Imaging For Treatment Verification Research Articles

AAPM task group report 302: Surface-guided radiotherapy.

The clinical use of surface imaging has increased dramatically, with demonstrated utility for initial patient positioning, real‐time motion monitoring, and beam gating in a variety of anatomical sites. The Therapy Physics Subcommittee and the Imaging for Treatment Verification Working Group of the American Association of Physicists in Medicine commissioned Task Group 302 to review the current clinical uses of surface imaging and emerging clinical applications. The specific charge of this task group was to provide technical guidelines for clinical indications of use for general positioning, breast deep‐inspiration breath hold treatment, and frameless stereotactic radiosurgery. Additionally, the task group was charged with providing commissioning and on‐going quality assurance (QA) requirements for surface‐guided radiation therapy (SGRT) as part of a comprehensive QA program including risk assessment. Workflow considerations for other anatomic sites and for computed tomography simulation, including motion management, are also discussed. Finally, developing clinical applications, such as stereotactic body radiotherapy (SBRT) or proton radiotherapy, are presented. The recommendations made in this report, which are summarized at the end of the report, are applicable to all video‐based SGRT systems available at the time of writing.

International recommendations for personalised selective internal radiation therapy of primary and metastatic liver diseases with yttrium-90 resin microspheres

PurposeA multidisciplinary expert panel convened to formulate state-of-the-art recommendations for optimisation of selective internal radiation therapy (SIRT) with yttrium-90 (90Y)-resin microspheres.MethodsA steering committee of 23 international experts representing all participating specialties formulated recommendations for SIRT with 90Y-resin microspheres activity prescription and post-treatment dosimetry, based on literature searches and the responses to a 61-question survey that was completed by 43 leading experts (including the steering committee members). The survey was validated by the steering committee and completed anonymously. In a face-to-face meeting, the results of the survey were presented and discussed. Recommendations were derived and level of agreement defined (strong agreement ≥ 80%, moderate agreement 50%–79%, no agreement ≤ 49%).ResultsForty-seven recommendations were established, including guidance such as a multidisciplinary team should define treatment strategy and therapeutic intent (strong agreement); 3D imaging with CT and an angiography with cone-beam-CT, if available, and 99mTc-MAA SPECT/CT are recommended for extrahepatic/intrahepatic deposition assessment, treatment field definition and calculation of the 90Y-resin microspheres activity needed (moderate/strong agreement). A personalised approach, using dosimetry (partition model and/or voxel-based) is recommended for activity prescription, when either whole liver or selective, non-ablative or ablative SIRT is planned (strong agreement). A mean absorbed dose to non-tumoural liver of 40 Gy or less is considered safe (strong agreement). A minimum mean target-absorbed dose to tumour of 100–120 Gy is recommended for hepatocellular carcinoma, liver metastatic colorectal cancer and cholangiocarcinoma (moderate/strong agreement). Post-SIRT imaging for treatment verification with 90Y-PET/CT is recommended (strong agreement). Post-SIRT dosimetry is also recommended (strong agreement).ConclusionPractitioners are encouraged to work towards adoption of these recommendations.

Interfraction movement and clinical outcome of immobilization for thoracic irradiation: A randomized controlled trial

AbstractObjectiveTo evaluate the impact of immobilization on set‐up errors and clinical outcomes in patients receiving radiation therapy to the thorax.MethodsPatients receiving curative intent radiation therapy to the lung and esophagus were randomized to no immobilization (control) or immobilization (chest jig or vacuum bag), and treatment verification images were acquired within 3 days of commencing treatment and then weekly. The primary outcome was the proportion of patients having a deviation >5 mm from the isocenter. Assessment was carried out blinded to immobilization assignment.ResultsOf the 77 patients, 75 patients were allocated to either immobilization or control. No statistical difference in the proportion of patients with bony displacements >5 mm from the isocenter were observed (P = 0.5), as was the case for both systematic and random errors between the groups. There was an increased risk of local failure in the immobilized control group (HR 1.46, 95% CI 0.78–2.71, P = 0.23) based on a competing risk analysis. The median overall survival was 18.4 months and 27.0 months in the control and immobilized groups, respectively (HR 0.73, 95% CI 0.51–1.04, P = 0.08).ConclusionsThe results failed to show benefit with immobilization in reducing set‐up errors, local control, and overall survival.

