Journal of radiosurgery and SBRT最新文献

Two automated treatment planning techniques were evaluated for multiple brain metastases using a single isocenter. One technique is knowledge-based planning (KBP) using a stereotactic radiosurgery (SRS) model in Eclipse treatment planning system (TPS); and the other is the Multiple Brain Mets (MBM) SRS technique in Brainlab Elements TPS. Eighteen plans each with 3-10 lesions were used for the study. Plan evaluation metrics included the planning target volume (PTV) coverage, conformity index (CI), total monitor units (MUs), plan optimization time, brain V_12 Gy, V_8 Gy, and V_5 Gy. Both the KBP and MBM planning techniques produced comparable plans to the manually generated clinical plans in terms of PTV coverage and CI. For irregularly shaped lesions, the KBP plans provided more conformal dose distribution to the PTV than the MBM plans. The KBP plans took significantly longer time to plan but have fewer MUs than the MBM plans. The MBM plans spared normal brain tissues better than the KBP plans in terms of V_5 Gy.

Objectives: Early identification of patients who will experience delayed-onset pain relief after GKRS for trigeminal neuralgia (TN) will allow optimal patient management, and avoidance of unnecessary procedures. A non-invasive tool to identify late responders to GKRS is currently unavailable. We sought to evaluate MRI based diffusivity metrics obtained at the 3-month post-GKRS time point as predictors of treatment response.

Methods: Pre-procedural and 3-month post-procedural 3T MRI examinations were obtained in 43 patients with TN. Diffusion tensor metrics including axial diffusivity (AD), radial diffusivity (RD), and fractional anisotropy (FA) were extracted from the bilateral trigeminal nerve intra-pontine fibers, cisternal radiosurgical targets (or corresponding contralateral nerve segments), and non-targeted cisternal nerve segments. A favorable treatment response was defined as pain intensity on the Barrow Neurological Institute (BNI) scale of I-II at last follow-up. Pain relief and treatment response at last follow-up were examined for correlation with the 3-month post-GKRS diffusivity metrics.

Results: At a median clinical follow-up of 5 months (range 0.5 to 24.5 months), all patients who did not experience pain relief at last follow-up had significantly reduced cisternal AD values (p=0.04) at the 3-month brain Diffusion Tensor image. In patients with classic TN, reduced mean cisternal AD (p=0.032), RD (p=0.026), and FA (p=0.042) values at the 3-month DTI follow-up were associated with BNI >2 at last follow-up. In addition, decreased mean cisternal AD (p=0.036), RD (p=0.029), and FA (p=0.037) were noted in patients with classic TN that failed to achieve a decrease of 2 points on the BNI scale at last follow-up.

Conclusion: Alterations of diffusivity metrics on the treated trigeminal nerve 3 months after GKRS for classic TN significantly correlated with no response to GKRS at last follow-up. Further studies to clarify the value of DTI as a non-invasive tool to predict response to treatment in patients with TN managed with GKRS are warranted.

Purpose: To determine factors associated with increased risk of finding new and/or enlarged brain metastases (BM) on GammaKnife™ (GK) MRI and their impact on patient outcomes.

Results: 43.9% of patients showed BM growth, 32.9% had additional brain metastases (aBM), and 18.1 % had both. Initial brain metastasis velocity (iBMV) was associated with finding aBM. Time between diagnostic MRI (dMRI) and GK MRI was associated with interval growth and each day increased this risk by 2%. Prior brain metastasectomy and greater time between either dMRI or latest extracranial RT and GK MRI predicted both aBM and BM growth. aBM and/or BM growth led to management change in 1.8% of cases and were not associated with OS or incidence of distant intracranial failure.

Conclusions: Number of metastases seen on dMRI and iBMV predicted both aBM and/or BM growth, however, these factors did not significantly affect survival or incidence of distant intracranial failure.

This study investigated the impact of patient motion on the dosimetric quality of treatment plans for metastatic patients undergoing frameless GammaKnife^® Icon™ treatments. By quantifying dosimetric robustness at increasing high definition motion management (HDMM) gating tolerances, this study investigated the possibility of increasing the HDMM threshold for patients treated at our centre from our current standard of 1 mm.

