Image-guided Radiotherapy Technologies Research Articles

National survey on image‐guided radiotherapy practice in New Zealand

This survey aimed to assess the use of image-guided radiotherapy (IGRT) within New Zealand (NZ) and evaluate the quality of IGRT delivery. All nine centres in NZ were invited to participate in an online survey in November 2015. Questions were asked on type of IGRT technologies available, IGRT use by tumour site and frequency of imaging. In addition, questions were asked in reference to the American Society for Radiation Oncology (ASTRO) White Paper recommendations on safe practice of IGRT. Seven of the nine centres (78%) responded. Kilovoltage cone-beam CT (CBCT), kilovoltage planar imaging and megavoltage electronic portal imaging were the most commonly used IGRT technologies. CBCT was most frequently used in gynaecology (100%), genitourinary (86%) and head and neck (86%) sites. Despite the availability of similar IGRT technologies, there was significant variation in their application between centres. All centres used online IGRT; however, the frequency of imaging varied across the tumour sites and individual centres. Daily online IGRT use ranged from 43% to 86% across the tumour sites. Overall, there was good compliance by the NZ centres to the White Paper recommendations, with at least 71% reached for each element. However, the compliance rates for the individual centres ranged between 50% and 100%. The most commonly identified barrier to IGRT use was lack of guidelines/education (43%). Image-guided radiotherapy is widely used in NZ; however, there is a wide variation in its application between centres. Detailed tumour site-specific, imaging modality-specific national guidelines will allow standardization of IGRT practices.

Stereotactic prostate adaptive radiotherapy utilising kilovoltage intrafraction monitoring: the TROG 15.01 SPARK trial

BackgroundThis paper describes the multi-institutional prospective phase II clinical trial, SPARK: Stereotactic Prostate Adaptive Radiotherapy utilizing Kilovoltage Intrafraction Monitoring (KIM). KIM is a real-time image guided radiotherapy technology being developed and clinically pioneered for prostate cancer treatment in Australia. It has potential for widespread use for target radiotherapy treatment of cancers of the pelvis, thorax and abdomen.MethodsIn the SPARK trial we will measure the cancer targeting accuracy and patient outcomes for 48 prostate cancer patients who will be treated in five treatment sessions as opposed to the conventional 40 sessions. The reduced number of treatment sessions is enabled by the KIM’s increased cancer targeting accuracy.DiscussionReal-time imaging in radiotherapy has the potential to decrease the time taken during cancer treatment and reduce the imaging dose required. With the imaging being acquired during the treatment, and the analysis being automated, there is potential for improved throughput. The SPARK trial will be conducted under the auspices of the Trans-Tasman Radiation Oncology Group (TROG).Trial registrationThis trial was registered on ClinicalTrials.gov on 09 March 2015. The identifier is: NCT02397317

Comparison of Image-guided Radiotherapy Technologies for Prostate Cancer

Radiation oncology has seen a rapid increase in the use of image-guided radiotherapy technology (IGRT) for prostate cancer patients over the past decade. The increase in the use of IGRT is largely driven by the fact that these technologies have been approved by the Food and Drug Administration and are now readily reimbursed by many insurance companies. Prostate cancer patients undergoing intensity modulated radiotherapy (IMRT) now have access to a wide variety of IGRTs that can cost anywhere from $500,000 or more in upfront costs, and can add anywhere from 10 to 15 thousand dollars to a course of IMRT. Some of the IGRT options include daily cone beam computed tomography, ultrasound, orthogonal x-ray units using implanted fiducial markers, implanted radiofrequency markers with the ability to localize and track prostate motion during radiotherapy (Calypso 4D), and cine magnetic resonance imaging. Although these technologies add to the cost of IMRT, there is little direct comparative effectiveness data to help patients, physicians, and policy makers decide if one technology is better than another. In our critical review, the first of its kind, we summarize the advantages, disadvantages, and the limitations of each technology. We also provide an overview of existing literature as it pertains to the comparison of existing IGRTs. Lastly, we provide insights about the need for future outcomes research that may have a significant impact on health policies as it comes to reimbursement in the modern era.