Patterns of Practice in Canadian Radiation Treatment Centres: Results of a National Survey

PurposeRadiation therapy has changed rapidly over the past decade due to the application of technological advances. A survey was conducted of radiation treatment centres in Canada to establish current patterns of practice across the country. Areas of inquiry included treatment techniques and image verification, as well as roles and responsibilities of radiation therapists (RTs). Methods and MaterialsIn January 2016, a survey was sent to managers of the 46 radiation treatment centres in Canada. This survey sought information on a range of staffing and practice variables for the fiscal year 2014/2015. ResultsOf the 46 centres contacted, 37 centres responded, representing an 80.4% response rate. Survey results showed that the use of volumetric arc therapy and intensity-modulated radiation therapy is common across Canada for several anatomic sites, as well as the use of daily pretreatment image verification. A high degree of variability exists for imaging modality (two dimensional vs. three dimensional) for some sites, including brain, head and neck, and lung. RTs' responsibilities have expanded uniformly across the country, with RTs involved in organ-at-risk contouring and on-treatment image approval at the majority of centres. Despite this role expansion, specialty roles in areas of quality and applications expertise are still rare. ConclusionsRadiation therapy in Canada has transitioned to high-technology treatment techniques with relative consistency across the country. There is, however, variation in the imaging modality used for daily verification. Canada may benefit from consensus guidelines on the application of three-dimensional imaging for treatment verification. While RTs have expanded their responsibilities, role definition for RTs working in supervisory or supporting positions has not kept pace at many centres and it is unclear if RTs are supported in their expanded accountabilities.

Accuracy Comparison of 4D Computed Tomography (4DCT) and 4D Cone Beam Computed Tomography (4DCBCT)

The ability of respiratory-correlated fan beam CT (4DCT) and respiratory-correlated cone beam CT (4DCBCT) to accurately estimate tumor volume is critical to accurate dosimetry and treatment verification for lung stereotactic body radiation therapy (SBRT) and other motion-managed therapies. However, it is known that 4DCT and 4DCBCT differ in aspects of image acquisition and reconstruction that may lead to discrepancies between the two modalities. To evaluate quantitative differences between 4DCT and 4DCBCT imaging under respiratory motion, we performed a phantom study in the ground truth setting. A programmable respiratory motion phantom was used to simulate the 1D S-I position of a known-size lesion. Ten sinusoidal and twenty patient-specific breathing waveforms were applied to drive lesion motion during the 4DCT and 4DCBCT acquisitions. The difference in lesion volume acquired between the two imaging modalities was as high as 34.4% and 18.4% for sinusoidal and patient-specific breathing motions, respectively. When compared to the true volume, 4DCT measurement often underestimated the lesion size whereas 4DCBCT overestimated the lesion volume in most of the cases. 4DCBCT gave more accurate recovery of the volume than 4DCT for most settings tested in this study. These findings may be helpful for improving the definition of internal target and planning target volume margins, and extracting quantitative information from on-board treatment verification imaging.

SU‐C‐209‐02: 3D Fluoroscopic Image Generation From Patient‐Specific 4DCBCT‐Based Motion Models Derived From Clinical Patient Images

