Individual lymph nodes: “See it and Zap it” Winkel, Dennis; Werensteijn-Honingh, Anita M.; Kroon, Petra S. ...
Clinical and translational radiation oncology,
09/2019, Letnik:
18
Journal Article
Recenzirano
Odprti dostop
•10 patients with lymph node oligometastases received SBRT using a 1.5T MR-linac.•Impact of planning strategies “adapt to shape” and “adapt to position” was compared.•ATS resulted in a slightly ...better target coverage compared to ATP.•A 3 mm isotropic GTV-PTV margin was adequate.•“Seeing and Zapping” metastatic lymph nodes comes within reach for MRI-guided SBRT.
With magnetic resonance imaging (MRI)-guided radiotherapy systems such as the 1.5T MR-linac the daily anatomy can be visualized before, during and after radiation delivery. With these treatment systems, seeing metastatic nodes with MRI and zapping them with stereotactic body radiotherapy (SBRT) comes into reach. The purpose of this study is to investigate different online treatment planning strategies and to determine the planning target volume (PTV) margin needed for adequate target coverage when treating lymph node oligometastases with SBRT on the 1.5T MR-linac.
Ten patients were treated for single pelvic or para-aortic lymph node metastases on the 1.5T MR-linac with a prescribed dose of 5x7Gy with a 3 mm isotropic GTV- PTV margin. Based on the daily MRI and actual contours, a completely new treatment plan was generated for each session (adapt to shape, ATS). These were compared with plans optimized on pre-treatment CT contours after correcting for the online target position (adapt to position, ATP). At the end of each treatment session, a post-radiation delivery MRI was acquired on which the GTV was delineated to evaluate the GTV coverage and PTV margins.
The median PTV V35Gy was 99.9% 90.7–100% for the clinically delivered ATS plans compared to 93.6% 76.3–99.7% when using ATP. The median GTV V35Gy during radiotherapy delivery was 100% 98–100% on the online planning and post-delivery MRIs for ATS and 100% 93.9–100% for ATP, respectively. The applied 3 mm isotropic PTV margin is considered adequate.
For pelvic and para-aortic metastatic lymph nodes, online MRI-guided adaptive treatment planning results in adequate PTV and GTV coverage when taking the actual patient anatomy into account (ATS). Generally, GTV coverage remained adequate throughout the treatment session for both adaptive planning strategies. “Seeing and zapping” metastatic lymph nodes comes within reach for MRI-guided SBRT.
At our institution a treatment for kidney tumours with an MRI-Linac is under development. In order to set inclusion criteria for this treatment the anatomical eligibility criteria and the influence ...of the motion compensation strategy on the delivered dose should be known. Twenty patients with a renal lesion underwent an MR-scan to image the kidney. Static treatment plans were made and the doses to the organs at risk were evaluated. Furthermore, to calculate the influence of remnant motion in a gated treatment, a convolution of the static dose plan with the residual motion in a gating window was done. For ten patients (50%) a static plan within the dose constraints could be obtained. For all patients where the kidney constraint was obeyed in the static plan, the dose to the gross tumour volume (GTV) and the ipsilateral kidney remained within limits for residual motion in a gating window up to and including 12 mm. For four patients (20%) no static plan without violation of the constraint to the ipsilateral kidney could be made. One of these patients had a tumour of 73 mm in the upper pole and the other patients had a tumour of at least 30 mm in the mid pole. In 6 patients (30%), where the bowels were within the planning target volume, the maximum dose to the bowels was above the limit used. Patient specific assessment might degrade this violation. For tumours smaller than 30 mm a clinically acceptable plan could be created. For other patients the feasibility depends on the geometry of the GTV and kidney. Neither the GTV coverage nor the ipsilateral kidney dose is compromised by breathing motion for gating with a gating window up to and including 12 mm.
The heart is important in radiotherapy either as target or organ at risk. Quantitative T1 and T2 cardiac magnetic resonance imaging (qMRI) may aid in target definition for cardiac radioablation, and ...imaging biomarker for cardiotoxicity assessment. Hybrid MR-linac devices could facilitate daily cardiac qMRI of the heart in radiotherapy. The aim of this work was therefore to enable cardiac-synchronized T1 and T2 mapping on a 1.5 T MR-linac and test the reproducibility of these sequences on phantoms and in vivo between the MR-linac and a diagnostic 1.5 T MRI scanner.
Cardiac-synchronized MRI was performed on the MR-linac using a wireless peripheral pulse-oximeter unit. Diagnostically used T1 and T2 mapping sequences were acquired twice on the MR-linac and on a 1.5 T MR-simulator for a gel phantom and 5 healthy volunteers in breath-hold. Phantom T1 and T2 values were compared to gold-standard measurements and percentage errors (PE) were computed, where negative/positive PE indicate underestimations/overestimations. Manually selected regions-of-interest were used for in vivo intra/inter scanner evaluation.
