Setup Correction Research Articles

Practice patterns and recommendations for pediatric image-guided radiotherapy: A Children's Oncology Group report.

This report by the Radiation Oncology Discipline of Children's Oncology Group (COG) describes the practice patterns of pediatric image-guided radiotherapy (IGRT) based on a member survey and provides practice recommendations accordingly. The survey comprised of 11 vignettes asking clinicians about their recommended treatment modalities, IGRT preferences, and frequency of in-room verification. Technical questions asked physicists about imaging protocols, dose reduction, setup correction, and adaptive therapy. In this report, the COG Radiation Oncology Discipline provides an IGRT modality/frequency decision tree and the expert guidelines for the practice of ionizing image guidance in pediatric radiotherapy patients.

Innovative Methods for Small Mixed Batches Production System Improvement: The Case of a Bakery Machine Manufacturer

One of the common problems of organizations with turn-key projects is the high scrap rate. There exist such traditional methods as Lean Six Sigma (LSS) and DMAIC tools that analyze causes and suggest solutions. New emerging intelligent technologies should influence these methods and tools as they affect many areas of our life. The purpose of this paper is to present the innovative Small Mixed Batches (SMB). The standard set of LSS tools is extended by intelligent technologies such as artificial neural networks (ANN) and machine learning. The proposed method uses the data-driven quality strategy to improve the turning process at the bakery machine manufacturer. The case study shows the step-by-step DMAIC procedure of critical to quality (CTQ) characteristics improvement. Findings from the data analysis lead to a change of measurement instrument, training of operators, and lathe machine set-up correction. However, the scrap rate did not decrease significantly. Therefore the advanced mathematical model based on ANN was built. This model predicts the CTQ characteristics from the inspection certificate of the input material. The prediction model is a part of a newly designed process control scheme using machine learning algorithms to reduce the variability even for input material with different properties from new suppliers. Further research will be focused on the validation of the proposed control scheme, and acquired experiences will be used to support business sustainability.

Surface-guided tomotherapy improves positioning and reduces treatment time: A retrospective analysis of 16835 treatment fractions.

PurposeIn this study, we have quantified the setup deviation and time gain when using fast surface scanning for daily setup/positioning with weekly megavoltage computed tomography (MVCT) and compared it to daily MVCT.MethodsA total of 16 835 treatment fractions were analyzed, treated, and positioned using our TomoTherapy HD (Accuray Inc., Madison, USA) installed with a Sentinel optical surface scanning system (C‐RAD Positioning AB, Uppsala, Sweden).Patients were positioned using in‐room lasers, surface scanning and MVCT for the first three fractions. For the remaining fractions, in‐room laser was used for setup followed by daily surface scanning with MVCT once weekly. The three‐dimensional (3D) setup correction for surface scanning was evaluated from the registration between MVCT and the planning CT. The setup correction vector for the in‐room lasers was assessed from the surface scanning and the MVCT to planning CT registration. The imaging time was evaluated as the time from imaging start to beam‐on.ResultsWe analyzed 894 TomoTherapy treatment plans from 2012 to 2018. Of all the treatment fractions performed with surface scanning, 90 % of the residual errors were within 2.3 mm for CNS (N = 284), 2.9 mm for H&N (N = 254), 8.7 mm for thorax (N = 144) and 10.9 for abdomen (N = 134) patients. The difference in residual error between surface scanning and positioning with in‐room lasers was significant (P < 0.005) for all sites. The imaging time was assessed as total imaging time per treatment plan, modality, and treatment site and found that surface scanning significantly reduced patient on‐couch time compared to MVCT for all treatment sites (P < 0.005).ConclusionsThe results indicate that daily surface scanning with weekly MVCT can be used with the current target margins for H&N, CNS, and thorax, with reduced imaging time.

Application of Optical Laser 3D Surface imaging system (Sentinel) in breast cancer radiotherapy

It has been clearly confirmed that radiation therapy (RT) after breast conserving surgery (BCS) is an effective treatment modality comparable to mastectomy for early breast cancer. The purpose of this study was to further evaluate the accuracy of 3D surface imaging system (Sentinel) for breast cancer patients received BCS. The optical surface scans and CBCT scans were acquired before and immediately after couch movement correction. The deviation of the CBCT scans from the reference planning CT was considered an estimate for the residual errors for patient setup correction. The planning target volume (PTV) margins for treatment sessions was calculated according to the setup errors. We obtained a total of 245 sets of data collected from 49 breast cancer patients. Compared with Sentinel setup errors, the residual setup errors as determined by the CBCT scans after couch movement correction were reduced in the six directions. The PTV margins derived from the CBCT residual errors were all less than 5 mm in X, Y, and Z directions. Our results suggested that Optical surface imaging can be applied in positioning for breast cancer patient accurately without unnecessary imaging dose.

