The impact of etiology in lesion-symptom mapping - A direct comparison between tumor and stroke

INTRODUCTION

Lesion-symptom mapping is a key tool in understanding the relationship between brain structures and behavior. However, the behavioral consequences of lesions from different etiologies may vary because of how they affect brain tissue and how they are distributed. The inclusion of different etiologies would increase the statistical power but has been critically debated. Meanwhile, findings from lesion studies are a valuable resource for clinicians and used across different etiologies. Therefore, the main objective of the present study was to directly compare lesion-symptom maps for memory and language functions from two populations, a tumor versus a stroke population.

METHODS

Data from two different studies were combined. Both the brain tumor (N = 196) and stroke (N = 147) patient populations underwent neuropsychological testing and an MRI, pre-operatively for the tumor population and within three months after stroke. For this study, we selected two internationally widely used standardized cognitive tasks, the Rey Auditory Verbal Learning Test and the Verbal Fluency Test. We used a state-of-the-art machine learning-based, multivariate voxel-wise approach to produce lesion-symptom maps for these cognitive tasks for both populations separately and combined.

RESULTS

Our lesion-symptom mapping results for the separate patient populations largely followed the expected neuroanatomical pattern based on previous literature. Substantial differences in lesion distribution hindered direct comparison. Still, in brain areas with adequate coverage in both groups, considerable LSM differences between the two populations were present for both memory and fluency tasks. Post-hoc analyses of these locations confirmed that the cognitive consequences of focal brain damage varied between etiologies.

CONCLUSION

The differences in the lesion-symptom maps between the stroke and tumor population could partly be explained by differences in lesion volume and topography. Despite these methodological limitations, both the lesion-symptom mapping results and the post-hoc analyses confirmed that etiology matters when investigating the cognitive consequences of lesions with lesion-symptom mapping. Therefore, caution is advised with generalizing lesion-symptom results across etiologies.

RADT-08. DOSIMETRIC FEASIBILITY OF DIRECT POST-OPERATIVE MRI-LINAC-BASED STEREOTACTIC RADIOSURGERY FOR RESECTION CAVITIES OF BRAIN METASTASES

Background

Post-operative stereotactic radiosurgery (SRS) of patients with brain metastases with single resection cavities is typically planned on a post-recovery MRI, 4-6 weeks after resection. However, meanwhile the intracranial metastasis may (re-)grow, and postponing adjuvant systemic treatment increases chance on extracranial progression as well. Anticipating direct post-operative SRS to minimize this interval would enable rapid start of systemic therapy. In this study, we considered treatment with MRI-Linac (MRL) SRS, because of the possibility to execute the post-operative MRI and SRS treatment combined on the MRL instead of on two separate systems, improving logistics and increasing patient comfort. However, it is unclear whether MRL-based SRS may be feasible from a dosimetric perspective. This study aims to shed light on the dosimetric feasibility of MRL-based SRS.

METHODS

We simulated MRL treatments including thirteen patients with resectable single brain metastases treated with single fraction CT-Linac (CTL) SRS. We therefore contoured direct post-operative gross tumor volumes (GTV) and compared them to post-recovery MRI GTV. Next, we compared a non-coplanar VMAT technique for CTL (ncVMAT) to a coplanar IMRT technique for MRL (cIMRT), creating three plans per patient: a ncVMAT plan and a cIMRT plan for the direct post-operative GTV, and a post-recovery ncVMAT plan as current clinical standard. RESULTSCompared to GTVs defined on direct post-operative MRI, on post-recovery MRI 15.5% of cavities shrunk by > 2cc, and 46% expanded by > 2cc. Although direct post-operative ncVMAT plans had lower median gradient index and higher median V3Gy of the skin, they were clinically acceptable according to clinical guidelines.

CONCLUSION

Although slightly inferior to non-coplanar CTL plans, direct post-operative MRL-based SRS for resection cavities of brain metastases is dosimetrically acceptable, at the trade-off between increased patient comfort and logistics. Additionally, MRL-based SRS enables substantially earlier start with adjuvant systemic therapies, thereby maximizing tumor control.