Purpose:We develop a method to generate time varying volumetric images (3D fluoroscopic images) using patient‐specific motion models derived from four‐dimensional cone‐beam CT (4DCBCT).Methods:Motion models are derived by selecting one 4DCBCT phase as a reference image, and registering the remaining images to it. Principal component analysis (PCA) is performed on the resultant displacement vector fields (DVFs) to create a reduced set of PCA eigenvectors that capture the majority of respiratory motion. 3D fluoroscopic images are generated by optimizing the weights of the PCA eigenvectors iteratively through comparison of measured cone‐beam projections and simulated projections generated from the motion model. This method was applied to images from five lung‐cancer patients. The spatial accuracy of this method is evaluated by comparing landmark positions in the 3D fluoroscopic images to manually defined ground truth positions in the patient cone‐beam projections.Results:4DCBCT motion models were shown to accurately generate 3D fluoroscopic images when the patient cone‐beam projections contained clearly visible structures moving with respiration (e.g., the diaphragm). When no moving anatomical structure was clearly visible in the projections, the 3D fluoroscopic images generated did not capture breathing deformations, and reverted to the reference image. For the subset of 3D fluoroscopic images generated from projections with visibly moving anatomy, the average tumor localization error and the 95th percentile were 1.6 mm and 3.1 mm respectively.Conclusion:This study showed that 4DCBCT‐based 3D fluoroscopic images can accurately capture respiratory deformations in a patient dataset, so long as the cone‐beam projections used contain visible structures that move with respiration. For clinical implementation of 3D fluoroscopic imaging for treatment verification, an imaging field of view (FOV) that contains visible structures moving with respiration should be selected. If no other appropriate structures are visible, the images should include the diaphragm.This project was supported, in part, through a Master Research Agreement with Varian Medical Systems, Inc, Palo Alto, CA.

SU‐F‐J‐116: Clinical Experience‐Based Verification and Improvement of a 4DCT Program

Purpose:To demonstrate the role of continuous improvement fulfilled by the Medical Physicist in clinical 4DCT and CBCT scanning.Methods:Lung (SABR and Standard) patients’ 4D respiratory motion and image data were reviewed over a 3, 6 and 12 month period following commissioning testing. By identifying trends of clinically relevant parameters and respiratory motions, variables were tested with a programmable motion phantom and assessed. Patient traces were imported to a motion phantom and 4DCT and CBCT imaging were performed. Cos6 surrogate and sup‐inf motion was also programmed into the phantom to simulate the long exhale of patients for image contrast tests.Results:Patient surrogate motion amplitudes were 9.9+5.2mm (3–35) at 18+6bpm (6–30). Expiration/Inspiration time ratios of 1.4+0.5second (0.6–2.9) showed image contrast effects evident in the AveCT and 3DCBCT images. Small differences were found for patients with multiple 4DCT data sets. Patient motion assessments were simulated and verified with the phantom within 2mm. Initial image reviews to check for reconstructed artefacts and data loss identified a small number of patients with irregularities in the automatic placement of inspiration and expiration points.Conclusion:The Physicist's involvement in the continuous improvements of a clinically commissioned technique, processes and workflows continues beyond the commissioning stage of a project. Our experience with our clinical 4DCT program shows that Physics presence is required at the clinical 4DCT scan to assist with technical aspects of the scan and also for clinical image quality assessment prior to voluming. The results of this work enabled the sharing of information from the Medical Physics group with the Radiation Oncologists and Radiation Therapists. This results in an improved awareness of clinical patient respiration variables and how they may affect 4D simulation images and also may also affect the treatment verification images.

An imaging evaluation of the simultaneously integrated boost breast radiotherapy technique.

IntroductionTo evaluate in-field megavoltage (MV) imaging of simultaneously integrated boost (SIB) breast fields to determine its feasibility in treatment verification for the SIB breast radiotherapy technique, and to assess whether the current-imaging protocol and treatment margins are sufficient.MethodsFor nine patients undergoing SIB breast radiotherapy, in-field MV images of the SIB fields were acquired on days that regular treatment verification imaging was performed. The in-field images were matched offline according to the scar wire on digitally reconstructed radiographs. The offline image correction results were then applied to a margin recipe formula to calculate safe margins that account for random and systematic uncertainties in the position of the boost volume when an offline correction protocol has been applied.ResultsAfter offline assessment of the acquired images, 96% were within the tolerance set in the current department-imaging protocol. Retrospectively performing the maximum position deviations on the Eclipse™ treatment planning system demonstrated that the clinical target volume (CTV) boost received a minimum dose difference of 0.4% and a maximum dose difference of 1.4% less than planned. Furthermore, applying our results to the Van Herk margin formula to ensure that 90% of patients receive 95% of the prescribed dose, the calculated CTV margins were comparable to the current departmental procedure used.ConclusionBased on the in-field boost images acquired and the feasible application of these results to the margin formula the current CTV-planning target volume margins used are appropriate for the accurate treatment of the SIB boost volume without additional imaging.