Impact of interfractional anatomical variation and setup correction methods on interfractional dose variation in IMPT and VMAT plans for pancreatic cancer patients: A planning study.

PurposeTo investigate the impact of interfractional anatomical changes and setup correction methods on dose distributions in pancreatic cancer patients under breath‐hold conditions.MethodsThree intensity‐modulated proton therapy (IMPT) plans with different beam arrangements and one volumetric‐modulated arc therapy (VMAT) plan prescribing 54 Gy in 30 fractions were created for 10 patients who underwent three additional CT scans performed at an interval of 1–2 weeks. The additional CT sets were rigidly registered to the simulation CT set using both bone‐matching (BM) and organ‐matching (OM) methods in each patient. Recalculated dose distributions and dose–volume indices on the additional CT sets using either the BM or the OM method were compared with the simulation values.ResultsDifferences in the gross tumor volume D98% value from the simulation sets ranged from −0.8 to −5.9% on average. In addition, the variations were larger with OM compared with BM for two IMPT plans. Meanwhile, differences in the D98% value in the region isotropically enlarged by 5 mm from the gross tumor volume were significantly improved with OM on two IMPT plans and the VMAT plan. Among the organs at risk, the dose–volume indices were significantly improved with OM only in the duodenum on all plans.ConclusionOrgan‐matching may be a better setup correction technique than BM for both photon therapy and IMPT plans. However, in some beam arrangements of IMPT, the dose distribution may be somewhat worse using OM, due to interfractional anatomical variation. Therefore, it is important to choose beam angles that are less likely to be influenced by changes in the gastrointestinal gas volume, especially in IMPT plans.

3-Dimensional target coverage assessment for MRI guided esophageal cancer radiotherapy

PurposeThis study aimed to quantify the coverage probability for esophageal cancer radiotherapy as a function of a preset margin for online MR-guided and (CB)CT-guided radiotherapy. MethodsThirty esophageal cancer patients underwent six T2-weighted MRI scans, 1 prior to treatment and 5 during neoadjuvant chemoradiotherapy at weekly intervals. Gross tumor volume (GTV) and clinical target volume (CTV) were delineated on each individual scan. Follow-up scans were rigidly aligned to the bony anatomy and to the clinical target volume itself, mimicking two online set-up correction strategies: a conventional CBCT-guided set-up and a MR-guided set-up, respectively. Geometric coverage probability of the propagated CTVs was assessed for both set-up strategies by expanding the reference CTV with an isotropic margin varying from 0 mm to 15 mm with an increment of 1 mm. ResultsA margin of 10 mm could resolve the interfractional changes for 118 out of the 132 (89%) analyzed fractions when applying a bone-match registration, whereas the CTV was adequately covered in 123 (93%) fractions when the registration was directly performed at the CTV itself (soft-tissue registration). Closer analyses revealed that target coverage violation predominantly occurred for distal tumors near the junction and into the cardia. ConclusionOnline MR-guided soft-tissue registration protocols exhibited modest improvements of the geometric target coverage probability as compared to online CBCT-guided bone match protocols. Therefore, highly conformal target irradiation using online MR-guidance can only be achieved by implementing on-table adaptive workflows where new treatment plans are daily generated based on the anatomy of the day.

Evaluation of the effect of random setup errors on dose delivery in Intensity Modulated Radiotherapy

Abstract Aim: To conduct a study on the effect of random setup errors inpatient for dose delivery in Intensity Modulated Radiotherapy plans using Octavius 4D phantom. Materials and methods: 11 patients with cancer of H&amp;N were selected for this study. An IMRT plan was created for each patient. The IMRT quality assurance plans were transferred to Mosaiq workstation in a linear accelerator. These plans were delivered at the reference treatment position. Subsequently, the QA plans were delivered on the Octavius 4D phantom after introducing errors in various translational and rotational directions. The setup inaccuracies introduced varied from 1 mm to 5 mm along X, Y. These setup uncertainties were then introduced along X and Y direction simultaneously in equal measures. Similarly, IMRT plans were delivered also after introducing roll and yaw rotation of 1, 2 and 3 degrees in phantom. The deviation of gamma indices at all these positions was analyzed with respect to the reference setup position. Results: The percentage of points passing the gamma acceptance criterion decrease as we increase the setup error. The change is found to be very insignificant with setup error up to 2 mm along X, Y or XY direction. Similarly, the rotational error of up to 3 degrees is found to be acceptable. Conclusions: Small setup (&lt; 2 mm) correction in patients may not adversely affect the dose delivery. But an error of similar magnitude in 2 directions simultaneously has a much greater impact on IMRT dose delivery.

