Surface guided radiotherapy

Modern radiotherapy aims to treat the decease while minimizing the radiation dose to the adjacent normal tissue, to minimize acute and late effects of the treatment. The foremost technological approaches have been intensity modulated radiotherapy (IMRT) and intensity modulated proton therapy (IMPT) in combination with image guided radiotherapy (IGRT). IMRT and IMPT is characterized by a more conform dose distribution, often accompanied by steep dose gradients. In turn, accurate patient localization and motion management becomes more important. Several image guidance systems are available for radiotherapy (RT), with 3-dimensional (3D) volumetric images with cone beam computed tomography (CBCT) as a gold standard. In recent years, surface imaging (SI) using an optical surface scanning system has been included in the IGRT toolbox. The SI system CatalystTM (C-rad Positioning AB, Uppsala Sweden) visualize 3D surface images of the patient topography, and direct correlate the patient localization to the initial planned position. SI offers the largest field-of-view in RT, does not contribute to radiation exposure, provides real-time feedback and sub-millimeter spatial resolution. These characteristics are suitable for both patient positioning and motion management during RT.Integration with the linac provides beam control and automatic couch shifts, which imposes rigorous attention to quality assurance (QA) of the SI systems. In order to integrate the beam control, beam latency times (beam-on and beam-off) should be characterized, which required the development PIN diode circuit as a QA tool. Of extra importance was the measurements of the beam-off latency time, since it represents the time the linac continues to irradiate after the beam hold signal was sent from the SI system. The automatic couch shift is calculated by a deformable image registration (DIR) algorithm, unique for the CatalystTM surface scanning system. Positioning accuracy is dependent on the image registration, and hence, a deformable thorax phantom was developed to investigate accuracy of the DIR with anatomical realistic deformations present as a QA tool.Compared to traditional 3-point localization for patient positioning, this thesis has shown that SI improve the positioning for both breast and prostate cancer patients. Also, the SI workflow has shown to be time efficient for positioning of prostate cancer patients. A respiratory motion management technique is deep inspiration breath hold (DIBH), where the patient is instructed to hold his/her breath during the treatment delivery. The aim using DIBH, is to create an anatomical distance between the treatment volume and surrounding organs-at-risk (OARs). Comparative treatment planning studies, within the work of this thesis, showed that DIBH can be an effective method for both left sided breast cancer and Hodgkin’s lymphoma (HL) in order to spare dose to the heart. For HL, the combination of IMPT and DIBH was found to spare dose to OARs, however, due to the spread in target localization individual deviations from this treatment technique were observed. The real-time feedback from the surface image system was used to investigate the reproducibility of the DIBH to ensure correct dose distribution during the treatment delivery. High reproducibility of the isocenter position during DIBH was observed, however, for a few breath holds larger deviations occurred which urges the need to use beam control tolerance for the isocenter. The overall conclusion is that optical imaging systems, developed within the work of this thesis, can be used as an imaging tool for accurate and faster patient setup, intrafractional motion monitoring and reduced dose to OARs during treatment in DIBH

Evaluation of the Catalyst system for patient positioning during breast cancer treatment