ALARA and paediatric imaging in radiation therapy: A survey of Canadian paediatric imaging practice

PurposeThere is little discussion in the literature regarding paediatric imaging dose reduction with respect to conventional imaging carried out in radiotherapy departments. This is in contrast to diagnostic radiography where dose optimization when imaging children is a very current topic. For this reason Canadian radiotherapy clinics were surveyed to look at paediatric imaging practice, knowledge and perspectives with respect to imaging dose reduction. MethodAs this was an exploratory study, a questionnaire was developed and sent to radiation therapy clinics across Canada, via email, to assess knowledge of paediatric imaging and dose reduction initiatives. The questionnaire focus was CT simulation and treatment verification imaging of children. ResultsPractice and knowledge of paediatric imaging varied across Canada. Forty percent of clinics reported using paediatric specific protocols for CT simulation and 20% of clinics reported using paediatric specific protocols for treatment verification imaging. There was variation in imaging practices among the clinics that reported treating the most children. The survey results show that while some measures are being taken to reduce paediatric imaging dose in radiation therapy, 46.7% of the respondents felt more could be done. ConclusionThe survey demonstrates interest in dose reduction in radiation therapy imaging as well as differences in current practice and knowledge across Canada. Paediatric imaging dose reduction would appear to be an area of practice that would benefit from more study and development of standards of practice.

Systematic measurements of whole‐body imaging dose distributions in image‐guided radiation therapy

The full benefit of the increased precision of contemporary treatment techniques can only be exploited if the accuracy of the patient positioning is guaranteed. Therefore, more and more imaging modalities are used in the process of the patient setup in clinical routine of radiation therapy. The improved accuracy in patient positioning, however, results in additional dose contributions to the integral patient dose. To quantify this, absorbed dose measurements from typical imaging procedures involved in an image-guided radiation therapy treatment were measured in an anthropomorphic phantom for a complete course of treatment. The experimental setup, including the measurement positions in the phantom, was exactly the same as in a preceding study of radiotherapy stray dose measurements. This allows a direct combination of imaging dose distributions with the therapy dose distribution. Individually calibrated thermoluminescent dosimeters were used to measure absorbed dose in an anthropomorphic phantom at 184 locations. The dose distributions from imaging devices used with treatment machines from the manufacturers Accuray, Elekta, Siemens, and Varian and from computed tomography scanners from GE Healthcare were determined and the resulting effective dose was calculated. The list of investigated imaging techniques consisted of cone beam computed tomography (kilo- and megavoltage), megavoltage fan beam computed tomography, kilo- and megavoltage planar imaging, planning computed tomography with and without gating methods and planar scout views. A conventional 3D planning CT resulted in an effective dose additional to the treatment stray dose of less than 1 mSv outside of the treated volume, whereas a 4D planning CT resulted in a 10 times larger dose. For a daily setup of the patient with two planar kilovoltage images or with a fan beam CT at the TomoTherapy unit, an additional effective dose outside of the treated volume of less than 0.4 mSv and 1.4 mSv was measured, respectively. Using kilovoltage or megavoltage radiation to obtain cone beam computed tomography scans led to an additional dose of 8-46 mSv. For treatment verification images performed once per week using double exposure technique, an additional effective dose of up to 18 mSv was measured. Daily setup imaging using kilovoltage planar images or TomoTherapy megavoltage fan beam CT imaging can be used as a standard procedure in clinical routine. Daily kilovoltage and megavoltage cone beam computed tomography setup imaging should be applied on an individual or indication based protocol. Depending on the imaging scheme applied, image-guided radiation therapy can be administered without increasing the dose outside of the treated volume compared to therapies without image guidance.