P01.04.A Lesion-symptom mapping based on stroke or glioma: etiology matters!

Background

Lesion-symptom mapping is a key tool in understanding the relationship between brain structures and behavior. However, the behavioral consequences of lesions from different etiologies may vary as a result of how they affect brain tissue, and how they are distributed. The inclusion of different etiologies would increase the statistical power and improve generalizability of results, but has been critically debated. Findings from lesion studies are a resource for clinicians and used across different etiologies. This study directly compared lesion-symptom maps (LSM) between two populations (diffuse glioma versus ischemic stroke) in order to investigate if brain areas with adequate coverage in both groups, show topographical overlap in lesion-symptom associations.

Material and Methods

Data from two studies were combined. Both the glioma (N = 196, WHO grade 2-4) and stroke (N = 147) population underwent neuropsychological testing and an MRI, pre-operatively for the tumor population and within three months after stroke. For the purpose of this study, we selected two widely used cognitive tasks, the Rey Auditory Verbal Learning Test and the verbal fluency test. We used a state-of-the-art machine learning-based, multivariate voxel-wise approach to produce LSM for these cognitive tasks for both populations separately.

Results

For both tumor and stroke, our etiology-specific LSM largely followed the expected neuroanatomical pattern based on previous literature. Nevertheless, for both tasks substantial differences in LSM-results were present between the populations in brain areas with adequate coverage in both groups, though we did find similar white matter tracts involved in memory and semantic fluency performance across etiologies. Post-hoc analyses of these locations confirmed an interaction between lesion presence and etiology for a majority of these regions; damage by a tumor, but not a stroke, was related to worse cognitive performance for these regions.

Conclusion

This study provides the first direct comparison of LSM in a large cohort of patients. Differences in LSM were found between the glioma and stroke group, confirming that etiology matters when investigating the cognitive consequence of lesions. These differences could partly be explained by differences in lesion volume and topography. Nonetheless, the pattern shown by glioma patients on the group level is consistent with localizations found in earlier studies on both stroke and glioma patients using different techniques. While glioma series thus can be used to provide converging evidence about functional localization, we do suggest that findings from LSM studies in neuro-oncological populations should be considered as cause-specific. Findings from functional localization research from non-glioma populations should only be applied to a glioma population with caution.

Synthetic CT for single-fraction neoadjuvant partial breast irradiation on an MRI-linac

A synthetic computed tomography (sCT) is required for daily plan optimization on an MRI-linac. Yet, only limited information is available on the accuracy of dose calculations on sCT for breast radiotherapy. This work aimed to (1) evaluate dosimetric accuracy of treatment plans for single-fraction neoadjuvant partial breast irradiation (PBI) on a 1.5 T MRI-linac calculated on a) bulk-density sCT mimicking the current MRI-linac workflow and b) deep learning-generated sCT, and (2) investigate the number of bulk-density levels required. For ten breast cancer patients we created three bulk-density sCTs of increasing complexity from the planning-CT, using bulk-density for: (1) body, lungs, and GTV (sCT_BD1); (2) volumes for sCT_BD1plus chest wall and ipsilateral breast (sCT_BD2); (3) volumes for sCT_BD2plus ribs (sCT_BD3); and a deep learning-generated sCT (sCT_DL) from a 1.5 T MRI in supine position. Single-fraction neoadjuvant PBI treatment plans for a 1.5 T MRI-linac were optimized on each sCT and recalculated on the planning-CT. Image evaluation was performed by assessing mean absolute error (MAE) and mean error (ME) in Hounsfield Units (HU) between the sCTs and the planning-CT. Dosimetric evaluation was performed by assessing dose differences, gamma pass rates, and dose-volume histogram (DVH) differences. The following results were obtained (median across patients for sCT_BD1/sCT_BD2/sCT_BD3/sCT_DLrespectively): MAE inside the body contour was 106/104/104/75 HU and ME was 8/9/6/28 HU, mean dose difference in the PTV_GTVwas 0.15/0.00/0.00/-0.07 Gy, median gamma pass rate (2%/2 mm, 10% dose threshold) was 98.9/98.9/98.7/99.4%, and differences in DVH parameters were well below 2% for all structures except for the skin in the sCT_DL. Accurate dose calculations for single-fraction neoadjuvant PBI on an MRI-linac could be performed on both bulk-density and deep learning sCT, facilitating further implementation of MRI-guided radiotherapy for breast cancer. Balancing simplicity and accuracy, sCT_BD2showed the optimal number of bulk-density levels for a bulk-density approach.

