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

Overall survival prediction for high-grade glioma patients using mathematical modeling of tumor cell infiltration

PURPOSE

This study aimed at applying a mathematical framework for the prediction of high-grade gliomas (HGGs) cell invasion into normal tissues for guiding the clinical target delineation, and at investigating the possibility of using tumor infiltration maps for patient overall survival (OS) prediction.

MATERIAL & METHODS

A model describing tumor infiltration into normal tissue was applied to 93 HGG cases. Tumor infiltration maps and corresponding isocontours with different cell densities were produced. ROC curves were used to seek correlations between the patient OS and the volume encompassed by a particular isocontour. Area-Under-the-Curve (AUC) values were used to determine the isocontour having the highest predictive ability. The optimal cut-off volume, having the highest sensitivity and specificity, for each isocontour was used to divide the patients in two groups for a Kaplan-Meier survival analysis.

RESULTS

The highest AUC value was obtained for the isocontour of cell densities 1000 cells/mm3 and 2000 cells/mm3, equal to 0.77 (p < 0.05). Correlation with the GTV yielded an AUC of 0.73 (p < 0.05). The Kaplan-Meier survival analysis using the 1000 cells/mm3 isocontour and the ROC optimal cut-off volume for patient group selection rendered a hazard ratio (HR) of 2.7 (p < 0.05), while the GTV rendered a HR = 1.6 (p < 0.05).

CONCLUSION

The simulated tumor cell invasion is a stronger predictor of overall survival than the segmented GTV, indicating the importance of using mathematical models for cell invasion to assist in the definition of the target for HGG patients.

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

Background

We 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.

Methods

Fourteen 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.

Results

The 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).

Conclusions

Nonrigid 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.

Radiosurgery and fractionated radiotherapy for cavernous sinus meningioma: a systematic review and meta-analysis

INTRODUCTION

Radiosurgery (RS) and fractionated radiotherapy (FRT) are part of the therapeutic armamentarium for the management of cavernous sinus meningiomas. We propose a systematic review of the local tumor control and clinical outcomes after monofractionated radiosurgical treatment, including gamma knife radiosurgery (GKRS) and linear accelerator (Linac RS), or fractionated radiotherapy.

MATERIALS AND METHODS

The current review and meta-analysis adhered to the PRISMA guidelines. We performed a search in PubMed, Embase, and Medline based on the following mesh terms, used alone or in diverse combinations, in both title and abstract: "cavernous sinus," "meningioma," "radiosurgery," "gamma knife," "linac," "cyberknife," and "radiotherapy". We screened 425 studies. We selected 36 studies, matching all selection criteria: 24 for GK, 5 for Linac, and 7 for FRT.

RESULTS

Were included 2817 patients (GKRS, n = 2047, LinacRS, n = 350, FRT, n = 420). Half of patients benefited from upfront RS or FRT; the other half benefited from adjuvant RS or FRT (combined approach or tumor recurrence). The mean gross target volume (GTV) was smaller for RS as compared to FRT (p = 0.07). The median marginal doses were 13.9 Gy (range, 11 to 28) for GKRS and 14 Gy (range, 12.8 to 17.7) for LinacRS. For FRT, patients received a mean dose of 51.2 Gy (25.5 fractions, 1.85 Gy each). The mean overall follow-up values were 48 months (range, 15 to 89) for GKRS, 69 months (range, 46 to 87) for Linac, and 59.5 months (range, 33 to 83) for FRT. PFS at 5 years for GKRS, LinacRS, and FRT were respectively 93.6%, 95.6%, and 97.4% (p = 0.32, the Kruskal-Wallis). Monofractionated treatments (GKRS and LinacRS) induced more tumor volume regression than FRT (p = 0.001). Tumor recurrence or progression ranged between 3 and 5.8%, without statistically significant differences between modalities (p > 0.05). Trigeminal symptoms improved in approximately 54%, and III-IV-VI cranial nerves (CN) palsies improved in approximately 45%. After GKRS, visual acuity improved in 21% (not enough data available for other modalities). De novo deficits occurred in 5 to 7.5%. Adverse radiation effects appeared in 4.6 to 9.3% (all techniques pooled).

CONCLUSION

RS achieved a twice-higher rate of tumor volume regression than FRT. GKRS series reported an improvement in visual acuity in 21% of the cases. GKRS, Linac, and FRT provided similar clinical post therapeutic outcomes for the trigeminal and oculomotor CN.

Multi-institutional study of the variability in target delineation for six targets commonly treated with radiosurgery

BACKGROUND

Although accurate delineation of the target is a key factor of success in radiosurgery there are no consensus guidelines for target contouring.

AIM

The aim of the present study was therefore to quantify the variability in target delineation and discuss the potential clinical implications, for six targets regarded as common in stereotactic radiosurgery.

