[ RadSafe ] Medical Breast Radiation Thread

[Robert Barish]

Fellow RADSAFERS, the ongoing and extensive back and forth communications regarding the woman with breast cancer who apparently set off a security monitor points out one fact that seems self-evident from the widely diverging opinions about the causes of this incident.

It seems that RADSAFE has lost almost all of the experienced medical radiological physicists who once subscribed here.

This unfortunate circumstance is most likely due to the preponderance of postings that have nothing to do with the scientific issues of radiation protection, but instead give voice to the opinions of the list’s subscribers about world events, political issues, personal grievances and the like.

I know that I am not the first person to note this, but it would be interesting to see how many subscribers there are now in comparison with, say, five years ago. 

Of course, this posting could itself count as one of the irrelevant messages I so abhor, unless I add some scientific facts. So let me do so using my background as an experienced radiotherapy physicist as well as a radiation protection specialist.

When, almost fifteen years ago, total mastectomy for the treatment of breast cancer was compared with local excision of the tumor followed by radiation treatments, it was noted that the survival benefits were statistically identical - with a clearly better cosmetic outcome since most of the breast was preserved.

Presently, the standard of treatment is external beam radiotherapy for those stages of the disease where regional as well as local control is necessary. For certain localized tumors following a minimal surgical intervention, often described as a lumpectomy, a local radiation boost to the area containing the tumor was shown to be all that was needed as adjuvant treatment. 

Presently, this radiation therapy is administered in one of two ways. For somewhat larger areas, a set of hollow catheters is inserted into the breast with connectors that enable them to be attached to a device known as a high-dose-rate afterloader (or HDR) unit. For a period of a few minutes on successive days an Iridium-192 source with an activity of approximately 370 GBq (10 Ci) is sent into these catheters by the machine in a placement pattern that is determined by a treatment planning process that attempts to optimize the dose distribution in the area that once contained tumor cells and is at risk for recurrence of the cancer.

For patients with invasive ductal carcinoma (DCIS), and tumor sizes that were measured as less than 3 cm in diameter, a new technique was developed several years ago utilizing a small balloon that is inserted into the breast and inflated with saline solution to form a small spherical cavity. This small balloon also has an exterior connector that allows the insertion of an HDR source, one that may be placed centrally in the sphere or possibly stepped in position by the computer-controlled servo motors of the HDR unit.

In both of these therapies, the high-activity Ir-192 source is brought back into its container following a few minutes of treatment that usually takes place on a daily basis over a one-week period. 

With a dose rate of almost 5 Gy per hour (500 rad per hour) at a distance of 10 cm from the source there is no possibility that the Iridium source leaves the treatment room inside the patient. Such an event did happen years ago when a source broke off its tether, with tragic consequences, but it is now a requirement that a physicist survey every patient following treatment to verify that the source was successfully returned to its container.

So what is left as a possible source of activity in a breast cancer patient that might be detected by a survey instrument at a baseball game?

In 2006, researchers in Canada reported the first trial of permanent seed implants (using Pd-103 seeds of the type often implanted for prostate cancer) in women with early stage breast cancer. This is very preliminary data and is unlikely to be the source of radiation in the case reported here on RADSAFE. Also, as has been mentioned here, the extremely low energy emissions from Pd-103 are not easily detected at anything other than very close range.

So what is left is simply a broad range of possibilities related to the administration of various radioactive substances for an equally broad range of possibilities related to the health issues of the specific patient. Yes, as has been mentioned, lymphoscintigraphy is often used to track the location of lymph nodes that might become pathways for the spread of breast cancer away from its primary site. And no, the radionuclide is not always completely removed when the nodes are dissected because the injection might be into breast tissue that drains into the nodes, rather than into the nodal chain itself. So some of the radionuclide might be left behind.  And it is, of course, also possible that any number of other nuclear medicine procedures including bone scans might have been performed on this patient. So, without a detailed medical history of this woman we may never know exactly what was detected.

That’s the science. And it's already been beaten to death! 

Now back to my own editorial. Of course it’s interesting to learn about new radiation detection devices. Advances in the science of radiation detection and measurement are perfectly appropriate for RADSAFE postings. But, in my opinion, comments about the political correctness of monitoring for radioactive materials in public places and the impact of such monitoring upon civil liberties of the population are certainly worthy topics for discussion on any number of internet bulletin boards. As a participant in Pacifica Radio programming for more than forty years, I will defend with all of my strength the freedom of all of you to voice the range of diverse opinions as have been presented. 

But just not here, please! Let RADSAFE be for scientific and technical communication, as it is intended.

Robert Barish, Ph.D., CHP, FAAPM