The superior soft-tissue visualization enabled with online MRI provides an opportunity for high-precision image guidance, response assessment and novel adaptive radiotherapy (ART) processes. At our institution, we developed a novel platform integrating a 1.5 T MR scanner-on-rails with a 6 MV linear accelerator capable of daily in-room MRI. The aim of this work was to develop a hybrid CBCT-MRI image-guided radiotherapy (IGRT) workflow and describe our preliminary experience with implementing in-room MRI for offline ART for intact-cervix cancer. Process mapping, hazard analysis and mock procedures were used to design a hybrid IGRT workflow consisting of CBCT-guided treatment delivery, immediately followed by post-delivery in-room MRI. Patients were transferred to the MR in the treated position via an air-cushion hover-board and then coils were placed for imaging. Treatment planning using VMAT was performed as per EMBRACE II (45 Gy/25 fractions). The primary CT was acquired with full-bladder, and simulation MRI with both full and empty-bladder were included to define the internal target volume (ITV). Daily CBCT guidance used the primary CT as the reference and in-room MRI consisted of a fast T2w axial scan covering the pelvis and primary target. All images were imported to the planning system, co-registered to the plan via the treatment position alignment and reviewed offline by a multi-disciplinary team for geometric assessment of organ motion and target coverage. Two patients with intact-cervix cancer were treated to date with the CBCT-MRI workflow. In-room MRI were acquired for 17/25 and 8/25 fractions. Facility down-time for servicing was the primary reason for missed MRI. The mean time between CBCT and MRI was 16 mins (range = 10–27 mins). The mean time between treatment delivery completion and MRI was 10 mins (6–18 mins). During offline review, large inter-fraction variations in bladder, rectum and target positioning were noted for the first patient. Systematic motion of the uterine fundus beyond the PTV was noted on CBCT, but complete visualization of the GTV, vagina and uterus required MRI. An adaptive replan with modified ITV was created for the final 7 fractions for this patient, which effectively maintained target coverage by the PTV. Comparing the CBCT and MRI, large intra-fraction variations in the bladder and primary target were observed. The mean change in bladder volume was 60 cc (1–161 cc) for the first patient and 29 cc (1–83 cc) for the second. We have successfully demonstrated a hybrid IGRT workflow with in-room MRI for offline ART for cervical cancer. Monitoring daily variations with MRI empowers a comprehensive adaptive paradigm that will become our new standard-of-care for intact-cervix cancer treated with VMAT. Further efforts are underway to optimize IGRT workflows with pre-delivery MRI, as well as to develop state-of-the-art dose accumulation and online ART processes.

The 177Lu DOTATATE (Lu) therapy can potentially improve progression free and overall survival in patients (pts) with progressive metastatic neuroendocrine tumors. We hypothesized that individualized dosimetry is effective in enabling normal tissue adapted prescription of Lu. A multi-institution prospective single arm study of Lu (4 cycles) with individualized dosimetry, in pts with 68Ga DOTATATE positive, progressive metastatic disease is ongoing in Ontario (NCT02743741). Dosimetry calculations are based on quantitative SPECT/CT images acquired at 4, 24, and 72 hours post Lu therapy. A 2cm spherical region of interest (ROI) is placed over normal kidneys and a vertebral body to estimate renal and bone marrow (BM) absorbed dose after each cycle. All pts received 7.4GBq for cycle (C) 1 (with modifications based on creatinine clearance and hematology for all cycles). Subsequent injected activities were varied based on renal absorbed dose (tolerance dose of 23Gy). Dose escalation was permitted to a max. of 11.1GBq/cycle. To quantify tumor absorbed dose, a ROI was placed over representative (highest SUV uptake) intra and extrahepatic areas. In addition, the liver was segmented and a threshold of >41%Max SUV was used to auto-segment liver tumors. To explore if tumor dose changed during treatment, we calculated the actual and normalized (using 7.4GBq) absorbed dose change. Between August 2016 and December 2018, 100 pts were accrued from the four consortium sites, 62 pts have completed the therapeutic phase, 53 pts have received all four cycles and were the basis of the current analysis. Using 29.6GBq (±10%) as the conventional total dose (when no Individualized dosimetry is used), 36 (68%) pts had dose escalation (>32.56GBq), 9 (17%) pts no change, and 8 (15%) pts had dose de-escalation (<26.64GBqi). The median (med) total renal dose absorbed was 18 (SD4, range 7 – 24) Gy. Only 1 pt received renal dose above tolerance. The med BM dose was 0.79 (SD1.3; range 0.15– 9.69) Gy. In 4 pts, the BM dose was >2Gy, attributable to multiple bone metastases and difficulty identifying a tumor free ROI. Using the threshold method, the med % liver containing tumor was 5% (SD 5; range 1-31%). The med liver tumor dose was 69 (SD 48; range 12 – 227) Gy. The med uninvolved liver dose was 10 (SD 8, range 5-33) Gy. Using the ROI method, the med liver tumor dose was 93Gy (SD64; range 20-291) Gy. The C1 med liver tumor dose was 21 (SD19 range: 4 – 112) Gy. In contrast, the C4 dose was 16 (SD 16; range 2 – 67) Gy. The normalized med difference was -4 (SD 15; range -45 to 38) Gy. Individualized dosimetry allowed dose escalation in 68% and de-escalation in 15% of pts while maintaining the renal dose within tolerance. Dose absorbed by tumor (ROI method) showed a >10-fold variation across patients. Longer follow-up is required to understand the impact of individualized dosimetry on outcomes.

