integration of enhanced optical tracking techniques and imaging in igrt

Patient setup/Optical tracking/IGRT/Treatment surveillance. In external beam radiotherapy, modern technologies for dynamic dose delivery and beam conformation provide high selectivity in radiation dose administration to the pathological volume. A comparable accuracy level is needed in the 3-D localization of tumor and organs at risk (OARs), in order to accomplish the planned dose distribution in the reality of each irradiation session. In-room imaging techniques for patient setup verification and tumor targeting may benefit of the combined daily use of optical tracking technologies, supported by techniques for the detection and compensation of organ motion events. Multiple solutions to enhance the use of optical tracking for the on-line correction of target localization uncertainties are described, with specific emphasis on the compensation of setup errors, breathing movements and non-rigid deformations. The final goal is the implementation of customized protocols where appropriate external landmarks, to be tracked in real-time by means of noninvasive optical devices, are selected as a function of inner target localization. The presented methodology features high accuracy in patient setup optimization, also providing a valuable tool for on-line patient surveillance, taking into account both breathing and deformation effects. The methodic application of optical tracking is put forward to represent a reliable and low cost procedure for the reduction of safety margins, once the patient-specific correlation between external landmarks and inner structures has been established. Therefore, the integration of optical tracking with in-room imaging devices is proposed as a way to gain higher confidence in the framework of Image Guided Radiation Therapy (IGRT) treatments

Registration accuracy for MR images of the prostate using a subvolume based registration protocol

<p>Abstract</p> <p>Background</p> <p>In recent years, there has been a considerable research effort concerning the integration of magnetic resonance imaging (MRI) into the external radiotherapy workflow motivated by the superior soft tissue contrast as compared to computed tomography. Image registration is a necessary step in many applications, e.g. in patient positioning and therapy response assessment with repeated imaging. In this study, we investigate the dependence between the registration accuracy and the size of the registration volume for a subvolume based rigid registration protocol for MR images of the prostate.</p> <p>Methods</p> <p>Ten patients were imaged four times each over the course of radiotherapy treatment using a T2 weighted sequence. The images were registered to each other using a mean square distance metric and a step gradient optimizer for registration volumes of different sizes. The precision of the registrations was evaluated using the center of mass distance between the manually defined prostates in the registered images. The optimal size of the registration volume was determined by minimizing the standard deviation of these distances.</p> <p>Results</p> <p>We found that prostate position was most uncertain in the anterior-posterior (AP) direction using traditional full volume registration. The improvement in standard deviation of the mean center of mass distance between the prostate volumes using a registration volume optimized to the prostate was 3.9 mm (p < 0.001) in the AP direction. The optimum registration volume size was 0 mm margin added to the prostate gland as outlined in the first image series.</p> <p>Conclusions</p> <p>Repeated MR imaging of the prostate for therapy set-up or therapy assessment will both require high precision tissue registration. With a subvolume based registration the prostate registration uncertainty can be reduced down to the order of 1 mm (1 SD) compared to several millimeters for registration based on the whole pelvis.</p

Systematisation of spatial uncertainties for comparison between a MR and a CT-based radiotherapy workflow for prostate treatments

<p>Abstract</p> <p>Background</p> <p>In the present work we compared the spatial uncertainties associated with a MR-based workflow for external radiotherapy of prostate cancer to a standard CT-based workflow. The MR-based workflow relies on target definition and patient positioning based on MR imaging. A solution for patient transport between the MR scanner and the treatment units has been developed. For the CT-based workflow, the target is defined on a MR series but then transferred to a CT study through image registration before treatment planning, and a patient positioning using portal imaging and fiducial markers.</p> <p>Methods</p> <p>An "open bore" 1.5T MRI scanner, Siemens Espree, has been installed in the radiotherapy department in near proximity to a treatment unit to enable patient transport between the two installations, and hence use the MRI for patient positioning. The spatial uncertainty caused by the transport was added to the uncertainty originating from the target definition process, estimated through a review of the scientific literature. The uncertainty in the CT-based workflow was estimated through a literature review.</p> <p>Results</p> <p>The systematic uncertainties, affecting all treatment fractions, are reduced from 3-4 mm (1Sd) with a CT based workflow to 2-3 mm with a MR based workflow. The main contributing factor to this improvement is the exclusion of registration between MR and CT in the planning phase of the treatment.</p> <p>Conclusion</p> <p>Treatment planning directly on MR images reduce the spatial uncertainty for prostate treatments.</p

