PurposeHistorically, the process of positioning a patient prior to imaging verification used a set of permanent patient marks, or tattoos, placed subcutaneously. After aligning to these tattoos, plan specific shifts are applied and the position is verified with imaging, such as cone‐beam computed tomography (CBCT). Due to a variety of factors, these marks may deviate from the desired position or it may be hard to align the patient to these marks. Surface‐based imaging systems are an alternative method of verifying initial positioning with the entire skin surface instead of tattoos. The aim of this study was to retrospectively compare the CBCT‐based 3D corrections of patients initially positioned with tattoos against those positioned with the C‐RAD CatalystHD surface imager system.MethodsA total of 6000 individual fractions (600–900 per site per method) were randomly selected and the post‐CBCT 3D corrections were calculated and recorded. For both positioning methods, four common treatment site combinations were evaluated: pelvis/lower extremities, abdomen, chest/upper extremities, and breast. Statistical differences were evaluated using a paired sample Wilcoxon signed‐rank test with significance level of <0.01.ResultsThe average magnitudes of the 3D shift vectors for tattoos were 0.9 ± 0.4 cm, 1.0 ± 0.5 cm, 0.9 ± 0.6 cm and 1.4 ± 0.7 cm for the pelvis/lower extremities, abdomen, chest/upper extremities and breast, respectively. For the CatalystHD, the average magnitude of the 3D shifts for the pelvis/lower extremities, abdomen, chest/upper extremities and breast were 0.6 ± 0.3 cm, 0.5 ± 0.3 cm, 0.5 ± 0.3 cm and 0.6 ± 0.2 cm, respectively. Statistically significant differences (P < 0.01) in the 3D shift vectors were found for all four sites.ConclusionThis study shows that the overall 3D shift corrections for patients initially aligned with the C‐RAD CatalystHD were significantly smaller than those aligned with subcutaneous tattoos. Surface imaging systems can be considered a viable option for initial patient setup and may be preferable to permanent marks for specific clinics and patients.

Purpose With the advent of volumetric modulated arc therapy (VMAT) and intensity‐modulated radiation therapy (IMRT) treatment techniques, the requirement for more elaborate approaches in reviewing linac components’ integrity has become even more stringent. A possible solution to this challenge is to employ the usage of log files generated during treatment. The log files generated by the new generation of Elekta linacs record events at a higher frequency (25 Hz) than their predecessors, which allows for retrospective analysis and identification of subtle changes and provides another means of quality assurance. The ability to track machine components based on log files for each treatment can allow for constant monitoring of fraction consistency in addition to machine reliability. Using Elekta Agility log files, a set of tests were developed to evaluate the reliability and robustness of the multileaf collimators (MLCs). Methods To evaluate Elekta log file utilization for linac MLC QA effectiveness, five MLC test patterns were constructed to review the effects of leaf velocity and acceleration on positional accuracy, including gravitational effects for the Elekta MLC system. Each test was run five times in a particular setting to obtain reproducibility data and statistical averages. This study was performed on two identical Versa HD machines, each delivering a full set of test plans with all possible variations. Plans were delivered using Elekta's iCOMcat software and recorded log files were extracted. Log files were reformatted for readability and automatically analyzed in Matlab®. Results The Elekta Agility MLC system was shown to be capable of obtaining speeds within the range of 5–35 mm/s. MLC step and shoot tests have demonstrated the MLC system's capability of having positional repeatability, averaging 0.03‐ and 0.08‐mm offsets with and without gravitational effects, respectively. The IMRT‐specific tests have shown that gravitational effects are negligible with all positional tests averaging 0.5‐mm offsets. The largest speed root‐mean‐square error (RMSE) for the MLC system was found at the maximum speed of 35 mm/s with an average error of 0.8 mm. For slower speeds, the value was found to be much lower. Conclusion Utilizing log files has demonstrated the feasibility for higher precision of MLC motions to be reviewed, based on the performance tests that were instituted. Log files provide insight on the effects of friction, acceleration, and gravity, with MU's delivered that previously could not be reviewed in such detail. Based on our results, log file‐based QA has enhanced our ability to review performance, functionality, and perform QA on Elekta's MLC system.

Electronic portal imaging devices (EPIDs) could potentially be useful for intensity‐modulated radiation therapy (IMRT) QA. The data density, high resolution, large active area, and efficiency of the MV EPID make it an attractive option. However, EPIDs were designed as imaging devices, not dosimeters, and as a result they do not inherently measure dose in tissue equivalent media. EPIDose (Sun Nuclear, Melbourne, FL) is a tool designed for the use of EPIDs in IMRT QA that uses raw MV EPID images (no additional build‐up and independent of gantry angle, but with dark and flood field corrections applied) to estimate absolute dose planes normal to the beam axis in a homogeneous media (i.e. similar to conventional IMRT QA methods). However, because of the inherent challenges of the EPID‐based dosimetry, validating and commissioning such a system must be done very carefully, by exploring the range of use cases and using well‐proven “standards” for comparison. In this work, a multi‐institutional study was performed to verify accurate EPID image to dose plane conversion over a variety of conditions. Converted EPID images were compared to 2D diode array absolute dose measurements for 188 fields from 28 clinical IMRT treatment plans. These plans were generated using a number of commercially available treatment planning systems (TPS) covering various treatment sites including prostate, head and neck, brain, and lung. The data included three beam energies (6, 10, and 15 MV) and both step‐and‐shoot and dynamic MLC fields. Out of 26,207 points of comparison over 188 fields analyzed, the average overall field pass rate was 99.7% when 3 mm/3% DTA criteria were used (range 94.0–100 per field). The pass rates for more stringent criteria were 97.8% for 2 mm/2% DTA (range 82.0–100 per field), and 84.6% for 1 mm/1% DTA (range 54.7–100 per field). Individual patient‐specific sites as well, as different beam energies, followed similar trends to the overall pass rates.PACS number: 87.53.Dq; 87.66.Jj

