Investigation on the accuracy of field widths and the quantitative relationship with energy variations for dynamic jaws helical tomotherapy.

BACKGROUND AND PURPOSE: TomoEDGE is an advanced technology for TomoTherapy treatment delivery by introducing a sliding-window dynamic jaw motion. The front and back jaws move independently at the start and end of a target volume along the longitudinal couch direction to reduce the undesired dose to the normal tissues. The accuracy of field width is essential to treatment delivery in this regard. The purpose of this work was to analyze the performance of dynamic jaws on helical tomotherapy and investigate the relationship with energy variation. METHODS: The Tomotherapy-Quality-Assurance (TQA) Dynamic Field Width procedure was performed monthly across three tomotherapy machines. All field widths were analyzed, especially the FWHM of the 10 mm field width. Field width measurements were compared with the ratio of Percentage Depth Dose at 20 and 10 cm to render the value of correlation. Changes in beam FWHM and energy were further discussed. Two-year data were collected for this purpose. RESULTS: On average, measured field widths in each unit agreed within 1% tolerance recommendation stated. The average absolute difference between reference and measured FWs in each unit was approximately 0.07 mm. An increase of 1.5% in the FW of the 10 mm nominal beam width was correlated with a 1% increase in PDD20,10 ratio, implying a positive correlation between the two factors (p < 0.002). CONCLUSIONS: A positive correlation between nominal 10 mm FW and PDD20,10 was observed. In the case that the PDD20,10 marginally passes the QA tests, users are recommended to consider further verification on Dynamic Jaws to ensure the smallest field width to be within tolerance, which is essential to maintain effective treatment in TomoEDGE system. Since the regression of this study was a single-factor model, other confounding factors such as the focal spot size of linear accelerator should also be considered when evaluating the machine status.

Performance evaluation of online motion synchronizing systems for patient-specific respiratory movements with helical tomotherapy.

Background and purpose.The introduction of online motion synchronizing system on helical tomotherapy paves way for robust motion tracking. A recent upgrade launches modifications on both hardware and software of the kV tracking system. An evaluation on the kV subsystems, prior (Version1) and post upgrade (Version2), was performed to compare tracking accuracy by means of fiducial tracking error and resulted root-mean-square (RMS). Impacts influenced by various patient-specific breathing pattern regularities and target movements were also investigated to refine motion tracking error estimations upon future selection of possible candidates.Materials and methods.Respiratory patterns from twenty-five lung cases were imported individually into a commercial dynamic platform model. Situating a phantom implanted with gold fiducial markers on the platform, superior-inferior (SI) movements of corresponding targets were simulated. Each case was delivered via an identical treatment plan in Version1 and was repeated in Version2. Motion tracking accuracy, by means of discrepancies between subsystem predicted model and raw data motion recorded in patient CT simulation, was analyzed statistically. Wilcoxon signed ranked test was employed to evaluate the difference in tracking error range between the two versions. Statistical model was fitted to inspect the dependence of internal target movement towards fiducial tracking errors.Results.A small difference of ±1 mm was exhibited in 99% of fiducial tracking errors for all cases experimented under both versions. RMS errors were all below 0.5 mm. Version2 demonstrated a greater extremity in fiducial tracking error (p = 0.04). A positive correlation was depicted between internal target amplitudes and 95% interval of fiducial tracking errors (p < 0.02). Overall, irregular respiratory patterns tended to have greater fiducial tracking errors.Conclusions.The excellent tracking performance in both kV subsystem versions offers motion compensations benefits, yet Version1 outperformed Version2 in fiducial tracking accuracy. It is noticeable that greater magnitude in internal target movement and irregular breathing patterns yield greater tracking error.

Dosimetric impact of phase shifts on Radixact Synchrony tracking system with patient-specific breathing patterns.