Comprehensive technical assessment of a MR-guided radiation therapy system, design, and integration of clinical workflows. A therapy vault was designed to house a Linac conventional setup and at the same time to allow a 1.5T MR-on-rails scanner to travel inside the vault at a pre-defined imaging location in the vicinity of the Linac. The Linac is a 6X FF/FFF system with a standard patient treatment table. The MR can travel on ceiling-mounted rails between a dedicated MR simulation suite and the Linac vault, the two rooms being separated by radiation and RF shielding doors. To allow MR imaging in the vault, the Linac and the patient table are stored behind specially designed RF doors. The separation between the Linac and MR was chosen to allow for a full magnetic field decoupling between all sub-components. With the MR at the imaging position the Linac/couch can be operated independently without posing safety risks or sub-optimal performance of the Linac/couch or MR scanner. The patient is moved between MR diagnostic table and Linac table via a patient transfer system operated as a hovercraft device. The MR/Linac configuration was assessed by considering the following aspects: a) magnetic field decoupling by experimental measurements – i.e. field mapping with Hall probes, magnetic pull forces on the Linac table, radiation beam specifications - output/flatness/symmetry, Linac on-board imaging, MR shimming and overall imaging performance – b) RF noise isolation (survey, MR testing), c) safety systems (interlocking system, redundancy measures), d) RT workflows (patient transfer, MR data flow, MR to kV matching), and QC procedures (MR image quality and B0 mapping, Linac/MR). Numerical simulations based on finite elements methods were also performed to model the entire MR-Linac environment including the Linac table. The MR scanner field was generated using a LP optimization technique and the Linac/table was represented as full-scale CAD geometries. The Linac beam performance and its kV imaging system were found to be unaffected by the MR presence in the treatment vault. The effects were measured and monitored over one year. The MR scanner was tested for optimal performance - the shimming and standard imaging procedures passed the clinical requirements. The numerical simulations and associated measurements for the magnetic field decoupling were in good agreement (forces, field mapping). RT workflows utilizing the kV and MR in-room imaging (independent and combined) are currently under development to facilitate the clinical integration of the system. Targeted applications are MR-based RT (adaptive) planning and guidance, fast imaging for the quantification of organ motion. Integrated quality control procedures were also developed for routine monitoring (MR shimming, image distortions – scanner-related and patient-induced, MR-to-kV matching). All aspects investigated support the feasibility of the MR-guided RT system for clinical deployment.