Methods: Motion was retrospectively simulated by shifting the stereotactic co-ordinates of shots in treatment plans using three motion models. Dosimetric quality indicators of original and shifted plans were compared. Influence of target location and size was determined.

Results: Motion models showed median (p-value) absolute changes in target coverage of up to -0.133% (<0.0001), -0.267% (<0.0001) and -0.667% (<0.0001) for HDMM tolerances of 1mm, 1.5mm and 3mm. The greatest median (p-value) absolute changes in Paddick Conformity Index (PCI) and Gradient Index (GI) were -0.008 (0.0032) and 0.017 (0.6893). A reduction in target size correlated weakly with greater changes in target coverage for all models and HDMM tolerances (r² =0.040-0.309). No location dependence was observed.

Conclusion: HDMM tolerances up to and including 3mm all resulted in negligible changes in PCI and GI. Target coverage exhibited greater sensitivity to motion, but only at 3mm was the target coverage reduced below local planning aims. Our HDMM tolerance could therefore potentially be increased to 1.5mm, with likely benefits to treatment delivery efficiency.

Objectives: Patients undergoing stereotactic radiosurgery (SRS) for brain metastases require additional radiation for relapse. Our objective is to determine the factors associated with salvage SRS versus whole brain radiation therapy (WBRT) for salvage of first intracranial failure (ICF) after upfront SRS.

Method: We identified a cohort of 110 patients with brain metastases treated with SRS in the definitive or postoperative setting followed by subsequent salvage WBRT or SRS at least one month after initial SRS. Clinical and demographic characteristics were retrospectively recorded.

Results: 78 Patients received SRS and 32 patients received WBRT at the time of first ICF. On multivariate analysis (MVA) factors associated with decreased use of salvage SRS were male gender (p=0.044) and local progression (p<0.001).

Conclusions: Local progression and male gender were the strongest factors associated with selection of salvage WBRT. Possible etiologies of this difference could be provider or patient driven, but warrant further exploration.

Purpose: There are no detailed data on volume changes of SpaceOAR hydrogel spacer. The purpose of this study was to quantitatively evaluate the volume changes of SpaceOAR during radiation therapy for prostate cancer.

Materials: The volume of SpaceOAR in seven prostate cancer patients was quantitatively measured every two weeks by Dixon-based water-only MRI scans.

Results: The volume of SpaceOAR increased and remained increased for 11 weeks after placement in all cases. The day to reach the maximum volume was 49.9 +/- 9.2 (mean +/- standard deviation [SD]) days after placement. The maximum rate of increase in Space OAR volume was 20% +/- 9% (mean +/- SD).

Conclusions: The volume of SpaceOAR was shown to be greater than the initial volume for 11 weeks after placement, with an increase of up to 20%. Therefore, care should be taken when creating a radiation treatment planning and positioning a patient during radiation therapy.

Stereotactic body radiotherapy (SBRT) planning target volume (PTV) margins are influenced by multiple factors. Data is limited on intrafraction motion in bone SBRT, particularly non-spine lesions. We analyzed intrafraction motion in bone SBRT patients treated on a standard treatment couch without 6 degrees-of-freedom (6-DOF) correction. Extracranial bone SBRT patients were included. Patients were treated using two volumetric-modulated arcs and targets were localized using daily cone-beam computed tomography (CBCT) prior to each arc. Alignments between the first and second CBCT images yielded intrafraction positional shift values used to compute translational 3-dimensional vector shifts. 125 fractions from 43 patients were reviewed. Median vector shift for all SABR fractions was 0.7 mm (range 0-6.6 mm); spine 0.7 mm (range:0-2.3 mm) and non-spine 0.9 mm (range:0-6.6 mm). Of the 125 fractions, 95% had IFM vectors within the prescribed PTV margin. Intrafraction motion is small for bone SBRT patients treated on a standard couch without 6-DOF correction capabilities. Intrafraction motion was slightly larger for non-spine sites and may require treatment with larger PTV margins than spine cases.

