Variability in target delineation for cavernous sinus meningioma and anaplastic astrocytoma in stereotactic radiosurgery with Leksell Gamma Knife Perfexion

Stewart

J Applied Clin Med Phys

et al. 2019

BackgroundWe study the changes in organs‐at‐risk (OARs) morphology as contoured on serial MRIs during chemoradiation therapy (CRT) of glioblastoma (GBM). The dosimetric implication of assuming non‐deformable OAR changes and the accuracy and feasibility of semi‐automatic OAR contour propagation are investigated.MethodsFourteen GBM patients who were treated with adjuvant CRT for GBM prospectively underwent MRIs on fractions 0 (i.e., planning), 10, 20, and 1 month post last fraction of CRT. Three sets of OAR contours — (a) manual, (b) rigidly registered (static), and (c) semi‐automatically propagated — were compared using Dice similarity coefficient (DSC) and Hausdorff distance (HD). Dosimetric impact was determined by comparing the minimum dose to the 0.03 cc receiving the highest dose (D0.03 cc) on a clinically approved reference, non‐adapted radiation therapy plan.ResultsThe DSC between the manual contours and the static contours decreased significantly over time (fraction 10: [mean ± 1 SD] 0.78 ± 0.17, post 1 month: 0.76 ± 0.17, P = 0.02) while the HD (P = 0.74) and the difference in D0.03cc did not change significantly (P = 0.51). Using the manual contours as reference, compared to static contours, propagated contours have a significantly higher DSC (propagated: [mean ± 1 SD] 0.81 ± 0.15, static: 0.77 ± 0.17, P < 0.001), lower HD (propagated: 3.77 ± 1.8 mm, static: 3.96 ± 1.6 mm, P = 0.002), and a significantly lower absolute difference in D0.03cc (propagated: 101 ± 159 cGy, static: 136 ± 243 cGy, P = 0.019).ConclusionsNonrigid changes in OARs over time lead to different maximum doses than planned. By using semi‐automatic OAR contour propagation, OARs are more accurately delineated on subsequent fractions, with corresponding improved accuracy of the reported dose to the OARs.

Section: Discussionsupporting

confidence: 49%

Improved dosimetric accuracy with semi‐automatic contour propagation of organs‐at‐risk in glioblastoma patients undergoing chemoradiation

Stewart

J Applied Clin Med Phys

et al. 2019

“…The use of mathematical models able to predict the actual geometry of the cancerous area seems therefore highly necessary for creating a standard practice in this type of treatment. Furthermore, the model of cell infiltration proposed in this study could be used to guide the contouring of high-grade glioma targets for GKRS, since the variability in contouring of high-grade gliomas appears to be very high (27)(28)(29). In their study, Sandström et al (28) reported major and clinically significant differences in target delineation for an anaplastic astrocytoma case.…”

Section: Discussionmentioning

confidence: 88%

“…Furthermore, the model of cell infiltration proposed in this study could be used to guide the contouring of high-grade glioma targets for GKRS, since the variability in contouring of high-grade gliomas appears to be very high (27)(28)(29). In their study, Sandström et al (28) reported major and clinically significant differences in target delineation for an anaplastic astrocytoma case. This is especially troublesome in conformal techniques, such as in GKRS, where no margins are applied.…”

Section: Discussionmentioning

confidence: 88%

Impact of Tumour Cell Infiltration on Treatment Outcome in Gamma Knife Radiosurgery: A Modelling Study

et al. 2019

Self Cite

Background: High-grade gliomas with a widespread infiltration beyond the lesion detectable on diagnostic images are increasingly treated with Gamma Knife™ Radiosurgery (GKRS). The aim of this study was to assess the cell infiltration impact on the GKRS outcome for invasive gliomas. Materials and Methods: Tumor cell distribution was predicted using a novel algorithm whose computations are iterated until they reach an agreement with histopathology results. Treatment plans with different combinations of dose prescription (20 Gy at 50%-20% isodose) and targets [Gross Tumour Volume (GTV), zone 1 with 100%-60% of the GTV cell density and zone 2 with 60%-0% of the GTV cell density] were evaluated using standard conformity indexes (CI) and radiobiological parameters. Results: Considerable differences in terms of tumor control probability were found between plans having similar CI but different targets. Conclusion: To account for tumor cell infiltration outside the target is of key importance in GKRS and a radiobiological evaluation should accompany well-established CI. High-grade gliomas (grades III and IV) are brain tumours with widespread infiltration in the surrounding brain tissue (1). The treatment of this aggressive type of tumour usually involves surgery, radiotherapy, and chemotherapy (2, 3). Gamma Knife™ Radiosurgery (GKRS) alone or in conjunction with other techniques, has also been used for salvage treatment of recurrent high-grade gliomas (4, 5).

“…All of them agreed that the consistency of contouring can be improved by education and training, consensus guidelines and multi-institutional collaborations [ 30 – 33 ]. Also, a high degree of inter-observer variability was seen for brain SRS [ 34 , 35 ]. Deviations between treatment planning based on individual and consensus structures may show a potential influence on patient outcome.…”

Section: Discussionmentioning

confidence: 99%

Variability in spine radiosurgery treatment planning – results of an international multi-institutional study

et al. 2016

BackgroundThe aim of this study was to quantify the variability in spinal radiosurgery (SRS) planning practices between five international institutions, all member of the Elekta Spine Radiosurgery Research Consortium.MethodsFour institutions provided one representative patient case each consisting of the medical history, CT and MR imaging. A step-wise planning approach was used where, after each planning step a consensus was generated that formed the basis for the next planning step. This allowed independent analysis of all planning steps of CT-MR image registration, GTV definition, CTV definition, PTV definition and SRS treatment planning. In addition, each institution generated one additional SRS plan for each case based on intra-institutional image registration and contouring, independent of consensus results.ResultsAveraged over the four cases, image registration variability ranged between translational 1.1 mm and 2.4 mm and rotational 1.1° and 2.0° in all three directions. GTV delineation variability was 1.5 mm in axial and 1.6 mm in longitudinal direction averaged for the four cases. CTV delineation variability was 0.8 mm in axial and 1.2 mm in longitudinal direction. CTV-to-PTV margins ranged between 0 mm and 2 mm according to institutional protocol. Delineation variability was 1 mm in axial directions for the spinal cord. Average PTV coverage for a single fraction18 Gy prescription was 87 ± 5 %; Dmin to the PTV was 7.5 ± 1.8 Gy averaged over all cases and institutions. Average Dmax to the PRV_SC (spinal cord + 1 mm) was 10.5 ± 1.6 Gy and the average Paddick conformity index was 0.69 ± 0.06.ConclusionsResults of this study reflect the variability in current practice of spine radiosurgery in large and highly experienced academic centers. Despite close methodical agreement in the daily workflow, clinically significant variability in all steps of the treatment planning process was demonstrated. This may translate into differences in patient clinical outcome and highlights the need for consensus and established delineation and planning criteria.