Purpose/Objective(s): Few treatment options exist for recurrent GBM. HFSRT has been used as a salvage treatment strategy. Gross tumor volume (GTV) is usually based on pretreatment contrast enhanced T1-weighted (T1-contrast pre ) MR image. T2-FLAIR pre may detect additional subtle signal of tumor infiltration. This study aimed to investigate the patterns of recurrence following salvage HFSRT using T2-FLAIR image in addition to T1-contrast in target delineation for HFSRT. Materials/Methods: We retrospectively examined 13 patients with recurrent GBM treated with HFSRT from 2015 to 2017 who had local recurrence following HFSRT. A median dose of 30 (25-35) Gy in 5 to 10 fractions was delivered. The median time between HFSRT and recurrence after HFSRT was 178 (48-259) days. Diagnostic MRI was performed before and 4 weeks after HFSRT, and then every 4 -8 weeks. Separate GTVs using T1-contrast pre only, T2-FLAIR pre only, or T1 pre +-T2 pre , were contoured blindly by a single radiation oncology physician. Recurrence volume was delineated on the post-treatment T1-contrast (T1-contrast post ) MRI at the time of progression. The volume overlapping between pretreatment GTV and recurrence volume was calculated. The centroid distance between pre-and post-treatment volumes was measured as well. Wilcoxon test was used to assess the statistical significance of differences. Results: The median volumes overlapping between T1-contrast pre , T2-FLAIR pre , T1 pre +T2 pre and T1-contrast post were 18% (range: 0-100%, Q1: 12%, Q3: 40%), 52% (range: 0-90%, Q1: 24%, Q3: 59%) and 53% (range: 0-100%, Q1: 26%, Q3: 77%), respectively. The recurrent volume overlapping with T1 pre +T2 pre was significantly larger than the overlap with T1-contrast pre (pZ0.003). The median volume difference between T1-contrast pre and T2-FLAIR pre volumes resided in the recurrence volume was 3.9 cm 3 (range: 0-11.5 cm 3 , Q1: 0.2 cm 3 , Q3 5.6 cm 3 ). The centroid distance between volumes did not show significant difference. The median centroid distances between recurrence volume and T1-contrast pre volume, T2-FLAIR pre volume, and T1 pre +T2 pre volume were 1.3 cm (range: 0.3-4.9 cm, Q1: 0.8, Q3: 2.00), 1.3 cm (range: 0.3-4.7 cm, Q1: 0.8 cm, Q3: 2 cm) and 1.2 cm (range: 0.2-1.2 cm, Q1: 0.7 cm, Q3: 2.1 cm), respectively. Conclusion: A significant volume of recurrence occurred in the T1 pre +T2 pre region beyond the T1-contrast pre region. Further studies to investigate techniques incorporating T2-FLAIR pre region may improve GTV delineation for salvage HFSRT.Purpose/Objective(s): The impact of rotational deviations is investigated for single fiducial tumor tracking. The hypothesis is that the yaw rotation of a single fiducial will increase the uncertainty parameter in the tracking system. Materials/Methods: When treating a moving target, tumor tracking can be employed using a single fiducial. However, tracking using a single fiducial is limited to linear chasing and does not track rotation. A mini ball cube with 3, gold fiducials on its surface was placed insi...
high priority in planning optimization (optic organs, brain stem and spinal cord) provided that other target and OAR dosimetry are approximately equivalent.
Purpose: To investigate the potential use of the Raven™ (LAP of America Laser Applications) for real time AQA of Cyberknife™ with InCise2 MLC (Accuray™ Medical). Methods: At setup, the Raven was rotated 45° on which an Accuray™ AQA cube was positioned. Three different AQA plans for fixed cone, InCise2MLC, and a modified MLC plan were delivered repeatedly ten times. The additional shapes in modified AQA plan enable additional reproducibility checks for all the MLC pairs. During the test, the cube was aligned by imbedded fiducials and irradiated. The two angled radiation beams aimed center tungsten ball of the cube and projected 45° to phosphor screen and registered by a CCD camera of the Raven device. The centricity of the metal ball in the irradiated field was then analyzed using Matlab codes. Results: For AP images, the average offsets of X, Y, and radial directions are 0.24 ± 0.04 mm, 0.25 ± 0.02 mm and 0.35 ±± 0.03 mm respectively for the cone; 0.34 ± 0.02 mm, 0.49 ± 0.04 mm and 0.60 ± 0.04 mm respectively for the MLC. For lateral images, they are 0.63 ± 0.05 mm, 0.11 ± 0.02 mm and 0.64 ± 0.04 mm respectively for the cone, 0.79 ± 0.08 mm, −0.23 ± 0.06 mm and 0.82 ± 0.09 mm respectively for the MLC. No inconsistent MLC shapes were found in the modified AQA group. Conclusion: The results are consistent with clinically acceptable values (≤1mm from baseline). The results suggest the potential of replacement of the standard AQA test with the novel real‐time Raven device for Cyberknife daily QA. The modified MLC based AQA provides a more comprehensive MLC daily QA capability. Further improvements in its resolution and automatic analyzing capability are warranted.
Purpose: To validate a novel real time quality assurance device, as a means to test coincidence of light fields to electron radiation fields. Method and Materials: Use a Raven™ (LAP of America Laser Applications) detector, both light fields and electron radiation fields of various electron cones and cutouts from two Clinacs (Varian Medical) were sensed by the phosphor screen and registered by a CCD camera of the device. During measurements, the screen surface of Raven was placed at ISO center level facing the radiation field at any setup angle. Subsequently the light field and the electron radiation field (with 100 MU) were captured separately by the device. The measurements were then analyzed using the Raven software with a maximal 25 by 25 cm^2 field size and 0.25 mm resolution. The results were further compared against those using chromic graphic film (EBT3). To ensure consistence only the dimensions through the central axis were recorded. All the films were analyzed with Dose Lab Pro™ v6.70. Coincidence comparisons were done within the tests on one Clinac and between the two Clinacs. Results: The similar difference means of the field coincidence are indicated from the 18 samples by EBT films and 34 by the Raven as 1.33 ± 0.87 mm verses 1.06 ± 0.58 mm (p = 0.74). The mean differences of the field coincidence between the two Clinacs, 1.16 ± 0.68 mm (n=16) and 1.16 ± 0.48 mm (n=18) respectively, also suggest no statistical difference (p= 0.40). Conclusion: The Raven™ is a comparable quality verification device to the chromic graphic film (EBT3) in checking the coincidence between light and electron radiation fields. In this investigation, the Raven device provided highly reproducible results with real time analysis. Further improvements in its resolution and automatic analyzing capability are warranted.
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