Cyberknife stereotactic radiosurgery and radiation therapy treatment planning system

CyberKnife is an image-guided stereotactical dose delivery system designed for both focal irradiation and radiation therapy (SRT). Focal irradiation refers the use of many small beams to deliver highly focus dose to a small target region in a few fractions. The system consists of a 6-MV linac mounted to a robotic arm, coupled with a digital x-ray imaging system. The radiation dose is delivered using many beams oriented at a number of defined or nodal positions around the patients. The CyberKnife can be used for both intracranial and extracranial treaments unlike the Gamma Knife which is limited to intracranial cases. Multiplan (Accuray Inc., Sunnyvale, CA) is the treatment planning system developed to cooperate with this accurate and versatile SRS and SRT system, and exploit the full function of Cyberknife in high-precision radiosurgery and therapy. Optimized inverse treatment plan can be achieved by fine-tuning contours and planning parameters. Precision is the newest version of Cyberknife treatment planning system (TPS) and an upgrade to Multiplan. It offers several new features such as Monte Carlo for multileaf collimator (MLC) and retreatment for other modalities that added more support for the Cyberknife system. The Cybeknife TPS is an easy-to-use and versatile inverse planning platform, suitable for stereotactic radiosurgery and radiation therapy. The knowledge and experience of the planner in this TPS is essential to improve the quality of patient care.     

难治性脑转移瘤的立体定向放射外科治疗策略及进展

脑转移瘤是发病率高、临床治疗难度大且预后较差的颅内常见恶性疾病,特别是其中的难治性脑转移瘤(大体积、多发、复发的转移瘤)常规治疗难以达到理想预后.立体定向放射外科(SRS)与常规治疗方式相比具有精准度高、单次照射剂量大、对周围组织损伤低等优势,已逐渐成为脑转移瘤患者治疗的首选方案.SRS治疗难治性脑转移瘤具有较好的效果...     

Use of stereotactic PET images in dosimetry planning of radiosurgery for brain tumors: clinical experience and proposed classification.

We developed a technique that allows the routine integration of PET in stereotactic neurosurgery, including radiosurgery. We report our clinical experience with the combined use of metabolic (i.e., PET) and anatomic (i.e., MRI and CT) images for the radiosurgical treatment of brain tumors. We propose a classification describing the relative role of the information provided by PET in this multimodality image-guided approach. METHODS: Between December 1999 and March 2003, 57 patients had stereotactic PET as part of their image acquisition for the planning of gamma knife radiosurgery. Together with stereotactic MRI and CT, stereotactic PET images were acquired on the same day using either (18)F-FDG or (11)C-methionine. PET images were imported in the planning software for the radiosurgery dosimetry, and the target volume was defined using the combined information of PET and MRI or CT. To analyze the specific contribution of the PET findings, we propose a classification that reflects the strategy used to define the target volume. RESULTS: The patients were offered radiosurgery with PET guidance when their tumor was ill-defined and we anticipated some limitation of target definition on MRI alone. This represents 10% of the radiosurgery procedures performed in our center during the same period of time. There were 40 primary brain lesions, 7 metastases, and 10 pituitary adenomas. Abnormal PET uptake was found in 62 of 72 targets (86%), and this information altered significantly the MRI-defined tumor in 43 targets (69%). CONCLUSION: The integration of PET in radiosurgery provides additional information that opens new perspectives for the optimization of the treatment of brain tumors.     

MRI-based treatment planning for brain stereotactic radiosurgery: Dosimetric validation of a learning-based pseudo-CT generation method

Magnetic resonance imaging (MRI)-only radiotherapy treatment planning is attractive since MRI provides superior soft tissue contrast without ionizing radiation compared with computed tomography (CT). However, it requires the generation of pseudo CT from MRI images for patient setup and dose calculation. Our machine-learning-based method to generate pseudo CT images has been shown to provide pseudo CT images with excellent image quality, while its dose calculation accuracy remains an open question. In this study, we aim to investigate the accuracy of dose calculation in brain frameless stereotactic radiosurgery (SRS) using pseudo CT images which are generated from MRI images using the machine learning-based method developed by our group. We retrospectively investigated a total of 19 treatment plans from 14 patients, each of whom has CT simulation and MRI images acquired during pretreatment. The dose distributions of the same treatment plans were calculated on original CT simulation images as ground truth, as well as on pseudo CT images generated from MRI images. Clinically-relevant DVH metrics and gamma analysis were extracted from both ground truth and pseudo CT results for comparison and evaluation. The side-by-side comparisons on image quality and dose distributions demonstrated very good agreement of image contrast and calculated dose between pseudo CT and original CT. The average differences in Dose-volume histogram (DVH) metrics for Planning target volume (PTVs) were less than 0.6%, and no differences in those for organs at risk at a significance level of 0.05. The average pass rate of gamma analysis was 99%. These quantitative results strongly indicate that the pseudo CT images created from MRI images using our proposed machine learning method are accurate enough to replace current CT simulation images for dose calculation in brain SRS treatment. This study also demonstrates the great potential for MRI to completely replace CT scans in the process of simulation and treatment planning.     