Cone beam CT verification for oesophageal cancer – impact of volume selected for image registration

Purpose. Oesophageal cancers are difficult to visualise on volumetric imaging and reliable surrogate are needed for accurate tumour registration. The aim of this investigation is to evaluate the effect of a user defined volume with automated registration techniques using commercially available software with the on-board volumetric imaging for treatment verification of oesophageal cancer and determine the optimum location of this volume. Material and methods. In 20 patients four ‘clipbox’(C) volumes were defined: C-planning target volume (PTV), C-carina, C-vertebrae, C-thorax. The set-up corrections (translational and rotational) for C-PTV were compared to the corrections using C-carina, C-vertebrae and C-thorax. Results. Six hundred and eight registrations were performed. The best concordance in set-up corrections was found in the superior/inferior direction between C-PTV and C-carina (76%). In the right/left and anterior/posterior direction, better agreement was found between C-PTV and C-thorax with 80% and 76% agreement, respectively. Automatic ‘bone’ registration using C-vertebrae failed in 28% of scans. The correlation ratio between C-PTV and C-carina (n = 4) for mid-oesophageal tumours was 0.88, 0.79, and 0.95 in the right/left, superior/inferior and anterior/posterior directions, respectively. Conclusion. The defined volume for matching is important for oesophageal tumours. The alignment ‘clipbox’ and registration method selected can affect the displacements obtained. This may best be determined by tumour location and highlights the need to diversify protocols within one tumour treatment site. Further analysis is required to validate carina as a tumour surrogate for mid-oesophageal tumours.

Successful Implementation of Image-Guided Radiation Therapy Quality Assurance in the Trans Tasman Radiation Oncology Group 08.01 PROFIT Study

The quality assurance (QA) of image-guided radiation therapy (IGRT) within clinical trials is in its infancy, but its importance will continue to grow as IGRT becomes the standard of care. The purpose of this study was to demonstrate the feasibility of IGRT QA as part of the credentialing process for a clinical trial. As part of the accreditation process for a randomized trial in prostate cancer hypofraction, IGRT benchmarking across multiple sites was incorporated. Each participating site underwent IGRT credentialing via a site visit. In all centers, intraprostatic fiducials were used. A real-time assessment of analysis of IGRT was performed using Varian's Offline Review image analysis package. Two-dimensional (2D) kV and MV electronic portal imaging prostate patient datasets were used, consisting of 39 treatment verification images for 2D/2D comparison with the digitally reconstructed radiograph derived from the planning scan. The influence of differing sites, image modality, and observer experience on IGRT was then assessed. Statistical analysis of the mean mismatch errors showed that IGRT analysis was performed uniformly regardless of institution, therapist seniority, or imaging modality across the three orthogonal planes. The IGRT component of clinical trials that include sophisticated planning and treatment protocols must undergo stringent QA. The IGRT technique of intraprostatic fiducials has been shown in the context of this trial to be undertaken in a uniform manner across Australia. Extending this concept to many sites with different equipment and IGRT experience will require a robust remote credentialing process.

Radiation therapy treatment verification imaging in Australia and New Zealand

An original questionnaire was used to investigate the available types of reference and treatment image verification equipment and specific practices related to image analysis. A section on treatment site-specific imaging was included. The questionnaire was distributed to all radiation oncology facilities in Australia and New Zealand. A response rate of 87% (40/46) was achieved. Most facilities (90%) in Australia and New Zealand reported the availability of electronic portal imaging devices. Use of computer software to assist with image interpretation was indicated by 92% of centres. Frequency of image acquisition and tolerance levels used for radical treatment sites were variable, but palliative treatment site protocols were more consistent between treatment facilities. In conclusion, departments should strive to use evidence-based protocols and guidelines to ensure acceptable accuracy in treatment delivery.

