November 2025 | Presented by Kiernan McCullough, Chief of Therapy Physics
Introduction
The field of radiation oncology stands at a remarkable intersection of technological innovation and clinical excellence. While the fundamental principles of radiation therapy remain rooted in the 130-year legacy of the X-ray’s discovery, the methods by which we deliver treatment have evolved dramatically. Today’s radiation therapy landscape is characterized not merely by incremental improvements but by transformative technologies that are reshaping how we approach cancer treatment.
This review examines the current state of radiation oncology technology and explores the emerging techniques that promise to enhance treatment precision, reduce toxicity, and improve patient outcomes. From advanced imaging systems to particle therapy and beyond, these innovations represent the collective efforts of physicists, engineers, clinicians, and radiation therapists working to push the boundaries of what’s possible in cancer care.
The Current Equipment Landscape
Market Overview
The radiation therapy equipment market today is characterized by consolidation. Varian Medical Systems and Elekta collectively command approximately 90% of the global market share for linear accelerators (LINACs). This duopoly has created a standardized foundation upon which most modern radiation therapy is built, with the C-arm LINAC design serving as the industry workhorse.
The Varian TrueBeam and Elekta Versa HD platforms represent the current gold standard for radiation delivery. These systems are capable of treating the vast majority of stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) cases with submillimeter accuracy and six degrees of freedom in patient positioning. Despite being mature technologies, with some platform designs dating back over a decade, these systems continue to deliver what can truly be called “academic-quality” treatments when paired with appropriate training, staffing, and quality assurance protocols.
The Evolution of Excellence
What has changed most dramatically in recent years is not necessarily the linear accelerators themselves, but rather the ecosystem of technologies surrounding them. Advanced treatment planning algorithms, sophisticated beam modeling processes, and dramatically increased computational power have enabled unprecedented optimization of treatment plans. The integration of artificial intelligence and machine learning into clinical workflows is beginning to automate tasks that once required hours of expert time, while simultaneously improving consistency and quality.
Additionally, the ancillary tools, including imaging systems, surface tracking technologies, and patient-specific devices, have evolved to provide radiation therapists and physicists with the confidence to treat with increasingly smaller margins and higher doses per fraction. This shift toward hypofractionated and ultra-hypofractionated regimens represents a fundamental change in how radiation therapy is conceptualized and delivered.
Advanced Imaging Technologies: Seeing More, Treating Better
Triggered Imaging: Real-Time Quality Assurance
An example of recent advances is triggered imaging technology.. This feature enables the acquisition of kilovoltage (kV) images during volumetric modulated arc therapy (VMAT) delivery at predetermined intervals, based on monitor units, beam-on time, or gantry angle.
Each triggered image serves as a go/no-go checkpoint during treatment. The system can automatically detect fiducial markers and determine whether they remain within acceptable tolerances. If migration is detected, which is a common occurrence with prostate treatments where internal motion can be substantial even during a single arc, the beam automatically pauses, allowing therapists to acquire a cone beam CT and make necessary corrections.
The clinical applications extend beyond prostate tracking. Recent publications have demonstrated creative implementations, including vertebral body tracking for spinal SBRT. By contouring the target vertebra plus adjacent vertebral bodies, clinics have successfully adapted this technology to function similarly to dedicated spine tracking systems like those found on CyberKnife or ExacTrac platforms. This exemplifies how thoughtful application of existing tools can expand clinical capabilities without requiring entirely new equipment purchases.
Four-Dimensional Cone Beam CT: Motion Management at the Treatment Machine
Four-dimensional cone beam CT (4D CBCT) technology brings the motion assessment capabilities of the simulation suite directly to the treatment vault. While not fundamentally different from 4D CT simulation, having this capability at the treatment machine provides valuable verification that tumor motion has not changed since initial planning.
This technology proves particularly valuable for lung tumors in the inferior thorax, where the diaphragm can obscure target visualization on standard imaging. Additionally, 4D CBCT can serve as a contingency tool when simulation equipment is unavailable, allowing clinics to proceed with treatment planning based on standardimaging solutions while using 4D CBCT to verify motion management strategies before treatment delivery.
Gated Cone Beam CT: Precision Imaging for Challenging Cases
Gated CBCT represents a complementary approach to 4D imaging. Rather than capturing the full respiratory cycle, gated CBCT acquires images at a specific respiratory phase, producing clean, static images of moving targets. This technique is particularly valuable for patients with comorbidities who cannot tolerate the breath-hold requirements of deep inspiration breath-hold (DIBH) techniques for full SBRT procedures.