Coping with interfraction time trends in tumor setup.

PurposeInterfraction tumor setup variations in radiotherapy are often reduced with image guidance procedures. Clinical target volume (CTV)–planning target volume (PTV) margins are then used to deal with residual errors. We have investigated characterization of setup errors in patient populations with explicit modelling of occurring interfraction time trends.MethodsThe core of a “trendline characterization” of observed setup errors in a population is a distribution of trendlines, each obtained by fitting a straight line through a patient's daily setup errors. Random errors are defined as daily deviations from the trendline. Monte Carlo simulations were performed to predict the impact of offline setup correction protocols on residual setup errors in patient populations with time trends. A novel CTV‐PTV margin recipe was derived that assumes that systematic underdosing of tumor edges in multiple consecutive fractions, as caused by trend motion, should preferentially be avoided. Similar to the well‐known approach by van Herk et al. for conventional error characterization (no explicit modelling of trends), only a predefined percentage of patients (generally 10%) was allowed to have nonrandom (systematic + trend) setup errors outside the margin. Additionally, a method was proposed to avoid erroneous results in Monte Carlo simulations with setup errors, related to decoupling of error sources in characterizations. The investigations were based on a database of daily measured setup errors in 835 prostate cancer patients that were treated with 39 fractions, and on Monte Carlo–generated patient populations with time trends.ResultsWith conventional characterization of setup errors in patient populations with time trends, predicted standard deviations of residual systematic errors (Σres) after application of an offline correction protocol could be underestimated by more than 50%, potentially resulting in application of too small margins. With the new trendline characterization this was avoided. With the novel CTV‐PTV margin recipe with an allowed 10% of patients having nonrandom errors outside the margin, the observed percentage was 10.0% ± 0.2%. When using conventional characterization of errors and the van Herk margin recipe, on average 58.0% ± 24.3% of patients had errors outside the margin, while 10% was prescribed. For populations with no time trends, the novel recipe simplifies to the generally applied M=2.5Σ+0.7σ formula proposed by van Herk et al.ConclusionsIn populations with time trends in setup errors, the use of trendline characterizations in Monte Carlo simulations for establishment of residual errors after a setup correction protocol can avoid application of erroneous margins. The novel margin recipe can be used to accurately control the percentage of patients with nonrandom errors outside the margin. In case of daily image guidance of patients with multiple targets with differential motion, the recipe can be used to establish margins for the targets that are not the primary target for the image guidance (e.g., nodal regions). Probabilistic planning might be improved by using trendline characterization for modelling of setup errors. Population analyses of interfraction setup errors need to take into account potential time trends.

Long-time clinical experience in patient setup for several particle therapy clinical indications: management of patient positioning and evaluation of setup reproducibility and stability.

Accurate patient positioning is crucial in particle therapy due to the geometrical selectivity of particles. We report and discuss the National Center for Oncological Hadrontherapy (CNAO) experience in positioning accuracy and stability achieved with solid thermoplastic masks fixed on index base plates and assessed by daily orthogonal X-ray imaging. Positioning data were retrospectively collected (between 2012 and 2018) and grouped according to the treated anatomical site. 19696 fractions of 1325 patients were evaluated.The study was designed to assess:(i) the number of fractions in which a single correction vector was applied(SCV);(ii) the number of fractions in which further setup verification was performed (SV);(iii) the number of fractions in which SV lead to an additional correction within (MCV<5min) or after (MCV>5min) 5 minutes from the first setup correction;(iv) the systematic (Σ) and random (σ) error components of the correction vectors applied. A SCV was applied in 71.5% of fractions, otherwise SV was required. In 30.6% of fractions with SV, patient position was not further revised. In the remaining fractions, MCV<5min and MCV>5min were applied mainly in extracranial and cranial sites respectively.Interfraction Σ was ≤ 1.7 mm/0.7° and σ was ≤ 1.2 mm/0.6° in cranial sites while in extracranial sites Σ was ≤ 5.5 mm/0.9° and σ was ≤4.4 mm/0.9°. Setup residuals were submillimetric in all sites. In cranial patients, maximum intrafractional Σ was 0.8 mm/0.4°. This report extensively quantifies inter- and intrafraction setup accuracy on an institutional basis and confirms the need of image guidance to fully benefit from the geometrical selectivity of particles. The reported analysis provides a board institutional data set on the evaluation of patient immobilization and bony anatomy alignment for several particle therapy clinical indications.

