Purpose: Stereotactic Body Radiation Therapy (SBRT) has been used increasingly for the management of spinal lesions. This study was performed to investigate the effect of respiratory motion on the ...dose distributions of spine SBRT patients. Method: 4D CT and treatment planning data for thoracic spinal lesions (T5 and T8) in two linac‐based SBRT patients was studied retrospectively. Bony structures of the spine were visually inspected in all 10 phases of the 4D CT images and there was no spinal motion observed. Tumors were contoured by radiation oncologists on the 50% phase of the 4D CT images, which corresponded to end exhalation. A single‐fraction dose of 20Gy and 14Gy was prescribed to CTV20 (gross tumor) and CTV14 (contiguous marrow cavity) respectively. Intensity modulated treatment plans were constructed on the 50% 4DCT phase and copied to all other phases of the 4D data set for comparative dose calculations. The DVHs of CTV20, CTV14, and the spinal cord were compared between actual dose, which is the sum of dose from all phases, and planned dose, which was done on 50% phase of 4D CT images. Results: The impacts of chest wall and diaphragm motion on the dose distribution were analyzed. Treatment plans that incorporated all respiratory phases resulted in improved CTV20 coverage less than 2% but the maximum dose within spinal cord was increased 3∼4%. Conclusion: Respiratory motion has a modest impact on the dose distribution of spine SBRT treatments including a 3–4% increase in cord dose. Motion control methods should be considered to reduce the uncertainties of dose delivery when motion amplitude is large.
Purpose: To present an impact of CBCT on efficiency and accuracy of SBRT treatments in case of lung and prostate tumors. Method and Materials: Patients interfraction and intrafaction setup errors ...have been analyzed for prostate SBRT treatments and for lung SBRT treatments. The CBCT has been utilized for this purpose. The CBCT measurements of shifts before the end of treatment have been also collected for comparisons. Results: Average interfractional shift for SBRT prostate treatments in vertical direction was −0.51cm with average deviation from mean of 0.29cm and with maximal shift of 1.3cm, in longitudinal direction these values were respectively −.01, 0.29 and 0.6cm and in lateral direction these values were 0.05, 0.22 and 0.8cm respectively. Average intrafractional shift for SBRT prostate treatments in vertical direction was −0.05cm with average deviation from mean of 0.07cm and with maximal shift of 0.2cm, in longitudinal direction these values were respectively 0.07, 0.12 and 0.5cm and in lateral direction these values were −0.08, 0.1 and 0.2cm respectively. Average interfractional shift for SBRT Lung treatments in vertical direction was −0.24cm with average deviation from mean of 0.37cm and with maximal shift of 1.1cm, in longitudinal direction these values were respectively −.06, 0.41 and 0.8cm and in lateral direction these values were −0.11, 0.34 and 0.9cm respectively. Average intrafractional shift for SBRT Lung treatments in vertical direction was −0.01cm with average deviation from mean of 0.06cm and with maximal shift of 0.2cm, in longitudinal direction these values were respectively 0.01, 0.04 and 0.3cm and in lateral direction these values were 0, 0.05 and 0.3cm respectively. Conclusion. Daily use of CBCT IGRT for patient setups indicates that daily corrections of setup errors at treatment justify reduction of margins in SBRT treatments of lung and prostate.
The LOFAR Two-metre Sky Survey Shimwell, T. W.; Hardcastle, M. J.; Tasse, C. ...
Astronomy and astrophysics (Berlin),
03/2022, Letnik:
659
Journal Article
Recenzirano
Odprti dostop
In this data release from the ongoing LOw-Frequency ARray (LOFAR) Two-metre Sky Survey we present 120–168 MHz images covering 27% of the northern sky. Our coverage is split into two regions centred ...at approximately 12h45m +44°30′ and 1h00m +28°00′ and spanning 4178 and 1457 square degrees respectively. The images were derived from 3451 h (7.6 PB) of LOFAR High Band Antenna data which were corrected for the direction-independent instrumental properties as well as direction-dependent ionospheric distortions during extensive, but fully automated, data processing. A catalogue of 4 396 228 radio sources is derived from our total intensity (Stokes
I
) maps, where the majority of these have never been detected at radio wavelengths before. At 6″ resolution, our full bandwidth Stokes
I
continuum maps with a central frequency of 144 MHz have: a median rms sensitivity of 83 μJy beam
−1
; a flux density scale accuracy of approximately 10%; an astrometric accuracy of 0.2″; and we estimate the point-source completeness to be 90% at a peak brightness of 0.8 mJy beam
−1
. By creating three 16 MHz bandwidth images across the band we are able to measure the in-band spectral index of many sources, albeit with an error on the derived spectral index of > ± 0.2 which is a consequence of our flux-density scale accuracy and small fractional bandwidth. Our circular polarisation (Stokes
V
) 20″ resolution 120–168 MHz continuum images have a median rms sensitivity of 95 μJy beam
−1
, and we estimate a Stokes
I
to Stokes
V
leakage of 0.056%. Our linear polarisation (Stokes
Q
and Stokes
U
) image cubes consist of 480 × 97.6 kHz wide planes and have a median rms sensitivity per plane of 10.8 mJy beam
−1
at 4′ and 2.2 mJy beam
−1
at 20″; we estimate the Stokes
I
to Stokes
Q
/
U
leakage to be approximately 0.2%. Here we characterise and publicly release our Stokes
I
,
Q
,
U
and
V
images in addition to the calibrated
uv
-data to facilitate the thorough scientific exploitation of this unique dataset.