Objectives: Stereotactic body radiation therapy (SBRT) for the spine is challenging due to high-dose gradients sparing the cord in the treatment plans. We present our findings of initial setup error and intrafraction motion from Cone-beam computed tomography (CBCT) imaging.

Materials and methods: A total of 47 patients treated with spine SBRT with a total of 154 fractions following a fractionation schedule of 16 Gy in 1, 24 Gy in 2, and 30 Gy in 5 fractions were part of this study. Pre-treatment CBCT was used for localization of the target and couch shifts were applied based on target volume matching to the planning CT image set. Post-treatment CBCT was acquired for all fractions. Intrafraction motion (IFM) was calculated by matching post-treatment CBCT to planning CT for the target volume.

Results: The average Intrafraction motion was 1.6 ± 0.9 mm for the study cohort. The average and standard deviation of intrafraction motion were 0.4 ± 1.1 (AP), 0.3 ± 0.9 (SI) and 0.2 ± 1.2 (RL) respectively. The average Initial setup error tabulated from the offline review showed a mean value of 7.8 ± 5.3 mm. The average and standard deviation of the initial setup error were 2.5 ± 5.5 (AP), 2.4 ± 5.3(SI), and 0.8 ± 4.5(RL) respectively. The correlation of intrafraction motion with body mass index (BMI) and the number of consecutive vertebrae levels did not show any statistical significance, however, there was a significant association with gender as women showed more IFM.

Conclusions: Our study on intrafraction motion from CBCT images reinforced the importance of immobilization and imaging for positioning spine SBRT patients.

Advances in knowledge: The need for CBCT and imagining for positional errors is emphasized while treating with SBRT spine and the need for proper immobilization techniques.

Purpose: Competing radiosurgery plans are compared based on their conformity and gradient of dose distribution to the target volume (TV). Most widely used quality metrics such as new conformity index (NCI) and gradient index (GI) are known to have strong volume dependency on the TV of interest. A simple quality measure without the volume dependency is presented for evaluating stereotactic radiosurgery plans, expressed in distance dimension compared to the unit-less volume ratio used in NCI and GI.

Methods and materials: The conformity distance measure (CDM) is defined as the effective radius of the union volume subtracted by that of the intersection volume, where volume operations are on TV and prescription isodose volume (PIV). Gradient distance measure (GDM) is defined as the effective radius of 50% PIV (low dose volume of the plan) subtracted by that of corresponding ideal low dose volume (iLDV). Volume independency and consistent sensitivity of CDM and GDM on PIV displacement and dose spillage are analyzed using a simple two-sphere model. 2429 cases of Gamma Knife and 76 cases of Linac based radiosurgery plans for brain metastasis were retrospectively studied to demonstrate volume independency of the new measures and their implication on target coverage.

Results: The sensitivity of NCI on PIV displacement and dose spillage was inversely proportional to the effective radius of the target volume, while the sensitivity of CDM on target motion and dose spillage was constant regardless the target volume. The iLDV for 50% PIV was approximately 2.4 times of PIV based on previous Linac based radiosurgery/IMRT/VMAT plans and single shot analysis from Gamma Knife (GK), ICON. Although NCI ranged from 1 to 14.7 for GK plans and from 1.2 to 20.8 for VMAT plans showing strong volume dependency, CDM showed negligible volume dependency of less than 2.1 mm for more than 90% cases and peak frequency was at 0.8 mm. CDM was correlated well with target coverage as a function of PIV displacement regardless of target volume. Target coverage, V100, was larger than 95% when PIV displacement is less than CDM.

Conclusions: The new conformity and gradient measure, CDM and GDM are proposed in this paper. The new measures are volume independent which is preferred for reliable evaluation of the radiosurgery plan quality over wide range of radiosurgery targets. As represented by distance dimension similar to PTV margin, the new measures may be more adequate for image guided radiosurgery applications.