Clinical Evaluation of a Rotational Set-up Correction Device for Multiple Brain Metastases Using Single-Isocenter Stereotactic Radiation Therapy

Stereotactic radiation therapy (SRT) using a single plan with one isocenter by helical tomotherapy (HT) can simultaneously treat multiple brain metastases with highly conformal dose distributions. This may reduce treatment time and intra-fractional motion. However, rotational set-up errors in the pitch and yaw angles cannot be corrected in the HT system. Therefore, increases in rotational set-up error and distance of the target-to-rotational-center may be associated with significant dosimetric uncertainties with this irradiation technique. Previous research shows that when rotational errors are increased to 2.0°, the prescription doses which cover 95% of the planning target volume were only 63% of all tested cases. Here, we developed a new head supporting device that allows for a highly-accurate correction of rotational errors during image-guided radiation therapy. In this study, we investigated the amounts of rotational correction required prior to irradiation, and evaluated the dosimetric efficacy of rotational correction for SRT, using HT unit to treat multiple brain metastases. A novel rotational set-up correction device was constructed from carbon material and conjected with the commonly-used head shell system on the top of our device. We were able to rotate in 0.1° increments for pitch and yaw angles using two screws. We retrospectively analyzed data from three patients irradiated by single-isocenter SRT for multiple brain metastases using the HT unit. The SRT plans were created with 30 Gy in three fractions prescribed for D99% to clinical target volumes. The required rotational correction values were determined by mega-voltage computed tomography (MVCT) before irradiation. Residual correction values were quantified after correction by the developed device. Moreover, dosimetric efficacy was evaluated using the calculated dose distribution with MVCT after rotational correction. Dose distribution was compared between 4D (three horizontal axes + roll) and 6D correction. We clarified efficacy of rotational correction depending on the distance of the target-to-rotational-center. The rotational correction for pitch was 1.2° ± 1.7°, roll: 0.9° ± 1.2°, and yaw: 1.3° ± 1.6°. The maximum correction value in pitch and yaw was 3.0°. The residual correction value after rotational correction was 0.2° ± 0.3° in both pitch and yaw angles. The difference in target dose between 4D and 6D corrections was improved by 2.5% in coverage index, and 1.0% on D99%. Dosimetric efficacy of rotational correction did not depend on the distance of the target-to-rotational-center. This suggests that irradiated doses for brain metastases in any location can be improved. Novel rotational set-up correction device can be corrected to within 0.5° in pitch and yaw angle error, and benefited rotational correction and irradiated dose distribution for single-isocenter SRT for multiple brain metastases.

Analysis of the inter-and intra-fraction setup errors and residual errors during stereotactic radiotherapy for brain metastasis

Objective To evaluate the necessity of arc by arc setup verification in patients with brain metastases receiving stereotactic radiotherapy (SRT) by analyzing the inter-and intra-fraction setup errors and residual errors collected from the ExacTrac X-ray portal image. Methods Clinical data of brain metastases patients treated with SRT in the previous two years were retrospectively analyzed. The ExacTrac X-ray setup images were collected after the normal setup procedure. Setup errors were calculated by registering the cranial bony structures of the ExacTrac X-ray setup images to that of the digitally reconstructed setup images. The inter-and intra-fraction setup errors and residual errors were statistically analyzed. Results Seventy-five patients from 116 lesions received 337 cycles of SRT of the head. The inter-and intra-fraction translational setup errors in the x, y and z directions were (0.93±0.86) mm and (0.15±0.59) mm; (1.83±1.27) mm and (0.25±0.73) mm; (0.96±0.80) mm and (0.14±0.56) mm, respectively. The inter-and intra-fraction rotational setup errors in the x, y, z directions were (0.65°±0.62°) and (0.19°±0.40°); (0.97°±0.94°) and (0.13°±0.25°); (0.92°±0.71°) and (0.10°±0.29°), respectively. The residual translational setup errors in the x, y, z directions were (0.06±0.23) mm, (0.08±0.24) mm and (0.08±0.22) mm, and (0.12°±0.27°), (0.09°±0.18°) and (0.06°±0.19°) for the residual rotational setup errors, respectively. For a reference setup error threshold of 0.7 mm/0.7°, 99.1% of the SRT exceeded the threshold and required setup correction. For 1 006 non-coplanar arcs, rotating the treatment couch from 0° to the treatment angle made 66.4% of arcs exceed the threshold and require at least once setup correction. Conclusions During SRT for brain metastasis, the inter-and intra-fraction setup errors should be emphasized. It is necessary to perform arc by arc setup error verification. Key words: Neoplasm metastasis, brain/Stereotactic radiotherapy; Setup error; Residual error