Constructing a clinical decision-making framework for image-guided radiotherapy using a Bayesian Network

A decision-making framework for image-guided radiotherapy (IGRT) is being developed using a Bayesian Network (BN) to graphically describe, and probabilistically quantify, the many interacting factors that are involved in this complex clinical process. Outputs of the BN will provide decision-support for radiation therapists to assist them to make correct inferences relating to the likelihood of treatment delivery accuracy for a given image-guided set-up correction. The framework is being developed as a dynamic object-oriented BN, allowing for complex modelling with specific subregions, as well as representation of the sequential decision-making and belief updating associated with IGRT. A prototype graphic structure for the BN was developed by analysing IGRT practices at a local radiotherapy department and incorporating results obtained from a literature review. Clinical stakeholders reviewed the BN to validate its structure. The BN consists of a sub-network for evaluating the accuracy of IGRT practices and technology. The directed acyclic graph (DAG) contains nodes and directional arcs representing the causal relationship between the many interacting factors such as tumour site and its associated critical organs, technology and technique, and inter-user variability. The BN was extended to support on-line and off-line decision-making with respect to treatment plan compliance. Following conceptualisation of the framework, the BN will be quantified. It is anticipated that the finalised decision-making framework will provide a foundation to develop better decision-support strategies and automated correction algorithms for IGRT.

Results of a Prospective Phase I Pilot Study Comparing Three Different Image Guided Radiotherapy Technologies for Prostate Localization

Results of a Prospective Phase I Pilot Study Comparing Three Different Image Guided Radiotherapy Technologies for Prostate Localization

KV Cone-Beam CT-Based IGRT

Delivery of high radiation doses while simultaneously sparing organs at risk requires advanced imaging for target volume definition, highly conformal dose distributions of intensity modulated radiotherapy (IMRT), and narrow planning target volume (PTV) margins. Three-dimensional image-guided radiotherapy (IGRT) with cone-beam computer tomography (CBCT), which results in more precise target localization, is quickly replacing two-dimensional (2D) IGRT. An overview on the clinical applications of kilovoltage gantry-mounted CBCT systems with emphasis on the most frequently targeted body sites (prostate, lung, head and neck) is provided based on a review of the relevant literature. Alternative imaging methods and their advantages/disadvantages are discussed. IGRT with soft tissue detection improves set-up accuracy and is currently replacing 2D verification and frame-based stereotactic treatments; safety margins are significantly reduced by this IGRT technology. In addition, systematic changes of tumor volume and shape and of the normal tissue can be monitored allowing for adaptation of radiotherapy. IGRT in combination with conformal treatment planning allows for hypofractionated dose escalation, which results in improved rates of local tumor control with low rates of toxicity. CBCT allows for daily pretreatment position verification and online correction of set-up errors which improves the precision of patient repositioning with the possibility of shrinking safety margins, sparing organs at risk, and escalating radiation doses. A trend for better clinical outcome can be observed.

Four-dimensional targeting error analysis in image-guided radiotherapy

Image-guided therapy (IGT) involves acquisition and processing of biomedical images to actively guide medical interventions. The proliferation of IGT technologies has been particularly significant in image-guided radiotherapy (IGRT), as a way to increase the tumor targeting accuracy. When IGRT is applied to moving tumors, image guidance becomes challenging, as motion leads to increased uncertainty. Different strategies may be applied to mitigate the effects of motion: each technique is related to a different technological effort and complexity in treatment planning and delivery. The objective comparison of different motion mitigation strategies can be achieved by quantifying the residual uncertainties in tumor targeting, to be detected by means of IGRT technologies. Such quantification requires an extension of targeting error theory to a 4D space, where the 3D tumor trajectory as a function of time measured (4D Targeting Error, 4DTE). Accurate 4DTE analysis can be represented by a motion probability density function, describing the statistical fluctuations of tumor trajectory. We illustrate the application of 4DTE analysis through examples, including weekly variations in tumor trajectory as detected by 4DCT, respiratory gating via external surrogates and real-time tumor tracking.

SU‐FF‐J‐17: Image‐Guided Radiotherapy Using Nanotube Stantionary Tomosynthesis Technology

