SGRT and NC-RAD: Comprehensive Study Notes

SGRT and NC-RAD: Comprehensive Study Notes

SGRT: Definition and Historical Context

• Surface Guided Radiation Therapy (SGRT) uses the patient’s surface as a surrogate for internal anatomy and the target during setup and treatment.
  • Traditional setup methods relied on visually aligning tattoos on the patient’s skin to room lasers.
  • Optical Distance Indicator (ODI) was used to measure source-to-surface distance on the skin.
  • Field light projections onto the patient surface served as alignment guides.
  • Reference pictures of the planned setup guided verification of correct alignment.
  • Closed-circuit television (CCTV) monitored the surface from outside the treatment vault.
• The fundamental process of using surface information for setup and intrafraction monitoring remains the same in modern SGRT.
• SGRT originated from these surface-guided practices and represents the evolution of patient positioning and monitoring in radiotherapy.

Tattoos vs SGRT: Evolution of Positioning Techniques

• Early techniques used tattoos and lasers for patient positioning.
• With advancing planning techniques, SGRT complements and eventually enhances positioning accuracy.
• SGRT is always on after setup, providing continuous monitoring of the patient before and after any IGRT adjustments.
• Tattoo/laser point positioning can still have pitch or roll errors that may be missed until IGRT, requiring staff to re-enter the treatment vault for manual adjustments.
• SGRT reduces these risks by providing real-time surface monitoring and reducing the need for additional manual repositioning.

SGRT and IGRT: Complementary Roles

• SGRT vs IGRT is not a strict rivalry; they are partners in radiotherapy.
• SGRT provides a surface surrogate for internal anatomy and supports intrafraction and interfraction motion management.
• IGRT provides internal anatomy verification; SGRT enhances safety, efficiency, and continuous monitoring.
• Key concepts:
  • Surface is a surrogate for internal anatomy and treatment target.
  • Inter-fraction and intra-fraction motion management are enabled by SGRT.

Clinical Benefits and Versatility of SGRT

• SGRT offers multiple benefits across safety, efficiency, and quality:
  • Safety Benefits
  • Clinical Efficiency
  • Risk Mitigation
  • Quality Assurance
  • Improved patient comfort
  • Continuous position monitoring
  • Supports conventional patient setup
  • Supports IGRT
  • Respiratory gating capabilities
  • Reduction of setup errors and treatment delivery errors
  • SRS (stereotactic radiosurgery) localisation
• Overall impact: improved workflow, reduced unnecessary imaging, and enhanced patient experience.

Key Advantages of SGRT

• Continuous tracking without additional radiation dose: SGRT is an oppotunity for dose-free monitoring.
• “Always-on” technology providing real-time guidance for initial positioning and fine-tuning before leaving the room.
• Reduces imaging dose and clinical workflow inefficiencies by minimizing repeat trips into the vault.
• Localisation of patient and target during deliveries that involve non-coplanar couch movements.
• Particularly beneficial in paediatric patients who may have difficulty staying still.
• Psychosocial benefits due to reduced skin marking and tattoo-less treatment.

SGRT in Clinical Risk Reduction

• Daily setup accuracy is crucial to ensure the right patient is in the correct position for each treatment day.
• SGRT enables verification of patient position prior to IGRT.
• Source: World Health Organization (WHO) Technical Report on Radiotherapy Risk Profile: https://www.who.int/patientsafety/activities/technical/radiotherapyriskprofile.pdf

Uses and Applications of SGRT

• Frameless SRS
• Whole brain radiotherapy
• Head and Neck treatments
• Standard breast with Deep Inspiration Breath Hold (DIBH) and other SBRT options
• Limbs and Sarcoma
• Prostate and Gynae
• Paediatric applications
• Benefits across uses:
  • Dose-free tracking
  • Marker-less positioning
  • Improved immobilisation and patient comfort
  • Speed and workflow efficiency
  • Improved patient compliance

SGRT in Breast Cancer

• Respiratory-gated techniques such as DIBH are widely adopted to reduce cardiac exposure.
• SGRT provides intra-fraction DIBH position monitoring that can co-exist with IGRT methods such as CBCT.
• SGRT uses no invasive equipment or skin markers.
• Aids in reproducibility of patient positioning, reducing margin uncertainties and preventing underestimation of cardiac doses due to setup errors.
• DIBH with SGRT has been shown to reduce dose to organs at risk (OARs) without compromising target dose.