First clinical retrospective investigation of limited projection CBCT for lung tumor localization in patients receiving SBRT treatment

To clinically investigate the limited-projection CBCT (LP-CBCT) technology for daily positioning of patients receiving breath-hold lung SBRT radiation treatment and to investigate the feasibility of reconstructing fast 4D-CBCT from 1 min 3D-CBCT scan.Eleven patients who underwent breath-hold lung SBRT radiation treatment were scanned daily with on-board full-projection CBCT (CBCT) using half-fan scan. A subset of the CBCT projections and the prior planning CT were used to estimate the LP-CBCT images using the weighted free-form deformation method. The limited projections are clusteringly sampled within fifteen sub-angles in 360° in order to simulate the fast 1 min scan for 4D-CBCT. The estimated LP-CBCTs were rigidly registered to the planning CT to determine the clinical shifts needed for patient setup corrections, which were compared with shifts determined by the CBCT for evaluation. Both manual and automatic registrations were performed in order to compare the systematic registration errors. Fifty CBCT volumes were obtained from the eleven patients in fifty fractions for this pilot clinical study.For the CBCT images, the mean (±standard deviation) shifts between CBCT and planning CT from manual registration in left–right (LR), anterior–posterior (AP), and superior–inferior (SI) directions are 1.1 ± 1.2 mm, 2.1 ± 1.9 mm, 5.2 ± 3.6 mm, respectively. The mean deviation difference between shifts determined by CBCT and LP-CBCT images are 0.3 ± 0.5 mm, 0.5 ± 0.8 mm, 0.4 ± 0.3 mm, in LR, AP, and SI directions, respectively. The mean vector length of CBCT shift for all fractions is 6.1 ± 3.6 mm, and the mean vector length difference between CBCT and LP-CBCT for all fractions studied is 1.0 ± 0.9 mm. The automatic registrations yield similar results as manual registrations.The pilot clinical study shows that LP-CBCT localization offers comparable accuracy to CBCT localization for daily tumor positioning while reducing the projection number to 1/10 for patients receiving breath hold lung radiation treatment. The cluster projection sampling in this study also shows the feasibility of reconstructing fast 4D-CBCT from 1 min 3D-CBCT scan.

Quantitative evaluation of 4D Cone beam CT scans with reduced scan time in lung cancer patients

PurposeImage guided radiotherapy (IGRT) based on respiration correlated cone-beam CT (4D-CBCT) provides accurate tumour localisation in lung cancer patients by taking into account respiratory motion when deriving setup correction. However, 4D-CBCT scan times are typically longer than for acquisition of 3D-CBCT scans, e.g. 4 min. This work aims to quantitatively evaluate the effect of reduced scan times on 4D-CBCT image quality and registration accuracy in lung cancer patients. Methods and materialsScan times down to 1 min were simulated by retaining only projection images corresponding to every second, third or fourth respiratory cycle in forty-four 4D-CBCTs from 15 lung cancer patients. In addition twenty 2-minute scans were acquired for 12 lung cancer patients. Image quality was quantified by assessing registration accuracy in the shorter scan times, comparing to the 4-minute scan registration result where available as reference. ResultsUse of 2-minute scans had little impact on registration accuracy or ability to detect tumour motion: automatic registration accuracy was within 2 mm in 6/8 scans analysed with 2-minute acquisitions, and 96.6% of registration discrepancies were within 2 mm for the simulated scans. When the scan time simulated was below 2 min, automatic registration results still agreed within 2 mm for 84.7% of scans, however visual image quality was considerably degraded. ConclusionA 4D-CBCT acquisition time of 2 min produces scans of sufficient image quality for IGRT in most lung cancer patients, as demonstrated quantitatively by assessing the impact on automatic registration accuracy in simulated and real acquisitions.