Magneettikuvaukseen perustuvan sädehoidon suunnittelun käyttöönotto lantion alueella

Modern radiation therapy delivery techniques enable ever conformal delivery of the radiation increasing the likelihood for successful treatment and reducing complications in nearby healthy tissue. In order to improve the treatment outcomes, in addition to advanced radiation delivery techniques, more accurate knowledge about the location and spread of both disease and organs at risk (OAR) is needed. Thus, the use of magnetic resonance imaging (MRI) has increased substantially during recent years. In MRI, the contrast resolution for soft tissue is superior compared to other imaging modalities enabling precise target definition and contouring of the OARs. Currently, the use of MRI in radiation therapy is based on co-registration of the images facilitating the use of the information provided by MRI while computed tomography (CT) is used for dose computation and as a reference image for patient positioning. Unfortunately, the dual modality workflow is laborious and cost inefficient. In addition, the co-registration uncertainty propagates to treatment uncertainty causing systematic error. During recent years several research groups have published methods enabling the generation of so-called synthetic CT (sCT). It can be used like traditional CT for density information in dose computation and as positioning reference images. The use of sCT enables external beam radiation therapy workflow using only MR imaging. In this work we studied the commissioning and accuracy of MRI-only workflow for external beam radiation therapy (EBRT) of pelvic malignancies. The commissioning test shall cover all steps in the radiation therapy workflow where geometric or dosimetric accuracy is affected by the substitution of the CT by the sCT. In publications I and III, we assessed the dosimetric accuracy of sCT images in pelvis by comparing to dose distributions computed using CT images. In publications II and III, we studied the patient positioning accuracy when sCT images are used as reference images. In addition, in publications I and III we evaluated the impact of geometric distortions to the total accuracy of MRI-only workflow. According to our results, the use of studied sCT method is sufficiently accurate for clinical use for pelvic indications. In addition, image-guided radiation therapy based on MR images is accurate enough so that the total geometric accuracy improves compared to current CT based work-flow.Modernit sädehoitotekniikat mahdollistavat yhä tarkemman kohteenmukaisen sädehoidon antamisen, mikä lisää hoidon onnistumisen todennäköisyyttä ja vähentää komplikaatioita ympäröivissä terveissä kudoksissa. Parempiin hoitotuloksiin pääsemiseksi sädehoidossa tarvitaan kuitenkin, kehittyneiden hoitotekniikoiden lisäksi, yhä tarkempaa tietoa hoitokohteen ja riskielinten sijainnista. Tämän takia ionisoimattoman säteilyn käyttöön perustuvan magneettikuvauksen (MK) käyttö on lisääntynyt voimakkaasti sädehoidossa viime vuosina. MK:ssa pehmytkudosten välinen kontrasti on muita kuvausmodaliteetteja parempi, mikä mahdollistaa tarkemman kohteen määrittelyn ja riskielinten rajauksen. Nykyinen käytäntö MK-kuvien osalta sädehoidossa perustuu tietokonetomografia- (TT) ja MK-kuvien rekisteröintiin, jolloin MK-kuvien antama lisäinformaatio voidaan hyödyntää, vaikka itse hoitokenttien annoslaskenta ja potilaan kohdistus on TT-kuviin perustuvaa. Kahden kuvausmoda-liteetin käytöstä aiheutuu ylimääräistä työtä ja kustannuksia. Lisäksi kuvien rekisteröintiin liittyvä virhe lisää epävarmuutta hoidon tarkkuudessa. Viime aikoina useat tutkimusryhmät ovat julkaisseet menetelmiä, joiden avulla on mahdollista muodostaa sädehoidon annoslaskennassa tarvittava tiheyskartta (laskennallinen TT-kuva) suoraan magneettikuvausta käyttäen. Näin sädehoito on mahdollista toteuttaa pelkän magneettikuvan perusteella, jolloin yllä mainitut kahden kuvausmodaliteetin käytöstä aiheutuvat ongelmat voidaan välttää. Tässä työssä tutkittiin MK-kuviin perustuvan laskennallisen TT-kuvan käyttöönottoa ja tarkkuutta lantion alueen ulkoisessa sädehoidossa. Käyttöönottotestien tulee kattaa kaikki sellaiset vaiheet, jossa MK-pohjainen suunnittelu vaikuttaa joko geometriseen tai dosimetriseen tarkkuuteen. Ensimmäisessä ja kolmannessa osatyössä tutkittiin mahdollisuutta käyttää MK:ta sädehoitopotilaiden lantion alueen annoslaskennassa säteilyn vaimennuskorjaukseen. Toisessa ja kolmannessa osatyössä määritettiin potilasasemoinnin epätarkkuus käytettäessä MK-pohjaista menetelmää vertaamalla perinteiseen TT-kuvaan pohjautuvaan menetelmään. Lisäksi ensimmäisessä ja kolmannessa osatyössä arvioitiin MK:n geometrisen vääristymän vaikutuksia kokonaistarkkuuteen. Tutkimuksen perusteella menetelmän käyttö lantion alueella on riittävän tarkka kliiniseen käyttöön. Lisäksi kuvantaohjattu sädehoito magneettikuvien pohjalta on riittävän tarkkaa, jotta potilaan asemointitarkkuus ei huonone suhteessa nykyiseen TT-pohjaiseen suunnitteluun

