IGRT

Background and purpose: This study explores methods to reduce dose due to kV-CBCT imaging for patients undergoing radiation therapy. Material and methods: Doses resulting from kV-CBCT scans were calculated using Monte Carlo techniques and were analyzed using dose-volume histograms. Patients were modeled as were CBCT acquisitions using both 360°and 200°gantry rotations. The effects of using the half fan bow-tie and the full fan bow-tie filters were examined. Results: Doses for OBI 1.3 are 15 times (head), 5 times (thorax) and 2 times (Pelvis) larger than the current OBI 1.4. When using 200°scans, the doses to eyes and cord are 0.2 (or 0.65) cGy and 0.35 (or 0.2) cGy when rotating the X-ray source underneath (or above) the patient, respectively. The 360°Pelvis scan dose is 1-2 cGy. The rectum dose is 1.1 (or 2.8) cGy when rotating the source above (or below) the patient with the 200°Pelvis scan. The dose increases up to two times as the patient size decreases. Conclusions: The dose can be minimized by reducing the scan length, the exposure settings, by selecting the gantry rotation angles, and by using the full fan bow-tie whenever possible.

Intensity-modulated radiation therapy (IMRT) is a revolutionary new paradigm that aims at improving the therapeutic ratio by increasing the dosegradient between target tissues and surrounding normal structures thereby offering probability of better loco-regional control with decreased risk of complications. IMRT is relatively intolerant to set-up uncertainties, warranting periodic image-guidance, making Image-Guided Radiation Therapy (IGRT) a natural corollary to IMRT. There are several challenges associated with the planning, delivery, and quality assurance of the IMRT and IGRT processes that must be addressed to realize the full potential of such exciting and promising technology. Given the complexities involved, it is quite intuitive to understand that IMRT and IGRT are resource-intensive, demanding increased labor, rigour, and expenses too. Other disadvantages associated with high-precision techniques include potentially increased risk of marginal failures, decreased dose homogeneity, and an increase in total body dose with increased risk of secondary carcinogenesis. The aim of this review is to define the role of IMRT and IGRT in contemporary head and neck oncologic practice through a critical appraisal of pertinent literature. Despite relatively short follow-up and limited clinical outcomes data, the weight of evidence suggests that loco-regional control is not inferior (either comparable or even better) and toxicity lesser with IMRT resulting in potentially improved quality-oflife, prompting the widespread adoption of such technology in community practice. Ongoing clinical trials in head and neck IMRT are currently addressing issues to optimize the IMRT process, adopting functional imaging for dose-painting, and incorporating adaptive re-planning strategies to further improve outcomes.

Radiation therapy has gone through a series of revolutions in the last few decades and it is now possible to produce highly conformal radiation dose distribution by using techniques such as intensity-modulated radiation therapy (IMRT). The improved dose conformity and steep dose gradients have necessitated enhanced patient localization and beam targeting techniques for radiotherapy treatments. Components affecting the reproducibility of target position during and between subsequent fractions of radiation therapy include the displacement of internal organs between fractions and internal organ motion within a fraction. Image-guided radiation therapy (IGRT) uses advanced imaging technology to better define the tumor target and is the key to reducing and ultimately eliminating the uncertainties. The purpose of this article is to summarize recent advancements in IGRT and discussed various practical issues related to the implementation of the new imaging techniques available to radiation ...

The purpose of this study is to establish a comprehensive set of dose measurements data obtained from the X-ray Volumetric Imager ͑XVI ® , Elekta Oncology Systems͒ and the On-Board Imager ͑OBI ® , Varian Medical Systems͒ cone-beam CT ͑CBCT͒ systems. To this end, two uniform-density cylindrical acrylic phantoms with diameters of 18 cm ͑head phantom͒ and 30 cm ͑body phantom͒ were used for all measurements. Both phantoms included ion chamber placement holes in the center and at periphery ͑2 cm below surface͒. For the XVI unit, the four standard manufacturer-supplied protocols were measured. For the OBI unit, the full bow tie and half bow tie ͑and no bow tie͒ filters were used in combination with the two scanning modes; namely, full-fan and half-fan. The total milliampereϫ seconds ͑mA s͒ setting was also varied for each protocol to establish the linear relationship between the dose deposited and the mA s used ͑with all other factors being held constant͒. Half-value layers in aluminum ͑Al͒ were also measured for beam characteristic determination. For the XVI unit, the average dose ranged from 0.1 to 3.5 cGy with the highest dose measured using the "prostate" protocol with the body phantom. For the OBI unit, the average dose ranged from 1.1 to 8.3 cGy with the highest dose measured using the full-fan protocol with the head phantom. The measured doses were highly linear as a function of mA s, for both units, where the measurement points followed a linear relationship very closely with R 2 Ͼ 0.99 for all cases. Halfvalue layers were between 4.6-and 7.0-mm-Al for the two CBCT units where XVI generally had more penetrating beams at the similar kVp settings. In conclusion, a comprehensive series of dose measurements were performed on the XVI and the OBI CBCT units. In the process, many of the important similarities and differences between the two systems were observed and summarized in this work.