While more resource-intensive and time-consuming than standard imaging protocols, gated CBCT provides a viable pathway for treating patients who might otherwise be excluded from advanced radiation therapy techniques due to physiological limitations.
HyperSight: Speed and Clarity
Varian’s recently released HyperSight technology represents a significant leap forward in cone beam imaging quality and efficiency. Through advanced reconstruction algorithms, HyperSight delivers cleaner images with potentially larger fields of view, ensuring complete patient surface capture for improved alignment.
The speed improvements are equally impressive. For TrueBeam systems, HyperSight increases gantry speed by 50% during cone beam acquisition. For the Halcyon platform, with its enclosed ring gantry design, cone beam acquisition time drops to under six seconds. This dramatic acceleration has meaningful clinical implications for DIBH and gated treatments, reducing patient burden and improving workflow efficiency.
Perhaps most intriguing are the potential paradigm shifts HyperSight enables. The image quality improvements, combined with consistent, large-field-of-view imaging, position cone beam CT as a viable tool for adaptive planning without requiring patient re-simulation. For resource-limited facilities, there is even speculation that HyperSight-equipped systems could potentially eliminate the need for dedicated CT simulators entirely, with patients being set up, imaged, and planned directly on the treatment machine.
RapidArc Dynamic: Redefining Treatment Delivery
Unveiled at the 2024 ASTRO Annual Meeting, Varian’s RapidArc Dynamic technology represents a genuine paradigm shift in photon beam delivery. This innovation combines the efficiency of VMAT with the conformality of static field intensity-modulated radiation therapy (IMRT), while introducing dynamic collimator rotation during treatment.
The moving collimator serves multiple purposes: it reduces multi-leaf collimator (MLC) leakage, improves conformality to complex target shapes, and enables the delivery of highly complex plans in potentially a single arc. For radiation therapists, this translates to reduced treatment times and simplified delivery without compromising plan quality. Early implementations suggest RapidArc Dynamic could fundamentally alter treatment planning optimization strategies and clinical workflows.
Adaptive Radiation Therapy: Responding to Change
The Rise of AI-Driven Adaptation
The concept of adaptive radiation therapy, adjusting treatment plans in response to anatomical or physiological changes, has long been a goal of the field. What has changed recently is the technological capability to make this vision practical for routine clinical implementation.
While this innovation has been evolving in the MR-delivery space, two competingplatforms have recently emerged: Varian’s Ethos system (built on the Halcyon platform) and Accuray’s Stellar (available on the Radixact system). Both leverage the rapid, high-quality imaging capabilities of enclosed ring gantry designs combined with artificial intelligence to enable online adaptive replanning.
Adaptive Workflow
The typical adaptive workflow involves acquiring a high-quality volumetric image at the treatment machine, using AI algorithms to auto-segment anatomical structures and deform planning contours to match the patient’s current anatomy, rapidly generating a new treatment plan optimized for that day’s anatomy, having a physician approve the adapted contours and plan, and delivering the new plan immediately.
The Radixact system offers both megavoltage (MV) and kilovoltage (kV) 3D imaging capabilities, providing flexibility for patients with metal hardware or other imaging challenges. The speed and automation provided by AI tools have made what was once a multi-hour process achievable within the time constraints of a standard treatment slot.
Resource Implications
The promise of adaptive radiation therapy must be balanced against its resource demands. Successful implementation requires physician time for daily plan approval, physicist oversight for quality assurance, and potentially dosimetrist or advanced therapist involvement in the contouring and planning process. As the field moves toward treating radiation therapy increasingly as a “procedure” rather than a routine daily task, staffing models and workflow designs must evolve accordingly.
Surface Tracking : An EverWatchful Treatment Companion
Surface tracking technology has become nearly ubiquitous in modern radiation therapy, transitioning from a specialized tool to a standard component of quality treatment delivery. Multiple vendors now compete in this space, each bringing unique capabilities.
Established Players and New Features
. Vision RT’s DoseRT represents a particularly innovative application: real-time visualization of radiation dose as it interacts with the patient’s surface during treatment delivery. By displaying entrance and exit dose distributions on the patient’s skin surface in real-time, DoseRT can detect positioning errors, bolus misalignment, or other issues that would be nearly impossible to identify through conventional quality assurance methods.