MR-guidance in clinical reality: current treatment challenges and future perspectives

Magnetic Resonance-guided radiotherapy (MRgRT) marks the beginning of a new era. MR is a versatile and suitable imaging modality for radiotherapy, as it enables direct visualization of the tumor and the surrounding organs at risk. Moreover, MRgRT provides real-time imaging to characterize and eventually track anatomical motion. Nevertheless, the successful translation of new technologies into clinical practice remains challenging. To date, the initial availability of next-generation hybrid MR-linac (MRL) systems is still limited and therefore, the focus of the present preview was on the initial applicability in current clinical practice and on future perspectives of this new technology for different treatment sites.MRgRT can be considered a groundbreaking new technology that is capable of creating new perspectives towards an individualized, patient-oriented planning and treatment approach, especially due to the ability to use daily online adaptation strategies. Furthermore, MRL systems overcome the limitations of conventional image-guided radiotherapy, especially in soft tissue, where target and organs at risk need accurate definition. Nevertheless, some concerns remain regarding the additional time needed to re-optimize dose distributions online, the reliability of the gating and tracking procedures and the interpretation of functional MR imaging markers and their potential changes during the course of treatment. Due to its continuous technological improvement and rapid clinical large-scale application in several anatomical settings, further studies may confirm the potential disruptive role of MRgRT in the evolving oncological environment.

Single dose partial breast irradiation using an MRI linear accelerator in the supine and prone treatment position

Background

In selected patients with early-stage and low-risk breast cancer, an MRI-linac based treatment might enable a radiosurgical, non-invasive alternative for current standard breast conserving therapy.

Aim

To investigate whether single dose accelerated partial breast (APBI) to the intact tumor in both the prone and supine radiotherapy positions on the MRI-linac is dosimetrically feasible with respect to predefined coverage and organs at risk (OAR) constraints.

Material & methods

For 20 patients with cTis or low-risk cT1N0M0 non-lobular breast carcinoma, previously treated with single dose preoperative APBI in the supine (n = 10) or prone (n = 10) position, additional intensity modulated radiotherapy plans with 7 coplanar beams in the presence of a 1.5T magnetic field were generated. A 20 Gy and 15 Gy dose was prescribed to the gross tumor and clinical target volume, respectively. The percentage of plans achieving predefined organ at risk (OAR) constraints, currently used in clinical practice, was assessed. Dosimetry differences between the prone versus supine approach and the MRI-linac versus clinically delivered plans were evaluated.

Results

All MRI-linac plans met the coverage and predefined OAR constraints. The prone approach appeared to be more favorable with respect to the chest wall, and ipsilateral lung dose compared to the supine position. No dosimetric differences were observed for the ipsilateral breast. No treatment position was clearly more beneficial for the skin or heart, since dosimetry varied among parameters. Overall, the MRI-linac and clinical plans were comparable, with minor absolute dosimetric differences.

Conclusion

MRI-linac based single dose APBI to the intact tumor is a promising and a dosimetrically feasible strategy in patients with low-risk breast cancer. Preliminary OAR dosimetry favored the prone radiotherapy position.