Hintergrund: Der Arbeitsablauf (Workflow) in der Radiotherapie (RT) ist gegenwärtig durch neue Techniken und Behandlungsparadigmen wie intensitätsmodulierte Radiotherapie (IMRT) und zunehmende bildgestützte Radiotherapie (IGRT ["image-guided radiotherapy"]) im Umbruch. Daraus resultiert eine starke Zunahme von Daten verschiedener Datenklassen. Dies erfordert für die Steuerbarkeit einer Abteilung eine zunehmende patienten-und behandlungsserienzentrierte Integration verschiedener Systeme. Methodik: Der Workflow in einer RT-Abteilung ist multidimensional und multidirektional und umfasst mindestens fünf Datenklassen (RT-/Bestrahlungsdaten, patientenbezogene Dokumente wie z.B. Befunde und Arztbriefe, ärztliche Akteneinträge, Bilddaten im DICOM-Format [Digital Imaging and Communications in Medicine] sowie Non-DICOM-Bilddaten). Diese Daten müssen sequentiell, u.U. auch im Rahmen von adaptiven Feedbackschleifen in die Patientenhistorie eingebunden werden. Dieses Vorgehen kontrastiert stark mit einer diagnostischen Radiologieabteilung, in der im Wesentlichen DICOM-Bilddaten und Befunde erzeugt werden und im Zugriff bleiben. Diese Daten müssen nach Abschluss des Prozesses kaum noch manipuliert werden. Es handelt sich also um einen überwiegend unidirektionalen Prozess. Im Gegensatz zu dieser innerhalb der diagnostischen Radiologie etablierten Standardkombination aus Radiologie-Informationssystem (RIS) und Picture Archiving and Communication System (PACS) muss ein integriertes elektronisches Radio-Onkologie-Klinik-Informationssystem (ROKIS) mit Möglichkeiten zur Speicherung/Administration von Bilddaten zusätzliche gesetzliche Rahmenbedingungen berücksichtigen (längere Speicherfristen, prozesssichere Dokumentation von wesentlichen Therapieentscheidungen sowie Abzeichnen von Bestrahlungsplänen und Dosisverschreibungen, komplexe Patienteneinverständnisse etc.). Schlussfolgerung: Der Übergang zu einer papier-und filmlosen Arbeitsumgebung in der Medizin, insbesondere in der Strahlentherapie, ist vor dem Hintergrund notwendiger Effizienzsteigerungen und steigender Archivierungskosten unausweichlich. Die vorliegende Übersichtsarbeit stellt eine mögliche apparative und organisatorische Struktur für ein ROKIS unter Führung eines Krankenhaus-Informationssystems (KIS) vor. Ein solches System vereinigt in einer Kombination und Erweiterung der originären Merkmale eines Record-and-Verify-(R&V-)Systems Merkmale einer elektronischen Patienten-/Fallakte (ePA) und integriertes Bildmanagement mit einem PACS.

Task Group 101 of the AAPM has prepared this report for medical physicists, clinicians, and therapists in order to outline the best practice guidelines for the external-beam radiation therapy technique referred to as stereotactic body radiation therapy ͑SBRT͒. The task group report includes a review of the literature to identify reported clinical findings and expected outcomes for this treatment modality. Information is provided for establishing a SBRT program, including protocols, equipment, resources, and QA procedures. Additionally, suggestions for developing consistent documentation for prescribing, reporting, and recording SBRT treatment delivery is provided.