Purpose: To describe and assess feasibility of a novel MR‐to‐Linac isocenter calibration tool for magnetic resonance guided radiotherapy (MRgRT™). Methods: The MRgRT system co‐developed by IMRIS and Varian employs a movable MR system, which travels into a Linac vault. To support MR‐based couch corrections based on MR‐to‐MR registration, we developed a software tool to calibrate the MR‐to‐Linac coordinate system transformation and apply it to MR images acquired for treatment guidance. To assess feasibility, we quantified repeatability of the movable MRI system at MR isocenter by securing an ACR phantom to a fixed IMRIS interventional table, and moving the MR system between the two adjacent rooms simulate normal function. We performed 18 cycles over two days in which we acquired 3D MRI datasets with 1 mm isotropic resolution. We assessed position variability by registering the MR volume for each cycle to the first volume, and tabulating transform parameters. Separately, we investigated if a calibrated position encoder on the magnet mover could minimize the z‐direction shift variability. Results: Greatest isocenter variability was observed in the z direction, with mean shift of 0.21 +/− 0.12 mm over both days. The greatest rotational variability was observed about the z‐axis, with mean rotation of 0.8 +/− 0.8 mrad over both days. Maximum shift was 0.51 mm in the z direction, and maximum rotation was 1.7 mrad about the z‐axis. In the separate repeatability experiment we found that the calibrated position encoder reduced the mean z‐shift variability from 0.59 +/− 0.35 mm to 0.17 +/− 0.13 mm. Conclusion: We showed that the movable MRI system provides a consistent within‐day and between‐day isocenter location, and z‐shift variability can be minimized with a position encoder. This work demonstrates the feasibility of using an MR‐to‐Linac isocenter calibration tool for the MRgRT system. Jeff Winter, Michael Westmore and Meir Dahan are all employees of IMRIS, the company co‐developing the MRgRT system. Funding for the MRgRT project at Princess Margaret Hospital was provided by the Canadian Foundation for Innovation.

Purpose: An MRI on rails is being installed at our institution to provide MR‐guided brachytherapy and teletherapy (MRgRT). The facility is comprised of collinear brachytherapy, MR‐Sim, and linac suites. The MR‐on‐rails translates into the adjacent suites for imaging. An existing bunker and adjacent space were renovated to permit the MR to be moved away from the linac during irradiation. This work describes the design and radiation shielding characteristics of the linac suite within the MRgRT facility. Methods: The original linac vault was designed with a two‐corner maze design to operate at 18 MV. The maze was removed and replaced with three direct‐shielded doors: a sliding console door allow for personnel and gurney access to the bunker; and two double sliding doors through which the MRI translates. The double doors employ an S‐shaped coupling surface to minimize radiation leakage when they are closed. These doors are also RF‐shielded as part of the MR RF cage. The shielding was designed for a workload of 5 × 106 cGy per year; 6 MV beam; maximum dose rate: 1400 MU/min; shielding level 0.05 mSv/year for members of the public and 1 mSv/year for nuclear energy workers. Results: The total thickness of the linac‐MRI sliding doors was 7 inches of lead and 2 inches of stainless steel, producing an equivalent thickness of 8 inches (20.3 cm) of lead. The dose rate at the distal surface of the linac‐MR door is 0.08 mSv/year or 10.9 μSv/hr. The final design includes a copper RF shield and bladder to provide RF shielding. Conclusion: A facility comprising three collinear brachytherapy, MR‐Sim, and linac facility has been designed to meet radiation and radiofrequency shielding limits.