Inter-observer agreement in GTV delineation of bone metastases on CT and impact of MR imaging: A multicenter study

BACKGROUND AND PURPOSE

The use of Stereotactic Body Radiotherapy (SBRT) for bone metastases is increasing rapidly. Therefore, knowledge of the inter-observer differences in tumor volume delineation is essential to guarantee precise dose delivery. The aim of this study is to compare inter-observer agreement in bone metastases delineated on different imaging modalities.

MATERIAL AND METHODS

Twenty consecutive patients with bone metastases treated with SBRT were selected. All patients received CT and MR imaging in treatment position prior to SBRT. Five observers from three institutions independently delineated gross tumor volume (GTV) on CT alone, CT with co-registered MRI and MRI alone. Four contours per imaging modality per patient were available, as one set of contours was shared by 2 observers. Inter-observer agreement, expressed in generalized conformity index [CIgen], volumes of contours and contours center of mass (COM) were calculated per patient and imaging modality.

RESULTS

Mean GTV delineated on MR (45.9±52.0cm³) was significantly larger compared to CT-MR (40.2±49.4cm³) and CT (34.8±41.8cm³). A considerable variation in CIgen was found on CT (mean 0.46, range 0.15-0.75) and CT-MRI (mean 0.54, range 0.17-0.71). The highest agreement was found on MRI (mean 0.56, range 0.20-0.77). The largest variations of COM were found in anterior-posterior direction for all imaging modalities.

CONCLUSIONS

Large inter-observer variation in GTV delineation exists for CT, CT-MRI and MRI. MRI-based GTV delineation resulted in larger volumes and highest consistency between observers.

Redefining radiotherapy for early-stage breast cancer with single dose ablative treatment: a study protocol

BACKGROUND

A shift towards less burdening and more patient friendly treatments for breast cancer is currently ongoing. In low-risk patients with early-stage disease, accelerated partial breast irradiation (APBI) is an alternative for whole breast irradiation following breast-conserving surgery. MRI-guided single dose ablative APBI has the potential to offer a minimally burdening, non-invasive treatment that could replace current breast-conserving therapy.

METHODS

The ABLATIVE study is a prospective, single arm, multicenter study evaluating preoperative, single dose, ablative radiation treatment in patients with early-stage breast cancer. Patients with core biopsy proven non-lobular invasive breast cancer, (estrogen receptor positive, Her2 negative, maximum tumor size 3.0 cm on diagnostic MRI) and a negative sentinel node biopsy are eligible. Radiotherapy (RT) planning will be performed using a contrast enhanced (CE) planning CT-scan, co-registered with a CE-MRI, both in supine RT position. A total of twenty-five consecutive patients will be treated with a single ablative RT dose of 20 Gy to the tumor and 15 Gy to the tumorbed. Follow-up MRIs are scheduled within 1 week, 2, 4 and 6 months after single-dose RT. Breast-conserving surgery is scheduled at six months following RT. Primary study endpoint is pathological complete response. Secondary study endpoints are the radiological response and toxicity. Furthermore, patients will fill out questionnaires on quality of life and functional status. Cosmetic outcome will be evaluated by the treating radiation oncologist, patient and 'Breast Cancer Conservation Treatment cosmetic results' software. Recurrence and survival rates will be assessed. The patients will be followed up to 10 years after diagnosis. If patients give additional informed consent, a biopsy and a part of the irradiated specimen will be stored at the local Biobank and used for future research on radiotherapy response associated genotyping.

DISCUSSION

The ABLATIVE study evaluates MRI-guided single dose ablative RT in patients with early-stage breast cancer, aiming at a less burdening and non-invasive alternative for current breast-conserving treatment.

TRIAL REGISTRATION

ClinicalTrials.gov registration number NCT02316561 . The trial was registrated prospectively on October 10th 2014.