Purpose: To develop image guidance approaches for clinical application of Nanotube Stationary Tomosynthesis (NST), a nanotechnology‐based online image‐guided radiotherapy (IGRT) technology that is capable of unprecedented temporal‐resolution and imaging speed. Method and Materials: NST is an accelerator gantry‐mounted multi‐source array kV imaging technology under development by Siemens. Using a single image panel, the patient can be imaged by 50 x‐ray sources on the array in the treatment volume within ∼ 2 sec before and even during treatment. However, translating the NST's imaging acquisition strengths into real clinical benefits requires significant software development including new image registration tools that take full advantage of the real‐time aspects of tomosynthesis imaging while minimizing its intrinsic resolution limitation. We propose a fast, versatile image registration approach that: integrates information from the large field‐of‐view projection images, the high‐temporal resolution tomosynthesis images, and the high spatial‐resolution planning 3D CT image; has tradeoffs to balance the user's needs of quality vs. speed; and potentially extracts a daily image deformation from NST tomosynthesis image for soft tissue based IGRT and treatment course dose accumulation. Results: We have developed the initial image registration approaches for clinical testing of the first protocol type NST IGRT system. In this presentation we will describe the proposed NST IGRT image registration approaches in lung and prostate treatments and discuss imaging dose and imaging dose reduction approaches. Other aspects of the NST technology including system design, NST reconstruction, image registration, and imaging geometry may be presented separately in the meeting. Conclusion: We have demonstrated that Nanotube Stationary Tomosynthesis technology has the potential to offer temporal resolution and imaging speed ‐ important features that have not been adequately addressed by the existing IGRT technology today.Conflict of Interest: This work is partially funded by a grant from Siemens Oncology Care System.

Optimization of couch translational corrections to compensate for rotational and deformable target deviations in image guided radiotherapy

The utilization of image-guided radiotherapy (IGRT) technologies helps correct temporal and spatial deviations of the target volume relative to planned radiation beams. With the aid of these IGRT technologies, it becomes possible to better identify the target volume before and even during radiation treatment. However, since components of the detected deviations may be translational, rotational, and deformable, the question remains whether simple treatment-couch translational movement can be optimized to compensate for these complicated deviations. Deviation of the target volume and changes in patient body shape from that acquired for treatment planning may further add to the variations from planned dose distribution. In this study, an optimization strategy is developed to investigate these issues. The optimization process involved the use of the hill climbing algorithm, the detected target volume and patient body shape, and the dose distribution based on acquired images at treatment. During the process, the planned dose distribution was iteratively adjusted to reflect the changes of depth and distance as the translational treatment couch movement was being optimized. The optimal treatment couch movement was considered achieved when the highest fraction of the detected target volume was covered by prescription dose. This optimization strategy was evaluated on clinical prostate cancer cases. For each of the cases, cone beam computed tomography (CBCT) images were acquired right after fiducial marker-based kilovolt orthogonal imaging verification and setup adjustment. Based on the CBCT images, the clinical target volume at the treatment was delineated and the translational treatment-couch movements were optimized with the developed strategy. The resultant dose coverage was compared to that without the optimization. The results showed that with the present strategy, rotational and deformable target deviations can be further compensated with translational couch correction.

WE-A-350-01: IMRT in the Treatment of Gynecological Malignancies

IMRT presented a major advancement in the radiotherapeutic management of gynecologic cancer. It has been shown that IMRT has reduced the incidence and severity of radiation‐related toxicity in this disease site. However, the precise dose distribution produced by IMRT is less forgiving and great care is required in order to achieve the intended results. An adequate understanding of the entire process ‐from proper patient selection to positioning/immobilization to treatment planning and delivery‐ is essential. The primary goal of this presentation is to provide a practical overview of IMRT for gynecological malignancies. A discussion of the steps in the GYN IMRT process will include patient selection, immobilization, simulation, structure delineation, planning strategies and parameters, PTV and critical organdose objectives, plan evaluation, QA, and potential delivery issues. Guidelines and practical examples of the GYN IMRT process will be presented. At our institution, gynecologic patients are treated in the supine position with customized immobilization devices (alpha cradles), which are indexed to the treatment table. Oral, intravenous and rectal contrasts are used to aid in the delineation of the CTV and surrounding normal tissues. The CTV consists of the contrast enhanced vessels to identify common, external, and internal nodal regions along with the upper half of the vagina, parametrial tissues, presacral region and uterus (if present). A PTV is added to the CTV based on measured set‐up uncertainties and organ motion data. Several recent studies have addressed these issues and will be reviewed here. For treatment planning, 9 equally spaced co‐planar beams are generally used. Input parameters derived for treatment planning were developed over time, and their evolution will be discussed. Treatment plans are evaluated primarily based on the PTV coverage and normal tissue DVHs. Evaluation of small bowel is based on a normal tissue complication probability (NTCP) curve for the incidence of acute gastrointestinal toxicity of IMRT patients treated in our clinic. From this analysis, acceptable plans are those in which <200 cc of the small bowel region receives 45 Gy (prescription dose). We have also recently defined bone marrow constraints for patients receiving concomitant chemotherapy, and these will be discussed. Finally, current research and future directions for GYN IMRT will be introduced. For instance, image‐guided radiotherapy (IGRT) has received increasing attention as a component of IMRT planning and delivery. We will discuss the potential role of novel image‐guidance techniques in GYN IMRT. In addition, we will present IGRT/IMRT techniques that are currently being considered to provide an alternative or supplement to brachytherapy. Clinical examples of each of these approaches will be presented. Educational Objectives: 1. To provide an educational review of the practical aspects of IMRT planning for gynecologic malignancies. 2. To understand and review the criteria for IMRT plan evaluation in gynecologic patients. 3. To review the planning methods used to achieve plan acceptance criteria. 4. To discuss the role of IGRT technologies in this disease site.