Purpose/Objective(s)MR imaging provides exquisite visualization of soft tissue anatomy as well as physiological assessment of normal and diseased tissues. Streamlined integration of MR into the RT treatment room without the deleterious effects of electron–B-field interaction requires coordinated operation of the linear accelerator, MR scanner, patient support, and shielding subsystems. The design, construction, and initial performance of a dedicated MR-guided treatment facility providing 1.5T MR imaging, non-coplanar external beam delivery, and HDR brachytherapy capabilities will be described.Materials/MethodsA dedicated MR-guidance suite (320 m2) satisfying ACR MR safety specifications has been designed to allow a movable 1.5T MR imager to be employed in three different environments: (i) MR-simulation, (ii) MR-guided HDR brachytherapy (10 Ci, Ir-192), and (iii) MR-guided external beam radiation delivery. MR-simulation includes the provision of a dedicate oncology coil system to enable large field-of-view imaging in the head, neck, and pelvis. The MR-guided HDR suite is shielded to satisfy CNSC radiation shielding requirements, as well as, RF isolation for intra-operative MR imaging during applicator/catheter placement. MR-guided external beam RT is achieved on the same platform through the use of a dedicated non-coplanar treatment machine (Dose Rate: 1400 MU/min), a modified treatment couch, and dedicated shielding systems that move in unison to enable RT delivery within 120s of MR imaging. Dedicated/removable MR imaging surface coils, calibration and data handling sub-systems, and patient support systems have been developed to facilitate the MR-guided external beam treatments.ResultsThe design of the integrated RF and radiation shielding facility with motorized RF-radiation doors has been completed with on-going installation and validation of performance. In-factory testing of the 1.5T MR and modified table have demonstrated compatibility to enable motorized displacement of the patient from accelerator isocenter to MR-imaging position. Mapping of the B field strength proximal to the linear accelerator suggests minimal interference (< 20 G). Repeat imaging studies between magnet displacements (and over time) demonstrate isocenter reproducibility for MR-guidance to be within 0.5 mm (3D MP-RAGE; 1mm isotropic; 4m25s). Image quality tests demonstrate diagnostic SNR performance for the RT-specific, large FOV head and neck and removable pelvis coil systems.ConclusionsThe development of a novel platform for MR-guided brachytherapy and external beam treatments using state-of-the-art delivery sub-systems is nearing completion. On-going testing during final construction demonstrates the potential for diagnostic MR image quality, efficient integration with current treatment technologies, and geometrically accurate MR-based guidance of RT. Purpose/Objective(s)MR imaging provides exquisite visualization of soft tissue anatomy as well as physiological assessment of normal and diseased tissues. Streamlined integration of MR into the RT treatment room without the deleterious effects of electron–B-field interaction requires coordinated operation of the linear accelerator, MR scanner, patient support, and shielding subsystems. The design, construction, and initial performance of a dedicated MR-guided treatment facility providing 1.5T MR imaging, non-coplanar external beam delivery, and HDR brachytherapy capabilities will be described. MR imaging provides exquisite visualization of soft tissue anatomy as well as physiological assessment of normal and diseased tissues. Streamlined integration of MR into the RT treatment room without the deleterious effects of electron–B-field interaction requires coordinated operation of the linear accelerator, MR scanner, patient support, and shielding subsystems. The design, construction, and initial performance of a dedicated MR-guided treatment facility providing 1.5T MR imaging, non-coplanar external beam delivery, and HDR brachytherapy capabilities will be described. Materials/MethodsA dedicated MR-guidance suite (320 m2) satisfying ACR MR safety specifications has been designed to allow a movable 1.5T MR imager to be employed in three different environments: (i) MR-simulation, (ii) MR-guided HDR brachytherapy (10 Ci, Ir-192), and (iii) MR-guided external beam radiation delivery. MR-simulation includes the provision of a dedicate oncology coil system to enable large field-of-view imaging in the head, neck, and pelvis. The MR-guided HDR suite is shielded to satisfy CNSC radiation shielding requirements, as well as, RF isolation for intra-operative MR imaging during applicator/catheter placement. MR-guided external beam RT is achieved on the same platform through the use of a dedicated non-coplanar treatment machine (Dose Rate: 1400 MU/min), a modified treatment couch, and dedicated shielding systems that move in unison to enable RT delivery within 120s of MR imaging. Dedicated/removable MR imaging surface coils, calibration and data handling sub-systems, and patient support systems have been developed to facilitate the MR-guided external beam treatments. A dedicated MR-guidance suite (320 m2) satisfying ACR MR safety specifications has been designed to allow a movable 1.5T MR imager to be employed in three different environments: (i) MR-simulation, (ii) MR-guided HDR brachytherapy (10 Ci, Ir-192), and (iii) MR-guided external beam radiation delivery. MR-simulation includes the provision of a dedicate oncology coil system to enable large field-of-view imaging in the head, neck, and pelvis. The MR-guided HDR suite is shielded to satisfy CNSC radiation shielding requirements, as well as, RF isolation for intra-operative MR imaging during applicator/catheter placement. MR-guided external beam RT is achieved on the same platform through the use of a dedicated non-coplanar treatment machine (Dose Rate: 1400 MU/min), a modified treatment couch, and dedicated shielding systems that move in unison to enable RT delivery within 120s of MR imaging. Dedicated/removable MR imaging surface coils, calibration and data handling sub-systems, and patient support systems have been developed to facilitate the MR-guided external beam treatments. ResultsThe design of the integrated RF and radiation shielding facility with motorized RF-radiation doors has been completed with on-going installation and validation of performance. In-factory testing of the 1.5T MR and modified table have demonstrated compatibility to enable motorized displacement of the patient from accelerator isocenter to MR-imaging position. Mapping of the B field strength proximal to the linear accelerator suggests minimal interference (< 20 G). Repeat imaging studies between magnet displacements (and over time) demonstrate isocenter reproducibility for MR-guidance to be within 0.5 mm (3D MP-RAGE; 1mm isotropic; 4m25s). Image quality tests demonstrate diagnostic SNR performance for the RT-specific, large FOV head and neck and removable pelvis coil systems. The design of the integrated RF and radiation shielding facility with motorized RF-radiation doors has been completed with on-going installation and validation of performance. In-factory testing of the 1.5T MR and modified table have demonstrated compatibility to enable motorized displacement of the patient from accelerator isocenter to MR-imaging position. Mapping of the B field strength proximal to the linear accelerator suggests minimal interference (< 20 G). Repeat imaging studies between magnet displacements (and over time) demonstrate isocenter reproducibility for MR-guidance to be within 0.5 mm (3D MP-RAGE; 1mm isotropic; 4m25s). Image quality tests demonstrate diagnostic SNR performance for the RT-specific, large FOV head and neck and removable pelvis coil systems. ConclusionsThe development of a novel platform for MR-guided brachytherapy and external beam treatments using state-of-the-art delivery sub-systems is nearing completion. On-going testing during final construction demonstrates the potential for diagnostic MR image quality, efficient integration with current treatment technologies, and geometrically accurate MR-based guidance of RT. The development of a novel platform for MR-guided brachytherapy and external beam treatments using state-of-the-art delivery sub-systems is nearing completion. On-going testing during final construction demonstrates the potential for diagnostic MR image quality, efficient integration with current treatment technologies, and geometrically accurate MR-based guidance of RT.