Bröstcancer är den vanligaste formen av cancer hos kvinnor. Fler än 7000 diagnostiseras med denna sjukdom varje år i Sverige. En del av behandlingen mot cancern är strålbehandling. För att strålbehandlingen ska ge goda effekter är det viktigt att det är den sjuka vävnaden som bestrålas, och att den friska vävnaden förskonas från strålningen i den mån det är möjligt. Detta uppnås genom noggranna stråldosplaner individuellt utformade för varje patient. Strålbehandling ges vanligtvis i 16 eller 25 fraktioner, det vill säga att patienten kommer tillbaka dagligen till kliniken 16 eller 25 gånger för behandling. Det är viktigt att patienten ligger i samma position vid varje tillfälle för att stråldosen ska kunna levereras exakt till tumörområdet. I denna studie har ett nytt positioneringssystem utvärderats som heter ”The CatalystTM system” (©2011 C-RAD Positioning AB). På Skånes Universitetssjukhus i Malmö placeras patienten under behandling liggandes i en ställning på behandlingsbritsen. Armarna placeras i skenor ovanför huvudet och ställningen lutar 7,5⁰ bakom ryggen. Dagens rutiner går till så att under planeringsstadiet i behandlingskedjan har patienten fått tre små tatueringsprickar. Dessa används under positioneringen ihop med laserstrålar som finns i behandlingsrummet. Då prickarna och laserstrålarna sammanfaller ligger patienten i rätt läge. Nästa steg för att försäkra sig om att patienten ligger i rätt position är att ta röntgenbilder på patienten. Man korrigerar patientens position efter resultatet från röntgenbilderna och sedan kan man starta strålbehandlingen. Röntgenbilder tas vanligtvis vid de tre första fraktionerna. Därefter gör man en medelvärdeskorrektion av bordspositionen om det krävs för att få patienten i det korrekta läget. Under behandlingsgången tas även röntgenbild vid en senare fraktion för att försäkra sig om att patienten fortfarande ligger i rätt läge. The CatalystTM är ett positionerings och övervakningssystem som inte använder sig av röntgen för att kontrollera patientens position utan det här systemet använder sig av optisk scanning av hudytan. Detta har en självklar fördel då det inte bidrar till någon extra stråldos till patienten och kan därmed användas vid varje behandlingstillfälle. Systemet använder sig av en icke-rigid kroppsalgoritm som beräknar hur patienten ska flyttas för att hamna i rätt position. De delar av kroppen som ligger i fel position lyses upp genom att rött eller gult ljus projiceras på patienten, beroende på åt vilket håll som flytten ska ske. Då en arm belyses med rött ljus kan sjuksköterskan enkelt positionera om armen för att få den i rätt position. The CatalystTM har även fördelen att den registrerar eventuella rörelser under bestrålningen. Skulle patienten flytta sig visar systemet detta direkt på en datorskärm så att sjuksköteskorna kan avbryta behandlingen och positionera om patienten. För att undersöka hur The CatalystTM fungerar i kliniken för att positionera patienter har tre studier utförts. Den första studien var en fantomstudie där fantomet flyttades inom mätvolymen för att undersöka systemets noggrannhet och mätvolymens utsträckning. Den andra studien utfördes med hjälp att det kliniska CBCT (Cone Beam CT) systemet som tar 3D bilder av skelettet och använder en automatisk benmatchningsfunktion för att ge patientens position. Fantomet i studien hade då inre benstruktur, vilket var mer patientlikt. I studien undersöktes om CBCT systemets automatiska benmatchning och The CatalystTM ytmatchning gav samma positioneringsresultat. Den tredje studien var en patient studie som innefattade tretton patienter där röntgenbilder och Catalyst bilder togs vid varje behandlingstillfälle för att undersöka hur väl systemen överrensstämmer. Resultaten från de tre studier som utförts visar att noggrannheten på systemet inte är inom en millimeter vilket är önskvärt. Systemet behöver vidare utveckling för att kunna säkert positionera patienter och The CatalystTM har potential för att lyckas med detta.Purpose: The CatalystTM system was tested and compared with an X-ray image verification system for patient positioning during breast cancer treatment. Included was to find the optimal reference image and the optimal cropping method for the reference image. Parameters that could lead to an optimization of the treatment routines were also evaluated. Method and Material: The study was divided into three parts, “Accuracy measurement of the scanning volume”, “The Catalyst system correspondence with CBCT verification images on a phantom” and “The Catalyst system correspondence with planar verification images on patients.” Accuracy measurements of the scanning volume were performed with a head shaped phantom which had skin equivalent characteristics. The phantom was positioned in a coordinate table and was moved in steps of 2 millimeters in lateral and longitudinal direction in four different planes to investigate the accuracy in the scanning volume. The CBCT study was performed with a pelvis phantom. The phantom was moved ten times and the deviation from the reference images in the CBCT system and the CatalystTM system were compared. The Catalyst system correspondence with planar verification images on patients included thirteen patients which at every treatment fraction were positioned with On-Board Imaging (OBI, Varian©), planar verification images (kV). The positioning results were also registered with the Catalyst system. Both systems used the same reference set-up from the CT scan and the positioning results were compared. The optimal cropping method for the reference image was also evaluated. Results: The results of the study “Accuracy measurement of the scanning volume” showed that the system has a limit at 7.5 cm above the isocenter and that the most accurate results were registered in the plane 5.0 centimeters above the isocenter. The error in the positioning result was 0-4.0 millimeters in the scanning volume. There was no detectable drift in the values in lateral, longitudinal or vertical direction. The CatalystTM system correspondence with CBCT verification images on a phantom resulted in a high accuracy in positioning in vertical and lateral direction with a correspondence of 0-2.0 millimeters. In the longitudinal direction the results differed between 4.0-6.0 millimeter and which was probably due to a flat structure of the phantom. The results from the patient positioning study varied depending on the patient. The optimal reference image was determined to be from the CT structure set. An optimal cropping method for the reference image was found and later used for the analysis of the patient positioning. Conclusions: The CatalystTM system shows accurate positioning result for the phantom studies. The limitation was due to flat or spherical surfaces where the algorithm had difficulties. The flat structure did not provide enough matching information for the algorithm and for the spherical shape the optimization method found a number of solutions. This implies that it is important that the reference image in a patient situation has some structure that the system can use for matching. In the patient positioning study the reference image for every patient were cropped in an optimal way, mainly to minimize the breathing motion. The results of the study indicated that the system does not correspond well with the planar verification images enough for all patients, possible due to that the verification image system matches due to bony structure and the Catalyst system matches due to the skin surface