LAP’s solution, Luna, developed by the company known primarily for laser positioning systems, offers a head-to-toe surface tracking solution with the flexibility to deploy multiple cameras as needed to eliminate blind spots. This scalability allows facilities to customize coverage based on their specific treatment needs and vault geometry.
BrainLab’s Multi-Modal Approach
BrainLab’s ExacTrac Dynamic represents a particularly sophisticated approach to position monitoring. The system integrates three complementary technologies: X-ray-based skeletal tracking, optical surface tracking, and thermal imaging. By fusing data from these distinct modalities,each with different strengths and limitations,ExacTrac Dynamic aims to provide robust, real-time position monitoring benchmarked to actual bony anatomy. The inclusion of thermal imaging is unique in the field and represents an innovative approach to detecting patient motion through an entirely different physical principle.
Specialized Treatment Systems: Purpose-Built Precision
CyberKnife: The Robotic Advantage
While C-arm LINACs dominate the market, specialized systems continue to fill important niches. The CyberKnife system, developed by neurosurgeon John Adler at Stanford, remains one of the most sophisticated platforms for SRS and SBRT. Its robotic arm design provides unparalleled flexibility in beam angle selection and real-time target tracking.
CyberKnife’s tracking capabilities span skull-based treatments (using skeletal landmarks), spine treatments (using vertebral body tracking), and lung treatments (using implanted fiducial markers or even direct tumor tracking). The system’s ability to actively track and correct for target motion during treatment delivery, rather than simply gating or limiting treatment to specific respiratory phases, remains relatively unique in the field.
The newest CyberKnife S7 system maintains all traditional fixed-cone capabilities for trigeminal neuralgia and acoustic neuroma treatments while adding a multi-leaf collimator option. This MLC integration improves treatment efficiency, making CyberKnife more competitive with conventional LINACs for treatment time,historically a weakness of the platform.
ZAP-X: Neurosurgical Independence
Also designed by John Adler, the ZAP-X system takes a different philosophical approach: creating an SRS platform that neurosurgeons can operate independently, with minimal radiation oncology involvement. The self-shielded, gyroscopic gantry design allows installation in spaces that would be unsuitable for conventional LINACs. While adoption remains limited, one system operates in Littleton, Colorado, ZAP-X represents an interesting alternative model for delivering specialized radiosurgery treatments.
MRI-Guided Radiation Therapy: The Vision and the Reality
MRI-guided radiation therapy represents one of the most scientifically exciting developments in the field, offering superior soft tissue contrast and the ability to image continuously during treatment without the ionizing radiation burden of CT-based approaches.
ViewRay’s Challenges
ViewRay, the pioneering company in MRI-guided radiation therapy, has encountered significant challenges. The company currently has new installations on hiatus, highlighting the gap between technological promise and clinical/business viability. The complexity of these systems, their high cost, and the substantial human resource requirements for daily adaptive workflows have limited adoption.
Clinical Applications and Future Potential
Despite current challenges, MRI-guided radiation therapy excels for specific clinical scenarios: pancreatic tumors, where real-time soft tissue visualization enables precise targeting of a moving organ surrounded by critical structures; liver tumors, where respiratory motion is substantial and soft tissue contrast is essential; and prostate treatments, where superior soft tissue contrast could potentially eliminate the need for fiducial marker implantation.
The ability to perform true real-time gating based on direct tumor visualization,rather than surrogate markers,represents a significant advantage for appropriate cases. However, the technology may simply be ahead of its time, waiting for workflow optimization, cost reduction, and adaptation of staffing models to make routine clinical implementation practical.
RefleXion: Biology-Guided Radiation Therapy
Perhaps no emerging technology is as conceptually innovative as RefleXion’s biology-guided radiotherapy approach. The system leverages positron emission tomography (PET) technology to track tumors in real-time during treatment delivery.
The Concept
Patients receive a PET radiotracer that accumulates in tumor tissue. The RefleXion system then uses the emitted positrons as both imaging contrast and targeting information, allowing real-time tracking of multiple tumor sites simultaneously. For patients with oligometastatic disease,multiple but limited metastatic sites,this approach theoretically enables treatment of all lesions in a single session.
Challenges and Questions
Significant questions remain about RefleXion’s practical implementation. The nuclear medicine regulatory requirements, radiotracer logistics, therapist training needs, and treatment workflow design all require careful consideration. With only one or two systems currently operational in the United States, RefleXion remains very much an emerging technology. Its ultimate success will depend on demonstrating clinical outcomes that justify its complexity and cost compared to increasingly capable conventional approaches.
