Radiation Oncology 101

[radoncbound]

Hi Everybody,

I am an intern going into radiation oncology. I am repeatedly disappointed and sometimes even appalled at how little most residents and even attendings know about radiation oncology, especially the basic science behind it. I would love to give a little presentation for my internal medicine residents; however, I am of course very busy. Would anybody happen to have a PowerPoint presentation already made that I could work off of (and appropriately credit) on the basics of radiation oncology and radiobiology?

Thanks

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[BlackSails]

You could start with review of basic radiation physics. Going over units, effective biological dose, etc.

 

[deleted4401]

I felt the same way, but 2 years out of internship, I'm thinking they really don't need to know what we do (most of my friends here are medicine), unless you have had some ridiculous things happen (people not consulting rad-onc for cord compression or SVC). Honestly, I'd save your breath for maybe giving a talk to the med-onc and surg-onc/ENT/urology/etc. fellows once you're a resident. You'll have a little more credibility, plus they will actually benefit from the knowledge.

S

 

[clintpark]

I felt the same way, but 2 years out of internship, I'm thinking they really don't need to know what we do (most of my friends here are medicine), unless you have had some ridiculous things happen (people not consulting rad-onc for cord compression or SVC). Honestly, I'd save your breath for maybe giving a talk to the med-onc and surg-onc/ENT/urology/etc. fellows once you're a resident. You'll have a little more credibility, plus they will actually benefit from the knowledge.

S

I agree with Simul. With all due respect , what you know about radiotherapy as a medical student or an intern may be spotty, especially if you want to cover the basic science of RT. If you want to cover radiation management of a specific condition, you can probably do a good job.

 

[stephew]

There is no reason that someone outside of radonc should know the basic sciences behind it, any more than they do behind chemotherapy.

some general principles (just for interests sake, because as you say, few understand the technique) and uses and when you should call radonc in house would be more appropriate.

However let me strongly discourage you from using someone else's ppt presentation. This is not academically sound or appropriate. I appreciate that you wish to give credit to the author. Nevertheless, this is not good form and is academically frowned upon. Generally, if you wish to give a talk, it should be based on your work. Otherwise invite someone to do it.


Good luck.

Hi Everybody,

I am an intern going into radiation oncology. I am repeatedly disappointed and sometimes even appalled at how little most residents and even attendings know about radiation oncology, especially the basic science behind it. I would love to give a little presentation for my internal medicine residents; however, I am of course very busy. Would anybody happen to have a PowerPoint presentation already made that I could work off of (and appropriately credit) on the basics of radiation oncology and radiobiology?

Thanks

 

[stephew]

You could start with review of basic radiation physics. Going over units, effective biological dose, etc.

Absolutely not. this is not at all useful to internal medicine docs. Not even to medical oncologists unless in the most general way. Aim your talk appropriately to your audience. As you say, you're very busy. So are they. They have no desire nor the time to learn something they will never use and have no inherent interest in.

 

[CNphair]

Internal Medicine docs need to know when to call us and how to explain the very basic principles of treatment to a patient (its everyday, you may have a skin reaction, etc...) They do not need to know anything fancy about physics or radiobiology anymore than I need to know exactly how a cardiac stent is placed. Save your precious, precious time as an intern on more productive things....like sleep.

 

[bearchop]

I'm not sure if I'm posting this in the right place. I have 2 basic questions. What are port films used for and how is cone-beam CT different than regular CT? I am interested in radiation oncology and have heard these terms, but am not sure what they mean. Thanks!

 

[Gfunk6]

Port films are taken by the radiation therapists during the patient's treatment. Generally, these are done qweekly or so. These are simply two dimesional images to make sure thare are no major errors in treatment set-up (e.g. the patient is not positioned properly). The port films are compared to the patient's original DRR (digitially reconstructed radiograph; obtained from planning CT) or simulation film.

Regular CT scans are lower energy than cone beam CTs. The former use the photoelectric effect to generate high-quality images. Cone beam CTs are done from the treatment machine themselves rather than a dedicated diagnostic scanner and use higher energies that rely on the Compton effect. Cone beam CTs have markedly inferior quality b/c at the higher energies they do not distinguish well between tissues w/ different atomic numbers (e.g. fat vs. bone vs. muscle). However, as a result, they do not cause scatter from metal artifacts (e.g. gold implants, hip prostheses) like regular CTs do.