PET imaging for treatment verification of ion therapy: Implementation and experience at GSI Darmstadt and MGH Boston

Ion beams offer the possibility of improved conformation of the dose delivered to the tumor with better sparing of surrounding tissue and critical structures in comparison to conventional photon and electron external radiation treatment modalities. Full clinical exploitation of this advantage can benefit from in vivo confirmation of the actual beam delivery and, in particular, of the ion range in the patient. During irradiation, positron emitters like 15O (half-life T 1/2≈2 min) and 11C ( T 1/2≈20 min) are formed in nuclear interactions between the ions and the tissue. Detection of this transient radioactivity via positron emission tomography (PET) and comparison with the expectation based on the prescribed beam application may serve as an in vivo, non-invasive range validation method of the whole treatment planning and delivery chain. For technical implementation, PET imaging during irradiation (in-beam) requires the development of customized, limited angle detectors with data acquisition synchronized with the beam delivery. Alternatively, commercial PET or PET/CT scanners in close proximity to the treatment site enable detection of the residual activation from long-lived emitters shortly after treatment (offline). This paper reviews two clinical examples using a dedicated in-beam PET scanner for verification of carbon ion therapy at GSI Darmstadt, Germany, as well as a commercial offline PET/CT tomograph for post-radiation imaging of proton treatments at Massachusetts General Hospital, Boston, USA. Challenges as well as pros and cons of the two imaging approaches in dependence of the different ion type and beam delivery system are discussed.

SU-FF-J-16: A Method to Determine the Necessity of Rotational Correction in Image Guided Radiotherapy

Introduction:IGRT technologies have enhanced the abilities to detect temporal and spatial deviations of target relative to beams. Correcting these deviations may improve the accuracy of dose delivery to target. Frequently, a clinical decision has to be made on the necessity to correct some of the deviations since the relevant dosimetric impact may or may not be significant. The decision should be based on an objective criterion. This study developed a method to determine the necessity of rotational correction during treatment verification process. Method and Materials: At treatment stage, treated volume should be almost geometrically identical to that of the PTV while the goal is to treat the CTV. Various uncertainties may move the CTV outside of the treated volume leading to suboptimum coverage. In many cases, the CTV can be approximated as an elastic semi‐rigid body and its geometry in the treatment space can be derived by using translational and rotational matrices. These matrices can be determined with an image registration tool between plan and treatment verification images. A software package was developed to perform the transformation, and to evaluate whether the transformed CTV remains inside the treatment volume. With the method, the spatial deviation caused by target rotation is computed and the margin size between the PTV and CTV is used as criterion for the necessity of rotational correction. Results: The related equations and algorithm have been developed and was evaluated by applying to a clinical prostate cancer case. For this particular patient, there existed a 26 degree rotation around one axis. Without rotational correction 30% of the CTV would be located outside the treatment volume. Conclusions: A method has been developed to evaluate the necessity of rotational correction. It is potentially useful in IGRT where elastic semi‐rigid body model is a good approximation for target volumes.

SU‐FF‐T‐408: The IAEA Initiative to Standardize Nuclear Data for Heavy Charged‐Particle Radiotherapy