MATERIAL AND METHODS

Twelve Gamma Knife centers participated in the study by contouring the targets and organs at risks and performing the treatment plans. Analysis of target delineation variability was based on metrics defined based on agreement volumes derived from overlapping structures following a previously developed method. The 50% agreement volume (AV₅₀), the common and the encompassing volumes as well as the Agreement Volume Index (AVI) were determined.

RESULTS

Results showed that the lowest AVI (0.16) was found for one of the analyzed metastases (range of delineated volumes 1.27-3.33 cm³). AVI for the other two metastases was 0.62 and 0.37, respectively. Corresponding AVIs for the cavernous sinus meningioma, pituitary adenoma and vestibular schwannoma were 0.22, 0.37 and 0.50.

CONCLUSIONS

This study showed that the variability in the contouring was much higher than expected and therefore further work in standardizing the contouring practice in radiosurgery is warranted.

Dependence of volume calculation and margin growth accuracy on treatment planning systems for stereotactic radiosurgery

OBJECTIVE

Uncertainties in radiotherapy target structures are partly dependent on differences between volume calculation and margin growing methods in treatment planning systems (TPS). These uncertainties are exacerbated with very small structures such as those common in stereotactic radiosurgery.

METHODS

Data from a national commissioning programme for SRS was used to assess variation in reported volumes for six benchmark cases, including malignant and benign indications. Reported volumes were compared both with and without any margins added according to local practice.

RESULTS

137 plans were submitted, with a total of 311 structures and covering seven TPS. For volumes < 1 cm³ agreement was within 0.05 cm³, and for volumes > 1 cm³ agreement was within 5%. Systematic differences were seen between TPS, partly because of different methods for calculating the end slice volume. About one third of structures had a margin added, of 1-2 mm. Most TPS over-grew the volumes, compared to the approximation of a perfect sphere, especially Pinnacle and Eclipse.

CONCLUSION

Differences between volume calculation methods may lead to 5-10% variation in reported volumes from different TPS. This should be taken into account when comparing multicentre studies, and it is recommended that a minimum volume of 0.05 cm³ be used for any near-point doses to allow more consistent comparisons. When margins are added to small structures, there may be up to 40% difference to nominal margin size. Such differences are still small compared to interobserver variation in delineation. Advances in knowledge: This study quantifies the potential uncertainties in clinical volume calculation and margin growth with small radiosurgical targets.

Evaluation of the stability of the stereotactic Leksell Frame G in Gamma Knife radiosurgery

The purpose of this study was to evaluate the stability of the Leksell Frame G in Gamma Knife radiosurgery (GKR). Forty patients undergoing GKR underwent pretreatment stereotactic MRI for GKR planning and stereotactic CT immediately after GKR. The stereotactic coordinates of four anatomical landmarks (cochlear apertures and the summits of the anterior post of the superior semicircular canals, bilaterally) were measured by two evaluators on two separate occasions in the pretreatment MRI and post‐treatment CT scans and the absolute distance between the observations is reported. The measurement method was validated with an independent group of patients who underwent both stereotactic MRI and CT imaging before treatment (negative controls; n: 5). Patients undergoing GKR for arteriovenous malformations (AVM) also underwent digital subtraction angiography (DSA), which could result in extra stresses on the frame. The distance between landmark localization in the scans for the negative control group (0.63 mm; 95% CI: 0.57–0.70; SD: 0.29) represents the overall consistency of the evaluation method and provides an estimate of the minimum displacement that could be detected by the study. Two patients in the study group had the fiducial indicator box accidentally misplaced at post‐treatment CT scanning. This simulated the scenario of a frame displacement, and these cases were used as positive controls to demonstrate that the evaluation method is capable of detecting a discrepancy between the MRI and CT scans, if there was one. The mean distance between the location of the landmarks in the pretreatment MRI and post‐treatment CT scans for the study group was 0.71 mm (95% CI: 0.68–0.74; SD:0.32), which was not statistically different from the overall uncertainty of the evaluation method observed in the negative control group (p=0.06). The subgroup of patients with AVM (n: 9), who also underwent DSA, showed a statistically significant difference between the location of the landmarks compared to subjects with no additional imaging: 0.78 mm (95% CI: 0.72–0.84) vs. 0.69 mm (95% CI: 0.66–0.72), p=0.016. This is however a minimal difference (0.1 mm) and the mean difference in landmark location for each AVM patient remained submillimeter. This study demonstrates submillimeter stability of the Leksell Frame G in GKR throughout the treatment procedure.

PACS number(s): 87.53.‐j, 87.53.Ly, 87.56.Fc

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

BACKGROUND

The 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.

METHODS

Four 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.

RESULTS

Averaged 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.

CONCLUSIONS

Results 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.