Adaptive Radiation Therapy in the Treatment of Hard-to-Reach Tumors - Impact of AI, Risk Factors and Implementations.

Introduction:

Adaptive radiation therapy (ART) is a sophisticated method introduced in the late 1990s to improve cancer radiation treatment. It's like a "closed-loop" system where we can adjust the treatment plan based on ongoing measurements. This helps ensure the treatment is both effective and safe by accounting for changes in the patient's body during treatment. These changes can be due to weight, tumor size, and how organs respond. ART can be applied in three ways: between treatment sessions, just before a session, or even in real-time during a session to ensure the treatment works well.

What Is the Impact of AI (Artificial Intelligence) on Adaptive Radiation Therapy?

Advancements in Adaptive Radiotherapy:

• Adaptive radiotherapy benefits from computational progress, enabling faster and more precise treatment planning, anatomical modeling, and image reconstruction.

• The future of adaptive radiotherapy depends on managing the growing volume of data, such as images, contouring, dosimetric constraints, and complex treatment plans.

• This creates both challenges and opportunities for innovation while addressing economic demands.

AI in Radiation Oncology:

• AI, including deep learning, is gaining widespread attention and transforming various fields, including radiation oncology.

• It has caused excitement and some concerns, but fundamentally, AI is a computer algorithm integrated into radiation oncology.

AI's Impact on Adaptive Radiotherapy:

• AI has the potential to significantly address one of the major obstacles to widespread clinical implementation: workload.

• AI can enhance various components of adaptive radiotherapy, including contouring, registration, planning, quality assurance, and decision-making.

• AI-based auto-segmentation algorithms offer improved accuracy, making previously deemed impossible ideas, like real-time targeting and rapid replanning, feasible.

• This technology opens up new possibilities for adaptive radiotherapy strategies.

What Are the Technological Considerations for Adaptive Radiation Therapy?

1. Image Acquisition:

• ART relies on high-quality images to accurately plan and adapt treatment.

• Various imaging modalities are used in ART, each with its advantages and limitations.

• New image reconstruction methods, such as iterative CBCT, are emerging, offering potential benefits.

2. Deformable Image Registration (DIR):

• DIR is vital in ART to account for organ shape and size changes during treatment.

• Errors in DIR may arise from image quality, algorithm accuracy, and manual adjustments.

• Validation methods for DIR accuracy are crucial but challenging.

3. Dose Accumulation and Tracking:

• ART requires tracking and accumulating doses over the treatment course.

• The accuracy of dose warping and accumulation depends on the quality of DIR and imaging.

• Errors may have clinical consequences, and accurate QA methods are needed.

4. Rapid Replanning:

• ART may involve offline or online replanning with fast contouring and plan optimization.

• Rapid recontouring, driven by AI and DIR, can expedite online replanning.

• Improved efficiency in online ART is essential for timely adaptation.

5. Pre-Treatment Plan and Delivery QA:

• QA for online ART must be accelerated to match the treatment timeline.

• In-house and commercial QA tools are emerging, but automated checks are still under development.

• Independent secondary dose calculation and adaptive plan QA are essential.

6. Dose Reporting:

• Dose reporting protocols need to be standardized for consistency across clinical trials.

• Decisions about the extent of organ delineation for reporting and tracking are crucial.

• As seen in brachytherapy, volume dose parameters can offer clear reporting guidelines.

What Cancers Are Treated With Adaptive Radiation Therapy?

Adaptive radiation therapy (ART) is employed to treat specific types of cancer, including:

• Anal cancer.

• Bladder cancer.

• Prostate cancer.

• Head and neck cancer.

• Cervical cancer.

• Uterine cancer.

• Ovarian cancer.

How Adaptive Radiation Therapy (A-ART) Is Implemented?

1. Identifying Patients for A-ART:

• Patients suitable for A-ART are chosen based on clinical factors, regular evaluations, or changes observed in diagnostic scans.

• These criteria may include weight loss, tumor size reduction, shifts in patient positioning, and mask-fitting issues.

• Some centers utilize dose recalculations to assess cumulative radiation dose delivered to the tumor and surrounding organs.