Purpose: Protons and heavy ions loose energy via atomic and nuclear interaction processes. When simulating charged‐particle beam characteristics, for example absorbed dose distributions or secondary particle fluences, accurate physics descriptions are required. Sophisticated computing techniques, e.g. Monte Carlo, are applied for high accuracy calculations. However, the availability of high‐quality cross‐section data for the simulation of heavy charged‐particle interactions is far from being satisfactory. For example, the intra‐nuclear cascade models that are employed for cross‐section calculations are strictly valid only at high energies (>200 MeV per nucleon). Data libraries of charged‐particle interactions are needed to validate the calculations using nuclear models and for direct use in calculations. Method and Materials: The new IAEA coordinated research project on heavy charged‐particle interaction data for radiotherapy comprises of a program to compile and evaluate charged‐particle nuclear data for therapeutic applications. Plan is to review data and parameterizations for protons and heavy ions. Sensitivity analysis for different applications will be done with different codes for representative examples. The outcome will be a recommendation of preferred universal parameterization for all applications. Further, the aim is to work with code developers of the Monte Carlo codes FLUKA, Geant4, MCNPX, and SHIELD‐HIT in order to implement reference models for use in charged‐particle therapy simulations. Results: This presentation will discuss the sensitivity of nuclear interaction data for various applications in heavy charged‐particle therapy. We will discuss the nuclear interaction component in patient dose calculations, neutron background estimations, absolute dosimetry, and PET imaging for treatment verification. Based on these examples we will outline the specific aims of the IAEA initiative. Conclusion: The IAEA initiative aims at standardizing the use of charged‐particle nuclear interaction data for Monte Carlo simulations in proton and heavy ion therapy in order to improve the accuracy and compatibility of dosimetric studies.

PET/CT imaging for treatment verification after proton therapy: A study with plastic phantoms and metallic implants

The feasibility of off-line positron emission tomography/computed tomography (PET/CT) for routine three dimensional in-vivo treatment verification of proton radiation therapy is currently under investigation at Massachusetts General Hospital in Boston. In preparation for clinical trials, phantom experiments were carried out to investigate the sensitivity and accuracy of the method depending on irradiation and imaging parameters. Furthermore, they addressed the feasibility of PET/CT as a robust verification tool in the presence of metallic implants. These produce x-ray CT artifacts and fluence perturbations which may compromise the accuracy of treatment planning algorithms. Spread-out Bragg peak proton fields were delivered to different phantoms consisting of polymethylmethacrylate (PMMA), PMMA stacked with lung and bone equivalent materials, and PMMA with titanium rods to mimic implants in patients. PET data were acquired in list mode starting within 20 min after irradiation at a commercial luthetium-oxyorthosilicate (LSO)-based PET/CT scanner. The amount and spatial distribution of the measured activity could be well reproduced by calculations based on the GEANT4 and FLUKA Monte Carlo codes. This phantom study supports the potential of millimeter accuracy for range monitoring and lateral field position verification even after low therapeutic dose exposures of 2 Gy, despite the delay between irradiation and imaging. It also indicates the value of PET for treatment verification in the presence of metallic implants, demonstrating a higher sensitivity to fluence perturbations in comparison to a commercial analytical treatment planning system. Finally, it addresses the suitability of LSO-based PET detectors for hadron therapy monitoring. This unconventional application of PET involves countrates which are orders of magnitude lower than in diagnostic tracer imaging, i.e., the signal of interest is comparable to the noise originating from the intrinsic radioactivity of the detector itself. In addition to PET alone, PET/CT imaging provides accurate information on the position of the imaged object and may assess possible anatomical changes during fractionated radiotherapy in clinical applications.

An observer study: comparison of computed radiography to electronic and film portal imaging

Introduction: Computed radiography (CR) is an imaging facility that does not require the use of hard copy film, digital images are obtained with a photostimulable phosphor plate, which replaces film, in a cassette. As the first UK radiotherapy site to trial CR, we are collecting data to assess the feasibility of using CR in radiotherapy treatment verification.Method: From 30 patients undergoing radical radiotherapy, 10 were consecutively accrued to three sites: pelvis, thorax and head and neck. Treatment verification images were taken using current protocols, but substituting standard imaging for CR images on one fraction. Four independent observers were used: two clinical oncologists and two therapy radiographers. Observers rated CR, electronic portal imaging (EPI) and enhanced contrast (EC) films of the three sites for both landmark visibility and ease of verification decision, using a numerical scoring system.Results: Ratings for visibility of landmarks and for verification decision were similar for CR and film/EPI images for most landmarks. However, CR images rated poorly compared to EC film in the head and neck region with landmarks such as thyroid cartilage and cricoid cartilage rating as ‘not clear’. CR images rated better than EPI images for both visibility and verification decision on the majority of landmarks in the pelvis region.Conclusion: Results gathered from a relatively small sample size have provided the following conclusion. The visibility of landmarks in CR images is comparable to that in film and EPI. Verification of treatment images based on CR is comparable to that of the current imaging media in the department.