Cardiac-synchronized T1 and T2 qMRI was enabled after successful hardware installation on the MR-linac. From the phantom experiments, the measured T1/T2 relaxation times had a maximum percentage error (PE) of −4.4%/−8.8% on the MR-simulator and a maximum PE of −3.2%/+8.6% on the MR-linac. Mean T1/T2 of the myocardium were 1012±34/51±2 ms on the MR-simulator and 1034±42/51±1 ms on the MR-linac.
Accurate cardiac-synchronized T1 and T2 mapping is feasible on a 1.5 T MR-linac and might enable novel plan adaptation workflows and cardiotoxicity assessments.
Rectal cancer patients that show a pathological complete response (pCR) after neo-adjuvant chemo-radiotherapy, have better prognosis. To increase pCR rates several studies escalate the tumor ...irradiation dose. However, due to lacking tumor contrast on online imaging techniques, no direct tumor setup can be performed and large boost margins are needed to ensure tumor coverage. The purpose of this study was to evaluate the feasibility of performing a setup on rectal wall for rectal cancer boost radiotherapy, thereby using rectal wall nearby the tumor as tumor position surrogate.
For sixteen patients, daily MRI's were performed during 1 week of radiotherapy. On each of these images, tumor and rectum were delineated. Residual displacements were determined per surface voxel after setup on bony anatomy or nearby rectal wall and setup errors for both setups were compared. Furthermore for every rectal wall voxel nearby the tumor, displacement was compared with the closest tumor point and correlation was determined.
Mean (SD) setup error was 2.7 mm (3.3 mm) and 2.2 mm (3.2 mm) after setup on bony anatomy and rectal wall respectively. Nevertheless, similar PTV-margin estimates i.e. 95th percentile distances, were found; 8.0 mm. Also, a merely moderate correlation; ρ = 0.66 was found between rectal wall and tumor displacement. Further investigation into tumor and rectal mobility differences showed that the rectal wall lacks appropriate anatomical landmarks to find true displacements, especially to capture motion along the rectal wall.
Setup on rectal wall slightly reduces mean setup errors but requires a similar PTV-margin as compared to setup on bony anatomy. Rectal mobility might be similar to tumor mobility, but due the absence of anatomical landmarks in the rectum, displacements along the rectal wall are not detected on current online imaging. Therefore, to further reduce tumor position uncertainties, direct or indirect online tumor visualization is needed.
Conventional treatment planning in intensity‐modulated radiation therapy (IMRT) is a trial‐and‐error process that usually involves tedious tweaking of optimization parameters. Here, we present an ...algorithm that automates part of this process, in particular the adaptation of voxel‐based penalties within normal tissue. Thereby, the proposed algorithm explicitly considers a priori known physical limitations of photon irradiation. The efficacy of the developed algorithm is assessed during treatment planning studies comprising 16 prostate and 5 head and neck cases. We study the eradication of hot spots in the normal tissue, effects on target coverage and target conformity, as well as selected dose volume points for organs at risk. The potential of the proposed method to generate class solutions for the two indications is investigated. Run‐times of the algorithms are reported. Physically constrained voxel‐based penalty adaptation is an adequate means to automatically detect and eradicate hot‐spots during IMRT planning while maintaining target coverage and conformity. Negative effects on organs at risk are comparably small and restricted to lower doses. Using physically constrained voxel‐based penalty adaptation, it was possible to improve the generation of class solutions for both indications. Considering the reported run‐times of less than 20 s, physically constrained voxel‐based penalty adaptation has the potential to reduce the clinical workload during planning and automated treatment plan generation in the long run, facilitating adaptive radiation treatments.
PACS number(s): 87.55.de
The superior soft tissue contrast provided by magnetic resonance (MR) images on the 1.5T MR-linac allows for the incorporation of patient anatomy information. In this retrospective case study, we ...present the simulated dosimetric effects and timings of full online replanning as compared to the five plan adaptation methods currently available on the 1.5T MR-linac treatment system. For this case, it is possible to create treatment plans with all six methods within a time slot suitable for an online treatment procedure. However, large dosimetric differences between the plan adaptation methods and full online replanning are present with regards to target coverage and dose to organs at risk (OARs).
Abstract Background and purpose To evaluate volume changes and position shifts and their contribution to treatment margins of pelvic and para-aortic lymph nodes during Intensity Modulated Radiation ...Therapy (IMRT) for advanced cervical cancer. Materials and methods Seventeen patients with visible nodes on MR images underwent T2-weighted MR scans before and weekly during the course of IMRT. Thirty-nine pelvic and para-aortic nodes were delineated on all scans. Margins accommodating for volume and position changes were taken from the boundaries of the nodal volumes in the six main directions. Results Nodal volume regression from the pre-treatment situation to week 4 was 58% on average (range: 11.7% increase to 100% decrease). Nodal volumes partly increased between the pre-treatment scans and the scans in weeks 1–3, but in week 4 all nodes except one had regressed. Around the nodal volumes manually derived ITV margins accounting for volume changes and position shifts of 7.0, 4.0, 7.0, 8.0, 7.0 and 9.0 mm to the medial, lateral, anterior, posterior, superior and inferior directions were needed to cover 95% of all nodes. Conclusions We used weekly MR scans to derive inhomogeneous margins that accommodate for nodal volume and position changes during treatment. These margins should be taken into consideration when planning external beam radiotherapy (EBRT) boosts, especially for highly conformal boosting techniques.