Investigation Of The Microsoft Kinect V2 Sensor As A Multi-Purpose Device For A Radiation Oncology Clinic

For a radiation oncology clinic, the number of devices available to assist in the workflow for radiotherapy treatments are quite numerous. Processes such as patient verification, motion management, or respiratory motion tracking can all be improved upon by devices currently on the market. These three specific processes can directly impact patient safety and treatment efficacy and, as such, are important to track and quantify. Most products available will only provide a solution for one of these processes and may be outside the reach of a typical radiation oncology clinic due to difficult implementation and incorporation with already existing hardware. This manuscript investigates the use of the Microsoft Kinect v2 sensor to provide solutions for all three processes all while maintaining a relatively simple and easy to use implementation. To assist with patient verification, the Kinect system was programmed to create a facial recognition and recall process. The basis of the facial recognition algorithm was created by utilizing a facial mapping library distributed by Microsoft within the Software Developers Toolkit (SDK). Here, the system extracts 31 fiducial points representing various facial landmarks. 3D vectors are created between each of the 31 points and the magnitude of each vector is calculated by the system. This allows for a face to be defined as a collection of 465 specific vector magnitudes. The 465 vector magnitudes defining a face are then used in both the creation of a facial reference data set and subsequent evaluations of real-time sensor data in the matching algorithm. To test the algorithm, a database of 39 faces was created, each with 465 vectors derived from the fiducial points, and a one-to-one matching procedure was performed to obtain sensitivity and specificity data of the facial identification system. In total, 5299 trials were performed and threshold parameters were created for match determination. Optimization of said parameters in the matching algorithm by way of ROC curves indicated the sensitivity of the system for was 96.5% and the specificity was 96.7%. These results indicate a fairly robust methodology for verifying, in real-time, a specific face through comparison from a pre-collected reference data set. In its current implementation, the process of data collection for each face and subsequent matching session averaged approximately 30 seconds, which may be too onerous to provide a realistic supplement to patient identification in a clinical setting. Despite the time commitment, the data collection process was well tolerated by all participants. It was found that ambient light played a crucial role in the accuracy and reproducibility of the facial recognition system. Testing with various light levels found that ambient light greater than 200 lux produced the most accurate results. As such, the acquisition process should be setup in such a way to ensure consistent ambient light conditions across both the reference recording session and subsequent real-time identification sessions. In developing a motion management process with the Kinect, two separate, but complimentary processes were created. First, to track large scale anatomical movements, the automatic skeletal tracking capabilities of the Kinect were utilized. 25 specific body joints (head, elbow, knee, etc) make up the skeletal frame and are locked to relative positions on the body. Using code written in C#, these joints are tracked, in 3D space, and compared to an initial state of the patient allowing for an indication of anatomical motion. Additionally, to track smaller, more subtle movements on a specific area of the body, a user drawn ROI can be created. Here, the depth values of all pixels associated with the body in the ROI are compared to the initial state. The system counts the number of live pixels with a depth difference greater than a specified threshold compared to the initial state and the area of each of those pixels is calculated based on their depth. The percentage of area moved (PAM) compared to the ROI area then becomes an indication of gross movement within the ROI. In this study, 9 specific joints proved to be stable during data acquisition. When moved in orthogonal directions, each coordinate recorded had a relatively linear trend of movement but not the expected 1:1 relationship to couch movement. Instead, calculation of the vector magnitude between the initial and current position proved a better indicator of movement. 5 of the 9 joints (Left/Right Elbow, Left/Right Hip, and Spine-Base) showed relatively consistent values for radial movements of 5mm and 10mm, achieving 20% - 25% coefficient of variation. For these 5 joints, this allowed for threshold values for calculated radial distances of 3mm and 7.5 mm to be set for 5mm and 10mm of actual movement, respectively. When monitoring a drawn ROI, it was found that the depth sensor had very little sensitivity of movement in the X (Left/Right) or Y (Superior/Inferior) direction, but exceptional sensitivity in the Z (Anterior/Posterior) direction. As such, the PAM values could only be coordinated with motion in the Z direction. PAM values of over 60% were shown to be indicative of movement in the Z direction equal to that of the threshold value set for movement as small as 3mm. Lastly, the Kinect was utilized to create a marker-less, respiratory motion tracking system. Code was written to access the Kinect’s depth sensor and create a process to track the respiratory motion of a subject by recording the depth (distance) values obtained at several user selected points on the subject, with each point representing one pixel on the depth image. As a patient breathes, a specific anatomical point on the chest/abdomen will move slightly within the depth image across a number of pixels. By tracking how depth values change for a specific pixel, instead of how the anatomical point moves throughout the image, a respiratory trace can be obtained based on changing depth values of the selected pixel. Tracking of these values can then be implemented via marker-less setup. Varian’s RPM system and the Anzai belt system were used in tandem with the Kinect in order to compare respiratory traces obtained by each using two different subjects. Analysis of the depth information from the Kinect for purposes of phase based and amplitude based binning proved to be correlated well with the RPM and Anzai systems. IQR values were obtained which compared times correlated with specific amplitude and phase percentage values against each product. The IQR spans of time indicated the Kinect would measure a specific percentage value within 0.077 s for Subject 1 and 0.164s for Subject 2 when compared to values obtained with RPM or Anzai. For 4D-CT scans, these times correlate to less than 1mm of couch movement and would create an offset of one half an acquired slice. These minimal deviations between the traces created by the Kinect and RPM or Anzai indicate that by tracking the depth values of user selected pixels within the depth image, rather than tracking specific anatomical locations, respiratory motion can be tracked and visualized utilizing the Kinect with results comparable to that of commercially available products