TH‐E‐230A‐05: Development of An Integrated Software Platform for Treatment Documentation and Outcome Analysis for IGRT

Purpose: Information generated in IGRT is tremendous. The long‐term goal of this work is to develop a software package (named RAPID, Research Analysis Platform and IGRT Databases) that is capable of storing patient diagnostic, treatment and follow‐up data for IGRT, which documents treatment outcome, and allows dose‐response analysis based on biophysical models. Presented here are several key components of this development. Method and Materials: The RAPID consists of a database, software tools and auxiliary applications. The database, developed using FileMaker software, includes modules for storing demographics, diagnosis, treatment, and follow up data. Diagnostic and planning images of different modalities (e.g., CT, PET, MR, US) and treatment verification images (e.g., CT, US, radiography) can be stored in DICOM format. Using an integrated auxiliary application these images can be brought into the desktop. The database is integrated with another software package, CERR, developed at Washington University, allowing display of contours and dose distributions on planning images. Various software tools are developed to perform dose response analysis that is linked to documented treatment outcome. For example, treatment related toxicity definitions for a given anatomic site were incorporated into the database, allowing standardized documentation of toxicity which, in turn, facilitates dose‐response analysis. Calculations of EUD, TCP and NTCP are enabled based on 3D dose distributions. Results: The newly developed RAPID is found to be useful. Patient data collected in our clinic for two anatomic sites have been entered into the system. Analysis of treatment and follow‐up toxicity was effectively carried out using the RAPID. With a FileMaker server installed to host the database, users can access password‐protected information remotely.Conclusion: We have developed a software platform, RAPID, to facilitate storage and analysis of IGRT clinical outcome data.

TH‐C‐ValB‐05: Rapid Low‐Dose 3D Image‐Guided Treatment Verification of Sites Prone to Respiratory Motion Using Breath‐Hold On‐Board Digital Tomosynthesis (DTS)

Purpose: This study examines the potential use of on‐board digital tomosynthesis (DTS) for image‐guided treatment verification of sites prone to respiratory motion. DTS is a fast, low‐dose method for reconstructing 3‐ D images from 2‐D projection data, acquired with a limited scan angle. In the treatment room, a 45° DTS scan can be acquired in less than 10 seconds, making rapid breath‐hold DTS a simple method for acquiring 3‐D treatment verification images, devoid of respiratory motion. Method and Materials: On‐board DTS images of ten human liver, pancreas, and lung subjects were reconstructed from kV CBCT projection data, acquired on a Varian 21EX Clinac equipped with an on‐board imager (OBI), either during a breath‐hold or while subjects were freely breathing. Corresponding reference DTS (RDTS) images were reconstructed from breath‐hold planning CT data. Soft‐tissue visibility was compared between breath‐hold DTS and free‐breathing DTS and CBCT, to assess the potential efficacy of the breath‐hold DTS strategy for 4‐D image‐guided treatment verification. Results: Breath‐hold DTS markedly improved the rendering of soft‐tissue abdominal and thoracic anatomy, compared with free‐breathing DTS or CBCT. Organ structures were clearly defined, and even low‐contrast target malignancies were often visible in breath‐hold DTS reconstructions. Free‐breathing DTS and CBCT reconstructions, on the other hand, often exhibited artificially enlarged target volumes and poor visibility of soft‐tissue anatomy, due to motion averaging effects. Conclusion: Rapid breath‐hold DTS enhances the visibility of bony and soft‐tissue anatomy in sites prone to respiratory motion, facilitating daily localization of soft‐tissue targets. Breath‐hold DTS localization is superior to free‐breathing on‐board CBCT for thoracic and abdominal image‐guidance. Conflict of Interest: This research was supported in part by a grant from Varian Medical Systems.