Koen Tournel

Innovations in image-guided radiotherapy

The limited ability to control for the location of a tumour compromises the accuracy with which radiation can be delivered to tumour-bearing tissue. The resultant requirement for larger treatment volumes to accommodate target uncertainty restricts the radiation dose because more surrounding normal tissue is exposed. With image-guided radiotherapy (IGRT) these volumes can be optimized and tumoricidal doses can be delivered, achieving maximal tumour control with minimal complications. Moreover, with the ability of high-precision dose delivery and real-time knowledge of the target volume location, IGRT has initiated the exploration of new indications for radiotherapy, some of which were previously considered infeasible.

Geometric accuracy of a novel gimbals based radiation therapy tumor tracking system.

PURPOSE VERO is a novel platform for image guided stereotactic body radiotherapy. Orthogonal gimbals hold the linac-MLC assembly allowing real-time moving tumor tracking. This study determines the geometric accuracy of the tracking. MATERIALS AND METHODS To determine the tracking error, an 1D moving phantom produced sinusoidal motion with frequencies up to 30 breaths per minute (bpm). Tumor trajectories of patients were reproduced using a 2D robot and pursued with the gimbals tracking system prototype. Using the moving beam light field and a digital-camera-based detection unit tracking errors, system lag and equivalence of pan/tilt performance were measured. RESULTS The system lag was 47.7 ms for panning and 47.6 ms for tilting. Applying system lag compensation, sinusoidal motion tracking was accurate, with a tracking error 90% percentile E(90%)<0.82 mm and similar performance for pan/tilt. Systematic tracking errors were below 0.14 mm. The 2D tumor trajectories were tracked with an average E(90%) of 0.54 mm, and tracking error standard deviations of 0.20 mm for pan and 0.22 mm for tilt. CONCLUSIONS In terms of dynamic behavior, the gimbaled linac of the VERO system showed to be an excellent approach for providing accurate real-time tumor tracking in radiation therapy.

Initial assessment of tumor tracking with a gimbaled linac system in clinical circumstances: A patient simulation study

PURPOSE To have an initial assessment of the Vero Dynamic Tracking workflow in clinical circumstances and quantify the performance of the tracking system, a simulation study was set up on 5 lung and liver patients. METHODS AND MATERIALS The preparatory steps of a tumor tracking treatment, based on fiducial markers implanted in the tumor, were executed allowing pursuit of the tumor with the gimbaled linac and monitoring X-rays acquisition, however, without activating the 6 MV beam. Data were acquired on workflow time-efficiency, tracking accuracy and imaging exposure. RESULTS The average time between the patient entering the treatment room and the first treatment field was about 9 min. The time for building the correlation model was 3.2 min. Tracking errors of 0.55 and 0.95 mm (1σ) were observed in PAN/TILT direction and a 2D range of 3.08 mm. A skin dose was determined of 0.08 mGy/image, with a source-to-skin distance of 900 mm and kV exposure of 1 mAs. On average 1.8 mGy/min kV skin dose was observed for 1 Hz monitoring. CONCLUSION The Vero tracking solution proved to be fully functional and showed performance comparable with other real-time tracking systems.

Clinical evaluation of a robotic 6-degree of freedom treatment couch for frameless radiosurgery.

PURPOSE To evaluate the added value of 6-degree of freedom (DOF) patient positioning with a robotic couch compared with 4DOF positioning for intracranial lesions and to estimate the immobilization characteristics of the BrainLAB frameless mask (BrainLAB AG, Feldkirchen, Germany), more specifically, the setup errors and intrafraction motion. METHODS AND MATERIALS We enrolled 40 patients with 66 brain metastases treated with frameless stereotactic radiosurgery and a 6DOF robotic couch. Patient positioning was performed with the BrainLAB ExacTrac stereoscopic X-ray system. Positioning results were collected before and after treatment to assess patient setup error and intrafraction motion. Existing treatment planning data were loaded and simulated for 4DOF positioning and compared with the 6DOF positioning. The clinical relevance was analyzed by means of the Paddick conformity index and the ratio of prescribed isodose volume covered with 4DOF to that obtained with the 6DOF positioning. RESULTS The mean three-dimensional setup error before 6DOF correction was 1.91 mm (SD, 1.25 mm). The rotational errors were larger in the longitudinal (mean, 0.23°; SD, 0.82°) direction compared with the lateral (mean, -0.09°; SD, 0.72°) and vertical (mean, -0.10°; SD, 1.03°) directions (p < 0.05). The mean three-dimensional intrafraction shift was 0.58 mm (SD, 0.42 mm). The mean intrafractional rotational errors were comparable for the vertical, longitudinal, and lateral directions: 0.01° (SD, 0.35°), 0.03° (SD, 0.31°), and -0.03° (SD, 0.33°), respectively. The mean conformity index decreased from 0.68 (SD, 0.08) (6DOF) to 0.59 (SD, 0.12) (4DOF) (p < 0.05). A loss of prescribed isodose coverage of 5% (SD, 0.08) was found with the 4DOF positioning (p < 0.05). Half a degree for longitudinal and lateral rotations can be identified as a threshold for coverage loss. CONCLUSIONS With a mask immobilization, patient setup error and intrafraction motions need to be evaluated and corrected for. The 6DOF patient positioning with a 6DOF robotic couch to correct translational and rotational setup errors improves target positioning with respect to treatment isocenter, which is in direct relation with the clinical outcome, compared with the 4DOF positioning.