SGRT in SBRT/SRS Treatments

• Surface imaging is an effective motion management tool for SRS/SRT/SBRT.
• A VacBag immobilisation device can provide adequate immobilisation while allowing good surface tracking and improved patient comfort without additional accessories.
• Open-face masks used with SGRT can alleviate claustrophobia in C-Spine metastases.
• SGRT helps track weight loss and contour changes that may affect dose calculations.
• Respiratory management and 4DCT are used for ITV (internal target volume) creation (DIBH or EEBH).
• Surface tracking helps correct posture changes when the spinal column is not palpable before IGRT (ALARA principle).
• Translational shifts are managed as couch moves; postural shifts are guided by colour projections.

Frame-Based vs SGRT: A Comparative View (SRS/Frame-based X-Ray Imaging)

• SGRT can reduce or replace certain aspects of frame-based procedures.
• Frame-based methods may involve longer treatment times and potential discomfort, while SGRT offers continuous monitoring and reduces reliance on rigid frames.
• Benefits of SGRT over traditional frame-based approaches include:
  • Non-ionising surface monitoring in real time
  • Potentially shorter treatment times
  • Ability to treat with open-face masks
  • Reduced risk of skin or soft tissue injury from frames

Tattoos: Limitations and Comparisons

• Tattoos involve minimal points on the skin that can be difficult to use accurately and may lead to guesswork in positioning.
• SGRT reduces reliance on tattoos and provides a more complete surface picture for setup and verification.

SGRT Workflow Overview

• With SGRT, workflow starts with a more complete picture of the patient surface prior to treatment.
• The surface-based data informs cPosition, cMotion, and cRespiration workflows to ensure accurate setup and delivery.

C-Rad NC-RAD: Product Overview and SGRT Workflow

• NC-RAD provides a suite of SGRT products and workflows designed to integrate surface imaging into radiotherapy.

Sentinel & Catalyst+ Overview

• Sentinel (CT-based SGRT solution)
  • DIBH (Prospective) and 4DCT (Retrospective)
  • Gated delivery and intrafraction surveillance
  • Setup features and 4D planning support
• Catalyst+ (Treatment room solution)
  • Handles positioning, motion, respiration, and SRS workflows

Sentinel in CT Room

• Sentinel is C-RAD’s SGRT CT room solution.
• It can be used in the CT room for both 4DCT (lung/liver patients) and DIBH in breast patients.

Sentinel System Hardware and How It Works

• The Sentinel unit comprises a red line laser and a rapidly rotating mirror (galvanometer).
• The laser projects lines onto the surface; reflections are detected by an optical camera.
• Known angles of the laser light and reflections are used to reconstruct a 3D surface image via triangulation.
• The couch is tracked with a laser pointer reflected off the end of the bed and a camera system for imaging.

Sentinel: Respiratory Motion and DIBH Coaching

• Sentinel provides information about respiratory motion during tumor localization in CT.
• It can coach patients into DIBH using a respiratory trace.
• 4DCT assists with ITV creation, including all positions during the breathing cycle.
• The CT scanner reconstructs images using Sentinel data as a movement surrogate.

Sentinel Prospective vs Retrospective Scans

• Prospective scan (Coached): Deep Inspiration Breath Hold (DIBH) used for breast treatments to spare OARs.
• Retrospective Scan: 4DCT SBRT for lung/liver (free breathing or coached).
• In prospective scanning, imaging occurs only during selected breathing phases.
• In retrospective scanning, image data is analyzed after acquisition and sorted into breathing phases.

Sentinel Workflow

• Laser sweeps over the patient.
• Adjust camera settings for patient respiration.
• If breathing trace is reproducible, initiate scan.

Catalyst+ Overview

• Catalyst+ is a treatment-room SGRT solution.
• Uses structured light to create 3D surface maps and continuously monitors surface deviations.
• Light patterns are projected, and a reconstruction algorithm compares projected vs captured patterns to identify pixel coordinates.
• The Catalyst system is robust to room light conditions.
• Reference images can be acquired by Sentinel at CT simulation or imported from the TPS to Catalyst at treatment setup.
• Visualization involves left and right cameras and a master camera with the primary beam.

Structured Light and Catalyst Surface Tracking

• Structured Light: A deformable image registration algorithm continuously calculates deviations between the 3D live surface and a reference image.
• Deformable algorithms allow Regions of Interest (ROIs) distant from the isocentre to have reduced impact on iso shifts relative to ROI near isocentre.

Non-Rigid vs Rigid Registration Concepts

• Non-Rigid (Deformable) Registration:
  • Effective for registering two 3D images that account for elastic surface changes.
  • Repeated corrections to ROI can be avoided; improves robustness of positioning.
• Rigid Registration:
  • Global misalignment (e.g., a shirt sleeve) can have a broad impact on registration; ROI reduction is time-consuming and can affect iso.
• Light projection aids both approaches by providing a real-time surface reference.

