Journal of radiosurgery and SBRT最新文献

Purpose: In the implementation of the use of Encompass^TM partially open immobilization mask to perform SRS of multiple brain metastasis, the evaluation of patient's intrafraction motion (IM) is deemed convenient to verify that the margins applied to the GTV are able to ensure adequate dose coverage to each lesion.

Methods: IM was determined by comparing the pre- and post-treatment CBCT images with respect to the simulation CT for a total of 23 fractions. The dosimetric impact on GTV coverage due to translational errors in patient positioning and rotational uncertainties of LINAC's performance was also evaluated.

Results: The absolute magnitude of IM was less than 1 mm in all cases. The dosimetric difference on GTV coverage due to patient's IM was inferior to 5%. There was not found any significant correlation between the dosimetric impact of rotational uncertainties with the distance to the isocenter.

Conclusion: The margins applied to the GTV are adequate when using Encompass^TM immobilization device.

Purpose: This study aims to establish criteria for convolution dose calculations and an efficient procedure to include the heterogeneity effects in GammaKnife radiosurgery (GKRS) treatment plans.

Methods and materials: We analyzed 114 GKRS cases of various disease types, tumor locations, sizes, the number of fractions, and prescription doses. There was a total of 205 tumors. CT scans were performed in addition to routine MRI scans for all treatments. All treatment plans were created using the TMR10 algorithm (TMR10). We repeated the dose calculations for this study with the convolution algorithm (Conv). We calculated the ratios between Conv and TMR10 of the treatment volume (TxtVol), the volume covered by half of the prescription dose (TxtVol2), the minimum, maximum, and mean doses in the tumor (minDose, maxDose, and meanDose), and the volume of tumor covered by the prescription isodose (covVol). We then categorized those quantities for locations of tumors represented by the shortest distance of the skull surface from the tumor center (distC) and the tumor edge (distE). [Table: see text].

Results: All six ratios increased with increasing distC and distE. For example, the median minDose ratio increased from 0.885 to 0.933 as distE increased. There was a statistically significant difference in the minDose ratio between tumors of distE < 2 cm and distE ≥ 2 cm. On the other hand, the median maxDose ratio was about 0.933 [0.928-0.939], being almost independent of distE. This suggested a 6.1% overestimation of the delivered dose with TMR10.

Conclusion: The heterogeneity effects must be considered for the volume dose calculations by applying the convolution algorithm when the distance of the skull surface from the closest point of the tumor is less than 2 cm to achieve less than 3% accuracy.

Objective: To assess dosimetric variation caused by breast deformation in breast radiosurgery based on deformable image registration.

Methods: This study included 30 patients who were treated in the prone position for preoperative partial breast radiosurgery. The biopsy clip in CBCT was aligned to the one from the planning CT. Deformable image registration (DIR) was performed to deform the planning CT into the CBCT, focusing on the breast shape. The treated plan (P_Tx) was recalculated based on the deformed CT. Thus, P_Tx represented the actual treatment delivered to the patient and was compared to the original plan (P_Org).

Results: The mean differences of target volumes covered by 95% and 100% of the prescribed dose between P_Org and P_Tx were less than 0.5%. The mean differences ± standard division for skin maximum dose (D_max), dose to 1cc (D_1cc) and D_10cc were 0.3 ± 0.7 Gy, 0.3 ± 0.6 Gy and 0.6 ± 0.6Gy between P_Org and P_Tx, respectively.

Conclusion: The treated plan was accurately recalculated based on the deformed CT. Despite slight variance in breast deformation, the dosimetric variation was very small, ensuring that adequate target coverage and skin dose were maintained during treatment as planned originally.

Background: While immunotherapy has been shown to improve survival and decrease neurologic death in patients with brain metastases, it remains unclear whether this improvement is due to prevention of new metastasis to the brain.

Method: We performed a retrospective review of patients presenting with brain metastases simultaneously with the first diagnosis of metastatic disease and were treated with upfront immunotherapy as part of their treatment regimen and stereotactic radiosurgery (SRS) to the brain metastases. We compared this cohort with a historical control population (prior to the immunotherapy era) who were treated with pre-immunotherapy standard of care systemic therapy and with SRS to the brain metastases.

Results: Median overall survival time was improved in the patients receiving upfront immunotherapy compared to the historical cohort (48 months vs 8.4 months, p=0.001). Median time to distant brain failure was statistically equivalent (p=0.3) between the upfront immunotherapy cohort and historical control cohort (10.3 vs 12.6 months). Brain metastasis velocity was lower in the upfront immunotherapy cohort (median 3.72 metastases per year) than in the historical controls (median 9.48 metastases per year, p=0.001). Cumulative incidence of neurologic death at one year was 12% in the upfront immunotherapy cohort and 28% in the historical control cohort (p=0.1).

Conclusions: Upfront immunotherapy appears to improve overall survival and decrease BMV compared to historical controls. While these data remain to be validated, they suggest that brain metastasis patients may benefit from concurrent immunotherapy with SRS.