PURPOSE: The Synchrony tracking system of Radixact is capable of real-time tumor tracking by building a correlation model between external light-emitting diodes on the patient's chest and an internal marker. A phase shift between the chest wall and a lung tumor has been reported. Hence, this study focused on evaluating the accuracy of the tracking system, especially under a patient-specific breathing pattern with respiratory phase shifts. METHODS: A phantom containing fiducial markers was placed on a moving platform. The intrinsic delivery accuracy was verified with a patient-specific breathing pattern. Three patient-specific breathing patterns were then implemented, for which phase shifts, φ, were introduced. Phase shifts with +0.3 s and +1 s were tested for dosimetric aspects, whereas ±0.3, ±0.6, and ±0.8 s shifts were used for tracking accuracy. The resultant dose distributions were analyzed by γ comparison. Dose profiles in the superior-inferior and lateral directions were compared. Logfiles of the tracking information were extracted from the system and compared with the input breathing pattern. The root mean square (RMS) difference was used to quantify the consistency. RESULTS: When the φ value was as large as 1 s, a severe inconsistency was observed. The target was significantly underdosed, down to 89% of the originally planned dose. γ analysis revealed that the failed portion was concentrated in the target region. The RMS of the tracking difference was close to 1 mm when φ was ±0.3 s and approximately 4 mm when φ was ±0.8 s. Tracking errors increased with an increase in the degree of phase shifts. CONCLUSION: Phase shifts between the patient chest wall and the internal target may hamper treatment delivery and jeopardize treatment using Synchrony Tracking. Hence, a larger planning target volume (PTV) may be necessary if a large phase shift is observed in a patient, especially when an external surrogate shows a lag in motion when compared with the tumor.

The impact of the ClearRT™ upgrade on target motion tracking accuracy in Radixact® Synchrony® lung treatments.

Background: The objective was to investigate the change in segmentation error of Radixact® Synchrony® lung treatment after its kV imaging system was upgraded from Generation 1 to Generation 2 in the ClearRT™ installation. Materials and methods: Radixact® Lung Synchrony® plans were created for the Model 18023 Xsight® Lung Tracking "XLT" Phantom combined with different lung target inserts with densities of 0.280, 0.500, 0.943 and 1.093 g/cc. After Radixact® Synchrony® treatment delivery using the Generation 1 and Generation 2 kV systems according to each plan, the tracking performance of the two kV systems on each density insert was compared by calculating the root mean square (RMS) error (δRMS) between the Synchrony-predicted motion in the log file and the known phantom motion and by calculating δ95%, the maximum error within a 95% probability threshold. Results: The δRMS and δ95% of Radixact® Synchrony® treatment for Gen1 kV systems deteriorated as the density of the target insert decreased, from 1.673 ± 0.064 mm and 3.049 ± 0.089 mm, respectively, for the 1.093 g/cc insert to 8.355 ± 5.873 mm and 15.297 ± 10.470 mm, respectively, for the 0.280 g/cc insert. In contrast, no such trend was observed in the δRMS or δ95% of Synchrony® treatment using the Gen2 kV system. The δRMS and δ95%, respectively, fluctuated slightly from 1.586 to 1.687 mm and from 2.874 to 2.971 mm when different target inserts were tracked by the Gen2 kV system. Conclusion: With improved image contrast in kV radiographs, the Gen2 kV imaging system can enhance the ability to track targets accurately in Radixact® Lung Synchrony® treatment and reduce the segmentation error. Our study showed that lung targets with density values as low as 0.280 cc/g could be tracked correctly in Synchrony treatment with the Gen2 kV imaging system.

Multiple Aneurysms AnaTomy CHallenge 2018 (MATCH)-phase II: rupture risk assessment.

PURPOSE: Assessing the rupture probability of intracranial aneurysms (IAs) remains challenging. Therefore, hemodynamic simulations are increasingly applied toward supporting physicians during treatment planning. However, due to several assumptions, the clinical acceptance of these methods remains limited. METHODS: To provide an overview of state-of-the-art blood flow simulation capabilities, the Multiple Aneurysms AnaTomy CHallenge 2018 (MATCH) was conducted. Seventeen research groups from all over the world performed segmentations and hemodynamic simulations to identify the ruptured aneurysm in a patient harboring five IAs. Although simulation setups revealed good similarity, clear differences exist with respect to the analysis of aneurysm shape and blood flow results. Most groups (12/71%) included morphological and hemodynamic parameters in their analysis, with aspect ratio and wall shear stress as the most popular candidates, respectively. RESULTS: The majority of groups (7/41%) selected the largest aneurysm as being the ruptured one. Four (24%) of the participating groups were able to correctly select the ruptured aneurysm, while three groups (18%) ranked the ruptured aneurysm as the second most probable. Successful selections were based on the integration of clinically relevant information such as the aneurysm site, as well as advanced rupture probability models considering multiple parameters. Additionally, flow characteristics such as the quantification of inflow jets and the identification of multiple vortices led to correct predictions. CONCLUSIONS: MATCH compares state-of-the-art image-based blood flow simulation approaches to assess the rupture risk of IAs. Furthermore, this challenge highlights the importance of multivariate analyses by combining clinically relevant metadata with advanced morphological and hemodynamic quantification.