Clinical paradigms and challenges in surface guided radiation therapy : Where do we go from here?

Surface guided radiotherapy (SGRT) is becoming a routine tool for patient positioning for specific clinical sites in many clinics. However, it has not yet gained its full potential in terms of widespread adoption. This vision paper first examines some of the difficulties in transitioning to SGRT before exploring the current and future role of SGRT alongside and in concert with other imaging techniques. Finally, future horizons and innovative ideas that may shape and impact the direction of SGRT going forward are reviewed

Development of a novel radiotherapy motion phantom using a stepper motor driver circuit and evaluation using optical surface scanning

Abstract: Recent developments in radiotherapy have focused on the management of patient motion during treatment. Studies have shown that significant gains in treatment quality can be made by ‘gating’ certain treatments, simultaneously keeping target coverage, and increasing separation to nearby organs at risk (OAR). Motion phantoms can be used to simulate patient breathing motion and provide the means to perform quality control (QC) and quality assurance (QA) of gating functionality as well as to assess the dosimetric impact of motion on individual patient treatments. The aim of this study was to design and build a motion phantom that accurately reproduces the breathing motion of patients to enable end-to-end gating system quality control of various gating systems as well as patient specific quality assurance. A motion phantom based on a stepper motor driver circuit was designed. The phantom can be programmed with both real patient data from an external gating system and with custom signals. The phantom was programmed and evaluated with patient data and with a square wave signal to be tracked with a Sentinel™ (C-Rad, Uppsala, Sweden) motion monitoring system. Results were compared to the original curves with respect to amplitude and phase. The comparison of patient curve data showed a mean error value of −0.09 mm with a standard deviation of 0.24 mm and a mean absolute error of 0.29 mm. The square wave signals could be reproduced with a mean error value of −0.03 mm, a standard deviation of 0.04 mm and a mean absolute error of 0.13 mm. Breathing curve data acquired from an optical scanning system can be reproduced accurately with the help of the in-house built motion phantom. The phantom can also be programmed to follow user designed curve data. This offers the potential for QC of gating systems and various dosimetric quality control applications. Graphical Abstract: [Figure not available: see fulltext.

The role of surface-guided radiation therapy for improving patient safety

Emerging data indicates SGRT could improve safety and quality by preventing errors in its capacity as an independent system in the treatment room. The aim of this work is to investigate the utility of SGRT in the context of safety and quality. Three incident learning systems (ILS) were reviewed to categorize and quantify errors that could have been prevented with SGRT: SAFRON (International Atomic Energy Agency), UW-ILS (University of Washington) and AvIC (Skåne University Hospital). A total of 849/9737 events occurred during the pre-treatment review/verification and treatment stages. Of these, 179 (21%) events were predicted to have been preventable with SGRT. The most common preventable events were wrong isocentre (43%) and incorrect accessories (34%), which appeared at comparable rates among SAFRON and UW-ILS. The proportion of events due to wrong accessories was much smaller in the AvIC ILS, which may be attributable to the mandatory use of SGRT in Sweden. Several case scenarios are presented to demonstrate that SGRT operates as a valuable complement to other quality-improvement tools routinely used in radiotherapy. Cases are noted in which SGRT itself caused incidents. These were mostly related to workflow issues and were of low severity. Severity data indicated that events with the potential to be mitigated by SGRT were of higher severity for all categories except wrong accessories. Improved vendor integration of SGRT systems within the overall workflow could further enhance its clinical utility. SGRT is a valuable tool with the potential to increase patient safety and treatment quality in radiotherapy

