Treatment Process
What processes are involved in proton therapy?
How frequent are proton therapy treatment cycles?
A Full Breakdown of the 7 Steps
Currently, typical proton treatment processes are similar to those of conventional radiotherapy. Other than the rare situation that can be completed with a single treatment, most situations call for fractionated treatment, and treatment frequency and total number of cycles are determined by clinical status.
A common situation is daily treatment once per day from Monday through Friday, with each treatment cycle lasting about 30 minutes. The process typically does not require anesthesia, and irradiation of the body does not burn or hurt.
The total number of treatment cycles may be as few as 3 to 5 cycles or as many as over 30 cycles.
Purpose：A physician explains the goals, efficacy, and side effects of treatment
A patient seeking medical advice arrives from either a radiation oncology clinic or by a consultation from another specialty. The doctor determines and explains whether proton therapy may be applied to each patient under different tumor statuses, the possible outcomes, and the side effects that may develop. After communicating and clarifying the details, they proceed to the treatment process.
Purpose：The treatment position and motor control method that are most appropriate and most effective for fixation are found
The first order of business upon entering treatment is the design and production of the fixation device. The purpose of this step is to find a suitable treatment posture and positioning for the site to be treated. At the same time, to ensure that the same pose and position can be maintained stably throughout the entire treatment process, often specific assistive devices must be designed to facilitate this. This part requires high personalization and relies on the expertise and experience of the medical team. For regions where tumors are less mobile (such as brain tumors, nasopharyngeal cancer, and head and neck cancers), we create personalized cushions and molds for patients so that they can conveniently undergo their daily treatments in the most comfortable position; As for tumors that move with breathing such as liver cancer and lung cancer, in addition to designing a fixation device, what is more important is to perform personalized respiratory movement evaluation and training to ensure that protons can be delivered correctly to the tumor site with the breathing movements during treatment. This highly important process emphasizes fixation and reproducibility, because regardless of how advanced the equipment is, a deviation in tumor position will also cause an deviation in proton accuracy.
Purpose：Obtain treatment images, including a simultaneous dynamic assessment of the tumor/organ
We proceed to the stage of obtaining images for treatment. The technical term is simulation.
Simply put, this step is to obtain images of the tumor and healthy organs inside the body, so as to design external proton irradiation that allows protons to strike the tissues they should strike and avoid the tissues they should avoid.
Simulation is routinely performed by computed tomography, and the author’s affiliated department also performs magnetic resonance imaging to facilitate accurate interpretation of the tumor site and normal tissues within the body.
For organs that may move or change shapes, simulation will also obtain four-dimensional imaging to facilitate subsequent treatment evaluation.
The various processes above all require the patient’s participation and cooperation;the work that follows are performed by healthcare personnel behind the scenes.
Purpose：The physician outlines the tumor site(s) to be treated and the normal tissue(s) to be protected
This work is highly reliant on the professional ability of the radiation oncologist. The process is similar to an operation by a surgeon. We put the patient images obtained during simulation onto a computer (as if the patient is lying on an operating table). Using the patient images obtained during simulation and evaluating them holistically with other reference data, we perform contour delineation on the tumor site(s) and normal tissue(s) for precise irradiation in creating the treatment plan. This is similar to tumor removal and separation from healthy tissue during an operation. This process has a direct impact on treatment outcomes and side effects and is a key item in the training of radiation oncologists. If a region of the tumor that should be irradiated is not correctly delineated, recurrence rate may increase; conversely, if normal tissue that should be avoided is not correctly delineated, side effects may develop alongside irradiation. Physician experience and relevant international research reports all serve as an important basis of reference for assessing contour delineation.
Purpose：Personalize treatment angles and dosage delivery based on the prescription
After the physician completes contour delineation, we proceed to treatment plan design. This steps acts on the delineated tumor images based on the physician’s prescription: include the dosages required for tumor irradiation and the tolerated dosages of normal tissues. Based on the conditions of the proton center equipment, a medical physicist or dosimetrist runs simulations on the computer to customize the design of proton irradiation, including the choice of irradiation angle and optimization calculations for dosimetric requirements; the goal is to achieve the physician’s prescription. As the intrinsic physical and biological properties of protons differ from those in conventional photon therapy, considerations during treatment plan design also differ greatly. Design considerations also vary for different proton therapy equipment. For example, the author’s affiliated department has a comprehensive 360-degree proton gantry which provides greater freedom of rotation in the treatment plan compared to units with smaller angles or a fixed angle configuration. Compared to proton equipment for scattering, proton equipment for pencil beam scanning can also accommodate more complex plans to address the needs for different tumors.
Purpose：Confirm that the computer simulation and actual treatment output match
Before executing the final step of treatment, quality assurance validation of the treatment plan must be completed to confirm a match between the treatment plan and the machine's output. Medical physicists perform validation content for quality assurance. Each patient and each irradiation must complete a quality assurance report for the treatment plan before allowing the patient to undergo treatment.
Purpose：Perform positioning, guidance, and treatment according to the completed empirical treatment.
At every treatment cycle, the medical technologist will assist the patient in lying on the treatment table, using the initially designed positioning and molds to fix the patient in the correct treatment position before treatment. Generally, pretreatment imaging guidance will be performed before actually emitting proton beams to ensure that the treatment is accurate and error-free. Although imaging guidance prolongs the time the patient must lie on the treatment table, it greatly increases the accuracy of clinical proton therapy. Different hospitals must also formulate an intradepartmental SOP based on their own equipment.
For these intricate, complex procedures, operator experience is key
Such a leading-edge treatment method involves many meticulous and complex procedures each time, requiring not only high-level professional medical evaluations and prescriptions but also cooperation between the patient and medical professionals in multiple aspects for the successful completion of each cycle’s treatment objectives. Although the equipment is advanced, people are the real key. To ensure treatment quality, we formulated a three-dimension guidance proton therapy process, which was rare at the time, even before we admitted our first patient. In the past few years, we have accumulated case treatment experience numbering nearly 30 thousand and discovered that three-dimensional guidance can in fact more effectively increase the accuracy of the proton therapy. We were also invited to give an oral presentation on this result at the 2022 International Conference of Particle Therapy held in the United States. We shared our experience with proton and heavy ion therapy centers across the world, providing international facilities with a reference and contributing our efforts on Taiwan’s road to proton therapy quality improvement.