Purpose/Objective: We studied the effect of a higher dose on tumor control for localized prostate cancer in a randomized trial with a median follow-up of 110 months.Materials and Methods: Patients with T1b-T4 prostate cancer were included in the period 1997-2003 (n=664) and randomized between 78 Gy (n=333) and 68 Gy (n=331).Primary endpoint was biochemical and/or clinical failure (BCF) according the guidelines of the American Society for Therapeutic Radiology and Oncology (ASTRO) (3 consecutive rises).Secondary endpoints were BCF using the Phoenix guidelines (nadir plus 2 µg/L), clinical failure (CF), local failure (LF), prostate cancer related death (PCRD), and overall survival (OS).Explorative subgroup analyses were performed.Results: Estimated freedom from BCF at 10 years according ASTRO was 45.9 % and 38.4 % for 78 Gy and 68 Gy, respectively (Log Rank, p=0.025).Freedom from BCF according Phoenix definition (Table ) was superior in the 78 Gy arm as well (p=0.046).CF and OS were similar in both arms (Table ).LF as a first event was significantly less observed in the 78 Gy arm (14 versus 27 events, p=0.036,Figure).For progression outside the prostate, i.e. documented regional or distant failure, we found more first events in the 78 Gy arm, which was not significant (59 versus 43 events, p=0.14).At the current update, 205 patients were deceased (104 in the 78 Gy arm), including 88 patients with

INTRODUCTION:An online Magnetic Resonance guided Radiation Therapy (MRgRT) system is under development. The system is comprised of an MRI with the capability of travel between and into HDR brachytherapy and external beam radiation therapy vaults. The system will provide on-line MR images immediately prior to radiation therapy. The MR images will be registered to a planning image and used for image guidance. With the intention of system safety we have performed a failure modes and effects analysis.METHODS:A process tree of the facility function was developed. Using the process tree as well as an initial design of the facility as guidelines possible failure modes were identified, for each of these failure modes root causes were identified. For each possible failure the assignment of severity, detectability and occurrence scores was performed. Finally suggestions were developed to reduce the possibility of an event.RESULTS/DISCUSSION:The process tree consists of nine main inputs and each of these main inputs consisted of 5 - 10 sub inputs and tertiary inputs were also defined. The process tree ensures that the overall safety of the system has been considered. Several possible failure modes were identified and were relevant to the design, construction, commissioning and operating phases of the facility. The utility of the analysis can be seen in that it has spawned projects prior to installation and has lead to suggestions in the design of the facility.

