External beam radiation therapy represents one of the major treatments in managing oncological patients. It is estimated that approximately 50% of all cancer patients require radiation therapy at some point during their therapeutic trajectory. The primary objective is the targeted eradication of tumor tissue while maximizing the preservation of adjacent healthy tissues utilizing high-energy electromagnetic radiation. To achieve this, the clinical workflow is meticulously structured into several multidisciplinary phases involving radiation oncologists, medical physicists, dosimetrists, and radiation therapists, each contributing uniquely to the precise delivery of treatment. Below we dive into the whole pathway a patient navigates through starting from the first consultation to the last fraction.
First Consultation:
The whole process starts with initial consultation. During this evaluation, the clinician reviews the patient’s comprehensive medical history, oncological diagnosis, prior diagnostic imaging, diagnostic workups, and previous therapeutic interventions. Based on this, the radiation oncologist determines the clinical appropriateness of incorporating radiation therapy into the current management plan. Furthermore, the intent of treatment is established, whether curative (often combined adjunctively with systemic therapy or surgical resection) or palliative for symptom management. The physician counsels the patient regarding potential acute and late adverse effects and addresses any clinical inquiries pertaining to the therapeutic course.
Adverse effects and the severity can differ from patient to patient and depend primarily on the anatomical site of irradiation. The most prevalent systemic symptom is fatigue, while localized manifestations frequently include cutaneous erythema, xerosis, or increased sensitivity, presenting similarly to a solar dermatitis.
Based on all of the above, the patient makes an informed decision and prepares for the subsequent phases of care. Upon obtaining informed consent, the clinical workflow proceeds to the next critical stage.
Simulation and patient immobilization:
The simulation procedure involves acquiring a computed tomography (CT) scan with the patient positioned precisely as they will be during treatment. To ensure daily reproducibility of this exact setup, various custom immobilization devices are utilized, such as thermoplastic masks for head and neck localizations, as well as specialized boards designed to secure the body in specific position.
Radiation therapy demands exceptional precision, as radiation dose deposition must be strictly localized to the tumor volume while sparing adjacent healthy tissues, ensuring that doses delivered to organs at risk remain within established tolerance constraints. To achieve this, it is essential to establish reference marks via cutaneous tattooing, which subsequently facilitates accurate daily patient alignment and setup verification.
Additionally, intravenous contrast administration is clinically indicated in selected cases to enhance diagnostic clarity and target delineation.
Between the simulation session and the delivery of the first treatment fraction, several essential phases must be completed, a process that typically requires a few days.
Contouring:
Following the completion of the simulation procedure and the acquisition of the patient’s CT imaging dataset, the workflow transitions to the contouring phase.
During this stage, the radiation oncologist delineates the target volumes and organs at risk (OARs), which vary distinctively depending on the tumor’s specific anatomical localization.
Taking into account the tumor localization, histological type, prior therapeutic interventions, and clinical intent, the radiation oncologist prescribes the radiation dose for the delineated target volumes, which subsequently guides the medical physicist during treatment planning. This prescription typically specifies a total radiation dose measured in grays delivered over a finite number of fractions, for example: 20 Gy administered in 5 fractions of 4 Gy each, commonly utilized for palliative intent targeting.
Treatment plan preparation:
Following the delineation of the target volumes and organs at risk, alongside the finalization of the therapeutic prescription, the medical physicist initiates the treatment planning process.
The role of the medical physicist is to develop a treatment plan capable of delivering the prescribed dose to the target volume while maximizing the sparing of organs at risk. This ensures that the radiation dose received by healthy structures remains within established tolerance constraints, thereby minimizing adverse effects and preventing treatment-related toxicity.
To put it simply, the medical physicist is tasked with configuring the treatment machine to achieve the physician’s prescribed clinical goals. To accomplish this, various treatment techniques and modalities are available. In many cases, multiple treatment plans are generated using different techniques, followed by the selection of the optimal plan. This process requires complex calculations, precise dose distribution modeling, and consequently, a dedicated amount of time.
Once the physicist already has a plan, the radiation oncologist reviews and approves it. The physician evaluates the target dose coverage to ensure it is homogeneous and appropriately conforms to the target volume, while also verifying that the doses delivered to organs at risk do not exceed established tolerance thresholds. If the treatment plan satisfies clinical criteria, it is ready for pre-treatment verification.
Pre-treatment plan verification:
Prior to the initiation of treatment, it is necessary to verify the clinical and technical deliverability of the treatment plan developed by the medical physicist, specifically, ensuring that the linear accelerator physically reproduces what has been programmed digitally.
To accomplish this, a patient-specific QA plan equivalent is executed on various dosimetry systems, allowing clinicians to compare the planned versus measured dose distributions and absolute dose values. If these parameters align within acceptable clinical tolerance limits, the plan is validated and ready for clinical implementation in patient treatment.
First fraction:
Following plan verification, the patient is scheduled for their first treatment fraction. Treatment is delivered in a specialized room, where the treatment machine, called linear accelerator, is installed. While the exact duration of each session depends on the number of treatment sites and other technical factors, the entire procedure typically takes about 15 to 30 minutes on average.
Radiation therapists position the patient on the treatment couch using the tattooed reference marks, ensuring the precise recreation of the setup achieved during the simulation phase. This step is critical so that the spatial coordinates of the target volume match the simulation data upon which the treatment plan was built, enabling the linear accelerator to deliver the radiation dose accurately to the intended anatomical region. The machine accomplishes this by dynamically altering beam angles, modulating beam intensity, and shaping the radiation field aperture using multileaf collimators. While these complex parameters continuously shift in various combinations depending on the chosen delivery technique, the patient simply experiences the machine rotating smoothly around them.
What happens after the radiation therapists exit the treatment room and close the door? The first step involves acquiring a low-dose cone-beam computed tomography (CBCT) scan to verify the patient’s spatial positioning against the planned setup. If any discrepancy or positional error is detected, the treatment couch is automatically or manually adjusted so that the spatial coordinates of the target volume perfectly align with the treatment plan. Following this verification and correction, the actual radiation delivery process begins. It is important to note that the procedure is completely painless and free of discomfort, with the only minor challenge being the requirement to lie completely still.
Depending on the prescription, treatment may be delivered in a single fraction or extended across multiple days, or even weeks, based on the therapeutic goals and tumor histology. Subsequent fractions follow an identical procedural workflow until the entire prescribed course of treatment is completed. Throughout an extended treatment course, the radiation oncologist continuously monitors precision and progress, actively managing any adverse effects that may arise.
Post-treatment surveillance:
Following the completion of treatment, the patient transitions into the surveillance phase. To accurately evaluate the therapeutic outcomes of radiation therapy, a specific latency period is required post-treatment. Typically, patients are scheduled for follow-up imaging studies approximately 2 to 3 months after treatment completion, which provides adequate time for tumor tissue to manifest expected radiation-induced destructive and regressive changes.
In addition, the patient remains under the continuous supervision of the clinical oncologist, who has the central role in the multidisciplinary care of the oncology patient.
Author: Mariam Zurashvili, Radiation Oncology Resident