Hyperacute changes in glucose metabolism of brain tumors after stereotactic radiosurgery: a PET study.

Cultured tumor cells show a marked increase in deoxyglucose uptake as early as 3 h after single high-dose irradiation, reflecting hyperacute response of the cells to noxious intervention. To evaluate the hyperacute effect of high-dose irradiation on tumor glucose metabolism in vivo, we measured 2-[18F]fluoro-2-deoxy-D-glucose (FDG) tumor uptake before and immediately after stereotactic radiosurgery. METHODS: A total of 19 brain tumors (17 metastatic and 2 primary, a meningioma and a central neurocytoma) in eight patients were treated with stereotactic radiosurgery. The received dose was between 24 and 32 Gy delivered to the central target point in the tumor. FDG PET was performed within 1 wk before radiosurgery and again 4 h after treatment. The net influx constant (Ki) was calculated on a pixel-by-pixel basis using graphical analysis, and the Ki ratio of tumor to ipsilateral cerebellum was used as an index of FDG uptake of the tumor. RESULTS: Eighteen of 19 irradiated tumors, all metastatic tumors and the meningioma, showed a 29.7% +/- 14.0% increase in the Ki ratio, which was significantly higher than that of nonirradiated tumors (4.1% +/- 3.6%, n = 8, P < 0.0001, analysis of variance). In metastatic tumors, an increase in the Ki ratio was significantly correlated with a decrease in the size of the irradiated tumors, as revealed by follow-up with CT or MRI (r = 0.61, P = 0.012, simple regression). The meningioma did not show a significant decrease in size, probably due to the short follow-up period. The central neurocytoma did not show any change in the Ki ratio or in tumor size. CONCLUSION: Serial FDG PET could be a potential tool for predicting the outcome of radiosurgery for brain tumors by detecting hyperacute changes in tumor glucose metabolism.     

Pancreatic and extrapancreatic lesions in patients with intraductal papillary mucinous neoplasms of the pancreas: a single-centre experience

Purpose

This study was performed to describe the possible presence of extrapancreatic neoplasms in patients with intraductal papillary mucinous neoplasm (IPMN) and to evaluate whether the extrapancreatic tumours were synchronous or metachronous to IPMNs.

Materials and methods

One hundred and forty-two patients (56 men and 86 women; mean age 69.5 years, range 37–98) with IPMN diagnosed using the Sendai criteria were enrolled. Six patients (4.2%) had type I, 103 (72.5%) type II and 33 (23.2%) type III IPMN. All patients were studied using the following imaging techniques: ultrasonography (US), multidetector computed tomography (MDCT) and magnetic resonance cholangiopancreatography (MRCP).

Results

Pancreatic IPMN was localised in the head in 43 patients (30.3%), in the body in 13 (9.2%), in the tail in ten (7.0%), in the head-body in 17 (12.0%), in the body-tail in 15 (10.6%) diffuse throughout the gland in 44 (31.0%). The mean size of the cystic lesions was [(mean±standard deviation (SD)] 1.9±1.9 cm (range 0.5–8.0 cm). Twenty patients (14.1%) had associated pancreatic or extrapancreatic diseases. In evaluating the distribution of pancreatic or extrapancreatic diseases according to IPMN type, we found that this was not significantly different among types I, II and III (p=0.776).

Conclusions

The majority of pancreatic and extrapancreatic cancers occur before the diagnosis of IPMNs is made and is not related to the type of IPMN.     

Dosimetric comparison of inverse and forward planning for Gamma Knife stereotactic radiosurgery of brain metastases