PURPOSE:To develop the operational workflow and safety systems of a magnetic resonance-guided radiotherapy system (MRgRT™), which comprises an MR scanner on rails that travels between a linac vault, MR simulation room and brachytherapy suite.METHODS:To develop a safe and streamlined clinical workflow, we conducted a comprehensive process review based on a layered approach to overall MRgRT safety that included i) facility design, (ii) workflow iii) system design and interlocks and iv) policies and procedures. We applied existing guidelines for MR and radiation safety, and employed system-level failure modes and effects analyses to design the MRgRT facility and clinical procedures.RESULTS:In the MRgRT system configuration, the MR and treatment systems are physically decoupled and used independently requiring novel administration of existing MR and radiation guidelines. A key element for the safe operation of the moving MR unit is the concept that all three rooms represent zone 4 areas (American College of Radiology guidelines). Using this concept, we applied MR guidelines to develop safe procedures for the overall suite, including screening of all persons entering the suite in zone 2 and control of ferromagnetic materials. We generated a clinical workflow that ensures expedient and safe transition between MR imaging and treatment delivery in both the linac and brachytherapy rooms. In addition, we designed emergency protocols for MRgRT, which helped drive requirements for the facility and system design, e.g., need for an accessible MR-safe stretcher.CONCLUSIONS:We designed the first comprehensive description of the MRgRT workflow, interlocking systems and safety procedures. With this layered approach to safety, we addressed critical aspects regarding safe operation and workflow for the system and provided multiple redundancies for key processes. Coupled with customized staff training, the proposed design ensures the safe operation of the MRgRT facility. This work has received research personnel support from IMRIS.

Purpose: To evaluate and identify safety system concerns and possible failure modes for a multimodality, linear accelerator (linac) — magnetic resonance imager (MRI) ‐ brachytherapy, radiotherapy system. Methods: A Delphi process is applied to investigate the safety system concerns and possible failure modes in a linac‐MRI‐brachytherapy system. Well established, for instance in the automotive or airline industries, system, design and process failure modes effect analysis can be applied to the design of a multimodality radiation therapy system. Results: Safety design, systems, processes and culture in radiation therapy is of great importance. When implementing new technologies a review of the necessary staff and patient safety may be necessary. To address patient and staff safety concerns a thoughtful design process must be implemented when an MRI is present or near a linac or a brachytherapy system. Each input into a patient specific process map, such as consent, screening, immobilization, planning, image guidance and machine movement coordination must be analyzed for safety and failure modes concerns. Numerous items have been identified as potential failure modes, these items have been classified into the following nine categories: screening, motion, interlocks, imaging, treatment delivery, dosimetry, plan adaptation, mechanical and miscellaneous. A broad range of failure modes have been identified some of these include and range from non‐compatible in‐room finishing to linac performance degradation under repeated small magnetic field influences to improper patient screening and the possibility of machine collisions. Conclusions: An abridged list of suggestions resulting from our safety systems analysis includes a rigorous staff educational and training program, the evaluation of current quality assurance devices used for mechanical and dosimetric tests, an interlocked computerized system for machine translations and rotations, machine servicing protocols and both fire and patient emergency protocols.

