Journal of radiosurgery and SBRT最新文献

The aim of this work is to verify the potential use of GAFchromic^TM EBT3 and FILMQA^TM pro software for patient specific quality assurance (QA) for stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT) treatment plans in clinical routine use. In particular, encephalic, pulmonary and lymph node treatments plans were selected for this study. The agreement between the calculated and measured dose distributions were evaluated in terms of ɣ index with 3%3mm, 2%2mm, 1.5%1.5mm and 3%1.5mm criteria. The obtained results were then compared to the routine pre-treatment verification method which uses electronic portal imaging device (EPID) and EPIQA analysis software. EBT3-FilmQA method results show a mean ɣ index passing rate >95% with 2%1.5mm analysis criteria and an improvement of about 7% compared with EPID-EPIQA method results.

Purpose/objectives: Accurate delineation of target is key to any successful radiosurgery. C-arm Dyna CT/ 3DCT angiography (3DCTA) has the potential of improving the accuracy of nidus delineation in intracranial arteriovenous malformations (AVM) due to high temporo-spatial resolution of vessel architecture. Here, we present a comparison of nidus delineation and dosimetric parameters between digital 3DCTA and MRI.

Materials/methods: Ten consecutive patients treated for intracranial AVMs were included in this study. All patients underwent MRI/MRA, and 3DCTA and all images were co-registered. AVM were delineated using 3DCTA (GTV_3DCTA) and contrast enhanced MRI/MRA (GTV_MRI). Hausdorff distance (HD) matrices and dice similarity coefficient (DSC) matrices were analysed. Stereotactic radiosurgery plans were developed for both the volumes for all patients and statistical analysis were performed with T-test.

Results: Mean volumes of GTV_3DCTA and GTV_MRI were 1.771 cc (SD 1.794cc, range 0.124-4.191cc) and 2.183cc (SD 2.16cc, range 0.221-6.133cc), respectively. Significant deviation (p=0.018) was found when taking GTV_MRI as a primary and comparing it to GTV_3DCTA (MD=0.723cc±0.816cc). Similar result was observed with GTV_3DCTA as primary and GTV_MRI as secondary (MD=0.188cc, SD=0.193cc, p=0.024). Maximum HD was in the range of 1.71 to 7.44mm (mean=4.27mm, SD=1.56). For GTV_3DCTA based plans, significant deviation was found between GTV_MRI and GTV_3DCTA in dose coverage and the mean difference was 22.17% (SD 16.73). In GTV_MRI based plans, the mean CIRTOG deteriorated from 1.33 to 2.18 for GTV_MRI and GTV_3DCTA, respectively. Significant deviation was found in CI_RTOG (0.005) and mean deviation was 0.86(SD=0.72) when comparing GTV_MRI and GTV_3DCTA. Highly significant (p=0.002) deviation was found in CI_Paddick between GTV_MRI and GTV_3DCTA for GTV_MRI based plans with mean difference of 0.26(SD=0.4, for GTV_MRI=0.3, GTV_3DCTA=0.46).

Conclusion: Nidus volume was significantly altered with the use of 3DCTA compared to that of MRA/MRI images. Multimodality imaging is crucial for accurate target delineation, and successful radiosurgical obliteration of nidus.

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.