Mean Random Errors Research Articles

Set-up errors in head and neck cancer treated with IMRT technique assessed by cone-beam computed tomography: a feasible protocol.

PurposeTo investigate set-up errors, suggest the adequate planning target volume (PTV) margin and image-guided radiotherapy frequency in head and neck (H&N) cancer treated with intensity-modulated radiotherapy (IMRT) assessed by kV cone-beam computed tomography (CBCT).MethodsWe analyzed 360 CBCTs in 60 patients with H&N cancer treated with IMRT. The target delineation was contoured according to ICRU62. PTVs were generated by adding a 3–5 mm margin in all directions to the respective clinical target volumes. The kV CBCT images were obtained at first three days of irradiation and weekly thereafter. The overall mean displacement, range, systematic (∑) and random (σ) errors were calculated. Adequate PTV margins were calculated according to the van Herk formula (2.5∑ + 0.7r).ResultsThe mean of set-up errors was less than 2 mm in any direction. The overall frequency of set-up displacements greater than 3 mm was 3.9% in medial-lateral (ML) direction, 8% in superior-inferior (SI) direction, and 15.5% in anterior-posterior (AP) direction. The range of translations shifts was 0–9 mm in ML direction, 0–5 mm in SI direction and 0–10 mm in AP direction, respectively. After systematic set-up errors correction, the adequate margin to overcome the problem of set-up errors was found to be less than 3 mm.ConclusionImage-guided kV CBCT was effective for the evaluation of set-up accuracy in H&N cancer. The kV CBCT at first three fractions and followed-by weekly appears adequate for reducing significantly set-up errors in H&N cancer treated with IMRT technique. Finally, 3–5 mm PTV margins appear adequate and safe to overcome the problem of set-up errors.

A Pilot Study: The Role of Radio-Opaque Hydrogel Tissue Marker in the Treatment of Postprostatectomy Intensity Modulated Radiation Therapy

It is well documented that the prostate bed is highly susceptible to inter-fraction motion leading to larger treatment planning margins to account for daily treatment set up uncertainties when matching to bony anatomy. The use of fiducial markers in the prostate bed has significantly improved accuracy of treatment delivery. This pilot study aims to investigate the role and benefits of radio-opaque hydrogel tissue marker in the treatment of post prostatectomy intensity modulated radiation therapy (IMRT). Twenty patients treated with IMRT to a dose of 70.2Gy in 39 fractions between Jan 2016 to Jan 2017 were included in this study. All patients underwent transperineal injection of hydrogel tissue marker at the level of vesico-urethral anastomosis and cystoscopically into the posterior bladder wall. Instructions for bladder and bowel preparation to be followed during CT simulation and daily treatments were provided to the patients. Daily on-line cone beam CT matching to the hydrogel tissue marker was performed prior to each treatment and off-sets relative to skin tattoos were recorded in 3 directions: left-right (LR); superior-inferior (SI) and anterio-posterior (AP). Daily image registration using bony matching was then assessed off-line and off-sets relative to skin tattoos were again recorded. The mean and standard deviation of the differences between the hydrogel tissue markers and bony off-sets were calculated for all fractions for each patient; then the overall mean and systematic (Σ) and random errors (σ) for the entire cohort were calculated. The planning target volume (PTV) margin required for bony matching was estimated using van Herk's formula of 2.5Σ + 0.7σ, which is designed to ensure a minimum dose of 95% of prescribed dose to the clinical target volume (CTV) in 90% of patients. These margins are relative to the hydrogel tissue markers which are assumed to be in the target tissue. A total of 1520 images were analysed. The overall mean shift differences between the hydrogel tissue markers and bones for the entire cohort were LR: 0.13mm (Σ 0.38mm, σ 1.35mm); SI: 0.92mm (Σ 1.40mm, σ 2.50mm) and AP: 0.40mm (Σ 1.98mm, σ 3.18mm). The calculated PTV margins for bony matching relative to hydrogel tissue markers were 1.90mm in LR, 5.25mm in SI and 7.17mm AP directions. Prostate bed motion is independent of pelvic bone anatomy and soft tissue matching has shown to be superior compared with pelvic bone matching. With a required PTV margin of 7.17mm in the AP direction, the use of hydrogel tissue marker can significantly improve treatment set up accuracy even in patients with optimal bowel and bladder preparations who undergo image guidance with pelvic bone matching. This will provide the best CTV coverage whilst minimising the current PTV margin and mitigating bladder and rectal toxicities.