In this work, the dosimetric characteristics of a new commercial carbon fiber treatment table are investigated. The photon beam attenuation properties of the Siemens image-guided radiation therapy (IGRT) tabletop were studied in detail. Two sets of dosimetric measurements were performed. In the first experiment a polystyrene slab phantom was used: the central axis attenuation and the skin-sparing detriment were investigated. In the second experiment, the off-axis treatment table transmission was investigated using a polystyrene cylindrical phantom. Measurements were taken at the isocenter for a 360°rotation of the radiation beam. Our results show that the photon beam attenuation of the Siemens IGRT carbon fiber tabletop varies from a minimum of 2.1% (central axis) to a maximum of 4.6% (120°and 240°beam incidence). The beam entrance dose increases from 82% to 97% of the dose at the depth of maximum for a clinical 6-MV radiation field. The depth of maximum also decreases by 0.4 cm. Despite the wedge cross section of the table the beam attenuation properties of the IGRT tabletop remain constant along the longitudinal direction. American Association of Medical Dosimetrists.

Treatment of locally advanced head and neck cancer remains a challenge because of the head and neck complex anatomy and the tumor invasion to the adjacent organs and/or metastases to the cervical nodes. Postoperative irradiation or concurrent chemoradiation may lead to damage of radiosensitive structures such as the salivary glands, mandible, cochlea, larynx, and pharyngeal muscles. Xerostomia, osteoradionecrosis, deafness, hoarseness of the voice, dysphagia, and aspiration remain serious complications of head and neck irradiation and impair patient quality of life. Intensity-modulated and image-guided radiotherapy by virtue of steep dose gradient and daily imaging may allow for decreased radiation of the organs at risk for complication while preserving loco-regional control.

The aim of the study was to measure the mean duration of treatments and to investigate the occasional events, with extreme influence on treatment time.Time measurements were performed from the start of patient treatments (n = 72) and one year later (n = 27) on TomoTherapy. The time interval of the different procedures during treatment was measured. The cause of extra long treatment time was examined. All patients received a MV-CT scan prior to treatment.The mean overall total treatment time per localization ranged from 21.3 to 27.4 min. In 4.1% of the total population extreme long time measurements have been observed, interruptions due to equipment malfunction being the main cause (57.5%).Comparison between time measurements performed after clinical implementation and time measurements performed one year later to examine the learning curve, showed no differences.Treating a patient on TomoTherapy takes approximately 25 min, yielding 19 patients to be treated within 8 h. However, occasional treatment interruptions and variations in time of irradiation have a certain impact on daily patient scheduling for treatment, and influences the workload from day-to-day.

Intensity-modulated radiation therapy (IMRT) is a revolutionary new paradigm that aims at improving the therapeutic ratio by increasing the dosegradient between target tissues and surrounding normal structures thereby offering probability of better loco-regional control with decreased risk of complications. IMRT is relatively intolerant to setup uncertainties, warranting periodic image-guidance, making Image-Guided Radiation Therapy (IGRT) a natural corollary to IMRT. There are several challenges associated with the planning, delivery, and quality assurance of the IMRT and IGRT processes that must be addressed to realize the full potential of such exciting and promising technology. Given the complexities involved, it is quite intuitive to understand that IMRT and IGRT are resource-intensive, demanding increased labor, rigour, and expenses too. Other disadvantages associated with high-precision techniques include potentially increased risk of marginal failures, decreased dose homogeneity, and an increase in total body dose with increased risk of secondary carcinogenesis. The aim of this review is to define the role of IMRT and IGRT in contemporary head and neck oncologic practice through a critical appraisal of pertinent literature. Despite relatively short follow-up and limited clinical outcomes data, the weight of evidence suggests that loco-regional control is not inferior (either comparable or even better) and toxicity lesser with IMRT resulting in potentially improved quality-oflife, prompting the widespread adoption of such technology in community practice. Ongoing clinical trials in head and neck IMRT are currently addressing issues to optimize the IMRT process, adopting functional imaging for dose-painting, and incorporating adaptive re-planning strategies to further improve outcomes.