OC-0083 MRI guided set-up corrections for esophageal cancer: what margin do we need?

OC-0083 MRI guided set-up corrections for esophageal cancer: what margin do we need?

The Effect of Lumpectomy Cavity Changes on Planning Dose in Breast Radiotherapy Boost

IntroductionThe addition of a postoperative tumour bed (cavity) boost after whole-breast radiotherapy (RT) is known to decrease the risk of local in-breast recurrence. The purpose of this retrospective study is to assess breast excision cavity changes and planned doses at the time of initial boost RT treatments after the completion of whole-breast RT. MethodsOver a 4-month period, women with highly visible cavity on computed tomography (CT) and treated with whole-breast RT followed by a conformal photon boost to the tumour bed were identified. The patient's day 1 boost online cone beam CT (CBCT) and corresponding setup corrections were overlaid with the planning CT image. The cavity and dose evaluation volumes (DEVs = 1 cm expansion of the cavity, excluding 5 mm of lung and skin) were assessed. Dosimetric evaluations were performed for maximum and minimum cavity doses, cavity volume receiving 90% (V90) and 95% (V95) of prescription dose, and DEV receiving 85% (V85), 95%, and 105% (V105) of the prescription dose. The two-tailed student t-test and Pearson's correlation test were performed for statistical analysis. ResultsEighteen patients were included in the analysis. The CT cavity (CAVCT) volume (mean: 28.8 cc, SD 27.9) was larger than the CBCT cavity (CAVCBCT) volume (mean: 21.1 cc, SD: 22.4) (P value= .003). The CT DEV similarly decreased at the time of boost; DEVCT (mean: 113.9 cc, SD: 63.2) versus DEVCBCT (mean: 92.3 cc, SD: 50.8), (P = .002). A strong correlation was observed between the initial CT cavity volume and cavity shrinkage observed at time of boost (day 1 CBCT) (Pearson's r = 0.697; r2= 0.486, P = .001). Both time periods from surgery to CT (median: 92 days, range: 31–227) and from surgery to day 1 CBCT (median: 141 days, range: 56–265) were not associated with cavity volume change. However, an inverse correlation was observed between time from initial CT to day 1 boost CBCT (median: 33 days, range: 24–54) and % cavity volume change (Pearson's r = −0.642; r2= 0.4121, P = .004). Dosimetric evaluations of the cavity and DEV showed no significant differences in maximum, minimum, and target dose coverage between the CT and boost volumes. ConclusionIn patients with breast cancer treated with a tumour bed boost after whole-breast RT, the postoperative cavity can shrink between the time of CT and day 1 boost. The extent of cavity reduction was greatest in patients with large postoperative cavities on initial CT. Despite the cavity size change, conformal boost fields provide adequate dose coverage to the cavity.

Automatic Shoreline Position and Intertidal Foreshore Slope Detection from X-Band Radar Images Using Modified Temporal Waterline Method with Corrected Wave Run-up

Automatic and accurate shoreline position and intertidal foreshore slope detection are challenging and significantly important for coastal dynamics. In the present study, a time series shoreline position and intertidal foreshore slope have been automatically detected using modified Temporal Waterline Method (mTWM) from time-averaged X-band radar images captured throughout the course of two-week tidal cycle variation over an area spanning 5.6 km on the Hasaki coast between 12 April 2005 and 31 December 2008. The methodology is based on the correlation map between the pixel intensity variation of the time-averaged X-band radar images and the binary signal of the tide level ranging from −0.8 m to 0.8 m. In order to ensure the binary signal represented each of the water levels in the intertidal shore profile, determining the water level direction-wise bottom elevation is considered as the modification. Random gaps were detected in the captured images owing to the unclear or oversaturation of the waterline signal. A horizontal shift in the detected shoreline positions was observed compared to the survey data previously collected at Hasaki Oceanographical Research Station (HORS). This horizontal shift can be attributed to wave breaking and high wave conditions. Wave set-up and run-up are the effects of wave breaking and high wave conditions, respectively. The correction of the wave set-up and run-up is considered to allow the upward shift of the water level position, as well as shoreline position, to the landward direction. The findings indicate that the shoreline positions derived by mTWM with the corrected wave run-up reasonably agree with the survey data. The mean absolute bias (MAB) between the survey data and the shoreline positions detected using mTWM with the corrected wave run-up is approximately 5.9 m, which is theoretically smaller than the spatial resolution of the radar measurements. The random gaps in the mTWM-derived shoreline positions are filled by Garcia’s data filling algorithm which is a Penalized Least Squares regression method by means of the Discrete Cosine Transform (PLS-DCT). The MAB between survey data and the gap filled shoreline positions detected using TWM with corrected wave run-up is approximately 5.9 m. The obtained results indicate the accuracy of the mTWM with corrected wave run-up integrated with Garcia’s method compared to the survey observations. The executed approach in this study is considered as an efficient and robust tool to automatically detect shoreline positions and intertidal foreshore slopes extracted from X-band radar images with the consideration of wave run-up correction.

