Search

A new template technique has been developed for implanting hyperthermia catheters in the treatment of brain tumors. The technique utilizes an imaging template and a drill template which can be rigidly secured to the head with three skull screws. The anatomic and vascular information needed for hyperthermia treatment planning may be assessed with three-dimensional magnetic resonance (MR) imaging and angiography acquisitions which use a surface coil. In the companioning treatment planning system the catheter positions and lengths and the electrodes in the catheter can be interactively manipulated relative to the anatomy and vasculature. The visualization of the blood vessels relative to the template allows the minimization of the risk on intracranial hemorrhages. This template technique is useful for any brain tumor implants, especially when a large number of catheters are involved. A phantom test has shown that this procedure has an accuracy in the order of 1 mm provided that the MR-related geometry distortions are minimized. Index Terms - Brain implants, implantation template, interstitial hyperthermia, treatment planning.

Purpose: To quickly and automatically propagate organ contours from pretreatment to fraction images in magnetic resonance (MR)‐guided prostate external‐beam radiotherapy. Methods: Five prostate cancer patients underwent 20 fractions of image‐guided external‐beam radiotherapy on a 1.5 T MR‐Linac system. For each patient, a pretreatment T2‐weighted three‐dimensional (3D) MR imaging (MRI) scan was used to delineate the clinical target volume (CTV) contours. The same scan was repeated during each fraction, with the CTV contour being manually adapted if necessary. A convolutional neural network (CNN) was trained for combined image registration and contour propagation. The network estimated the propagated contour and a deformation field between the two input images. The training set consisted of a synthetically generated ground truth of randomly deformed images and prostate segmentations. We performed a leave‐one‐out cross‐validation on the five patients and propagated the prostate segmentations from the pretreatment to the fraction scans. Three variants of the CNN, aimed at investigating supervision based on optimizing segmentation overlap, optimizing the registration, and a combination of the two were compared to results of the open‐source deformable registration software package Elastix. Results: The neural networks trained on segmentation overlap or the combined objective achieved significantly better Hausdorff distances between predicted and ground truth contours than Elastix, at the much faster registration speed of 0.5 s. The CNN variant trained to optimize both the prostate overlap and deformation field, and the variant trained to only maximize the prostate overlap, produced the best propagation results. Conclusions: A CNN trained on maximizing prostate overlap and minimizing registration errors provides a fast and accurate method for deformable contour propagation for prostate MR‐guided radiotherapy. [ABSTRACT FROM AUTHOR]

To report an interim clinical evaluation of combined external beam irradiation (EBRT) and interstitial or regional hyperthermia in the treatment of locally advanced prostate cancer. From 1997 to 2001, 26 patients with T3-4/NX/0M0 prostate carcinoma were treated with a combination of conformal EBRT and hyperthermia. Fourteen patients received five weekly regional hyperthermia treatments within an optimization (phase II) study, using the coaxial transverse electrical magnetic system. Twelve patients received one interstitial hyperthermia treatment within a feasibility study (phase I), using the multi-electrode current source system. Irradiation was delivered using a conformal three-field technique, administering 70 Gy in 2-Gy fractions in 7 weeks. The mean initial prostate-specific antigen level was 26 ng/mL. Three patients had a T4 and 23 a T3 tumour; the tumours were classified as well (four), moderately (16) and poorly (six) differentiated. The mean follow-up was 36 months. In the combined treatments there was no toxicity of more than grade 2. In regional hyperthermia the mean index temperature (T90 and T50, i.e. exceeded by 90% and 50% of the measurements) was 40.2 °C and 40.8 °C, and for interstitial hyperthermia 39.4 °C and 41.8 °C, respectively. All patients survived; seven patients had a biochemical relapse (27%), three in the regional and four in the interstitial group. The actuarial probability of freedom from biochemical relapse was 70% at 36 months for all patients together, 79% for regional and 57% for interstitial. No factors were found that could be used to predict relapse. The clinical outcome in these patients with advanced localized prostate cancer seems to compare favourably with most series using irradiation alone, and the treatment caused no severe complications. [ABSTRACT FROM AUTHOR]

