As one of the most important high-tech nanomaterials, fumed silica has been widely used in many industrial fields due to its unique properties. However, particle size uniformity is still the ...technical barrier in this industry after years of development. Therefore, numerical simulations are employed to optimize the process parameters of a premixed multiring high-speed jet oxyhydrogen combustion reactor, and the result is applied to actual process units used in fumed silica production. By maintaining temperature consistency between inlet 2 and inlet 1 and increasing the gas flow rates of inlet 3 and inlet 4, the HCl flow and temperature field distribution in the reactor are improved significantly. The back mixing of HCl and the blocking of particles to the combustion reactor are suppressed. Compared to the original process, the median diameter (D50) of agglomerates particles and the 45 μm sieve residue content are decreased by 6.4 μm and 19.0 mg g–1, respectively. In addition, the tensile strength of high-temperature vulcanized rubber is increased by 1–1.5 MPa. The presented simulations provide technical support for quality improvements of fumed silica and a theoretical basis for the rational design of industrial combustion reactors.
The feedstock prepared by polyoxymethylene (POM)-based binder usually has high viscosity and poor fluidity in the injection process, which can easily cause defects such as insufficient injection, ...flow lines and cracking and has great wear on the injection equipment. In this experiment, in order to further improve the performance of POM-based binder, polytetrahydrofuran (PTHF) is used to modify POM-based binder. The results show that the effect of PTHF on improving the rheological properties of feedstock is better than that of acid (SA). When the content of PTHF is 3 wt%, the non-newtonian index (
n
), viscous flow activation energy (
E
) and comprehensive rheological factor (
α
STV
) of the feedstock are 0.39, 16.63 kJ/mol and 13.33 × 10
–7
, respectively, at 185 °C and 965 S
−1
shear rate, which means feedstock has a good comprehensive rheological performance. In addition, PTHF has no obvious effect on the mechanical properties of green part and is removed in the catalytic degreasing stage.
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.
Purpose
Radiosurgery is an established technique to treat cerebral arteriovenous malformations (AVMs). Obliteration of larger AVMs (> 10–15 cm3 or diameter > 3 cm) in a single session is challenging ...with current radiosurgery platforms due to toxicity. We present a novel technique of multistage stereotactic radiosurgery (SRS) for large intracranial arteriovenous malformations (AVM) using the Gamma Knife system.
Materials/Methods
Eighteen patients with large (> 10–15 cm3 or diameter > 3 cm) AVMs, which were previously treated using a staged SRS technique on the Cyberknife platform, were retrospectively selected for this study. The AVMs were contoured and divided into 3–8 subtargets to be treated sequentially in a staged approach at half to 4 week intervals. The prescription dose ranged from 15 Gy to 20 Gy, depending on the subtarget number, volume, and location. Gamma Knife plans using multiple collimator settings were generated and optimized. The coordinates of each shot from the initial plan covering the total AVM target were extracted based on their relative positions within the frame system. The shots were regrouped based on their location with respect to the subtarget contours to generate subplans for each stage. The delivery time of each shot for a subtarget was decay corrected with 60Co for staging the treatment course to generate the same dose distribution as that planned for the total AVM target. Conformality indices and dose–volume analysis were performed to evaluate treatment plans.
Results
With the shot redistribution technique, the composite dose for the multistaged treatment of multiple subtargets is equivalent to the initial plan for total AVM target. Gamma Knife plans resulted in an average PTV coverage of 96.3 ± 0.9% and a PITV of 1.23 ± 0.1. The resulting Conformality indices, V12Gy and R50 dose spillage values were 0.76 ± 0.05, 3.4 ± 1.8, and 3.1 ± 0.5 respectively.
Conclusion
The Gamma Knife system can deliver a multistaged conformal dose to treat large AVMs when correcting for translational setup errors of each shot at each staged treatment.
Abstract Purpose To investigate a multi-staged robotic stereotactic radiosurgery (SRS) delivery technique for the treatment of large cerebral arteriovenous malformations (AVMs). The treatment ...planning process and strategies to optimize both individual and composite dosimetry are discussed. Methods Eleven patients with large (30.7 ± 19.2 cm3 ) AVMs were selected for this study. A fiducial system was designed for fusion of targets between planar angiograms and simulation CT scans. AVMs were contoured based on single contrast CT, MRI and orthogonal angiogram images. AVMs were divided into 3–8 sub-target volumes (3–7 cm3 ) for sequential treatment at 1–4 week intervals to a prescription dose of 16–20 Gy. Forward and inversely developed treatment plans were optimized for 95% coverage of the total AVM volume by dose summation from each sub-volume, while minimizing dose to surrounding tissues. Dose-volume analysis was used to evaluate the PTV coverage, dose conformality (CI), and R50 and V12Gy parameters. Results The treatment workflow was commissioned and able to localize within 1 mm. Inverse optimization outperformed forward planning for most patients for each index considered. Dose conformality was shown comparable to staged Gamma Knife treatments. Conclusion The CyberKnife system is shown to be a practical delivery platform for multi-staged treatments of large AVMs using forward or inverse planning techniques.