The Leksell GammaPlan (LGP) with an inverse planning (IP) tool has been upgraded to version 11.1 since its launch in 2010. We evaluated its IP planning performance by re-planning 16 targets that had been planned using forward planning (FP). The FP and IP plans were compared. A planning guideline for IP process was developed aiming for an unbiased comparison. Sixteen brain metastases (BMs) without nearby critical structures were included in the study (size > 1 cm for all targets). All prior FP were re-planned in the LGP using IP and maintaining the same beam-on time and coverage. The dose to all the targets was scaled to 20 Gy in a single fraction at 50% isodose line (IDL) for FP and IP comparison purpose. The coverage and beam-on time were nearly the same for both the FP and IP plans. For all the IP plans, the mean selectivity was 0.85 ± 0.04 (vs 0.83 ± 0.04 in FP plans, p = 0.02), the mean GI was 2.92 ± 0.21 (vs 3.18 ± 0.60 in FP plans, p = 0.047), the mean V12Gy was 8.18 ± 8.57 cc (vs 9.09 ± 9.08 cc in FP plans, p = 0.001), the mean V8Gy was 14.63 ± 15.14 cc (vs 16.34 ± 16.17 cc in FP plans, p = 0.001), and the mean V5Gy was 29.01 ± 28.77 cc (vs 32.77 ± 31.41 cc in FP plans, p = 0.001). The number of shots was higher in IP plans (means of 16.69 ± 8.11 vs 10.81 ± 6.87 in FP plans, p = 0.001). We retrospectively re-planned 16 FP plans using the IP tool while meeting the quality limiting factors for the FP plans. The dosimetry parameters from the IP plans outperformed the treated FP plans and the IP tool should be preferred for tumors with size > 1 cm.     

Effect of collimator angle on HyperArc stereotactic radiosurgery planning for single and multiple brain metastases

We assessed the effect of collimator angle on the dosimetric parameters for targets and organs at risk (OARs) for collimator-optimized HA (CO-HA) and non-CO-HA (nCO-HA) plans. The nCO-HA and CO-HA plans were retrospectively generated for 26 patients (1 to 8 brain metastases). The dosimetric parameters for planning target volume (homogeneity index [HI]; conformity index [CI]; gradient index [GI]) and for OARs were compared. The modulation complexity score for volumetric modulated arc therapy (MCSV) and monitor units (MUs) were calculated. Doses were measured using the electronic portal imaging device and compared with the expected doses. Dosimetric parameters of the HI, CI, and GI for single (n = 12) and multiple (n = 14) metastases cases were comparable (p > 0.05). For multiple metastases cases, the CO-HA plan provided lower V_4Gy, V_12Gy, V_14Gy, V_16Gy for brain tissue compared to the nCO-HA plan (p < 0.05). Doses for OARs (D_0.1cc) (brainstem, chiasm, Hippocampus, lens, optic nerves, and retinas) were comparable (p > 0.05). For multiple metastases cases, the CO-HA plan resulted in less complex multileaf collimator (MLC) patterns (MCSV = 0.19 ± 0.04, p < 0.01), lower MUs (8596 ± 1390 MUs, p < 0.01), and shorter beam-on time (6.2 ± 1.0 min, p < 0.01) compared to the nCO-HA plan (0.16 ± 0.04, 9365 ± 1630, and 6.7 ± 1.2 for MCSV, MUs, and beam-on time, respectively). For both treatment approach, the equivalent gamma passing rate was obtained with the 3%/3 mm and 2%/2 mm criteria (p > 0.05). The collimator optimization in the HA planning reduced doses to brain tissues and improved the treatment efficacy.     

Acute hyperthermia following stereotactic radiosurgery for pituitary adenoma

A 71-year-old male presented with a large pituitary adenoma with superior extension into the optic chiasm and suprasellar cistern. He was treated with stereotactic radiosurgery to a dose of 16 Gy. Approximately 1 h after radiosurgery he developed fever; his temperature peaked at 105.1 degrees F and normalized about 20 h later. This case demonstrates that acute hyperthermia is a potential complication following high dose stereotactic radiosurgery for large pituitary tumours.     

IMRT planning parameter optimization for spine stereotactic radiosurgery

Spine stereotactic radiosurgery (SSRS) is a noninvasive treatment for metastatic spine lesions. MD Anderson Cancer Center reports a quality assurance (QA) failure rate approaching 15% for SSRS cases, which we hypothesized is due to difficulties in accurately calculating dose resulting from a large number of small-area segments. Clinical plans typically use 9 beams with an average of 10 segments per beam and minimum segment area of 2-3 cm². The purpose of this study was to identify a set of intensity-modulated radiation therapy (IMRT) planning parameters that attempts to optimize the balance among QA passing rate, plan quality, dose calculation accuracy, and delivery time for SSRS plans. Using Pinnacle version 9.10, we evaluated the effects of 2 IMRT parameters: maximum number of segments and minimum segment area. Initial evaluation of the data revealed that 5 segments per beam along with minimum segment area of 4 cm² and 4 monitor units (MU) per segment (5-4-4 plans) was the most promising. IMRT QA was performed using a PTW OCTAVIUS 4D phantom with a 2D detector array. Our data showed no significant plan quality change with decreased number of segments and increased minimum segment area. The average coverage of GTV and CTV was 82.5 ± 13% (clinical) vs 82.5 ± 13% (5-4-4) and 92.3 ± 8% (clinical) vs 91.5 ± 8% (5-4-4). Maximum point dose to cord was 11.4 ± 3.5 Gy (clinical) vs 11.0 ± 4.0 Gy (5-4-4). Total plan delivery time was decreased by an average of 11.3% for the 5-4-4 plans. For IMRT QA, the gamma index passing rate (distance to agreement: 2.5 mm, local dose difference: 4%) for the original plans vs the 5-4-4 plans averaged 90.3% and 91.9%, respectively. In conclusion, IMRT parameters of 5 segments per beam and 4 cm² minimum segment areas provided a better balance of plan quality, delivery efficiency, and plan dose calculation accuracy for SSRS.     

