Real-time Position Management Research Articles

Evaluation of two synchronized external surrogates for 4D CT sorting

The purpose of this study was to quantify the performance and agreement between two different external surrogate acquisition systems: Varian's Real‐Time Position Management (RPM) and Philips Medical Systems' pneumatic bellows, in the context of waveform and 4D CT image analysis. Eight patient displacement curves derived from RPM data were inputted into a motion platform with varying amplitudes (0.5 to 3 cm) and patterns. Simultaneous 4D CT acquisition, with synchronized X‐ray on detection, was performed with the bellows and RPM block placed on the platform. Bellows data were used for online retrospective phase‐based sorting, while RPM data were used for off‐line reconstruction of raw 4D CT data. RPM and bellows breathing curves were resampled, normalized, and analyzed to determine associations between different external surrogates, relative amplitude differences, and system latency. Maximum intensity projection (MIP) images were generated, phantom targets were delineated, and volume differences, overlap index, and Dice similarity coefficient differences were evaluated. A prospective patient study of ten patients was performed and waveforms were evaluated for latency (i.e., absolute time differences) and overall agreement. 4D CT sorting quality and subtraction images were assessed. Near perfect associations between the RPM and bellows‐acquired breathing traces were found (Pearson′sr=0.987−0.999). Target volumes were 200.4±12ccand199.8±12.6cc for RPM and bellows targets, respectively, which was not significantly different (U=33,p>0.05). Negligible centroid variations were observed between bellows and RPM‐contoured MIP targets (largest discrepancy=−0.24±0.31mm in superior‐inferior direction). The maximum volume difference was observed for an RPM target 2.5 cc (1%) less than bellows, yielding the largest difference in centroid displacement (0.9 mm). Strong correlations in bellows and RPM waveforms were observed for all patients (0.947±0.037). Latency between external surrogates was <100ms for phantom and patient data. Negligible differences were observed between MIP, end‐exhale, and end‐inhale phase images for all cases, with delineated RPM and bellows lung volumes demonstrating a mean difference of −0.3±0.51%. Dice similarity coefficients and overlap indices were near unity for phantom target volumes and patient lung volumes. Slight differences were observed in waveform and latency analysis between Philips bellows and Varian's RPM, although these did not translate to differences in image quality or impact delineations. Therefore, the two systems were found to be equivalent external surrogates in the context of 4D CT for treatment planning purposes.PACS numbers: 87.57.Q‐, 07.07.Df

Implementing In-Room Visual Guidance Using a Digital Projector for Breath-Hold Treatment of Left Breast Cancer

Implementing In-Room Visual Guidance Using a Digital Projector for Breath-Hold Treatment of Left Breast Cancer

A new respiratory monitoring and processing system based on Wii remote: Proof of principle

To create a patient respiratory management system and patient self-practice tool using the Wii remote, a widely available consumer hardware product. The Wii remote (Wiimote) (Nintendo, Redmond, WA) contains an infrared (IR) camera that can track up to four spots whose coordinates are reported to a host computer via Bluetooth. The Wiimote is capable of tracking a fiducial box currently used by a commercial monitoring system [Real-time Position Management(TM) (RPM) system, Varian Associates, Palo Alto, CA], if the correct IR source is used. The authors validated the Wiimote tracking by comparing the amplitude and frequency of signals among those reported by Wiimote with known movements from an inhouse servo-driven respiratory simulator, as well as with those measured using the RPM. The simulator comparison was done using standard sinusoid signals with amplitude of 2.0 cm as well as recorded patient respiratory traces. The RPM comparisons were done by simultaneously recording the RPM reflective box position with the Wiimote and the RPM. Timing was compared between these two systems by using the digital beam-on signal from the CT scanner, for the 4DCT to synchronize these acquisitions. The data acquisition rate from the Wiimote was 100.0 ± 0.4 Hz with a version 2.1 Bluetooth adaptor. The standard deviation of the height of the motion extrema was 0.06 and 1.1 mm when comparing those measured by the Wiimote and the servomotor encoder for standard sinusoid signal and prerecorded patient respiratory signal, respectively. The standard deviation of the amplitude of motion extrema between the Wiimote and RPM was 0.9 mm and the timing difference was 253 ms. The performance of Wiimote shows promise for respiratory monitoring for its faster sampling rate as well as the potential optical and GPU abilities. If used with care it can deliver reasonable spatial and temporal accuracy.