Preoperative Helical Tomotherapy and Megavoltage Computed Tomography for Rectal Cancer: Impact on the Irradiated Volume of Small Bowel

PURPOSE Preoperative (chemo)radiotherapy is considered to be standard of care in locally advanced rectal cancer, but is associated with significant small-bowel toxicity. The aim of this study was to explore to what extent helical tomotherapy and daily megavolt (MV) CT imaging may reduce the irradiated volume of small bowel. METHODS AND MATERIALS A 3D-conformal radiotherapy (3D-CRT) plan with CTV-PTV margins adjusted for laser-skin marks (15, 15, and 10 mm for X, Y, and Z directions, respectively) was compared with helical tomotherapy (IMRT) using the same CTV-PTV margins, and to helical tomotherapy with margins adapted to daily MV-CT imaging (IMRT/IGRT; 8, 11, 7, and 10 mm for X, Y(ant), Y(post) and Z resp.) for 11 consecutive patients. The planning goals were to prescribe 43.7 Gy to 95% of the PTV, while minimizing the volume of small bowel receiving more than 15 Gy (V(15 SB)). RESULTS The mean PTV was reduced from 1857.4 +/- 256.6 cc to 1462.0 +/- 222.3 cc, when the CTV-PTV margins were adapted from laser-skin marks to daily MV-CT imaging (p < 0.01). The V(15 SB) decreased from 160.7 +/- 102.9 cc to 110.9 +/- 74.0 cc with IMRT and to 81.4 +/- 53.9 cc with IMRT/IGRT (p < 0.01). The normal tissue complication probability (NTCP) for developing Grade 2+ diarrhea was reduced from 39.5% to 26.5% with IMRT and to 18.0% with IMRT/IGRT (p < 0.01). CONCLUSION The combination of helical tomotherapy and daily MV-CT imaging significantly decreases the irradiated volume of small bowel and its NTCP.

Six dimensional analysis with daily stereoscopic x-ray imaging of intrafraction patient motion in head and neck treatments using five points fixation masks.

The safety margins used to define the Planning Target Volume (PTV) should reflect the accuracy of the target localization during treatment that comprises both the reproducibility of the patient positioning and the positional uncertainty of the target, so both the inter- and intrafraction motion of the target. Our first aim in this study was to determine the intrafraction motion of patients immobilized with a five-point thermoplastic mask for head and neck treatments. The five-point masks have the advantage that the patients shoulders as well as the cranial part of the patients head is covered with the thermoplastic material that improves the overall immobilization of the head and neck region of the patient. Thirteen patients were consecutively assigned to use a five-point thermoplastic mask. The patients were positioned by tracking of infrared markers (IR) fixed to the immobilization device and stereoscopic x-ray images were used for daily on-line setup verification. Repositioning was carried out prior to treatment as needed; rotations were not corrected. Movements during treatment were monitored by real-time IR tracking. Intrafraction motion and rotation was supplementary assessed by a six-degree-of-freedom (6-D) fusion of x-ray images, taken before and after all 385 treatments, with DRR images generated from the planning CT data. The latter evaluates the movement of the patient within the thermoplastic mask independent from the mask movement, where IR tracking evaluates the movement of the mask caused by patient movement in the mask. These two movements are not necessarily equal to each other. The maximum intrafraction movement detected by IR tracking showed a shift [mean (SD; range)] of -0.1(0.7; 6.0), 0.1(0.6; 3.6), -0.2(0.8;5.5) mm in the vertical, longitudinal, and lateral direction, respectively, and rotations of 0.0(0.2; 1.6), 0.0(0.2; 1.7) and 0.2(0.2; 2.4) degrees about the vertical, longitudinal, and lateral axis, respectively. The standard deviations and ranges found with the 6-D fusion demonstrate intrafraction patient displacements of -0.5(1.2; 7.4), 0.3(0.7; 5.3), 0.0(0.7; 5.7) mm in the vertical, longitudinal, and lateral direction, respectively, and rotations of -0.1(0.6; 4.1), 0.1(0.7; 8.3) and -0.2(0.8; 8.2) degrees about the vertical, longitudinal, and lateral axis, respectively. The 6-D fusions are considerably larger (p < 0.05) than detected by IR tracking. This indicates that the external marker tracking underestimates the magnitude of the actual intrafraction motion and rotation of the patient. The intrafraction motion detected for the patients immobilized with a conventional thermoplastic mask was relatively large. The feasibility to reduce this intrafraction movement by the application of alternative five-point thermoplastic mask types was evaluated as a second aim of this study. The preliminary results showed a clear reduction in the range, being an indication for the random movements, of both the intrafraction shift and rotation for both alternative mask types. The 6-D fusion is found a useful tool for a fast evaluation of the actual patients intrafraction shift and rotation and shows the latter is not negligible and needs to be taken into account additional to the initial setup accuracy when determining the PTV margin.