Test-retest reliability and validity of a motion capture (MOCAP) system for measuring thoracic and lumbar spinal curvatures and sacral inclination in the sagittal plane.

To evaluate the test-retest reliability and validity of the MOCAP system for measuring spinal sagittal thoracic and lumbar curvatures and sacral inclination in a standing posture. Twenty-five male adults were evaluated on lateral standing radiographs. The thoracic and lumbar curvatures were calculated by Harrison's posterior tangent method. The sacral inclination was defined as the angle between the tangent line of the sacral and vertical plane. In addition, MOCAP was used to calculate the spinal curvatures and sacral inclination. The thoracic and lumbar spine and sacral inclination demonstrated excellent reliability, with mean ICCs levels greater than 0.980 and low CVs (mean: 2.15%). Systematic biases were not significant and were very near 0, and the mean standard errors were 0.257∘. ANOVA of the radiographic and MOCAP measures did not report any statistically significant differences in the comparisons. The systematic biases and mean random errors were lower than 1∘, with CVs lower than 5% and mean ICCs higher than 0.90 between sessions. The MOCAP system delivered consistently reliable and valid results for standing curvatures compared with a radiographic technique. This system could be used with confidence in research and clinical environments for sagittal spinal curvature measurements.

Sweat Sodium Concentration: Inter-Unit Variability of a Low Cost, Portable, and Battery Operated Sodium Analyzer.

The B-722 Laqua Twin is a low cost, portable, and battery operated sodium analyzer, which can be used for the assessment of sweat sodium concentration. The Laqua Twin is reliable and provides a degree of accuracy similar to more expensive analyzers; however, its interunit measurement error remains unknown. The purpose of this study was to compare the sodium concentration values of 70 sweat samples measured using three different Laqua Twin units. Mean absolute errors, random errors and constant errors among the different Laqua Twins ranged respectively between 1.7 mmol/L to 3.5 mmol/L, 2.5 mmol/L to 3.7 mmol/L and -0.6 mmol/L to 3.9 mmol/L. Proportional errors among Laqua Twins were all < 2%. Based on a within-subject biological variability in sweat sodium concentration of ± 12%, the maximal allowable imprecision among instruments was considered to be £ 6%. In that respect, the within (2.9%), between (4.5%), and total (5.4%) measurement error coefficient of variations were all < 6%. For a given sweat sodium concentration value, the largest observed difference in mean and lower and upper bound error of measurements among instruments were, respectively, 4.7 mmol/L, 2.3 mmol/L, and 7.0 mmol/L. In conclusion, our findings show that the interunit measurement error of the B-722 Laqua Twin is low and methodologically acceptable.

Test-retest reliability and validity of a motion capture (MOCAP) system for measuring thoracic and lumbar spinal curvatures and sacral inclination in the sagittal plane

To evaluate the test-retest reliability and validity of the MOCAP system for measuring spinal sagittal thoracic and lumbar curvatures and sacral inclination in a standing posture. Twenty-five male adults were evaluated on lateral standing radiographs. The thoracic and lumbar curvatures were calculated by Harrison's posterior tangent method. The sacral inclination was defined as the angle between the tangent line of the sacral and vertical plane. In addition, MOCAP was used to calculate the spinal curvatures and sacral inclination. The thoracic and lumbar spine and sacral inclination demonstrated excellent reliability, with mean ICCs levels greater than 0.980 and low CVs (mean: 2.15%). Systematic biases were not significant and were very near 0, and the mean standard errors were 0.257∘. ANOVA of the radiographic and MOCAP measures did not report any statistically significant differences in the comparisons. The systematic biases and mean random errors were lower than 1∘, with CVs lower than 5% and mean ICCs higher than 0.90 between sessions. The MOCAP system delivered consistently reliable and valid results for standing curvatures compared with a radiographic technique. This system could be used with confidence in research and clinical environments for sagittal spinal curvature measurements.