Performance evaluation of the CyberKnife system in real-time target tracking during beam delivery using a moving phantom coupled with two-dimensional detector array.

The aim of the current study was to evaluate the tracking error of the Synchrony Respiratory Tracking system by conducting beam-by-beam analyses to determine the variation in the tracking beams measured during target motion. A moving phantom of in-house design coupled with a two-dimensional (2D) detector array was used to simulate respiratory motion in the superoinferior (SI) and anteroposterior (AP) direction. A styrofoam block with four implanted fiducial markers was placed on top of the detector to enable the fiducial-based respiratory tracking. Measurements were performed with the phantom under either stationary mode or sinusoidal motion of 6-s cycle and 15/20-mm amplitude at SI and AP direction. The measurement data were saved as movie files that were used to calculate the center shift of the beam with 100-ms sampling time. The tracking accuracy of the system was defined as the targeting error, which could be tracked with probability of > 95% (Ep95). The mean ± standard deviation of Ep95 was 0.28 ± 0.08 mm under stationary condition; 0.66 ± 0.23 mm (range: 0.28-1.22 mm) under sinusoidal respiratory motion. The maximum drift of the beam center for all beam paths was 2.7 mm. The tracking accuracy of CyberKnife Synchrony system was successfully evaluated using a moving phantom and 2D detector array; the maximum tracking error was < 1.5 mm for sinusoidal motion of amplitude ≤ 20 mm.

Development of a novel methodology for QA of respiratory-gated and VMAT beam delivery using Octavius 4D phantom.

The objective of this study was to develop and evaluate a series of quality assurance (QA) techniques based on Octavius 4D phantom for testing of respiratory-gated treatment delivery, integrity of dose rate vs gantry speed in volumetric-modulated arc therapy (VMAT) commissioning, and multileaf collimator (MLC) positioning accuracy of a linear accelerator. An Octavius 4D phantom capable of rotating with the gantry and recording the detector signal with a sampling rate of 10 Hz was isocentrally set up and an inclinometer was also installed to measure the gantry angle simultaneously. A simple arc test was created and delivered with gating function activated to measure the timing accuracy of the gating window. A tailor-made dose rate vs gantry speed plan was also designed to test the accuracy of measured dose rate, gantry speed, and actual control points. All experiments were conducted while machine log files were collected for comparison. The variations of beam flatness, symmetry, and field size were analyzed as a function of gantry angle to evaluate the influence from the modulation of dose rate and gantry speed. MLC position accuracy was evaluated based on specific garden fence plans. The time of gating window was measured to be less than 10-millisecond deviation from the log data. Gantry backlash was observed and quantified to be 1.72° with an extra stabilization time of 1.16 seconds for a gating arc with gantry speed of 6°/s. In the dose rate vs gantry speed test, the mean deviation between measured gantry angle and log data was less than 0.2° after a time delay of 0.25 second was corrected. The measured dose rate agreed with the log data very well with a mean deviation of 0.05%, and even the transit of modulation was tracked successfully. There was a statistically significant difference on the variation of beam parameters between a VMAT plan and a simple arc plan. The induced MLC position errors were detected with an accuracy of 0.05 mm. The leaf position reproducibility was found to be better than 0.02 mm, whereas the routine MLC position accuracy was better than 0.1 mm. A time-resolved method using Octavius 4D phantom has been developed and proven to be convenient for respiratory gating QA, dose rate vs gantry speed test, and MLC QA. Gating time, dose rate, and gantry speed-induced leave position error could be directly measured with high accuracy after comparison with the machine log data. This study also highlights the capability of the phantom in quantifying the variation of flatness, symmetry, and field size during gantry rotation.