Dosimetric assessment of static and helical TomoTherapy in the clinical implementation of breast cancer treatments

BACKGROUND AND PURPOSE Investigation of the use of TomoTherapy and TomoDirect versus conventional radiotherapy for the treatment of post-operative breast carcinoma. This study concentrates on the evaluation of the planning protocol for the TomoTherapy and TomoDirect TPS, dose verification and the implementation of in vivo dosimetry. MATERIALS AND METHODS Eight patients with different breast cancer indications (left/right tumor, axillary nodes involvement (N+)/no nodes (N0), tumorectomy/mastectomy) were enrolled. TomoTherapy, TomoDirect and conventional plans were generated for prone and supine positions leading to six or seven plans per patient. Dose prescription was 42Gy in 15 fractions over 3weeks. Dose verification of a TomoTherapy plan is performed using TLDs and EDR2 film inside a home-made wax breast phantom fixed on a rando-alderson phantom. In vivo dosimetry was performed with TLDs. RESULTS It is possible to create clinically acceptable plans with TomoTherapy and TomoDirect. TLD calibration protocol with a water equivalent phantom is accurate. TLD verification with the phantom shows measured over calculated ratios within 2.2% (PTV). An overresponse of the TLDs was observed in the low dose regions (<0.1Gy). The film measurements show good agreement for high and low dose regions inside the phantom. A sharp gradient can be created to the thoracic wall. In vivo dosimetry with TLDs was clinically feasible. CONCLUSIONS The TomoTherapy and TomoDirect modalities can deliver dose distributions which the radiotherapist judges to be equal to or better than conventional treatment of breast carcinoma according to the organ to be protected.

Longitudinal Assessment of Parotid Function in Patients Receiving Tomotherapy for Head-and-Neck Cancer

Background and Purpose:Conventional radiotherapy is associated with high doses to the salivary glands which causes xerostomia and adverse effects on quality of life. The study aims to investigate the potential of helical tomotherapy (Hi-Art Tomotherapy®) to preserve parotid function in head-and-neck cancer patients.Patients and Methods:Seven consecutive patients treated with helical tomotherapy at the UZ Brussel, Belgium, were included. During planning, priority was attributed to planning target volume (PTV) coverage: ≥ 95% of the dose must be delivered to ≥ 95% of the PTV. Elective nodal regions received 54 Gy (1.8 Gy/fraction). A dose of 70.5 Gy (2.35 Gy/fraction) was prescribed to the primary tumor and pathologic lymph nodes = simultaneous integrated boost scheme. If possible, the mean parotid dose was kept below 26 Gy. Salivary gland function was assessed by technetium scintigraphy.Results:There was a significant dose-response relationship between mean parotid dose and functional recuperation. If the mean dose was kept < 31 Gy, a recuperation of 75% can be expected at 12 months. The authors equally observed a significant correlation between salivary excretion (SE) and the percentage of parotid gland receiving a dose < 26 Gy (V26%). In order to preserve 75% of SE, 46% of the parotid volume should receive a dose < 26 Gy.Conclusion:With the use of helical tomography the parotid gland function can largely be preserved since the mean dose to the entire gland as well as glandular volume receiving > 26 Gy can be reduced.Hintergrund und Ziel:Die konventionelle Strahlentherapie zur Behandlung von Kopf-Hals-Tumoren steht häufig im Zusammenhang mit hohen Dosisbelastungen der Speicheldrüsen. Dies verursacht Xerostomie, welche eine Beeinträchtigung der Lebensqualität zur Folge hat. Das Ziel dieser Studie ist die Untersuchung eines möglichen Vorteils helikaler Tomotherapie für die Funktionserhaltung der Ohrspeicheldrüsen.Patienten und Methodik:Eingeschlossen wurden sieben aufeinanderfolgende Patienten mit einer Nachbeobachtungszeit von 12 Monaten, die am Universitätsklinikum Brüssel (UZ Brussel), Belgien, eine helikale Tomotherapie (Hi-Art Tomotherapy®) erhielten. Bei der Planung wurde der Abdeckung des Planungszielvolumens (PTV) höchste Priorität zuerkannt: ≥ 95% des PTV mussten ≥ 95% der Dosis erhalten. Elektive Lymphabstromgebiete erhielten 54 Gy (1,8 Gy/Fraktion). Die Zielvolumendosis im Primärtumor und in pathologischen Lymphknoten betrug 70,5 Gy (2,35 Gy/Fraktion) = simultaner integrierter Boost. Nach Möglichkeit wurde die mittlere Dosis der Parotiden auf 26 Gy beschränkt. Die Funktion der Speicheldrüsen wurde durch Technetium-Szintigraphie ermittelt.Ergebnisse:Es fand sich eine signifikante Dosis-Wirkungs-Beziehung zwischen der mittleren Dosis in der Parotis und der Wiederherstellung ihrer Funktion. Bei einer mittleren Dosis < 31 Gy kann mit einer 75%igen Wiederherstellung innerhalb von 12 Monaten gerechnet werden. Die Autoren beobachteten eine signifikante Korrelation zwischen Speichelfluss (SF) und prozentualem Anteil der Parotis, der eine Dosis < 26 Gy erhielt (V26%). Um 75% des SF zu erhalten, sollten 46% des Parotisvolumens eine Dosis < 26 Gy erhalten.Schlussfolgerung:Die Möglichkeit, mittels helikaler Tomotherapie die Funktion der Speicheldrüsen zu erhalten, hängt nicht nur von der applizierten mittleren Dosis, sondern auch vom prozentualen Anteil des Volumens ab, das < 26 Gy erhält.