Setup Error Assessment and Correction in Planar kV Image- Versus Cone Beam CT Image-Guided Radiation Therapy: A Clinical Study of Early Breast Cancer Treated With External Beam Partial Breast Irradiation

Objective:To compare differences in setup error assessment and correction between planar kilovolt images and cone beam computed tomography images for external beam partial breast irradiation during free breathing.Methods:Nineteen patients who received external beam partial breast irradiation after breast-conserving surgery were recruited. Interfraction setup error was acquired using planar kilovolt images and cone beam computed tomography. After online setup correction, the residual error was calculated, and the setup error was compared. The residual error and setup margin were quantified for planar kilovolt and cone beam computed tomography images.Results:The largest setup error was observed in the anteroposterior direction for both cone beam computed tomography and planar kilovolt imaging (−1.45 mm, 1.74 mm). The cone beam computed tomography–based setup error (systematic error [Σ]) was less than the planar kilovolt images based on Σ in the anteroposterior direction (–1.2 mm vs 2.00 mm; P = .005), and no significant differences were observed for random error (σ) in 3 dimensions (P = .948, .376, .314). After online setup correction, cone beam computed tomography significantly reduced the residual setup error compared with planar kilovolt images in the anteroposterior direction (Σ: −0.20 mm vs 0.50 mm, P = .008; σ: 0.45 mm vs 1.34 mm, P = .002). The cone beam computed tomography–based setup margin was smaller than the planar kilovolt image-based setup margin in the anteroposterior direction (−1.39 mm vs 5.57 mm, P = .003; 0.00 mm vs 3.20 mm, P = .003).Conclusions:Discrepancy between the setup errors observed with planar kilovolt and cone beam computed tomography was obvious in the anteroposterior direction. Compared to cone beam computed tomography, the elapsed treatment time was smaller when the initial alignment used kilovolt planar imaging. Whether using planar kilovolt or cone beam computed tomography, residual errors can be reduced to 1.5 mm for external beam partial breast irradiation procedures.

207. Impact of IGRT on correct set-up of patients with prostate cancer: Experience of our center

Purpose The purpose of this study is to quantify displacements in image-guided radiotherapy (IGRT) for prostate cancer patients and to evaluate the impact of IGRT on the quality of radiotherapy treatments in terms of rectal toxicities. Methods From January to October 2017, 46 patients with prostate cancer were treated. All patients were planned with volumetric-modulated arc therapy (VMAT) technique, receiving hypofractionated radiotherapy for a total dose of 67.5 Gy in 25 fractions or conventionally fractionated radiotherapy for a total dose of 70–80 Gy in 35–40 fractions. Daily IGRT using cone-beam computed tomography (CBCT) was performed for all patients. Setup corrections were determined and corrected by means of registrations of CBCT images with the planning CT using online 3D fusion and for each session displacements were evaluated to analyze the setup errors. Weekly clinical visits were made to all patients; rectal toxicities were evaluated according to CTCAE (Common Terminology Criteria for Adverse Events) scales and compared with a group of prostate cancer patients treated with intensity modulated radiotherapy without daily CBCT from January 2013 to July 2014. Results Significative differences in setup displacements were found for each treatment session. The range of displacements in the three space directions was calculated for each patient, as showed in Fig. 1, and the average of all ranges was 1.6 cm in vertical direction, 1.3 cm in lateral direction and 1.4 cm in longitudinal direction. Symptomatic grade 1 (G1) rectal toxicity was found in 17% of daily IGRT patients and in 49% of no-daily IGRT patients; asymptomatic G1 rectal toxicity was found in 79% and 47% of IGRT and no-daily IGRT patients, respectively (Fig. 2). Conclusions Daily CBCT allows real-time verification and correction of set-up and organ-motion errors and improves treatment quality by reducing rectal toxicity. More cases and a longer follow-up are needed to confirm the preliminary results of this study. Download : Download high-res image (413KB) Download : Download full-size image Download : Download high-res image (236KB) Download : Download full-size image