Purpose:
Although modern technology has allowed for target dose escalation by minimizing normal tissue dose, the dose delivered to a tumor and surrounding tissues still depends largely on the ...inherent characteristics of the radiation delivery platform. This work aims to determine the optimal prescription isodose line that minimizes normal tissue irradiation for stereotactic body radiation therapy (SBRT) for a conventional linear accelerator and a robotic delivery platform.
Methods:
Spherical targets with diameters of 10, 20, and 30 mm were constructed in the lungs and liver of a computer based digital torso phantom which simulates respiratory and cardiac motion. Normal tissue contours included normal lung, normal liver, and a concentric 10 mm shell of normal tissue extending from the spherical target surface. For linac planning, noncoplanar, nonopposing three dimensional (3D) conformal beams were designed, and variable prescription isodose lines were achieved by varying the MLC block margin. For CyberKnife planning, variable prescription isodose lines were achieved by inverse planning. True 4D dose calculations were used for the moving target and surrounding tissue based on each of ten phases of a 4D CT dataset. Doses of 60 Gy in three fractions were prescribed to cover 95% of the target tumor. Commonly used conformality, dosimetric, and radiobiological indices for lung and liver SBRT were used to compare different plans and determine the optimally prescribed isodose line for each treatment platform.
Results:
For linac plans, the average optimal prescription isodose line based on all indices evaluated occurred between 59% and 69% for lung tumors and between 67% and 77% for liver tumors depending on the tumor size. CyberKnife plans had average optimal prescription isodose lines occurring between 40% and 48% for lung tumors and between 41% and 42% depending on the tumor size. However, prescription isodose lines under 50% are not advised to prevent large heterogeneous dose distributions within the target.
Conclusions:
The choice of prescription isodose line was shown to have a significant impact on parameters commonly used as constraints for lung and liver SBRT treatment planning for both linac-based and CyberKnife delivery platforms. By methodically choosing the prescription isodose line, normal tissue toxicities from SBRT may be reduced.
The purpose of this study was to commission and clinically test a robotic stereotactic delivery system (CyberKnife, Sunnyvale, CA) to treat early-stage glottic laryngeal cancer. We enrolled 15 ...patients with cTis-T2N0M0 carcinoma of the glottic larynx onto an institutional review board (IRB)-approved clinical trial. Stereotactic body radiotherapy (SBRT) plans prescribed 45 Gy/10 fractions to the involved hemilarynx. SBRT dosimetry was compared with (1) standard carotid-sparing laryngeal intensity-modulated radiation therapy (IMRT) and (2) selective hemilaryngeal IMRT. Our results demonstrate that SBRT plans improved sparing of the contralateral arytenoid (mean 20.0 Gy reduction, p <0.001), ipsilateral carotid D
(mean 20.6 Gy reduction, p <0.001), contralateral carotid D
(mean 28.1 Gy reduction, p <0.001), and thyroid D
(mean 15.0 Gy reduction, p <0.001) relative to carotid-sparing IMRT. SBRT also modestly improved dose sparing to the contralateral arytenoid (mean 4.8 Gy reduction, p = 0.13) and spinal cord D
(mean 4.9 Gy reduction, p = 0.015) relative to selective hemilaryngeal IMRT plans. This "phantom-to-clinic" feasibility study confirmed that hypofractionated SBRT treatment for early-stage laryngeal cancer can potentially spare dose to adjacent normal tissues relative to current IMRT standards. Clinical efficacy and toxicity correlates continue to be collected through an ongoing prospective trial.