Software toolbox for analysis of the endometrial myometrial junction - a pilot study

To develop and evaluate an algorithm for computerized evaluation and measurement of the endometrial-myometrial junction (EMJ). The advanced image processing toolbox of the Matlab software package was used for identificiation and quantitative analysis of the EMJ area on three-dimensional (3D) rendered coronal plane uterine images, with clear-cut borders of the EMJ. The algorithm was used to process the images and calculate the geometric parameters characterizing the identified EM The manual measurements of the maximum thickness of the EMJ were compared to automated measurements performed by the algorithm on the same images. For all three interfaces, the mean maximum manual measurement was less than the mean maximui computed measurement. The differences between the two measurements were not statistically significant (p = 0.275, 0.608 and 0.41 for the right wall, left wall, and fundus, respectively). The mean systematic and random errors ranged from 5.4% tol9.3% and 20.4 to 48.6%, respectively. Pearson correlations for the right wall, left wall and fundus (r = 0.642, p = 0.001; r = 0.730, p < 0.001, and r 0.694, p < 0.001, respectively) were good. Maximum EMJ thickness measurements performed by the innovative Matla software algorithm are as accurate as manual measurements, and have the potential to reduce inter-observer variability.

The Effect of the Amniotic Fluid Index on the Accuracy of Ultrasonographic-Estimated Fetal Weight.

Fetal weight estimation is one of the most important aspects of antenatal care. The effects of amniotic fluid volume on the accuracy of estimated fetal weight (EFW) depend on the amount of fluid, in particular whether it is polyhydramnios or oligohydramnios. Previous studies have reported conflicting results of the effects of amniotic fluid volume on EFW accuracy. The aim of the study was to evaluate the effects of isolated oligohydramnios cases and polyhydramnios on the accuracy of EFW. A retrospective study was conducted at a tertiary center. The study groups consisted of 1069 term isolated oligohydramnios cases, 182 term isolated polyhydramnios cases, and 392 term-matched cases with a normal volume of amniotic fluid. Estimated fetal weight error was determined and expressed in terms of systematic error, calculated from mean percentage error and random error. The systematic error did not differ significantly between polyhydramnios and oligohydramnios cases (-3.60 [8.94%] vs -2.73 [9.7%]). The random error was 8.94% in polyhydramnios cases and 9.7% in oligohydramnios cases. The overestimation rate was 63.6% in polyhydramnios cases and 66.3% in oligohydramnios cases. There were no significant differences in the accuracy of EFW between oligohydramnios and polyhydramnios. However, there was a tendency for overestimation in both types of cases.

Automated Fractional Limb Volume Measurements Improve the Precision of Birth Weight Predictions in Late Third-Trimester Fetuses.

Fetal soft tissue can be assessed by using fractional limb volume as a proxy for in utero nutritional status. We investigated automated fractional limb volume for rapid estimate fetal weight assessment. Pregnant women were prospectively scanned for 2- and 3-dimensional fetal biometric measurements within 4 days of delivery. Performance of birth weight prediction models was compared: (1) Hadlock (Am J Obstet Gynecol 1985; 151:333-337; biparietal diameter, abdominal circumference, and femur diaphysis length); and (2) Lee (Ultrasound Obstet Gynecol 2009; 34:556-565; biparietal diameter, abdominal circumference, and automated fractional limb volume). Percent differences were calculated: [(estimated birth weight - actual birth weight) ÷ (actual birth weight] × 100. Systematic errors (accuracy) were summarized as signed mean percent differences. Random errors (precision) were calculated as ± 1 SD of percent differences. Fifty neonates were delivered at 39.4 weeks' gestation. The Hadlock model generated the most accurate birth weight (0.31%) with a mean random error of ±7.9%. Despite systematic underestimations, the most precise results occurred with fractional arm volume (-9.1% ± 5.1%) and fractional thigh (-5.2% ± 5.2%) models. The size and distribution of these prediction errors were improved after correction for systematic errors. Automated fractional limb volume measurements can improve the precision of weight predictions in third-trimester fetuses. Correction factors may be necessary to adjust underestimated systematic errors when using automated fractional limb volume with prediction models that are based on manual tracing of fetal limb soft tissue borders.