Particle Therapy: Beyond Photons
Proton Therapy: Pediatric Promise and Adult Questions
Proton therapy has existed since the 1980s, but high costs have limited accessibility. Currently, 46 proton therapy centers operate across the United States, though geographic distribution remains uneven. The nearest facility to Colorado is at the University of Utah in Salt Lake City, with potential plans for a facility in Castle Pines, south of Denver.
The physical advantage of protons is clear: the Bragg peak phenomenon allows proton beams to deposit maximum energy precisely at depth, with minimal exit dose beyond the target. This dosimetric advantage translates to substantially reduced integral dose to the patient, a critical consideration for pediatric patients, where minimizing exposure to developing tissues can reduce late effects and secondary malignancy risk.
For adult patients, however, the clinical benefit of protons over advanced photon techniques remains debated. While dosimetric advantages are clear on paper, whether these translate to meaningful clinical outcome differences continues to be investigated.
Multiple vendors now compete in the proton therapy space, including IBA, Varian, Mevion, and Hitachi, among others. This increased competition may eventually drive costs down, potentially expanding access.
Heavy Ion Therapy: The Next Frontier
Carbon ion therapy represents an even more exotic modality. Heavy ions combine the physical advantages of protons (finite range, minimal exit dose) with enhanced biological effectiveness,essentially hitting tumors like a “cannonball” compared to the “bullets” of protons.
Currently, 13 heavy ion facilities operate worldwide, concentrated in Japan with additional sites in Europe, Korea, and China. Zero facilities exist in the Western Hemisphere. The Osaka Heavy Ion Therapy Center exemplifies the massive scale of these installations: a central beam line servicing three treatment rooms, with the entire facility representing a $150-200 million investment.
The clinical justification for heavy ions remains unclear. If proton therapy struggles to demonstrate clear advantages over photons for many indications, establishing the incremental benefit of heavy ions over protons presents an even greater challenge. These systems will likely remain limited to highly specialized academic centers pursuing specific clinical and research questions.
FLASH Radiotherapy: Speed as a Therapeutic Variable
FLASH radiotherapy represents one of the most scientifically intriguing concepts in radiation biology in decades. The hypothesis: delivering radiation at ultra-high dose rates (40-50 Gy/second compared to conventional rates of approximately 0.1 Gy/minute) may preserve normal tissue while maintaining tumor killing.
The Biological Rationale
The proposed mechanism involves free radical chemistry. At conventional dose rates, free radicals generated by radiation accumulate in both tumor and normal tissues, causing DNA damage and cellular stress. At FLASH dose rates, the hypothesis suggests that normal tissues can manage the acute free radical burst, while tumors with compromised antioxidant systems and abnormal vasculature cannot.
Technical Challenges
Translating FLASH from concept to clinical reality faces substantial obstacles. Some proton therapy systems can already achieve FLASH dose rates for small targets, but treating full organs at these speeds with photon beams remains beyond current technical capabilities. Additionally, the ultra-high dose rate creates unique challenges for motion management: when treatment lasts milliseconds, conventional motion management strategies become irrelevant. New approaches to ensuring targeting accuracy at these timescales will be essential.
Despite these challenges, FLASH radiotherapy holds genuine promise for improving the therapeutic ratio, maintaining tumor control while reducing toxicity. Success would represent a fundamental shift in how radiation therapy works at the biological level.
Theranostics: The Convergence of Imaging and Therapy
Theranostics, a portmanteau of “therapy” and “diagnostics”, represents a conceptually different approach to cancer treatment. The technique uses tumor-specific molecular targeting agents that can be labeled with either diagnostic or therapeutic radioisotopes.
The Approach
A targeting molecule (peptide, antibody, or small molecule) with high affinity for a specific cancer marker is synthesized. For diagnosis, this molecule is labeled with a radiation-emitting isotope, creating a tracer that reveals disease distribution throughout the body. For therapy, the same targeting molecule is labeled with a beta or alpha-emitting isotope, delivering radiation directly to cancer cells wherever they exist.
Several theranostic agents have already gained FDA approval, with Lutetium-177 PSMA for prostate cancer being a prominent example. As more tumor-specific targets are identified and corresponding agents developed, theranostics could expand to many cancer types.