SU-D-105-05: Independent Evaluation of Respiratory-Gated Treatments Using In-House Quality Assurance Tool

Purpose: To quantitatively evaluate the reproducibility of patient breathing between the calculated phase from respiratory signal and RPM (real-time position management system, Varian Medical Systems, Palo Alto, CA) within treatment. We developed an independent retrospective verification system (RVS) for gated-radiotherapy using full signal and gating window in RPM system. Methods: RVS was programmed by LabVIEW 2009 with wavelet-based multi-resolution analysis, which is a useful and accurate technique for identifying peaks and valleys of noisy signals. The respiratory signal and real-time calculated phase information from RPM was exported to RVS as a text file. Using this text file, several respiratory parameters were calculated by RVS, and were compared with the generated parameters from RPM. The evaluated parameters included phase-shift, total displacement, residual motion, baseline shift, and so forth. The analysis was conducted for both in-gate and full respiratory signal separately. The analysis report was automatically generated in Excel file format. Eleven patients of abdominal cancer were retrospectively analyzed for the evaluation. Results: The mean phase error of gated signal and full signal between RPM and our software ranged from 1.50% to 3.08% and 1.52% to 3.08%, respectively. Average phase shift was not significant but in-gate phase difference between RVS and RPM was found to be higher than 4% in two cases. At times, real-time phase calculation from RPM caused the beam to be turned on at incorrect time of the breathing cycle when the patient breathing was not regular. The total displacement varied from 0.672 cm to 1.732 cm, which showed patient-specific baseline shift during treatment. Conclusion: The developed software demonstrated competency in analyzing RPM signal and evaluating patient-specific respiratory parameters of radiotherapy. Thus, it can be used as an independent quality assurance tool for RPM phase-based gating treatment.

SU‐E‐T‐399: Improving Gated Delivery Efficiency Using Brief Breath Holds at Both Inhale and Exhale

Purpose: Respiration‐gated intensity modulated radiation therapy (IMRT) and volumetric modulated radiation therapy (VMAT) deliver the treatment beam at a single phase to reduce dose uncertainties resulting from respiratory‐induced organ motion. In some cases, gating can significantly prolong treatment times, leading to increased patient discomfort, treatment duration, and dose uncertainty due to patient postural shifts. To decrease treatment duration without increasing dose uncertainty, we propose dual‐gating in conjunction with with alternating coached five to ten second breath holds at inhale and exhale. In this study, we examine the feasibility of maintaining reproducible inhale and exhale RPM marker positions in a healthy volunteer and compare the expected dual‐gated delivery speedup over the free breathing case.Materials/Methods: Varian Real‐Time Position Management (RPM) respiratory signals from a volunteer were recorded during free breathing and during alternating ten second inspiration and exhalation breath hold coaching. The signals were then processed to examine the volunteer's ability to consistently reproduce RPM marker position during subsequent breath holds. Conventionally‐gated and dual‐gated treatment times were simulated for a given treatment plan under both normal and alternating breath hold conditions and compared. Results: Dual‐gated delivery under free breathing increases the duty cycle from 30.3% to 58.3% as compared with gating at exhale only. Alternated breath hold coaching further improves the duty cycle to 85.1%. Treatment delivery requiring 29.05 minutes to complete under normal exhale gating conditions is reduced to 16.58 minutes for dual‐gating during free breathing and only 5.88 minutes with dual‐gated alternated breath holds. RPM marker reproducibility was within 8% over the course of the delivery time. Conclusion: While additional improvements and testing are necessary, dual‐gated treatment delivery during alternated breath hold coaching is a feasible method for increasing duty cycle and thus improving treatment efficiency for tumors undergoing respiratory‐motion.

Gated rapidarc using KV images acquired during dose delivery for liver stereotactic treatment