Intra-fraction motion of lesions in the thorax and abdomen due to respiration is an important source of uncertainty in SBRT. MR-Linacs provide the ability to continuously track the target and gate the radiation beam accordingly. Gating allows for smaller margins and can facilitate hypo-fractionation, but also lengthens the treatment due to the typically reduced delivery efficiency. Offering biofeedback (BF) and providing breathing instructions to the patient potentially helps counteracting the delivery efficiency penalty introduced by gating. In this work we present the first results of a patient study on a 1.5 T MR-Linac, using a prototype visual BF system, compatible with the vendor-provided motion management software. Experiments were conducted on a 1.5 T MR-Linac, equipped with clinical motion monitoring and gating functionality. 12 healthy volunteers (age: 24-79y, female/male: 6/6) were included in the study in phase 1, followed by 6 cancer patients (age: 30-74y, female/male: 2/4), in phase 2. Target motion was estimated in real-time based on 6 Hz sagittal/coronal interleaved 2D cine-MRI data. The resulting target position was streamed to in-house developed BF software and displayed to the study participants on an MRI-compatible monitor positioned at the rear of the MR-Linac bore, visible via an in-bore mirror. End-exhale and end-inhale breath hold (BH) workflows with 6 mm gating windows (GW) were simulated. Each study participant received BF for two consecutive 5-minute sessions. In phase 1, participants were used to select the preferred graphical user interface (GUI) from two GUI concepts (no data shown). In phase 2, patients received instructions and BF using a graph-style GUI to maintain a subject-determined BH (SDBH) as long as comfortable. The duration of each BH was not specified. SDBHs were conducted by three patients in end-exhale and by three patients in end-inhale. For the SDBH workflow, the average estimated delivery efficiency, defined as the ratio between the time spend within the GW and the total session time (5 min), was 49% (62%, 41%, 40%) for end-exhale SDBHs and 69% for end-inhale SDBHs (50%, 74%, 84%) and. Three patients showed a strong learning effect (+8, +6, +18 percentage points) between the subsequent sessions. Questionnaires revealed that all patients fully agreed that it was clear when to perform a BH and when to breathe normally. Two patients, performing an end-exhale SDBH, indicated that they might have found an end-inhale SDBH easier and more intuitive. Visual BF is expected to dramatically improve the delivery efficiency during gating treatments on the MR-Linac. Patient selection for BF systems is important, especially with regards to visual or cognitive impairments. Performance improvements over time in individual patients point towards the value of dedicated training sessions. [ABSTRACT FROM AUTHOR]

Poster: RTT track: Treatment planning and dose calculation / QC and QA PO-1868: In silico hypofractionation feasibility study for lymph node oligometastases SBRT on the MRI-linac D. Winkel, W.S.C. Eppinga, M.P.W. Intven, A.M. Werensteijn-Honingh, J. Hes, L.M.W. Snoeren, G.H. Bol, B.W. Raaymakers, I.M. Jürgenliemk-Schulz, P.S. Kroon. [Extracted from the article]

Teaching Lecture: Dosimetry and QA for MR-Linacs SP-0727: Dosimetry and QA for MR-Linacs B. Van Asselen, S.L. Hackett, S.J. Woodings, B.W. Raaymakers, J.W.H. Wolthaus. [Extracted from the article]

Poster discussion: RTT 2 PD-0672: Effect of a vacuum mattress on bone & target intra-fraction motion during MR-guided lymph node SBRT A.M. Werensteijn-honingh, P.S. Kroon, D. Winkel, C.G. Gadellaa-Van Hooijdonk, G.G. Sikkes, N.G.P.M. Vissers, W.S.C. Eppinga, M. Intven, B.W. Raaymakers, I.M. Jürgenliemk-Schulz. [Extracted from the article]

Poster discussion: PH: Adaptive radiotherapy and interfraction motion management 2 PD-0557: Biomechanical quality assurance criteria for deformable registration in image guided radiotherapy C. Zachiu, B. Denis de Senneville, M. Ries, B.W. Raaymakers. [Extracted from the article]

Proffered Papers: Proffered papers 18: Intra-fractional motion management OC-0341: Seminal vesicle motion tracking in 3D cine-MR during MR-Linac prostate treatments D. De Muinck Keizer, T. Willigenburg, M.D. Den Hartogh, J.R.N. Van der Voort van Zyp, B.W. Raaymakers, J.J.W. Lagendijk, H.C.J. De Boer. [Extracted from the article]

Poster Highlights: Poster highlights 17 CL: Palliation PH-0529: Prostate intrafraction motion during the full course of MR-guided radiotherapy sessions D. De Muinck Keizer, L.G.W. Kerkmeijer, T. Willigenburg, M.D. Den Hartogh, J.R.N. Van der Voort van Zyp, E.N. De Groot-van Breugel, B.W. Raaymakers, J.J.W. Lagendijk, H.C.J. De Boer. [Extracted from the article]