In breast cancer treatment, intensity-modulated radiation therapy (IMRT) can be utilized to deliver more homogeneous dose to target tissues to minimize the cosmetic impact. We have investigated the ...effect of the respiratory cycle and radiation beam-on timing on the dose distribution in free-breathing dynamic breast IMRT treatment. Six patients with early stage cancer of the left breast were included in this study. A helical computed tomography (CT) scan was acquired for treatment planning. A four-dimensional computed tomography (4D CT) scan was obtained right after the helical CT scan with little or no setup uncertainty to simulate patient respiratory motion. After optimizing based on the helical CT scan, the sliding-window dynamic multileaf collimator (DMLC) leaf sequence was segmented into multiple sections that corresponded to various respiratory phases per respiratory cycle and radiation beam-on timing. The segmented DMLC leaf sections were grouped according to respiratory phases and superimposed over the radiation fields of corresponding 4D CT image set. Dose calculation was then performed for each phase of the 4D CT scan. The total dose distribution was computed by accumulating the contribution of dose from each phase to every voxel in the region of interest. This was tracked by a deformable registration program throughout all of the respiratory phases of the 4D CT scan. A dose heterogeneity index, defined as the ratio between
(
D
20
−
D
80
)
and the prescription dose, was introduced to numerically illustrate the impact of respiratory motion on the dose distribution of treatment volume. A respiratory cycle range of
4
–
8
s
and randomly distributed beam-on timing were assigned to simulate the patient respiratory motion during the free-breathing treatment. The results showed that the respiratory cycle period and radiation beam-on timing presented limited impact on the target dose coverage and slightly increased the target dose heterogeneity. This motion impact tended to increase the variation of target dose coverage and heterogeneity between treatment fractions with different radiation beam-on timing. The target dose coverage and heterogeneity were more susceptible to the radiation beam-on timing for patients with long respiratory cycle (longer than
6
s
) and large breast motion amplitudes (larger than
0.7
cm
). The same results could be found for respiratory cycle up to
8
s
and respiratory motion amplitude up to
1
cm
. The heart dose distribution did not change significantly regardless of respiratory cycle and radiation beam-on timing.
The retroperitoneal margin is a common site of positive surgical margins in patients with resectable pancreatic cancer. Preoperative margin-intensive therapy (MIT) involves delivery of a single high ...dose of ablative radiotherapy (30 Gy) focused on this surgically inaccessible margin, utilizing stereotactic techniques in an effort to reduce local failure following surgery. In this study, we investigated the motion of regional organs at risk (OAR) utilizing 4DCT, evaluated the dosimetric effects of abdominal compression (AC) to reduce regional motion, and compared various planning techniques to optimize MIT.
10 patients were evaluated with 4DCT scans. All 10 patients had scans using AC and seven of the 10 patients had scans both with and without AC. The peak respiratory abdominal organ and major vessel centroid excursion was measured. A "sub-GTV" region was defined by a radiation oncologist and surgical oncologist encompassing the retroperitoneal margin typically lateral and posterior to the superior mesenteric artery (SMA), and a 3-5 mm margin was added to constitute the PTV. Identical 3D non-coplanar SABR (3DSABR) plans were designed for the average compression and non-compression scans. Compression scans were planned with 3DSABR, coplanar IMRT (IMRT), and Cyberknife (CK) planning techniques. Dose volume analysis was undertaken for various endpoints, comparing OAR doses with and without AC and for different planning methods.
The mean PTV size was 20.2 cm3. Regional vessel motion of the SMA, celiac trunk, and renal vessels was small (< 5 mm) and not significantly impacted by AC. Mean pancreatic motion was > 5 mm, so AC has been used in all patients enrolled thus far. AC did not significantly increase OAR dose including the stomach and traverse colon. There were several statistically significant differences in the doses to OARs as a function of the type of planning modality used.
AC does not significantly reduce the limited motion of structures in close proximity to the MIT target and does not significantly increase the dose to OARs that can be displaced by the compression plate. The treatment planning techniques evaluated in this study have different advantages with no clearly superior method in our analysis. Dose to adjacent vessels may be reduced with 3DSABR or IMRT techniques, while conformality is increased with IMRT or CK.
Early-stage glottic larynx squamous cell carcinoma (GLC) is a relatively common disease with excellent oncologic control, but treatment is associated with acute dysphagia and long-term voice quality ...changes. This phase 1 study of hypofractionated radiation therapy for early-stage GLC increased the fraction size while reducing the number of fractions until 5-fraction stereotactic ablative radiation therapy (SABR) was delivered.
Eligible patients had received a diagnosis of stage Tis to T2 GLC. Patients who had undergone prior curative-intent surgery were excluded. The equipotent dose levels were as follows: (1) level 0, 50 Gy in 15 fractions (n = 4); (2) level 1, 45 Gy in 10 fractions (n = 13); and (3) level 2, 42.5 Gy in 5 fractions (SABR level, n = 12). Grade 3 or 4 laryngeal edema, voice, dyspnea, stridor, or cough were the predefined dose-limiting toxicities.
Twenty-nine patients were enrolled from November 2013 to March 2017. The median and minimum follow-up times were 39.2 and 13 months, respectively. Two actively smoking patients, 1 treated in level 1 (grade 4 laryngeal edema, grade 3 dysphagia) and 1 treated in level 2 (grade 3 laryngeal necrosis, dysphagia), developed dose-limiting toxicities. The former patient soon developed a local recurrence, and the latter patient recovered. There were a total of 5 local recurrences: 2 in level 0 and 3 in level 1. The Voice Handicap Index results showed robust long-term voice quality with median values of 7 and 0 at 6 and 12 months, respectively.
Given the tolerability, excellent voice outcomes, and preliminary efficacy data of 5-fraction glottic larynx SABR, this regimen warrants further study.
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