The technical feasibility of using IMRT for treating early glottic squamous cell carcinoma, particularly in relation to normal tissue sparing, has been demonstrated. There is, however, a lack of data regarding the clinical outcomes produced by IMRT compared with standard non-conformal radiotherapy techniques (RT). The locoregional control rates of patients with T2N0M0 squamous cell carcinoma of the glottis treated radically with radiotherapy in Princess Margaret Hospital between 2003 and 2008 were determined. Patients were treated with either RT (parallel opposed/angled down pairs using physical wedges or multi-leaf collimated virtual wedges), or with IMRT (using a 5 field IMRT plan with 15 to 20 segments). All patients underwent CT simulation and contouring of the GTV. Patients in the RT group were treated with opposed lateral fields defined to treat the GTV including the whole larynx (majority 6 x 6 cm fields) to 60 Gy in 25 fractions. Two CTVs were defined for patients managed with IMRT plans. A 60 Gy dose (CTV60) was defined as a 0.5 to 1.0 cm expansion on the GTV, and a surrounding 50 Gy dose (CTV50) was variably defined to include a further expansion of 0.5 to 2.0 cm on the CTV60. For 17/50 cases the CTV50 was expanded to include the whole larynx. PTVs were defined as 0.5 cm expansions on the CTVs. On-treatment position verification consisted of either electronic portal imaging or cone beam CT imaging with matching of bony anatomy. During the study period, there were 48 patients treated with RT and 50 patients treated with IMRT. These sequential cohorts were balanced with respect to gender, smoking status, cord mobility, anterior commissure and supra and subglottic involvement. The median follow-up time was 2.8 years (range, 0.3-6.9). The 3-year actuarial local recurrence rate was 32% for IMRT (crude rate 14/50) and 20% for RT (crude rate 11/48) (p = 0.54). Overall survival was 74% with nc-RT compared with 65% for IMRT (p = 0.21). The location of local relapses in all cases were the ipsilateral cord 100% (25/25), contralateral cord 72% (18/25), supraglottis 64% (16/25) and subglottis 88% (22/25). Though local recurrence rates were not statistically higher for the IMRT cohort these results warrant careful consideration when contemplating the use of IMRT with partial laryngeal irradiation in this patient population. Uncertainties in daily setup and verification may result in suboptimal dose delivery and must be accounted for in defining IMRT treatment planning and delivery procedures for these patients.

Purpose: To improve target delineation in the radiation therapy planning process by quantitatively registering endoscopic contours traced on endoscopic images to volumetric imaging. This method is especially useful for target delineation in head and neck and esophageal cancers. Methods: We have developed technology that registers endoscopic images to CTimages by tracking and registering the position and orientation of the endoscope relative to the CTimage set using electromagneticsensors embedded in the endoscope. After 2D to 3D image registration, users can contour regions‐of‐interest visible in the 2D endoscopic view. A mesh is created on the interior of the ROI and projected onto the 3D image data, registering the ROI with the volumetric image. This 3D ROI can be exported into the treatment planning software (TPS).The technology was tested on an anatomical head phantom based on a subject image with test “lesion” created by soaking a pad with CT contrast agent so that the lesion was visible in the TPS images. The contouring accuracy was tested by comparing the average minimum distance between the endoscopy‐derived and TPS contours. Results: A CTimage of the head phantom was acquired followed by endoscopic imaging. The lesion was contoured in the endoscopic image and the resulting mesh contour imported imported into Pinnacle. The lesion was contoured in Pinacle using CT# threshold. The average minimum distance between the endoscopy and TPS contours was 0.96mm with 93% of all points in the endoscopy ROI within 1.5 mm of any point within the TPS ROI. This accuracy is limited by the CTimaging resolution and the EM sensor accuracy. Conclusions: We have demonstrated that lesions can be contoured from 2D endoscopic images and registered to 3D volumetric data sets with an accuracy of ±1 mm.

Radiation therapy has been on the march toward highly conformal and precise placement of radiation dose within the human body. Development of image-guidance systems based upon x-ray and ultrasound have advanced our capabilities to the level of a few millimeters of uncertainty in many sites. However, there are a subset of existing applications, and potentially many new applications that could be improved upon or pursued if greater targeting accuracy could be achieved. This is motivating the creation of magnetic resonance image-guided radiation treatment units (MRgRT) that either operate simultaneously or provide pre-treatment MR-based targeting capabilities. In this review, the motivation for these pursuits, an overview of recent developments, and a commentary on the challenges they face is presented.