Purpose In this paper, we used the Intrafration Motion Review technique (IMR, Varian medical system), which allows simultaneous kV/MV utilization to analyse the liver motion during gated RapidArc stereotactic treatment. Materials and methods Eight liver cancer patients with implanted fiducial markers were treated using the gated RapidArc technique with a Varian Novalis Truebeam linear accelerator. Four 4D computed tomography (CT) scans were acquired using Real time Position Management (RPM) system to study the reproducibility of liver motion. The cine 4D CT images were separated into 10 phases CT series based on respiratory motion information. A Maximum Intensity Projection (MIP) and an Average Intensity Projection (Ave-IP) CT series were generated. The Internal Target Volume (ITV) was outlined in the MIP CT series. The Planning Target Volume (PTV) was created by adding a 5 mm margin from the ITV. The fiducials were marked in the exhalation and/or in the inhalation phase making possible the intrafraction verification. The treatment planning is realized in the Ave-IP CT series. The patient's alignment is set based on markers using daily cone beam CT (CBCT). During the treatment, kV images were acquired at each exhalation or inhalation phase when the respiratory signal cross the upper and lower gating threshold defined during the respiratory learning process. The positions of the fiducials markers were compared with their expected positions. Results The average (±SD) conformity index CIPTV = (VPTV95% (cc)/ VPTV (cc)) * (VPTV95% (cc)/ Viso95% (cc)) was 0.93 ± 0.02 and homogeneity index HIPTV = (D2% - D98%)/Dmedian was 0.09 ± 0.02. The average MU/Gy was 147 ± 25. The room occupation's time was 53, 30, 20, 24, 24 min respectively for the five first fractions. The average kV images acquired per fraction were 35 with a maximum of 74 images and a minimum of 12 images. The average gating errors of the fiducials in the Superior–Inferior (SI) direction during the intrafraction was 0,91 mm with a maximum of 6 mm. Conclusion For tumor motion, monitoring intra-fraction by IMR ensures with certainty the PTV irradiation estimates with a systematic checking of the position of the target volume (fiducials) when this one come inside the region of treatment. In this paper, we used the Intrafration Motion Review technique (IMR, Varian medical system), which allows simultaneous kV/MV utilization to analyse the liver motion during gated RapidArc stereotactic treatment. Eight liver cancer patients with implanted fiducial markers were treated using the gated RapidArc technique with a Varian Novalis Truebeam linear accelerator. Four 4D computed tomography (CT) scans were acquired using Real time Position Management (RPM) system to study the reproducibility of liver motion. The cine 4D CT images were separated into 10 phases CT series based on respiratory motion information. A Maximum Intensity Projection (MIP) and an Average Intensity Projection (Ave-IP) CT series were generated. The Internal Target Volume (ITV) was outlined in the MIP CT series. The Planning Target Volume (PTV) was created by adding a 5 mm margin from the ITV. The fiducials were marked in the exhalation and/or in the inhalation phase making possible the intrafraction verification. The treatment planning is realized in the Ave-IP CT series. The patient's alignment is set based on markers using daily cone beam CT (CBCT). During the treatment, kV images were acquired at each exhalation or inhalation phase when the respiratory signal cross the upper and lower gating threshold defined during the respiratory learning process. The positions of the fiducials markers were compared with their expected positions. The average (±SD) conformity index CIPTV = (VPTV95% (cc)/ VPTV (cc)) * (VPTV95% (cc)/ Viso95% (cc)) was 0.93 ± 0.02 and homogeneity index HIPTV = (D2% - D98%)/Dmedian was 0.09 ± 0.02. The average MU/Gy was 147 ± 25. The room occupation's time was 53, 30, 20, 24, 24 min respectively for the five first fractions. The average kV images acquired per fraction were 35 with a maximum of 74 images and a minimum of 12 images. The average gating errors of the fiducials in the Superior–Inferior (SI) direction during the intrafraction was 0,91 mm with a maximum of 6 mm. For tumor motion, monitoring intra-fraction by IMR ensures with certainty the PTV irradiation estimates with a systematic checking of the position of the target volume (fiducials) when this one come inside the region of treatment.

A new respiratory gating device to improve 4D PET/CT

Purpose Respiratory motion creates artifacts in position emission tomography with computed tomography (PET/CT) images especially for lung tumors, and can alter diagnosis. To account for motion effects, respiratory gating techniques have been developed. However, the lack of measures strongly correlated with tumor motion limits their accuracy. The authors developed a real-time pneumotachograph device (SPI) allowing to sort PET and CT images depending on lung volumes. Methods The performance of this innovative respiratory tracking system was characterized and compared to a standard system. Our experimental setup consisted in a movable platform and a thorax phantom with six fillable spheres simulating lung tumors. The accuracy of SPI to detect inhalation peaks was also determined on volunteers. A comparison with the real-time position management (RPM) device, that relies on abdominal height measurement, was then investigated. Results Experiments showed a high accuracy of the measured signal compared to the input signal ( R = 0.88 to 0.99), and of the detection of the inhalation peaks (error of 0.1 ± 5.8 ms) necessary for prospective binning mode. Activity recovery coefficient was improved (until +39%) and the smearing effect was reduced (until 2.74 times lower) with SPI compared to ungated PET/CT acquisition. The spatial distribution of activity in spheres was similar for 4D PET gated with SPI and RPM. Significant improvement of the binning stability and matching between PET and CT were highlighted for irregular breathing patterns with SPI. Conclusions SPI is an innovative device that provides better binning performance than the current gating device on phantom experiments. Future works will focus on patients where the authors expect a significant improvement of specificity and sensitivity of PET/CT examinations.