Both port films and cone beam CTs are used to verify patient set up. Given that the latter is in three dimensions there is theoretical benefit for certain types of tumor geometries. There is more to both than I stated but you get the general idea.

 

[Mulletfluf]

Regular CT scans are lower energy than cone beam CTs. The former use the photoelectric effect to generate high-quality images. Cone beam CTs are done from the treatment machine themselves rather than a dedicated diagnostic scanner and use higher energies that rely on the Compton effect. Cone beam CTs have markedly inferior quality b/c at the higher energies they do not distinguish well between tissues w/ different atomic numbers (e.g. fat vs. bone vs. muscle). However, as a result, they do not cause scatter from metal artifacts (e.g. gold implants, hip prostheses) like regular CTs do.

Both port films and cone beam CTs are used to verify patient set up. Given that the latter is in three dimensions there is theoretical benefit for certain types of tumor geometries. There is more to both than I stated but you get the general idea.

I was under the impression that CBCT images were kV rather than MV, or at least in some cases. For example, Varian's trilogy uses a kV imager to capture pt images, but utilizes a cone beam because the patient is not translated into or out of the beam (essentially capturing multiple slices at once). However, Tomotherapy machines use MV imaging and do not utilize cone beam technology because the patient is actually moved into and out of the bore.

 

[Gfunk6]

I was under the impression that CBCT images were kV rather than MV, or at least in some cases.

That may very well be, it was pure institutional bias on my part. We use Siemens machines w/ on-board CBCTs.

 

[Tanner]

Regular CT scans are lower energy than cone beam CTs. The former use the photoelectric effect to generate high-quality images. Cone beam CTs are done from the treatment machine themselves rather than a dedicated diagnostic scanner and use higher energies that rely on the Compton effect. Cone beam CTs have markedly inferior quality b/c at the higher energies they do not distinguish well between tissues w/ different atomic numbers (e.g. fat vs. bone vs. muscle). However, as a result, they do not cause scatter from metal artifacts (e.g. gold implants, hip prostheses) like regular CTs do.

The difference between "regular CT" vs. cone-beam CT is not the energy used but how it obtains the images. "Regular CT" as we know it, involving that donut-shaped scanner, utilizes a fan-beam array. It's basically a thin slit-like detector. And because it's a slit, you have to scan the patient with multiple rotations in order to obtain an aggregate tomographic picture.

Cone-beam CT, however, utilzes a flat planar detector and in essence, it's like stacking many slit detectors together, so instead of requiring multiple rotations, all you really need is to do one rotation and a computed tomographic-like image can be obtained.

Logistically and structurally-wise, it is difficult to incorporate a fan-beamed CT system on a linac, though it's been done- look into "CT on rails". On the other hand, it's easy to put a cone-beam CT on a linac. With MV cone-beam CT, the cone-beam detector is directly opposed to the treatment head, since the treatment head is the xray source. With the kV cone-beam CT, the current method is to have the detector and kV xray source axis orthogonal to the treatment head, though research is ongoing to have the axis directly opposed, like the MV version.


Hope that's clear as mud...

 

[radiaterMike]

Hope that's clear as mud...

actually- very concise and easy to understand!

 

[stephew]

very nice explanation.

The difference between "regular CT" vs. cone-beam CT is not the energy used but how it obtains the images. "Regular CT" as we know it, involving that donut-shaped scanner, utilizes a fan-beam array. It's basically a thin slit-like detector. And because it's a slit, you have to scan the patient with multiple rotations in order to obtain an aggregate tomographic picture.

Cone-beam CT, however, utilzes a flat planar detector and in essence, it's like stacking many slit detectors together, so instead of requiring multiple rotations, all you really need is to do one rotation and a computed tomographic-like image can be obtained.

Logistically and structurally-wise, it is difficult to incorporate a fan-beamed CT system on a linac, though it's been done- look into "CT on rails". On the other hand, it's easy to put a cone-beam CT on a linac. With MV cone-beam CT, the cone-beam detector is directly opposed to the treatment head, since the treatment head is the xray source. With the kV cone-beam CT, the current method is to have the detector and kV xray source axis orthogonal to the treatment head, though research is ongoing to have the axis directly opposed, like the MV version.


Hope that's clear as mud...

 

[Gfunk6]

The difference between "regular CT" vs. cone-beam CT is not the energy used but how it obtains the images.

Well, there are many differences between the two and energy (@ least with the hardware we use) is one of them. Kudos for the explanation though!