Purpose/objectives: Treatment planning systems (TPS) for Gamma Knife stereotactic radiosurgery (GK-SRS) include TMR10 algorithms, which assumes tissue homogeneity equivalent to water, and collapsed-cone convolutional (CCC) algorithms, which accounts for tissue inhomogeneity. This study investigated dosimetric differences between TMR10 and CCC TPS for acoustic neuromas (ANs) treated with GK-SRS.

Materials/methods: A retrospective review of 56 AN treated with GK-SRS was performed. All patients underwent MRI and CT imaging during their initial treatment and were planned using TMR10. Each plan was recalculated with CCC using electron density extracted from CT. Parameters of interest included D_max, D_min, D_50%, cochlea D_max, mean cochlea dose, target size, and laterality (>20 mm from central axis).

Results: Median target volume of patients was 1.5 cc (0.3 cc-2.8 cc) with median dose of 12 Gy prescribed to the 50% isodose line. Compared to CCC algorithms, the TMR10 calculated dose was higher: D_max was higher by an average 6.2% (p < 0.001), D_min was higher by an average 3.1% (p < 0.032), D_50% was higher by an average of 11.3%. For lateralized targets, calculated D_max and D_50% were higher by 7.1% (p < 0.001) and 10.6% (p < 0.001), respectively. For targets <1 cc, D_max and D_50% were higher by 8.9% (p ≤ 0.009) and 12.1% (p ≤ 0.001), respectively. Cochlea D_max was higher, by an average of 20.1% (p < 0.001).

Conclusion: There was a statistically significant dosimetric differences observed between TMR10 and CCC algorithms for AN GK-SRS, particularly in small and lateralized ANs. It may be important to note these differences when relating GK-SRS with standard heterogeneity-corrected SRS regimens.

Gamma angle plays a major role in Gamma Knife Radiosurgery (GKRS) treatment planning. Selecting an appropriate gamma angle may help in mitigating unnecessary radiation exposure to organs at risk (OARs). The aims in GKRS of vestibular schwannoma (VS) is to deliver sufficient radiation to the tumor extending into internal auditory canal (IAC) while keeping basal turn of cochlea and brain stem away from 4 and 12 Gy radiation exposure, respectively. This study analyses the optimal gamma angle in GKRS for VS treatment planning. The study was performed using old MRI datasets of 16 patients of VS in Leksell GammaPlan version 10.1.1. T2 weighted contrast MRIs were used for the planning purposes. Three different plans were made for each patient at gamma angles 90°, 110° and 70° using hybrid inverse planning technique. Dynamic shaping was used to achieve as low as reasonably achievable (ALARA) doses to the cochlea without compromising target coverage (i.e. coverage of more than 97% of tumor volume). This comparative analysis shows minimal radiation exposure to cochlea for plans made at gamma angle 110° compared to 90° and 70°. Average percentage volume of cochlea receiving 4 Gy were 9.63 ± 12.32%, 6.19 ± 8.24%, and 25.25 ± 31.82% at gamma angles 90°, 110° and 70°, respectively (one-way ANOVA p = 0.0247). The average selectivity indices were 83.44 ± 7.13, 84.06 ± 7.84 and 83.56 ± 7.22 at gamma angles 90°, 110° and 70° respectively. Similarly, the gradient indices and beam on time were 2.80 ± 0.23, 2.81 ± 0.23 and 2.80 ± 0.25 and 120.65 ± 59.63, 117.95 ± 58.06 and 123.99 ± 61.61 min, respectively, at 90°, 110° and 70°. The selectivity index, gradient index and beam on time were minimal at gamma angle 110° compared to the other two angles, but not statistically significant (one-way ANOVA p-values were 0.9686, 0.9942 and 0.9598, respectively). The gamma angle of 110° is a good choice for treatment planning of VS patient in Gamma Knife as it gives better treatment plans (minimal cochlea doses).

Purpose/objective: Linear accelerator (LINAC) based stereotactic radiosurgery (SRS) for arteriovenous malformations (AVMs) is delivered with cone or multileaf collimators (MLCs), and favorable dosimetry is associated with reduced radionecrosis in normal brain tissue. This study aims to determine whether cones or MLCs has better dosimetric characteristics, to predict differences in toxicity.

Methods: All patients treated for AVMs using LINAC SRS from 2003-2017 were examined retrospectively. Demographic data, volumes of normal tissue exposed to 12Gy (V12Gy[cc]) and 4Gy (V4Gy[cc]), maximal dose, and dose gradient were analyzed. Univariate and multivariate analyses were used to evaluate relationships between collimator type, dosimetric parameters, and toxicity. Propensity score matching was used to adjust for AVM size.

Results: Compared to MLC, cones were independently associated with reduced V12Gy[cc] after propensity score matching (p=0.008) and reduced neurotoxicity (p=0.016). Higher V12Gy[cc] (p=0.0008) and V4Gy[cc] (p=0.002) were associated with increased neurotoxicity.

Conclusions: Treating AVMs with cone-based SRS over MLC-based SRS may improve dosimetry and reduce toxicities.