Catalyst Non-Rigid Algorithm: Local Positioning and Real-Time Guidance

• Catalyst can identify specific areas of the patient that are out of position and relevant to the tumor location.
• The system highlights local mismatches using color projections to guide therapists to correct posture.
• It captures the patient’s surface image and computes relative tumor position in real-time with high speed (hundreds of images per second).
• The deformable registration algorithm updates the position repeatedly during treatment delivery.
• Visualization shows a blue live image and a green reference image with image registration overlays.

Catalyst+ HD: Surface Options and Visual Coaching

• All patients can be treated with Catalyst+ HD.
• Patented color back projection (red/yellow) to keep focus on the patient.
• Not affected by room light conditions; room lighting can be used for visual coaching.
• Surface choices:
  • Sentinel surface
  • CT surface
  • Catalyst surface

Clinical Modes and General Workflow (Catalyst+cPosition/cMotion)

• General workflow includes: Exit, Patient Selection, Pre-SetUp, cPosition, cMotion, Daily Check, Daily Check.
• Pre-SetUp: Settings optimize scan volume size and camera parameters per patient.
  • Crop ROIs to remove unnecessary items (immobilisation devices, oxygen tubes, stoma bags).
  • Choose templates; customize camera settings (Over exposed, Under exposed, Optimal).

cPosition: Initial Patient Setup and Verification

• Goal: position the patient as CT simulation; verify precise positioning prior to irradiation.
• Features:
  • Override option
  • Capture cPosition reference
  • Couch synchronization

cPosition: Corrections and Posture Alignment

• Corrections use a colour map projection and marker-less setup.
• You cannot move to treatment mode (cMotion) if the patient is not aligned or out of tolerance.
• Separation of isocenter and posture corrections for tolerance; arms need to be lowered.

cMotion: Real-Time Monitoring During Treatment

• The last live view in cPosition becomes the cMotion reference.
• cMotion monitors:
  • Isocenter movement
  • Surface movement
• If motion exceeds tolerance, a beam hold is triggered via the interface.
• Interfaces include Elekta: iCom, Elekta Response; Varian: MMI Blue Dot for Beam Hold status.

cRespiration: Dedicated Respiratory Module

• cRespiration offers a dedicated respiratory module for motion management.
• Modes include Free Breathing and Deep Inspiration Breath Hold (DIBH).
• Visual indicators show differences between reference and live surface; when they match, gating can occur.

cRespiration: Gating and Visual Coaching

• Gating spot updates vertical surface position with high time resolution.
• BEAM HOLD is triggered when surface motion or isocenter motion exceed gating windows.
• SGRT-based gating prevents arching of the back during a hold and provides visual coaching and audio feedback.
• Visual coaching tools include light panels, goggles, and a tablet for breath-hold cues.

cSRS: Dedicated High-Precision SRS Module

• cSRS is a specialized module for stereotactic radiotherapy.
• The Catalyst+ HD system equipped with SRT module supports open-mask treatments, semi-rigid approaches, and sub-millimeter, non-coplanar treatments with high accuracy.
• Tracks the patient, not the mask; achieves sub-millimeter accuracy without ionizing radiation (approx. $0.5 ext{ mm}$).
• Features 4x higher surface resolution and an optimized algorithm for intracranial stereotactic treatments.
• Includes automatic facial recognition and does not require excluding moving parts (eyes, lips, nose, etc.).

SRS: Non-Coplanar and 6DoF Corrections

• cSRS supports non-coplanar treatment with 6 degrees of freedom (6DoF) corrections.
• Automatic validation of couch rotation and validation of all fields during treatment.
• Continuous monitoring of the patient during stereotactic treatment with sub-millimeter accuracy.
• Couch rotation up to 270^rac{1}{1}0^ ext{o} (270°) for optimized treatment geometry.

Overall Takeaways

• SGRT integrates surface imaging to enhance accuracy, safety, and efficiency across a wide range of treatments including breast, SBRT/SRS, and pediatric care.
• Sentinel provides CT-room-based SGRT with 4DCT/DIBH capabilities; Catalyst+ provides in-room SGRT with advanced surface tracking, deformable registration, and high-precision SRS workflows.
• The architecture supports both rigid and deformable (non-rigid) registration to cope with patient surface changes and movement.
• A unified workflow with cPosition, cMotion, cRespiration, and cSRS modules enables a comprehensive, real-time monitoring and guidance system.

References and Credits

• WHO Radiotherapy Risk Profile: https://www.who.int/patientsafety/activities/technical/radiotherapyriskprofile.pdf

End of Notes