SU‐E‐T‐178: Dosimetric Evaluation of Gated and Non‐Gated IMRT Treatments Using Portal Dose Image Prediction Software

Purpose: The aim of the study is to compare the planar dose of IMRT fields on RPM gated delivery (for different duty cycles) with non‐gated delivery. Methods: Clinac NovalisTx Linear Accelerator equipped with Real‐Time Position Management (RPM) gating system is used to deliver the gated treatments. Varian Eclipse Treatment Planning System is used to perform the IMRT Planning. Quality Assurance of IMRT fields are performed on Electronic Portal Imaging Detector (aS1000) with Portal Dosimetry software. Portal Dose Image Prediction software is used to analyze the gamma of planar doses for gated to the reference of non‐gated IMRT delivery. In this retrospective study, 60 IMRT fields from various IMRT plans were analyzed and compared for three different duty cycles (20%, 30% &amp; 40% Duty cycle, which are generally used for treatment) of gated delivery with that of non‐gated delivery. The measured dose planes were analyzed for gamma agreement with criteria of 1% to 1mm. In addition to that, the measured dose planes of gated &amp; non‐gated delivery are compared with the TPS Calculated dose planes for gamma with criteria of 3% to 3mm. Results: The mean values of average area gamma greater than one for measured planar doses for 60 IMRT fields of 20%, 30% and 40% duty cycles were 1.50, 0.79 and 0.58 respectively for the gated delivery to the reference of non‐gated delivery. Conclusion: The Gamma results suggest that the gated deliveries for various duty cycles are comparable with the normal non‐gated delivery. The Results exhibits that the increase in duty cycle reduces the deviation between the gated and non‐gated delivery. This deviation is attributed due to the frequent breakage of beam for 20% duty cycles compared with the 30% and 40% duty cycles.

WE-G-134-06: Image Quality in Thoracic 4D Cone-Beam CT: A Sensitivity Analysis of Respiratory Signal Source, Binning Method, and Reconstruction Algorithm

Purpose: Respiratory signal source, binning method, and reconstruction algorithm are three major factors affecting thoracic 4D cone-beam CT (4D-CBCT) image quality. Various studies have investigated each of them individually, but no sensitivity analysis to these factors has been performed. This study quantitatively compares the impacts of the three factors on thoracic 4D-CBCT image quality. Methods: A 4D-CBCT patient projection dataset acquired using audio-visual biofeedback with known degree of baseline shift in respiratory motion was reconstructed with the following factors: (i) respiratory signal source (via real-time position management or projection image based method), (ii) binning method (phase, displacement, or equal-projection-density (EPD) displacement binning), and (iii) reconstruction algorithm (Feldkamp-Davis-Kress (FDK), McKinnon-Bates (MKB), or adaptive-steepest-descent projection-onto-convex-sets (ASD-POCS)). The image quality was quantified using signal-to-noise ratio (SNR), contrast ratio (CR), and edge-response width (ERW) to assess noise, contrast, and sharpness, respectively. Results: Respiratory signal sources had no significant effect on any of the three metrics. Displacement binning was found to produce slightly more inconsistent SNR values owing to unevenly distributed angular views. The binning method otherwise had minimal effects on image quality. For the reconstruction algorithms, MKB resulted in a slightly higher SNR than FDK, while ASD-POCS improved SNR by a factor of three. Conversely, degradation in CR was observed with MKB and ASD-POCS. FDK and MKB produced very similar ERW, while slightly higher values were observed with ASD-POCS, indicating a small degree of blurriness. Conclusion: Respiratory signal sources and binning methods had a negligible impact on image quality, and did not introduce apparent motion artifacts. The MKB and ASD-POCS reconstruction algorithms reduced the noise and streaking but produced poorer image contrast. Of the reconstruction factors tested, reconstruction algorithms play the most important role in improving 4D-CBCT image quality and therefore represent the highest priority for further development. This project is supported by an NHMRC Australia Fellowship, NHMRC project grant 1034060, US NCI P01CA116602, an International Postgraduate Research Scholarships, and an Australian Postgraduate Award.

