I have taken a quick listen to the Senate Veterans’ Affairs Committee field hearing in Philadelphia on Monday (you can find the mp3 files here, along with witness statements). Nothing came out that was not already in the NRC report. However, Sen. Specter indicated that a hearing of the full committee in Washington will be forthcoming. That said, here are a few of my thoughts.
Continue reading Not much new from the Philadelphia VA hearing
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Sen. Arlen Specter’s field hearing on the Philadelphia VA mess is set to begin today. It will be interesting to see if any new details will come out. Apparently, Dr. Kao will be answering questions at the hearing, so at least we will hear his side of the story. Before the spinning starts, though, we can look at the NRC special inspection report to get a better idea of the facts of the case. The NRC report can be found by going the NRC ADAMS search site and searching for document accession number ML090900382. It’s always nice when one of your favorite bloggers writes about one of your favorite subjects. PalMD has been writing a series of blog posts discussing the basics of the biology and treatment of cancer. His latest post is an overview of radiation therapy. As usual, he does a good job explaining difficult concepts in a way that anyone can understand. Check it out. The Philadelphia VA hospital story has really taken off. Usually when there is a high profile radiation therapy accident, like with the unfortunate Lisa Norris, the interest dies off fairly quickly. However, in this case, the interest seems to be just beginning to ramp up. A story that had been brewing for months has finally broken into the I’m still tied up with the annual calibration on one of our accelerators, but I can see the light at the end of the tunnel. In the meantime, here are a few updates on the Molybdenum-99 shortage. The American College of Radiology has posted an article from Reuters describing some of the ways that US hospitals are coping with the loss of needed medical isotopes. Basically, it involves wait lists, rationing or switching to more expensive or less accurate tests. The Society for Nuclear Medicine has put together a clearing house of information and recommendations here. One person subscribes to the notion that the Chinese symbol for crisis is also the symbol for opportunity. In an unrelated story, Orac celebrates Homeopathy Awareness Week by pointing out a story about a British store that sells homeopathic plutonium. We’re going back to the 80’s with this biweek’s installation of one star Mondays. It’s that favorite of Karaoke bars and American Idol semi-finalists: Total Eclipse of the Heart. This is one of those songs, like All Along the Watchtower, in which the cover surpasses the original. However, in this case, the song is so bad that two cover versions surpass it. So without further ado, here are The Dan Band and Norwegian pop sensation Hurra Torpedo (both NSFW unless you’re in Norway).
Nothing is finer in life than sitting in your recliner, watching sports on TV and eating fried, lard encrusted food. Surprisingly, it turns out that it may have some serious health consequences. No, I’m not talking about the obesity epidemic. I’m talking about radioactive La-Z-Boys. In 1998, an Indiana company unknowingly used metal contaminated with the radioactive isotope Cobalt-60 to make brackets for 1,000 La-Z-Boy Reclina-Rockers. Fortunately, the problem was discovered when metal leftovers were sent to a scrap yard that detected the radiation and refused the shipment. The discovery led to a massive state and federal effort that managed to recall all of the recliners before they had left the warehouse. A spokesman for the No-Sag Products Co. that manufactured the brackets stated that any health threat was minimal, but asked the federal government to create standards for the radioactive material content of consumer products. While there may not be standards for radioactive content, there are standards for the radioactive dose allowed to be given to members of the general public. In radiation therapy, we have to design our facilities to meet those standards. Would a radioactive La-Z-Boy meet those standards? Was the health threat only minimal? The last post in this series showed how a linear accelerator is used to create a beam of radiation. Now we will talk about how we can conform the beam to the shape of the tumor we are trying to treat while blocking the beam from irradiating normal tissue. Once the beam is generated, it is collimated so that only photons travelling forward are let through. This beam is much more intense in the forward direction, so a filter is put in place to cool the beam down towards the center. After passing through this flattening filter, the beam profile is more uniform across its width. This is important since we do not want one side of the tumor to get less dose than another. Once we have a relatively flat beam to work with, we can begin to shape the field to the patient. Most linear accelerators have a pair of collimating “jaws”. These jaws are made of lead or tungsten, and are movable so that the field can be blocked to make it square or rectangular with sides up to 40 cm long (for a typical linac). These collimators are housed in the “head” of the linear accelerator.  The directions in which a linear accelerator can rotate. The beam then exits the linac through a window. Further tools to shape the beam can be mounted to the outside of the window between the beam and the patient. One such device is a wedge, a physical wedge of metal that lowers the dose on one side of the field relative to the other. Another is a block, a layer of attenuating material that stops the beam in certain areas to shield normal tissue beneath it. These blocks are usually custom made for each patient to conform to the edges of the treatment volume. Usually the material used is called cerrobend or Wood’s metal. This is a lead alloy that has a very low melting point, only 70 degrees Celsius. This makes it very convenient to melt down and form. The downside is that forming cerrobend blocks is very labor intensive, and for a busy clinic, making blocks is a full time job. In addition, any change that needs to be made during a patient’s treatment means that you have to start from scratch with a new block. Since lead is a hazardous material, making blocks is complicated from an occupational safety standpoint as well. For these reasons, the multi-leaf collimator or MLC was developed.  The leaves of a multi-leaf collimator  Shielding the eye from radiation using a block or mlc. This image is of a patient that had a tumor (shown in green) in the sinus cavity. This is called a beams eye view and shows what you would see if you could look from the linac head directly down the beam toward the patient. The image on the left shows the position of the collimating jaws, outlining in yellow the treatment field. As you can see, the patient’s eye, outlined in blue, is within the field and will receive a significant amount of radiation unless it is shielded. The middle image shows how a block would shield the eye and only leave the tumor, plus a slight amount of margin, treated. The right image shows how the same thing could be accomplished using an MLC. Conforming the beam to match the desired field is where the physics staff (physicists and dosimetrists) start to make the physician’s treatment plan a reality. It is where we work closest with the physician to make sure the right balance between tumor dose and normal tissue dose is struck. So what goes into that decision? My next post in this series will explore how the beam of radiation delivers the dose to the patient, and future posts will discuss how we use that information to create a treatment plan. Image licensed under the Creative Commons Attribution ShareAlike 2.5 license from Vojtěch Hála. Things have been so busy lately that I forgot to post an awful song yesterday. On each of our accelerators we are required to perform an annual calibration. This takes quite a bit of time and obviously cannot be performed during patient treatment hours. That means a lot of nights and weekends. Working on and off, it usually takes about one or two months to complete. So posting will probably be a light for the next month or so. In the meantime, to salve your disappointment, here is Debbie Boone, live from the Grammys in 1977.
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