relying on their own encounter.

Dr. Michael J. Zelefsky, a radiation oncologist who treated Mr. Kolnik there, said that several years ago, 90 percent of his patients had the standard course of treatment. Now 90 percent pick the shorter course. On the basis of Sloan Kettering’s knowledge with several hundred males who had the intense radiation therapy more than the past 3 years, the remedy, he said, “is emerging as a extremely thrilling form of therapy.”

Mr. Kolnik is far more than satisfied.

In the course of his treatment, he stated, “I entirely kept up with my schedule.” He did not even tell anybody other than a couple of close buddies that he was possessing radiation therapy.

“The remedy starts and it finishes just before you even realize it,” Mr. Kolnik stated.