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Title: SU-F-T-645: To Test Spatial Anddosimetric Accuracy of Small Cranial Target Irradiation Based On 1.5 T MRIscans Using Static Arcs with MLCDefined Fields

Abstract

Purpose: To test spatial and dosimetric accuracy of small cranial target irradiation based on 1.5 T MRI scans using static arcs with MLC-defined fields Methods: A plastic (PMMA) phantom simulating a small brain lesion was mounted on a GammaKnife headframe equipped with MRI localizer. The lesion was a 3 mm long, 3.175 mm diameter cylindrical cavity filled with MRI contrast. Radiochromic film passing through the cavity was marked with pin pricks at the cavity center. The cavity was contoured on an MRI image and fused with CT to simulate treatment of a lesion not visible on CT. The transfer of the target to CT involved registering the MRI contrast cannels of the localizer that were visible on both modalities. Treatments were planned to deliver 800 cGy to the cavity center using multiple static arcs with 5.0×2.4 mm MLC-defined fields. The phantom was aligned on a STx accelerator by registering the conebeam CT with the planning CT. Films from coronal and sagittal planes were scanned and evaluated using ImageJ software Results: Geographic errors in treatment based on 1.5 T scans agreed within 0.33, −0.27 and 1.21 mm in the vertical, lateral and longitudinal dimensions, respectively. The doses delivered to the cavitymore » center were 7.2% higher than planned. The dose distributions were similar to those of a GammaKnife. Conclusion: Radiation can be delivered with an accelerator at mm accuracy to small cranial targets based on 1.5 MRI scans fused to CTs using a standard GammaKnife headframe and MRI localizer. MLC-defined static arcs produce isodose lines very similar to the GammaKnife.« less

Authors:
; ; ; ; ; ; ; ;
Publication Date:
OSTI Identifier:
22649203
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; ACCURACY; CAVITIES; COMPUTER CODES; CYLINDRICAL CONFIGURATION; IRRADIATION; NMR IMAGING; RADIATION DOSE DISTRIBUTIONS