Robustness to obstacles is the most important factor necessary to achieve accurate tumor tracking without fiducial markers. Some high-density structures, such as bone, are enhanced on X-ray fluoroscopic images, which cause tumor mistracking. Tumor tracking should be performed by controlling ‘‘importance recognition’’: the understanding that soft-tissue is an important tracking feature and bone structure is unimportant. We propose a new real-time tumor-contouring method that uses deep learning with importance recognition control. The novelty of the proposed method is the combination of the devised random overlay method and supervised deep learning to induce the recognition of structures in tumor contouring as
important or unimportant. This method can be used for tumor contouring because it uses deep learning to perform image segmentation. Our results from a simulated fluoroscopy model showed accurate tracking of a low-visibility tumor with an error of approximately 1 mm, even if enhanced bone structure acted as an obstacle. A high similarity of approximately 0.95 on the Jaccard index was observed between the segmented and ground truth tumor regions. A short processing time of 25 ms was achieved. The results of this simulated fluoroscopy model support the feasibility of robust real-time tumor contouring with fluoroscopy. Further studies using clinical fluoroscopy are highly anticipated.

The aim of this study is to evaluate the feasibility of using cone-beam CT system as a near real-time measurement device in dose estimation with normoxic polymer gel dosimetry (MAG). Each vial was filled with MAG gel and irradiated with uniform doses of 0-10 Gy to generate dose response curves. After irradiation, a cone-beam CT was used to perform the 3D dose measurement. In this study, two groups of gel samples were irradiated and measured in two ways for comparison: near real-time measurement, in which the gel phantom was read right after the irradiation, and delayed measurement, in which the measurement was performed 30 min, 4 h and 1 day after the irradiation for the gel phantom to be exposed to oxygen. All groups were also performed with and without a full bowtie filter to estimate the influence of a full bowtie filter to dose response. The linear dose response curves with and without a full bowtie filter for the four different CT imaging times were within a range 0.044-0.049DN CT cGy À 1 and 0.061-0.063DN CT cGy À 1 , respectively, with no significant difference at different imaging times. Nevertheless, dose response curves with the full bowtie filter were higher than those without, with p-value o 0.05 for all the different imaging times tested. Normoxic polymer gel dosimetry combined with cone-beam CT provides a useful method for near real-time dose measurement.

Purpose: The feasibility to use visually guided voluntary breath-hold with and without audio assistance to reduce the total treatment time was evaluated. Materials and methods: Patients referred for gated SBRT received hypofractionation schedules for lung or liver treatments. The patients were treated with the Novalis Ò system (BrainLAB AG, Feldkirchen, Germany) and IGRT was performed with ExacTrac5.0/NovalisBody Ò allowing gated irradiation. Video glasses, used for visual feedback to guide voluntary breath-hold, allowed additional audio assistance during treatment. The technique was applied for 25 patients of whom 9 were treated in free breathing, 7 had only visual feedback and another 9 had both audio and visual feedback.

The purpose of this study was to evaluate the capabilities of a kilovoltage (kV) on-board imager (OBI)-equipped linear accelerator in the setting of on-line verification imaging for external-beam partial breast irradiation. Available imaging techniques were optimized and assessed for image quality using a modified anthropomorphic phantom. Imaging dose was also assessed. Imaging techniques were assessed for physical clearance between patient and treatment machine using a volunteer. Nonorthogonal kV image pairs were identified as optimal in terms of image quality, clearance, and dose. After institutional review board approval, this approach was used for 17 patients receiving accelerated partial breast irradiation. Imaging was performed before every fraction verification with online correction of setup deviations >5 mm (total image sessions ‫؍‬ 170). Treatment staff rated risk of collision and visibility of tumor bed surgical clips where present. Image session duration and detected setup deviations were recorded. For all cases, both image projections (n ‫؍‬ 34) had low collision risk. Surgical clips were rated as well as visualized in all cases where they were present (n ‫؍‬ 5). The average imaging session time was 6 min, 16 sec, and a reduction in duration was observed as staff became familiar with the technique. Setup deviations of up to 1.3 cm were detected before treatment and subsequently confirmed offline. Nonorthogonal kV image pairs allowed effective and efficient online verification for partial breast irradiation.

Tel: 925 602 8005 Fax: 925 246 8252 Total number of pages: 33 Total number of references: 26 Total number of figures: 9 Total number of tables: 2 Running title: A multi-platform approach to IGRT 11/16/2005 2 Introduction Several studies using serial CT [1-4] to investigate setup uncertainty of patients undergoing radiation treatment have demonstrated the need for 3D and possibly 4D imaging to improve the accuracy and safety of radiotherapy delivery. The integration of 3D imaging capabilities in the radiation dose delivery systems introduces treatment sitespecific task-optimized IGRT into routine clinical practice. Siemens Medical Solutions, Oncology Care Systems Group (SMSOCSG) is developing several technologies to support the image acquisition and decision making processes required for IGRT in various clinical settings. Clinical objectives as well as market demands and opportunities

The improvement in conformal radiotherapy techniques enables us to achieve steep dose gradients around the target which allows the delivery of higher doses to a tumor volume while maintaining the sparing of surrounding normal tissue. One of the reasons for ...