Thermomechanical Analysis and Characterization of a Press-Pack Structure for SiC Power Module Packaging Applications

This paper presents an experimental methodology for the characterization of thermomechanical displacement and friction properties in a free-floating press-pack structure, and evaluation of the tensile stress on the semiconductor die through simulation of different mechanical and thermal loading conditions. The press-pack structure consists of a single silver-metallized (1 $\mu \text{m}$ ) silicon carbide die ( $400~\mu \text{m}$ ) in contact with rhodium-coated (0.4 $\mu \text{m}$ ) molybdenum square plates. The thermomechanical displacements in the press-pack structure have been obtained using the digital image correlation technique, and the mean random error has been ±0.1 $\mu \text{m}$ , which is approximately 10 ppm of the measured length (10.5 mm). The developed experimental method has led to an analytical estimation of friction coefficients on the interfaces’ silicon carbide-molybdenum and molybdenum-copper. The results demonstrate that the thin silver layer behaves as a solid film lubricant. A 2-D finite-element model representing the experimental setup has been implemented. The difference in displacement between measurement and simulation is less than 8%. Furthermore, the coinfluence of the design parameters on the thermomechanical performance of the stacked structure has been analyzed through simulations. Finally, design guidelines to reduce the tensile stress on the silicon carbide die have been proposed regarding free-floating press-pack power electronics packaging.

Setup uncertainties for inter-fractional head and neck cancer in radiotherapy.

PurposeThe aim of this study is to determine the inter-fractional motion of cervical spine in radiotherapy (RT).Materials and MethodsEleven localized head and neck cancer patients who were treated from April 2014 to September 2015 were evaluated. Every patient underwent 3 times of computed tomography (CT) simulation with equivalent setting. Left-right (LR, x) and antero-posterior (AP, z) directional shift of cervical spine were evaluated using 33 number of CT image. In regard to random error, geometric changes were evaluated by 22 data set (compared the first obtained CT to second or third CT) by one-sample T test. Systemic error was evaluated by each patients’ data set (11 pairs) by paired T test.ResultsThe mean random error of LR and AP translational shift of cervical spine were −0.39 ± 3.24 mm and −0.57 ± 0.99 mm respectively. The mean random error of translational change of AP direction showed statistical significance (p = 0.014). The mean random error of x and z rotational shift were −0.07 ± 0.29° and −0.05 ± 0.35°, respectively. The mean systemic error of translational shift of LR and AP direction were −0.64 ± 2.57 mm and −0.33 ± 1.22 mm, respectively. The mean systemic error of rotational shift of x and z were 0.01 ± 0.18° and −0.27 ± 0.33°, respectively. The mean systemic error of rotational changes of z direction showed statistical difference (p = 0.022).ConclusionsWe have to be aware of the inter-fractional motion of cervical spine in head and neck RT and give enough margins in RT planning.

An Evaluation of Inter-Fractional Set-Up Errors in Patients Treated with Distinct Immobilization Equipment for Varying Anatomical Regions

This study aims to evaluate inter-fractional set-up errors in patients treated with distinct immobilization equipment (thermoplastic mask, knee-fix and feet-fix, wing board and vac-lok) for four anatomical regions including brain, head and neck (HN), thorax and pelvis. Data of randomly selected 140 patients who were treated for four anatomical regions were obtained using Hi-Art Helical Tomotherapy (HT) system. Pre-treatment planning was based on automatic registration readings of computed tomography (CT) and mega-voltage computed tomography (MVCT) on a daily basis. Distinct immobilization equipment was used for varying anatomical regions. Individual mean set-up error (M), systematic error (Σ), and random error (σ) values were calculated through daily translational and rotational deviation values. The size of translational, systematic and random error was 1.31 - 4.93 mm for brain, 2.28 - 4.88 mm for HN, 4.04 - 9.90 mm for thorax, and 6.34 - 14.68 mm for pelvis. Rotational values were as follows: 0.06˚ - 0.73˚ for brain, 0.42˚ - 0.6˚ for HN, 0.48˚ - 1.14˚ for thorax and 0.65˚ - 1.05˚ for pelvis. The highest translational, systematic and random error value was obtained from the pelvic regional. The highest standard and random error value in pitch and roll was produced in the rotational direction of the pelvis (0.05˚ and 0.71˚), while the highest error value in yaw was (1.14˚) produced from thorax. Inter-fractional set-up errors were most commonly produced in the pelvis, followed by thorax. Our study results suggest that the highest systematic and random errors are found for thorax and pelvis. Distinct immobilization equipment was important in these results. Safety margins around the clinical target volume (CTV) are changeable for different anatomical regions. A future work could be developed to new equipment for immobilization because of the reduced margins CTV.

