The two terms “adaptive radiation therapy” and “dynamic adaptive radiation therapy” are likely to become much more commonly used in the next few years as the use of these techniques expand out from academic and highly specialized radiotherapy centers into the community setting.
Back in 2006, Dr. James Cox of the M. D. Anderson Cancer Center, in an article entitled “Radiation oncology of the future,” wrote that, “Dynamic adaptive radiation therapy implies the possibility of frequent repetitions of imaging and treatment planning.” And historically that had not been how radiation therapy was carried out.
In the past, a man going for prostate cancer radiation would have undergone a “treatment planning” session, in which the radiotherapy team carefully scanned the patient’s lower abdomen with either CT scans or MRI scans to carefelly determine the size and position of the patient’s prostate. The radiotherapy team would then have constructed a system to hold that individual patient in exactly the same physicial position relative to the beams of radiation each time he came in for his subsequent. And thirdly they would have set the intensity and precise direction of the various beams of radiation in order to “conform” to the shape and size and position of that patient’s prostate based on the initial CT or MRI scan. The patient would then have come and had his 35 to 40 or so radiation sessions over 7 or 8 weeks, being placed in exactly the same position every single time. This was the basic idea behind “3D conformal beam radiation therapy” (3D-CBRT), which was a big advance that happened in the early to mid 1990s and which vastly improved the ability to radiate the prostate through the use of external beam radiation without radiating as much of the surrounding tissue as had been customary before. This increase in the accuracy of delivery of the radiation also allowed radiation oncologists to start increasing the dose of radiation that could be delivered to the prostate — thereby increasing the probability that radiation would actually kill all of the cancer cells in the patient’s prostate.
However (and it is a big “however”), the prostate is not a static organ within the body. It moves around a litttle bit almost all the time. So, using traditional 3D-CBRT, what would really be happening was that all the radiation being aimed at the patient’s prostate was being aimed at where that patient’s prostate was at the time the initial CT scan or MRI was given, not (necessarily) at the exact position of the prostate when the radiation was being delivered.
We have been through a long series of evolutionary steps in methodology to reach where we are today. Any patient who is considering external beam radiation therapy for the treatment of localized prostate cancer today needs to ask his radiation oncologist just how accurately the radiation is going to be delivered not just because of the initial treatment planning but through dynamic adaptive radiation therapy processes.
These processes basically allow for the precise position of the patient’s prostate to be determined multiple times during the course of the delivery of every single dose of radiation over a course of therapy. Through the repetitive combination of accurate determination of the position of the target tissues and actual delivery of the radiation, along with the implantation of what are known as “fiducial markers,” it is now possible to program the delivery of radiation with extreme precision to conform exactly to the size and position of a patient’s prostate at an exact point in time. This has again allowed for an increase in the amount of radiation that can be delivered to the prostate and to a further reduction in the risk of excess radiation of tissues surrounding an near to the prostate.
Now there are lots of highly specific terms you might hear that relate to all of this. Varian Medical Systems, which is major manufacturer of radiotherapy equipment refers to:
- Offline adaptation which occurs between treatment fractions and which allows the radiotherapy team to generate new, more accurate treatment plans as gradual changes occur.
- Real-time adaptation under which radiotherapy systems combine continuous patient monitoring during treatment with preplotted beam trajectories to make sure that the maximum dose is delivered to the precise target are while avoiding other organs.
- Online adaptation, through which the radiation team can adapts treatment based on new information on a specific day to account for variations in patient anatomy or physiology, which cannot be corrected by repositioning the patient alone.
Another company, Calypso Medical, has developed and brought to market a revolutionary system through which the clinician is provided with continuous, real-time monitoring of the position of the prostate and can immediately let the radiation team know if the target tissues move outside preset boundaries due to organ motion, thereby enabling corrections during treatment delivery. And specific types of markers (“fiducial markers”) are implanted into the target area prior to radiation. These markers emit a radiofrequency that allow sensors to determine the precise information about the position and movement of the traget tissues with extreme accuracy. The Calypso system eliminates the otherwise cumbersome need for repetitive CT or MRI scans to detemine the position of the prostate, as implied by Dr. Cox, in the quotation at the beginning of this article.
We have no intention here of trying to provide a complete and detailed review of the technologies that underlie all of these rapid advances in the ability to accurately deliver radiation to the prostate. What is important is that patients understand that the level of sophistication with which radiation therapy can now be delivered has been vastly improved over the situation from even 5-10 years ago. The technology now available has revolutionized radiation therapy in the same way as laparoscopic surgery has revolutionized radical prostatectomy. Indeed, it is probably true that dynamic adaptive radiation therapy has increased the effectiveness and safety of external beam radiation a good deal more than the daVinci robot may have impacted the effectiveness and safety of a radical prostatectomy!
If a newly diagnosed patient is considering external beam radiation therapy for the treatment of localized prostate cancer today, one of most important questions that patient needs to be able to ask his doctor is, “Does the radiation system you use allow for real-time control over delivery of radiation to the target tissue so that you are as sure as you can be that all of the radiation is being accurately delivered to my prostate?”