SU-E-T-120: Measurement of Time Delays in Gated Radiotherapy for Realistic Breath Motions

Purpose: The accuracy of treatment delivery in gated radiotherapy depends on time delays between target entry into the gated region and beam-on, as well as target exit from the gated region and beam-off. This study measures time delays, extending past work with simple sinusoidal motion to more realistic breath motions. Methods: The setup consisted of two platforms moving synchronously, programmed with realistic breathing motion. The vertical platform supported an infrared marker block, tracked by the Varian Truebeam Real-time Position Management system. The horizontal platform supported an x-ray sensitive film with a copper sheet for build-up. A stationary cone mounted above the film defined a spot, translated into streaks by the moving platform. These film streaks were measured to determine the treatment-beam delivery time, based on the speed of the platform. Time delays were determined from differences between the duration of the gating window and treatment-beam delivery time. To discriminate beam-on and beam-off time delays, either the start or the end of the gating window coincided with a stable point of motion. Time delays were measured for different beam energies and motion patterns. Results: At 6MV beam energy, beam-on time delay was significantly longer (p=0.01) for realistic (mean±SEM of 172±8 ms) than for sinusoidal (mean±SEM of 133±3 ms) motion and beam-off time delay was significantly longer (p=0.05) for realistic (mean±SEM of 83±6 ms) than for sinusoidal (mean±SEM of 64±4 ms) motion. 15 MV results were consistent for beam-on and beam-off delays. The observed late time delays can Results: in treatment inefficiency (beam-on delays) or, more importantly, to geographical miss (beam-off delays). Conclusion: The shape of breath motions may be a significant factor determining the time delay. These preliminary findings suggest that the use of sinusoidal motion may underestimate time delays. Further work is needed to determine if sinusoidal motion is sufficient.

External respiratory motion analysis and statistics for patients and volunteers

We analyzed a large patient and volunteer study of external respiratory motion in order to develop a population database of respiratory information. We analyzed 120 lung, liver, and abdominal patients and 25 volunteers without lung disease to determine the extent of motion using the Varian Real‐Time Position Management system. The volunteer respiratory motion was measured for both abdominal and thoracic placement of the RPM box. Evaluation of a subset of 55 patients demonstrates inter‐ and intrafraction variation over treatment. We also calculated baseline drift and duty cycle for patients and volunteers. The mean peak‐to‐peak amplitude (SD) for the patients was 1.0 (0.5) cm, and for the volunteers it was abdomen 0.8 (0.3) cm and thoracic 0.2 (0.2) cm. The mean period (SD) was 3.6 (1.0) s, 4.2 (1.1) s, and 4.1 (0.8) s, and the mean end exhale position (SD) was 60% (6), 58% (7), and 56% (7) for patient, volunteer abdomen, and volunteer thoracic, respectively. Baseline drift was greater than 0.5 cm for 40% of patients. We found statistically significant differences between the patient and volunteer groups. Peak‐to‐peak amplitude was significantly larger for patients than the volunteer abdominal measurement and the volunteer abdominal measurement is significantly larger than the volunteer thoracic measurement. The patient group also exhibited significantly larger baseline drift than the volunteer group. We also found that peak‐to‐peak amplitude was the most variable parameter for both intra‐ and interfraction motion. This database compilation can be used as a resource for expected motion when using external surrogates in radiotherapy applications.PACS number: 87.19.Wx, 87.55.Km

A new respiratory gating device to improve 4D PET/CT

Respiratory motion creates artifacts in positon emission tomography with computed tomography (PET/CT) images especially for lung tumors, and can alter diagnosis. To account for motion effects, respiratory gating techniques have been developed. However, the lack of measures strongly correlated with tumor motion limits their accuracy. The authors developed a real-time pneumotachograph device (SPI) allowing to sort PET and CT images depending on lung volumes. The performance of this innovative respiratory tracking system was characterized and compared to a standard system. Our experimental setup consisted in a movable platform and a thorax phantom with six fillable spheres simulating lung tumors. The accuracy of SPI to detect inhalation peaks was also determined on volunteers. A comparison with the real-time position management (RPM) device, that relies on abdominal height measurement, was then investigated. Experiments showed a high accuracy of the measured signal compared to the input signal (R = 0.88 to 0.99), and of the detection of the inhalation peaks (error of 0.1 +/- 5.8 ms) necessary for prospective binning mode. Activity recovery coefficient was improved (until +39%) and the smearing effect was reduced (until 2.74 times lower) with SPI compared to ungated PET/CT acquisition. The spatial distribution of activity in spheres was similar for 4D PET gated with SPI and RPM. Significant improvement of the binning stability and matching between PET and CT were highlighted for irregular breathing patterns with SPI. SPI is an innovative device that provides better binning performance than the current gating device on phantom experiments. Future works will focus on patients where the authors expect a significant improvement of specificity and sensitivity of PET/CT examinations.