To determine which MR imaging sequences are necessary to assess for spinal metastases.
Hypothetical MR imaging interpretations and management plans were made prospectively for consecutive adult cases ...acquired retrospectively. Standardized MR imaging protocols were independently interpreted by 2 neuroradiologists. MR imaging protocol types varied: 1) T1-weighted images only; 2) T1-weighted and T2-weighted images; 3) T1-weighted and postcontrast T1-weighted images; and 4) T1- and T2-weighted images and postcontrast T1-weighted images. Hypothetical management plans were created by 2 radiation oncologists. Logit model was used to investigate the effect of MR imaging protocol type on the probability of recommending radiation therapy (RT). Mixed effect models were used to investigate whether median spinal level or total number of spinal levels of planned RT was associated with MR imaging protocol type.
Thirty-one subjects were evaluated, each with multiple scan interpretations. Logit model showed that neither MR imaging protocol type nor neuroradiologist reader affected the probability that the oncologist would recommend RT (all P > .50). Mixed models showed that neither ML nor NL was affected by MR imaging protocol type or by neuroradiologist reader (all P > .12).
Although MR imaging is known to be the most useful diagnostic test in suspected spinal cord compression, which particular MR images are necessary remain unclear. Compared with T1-weighted images alone, the additional use of T2-weighted and/or postcontrast T1-weighted sequences did not significantly affect the probability that RT would be recommended or the levels that would be chosen for RT in our study. Our data suggest that unenhanced T1-weighted images may be sufficient for evaluation of possible cord compression.
Purpose: To evaluate the accuracy of cone beam computed tomography (CBCT) guided positioning in the case of motion patterns associated with regular and irregular breathing for lung cancer ...stereotactic body radiation therapy (SBRT). Methods and Materials: Five irregular motion patterns have been used in phantom‐simulated cases using a solid ball to create four‐dimensional (4D) CT datasets. Images are transferred to the Pinnacle Planning System 8.0m (Phillips) where a planning treatment volume (PTV) is constructed for planning. Subsequently the same phantom simulated cases are imaged with a CBCT (Elekta XVI) in volumetric reconstruction mode. Images defining the PTV using CBCT are compared with PTV determined from 4DCT images. Breathing motion patterns used in these phantom studies were from actual patients' data taken at random. For comparisons regular breathing motion data have been also used for reference in PTV matching derived from 4DCT and CBCT. The actual time dependant target position was known in each phantom‐simulated case from the driver files associated with the motion generator. Results For regular motion, CBCT exhibited up to 2mm shift between 4DCT derived PTV and CBCT defined PTV. For irregular motion, the CBCT derived PTV exhibited up to3.7mm shift relative to 4DCT derived PTV. However, we found that neither the 4DCT nor the CBCT accurately reflect of the actual PTV motion and geometry (up to 4.9mm) derived from known target dimensions and knowledge of motion data. Dosimetric impact of this error will be reported. Conclusions The setup of target for SBRT treatment of lung tumor based on CBCT derived PTV is consistent with treatment plan based on 4DCT. This clinically positive result is not based, however, on accurate representation of clinically used PTV with true geometrical representation of PTV target derived from known target dimensions and known pattern of target motion in the phantom.
Radio-mode feedback associated with the active galactic nuclei (AGNs) at the cores of galaxy clusters injects a large amount of energy into the intracluster medium (ICM), offsetting radiative losses ...through X-ray emission. This mechanism prevents the ICM from rapidly cooling down and fueling extreme starburst activity as it accretes onto the central galaxies, and it is therefore a key ingredient in the evolution of galaxy clusters. However, the influence and mode of feedback at high redshifts ( z ∼ 1) remains largely unknown. Low-frequency sub-arcsecond-resolution radio observations taken with the International LOFAR Telescope have demonstrated their ability to assist X-ray observations with constraining the energy output from the AGNs (or “cavity power”) in galaxy clusters, thereby enabling research at higher redshifts than before. In this pilot project, we tested this hybrid method on a high-redshift (0.6 < z < 1.3) sample of 13 galaxy clusters for the first time with the aim of verifying the performance of this method at these redshifts and providing the first estimates of the cavity power associated with the central AGN for a sample of distant clusters. We were able to detect clear radio lobes in three out of 13 galaxy clusters at redshifts of 0.7 < z < 0.9, and we used these detections in combination with ICM pressures surrounding the radio lobes obtained from standard profiles to calculate the corresponding cavity powers of the AGNs. Combining our results with the literature, the current data appear to suggest that the average cavity power peaked at a redshift of z ∼ 0.4 and slowly decreases toward higher redshifts. However, we require more and tighter constraints on the cavity volume and a better understanding of our observational systematics to confirm any deviation of the cavity power trend from a constant level.
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