2. Re-Simulation:

• Once a patient is identified for A-ART, prompt re-simulation is crucial.

• This may involve creating a new mask if the existing one doesn't fit properly.

3. Re-Contouring:

• After re-simulation, the physician needs to adjust the treatment plan.

• This can be done manually through deformable image registration or automated segmentation techniques.

• Artificial intelligence is being developed to make this process more efficient.

4. Re-Planning:

• The treatment plan is then re-optimized as per the physician's judgment.

5. Challenges in A-ART:

• One major challenge is the time and resources required for manual re-simulation, re-contouring, and re-planning.

• Finding the optimal trigger for implementing A-ART is a top priority to streamline the process.

6. Timing of A-ART:

• The timing of A-ART during radiotherapy varies between centers.

• Some perform adaptive re-planning based on clinical indicators, while others use regular intervals.

• Studies suggest potential benefits of A-ART within the first weeks of treatment, with varying dosimetric improvements.

7. Individualized A-ART Indications:

• A one-size-fits-all approach for A-ART is only suitable for some patients.

• Factors like initial mean parotid gland dose, tumor size, weight, and rate of weight loss may influence the need for A-ART.

• However, predictive variables need further validation as they may not apply to all cases.

8. Recent Advances in A-ART:

• New approaches focus on individualized indications for A-ART by recalculating cumulative target and organ doses regularly.

• This can help identify changes in dosimetry that require re-planning.

• Some studies use weekly CT scans to trigger A-ART, and there's potential to use daily cone-beam CTs for dose calculations.

• Advances in technology and artificial intelligence are expected to automate and streamline the A-ART process.

What Is the Radiation Therapy for Different Cancer Treatments?

1. Radiation Therapy for Rectal Cancer Treatment: Rectal cancer radiation therapy includes 3D-CRT, offering precise tumor targeting with higher radiation doses. Studies support over 55 Gy doses for better responses. IMRT, an advanced form of 3D-CRT, allows more precise radiation control, often increasing tumor doses with fewer side effects. Brachytherapy combines internal and external radiation, achieving varying response rates. Adaptive approaches tailor radiation doses based on real-time tumor responses, with potential advancements using MRI guidance.

2. Radiation Therapy for Head and Neck Treatment: In head and neck radiation therapy, image guidance ensures accurate patient positioning without altering the treatment plan. Deformable image registration automates contouring and adaptation of plans based on changes in anatomy. ART can occur offline, online, or in real-time, allowing precise dose control. Real-world trials are testing automated ART, with early results showing improved dosimetry and outcomes. This approach aims to make radiation therapy more effective and reduce side effects in head and neck cancer patients.

3. Radiation Therapy for Bladder Treatment: MRI improves bladder tumor visualization compared to CT scans, reducing uncertainties and variability in defining the tumor and surrounding structures. Radio-opaque markers like surgical clips help visualize tumors, but they can migrate. Radiographic gel-like markers are also explored. The bladder's varying shape and size pose challenges. Adaptive radiotherapy strategies, such as the composite volume method and library of patient-specific treatment plans, aim to reduce normal tissue exposure while covering the bladder target. Real-time MRI scans before each treatment fraction offer potential improvements in bladder cancer radiotherapy.

What Are the Side Effects of Radiation Therapy?

• Radiation therapy can cause side effects in the mouth and throat area.

• Common side effects include skin changes resembling a sunburn, hoarseness, altered taste, dry mouth, weakened teeth, and mouth pain or sores.

• MSK's dental oncology team can help with teeth-related issues and provide custom mouth guards for protection during treatment.

• The rehabilitation team, including speech and swallowing specialists, is experienced in managing radiation therapy side effects.

• They'll discuss potential speech, voice, or swallowing changes before treatment, offer exercises to minimize side effects during and after treatment and ensure mobility of your tongue, jaw, and neck.

Conclusion:

Adaptive radiation therapy (ART) is a promising approach to reduce damage to healthy tissues and enhance targeting during radiation treatment. As technology and workflows improve, the chances of using ART more regularly when needed increase.