Investigation of sliced body volume (SBV) as respiratory surrogate

The purpose of this study was to evaluate the sliced body volume (SBV) as a respiratory surrogate by comparing with the real‐time position management (RPM) in phantom and patient cases. Using the SBV surrogate, breathing signals were extracted from unsorted 4D CT images of a motion phantom and 31 cancer patients (17 lung cancers, 14 abdominal cancers) and were compared to those clinically acquired using the RPM system. Correlation coefficient (R), phase difference (D), and absolute phase difference (DA) between the SBV‐derived breathing signal and the RPM signal were calculated. 4D CT reconstructed based on the SBV surrogate (4D CTSBV) were compared to those clinically generated based on RPM (4D CTRPM). Image quality of the 4D CT were scored (SSBV and SRPM, respectively) from 1 to 5 (1 is the best) by experienced evaluators. The comparisons were performed for all patients, and for the lung cancer patients and the abdominal cancer patients separately. RPM box position (P), breathing period (T), amplitude (A), period variability (VT), amplitude variability (VA), and space‐dependent phase shift (F) were determined and correlated to SSBV. The phantom study showed excellent match between the SBV‐derived breathing signal and the RPM signal (R=0.99, D=−3.0%, DA=4.5%). In the patient study, the mean (± standard deviation (SD)) R, D, DA, T, VT, A, VA, and F were 0.92(±0.05), −3.3% (±7.5%), 11.4% (±4.6%), 3.6 (± 0.8) s, 0.19 (± 0.10), 6.6 (± 2.8) mm, 0.20 (± 0.08), and 0.40 (± 0.18) s, respectively. Significant differences in R and DA (p=0.04 and 0.001, respectively) were found between the lung cancer patients and the abdominal cancer patients. 4D CTRPM slightly outperformed 4D CTSBV: the mean (± SD) SRPM and SSBV were 2.6 (± 0.6) and 2.9 (± 0.8), respectively, for all patients, 2.5 (± 0.6) and 3.1 (± 0.8), respectively, for the lung cancer patients, and 2.6 (± 0.7) and 2.8 (± 0.9), respectively, for the abdominal cancer patients. The difference between SRPM and SSBV was insignificant for the abdominal patients (p=0.59). F correlated moderately with SSBV (r=0.72). The correlation between SBV‐derived breathing signal and RPM signal varied between patients and was significantly better in the abdomen than in the thorax. Space‐dependent phase shift is a limiting factor of the accuracy of the SBV surrogate.PACS number: 87.59.bd

Evaluation of the Accuracy for Respiratory-gated RapidArc

The position of the internal organs can change continually and periodically inside the body due to the respiration. To reduce the respiration induced uncertainty of dose localization, one can use a respiratory gated radiotherapy where a radiation beam is exposed during the specific time of period. The main disadvantage of this method is that it usually requests a long treatment time, the massive effort during the treatment and the limitation of the patient selection. In this sense, the combination of the real-time position management (RPM) system and the volumetric intensity modulated radiotherapy (RapidArc) is promising since it provides a short treatment time compared with the conventional respiratory gated treatments. In this study, we evaluated the accuracy of the respiratory gated RapidArc treatment. Total sic patient cases were used for this study and each case was planned by RapidArc technique using varian ECLIPSE v8.6 planning machine. For the Quality Assurance (QA), a MatriXX detector and I’mRT software were used. The results show that more than 97% of area gives the gamma value less than one with 3% dose and 3 mm distance to agreement condition, which indicates the measured dose is well matched with the treatment plan’s dose distribution for the gated RapidArc treatment cases. 󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏

The retrospective binning method improves the consistency of phase binning in respiratory-gated PET/CT

This study assesses the accuracy of prospective phase-gated PET/CT data binning and presents a retrospective data binning method that improves image quality and consistency. Respiratory signals from 17 patients who underwent 4D PET/CT were analysed to evaluate the reproducibility of temporal triggers used for the standard phase-based gating method. Breathing signals were reprocessed to implement retrospective PET data binning. The mean and standard deviation of time lags between automatic triggers provided by the Real-time Position Management (RPM, Varian) gating device and inhalation peaks derived from respiratory curves were computed for each patient. The total number of respiratory cycles available for 4D PET/CT according to the binning mode (prospective versus retrospective) was compared. The maximum standardized uptake value (SUVmax), biological tumour volume (BTV) and tumour trajectory measures were determined from the PET/CT images of five patients. Compared to retrospective binning (RB), prospective gating approach led to (i) a significant loss in breathing cycles (15%) and (ii) the inconsistency of data binning due to temporal dispersion of triggers (average 396 ms). Consequently, tumour characterization could be impacted. In retrospective mode, SUVmax was up to 27% higher, where no significant difference appeared in BTV. In addition, prospective mode gave an inconsistent spatial location of the tumour throughout the bins. Improved consistency with breathing patterns and greater motion amplitude of the tumour centroid were observed with retrospective mode. The detection of the tumour motion and trajectory was improved also for small temporal dispersion of triggers. This study shows that the binning mode could have a significant impact on 4D PET images. The consistency of triggers with breathing signals should be checked before clinical use of gated PET/CT images, and our RB method improves 4D PET/CT image quantification.