Assessment of optical CT as a future QA tool for synchrotron x-ray microbeam therapy.

Synchrotron microbeam radiation therapy (MRT) is an advanced form of radiotherapy for which it is extremely difficult to provide adequate quality assurance. This may delay or limit its clinical uptake, particularly in the paediatric patient populations for whom it could be especially suitable. This study investigates the extent to which new developments in 3D dosimetry using optical computed tomography (CT) can visualise MRT dose distributions, and assesses what further developments are necessary before fully quantitative 3D measurements can be achieved. Two experiments are reported. In the first cylindrical samples of the radiochromic polymer PRESAGE(®) were irradiated with different complex MRT geometries including multiport treatments of collimated 'pencil' beams, interlaced microplanar arrays and a multiport treatment using an anthropomorphic head phantom. Samples were scanned using transmission optical CT. In the second experiment, optical CT measurements of the biologically important peak-to-valley dose ratio (PVDR) were compared with expected values from Monte Carlo simulations. The depth-of-field (DOF) of the optical CT system was characterised using a knife-edge method and the possibility of spatial resolution improvement through deconvolution of a measured point spread function (PSF) was investigated. 3D datasets from the first experiment revealed excellent visualisation of the 50 μm beams and various discrepancies from the planned delivery dose were found. The optical CT PVDR measurements were found to be consistently 30% of the expected Monte Carlo values and deconvolution of the microbeam profiles was found to lead to increased noise. The reason for the underestimation of the PVDR by optical CT was attributed to lack of spatial resolution, supported by the results of the DOF characterisation. Solutions are suggested for the outstanding challenges and the data are shown already to be useful in identifying potential treatment anomalies