A study of turbulent fluxes and their measurement errors for different wind regimes over the tropical Zongo Glacier (16° S) during the dry season

Abstract. Over glaciers in the outer tropics, during the dry winter season, turbulent fluxes are an important sink of melt energy due to high sublimation rates, but measurements in stable surface layers in remote and complex terrains remain challenging. Eddy-covariance (EC) and bulk-aerodynamic (BA) methods were used to estimate surface turbulent heat fluxes of sensible (H) and latent heat (LE) in the ablation zone of the tropical Zongo Glacier, Bolivia (16° S, 5080 m a.s.l.), from 22 July to 1 September 2007. We studied the turbulent fluxes and their associated random and systematic measurement errors under the three most frequent wind regimes. For nightly, density-driven katabatic flows, and for strong downslope flows related to large-scale forcing, H generally heats the surface (i.e. is positive), while LE cools it down (i.e. is negative). On average, both fluxes exhibit similar magnitudes and cancel each other out. Most energy losses through turbulence occur for daytime upslope flows, when H is weak due to small temperature gradients and LE is strongly negative due to very dry air. Mean random errors of the BA method (6 % on net H + LE fluxes) originated mainly from large uncertainties in roughness lengths. For EC fluxes, mean random errors were due mainly to poor statistical sampling of large-scale outer-layer eddies (12 %). The BA method is highly sensitive to the method used to derive surface temperature from longwave radiation measurements and underestimates fluxes due to vertical flux divergence at low heights and nonstationarity of turbulent flow. The EC method also probably underestimates the fluxes, albeit to a lesser extent, due to underestimation of vertical wind speed and to vertical flux divergence. For both methods, when H and LE compensate each other in downslope fluxes, biases tend to cancel each other out or remain small. When the net turbulent fluxes (H + LE) are the largest in upslope flows, nonstationarity effects and underestimations of the vertical wind speed do not compensate, and surface temperature errors are important, so that large biases on H + LE are expected when using both the EC and the BA method.

Prolonged treatment time deteriorates positioning accuracy for stereotactic radiosurgery.

IntroductionThe accuracy of radiation delivery is increasingly important as radiotherapy technology continues to develop. The goal of this study was to evaluate intrafractional motion during intracranial radiosurgery and the relationship between motion change and treatment time.Methods and MaterialsA total of 50 treatment records with 5988 images, all acquired during treatments with the CyberKnife Radiosurgery System, were retrospectively analyzed in this study. We measured translation and rotation motion including superior-inferior (SI), right-left (RL), anterior-posterior (AP), roll, tilt and yaw. All of the data was obtained during the first 45 minutes of treatment. The records were divided into 3 groups based on 15-min time intervals following the beginning of treatment: group A (0-15 min), group B (16-30 min) and group C (31-45 min). The mean deviations, systematic errors, random errors and margin for planning target volume (PTV) were calculated for each group.ResultsThe mean deviations were less than 0.1 mm in all three translation directions in the first 15 minutes. Greater motion occurred with longer treatment times, especially in the SI direction. For the 3D vector, a time-dependent change was observed, from 0.34 mm to 0.77 mm (p=0.01). There was no significant correlation between the treatment time and deviations in the AP, LR and rotation axes. Longer treatment times were associated with increases in systematic error, but not in random error. The estimated PTV margin for groups A, B and C were 0.86 / 1.14 / 1.31 mm, 0.75 / 1.12 / 1.20 mm, and 0.43 / 0.54 / 0.81 mm in the SI, RL, and AP directions, respectively.ConclusionsDuring intracranial radiosurgery, a consistent increase in the positioning deviation over time was observed, especially in the SI direction. If treatment time is greater than 15 minutes, we recommend increasing the PTV margins to ensure treatment precision.

Analysis of positioning errors and weight variability in the radiation for head and neck cancer based on cone-beam computed tomography