Citation Formats

Brezovich, I, Wu, X, Popple, R, Shen, S, Cardan, R, Bolding, M, Fiveash, J, Kraus, J, and Spencer, S. SU-F-T-645: To Test Spatial Anddosimetric Accuracy of Small Cranial Target Irradiation Based On 1.5 T MRIscans Using Static Arcs with MLCDefined Fields. United States: N. p., 2016. Web. doi:10.1118/1.4956830.
Brezovich, I, Wu, X, Popple, R, Shen, S, Cardan, R, Bolding, M, Fiveash, J, Kraus, J, & Spencer, S. SU-F-T-645: To Test Spatial Anddosimetric Accuracy of Small Cranial Target Irradiation Based On 1.5 T MRIscans Using Static Arcs with MLCDefined Fields. United States. doi:10.1118/1.4956830.
Brezovich, I, Wu, X, Popple, R, Shen, S, Cardan, R, Bolding, M, Fiveash, J, Kraus, J, and Spencer, S. 2016. "SU-F-T-645: To Test Spatial Anddosimetric Accuracy of Small Cranial Target Irradiation Based On 1.5 T MRIscans Using Static Arcs with MLCDefined Fields". United States. doi:10.1118/1.4956830.
@article{osti_22649203,
title = {SU-F-T-645: To Test Spatial Anddosimetric Accuracy of Small Cranial Target Irradiation Based On 1.5 T MRIscans Using Static Arcs with MLCDefined Fields},
author = {Brezovich, I and Wu, X and Popple, R and Shen, S and Cardan, R and Bolding, M and Fiveash, J and Kraus, J and Spencer, S},
abstractNote = {Purpose: To test spatial and dosimetric accuracy of small cranial target irradiation based on 1.5 T MRI scans using static arcs with MLC-defined fields Methods: A plastic (PMMA) phantom simulating a small brain lesion was mounted on a GammaKnife headframe equipped with MRI localizer. The lesion was a 3 mm long, 3.175 mm diameter cylindrical cavity filled with MRI contrast. Radiochromic film passing through the cavity was marked with pin pricks at the cavity center. The cavity was contoured on an MRI image and fused with CT to simulate treatment of a lesion not visible on CT. The transfer of the target to CT involved registering the MRI contrast cannels of the localizer that were visible on both modalities. Treatments were planned to deliver 800 cGy to the cavity center using multiple static arcs with 5.0×2.4 mm MLC-defined fields. The phantom was aligned on a STx accelerator by registering the conebeam CT with the planning CT. Films from coronal and sagittal planes were scanned and evaluated using ImageJ software Results: Geographic errors in treatment based on 1.5 T scans agreed within 0.33, −0.27 and 1.21 mm in the vertical, lateral and longitudinal dimensions, respectively. The doses delivered to the cavity center were 7.2% higher than planned. The dose distributions were similar to those of a GammaKnife. Conclusion: Radiation can be delivered with an accelerator at mm accuracy to small cranial targets based on 1.5 MRI scans fused to CTs using a standard GammaKnife headframe and MRI localizer. MLC-defined static arcs produce isodose lines very similar to the GammaKnife.},
doi = {10.1118/1.4956830},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • Purpose: Neurocognitive impairment (NI) in patients with small cell lung cancer (SCLC) after whole brain radiation treatment (WBRT) is a significant cause of morbidity. Hippocampal avoidance (HA) during WBRT may mitigate or prevent NI in such patients. However, this has not been tested in SCLC patients. The estimated risk of metastases in the HA region (HM) in patients with SCLC at diagnosis or after WBRT is unknown. Our study aimed to determine the risk of HM in patients with SCLC and to assess correlated clinical factors. Methods and Materials: Patients with SCLC who experienced brain metastases (BM) at presentation (demore » novo) or after WBRT treated at the Saskatoon Cancer Centre between 2005 and 2012 were studied. Relevant neuroimaging was independently reviewed by a neuroradiologist. HM was defined as metastases within 5 mm of the hippocampus. Logistic regression analysis was performed to assess correlation between various clinical variables and HM. Results: Seventy eligible patients were identified. Of 59 patients presenting with de novo BM, 3 patients (5%, 95% confidence interval [CI]: 0%-10.7%) had HM. Collectively there were 359 (range, 1-33) de novo BM with 3 (0.8%, 95% CI: 0%-1.7%) HM deposits. Twenty patients experienced progression of metastatic disease in the brain after WBRT. Of the 20 patients, only 1 patient (5%, 95% CI: 0%-14.5%) experienced HM. On logistic regression, no factors significantly correlated with HM. Conclusion: The overall incidence of HM before or after WBRT in SCLC patients is low, providing preliminary support for the safety of HA during planned clinical trials of HA-WBRT for SCLC.« less
  • Computed cranial tomographic scans were performed as part of the pretreatment evaluation and at six- to nine-month intervals posttreatment in 13 patients with small cell lung carcinoma. All patients received 3000 rad of prophylactic cranial irradiation delivered over two weeks in ten treatment fractions in conjunction with multiagent chemotherapy. Posttreatment scans documented an extraordinarily high frequency of abnormalities including cerebral atrophy (100%), ventricular dilatation (70%), and decreased coefficient of absorption in the white matter (15%). Unexplained neurologic abnormalities developed in four of six patients living at least 15 months after institution of therapy. As the number of long-term survivors ofmore » this type of lung cancer increases, the need for prospective comprehensive neuropsychologic assessment to determine the clinical significance of these changes is needed.« less
  • Purpose: To determine the 6 degree of freedom systematic deviations between 2D/3D and CBCT image registration with various imaging setups and fusion algorithms on the Varian Edge Linac. Methods: An anthropomorphic head phantom with radio opaque targets embedded was scanned with CT slice thicknesses of 0.8, 1, 2, and 3mm. The 6 DOF systematic errors were assessed by comparing 2D/3D (kV/MV with CT) with 3D/3D (CBCT with CT) image registrations with different offset positions, similarity measures, image filters, and CBCT slice thicknesses (1 and 2 mm). The 2D/3D registration accuracy of 51 fractions for 26 cranial SRS patients was alsomore » evaluated by analyzing 2D/3D pre-treatment verification taken after 3D/3D image registrations. Results: The systematic deviations of 2D/3D image registration using kV- kV, MV-kV and MV-MV image pairs were within ±0.3mm and ±0.3° for translations and rotations with 95% confidence interval (CI) for a reference CT with 0.8 mm slice thickness. No significant difference (P>0.05) on target localization was observed between 0.8mm, 1mm, and 2mm CT slice thicknesses with CBCT slice thicknesses of 1mm and 2mm. With 3mm CT slice thickness, both 2D/3D and 3D/3D registrations performed less accurately in longitudinal direction than thinner CT slice thickness (0.60±0.12mm and 0.63±0.07mm off, respectively). Using content filter and using similarity measure of pattern intensity instead of mutual information, improved the 2D/3D registration accuracy significantly (P=0.02 and P=0.01, respectively). For the patient study, means and standard deviations of residual errors were 0.09±0.32mm, −0.22±0.51mm and −0.07±0.32mm in VRT, LNG and LAT directions, respectively, and 0.12°±0.46°, −0.12°±0.39° and 0.06°±0.28° in RTN, PITCH, and ROLL directions, respectively. 95% CI of translational and rotational deviations were comparable to those in phantom study. Conclusion: 2D/3D image registration provided on the Varian Edge radiosurgery, 6 DOF-based system provides accurate target positioning for frameless image-guided cranial stereotactic radiosurgery.« less