Posterior repair quantification (PR-Q) using key anatomical indicators (KAI): preliminary report.

INTRODUCTION AND HYPOTHESIS: Posterior vaginal compartment repairs (PR) have traditionally involved a subjective approach. We aim to quantify such repairs using key anatomical indicators (KAI). METHODS: At 50 consecutive PRs: perineal gap (PG); posterior vaginal vault descent (PVVD); mid-vaginal laxity (MVL-vault undisplaced/displaced); and recto-vaginal fascial laxity (RVFL) were measured. The total posterior vaginal length (TPVL) and from POP-Q, TVL, GH, Ap, Bp C, D were also measured. Surgical details deemed appropriate to each repair were recorded. RESULTS: A mean preoperative PG of 2.5 cm was reduced to 0.0 cm postoperatively by excision (100 % cases) with an average increase of 21.6 % in total vaginal length over that if the repair was commenced at the hymen. There was an average reduction of 25.0 % in the genital hiatus (GH). Mean PVVD was 5.3 cm overall; 6.4 cm for 31 out of 50 (62 %) undergoing sacrospinous colpopexy; 3.5 cm for 19 out of 50 (38 %) with no ligamentous vault fixation. An approximate "cut-off" for PVVD of 5 cm may assist with the differentiation of cases where vault fixation may be desirable. Up to 52 % (1.4/2.7 cm) of preoperative MVL displacement was due to vaginal vault descent. The MVL undisplaced (mean 1.3 cm) may better guide vaginal mucosal trimming. RVFL averaged just 0.8 cm with 22 out of 50 (44 %) RVFL being 0.5 cm or less, and not requiring any RVF plicatory sutures. CONCLUSIONS: It is possible to use KAI to assist the planning and execution of posterior vaginal compartment surgery. The PG, PVVD, MVL, and RVFL can indicate surgical measures in the perineum, vaginal vault, vaginal mucosa, and recto-vaginal space respectively.

Severe adolescent female stress urinary incontinence (SAFSUI): case report and literature review.

INTRODUCTION: Severe adolescent female stress urinary incontinence (SAFSUI) can be defined as female adolescents between the ages of 12 and 17 years complaining of involuntary loss of urine multiple times each day during normal activities or sneezing or coughing rather than during sporting activities. An updated review of its likely prevalence, etiology, and management is required. MATERIALS AND METHODS: The case of a 15-year-old female adolescent presenting with a 7-year history of SUI resistant to antimuscarinic medications and 18 months of intensive physiotherapy prompted this review. Issues of performing physical and urodynamic assessment at this young age were overcome in order to achieve the diagnosis of urodynamic stress incontinence (USI). Failed use of tampons was followed by the insertion of (retropubic) suburethral synthetic tape (SUST) under assisted local anesthetic into tissues deemed softer than the equivalent for an adult female. RESULTS: Whereas occasional urinary incontinence can occur in between 6 % and 45 % nulliparous adolescents, the prevalence of non-neurogenic SAFSUI is uncertain but more likely rare. Risk factors for the occurrence of more severe AFSUI include obesity, athletic activities or high-impact training, and lung diseases such as cystic fibrosis (CF). This first reported use of a SUST in a patient with SAFSUI proved safe and completely curative. Artificial urinary sphincters, periurethral injectables and pubovaginal slings have been tried previously in equivalent patients. CONCLUSIONS: SAFSUI is a relatively rare but physically and emotionally disabling presentation. Multiple conservative options may fail, necessitating surgical management; SUST can prove safe and effective.

Multifocal multicentric squamous cell carcinomas arising in vulvovaginal lichen planus.

OBJECTIVE: To describe a case of squamous cell carcinoma (SCC) arising in vulvovaginal lichen planus (LP) and to highlight difficulties in occult cancer surveillance in the setting of severe vaginal stenosis. CASE: A 67-year-old woman with long-standing systemic and vulvovaginal LP presented with multifocal vulvar SCC. Four months after radical vulvectomy and bilateral groin node dissection for stage IB carcinomas, she presented with stage III vaginal SCC arising in an obliterated vagina. CONCLUSIONS: Multifocal, multicentric carcinomas may arise in the vulva and stenosed vagina in women with LP.