The goal of this work was to develop and evaluate an end-to-end test for determining and verifying image-guided radiation therapy setup accuracy relative to the radiation isocenter. This was done by placing a cube phantom with a central tungsten sphere directly on the treatment table and offset from isocenter either by 5.0 mm in the longitudinal, lateral, and vertical dimensions or by a random amount. A high-resolution cone-beam CT image was acquired and aligned with the tungsten sphere in the reference CT image. The table was shifted per this alignment, and megavoltage anterior-posterior and lateral images were acquired with the electronic portal imaging device. Agreement between the radiation isocenter (based on the MV field) and the center of the sphere (i.e., the alignment point based on kV imaging) was determined for each image via Winston-Lutz analysis. This procedure was repeated 10 times to determine short-term reproducibility, and then repeated daily for 51 days in a clinic...

Purpose: To perform kilovoltage (kV) cone beam computed tomography (CBCT) imaging concomitant with the delivery of megavoltage (MV) RapidArc treatment, and demonstrate the feasibility of obtaining MV-scatter-free kV CBCT images. Methods and materials: RapidArc/CBCT treatment and imaging plans are designed, and delivered on the Varian TrueBeam, using its Developer Mode. The plan contains 250 control points for MV-radiation delivery, each over an arc of 0.4-0.7 o . Interlaced between successive MV delivery control points are imaging control points, each over an arc of 0.7-1.1 o . During the 360 o gantry rotation for the RapidArc delivery, CBCT projections of a phantom are acquired at 11 frames per second. The kV projections with minimal MV-scatter are selected, based on gantry angle, and the CBCT s image reconstructed. For comparison, a reference CBCT r image is acquired in the normal way. In addition, to examine the effect of MV-scatter we acquire CBCT c using the same treatment plan without the imaging control points, i.e. with continuous MV delivery during the 360 o rotation. Quantitative evaluation of image qualities is performed based on the concepts of CNR (contrast-to-noise ratio) and NSTD (normalized standard deviation). Results: The different types of CBCT images were reconstructed, evaluated, and compared. Visual comparison indicates that the image quality of CBCT s is similar to that of the reference CBCT r , and that the quality of CBCT c is significantly degraded by the MV-scatter. Quantitative evaluation of the image quality indicates that MV-scatter significantly decreases the CNR of CBCT (from $7 to $3.5 in one comparison). Similarly, MV-scatter significantly increases the inhomogeneity of image intensity, e.g. from $0.03 to $0.06 in one comparison. Conclusion: We have developed a method to acquire MV-scatter-free kV CBCT images concomitant with the delivery of RapidArc treatment. Engineering development is necessary to improve the process, e.g. by synchronization of the MV and kV beams.

The aim of this study is to evaluate the accuracy of daily prostate localization with ultrasound imaging of various radiation oncologists with nonhomogeneous expertise. For ten patients who underwent radical radiotherapy for localized prostate cancer, 11 radiation oncologists reviewed daily ultrasound scans acquired during three different treatment sessions. The average values of two senior radiation oncologists, considered to be expert observers, were selected as reference. The remaining nine observers were divided into two groups, Group 1 and Group 2, with more and less than one year of experience, respectively. The recorded shifts in prostate position were divided in three classes: <3 mm, 3-5 mm, and > 5 mm. Deviations from reference were less than 3 mm in all directions in 91% and 81% of measurements in Groups 1 and 2, respectively. The maximum difference in terms of root mean square error (RMSE) was reported for superior-inferior (SI) direction, in particular a mean diffe...

The improved accuracy in tumor identification with FDG-PET has led to its increased utilization in target volume delineation for radiotherapy treatment planning in the treatment of lung cancer. However, PET/CT has constantly been influenced by respiratory motionrelated image degradation, which is especially prominent for small lung tumors in the peri-diaphragmatic regions of the thorax. Here, we describe the current findings on respiratory motion-related image degradation in PET/CT, which may bring uncertainties to target volume delineation for image guided radiotherapy (IGRT) for lung cancer. Furthermore, we describe the evidence suggesting 4D PET/CT to be one strategy to minimize the impact of respiratory motion-related image degradation on tumor target delineation for thoracic IGRT. This, in our opinion, warrants further investigation in future IGRT-based lung cancer trials.