A DNA dosimeter can accurately determine the probability of DNA double-strand break (DSB), one of the most toxic effects of radiotherapy, for absorbed radiation doses from 25 to 200 Gy. This is an important step in demonstrating the viability of DNA dosimeters as a measurement technique for radiation.

The reproducibility and accuracy of routine echocardiographic measurements made by an inexperienced doctor using tele-instruction were evaluated. Thirty-eight patients were first examined at a local hospital by an inexperienced doctor instructed by a specialist 450 km away at a university hospital. The specialist then examined the patients at the local hospital using the same equipment, after an average of 50 days. The accuracy of M-mode and quantitative Doppler measurements was comparable to that observed in reproducibility studies made under normal examination conditions. There were no systematic measurement errors. No important M-mode information was missed except evidence of left ventricular hypertrophy in six patients. In the two-dimensional examination there were differences of clinical significance in only three patients. There were no clinically important differences in the Doppler quantification of mitral and aortic regurgitation. Tele-instructed echocardiography is also an excellent educational tool, allowing an inexperienced examiner gradually to take responsibility for the local echocardiographic service.

No abstract

Purpose Prognostic indices such as the Brain Metastasis Graded Prognostic Assessment have been used in clinical settings to aid physicians and patients in determining an appropriate treatment regimen. These indices are derivative of traditional survival analysis techniques such as Cox proportional hazards (CPH) and recursive partitioning analysis (RPA). Previous studies have shown that by evaluating CPH risk with a nonlinear deep neural network, DeepSurv, patient survival can be modeled more accurately. In this work, we apply DeepSurv to a test case: breast cancer patients with brain metastases who have received stereotactic radiosurgery. Methods Survival times, censorship status, and 27 covariates including age, staging information, and hormone receptor status were provided for 1673 patients by the NCDB. Monte Carlo cross‐validation with 50 samples of 1400 patients was used to train and validate the DeepSurv, CPH, and RPA models independently. DeepSurv was implemented with L2 regularization, batch normalization, dropout, Nesterov momentum, and learning rate decay. RPA was implemented as a random survival forest (RSF). Concordance indices of test sets of 140 patients were used for each sample to assess the generalizable predictive capacity of each model. Results Following hyperparameter tuning, DeepSurv was trained at 32 min per sample on a 1.33 GHz quad‐core CPU. Test set concordance indices of 0.7488 ± 0.0049, 0.6251 ± 0.0047, and 0.7368 ± 0.0047, were found for DeepSurv, CPH, and RSF, respectively. A Tukey HSD test demonstrates a statistically significant difference between the mean concordance indices of the three models. Conclusion Our results suggest that deep learning‐based survival prediction can outperform traditional models, specifically in a case where an accurate prognosis is highly clinically relevant. We recommend that where appropriate data are available, deep learning‐based prognostic indicators should be used to supplement classical statistics.

Purpose Single‐isocenter multiple brain metastasis stereotactic radiosurgery is an efficient treatment modality increasing in clinical practice. The need to provide accurate, patient‐specific quality assurance (QA) for these plans is met by several options. This study reviews some of these options and explores the use of the Octavius 4D as a solution for patient‐specific plan quality assurance. Methods The Octavius 4D Modular Phantom (O4D) with the 1000 SRS array was evaluated in this study. The array consists of 977 liquid‐filled ion chambers. The center 5.5 cm × 5.5 cm area has a detector spacing of 2.5 mm. The ability of the O4D to reconstruct three‐dimensional (3D) dose was validated against a 3D gel dosimeter, ion chamber, and film measurements. After validation, 15 patients with 2–11 targets had their plans delivered to the phantom. The criteria used for the gamma calculation was 3%/1 mm. The portion of targets which were measurable by the phantom was countable. The accompanying software compiled the measured doses allowing each target to be counted from the measured dose distribution. Results Spatial resolution was sufficient to verify the high dose distributions characteristic of SRS. Amongst the 15 patients there were 74 targets. Of the 74 targets, 61 (82%) of them were visible on the measured dose distribution. The average gamma passing rate was 99.3% (with sample standard deviation of 0.68%). Conclusions The high resolution provided by the O4D with 1000 SRS board insert allows for very high‐resolution measurement. This high resolution in turn can allow for high gamma passing rates. The O4D with the 1000 SRS array is an acceptable method of performing quality assurance for single‐isocenter multiple brain metastasis SRS.