•Dose distributions for prostate SBRT were comparable between MRI-linac and conventional plans.
Recently, intermediate and high-risk prostate cancer patients have been treated in a multicenter phase ...II trial with extremely hypofractionated prostate radiotherapy (hypo-FLAME trial). The purpose of the current study was to investigate whether a 1.5 T magnetic resonance imaging guided linear accelerator (MRI-linac) could achieve complex dose distributions of a quality similar to conventional linac state-of-the-art prostate treatments.
The clinically delivered treatment plans of 20 hypo-FLAME patients (volumetric modulated arc therapy, 10 MV, 5 mm leaf width) were included. Prescribed dose to the prostate was 5 × 7 Gy, with a focal tumor boost up to 5 × 10 Gy. MRI-linac treatment plans (intensity modulated radiotherapy, 7 MV, 7 mm leaf width, fixed collimator angle and 1.5 T magnetic field) were calculated. Dose distributions were compared.
In both conventional and MRI-linac treatment plans, the V35Gy to the whole prostate was >99% in all patients. Mean dose to the gross tumor volume was 45 Gy for conventional and 44 Gy for MRI-linac plans, respectively. Organ at risk doses were met in the majority of plans, except for a rectal V35Gy constraint, which was exceeded in one patient, by 1 cc, for both modalities. The bladder V32Gy and V28Gy constraints were exceeded in two and one patient respectively, for both modalities.
Planning of stereotactic radiotherapy with focal ablative boosting in prostate cancer on a high field MRI-linac is feasible with the current MRI-linac properties, without deterioration of plan quality compared to conventional treatments.
Current treatments for renal cell carcinoma have a high complication rate due to the invasiveness of the treatment. With the MRI-linac it may be possible to treat renal tumours non-invasively with ...high-precision radiotherapy. This is expected to reduce complications. To deliver a static dose distribution, radiation gating will be used. In this study the reproducibility and efficiency of free breathing gating and a breath hold treatment of the kidney was investigated. For 15 patients with a renal lesion the kidney motion during 2 min of free breathing and 10 consecutive expiration breath holds was studied with 2D cine MRI. The variability in kidney expiration position and treatment efficiency for gating windows of 1 to 20 mm was measured for both breathing patterns. Additionally the time trend in free breathing and the variation in expiration breath hold kidney position with baseline shift correction was determined. In 80% of the patients the variation in expiration position during free breathing is smaller than 2 mm. No clinically relevant time trends were detected. The variation in expiration breath hold is for all patients larger than the free breathing expiration variation. Gating on free breathing is, for gating windows of 1 to 5 mm more efficient than breath hold without baseline correction. When applying a baseline correction to the breath hold it increases the treatment efficiency. The kidney position is more reproducible in expiration free breathing than non-guided expiration breath hold. For small gating windows it is also more time efficient. Since free breathing also seems more comfortable for the patients it is the preferred breathing pattern for MRI-Linac treatments of the kidney.
The heart is important in radiotherapy either as target or organ at risk. Quantitative T
and T
cardiac magnetic resonance imaging (qMRI) may aid in target definition for cardiac radioablation, and ...imaging biomarker for cardiotoxicity assessment. Hybrid MR-linac devices could facilitate daily cardiac qMRI of the heart in radiotherapy. The aim of this work was therefore to enable cardiac-synchronized T
and T
mapping on a 1.5 T MR-linac and test the reproducibility of these sequences on phantoms and
between the MR-linac and a diagnostic 1.5 T MRI scanner.
Cardiac-synchronized MRI was performed on the MR-linac using a wireless peripheral pulse-oximeter unit. Diagnostically used T
and T
mapping sequences were acquired twice on the MR-linac and on a 1.5 T MR-simulator for a gel phantom and 5 healthy volunteers in breath-hold. Phantom T
and T
values were compared to gold-standard measurements and percentage errors (PE) were computed, where negative/positive PE indicate underestimations/overestimations. Manually selected regions-of-interest were used for
intra/inter scanner evaluation.
Cardiac-synchronized T
and T
qMRI was enabled after successful hardware installation on the MR-linac. From the phantom experiments, the measured T
/T
relaxation times had a maximum percentage error (PE) of -4.4%/-8.8% on the MR-simulator and a maximum PE of -3.2%/+8.6% on the MR-linac. Mean T
/T
of the myocardium were 1012
34/51
2 ms on the MR-simulator and 1034
42/51
1 ms on the MR-linac.
Accurate cardiac-synchronized T
and T
mapping is feasible on a 1.5 T MR-linac and might enable novel plan adaptation workflows and cardiotoxicity assessments.
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