Objective To analyzed the effects of the positioning errors and weight variability of the head and neck cancer patients with intensity modulated radiation therapy (IMRT), or volumetric modulated arctherapy (VMAT) based on the kilovoltage cone-beam computed tomography (kV-CBCT). Methods CBCT images of 102 patients with head and neck cancer patients receiving IMRT or VMAT were screened by CBCT once a week for consecutively 6 weeks. The positioning errors were measured by comparing CBCT and planning CT in left-right (LR), anterior-posterior (AP) and cranio-caudal (CC) directions. Meanwhile, the weight of patients were measured every week. Results The positioning errors were (0.011 5±0.125 3) cm, (-0.017 6±0.123 3) cm and (-0.014 1±0.156 7) cm in LR, AP and CC directions, respectively. The mean systematic errors were all less than 0.02 cm in three axial directions, while the mean random errors were all within 0.2 cm. There was no statistically significant difference was observed among the setup errors in all three axial directions according to different week. Though the body weight of patients continued to drop during the radiation by with the mean weight loss of 3.5 kg and had a negative correlation with treatment course. Bivariate correlation analysis showed just the positioning errors in CC direction were significantly correlated with body weights loss. Conclusion There is no statistical relationship with in position errors of the patients with their treatment course, and the body weight loss seemed to influence the position errors in CC direction. Key words: Head and neck neoplasms; Radiotherapy; Setup errors; Cone-beam computed tomography

Assessment of Three-dimensional Set-up Errors using Megavoltage Computed Tomography (MVCT) during Image-guided Intensity-modulated Radiation Therapy (IMRT) for Craniospinal Irradiation (CSI) on Helical Tomotherapy (HT)

The purpose of this study was to assess three-dimensional (3D) set-up errors using megavoltage computed tomography (MVCT) during image-guided intensity-modulated radiation therapy (IMRT) for supine craniospinal irradiation (CSI) on helical tomotherapy (HT). Patients were immobilized in a customized 4-clamp thermoplastic head mask with or without whole-body vacuum cradle. Set-up was based primarily on a set of cranial fiducial markers. MVCT scans were acquired and co-registered with planning scan separately at three different levels (brain, upper, and lower spine) at every fraction. Only translational displacements were analysed, wherein positive sign denotes deviation in anterior, left, and superior direction; while negative sign denotes deviation in posterior, right, and inferior direction. Mean displacements, systematic, and random errors of the study population were calculated at all three levels separately. Local residual uncertainty of the upper and lower spine was also derived assuming perfect co-registration of the skull. Set-up margins for clinical target volume (CTV) to planning target volume (PTV) were derived at these three levels separately using published margin recipes. Data from 1868 co-registrations in 674 fractions on 33 patients was included. The mean displacements in the lateral, longitudinal, and vertical directions were -1.21, -1.36, and 1.38 mm; -1.25, -0.34, and 0.65 mm; and -1.47, -2.78, and 0.22 mm for the brain; upper spine; and lumbar spine respectively. The corresponding 3D vector of displacement was 2.28; 1.45; and 3.15 mm respectively. There was a distinct systematic trend towards increasing inaccuracy from the brain towards the lower spine. Using Stroom's formula, the minimum recommended CTV to PTV margins in absence of daily image-guidance were 6.5; 7.0; and 9.5 mm for the brain; upper spine; and lower spine respectively. This increased to 7.5; 8.5; and 11.5 mm using van Herk's formula. Subset and sensitivity analyses could not identify any factor predictive of increased inaccuracy. Residual uncertainty of the spinal column was lesser after daily co-registration referenced to the skull, suggesting that smaller set-up margins maybe appropriate while using daily image-guidance with an online correction protocol. Daily MVCT imaging during supine CSI on HT provides volumetric verification of the set-up process. There is substantial site-dependent variability in translational displacements that increases systematically from brain towards the lower spine with implications for differential set-up -margins for the brain, upper, and lower spine.

Assessment of Three-Dimensional Set-up Errors in Pelvic Radiation Therapy

Set-up errors are the inevitable features of the radiation treatment process. Coverage of target volume is a direct function of set-up margins, which should be optimized to prevent inadvertent irradiation of adjacent normal tissues. The aim of this study is to evaluate three dimensional set-up errors and propose optimum margins for target volume coverage in pelvic radiation therapy. 100 Portal images are obtained for the first two fractions for 50 pelvic cancer patients with Hip Fix thermoplastics. Displacements between Digitally Reconstructed Radiographs (DRR) and Electronic Portal Images (EPI) are estimated and analyzed along major three axes. Mean displacements, population systematic and random errors and three dimensional vectors of displacements are calculated. Set-up margins are calculated using published margin recipes; International Commission on Radiation Units and measurements (ICRU), Stroom and van Herk. The random errors are 0.2339, 0.1603, and 0.1628 cm respectively along antero-posterior (AP), supero-inferior (SI) and medio-lateral (ML) axes. Similarly; the systematic errors are 0.2698, 0.3284, and 0.2568 cm along AP, SI and ML axes respectively. The mean displacement in vertical, longitudinal and lateral axes are 0.103, -0.177, 0.075 cm respectively and standard deviation in vertical, longitudinal and lateral axes are 0.2698, 0.3284, 0.2568 respectively for pelvic cancer. Based on ICRU report 62, the clinical target volume to planning target volume margins are 0.357, 0.365 and 0.304 cm along AP, SI and ML axes respectively. The corresponding values are 0.703, 0.769 and 0.627 cm with Stroom’s formula and 0.838, 0.933 and 0.756 cm with van Herk’s formula. The results suggest that there is a significant difference within the three major axes. Approximately 22% of portal images have exceeded the tolerance limit (>5mm) of pelvic cancer patients with Hip Fix thermoplastics. Calculated set-up margins are compared well with published margin recipes.