The improved accuracy in tumor identification with FDG-PET has led to its increased utilization in target volume delineation for radiotherapy treatment planning in the treatment of lung cancer. However, PET/CT has constantly been influenced by respiratory motion-related image degradation, which is especially prominent for small lung tumors in the peri-diaphragmatic regions of the thorax. Here, we describe the current findings on respiratory motion-related image degradation in PET/CT, which may bring uncertainties to target volume delineation for image guided radiotherapy (IGRT) for lung cancer. Furthermore, we describe the evidence suggesting 4D PET/CT to be one strategy to minimize the impact of respiratory motion-related image degradation on tumor target delineation for thoracic IGRT. This, in our opinion, warrants further investigation in future IGRT-based lung cancer trials.

Background and purpose: This study explores methods to reduce dose due to kV-CBCT imaging for patients undergoing radiation therapy. Material and methods: Doses resulting from kV-CBCT scans were calculated using Monte Carlo techniques and were analyzed using dose-volume histograms. Patients were modeled as were CBCT acquisitions using both 360°and 200°gantry rotations. The effects of using the half fan bow-tie and the full fan bow-tie filters were examined. Results: Doses for OBI 1.3 are 15 times (head), 5 times (thorax) and 2 times (Pelvis) larger than the current OBI 1.4. When using 200°scans, the doses to eyes and cord are 0.2 (or 0.65) cGy and 0.35 (or 0.2) cGy when rotating the X-ray source underneath (or above) the patient, respectively. The 360°Pelvis scan dose is 1-2 cGy. The rectum dose is 1.1 (or 2.8) cGy when rotating the source above (or below) the patient with the 200°Pelvis scan. The dose increases up to two times as the patient size decreases. Conclusions: The dose can be minimized by reducing the scan length, the exposure settings, by selecting the gantry rotation angles, and by using the full fan bow-tie whenever possible.

Introduction: Undergraduate students studying the Bachelor of Radiation Therapy at Queensland University of Technology (QUT) attend clinical placements in a number of department sites across Queensland. To ensure that the curriculum prepares students for the most common treatments and current techniques in use in these departments, a curriculum matching exercise was performed. Methods: A cross-sectional census was performed on a predetermined "Snapshot" date in 2012. This was undertaken by the clinical education staff in each department who used a standardized proforma to count the number of patients as well as prescription, equipment, and technique data for a list of tumour site categories. This information was combined into aggregate anonymized data. Results: All 12 Queensland radiation therapy clinical sites participated in the Snapshot data collection exercise to produce a comprehensive overview of clinical practice on the chosen day. A total of 59 different tumour sites were treated on the chosen day and as expected the most common treatment sites were prostate and breast, comprising 46% of patients treated. Data analysis also indicated that intensity-modulated radiotherapy (IMRT) use is relatively high with 19.6% of patients receiving IMRT treatment on the chosen day. Both IMRT and image-guided radiotherapy (IGRT) indications matched recommendations from the evidence. Conclusion: The Snapshot method proved to be a feasible and efficient method of gathering useful data to inform curriculum matching. Frequency of IMRT use in Queensland matches or possibly exceeds that indicated in the literature. It is recommended that future repetition of the study be undertaken in order to monitor trends in referral patterns and new technology implementation.

To investigate setup discrepancies measured with ExacTrac X-ray 6 degree-of-freedom (6D) and cone-beam computed tomography (CBCT) for patients under treatments of stereotactic body radiation therapy (SBRT). Materials and methods: In this work, phantom and patient studies were performed. In the phantom studies, an anthropomorphic phantom was placed with pre-defined positions, and imaged with ExacTrac Xray 6D and CBCT to test the accuracy of the imaging systems. In the patient studies, 16 spinal SBRT patient cases were retrospectively analyzed. The patients were initially positioned in customized immobilization cradles and then aligned with ExacTrac X-ray 6D and CBCT. The setup discrepancies were computed and quantitatively analyzed. Results: This study indicates modest discrepancies between ExacTrac X-ray 6D and CBCT with spinal SBRT. The phantom experiments showed that translational and rotational discrepancies in root-meansquare (RMS) between ExacTrac X-ray 6D and CBCT were, respectively, <1.0 mm and <1°. In the retrospective patient studies, translational and rotational discrepancies in RMS between ExacTrac X-ray 6D and CBCT were <2.0 mm and <1.5°. Conclusions: ExacTrac X-ray 6D represents a potential alternative to CBCT; however, precaution should be taken when only ExacTrac X-ray 6D is used to guide SBRT with small setup margins.