Abstract P5-14-17: Post-lumpectomy tumorbed delineation for breast boost or partial breast irradiation: The influence of additional MRI and CT imaging

Rationale/Purpose

In early stage breast cancer patients, most recurrences occur in the vicinity of the original tumor location. Therefore, after initial lumpectomy it is important to accurately delineate the tumorbed (TB) area for breast boost and partial breast irradiation on the planning-CT scan. However, consistency in TB delineation among radiation oncologists is low on standard CT imaging.

The purpose of this study was to determine whether additional pre- and postoperative MRI and CT imaging could increase consistency in standard CT-guided target volume delineation among radiation oncologists.

Methods

Fourteen cT1-2 patients underwent MRI and CT imaging in supine radiotherapy position before and after lumpectomy. TBs were delineated by 4 breast radiation oncologists following delineation guidelines on the standard postoperative planning-CT alone, and planning-CT registered to 1) postoperative MRI (T1 (with and without fat suppression) and T2 weighted sequences) 2) preoperative contrast-enhanced (CE) CT, and 3) preoperative CE-MRI (T1 weighted sequence with fat suppression). Consistency was defined by the conformity index (CI), which was calculated by dividing the encompassing volume of each observer pair, by the volume of overlap for each observer pair. Furthermore, volumes and the distance between centres of mass (dCOM) of the delineated TBs were determined. A Wilcoxon signed-rank test was performed to compare variables between different imaging modalities, with a significance level of a = 0.05.

Results

Results of the analysis are shown in Table 1. Addition of a postoperative MRI to the standard postoperative planning CT did not influence the CI (p = 0.176) or dCOM (p = 0.110). However, the TB volumes increased significantly with a median increase of 6 cm3 (p<0.001). Addition of a preoperative CT or MRI increased the CI by 0.01 and 0.02 (both p<0.001). Furthermore, preoperative CT and MRI increased dCOM (p = 0.004 and p = 0.001) and volumes (both p<0.001).

Table 1 medianrange  p-valueVolume (cm3)     CT224-934 CT + postoperative MRI283-964<0.001CT + preoperative CT266-933<0.001CT + preoperative MRI257-933<0.001      Conformity index     CT0.570.00-0.90 CT + postoperative MRI0.610.00-0.890.176CT + preoperative CT0.580.00-0.90<0.001CT + preoperative MRI0.590.00-0.89<0.001      dCOM (mm)     CT50-53 CT + postoperative MRI40-520.110CT + preoperative CT31-420.004CT + preoperative MRI50-480.001

Conclusion

Although significant, the addition of postoperative MRI, preoperative CE-CT or preoperative CE-MRI did not result in a clinically relevant improvement of the consistency in postoperative CT-guided TB delineation among radiation oncologists. Furthermore, target volumes increased with all imaging modalities.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-14-17.

Characterization of late radiation effects in the rat thoracolumbar spinal cord by MR imaging using USPIO

The aim of this study was to detect late radiation effects in the rat spinal cord using MR imaging with ultra-small particles of iron oxide (USPIO) contrast agent to better understand the development of late radiation damage with emphasis on the period preceding neurological signs. Additionally, the role of an inflammatory reaction was assessed by measuring macrophages that internalized USPIO. T2-weighted spin echo MR measurements were performed at 7T in six rats before paresis was expected (130-150 days post-irradiation, early group), and in six paretic rats (150-190 days post-irradiation, late group). Measurements were performed before, directly after and, only in the early group, 40 h after USPIO administration and compared with histology. In the early group, MR images showed focal regions in grey matter (GM) and white matter (WM) with signal intensity reduction after USPIO injection. Larger lesions with contrast enhancement were located in and around edematous GM of three animals of the early group and five of the late group. Forty hours after injection, additional lesions in WM, GM and nerve roots appeared in animals with GM edema. In the late paretic group, MR imaging showed WM necrosis adjacent to areas with large contrast enhancement. In conclusion, detection of early focal lesions was improved by contrast administration. In the animals with extended radiation damage, large hypo-intense regions appeared due to USPIO, which might be attributed to blood spinal cord barrier breakdown, but the involvement of blood-derived iron-loaded macrophages could not be excluded.