Assessment of interfractional variation of the breast surface following conventional patient positioning for whole‐breast radiotherapy

The purpose of this study was to quantify the variability of the breast surface position when aligning whole‐breast patients to bony landmarks based on MV portal films or skin marks alone. Surface imaging was used to assess the breast surface position of 11 whole‐breast radiotherapy patients, but was not used for patient positioning. On filmed fractions, AlignRT v5.0 was used to capture the patient's surface after initial positioning based on skin marks (28 “preshifts” surfaces), and after treatment couch shifts based on MV films (41 “postshifts” surfaces). Translations and rotations based on surface captures were recorded, as well as couch shifts based on MV films. For nonfilmed treatments, “daily” surface images were captured following positioning to skin marks alone. Group mean and systematic and random errors were calculated for all datasets. Pearson correlation coefficients, setup margins, and 95% limits of agreement (LOA) were calculated for preshifts translations and MV film shifts. LOA between postshifts surfaces and the filmed treatment positions were also computed. All the surface captures collected were retrospectively compared to both a DICOM reference surface created from the planning CT and to an AlignRT reference surface. All statistical analyses were performed using the DICOM reference surface dataset. AlignRT reference surface data was only used to calculate the LOA with the DICOM reference data. This helped assess any outcome differences between both reference surfaces. Setup margins for preshifts surfaces and MV films range between 8.3–12.0 mm and 5.4–13.4 mm, respectively. The largest margin is along the left–right (LR) direction for preshift surfaces, and along craniocaudal (CC) for films. LOA ranges between the preshifts surfaces and MV film shifts are large (12.6–21.9 mm); these decrease for postshifts surfaces (9.8–18.4 mm), but still show significant disagreements between the two modalities due to their focus on different anatomical landmarks (patient's topography versus bony anatomy). Pearson's correlation coefficients further support this by showing low to moderate correlations in the anterior–posterior (AP) and LR directions (0.47–0.69) and no correlation along CC(<0.15). The use of an AlignRT reference surface compared to the DICOM reference surface does not significantly affect the LOA. Alignment of breast patients based solely on bony alignment may lead to interfractional inconsistencies in the breast surface position. The use of surface imaging tools highlights these discrepancies, and allows the radiation oncology team to better assess the possible effects on treatment quality.PACS number: 87

SU‐E‐J‐202: Is Pretreatment Imaging at Each Treatment Fraction Needed in Spine SBRT to Enable Margin Reduction?

Purpose:To study translational setup errors of Spine SBRT treatments using BodyFIX immobilization system and the potential for margin reduction using pretreatment imaging.Methods:148 online match results of 39 Spine SBRT patients treated at our institution were reviewed. All treatments performed using Varian, TrueBeam and MI™, BodyFIX immobilization device. Prescriptions (dose‐fractionation schedules) for the patients in the study are 8 Gy X 3 (n=24), 6 Gy X 4 (n=10) and 16Gy X 1 (n=5). For all patients, OBI was performed on verification day and before each treatment. Recorded shifts are from adopted couch positions after physician online review of KV image‐pair and CBCT. Data analyzed by computing Mean error (M), Systematic error (Σ) and Random error (σ) for three translation directional shifts and 3D Vector length. To estimate correlation between imaging sessions, Anova‐test and T‐Test with alpha of 0.05 performed over the data.Results:Mean error (M), Systematic error (Σ) and Random error (σ) of Vertical direction are ‐1.81mm, 4.05mm and 2.01mm respectively. Similarly, Errors in Longitudinal direction are 0.76mm (M), 4.21mm (Σ) and 1.34mm (σ). Errors in Lateral direction are – 0.16mm (M), 3.22mm (Σ) and 1.83 mm (σ). Mean, SD and CI95% of 3D Vector lengths are 7.93mm, 4.41mm and 0.7mm respectively. Anova‐test results show, P‐Values for longitudinal and lateral shifts are &gt; 0.3 and P‐value of vertical shift is 0.054. This signifies mean of the each imaging session are not significantly different. T‐Test on treatment sessions data of vertical shifts with respect to verification day shows, mean of Vertical shifts on verification day are different from Vertical shifts on treatment sessions.Conclusion:Results shows immobilization with BodyFIX is reproducible in the mm range. To eliminate systematic error component and to enable margin reduction, pretreatment imaging prior to each treatment fraction is indispensable.