Amplitude Restricted RPM Technique for Lung Cancer Radiation Therapy

Baseline shifts in lung tumor position are one of the most important sources of geometric uncertainty, and they can occur from the time of planning to the time of treatment, between fractions and possibly within fractions. In this study, we developed a new technique, Amplitude Restricted Real-time Position Management (ARRPM), to reduce baseline shifts problem in respiratory gated treatment of lung tumors using linac.

Calculation of Cranial and Caudal Margins to Compensate Tumor Motion Change in Lung SBRT Using EPID Cine

In radiation therapy for lung cancer (LC), treatment margins are added to compensate respiratory pattern change. The aim of this study was to evaluate tumor motion change with EPID cine at the cranial and caudal sides separately. The subjects were 16 patients with stage I non-small LC treated with SBRT. Simulation processes included respiratory correlated 4-dimensional CT (4DCT) and a Real-Time Position Management system (RPM). 4DCT data were divided into 10 respiratory phases. The coordinates of the geometrical tumor center (TC) along the cranio-caudal (CC) direction was obtained on each bin. During the100% duty cycle (no gating: DC100) and the 50% duty cycle centered on exhalation (gating window 30% - 70%: DC50), the CC coordinates of TC were decided at the most cranial (craTC-4D) and the most caudal positions (cauTC-4D). The average CC coordinate of TC (mean tumor position: MTP-4D) was calculated. Tumor motion on 4DCT was ≥ 5.0 mm for all subjects. In 4 sessions, EPID cine and respiratory motion detected by RPM were consecutively acquired for one treatment beam for every case (64 sets in total) with a common temporal axis. The coordinates of TC along the CC direction were also obtained on every EPID cine frame by in-house software. In DC100 and DC50, the CC coordinates of TC were decided at the most cranial (craTC-cine) and the most caudal positions (cauTC-cine). The average CC coordinates of TC (MTP-cine) was calculated. Patient position was normalized according to MTP-4D and MTP-cine. Margins to compensate difference between craTC-4D and craTC-cine and between cauTC-4D and cauTC-cine were separately calculated using the formula described by Stroom et al. The Table shows differences in CC coordinates of craTC and cauTC between 4DCT and EPID cine and calculated margins to compensate these differences. Positive difference indicates that TC of EPID cine shifted to the caudal side compared with 4DCT. The difference of cauTC was significantly larger than that of craTC in both DC100 (p = 0.005) and DC50 (p = 0.0005). As a consequence, margins to compensate the variations were larger for the caudal side than for the cranial side. We separately assessed variations of tumor motion at the cranial and caudal sides. Patient breathing level is unstable in the inspiratory phase compared with the expiratory phase. This could be the reason of greater variations of TC positions of the caudal side.Poster Viewing Abstract 3595; TableDifferences in CC coordinates of craTC and cauTC between 4DCT and EPID cine and calculated marginsDuty cycle [%]10050craTCcauTCcraTCcauTCDifference: mean (SD) [mm]0.0 (0.1)1.2 (2.4)-0.4 (0.9)1.5 (3.0)Margin [mm]2.45.01.96.5 Open table in a new tab

External respiratory motion: Shape analysis and custom realistic respiratory trace generation

The authors developed a realistic respiratory trace generating (RTG) tool for use with phantom and simulation studies. The authors analyzed the extent of abdominal wall motion from a real-time position management system database comprised of 125 lung, liver, and abdominal patients to determine the shape and extent of motion. Using Akaike's information criterion (AIC), the authors compared different model types to find the optimal realistic model of respiratory motion. The authors compared a family of sigmoid curves and determined a four parameter sigmoid fit was optimal for over 98% patient inhale and exhale traces. This fit was also better than sin (2)(x) for 98% of patient exhale and 70% of patient inhale traces and better than sin (x) for 100% of both patient inhale and exhale traces. This analysis also shows that sin (2)(x) is better than sin (x) for over 95% of patient inhale and exhale traces. With results from shape and extent of motion analysis, we developed a realistic respiratory trace generating (RTG) software tool. The software can be run in two modes: population and user defined. In population mode, the RTG draws entirely from the population data including inter- and intra fraction amplitude and period variability and baseline drift. In user-defined mode, the user customizes the respiratory parameters by inputting the peak-to-peak amplitude, period, end exhale position, as well as controls variability in these parameters and baseline drift. This work provides a method of generating custom respiratory data that can be used for initial implementation and testing of new technologies.