Progress in radiotherapy is guided by the need to realize improved dose distributions, i.e. the ability to reduce the treatment volume toward the target volume and still ensuring coverage of that target volume in all dimensions. Poor ability to control the tumour's location limits the accuracy with which radiation can be delivered to tumour-bearing tissue. Image-guided radiation therapy (IGRT) aims at in-room imaging guiding the radiation delivery based on instant knowledge of the target location and changes in tumour volume during treatment. Advancements are usually not to be attributed to a single event, but rather a combination of many small improvements that together enable a superior result. Image-guidance is an important link in the treatment chain and as such a major factor in this synergetic process. A historic review shows that many of the so-called new developments are not so new at all, but did not make it into mainstream radiotherapy practice at that time. Recent developments in improved IT infrastructures, novel irradiation techniques, and better knowledge of functional and morphologic information may have created the need and optimal environment to revive the interest in IGRT.

The improvement in conformal radiotherapy techniques enables us to achieve steep dose gradients around the target which allows the delivery of higher doses to a tumor volume while maintaining the sparing of surrounding normal tissue. One of the reasons for this improvement was the implementation of intensity-modulated radio therapy (IMRT) by using linear accelerators fitted with multi-leaf collimator (MLC), Tomo therapy and Rapid arc. In this situation, verification of patient setup and evaluation of internal organ motion just prior to radiation delivery become important. To this end, several volumetric image-guided techniques have been developed for patient localization, such as Siemens OPTIVUE/MVCB and MVision megavoltage cone beam CT (MV-CBCT) system. Quality assurance for MV-CBCT is important to insure that the performance of the Electronic portal image device (EPID) and MV-CBCT is suitable for the required treatment accuracy. In this work, the commissioning and clinical implementation of the OPTIVUE/MVCB system was presented. The geometry and gain calibration procedures for the system were described. The image quality characteristics of the OPTIVUE/MVCB system were measured and assessed qualitatively and quantitatively, including the image noise and uniformity, low-contrast resolution, and spatial resolution. The image reconstruction and registration software were evaluated. Dose at isocenter from CBCT and the EPID were evaluated using ionization chamber and thermo-luminescent dosimeters; then compared with that calculated by the treatment planning system (TPS-XiO 4.4). The results showed that there are no offsets greater than 1 mm in the flat panel alignment in the lateral and longitudinal direction over 18 months of the study. The image quality tests showed that the image noise and uniformity were within the acceptable range, and that a 2 cm large object with 1% electron density contrast can be detected with the OPTIVUE/MVCB system with 5 monitor units (MU) protocol. The registration software was accurate within 2 mm in the anterior-posterior, left-right, and superior-inferior directions. The additional dose to the patient from MV-CBCT study set with 5 MU at the isocenter of the treatment plan was 5 cGy. For Electronic portal image device (EPID) verification using two orthogonal images with 2 MU per image the additional dose to the patient was 3.8 cGy. These measured dose values were matched with that calculated by the TPS-XiO, where the calculated doses were 5.2 cGy and 3.9 cGy for MVCT and EPID respectively.

This study highlights the use of adaptive planning to accommodate testicular shielding in helical tomotherapy for malignancies of the proximal thigh. Two cases of young men with large soft tissue sarcomas of the proximal thigh are presented. After multidisciplinary evaluation, preoperative radiation therapy was recommended. Both patients were referred for sperm banking and lead shields were used to minimize testicular dose during radiation therapy. To minimize imaging artifacts, kilovoltage CT (kVCT) treatment planning was conducted without shielding. Generous hypothetical contours were generated on each "planning scan" to estimate the location of the lead shield and generate a directionally blocked helical tomotherapy plan. To ensure the accuracy of each plan, megavoltage fan-beam CT (MVCT) scans were obtained at the first treatment and adaptive planning was performed to account for lead shield placement. Two important regions of interest in these cases were femurs and femoral heads. During adaptive planning for the first patient, it was observed that the virtual lead shield contour on kVCT planning images was significantly larger than the actual lead shield used for treatment. However, for the second patient, it was noted that the size of the virtual lead shield contoured on the kVCT image was significantly smaller than the actual shield size. Thus, new adaptive plans based on MVCT images were generated and used for treatment. The planning target volume was underdosed up to 2% and had higher maximum doses without adaptive planning. In conclusion, the treatment of the upper thigh, particularly in young men, presents several clinical challenges, including preservation of gonadal function. In such circumstances, adaptive planning using MVCT can ensure accurate dose delivery even in the presence of high-density testicular shields.