Implications for Radiation Oncology
Theranostics may fundamentally alter radiation oncology’s role in treating metastatic disease. Rather than delivering full-course external beam treatment to all sites, radiation oncology might focus on treating single sites to trigger immune responses while theranostics address systemic disease. This would represent a shift from radiation therapy as primary treatment to radiation therapy as immune sensitization, a form of combination therapy that leverages both local and systemic anti-cancer effects.
Clinical Innovations: Osteoarthritis and Upright Treatment
Low-Dose Radiation for Osteoarthritis
Osteoarthritis treatment with low-dose radiation (typically 3 Gy in six fractions) represents a non-standardapplication of radiation therapy technology. While not a new treatment technique, the practice has historical precedent, renewed interest has made it increasingly common.
The implications for radiation oncology departments are primarily operational rather than technical. These treatments require minimal technical sophistication but can significantly impact workflow and scheduling. Whether dedicated systems might emerge to handle osteoarthritis treatments outside traditional radiation oncology departments remains an open question, potentially reconfiguring how these services are delivered.
Upright Treatment: An Ergonomic Revolution?
Upright treatment systems represent a conceptual departure from the supine positioning that has dominated radiation therapy since its inception. Proponents argue that upright positioning offers several advantages: easier breathing for patients, more stable positioning, reduced respiratory motion for thoracic targets, and improved comfort for patients with dysphagia or difficulty lying flat.
Despite these potential benefits, upright systems have not gained significant traction. The technical challenges of designing gantries, couches, and imaging systems for upright treatment, combined with the inertia of existing treatment paradigms, have limited adoption. However, for specific patient populations, particularly head and neck patients, the advantages may be substantial enough to eventually drive broader implementation.
Future Trends: Toward Precision and Procedure
Several overarching trends emerge from this survey of emerging technologies:
Treatment as Procedure: Radiation therapy is increasingly delivered as a procedure requiring real-time decision-making rather than a routine daily task executed from a predetermined plan. This shift has profound implications for staffing, training, and workflow design.
Margin Reduction and Hypofractionation: Improved imaging, tracking, and adaptive capabilities enable treatment with increasingly smaller margins and fewer, larger fractions. This trend improves patient convenience and potentially outcomes while creating new technical challenges.
Growth in Ancillary Technology: Even as the linear accelerators themselves evolve slowly, the ecosystem of supporting technologies, surface tracking, advanced imaging, motion management, patient-specific devices, and 3D-printed accessories, continues to advance rapidly.
AI Integration: Artificial intelligence is moving from research curiosity to clinical reality, automating contouring, planning, and quality assurance tasks while enabling adaptive workflows that would be impractical with manual processes.
Specialized Systems for Specialized Needs: While C-arm LINACs remain the workhorse of radiation oncology, specialized systems like CyberKnife, ZAP-X, and RefleXion demonstrate that niche applications may justify purpose-built solutions. The field has room for both generalist and specialist approaches.
Increased Resource Intensity: Advanced techniques generally require more human resources, physician time, physicist oversight, therapist expertise, concentrated at the point of treatment. This shift challenges traditional staffing models and raises questions about cost-effectiveness and scalability.
Conclusion
The field of radiation oncology is in a period of remarkable innovation occurring not through replacement of existing technology, but through incremental improvements, clever applications of existing tools, and the integration of enabling technologies like artificial intelligence and advanced imaging.
The C-arm linear accelerator remains the foundation of radiation therapy, but it now operates within an increasingly sophisticated ecosystem that enables treatments that would have been unthinkable a decade or two ago. Margins measured in millimeters, treatments delivered in single fractions, and real-time plan adaptation all represent the fruits of sustained innovation by teams of physicists, engineers, clinicians, and radiation therapists.
Looking forward, the challenges are as much organizational and economic as technical. The most advanced technologies require new staffing models, training paradigms, and workflow designs. Questions of cost-effectiveness must be rigorously addressed, particularly for expensive technologies like proton therapy, heavy ions, and MRI-guided systems. The promise of emerging techniques like FLASH and theranostics must be validated through careful clinical trials.
Yet the trajectory is clear: radiation oncology continues its evolution toward ever-greater precision, lower toxicity, and improved outcomes. Each advance represents not just technological achievement, but the collective commitment of the radiation oncology community to serving patients better. As we celebrate the 130th anniversary of the X-ray’s discovery and recognize the dedication of radiation therapists during their appreciation week, we can look with justified pride at how far the field has come,and with anticipation at the innovations yet to emerge.
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