  • Purpose: To evaluate a commercial volumetric modulated arc therapy (VMAT), using multiple noncoplanar arcs, for linac-based cranial radiosurgery, as well as evaluate the combined accuracy of the VMAT dose calculations and delivery. Methods: Twelve patients with cranial lesions of variable size (0.1-29 cc) and two multiple metastases patients were planned (Eclipse RapidArc AAA algorithm, v8.6.15) using VMAT (1-6 noncoplanar arcs), dynamic conformal arc (DCA, {approx}4 arcs), and IMRT (nine static fields). All plans were evaluated according to a conformity index (CI), healthy brain tissue doses and volumes, and the dose to organs at risk. A 2D dose distribution was measuredmore » (Varian Novalis Tx, HD120 MLC, 1000 MU/min, 6 MV beam) for the {approx}4 arc VMAT treatment plans using calibrated film dosimetry. Results: The CI (0-1 best) average for all plans was best for {approx}4 noncoplanar arc VMAT at 0.86 compared with {approx}0.78 for IMRT and a single arc VMAT and 0.68 for DCA. The volumes of healthy brain receiving 50% of the prescribed target coverage dose or more (V{sub 50%}) were lowest for the four arc VMAT [RA(4)] and DCA plans. The average ratio of the V{sub 50%} for the other plans to the RA(4) V{sub 50%} were 1.9 for a single noncoplanar arc VMAT [RA(1nc)], 1.4 for single full coplanar arc VMAT [RA(1f)] and 1.3 for IMRT. The V{sub 50%} improved significantly for single isocenter multiple metastases plan when two noncoplanar VMAT arcs were added to a full single coplanar one. The maximum dose to 5 cc of the outer 1 cm rim of healthy brain which one may want to keep below nonconsequential doses of 300-400 cGy, was 2-3 times greater for IMRT, RA(1nc) and RA(1f) plans compared with the multiple noncoplanar arc DCA and RA(4) techniques. Organs at risk near (0-4 mm) to targets were best spared by (i) single noncoplanar arcs when the targets are lateral to the organ at risk and (ii) by skewed nonvertical planes of IMRT fields when the targets are not lateral to the organ at risk. The highest dose gradient observed between an organ at risk and a target at the edge of a VMAT arc plane or plane of IMRT fields was 17%/mm. The average absolute percent difference between the measured and calculated central axis dose for all the VMAT plans was 3.6 {+-} 2.2%. The measured perpendicular profile widths and shifts were on average within 0.5 mm of planned values. The average total MUs for VMAT plans was double the DCA average and similar to the IMRT average. Conclusions: For the aforementioned planning and delivery system and cranial lesions greater than 7 mm in diameter, multiple noncoplanar arc VMAT consistently provides accurate and high quality cranial radiosurgery dose distributions with low doses to healthy brain tissue and high dose conformity to the target. These qualities may make multiple noncoplanar arc VMAT suitable for a greater range of prescription doses or larger and more irregular lesions. For smaller and/or rounder lesions there are other clinically acceptable treatment techniques that may involve fewer couch angles or arcs and reduce treatment times.« less
  • Purpose: Patient-specific quality assurance in volumetric modulated arc therapy (VMAT) brain stereotactic radiosurgery raises specific issues on dosimetric procedures, mainly represented by the small radiation fields associated with the lack of lateral electronic equilibrium, the need of small detectors and the high dose delivered (up to 30 Gy). Gafchromic{sup TM} EBT2 and EBT3 films may be considered the dosimeter of choice, and the authors here provide some additional data about uniformity correction for this new generation of radiochromic films.Methods: A new analysis method using blue channel for marker dye correction was proposed for uniformity correction both for EBT2 and EBT3more » films. Symmetry, flatness, and field-width of a reference field were analyzed to provide an evaluation in a high-spatial resolution of the film uniformity for EBT3. Absolute doses were compared with thermoluminescent dosimeters (TLD) as baseline. VMAT plans with multiple noncoplanar arcs were generated with a treatment planning system on a selected pool of eleven patients with cranial lesions and then recalculated on a water-equivalent plastic phantom by Monte Carlo algorithm for patient-specific QA. 2D quantitative dose comparison parameters were calculated, for the computed and measured dose distributions, and tested for statistically significant differences.Results: Sensitometric curves showed a different behavior above dose of 5 Gy for EBT2 and EBT3 films; with the use of inhouse marker-dye correction method, the authors obtained values of 2.5% for flatness, 1.5% of symmetry, and a field width of 4.8 cm for a 5 × 5 cm{sup 2} reference field. Compared with TLD and selecting a 5% dose tolerance, the percentage of points with ICRU index below 1 was 100% for EBT2 and 83% for EBT3. Patients analysis revealed statistically significant differences (p < 0.05) between EBT2 and EBT3 in the percentage of points with gamma values <1 (p= 0.009 and p= 0.016); the percent difference as well as the mean difference between calculated and measured isodoses (20% and 80%) were found not to be significant (p= 0.074, p= 0.185, and p= 0.57).Conclusions: Excellent performances in terms of dose homogeneity were obtained using a new blue channel method for marker-dye correction on both EBT2 and EBT3 Gafchromic{sup TM} films. In comparison with TLD, the passing rates for the EBT2 film were higher than for EBT3; a good agreement with estimated data by Monte Carlo algorithm was found for both films, with some statistically significant differences again in favor of EBT2. These results suggest that the use of Gafchromic{sup TM} EBT2 and EBT3 films is appropriate for dose verification measurements in VMAT stereotactic radiosurgery; taking into account the uncertainty associated with Gafchromic film dosimetry, the use of adequate action levels is strongly advised, in particular, for EBT3.« less