Image-guided radiation therapy implies the use of a variety of imaging techniques in the treatment room to determine the location of target areas with the patient in the treatment position. This is particularly relevant for prostate cancer radiation therapy since the prostate gland can differ in its position within the pelvis from one treatment to another. The different imaging techniques include transabdominal ultrasound, in-room X-rays with and without the use of intraprostatic implanted fiducials, kilovoltage and megavoltage CT techniques, and even in-room MRI. The workflow and capabilities of each imaging system need to be evaluated and investigated individually.

Aims: To analyse the relationship between body mass index (BMI) and intrafraction displacement in patients undergoing prostate cancer image-guided radiotherapy. Materials and methods: An analysis was carried out on 151 prostate cancer patients treated with radical dose radiotherapy between January 2007 and March 2009. Patients had their height, weight and daily intrafraction prostate displacement data collected prospectively during fiducial marker image-guided radiotherapy with orthogonal imaging. For each of anterioreposterior, lefteright and superioreinferior axes, a univariable linear regression analysis was carried out with the individual patient standard deviation of shift as the response variable and BMI as a continuous explanatory variable. Results: Displacement measurements were recorded from 4764 pre-and post-treatment image sets. Patients were grouped according to BMI as normal weight (24%), overweight (52%), obese (18%), severely obese (3%) or morbidly obese (3%). For intrafraction displacement, a one unit increase in BMI affected the standard deviation of shift by: anterioreposterior À0.02 (95% confidence interval À0.040 to 0.000), lefteright À0.006 (95% confidence interval À0.020 to 0.008) and superioreinferior À0.020 (95% confidence interval À0.037 to À0.003). Conclusions: Our data indicate that patients with a higher BMI have less intrafraction displacement of the prostate in the superioreinferior dimension compared with patients with a lower BMI. This has implications for individualised treatment margins for future prostate cancer patients undergoing image-guided radiotherapy. Further study is recommended.

To test the feasibility of salvage radiotherapy using PET-guided helical tomotherapy in patients with progressive malignant pleural mesothelioma (MPM). Patients and Methods: A group of 12 consecutive MPM patients was treated with 56 Gy/25 fractions to the planning target volume (PTV); FDG-PET/CT simulation was always performed to include all positive lymph nodes and MPM infiltrations. Subsequently, a second group of 12 consecutive patients was treated with the same dose to the whole pleura adding a simultaneous integrated boost of 62.5 Gy to the FDG-PET/CT positive areas (BTV). Results: Good dosimetric results were obtained in both groups. No grade 3 (RTOG/EORTC) acute or late toxicities were reported in the first group, while 3 cases of grade 3 late pneumonitis were registered in the second group: the duration of symptoms was 2-10 weeks. Median overall survival was 8 months (1.2-50.5 months) and 20 months (4.3-33.8 months) from the beginning of radiotherapy, for groups I and II, respectively (p = 0.19). A significant impact on local relapse from radiotherapy was seen (median time to local relapse: 8 vs 17 months; 1-year local relapse-free rate: 16% vs 81%, p = 0.003).

A quality assurance (QA) procedure was developed to evaluate the congruence between the cone-beam computed tomography (CBCT) image center and the radiation isocenter on a Varian Trilogy linac. In contrast to the published QA procedures, this method did not require a ball bearing (BB) phantom to be placed exactly at the radiation isocenter through precalibrated room lasers or light field crosshairs. The only requirement was that the BB phantom be in a stationary position near the radiation isocenter during the image acquisition process. The radiation isocenter was determined with respect to the center of the BB using a Winston-Lutz test. The CBCT image center was found to have excellent short-term positional repro-ducibility (i.e., less than 0.1 mm of wobble in each of the x (lateral), y (vertical), and z (longitudinal) directions) in 10 consecutive acquisitions. Measured over a seven-month period, the CBCT image center deviated from the radiation isocenter by 0.40 ± 0.12 mm (x), 0.4...