Comments on: Extensions of some classical methods in change point analysis

The authors must be congratulated on an extensive and at the same time detailed and very informative survey of the most recent developments in change-point analysis. In my comments, I will focus on an extension of the results discussed in their Section 7: detection of a change point in functional observations. This contribution is based on the work presented in Gromenko et al. (2014). Climatic data, like temperature and rainfall, are collected at a number of locations, so they can be viewed as sequences of annual curves with an additional index referring to the spatial location of the measurement station; denote a measurement made in year n, at spatial location s ∈ S, and time (of year) t ∈ T , as Xn(s, t). The interest of climatologists is in trends and changes in climate over a region, the United States is typically divided into 5–10 climatic regions. Gromenko et al. (2014) work with precipitation data at K = 59 locations in 12 states in the midwestern US, over the course of N = 60 years, there are 365 measurements per year at each location. These values are typical of such data sets: depending on the part of the world, records may reach 50–150 years back and there are several dozen stations in a climatic region. The statistical model for such data is Xn(s; t) = μn(s; t) + en(s; t), where μn ∈ L2(S × T ) is a deterministic mean function and en ∈ L2(S × T ) is a zero mean random error term. The goal is to test the null hypothesis that the mean functions μn are the same across n. If this hypothesis is true, the long-term annual pattern over a region does not change. The testing problem can thus be stated as H0 : μ1 = · · · = μN vs. HA : μ1 = · · · = μn∗ = μn∗+1 = . . . μN , for some 1 < n∗ < N . In this spatio-temporal setting, it is necessary to specify the spatial covariances as well. It is

Estimation of daily interfractional larynx residual setup error after isocentric alignment for head and neck radiotherapy: quality assurance implications for target volume and organs-at-risk margination using daily CT on- rails imaging.

Larynx may alternatively serve as a target or organs at risk (OAR) in head and neck cancer (HNC) image‐guided radiotherapy (IGRT). The objective of this study was to estimate IGRT parameters required for larynx positional error independent of isocentric alignment and suggest population‐based compensatory margins. Ten HNC patients receiving radiotherapy (RT) with daily CT on‐rails imaging were assessed. Seven landmark points were placed on each daily scan. Taking the most superior‐anterior point of the C5 vertebra as a reference isocenter for each scan, residual displacement vectors to the other six points were calculated postisocentric alignment. Subsequently, using the first scan as a reference, the magnitude of vector differences for all six points for all scans over the course of treatment was calculated. Residual systematic and random error and the necessary compensatory CTV‐to‐PTV and OAR‐to‐PRV margins were calculated, using both observational cohort data and a bootstrap‐resampled population estimator. The grand mean displacements for all anatomical points was 5.07 mm, with mean systematic error of 1.1 mm and mean random setup error of 2.63 mm, while bootstrapped POIs grand mean displacement was 5.09 mm, with mean systematic error of 1.23 mm and mean random setup error of 2.61 mm. Required margin for CTV‐PTV expansion was 4.6 mm for all cohort points, while the bootstrap estimator of the equivalent margin was 4.9 mm. The calculated OAR‐to‐PRV expansion for the observed residual setup error was 2.7 mm and bootstrap estimated expansion of 2.9 mm. We conclude that the interfractional larynx setup error is a significant source of RT setup/delivery error in HNC, both when the larynx is considered as a CTV or OAR. We estimate the need for a uniform expansion of 5 mm to compensate for setup error if the larynx is a target, or 3 mm if the larynx is an OAR, when using a nonlaryngeal bony isocenter.PACS numbers: 87.55.D‐, 87.55.Qr