A strategy to objectively evaluate the necessity of correcting detected target deviations in image guided radiotherapy

Image guided radiotherapy technologies are being increasingly utilized in the treatment of various cancers. These technologies have enhanced the ability to detect temporal and spatial deviations of the target volume relative to planned radiation beams. Correcting these detected deviations may, in principle, improve the accuracy of dose delivery to the target. However, in many situations, a clinical decision has to be made as to whether it is necessary to correct some of the deviations since the relevant dosimetric impact may or may not be significant, and the corresponding corrective action may be either impractical or time consuming. Ideally this decision should be based on objective and reproducible criteria rather than subjective judgment. In this study, a strategy is proposed for the objective evaluation of the necessity of deviation correction during the treatment verification process. At the treatment stage, without any alteration from the planned beams, the treatment beams should provide the desired dose coverage to the geometric volume identical to the planning target volume (PTV). Given this fact, the planned dose distribution and PTV geometry were used to compute the dose coverage and PTV enclosure of the clinical target volume (CTV) that was detected from imaging during the treatment setup verification. The spatial differences between the detected CTV and the planning CTV are essentially the target deviations. The extent of the PTV enclosure of the detected CTV as well as its dose coverage were used as criteria to evaluate the necessity of correcting any of the target deviations. This strategy, in principle, should be applicable to any type of target deviations, including both target deformable and positional changes and should be independent of how the deviations are detected. The proposed strategy was used on two clinical prostate cancer cases. In both cases, gold markers were implanted inside the prostate for the purpose of treatment setup verification and were used to determine potential target deviations. To derive the detected CTV geometry from the planning CTV based on the locations of the gold markers, the CTV was approximated with an elastic semirigid body model. The derived CTV geometry and shape were confirmed with CBCT imaging. The evaluation results and the related mathematical equations and computational algorithm are presented. It is concluded that the proposed strategy is potentially useful in establishing objective criteria for the necessity of correction of the target deviations.

SU-FF-J-106: Comparison of Image Guided Radiotherapy Technologies: Tomotherapy, Varian Trilogy and Elekta Synergy

Purpose: Three different Image Guided Radiotherapy(IGRT) delivery systems were evaluated for CTDose Index (CTDI),image quality and accuracy of CT number with electron density. Methods & Materials: a) We evaluated the CTDI using the CIRS CTdose phantom. b) We investigated the relationship of CT number of the Cone Beam/MVCT scans with the electron density using COM‐TOM CT phantom. c) We investigated the image quality by using Catphan 500 phantom. Results: The CTDI for Elekta ranged from of a maximum 3.42 cGy for prostate to 0.2 cGy for Head & Neck treatment. For the Varian, CTDIdose was a function of the bow‐tie filter used and ranged from 4.15 cGy for body phantom to 8.3 cGy in the head phantom. For the tomotherapy system the CTDI is a function of the pitch and ranged from a maximum of 1.76 cGy in the body phantom to 2.47 cGy in the Head Phantom. The CT number to electron density were similar and linear for the Tomotherapy and conventional multislice CT scanners. For the Elekta and Varian the CT number from the cone beam CT were not linear and there is a variation of CT number because of changes in X‐ray scatter from the cone beam geometry. We report quantitatively low contrast resolution, high contrast resolution, noise and uniformity. Conclusion: There is large variation in imagingdose between the IGRT delivery systems. The CT number to ED was linear for tomotherapy system and as such can be used for dose recomputation. For the Elekta and Varian one has to characterize the non linearities carefully before attempting to use the cone beam CT data for dose recomputation. All three delivery systems provide sufficient contrast resolution for soft tissue visualization.