Target delineation in Head and Neck cancer is a critical step in intensity modulated radiation therapy. Current methods to identify targets for delineation rely on volumetric imaging combined with other clinical findings including physical exam and endoscopy. Endoscopy and physical exam often reveal areas of visible or palpable disease which are not clearly demonstrated on volumetric imaging. However, relating endoscopy images to the volumetric imaging is subject to potential error relying on clinician recall of anatomy visible on both CT and endoscopy. We have developed technology that registers endoscopic images to CT images by tracking and registering the position and orientation of the endoscope relative to the CT image set using electromagnetic sensors embedded in the endoscope. After 2D to 3D image registration, users can contour regions-of-interest visible in the 2D endoscopic view. A mesh is created on the interior of the ROI and projected onto the 3D image data, registering the ROI with the volumetric image. This 3D ROI can be exported in a format that can be read by standard clinical treatment planning software. The technology was tested on an anatomical head phantom based on a subject image. Following CT imaging, endoscopy was performed on the head phantom. ROI's were contoured in the 2D endoscopic image, with points targeting known landmarks in the phantom. The ROI's were imported into Pinnacle. The accuracy of the ROI position was measured by comparison with the CT-visible landmarks used to guide the initial 2D contouring, demonstrating a registration accuracy of ±1mm.

PURPOSE:Effective target definition and broad employment of treatment response assessment with dynamic contrast-enhanced CT in radiation oncology requires increased speed and coverage for use within a single bolus injection. To this end, a novel volumetric CT scanner (Aquilion One, Toshiba, Tochigi Pref., Japan) has been installed at the Princess Margaret Hospital for implementation into routine CT simulation. This technology offers great advantages for anatomical and functional imaging in both scan speed and coverage. The aim of this work is to investigate the system's imaging performance and quality as well as CT quantification accuracy which is important for radiotherapy dose calculations.METHODS:The 320-slice CT scanner uses a 160 mm wide-area (2D) solid-state detector design which provides the possibility to acquire a volumetric axial length of 160 mm without moving the CT couch. This is referred to as "volume" and can be scanned with a rotation speed of 0.35-3 s. The scanner can also be used as a 64-slice CT scanner and perform conventional (axial) and helical acquisitions with collimation ranges of 1-32 and 16-32 mm, respectively. Commissioning was performed according to AAPM Reports TG 66 and 39 for both helical and volumetric imaging. Defrise and other cone-beam image analysis tests were performed.RESULTS:Overall, the imaging spatial resolution and geometric efficiency (GE) were found to be very good (>10 lp/mm, <1 mm spatial integrity and GE160 mm=85%) and within the AAPM guidelines as well as IEC recommendations. Although there is evidence of some cone-beam artifacts when scanning the Defrise phantom, image quality was found to be good and sufficient for treatment planning (soft tissue noise <10 HU). Measurements of CT number stability and contrast-to-noise values across the volume indicate clinically acceptable scan accuracy even at the field edge.CONCLUSIONS:Initial experience with this exciting new technology confirms its accuracy for routine CT simulation within radiation oncology and allows for future investigations into specialized dynamic volumetric imaging applications.

Purpose: Thresholding of fluorodeoxyglucose (FDG) uptake imaged with positron emission tomography (PET) has been proposed for radiotherapy target delineation. However, there exists no consensus on the threshold best corresponding to disease extent, due to a lack of truth for validation. The purpose of this investigation was to establish criteria under which a fixed FDG-PET threshold may be useful for target delineation. An image-based surrogate of target definition ‘truth’ is proposed, derived from a measure of the concordance between multiple expert observers defining the gross tumor volume (GTV) with FDG-PET and CT. A method was developed that can automatically localize these regions and was used to evaluate the coincident FDG uptake threshold. Methods and Materials: 10 patients with head and neck (H&N) cancers underwent FDG-PET-CT imaging using a hybrid scanner (Biograph 16, Siemens Medical Systems). For each patient, 8 observers specializing in H&N cancers delineated the GTV on concurrently-displayed FDG-PET-CT. Regions of high target definition concordance were localized by forming the union of observer target definitions, applying a gradient filter and selecting an intensity threshold equivalent to 6 of 8 observers. At regions of high concordance not attributable exclusively to CT information, the FDG uptake threshold relative to maximum uptake in the GTV was measured. Results: In 4 patients, the mean FDG uptake threshold was 40.9%. In regions of concordance not attributable to CT, the mean threshold in 6 patients was 32.8%. Conclusion: A method was developed for localizing regions of high inter-observer concordance. These regions served as a surrogate truth for disease extent against which FDG-PET uptake thresholds were evaluated. For primary H&N cancers, a threshold of approximately 30–40% was able to delineate the tumor at regions of the target boundary where CT information was not definitive. The application of uniform thresholds for H&N target delineation is not recommended.