Experience with the CyberKnife for intracranial stereotactic radiosurgery: Analysis of dosimetry indices

We evaluated coverage, dose homogeneity, dose conformity, and dose gradient in CyberKnife VSI treatment plans. Several dosimetric indices were calculated, and the results were compared with those of previous publications. The effect of target volume on the radiosurgical treatment indices selected was also investigated. The study population comprised the first 40 patients treated at our department from March 2011 to September 2012. Dosimetric indices were calculated and compared with published results for other frame-based and frameless intracranial stereotactic radiotherapy techniques. A comparison of the indices confirmed the ability of the CyberKnife VSI system to provide very high-quality dosing plans. The results were independent of target volume for coverage, homogeneity, and dose conformity. However, a dependence on target volume was observed for the dose-gradient indices analyzed. Based on the indices proposed, CyberKnife provides very good treatment plans and compares favorably with other techniques in most cases. However, greater consensus on the radiosurgery indices calculated would be desirable to facilitate comparison of the various techniques or the same techniques when applied by different users.     

Clinical results of LINAC-based stereotactic radiosurgery for pituitary adenoma

PURPOSE: We retrospectively evaluated our clinical results of stereotactic radiosurgery (SRS) for pituitary adenoma. MATERIALS AND METHODS: Between 1995 and 2000, 13 patients were treated with SRS for pituitary adenoma. In all cases, the tumors had already been surgically resected. The adenomas were functional in 5 and non-functional in 8 patients. The median follow-up period was 30 months. SRS was performed with the use of a dedicated stereotactic 10-MV linear accelerator (LINAC). The median dose to the tumor margin was 15 Gy. The dose to the optic apparatus was limited to less than 8 Gy. RESULTS: MR images of 12 patients revealed tumor CR in one case and PR in 9 cases; in the remaining two patients, tumor size decreased by less than 50%. There was no recognizable regrowth of any of the tumors. In two of four GH-secreting adenomas, hormonal overproduction normalized, while the other two showed reduced hormonal production. One PRL-secreting adenoma did not respond. Reduction of visual acuity and field was seen in one patient. This patient also had a brain infarction. None of the patients developed brain radionecrosis or radiation-induced hypopituitarism. CONCLUSION: Although further studies based on greater numbers of cases and longer follow-up periods are needed, our results suggest that SRS seems to be a safe, effective treatment for pituitary adenoma.     

Management of dural carotid cavernous fistulas: a single-centre experience

Objectives

To report the epidemiological features, clinical presentation, angiographic characteristics and therapeutic options, success and complication rates in patients with dural carotid cavernous fistulas (dural CCFs).

Methods

Retrospective evaluation of patients followed in our institution between January of 2005 and September of 2013.

Results

There were 38 patients, 76 % females, with an average age of 63 years. Ocular symptoms and signs were the most frequent clinical findings. Dural CCFs were Barrow type B in 8 %, type C in 10 % and type D in 82 %. Cortical venous reflux was present in 50 % of cases. Medical treatment was performed in 16 % of patients, external ocular compression in 8 %, transarterial embolisation in 13 %, transvenous embolisation in 60 % and radiosurgery in 3 %. Clinical and angiographic follow-up data were available in 89 % and 82 % of patients with a mean follow-up time of 9 and 7 months, respectively. Clinical cure was achieved in 58 % of patients and improvement in 24 %. Anatomical cure was demonstrated in 68 %. Transient worsening or new onset of ocular symptoms was observed in 29 %. There was no permanent morbidity or mortality.

Conclusions

In properly selected patients, endovascular embolisation, particularly by transvenous approach, represents a safe and effective treatment for dural CCFs.

Key points

? Dural carotid cavernous fistulas are more common in elderly women ? Dural CCFs most commonly present with ocular symptoms and signs ? Endovascular treatment is effective and safe in properly selected patients