Radiation Part II
And we’re back! I meant to have this up last week, but between the holidays and family in town, that ambition crashed and burned in merry, yuletide fashion. We left off last post with a promise of a deeper dive into what a radiation treatment, specifically stereotactic radiation, might look like from beginning to end. With that in mind, we’ll return to the brilliant Dr. Stephans to take us through the ins and outs of a hypothetical treatment.
Preparation Part I – Planning Session
According to Dr. Stephans, the first medical step in preparing to administer SBRT would be ‘simulation’, a process by which the team walks through the procedure with the patient including time on the table to practice (more on that below). Radiation of the liver specifically can be tricky given movement anything around the diaphragm undergoes during respiration. When we breathe in, the liver shifts down in the abdomen as the lungs expand and the diaphragm pushes down on the organs beneath it. This poses a challenge for radiation oncologists aiming at often small lesions with high doses of radiation. The two most common strategies to navigate this complexity would be to implant a tracker or to immobilize the patient through breath holds/abdominal compression.
Either breath holds or abdominal compression are the preferred technique as they save the patient an additional procedure to implant the marker, so a patient is first assessed to see if they are able to hold their breath for the required periods of time. As with most of this amazing technology, human error is accounted for, so if a patient can hold their breath they are tested with the automatic breathing control, an apparatus that Dr. Stephans likened to a snorkel. The aptly named automatic breathing control functions as the name implies – it controls the patient’s breathing and breath holds in a predictable way for the machine to administer radiation along a reliable pattern of treatment during immobility and breaks while the patient breathes.
As an alternative, there is an option to fit the patient with essentially a torso sized blood pressure cuff, which is wrapped around the abdomen and controls breathing through inflation and deflation. Fortunately, patients being seen for radiation of the liver region are typically able to tolerate an immobilizing option eliminating the need to implant a tracking device.
During the planning session appointment, a patient is walked through the process including some practice with the chosen immobilization technique. During this phase the team also captures updated imaging of the patient while in that immobilized state and makes marks on the patient’s skin to enable precise, reproducible placement each day throughout the treatment. From the simulation appointment the patient gets a week break while the radiation team goes to work engineering the very patient-specific treatment.
Preparation Part II – Behind the Scenes
The first step the radiation team performs is to fuse all previous imaging with the most recent pictures to give the best visual of the tumor that they are targeting. In addition to calling out the tumor, the physician maps out the surrounding tissue that the team aims to protect during the course of treatment, prioritizing the tissue that is most critical to preserve. While the goal is to be as precise as possible, some healthy tissue may be compromised through the process, so the physician is very specific in specifying which anatomy is most important to protect.
From there the 3D blueprint of sorts is handed off to a physicist who helps plot the trajectory of the many beams that will be used to converge on the target. The physicist designs treatment from hundreds of different angles, using a computer program to test thousands of scenarios to help identify which have the highest chance of success and least risk to sensitive structures. Once the best scenario has been identified, the physicist and physician meet to review the plan and give the physician a chance to imbue some final human finesse into the design.
Preparation Part III – “Dry” Run
As an added step of design confirmation, the team then moves on to ingenuous test. They place a tank of water that serves as a patient replica onto the table and run a treatment scenario. Measurement devices evaluate if the machine is properly executing the complex treatment instructions and deliver the beam arrangement correctly. Upon successful completion of this final pre-treatment step, everything is in place for the patient’s first radiation appointment.
Treatment – Day 1
On the day of the first treatment, the patient is again fitted with the immobilization apparatus and imaging is obtained. The treatment team, radiation oncologist, physicist, and technicians, together review this final imaging to confirm everything is lining up the same as the simulation appointment. They program any final adjustments into the machine which moves up, down, or rotationally all around to maximize the therapy.
While this final check and planning takes roughly 1-2 hours, the treatment itself runs a matter of about 2-3 minutes. The patient’s portion clocks in, optimally, at around half an hour from when they lay down on the table to when the treatment has been administered. According to Dr. Stephans, the patient tends not to feel anything during the treatment itself aside from the immobilization process. This comes as a welcome surprise to some patients as intuitively one might assume radiation would come with some form of pain.
Treatment – Day 2 and Beyond
In some instances, SBRT is a one and done therapy. Many variables factor into the number of sessions and the dosage, but one common reason the treatment might extend into further visits would be the location of the tumor in relation to sensitive structure. The more complex the environment, the more time radiation oncologists allow for healing to occur between treatments.
While patients don’t feel the treatment being applied, radiation does not come without side effects. In Dr. Stephans’ experience, about half of patients experience fatigue in the short-term following treatment with the effect being cumulative over time. The other half experience no side effects in the short term. Another possible side effect, nausea, is less common, and when it does occur, it is closely controlled with anti-nausea medication. Interestingly, there can be a delay to radiation side effects. For example, a patient might feel well through treatment, but a week or two after the final dose, they might experience pronounced fatigue. Like much of the medicine around cancer treatment, the side effects are patient-specific and not entirely predictable.
Some patients experience a curative response to SBRT, and depending on the scenario, that is sometimes the goal. In instances where additional radiation is needed down the road, SBRT is proving safe in patients whose liver is otherwise healthy and in instances where the ratio of diseased tissue to healthy tissue is strongly in the healthy tissue’s favor. Also, it is important to note that this hypothetical walkthrough is not representative of every patient and every experience. It is also one scenario in which radiation is employed, so if you have questions around treatment using other forms of radiation, be sure to jot them down for your next appointment with your doctor to learn more about this intriguing treatment modality.
Tune in next time for the first in a series of three weekly patient profiles leading up to the annual Cholangiocarcinoma Foundation Conference! The first post will go up on the 16th, and if there is someone you would like to see featured, shoot me an email at cait.telaak@cholangiocarcinoma.org.
Happy New Year!