Assessment of Intrafractional Movement and Internal Motion in Radiotherapy of Rectal Cancer Using Megavoltage Computed Tomography

PURPOSE The aim of this study was to provide estimates of setup and internal margins of patients treated for rectal carcinoma using helical tomotherapy and to assess possible margin adaptations. Using helical tomotherapy, highly conformal dose distributions can be created, and the integrated megavoltage computed tomography (MVCT) modality allows very precise daily patient positioning. In clinical protocols, however, margins originating from traditional setup procedures are still being applied. This work investigates whether this modality can aid in redefining treatment margins. METHODS AND MATERIALS Ten patients who were treated with tomotherapy underwent MVCT scanning before and after 10 treatments. Using automatic registration the necessary setup margin was investigated by means of bony landmarks. Internal margins were assessed by delineating and describing the mesorectal movement. RESULTS Based on bony landmarks, movement of patients during treatments was limited to 2.45 mm, 1.99 mm, and 1.09 mm in the lateral, longitudinal, and vertical direction, respectively. Systematic errors were limited to <1 mm. Measured movement of the mesorectal space was -1.6 mm (+/- 4.2 mm) and 0.1 mm (+/- 4.0 mm) for left and right lateral direction. In the antero-posterior direction, mean shifts were -2 mm (+/- 6.8 mm) and -0.4 mm (+/- 3.8 mm). Mean shifts in the cranio-caudal direction were respectively -3.2 mm (+/- 5.6 mm) and -3.2 mm (+/- 6.8 mm). CONCLUSIONS The use of the integrated MVCT on the tomotherapy system can minimize the setup margin for rectal cancer, and can also be used to adequately describe the internal margin allowing for direct treatment margin adaptation.

An overview of volumetric imaging technologies and their quality assurance for IGRT

Image-guided radiation therapy (IGRT) aims at frequent imaging in the treatment room during a course of radiotherapy, with decisions made on the basis of this information. The concept is not new, but recent developments and clinical implementations of IGRT drastically improved the quality of radiotherapy and broadened its possibilities as well as its indications. In general IGRT solutions can be classified in planar imaging, volumetric imaging using ionising radiation (kV- and MV- based CT) or non-radiographic techniques. This review will focus on volumetric imaging techniques applying ionising radiation with some comments on Quality Assurance (QA) specific for clinical implementation. By far the most important advantage of volumetric IGRT solutions is the ability to visualize soft tissue prior to treatment and defining the spatial relationship between target and organs at risk. A major challenge is imaging during treatment delivery. As some of these IGRT systems consist of peripheral equipment and others present fully integrated solutions, the QA requirements will differ considerably. It should be noted for instance that some systems correct for mechanical instabilities in the image reconstruction process whereas others aim at optimal mechanical stability, and the coincidence of imaging and treatment isocentre needs special attention. Some of the solutions that will be covered in detail are: (a) A dedicated CT-scanner inside the treatment room. (b) Peripheral systems mounted to the gantry of the treatment machine to acquire cone beam volumetric CT data (CBCT). Both kV-based solutions and MV-based solutions using EPIDs will be covered. (c) Integrated systems designed for both IGRT and treatment delivery. This overview will explain some of the technical features and clinical implementations of these technologies as well as providing an insight in the limitations and QA procedures required for each specific solution.