SU-E-J-166: Development of Real-Time Motion Verification System for Respiratory-Gated Radiotherapy.

To develop an on-line quality assurance tool for RPM (real-time position management system, Varian Medical Systems, Palo Alto, CA) phase-based gated radiotherapy. A real-time motion verification system (RMVS) was developed to verify the positional reproducibility of patient breathing between CT simulation and treatment. Phase-resolved anterior body midlines were extracted from the 4D-CT simulation data to constitute 4D reference lines. During the treatment, multiple infrared reflective markers attached on patient's body midline were tracked by a custom stereo camera system. The RPM-generated phase value was delivered to RMVS via in-house network communication software. The real-time positions of tracked markers were simultaneously compared with the 4D reference line dynamically selected according to the phase value. The technical feasibility of the system was evaluated by simulating a motion phantom under several scenarios such as ideal case (with identical motion parameters between simulation and treatment; cycle = 3.1 s, baseline = 0.0 mm, amplitude = 31.0 mm), cycle change, baseline shift, and amplitude change. The developed system (i.e., RMVS) was fully compatible with RPM. In the phantom experiments, RMVS detected 5.2 ± 1.3, 4.7 ± 1.2, and 9.8 ± 1.2 mm mean absolute errors (MAE) for -5.0, 5.0, and 10.0 mm baseline shifts, respectively. However, revealing about 1.0 mm MAE for both ideal and cycle change scenarios, RMVS turned out to have a systematic error. With 22.0, 26.0, 35.0, and 41.5 mm amplitudes, RMVS detected 2.3 ± 1.3, 1.5 ± 1.1, 2.3 ± 1.4, and 4.9 ± 2.5 mm MAE, respectively. The developed system demonstrated a competence for phase-matching error detection between real-time patient's motion and 4D-CT-based reference. Thus, it could be used as an on-line quality assurance tool for RPM phase-based radiotherapy. This work was supported in part by the SNU Brain Fusion Program Research Grant No. 400-20100049 (2010-2011) and the National Research Foundation of Korea (NRF) grant (800-20110212) funded by the Korea government (MEST).

SU-E-J-156: Dosimetric Evaluation of Proper Width of Respiratory Gating Window According to Dose Distribution of EBT2 Film.

We analyzed dose distribution depending on the width of gating window to determine the proper width of gating window in gated radiation therapy. A three dimensional breathing simulator with house phantom was built to simulate periodic sinusoidal breathing motion of 4 seconds/cycle and 3cm fan shape movement. This was driven synchronized with Real-time Position Management (RPM) system (Varian Medical Systems, Palo Alto, CA, USA), and thereafter 4D-CT images were acquired. Three treatment fields (0°, 120°, 240°) with gating plan using treatment planning system (Eclipse, Varian, USA) were performed aimed to be exposed 200cGy to isocenter. Dose evaluations regarding static, non-gated motion, 60% (phase of 20%-80%), 40% (phase of 30%-70%), 30% (phase of 40%-70%), 20% (phase of 40%-60%) and 15% (phase of 40%-55%) of gated motion were carried out using EBT2 film, and extents of field size, high dose exposed, penumbra were analyzed. In most cases, dose differences compared to static were getting decreased as the width of gating window was decreased. Non-gated motion showed -74.5% dose discrepancies compared to static exposed, whereas 15% respiratory gating window showed within 1% dose difference. Dose differences of 40% gating window was -30.7% whereas 30% gating window showed -6.3% dose discrepancies. Dose difference was rapidly reduced from 30% gating window against non-gated motion to 40% gating window in all cases of field size, high dose area, and penumbra. 15% respiratory gating window was regarded the most ideal width of gating window, but it will significantly increase beam delivery time over a conventional treatment. Therefore, considering beam delivery time and dose distributions of high dose area, field size, and penumbra, 30% respiratory gating window would be recommended. This work was supported by Nuclear Research & Development Program of the National Research Foundation of Korea (NRF) grant funded by the Korean government (MEST).