Feasibility of a novel dose fractionation strategy in TMI/TMLI

BackgroundTo report our experience in planning and delivering total marrow irradiation (TMI) and total marrow and lymphatic irradiation (TMLI) in patients with hematologic malignancies.MethodsTwenty-seven patients undergoing bone marrow transplantation were treated with TMI/TMLI using Helical Tomotherapy (HT). All skeletal bones exclusion of the mandible comprised the treatment target volume and, for TMLI, lymph node chains, liver, spleen and/or brain were also included according to the clinical indication. Planned dose of 8Gy in 2 fractions was delivered over 1 day for TMI while 10Gy in 2 fractions BID was used for TMLI. Organs at risk (OAR) contoured included the brain, brainstem, lens, eyes, optic nerves, parotids, oral cavity, lungs, heart, liver, kidneys, stomach, small bowel, bladder and rectum. In particular, a simple method to avoid hot or cold doses in the overlapping region was implemented and the plan sum was adopted to evaluate dose inhomogeneity. Furthermore, setup errors from 54 treatments were summarized to gauge the effectiveness of immobilization.ResultsDuring the TMI/TMLI treatment, no acute adverse effects occurred during the radiation treatment. Two patients suffered nausea or vomiting right after radiation course. For the 9 patients treated with TMI, the median dose reduction of major organs varied 30–65% of the prescribed dose, substantially lower than the traditional total body irradiation (TBI). Meanwhile, average biological equivalent doses to OARs with 8Gy/2F TMI approach were not different from the conventional 12Gy/6F TMI approach. In the dose junction region, the 93% of PTV was covered by the prescribed dose without obvious hotspots. For the 27 patients, the overall setup corrections were lower than 3 mm except those in the SI direction for abdomen-pelvis region, demonstrating excellent immobilization.ConclusionThe present study confirmed the technical feasibility of HT-based TMI/TMLI delivering 8-10Gy in 2 fractions over 1 day. For patients undergoing hematopoietic cell transplantation the proposed 8Gy/2F TMI (or 10Gy/2F TMLI) strategy may be a novel approach to improve delivery efficiency, increase effective radiation dose to target while maintaining low risk of severe organ toxicities.

197. Stereotactic Body Radiotherapy: Comparison between two IGRT systems

Purpose The aim of this work is to compare the residual setup errors measured with ExacTrac X-ray 6 degree-of-freedom (6D) and kilo-voltage cone-beam computed tomography (CBCT) for patients receiving stereotactic body radiotherapy (SBRT) at Fondazione IOM in collaboration with REM Radioterapia. The first device employs an infrared optical system that performs patients pre-positioning through body markers and isocenter coordinates, and an X-ray imaging system that verifies target position using bone anatomy. CBCT imaging allows positioning verification using not only bone anatomy but also soft tissues. Methods On a TrueBeam-Novalis STx treatment unit, from January to November 2017, 45 patients with extracranial tumours were treated with SBRT for a total of 53 lesions (some patients having more than one lesion) and 152 treatment sessions. Prescribing doses ranged from 24 to 60 Gy in 3 fractions or 20 Gy in a single fraction and planning techniques were dynamic conformal arc therapy or hybrid intensity modulated radiotherapy, with no-coplanar fields. All patients were initially located using personalized immobilization systems and setup corrections were determined and corrected by means of registrations of ExacTrac X-ray images with the corresponding digitally reconstructed radiographs using the ExacTrac 6D fusion. At the end of each treatment session, with the couch at 0°, the residual setup errors were determined by means of registrations of CBCT images with the planning CT using online 3D fusion and for each session, displacements were evaluated to analyse the residual setup errors. Results A modest difference in residual setup errors was found between ExacTrac system and CBCT (figure below). The average of the observed residual displacements for the three space directions, in absolute value, was 1.5 mm in vertical and in lateral directions, 1.2 mm in longitudinal direction. Conclusion This work showed the good agreement on the setup accuracy between ExacTrac X-ray and CBCT for patients treated with SBRT. The two systems present comparable precision, but ExacTrac offers additional benefits such the capability to quantify all rotational errors, fastest automated positioning in 6D even for no-coplanar fields and smaller doses, representing a valid alternative to CBCT with complementary information in image-guided stereotactic radiotherapy.