Surface guided radiotherapy decreases the uncertainty in breast cancer patient setup

(Sunday, 7/29/2018) 3:00 PM - 6:00 PMRoom: Exhibit HallPurpose: The aim was to investigate if the setup of breast cancer patients could be improved using surface guided radiotherapy, compared to the conventional method using lasers and skin markings.Methods: Forty-seven patients, who received tangential or locoregional adjuvant radiotherapy, were positioned using a surface-based setup (SBS). Thirty-eight patients were positioned using the conventional laser-based setup (LBS). For the patient group positioned using a SBS, correction for posture was performed under guidance of a color map projected onto the patients' skin in real time. The surface tolerance for the color map was 5 mm. For both setup techniques the deviation of the breast position was measured using verification images. In total, 897 images were analysed. The frequency distributions of the deviations were analysed.Results: The result showed a significant improvement in the interfractional variation of the setup deviation for SBS compared to the LBS (pConclusion: Conventional laser-based setup can be replaced by surface-based setup, both for tangential and locoregional breast cancer treatments

Comparative treatment planning study for mediastinal Hodgkin’s lymphoma : impact on normal tissue dose using deep inspiration breath hold proton and photon therapy

Background: Late effects induced by radiotherapy (RT) are of great concern for mediastinal Hodgkin’s lymphoma (HL) patients and it is therefore important to reduce normal tissue dose. The aim of this study was to investigate the impact on the normal tissue dose and target coverage, using various combinations of intensity modulated proton therapy (IMPT), volumetric modulated arc therapy (VMAT) and 3-dimensional conformal RT (3D-CRT), planned in both deep inspiration breath hold (DIBH) and free breathing (FB). Material and methods: Eighteen patients were enrolled in this study and planned with involved site RT. Two computed tomography images were acquired for each patient, one during DIBH and one during FB. Six treatment plans were created for each patient; 3D-CRT in FB, 3D-CRT in DIBH, VMAT in FB, VMAT in DIBH, IMPT in FB and IMPT in DIBH. Dosimetric impact on the heart, left anterior descending (LAD) coronary artery, lungs, female breasts, target coverage, and also conformity index and integral dose (ID), was compared between the different treatment techniques. Results: The use of DIBH significantly reduced the lung dose for all three treatment techniques, however, no significant difference in the dose to the female breasts was observed. Regarding the heart and LAD doses, large individual variations were observed. For VMAT, the mean heart and LAD doses were significantly reduced using DIBH, but no significant difference was observed for 3D-CRT and IMPT. Both IMPT and VMAT resulted in improved target coverage and more conform dose distributions compared to 3D-CRT. IMPT generally showed the lowest organs at risk (OAR) doses and significantly reduced the ID compared to both 3D-CRT and VMAT. Conclusions: The majority of patients benefited from treatment in DIBH, however, the impact on the normal tissue dose was highly individual and therefore comparative treatment planning is encouraged. The lowest OAR doses were generally observed for IMPT in combination with DIBH

Faster and more accurate patient positioning with surface guided radiotherapy for ultra-hypofractionated prostate cancer patients

Introduction: The aim of this study was to evaluate if surface guided radiotherapy (SGRT) can decrease patient positioning time for localized prostate cancer patients compared to the conventional 3-point localization setup method. The patient setup accuracy was also compared between the two setup methods. Materials and methods: A total of 40 localized prostate cancer patients were enrolled in this study, where 20 patients were positioned with surface imaging (SI) and 20 patients were positioned with 3-point localization. The setup time was obtained from the system log files of the linear accelerator and compared between the two methods. The patient setup was verified with daily orthogonal kV images which were matched based on the implanted gold fiducial markers. Resulting setup deviations between planned and online positions were compared between SI and 3-point localization. Results: Median setup time was 2:50 min and 3:28 min for SI and 3-point localization, respectively (p < 0.001). The median vector offset was 4.7 mm (range: 0–10.4 mm) for SI and 5.2 mm for 3-point localization (range: 0.41–17.3 mm) (p = 0.01). Median setup deviation in the individual translations for SI and 3-point localization respectively was: 1.1 mm and 1.9 mm in lateral direction (p = 0.02), 1.8 and 1.6 mm in the longitudinal direction (p = 0.41) and 2.2 mm and 2.6 mm in the vertical direction (p = 0.04). Conclusions: Using SGRT for positioning of prostate cancer patients provided a faster and more accurate patient positioning compared to the conventional 3-point localization setup