Real-time Position Management System Research Articles

Data driven surrogate signal extraction for dynamic PET using selective PCA: time windows versus the combination of components.

Respiratory motion correction is beneficial in PET, as it can reduce artefacts caused by motion and improve quantitative accuracy. Methods of motion correction are commonly based on a respiratory trace obtained through an external device (like the Real Time Position Management System) or a data driven method, such as those based on dimensionality reduction techniques (for instance PCA). PCA itself being a linear transformation to the axis of greatest variation. Data driven methods have the advantage of being non-invasive, and can be performed post-acquisition. However, their main downside being that they are adversely affected by the tracer kinetics of the dynamic PET acquisition. Therefore, they are mostly limited to static PET acquisitions. This work seeks to extend on existing PCA-based data-driven motion correction methods, to allow for their applicability to dynamic PET imaging. The methods explored in this work include; a moving window approach (similar to the Kinetic Respiratory Gating method from Schleyer et al.), extrapolation of the principal component from later time points to earlier time points, and a method to score, select, and combine multiple respiratory components. The resulting respiratory traces were evaluated on 22 data sets from a dynamic 18FFDG study on patients with Idiopathic Pulmonary Fibrosis. This was achieved by calculating their correlation with a surrogate signal acquired using a Real Time Position Management System. The results indicate that all methods produce better surrogate signals than when applying conventional PCA to dynamic data (for instance, a higher correlation with a gold standard respiratory trace). Extrapolating a late time point principal component produced more promising results than using a moving window. Scoring, selecting, and combining components held benefits over all other methods. This work allows for the extraction of a surrogate signal from dynamic PET data earlier in the acquisition and with a greater accuracy than previous work. This potentially allows for numerous other methods (for instance, respiratory motion correction) to be applied to this data (when they otherwise could not be previously used).

BRAVEHeart: a randomised trial comparing the accuracy of Breathe Well and RPM for deep inspiration breath hold breast cancer radiotherapy

BackgroundDeep inspiration breath hold (DIBH) reduces radiotherapy cardiac dose for left-sided breast cancer patients. The primary aim of the BRAVEHeart (Breast Radiotherapy Audio Visual Enhancement for sparing the Heart) trial is to assess the accuracy and usability of a novel device, Breathe Well, for DIBH guidance for left-sided breast cancer patients. Breathe Well will be compared to an adapted widely available monitoring system, the Real-time Position Management system (RPM).MethodsBRAVEHeart is a single institution prospective randomised trial of two DIBH devices. BRAVEHeart will assess the DIBH accuracy for Breathe Well and RPM during left-sided breast cancer radiotherapy. After informed consent has been obtained, 40 patients will be randomised into two equal groups, the experimental arm (Breathe Well) and the control arm (RPM with in-house modification of an added patient screen). The primary hypothesis of BRAVEHeart is that the accuracy of Breathe Well in maintaining the position of the chest during DIBH is superior to the RPM system. Accuracy will be measured by comparing chest wall motion extracted from images acquired of the treatment field during breast radiotherapy for patients treated using the Breathe Well system and those using the RPM system.DiscussionThe Breathe Well device uses a depth camera to monitor the chest surface while the RPM system monitors a block on the patient’s abdomen. The hypothesis of this trial is that the chest surface is a better surrogate for the internal chest wall motion used as a measure of treatment accuracy. The Breathe Well device aims to deliver an easy-to-use implementation of surface monitoring. The findings from the study will help inform the technology choice for other centres performing DIBH.Trial registrationClinicalTrials.govNCT02881203. Registered on 26 August 2016.

Multi-channel respiratory signal detection system for 4D-CT in radiotherapy by measuring the back pressure.

This study proposes a novel respiratory signal detection system for 4D-CT in radiotherapy by measuring back pressure changes at multiple positions on CT couch. The 12-channel pressure sensor is fixed on CT couch to obtain patient's back pressure signal. The 12-channel signal is transmitted to a PC at a sampling rate of 50 Hz after a signal conditioning circuit and an analog-digital converter. The amplitude of pressure changes is characterized to select the optimal channel. This system is validated by comparing with the respiratory signal collected synchronously with a real-time position management (RPM) system on 10 healthy volunteers. The correlation coefficient between the signals is 0.82 ± 0.09 (standard deviation) and the time shift is 0.32 ± 0.15 second. We conclude that the back pressure signal acquired by the proposed system has the potential to replace the clinical RPM system for respiratory signal detection in 4D-CT data acquisition.

Appropriate margin for planning target volume for breast radiotherapy during deep inspiration breath-hold by variance component analysis

BackgroundThis study aimed to quantify errors by using a cine electronic portal imaging device (cine EPID) during deep inspiration breath-hold (DIBH) for left-sided breast cancer and to estimate the planning target volume (PTV) by variance component analysis.MethodsThis study included 25 consecutive left-sided breast cancer patients treated with whole-breast irradiation (WBI) using DIBH. Breath-holding was performed while monitoring abdominal anterior–posterior (AP) motion using the Real-time Position Management (RPM) system. Cine EPID was used to evaluate the chest wall displacements in patients. Cine EPID images of the patients (309,609 frames) were analyzed to detect the edges of the chest wall using a Canny filter. The errors that occurred during DIBH included differences between the chest wall position detected by digitally reconstructed radiographs and that of all cine EPID images. The inter-patient, inter-fraction, and intra-fractional standard deviations (SDs) in the DIBH were calculated, and the PTV margin was estimated by variance component analysis.ResultsThe median patient age was 55 (35–79) years, and the mean irradiation time was 20.4 ± 1.7 s. The abdominal AP motion was 1.36 ± 0.94 (0.14–5.28) mm. The overall mean of the errors was 0.30 mm (95% confidence interval: − 0.05–0.65). The inter-patient, inter-fraction, and intra-fractional SDs in the DIBH were 0.82 mm, 1.19 mm, and 1.63 mm, respectively, and the PTV margin was calculated as 3.59 mm.ConclusionsErrors during DIBH for breast radiotherapy were monitored using EPID images and appropriate PTV margins were estimated by variance component analysis.

Prone Positioning With Deep Inspiration Breath Hold for Left Breast Radiotherapy

BackgroundWith advances in treatment, outcomes for early-stage breast cancer are improving. We investigated the combination of prone position and deep inspiration breath hold to decrease cardiac doses for left-sided breast radiotherapy. Material and MethodsFifteen patients with left-sided breast cancer were enrolled on a single-institution prospective study. Each patient underwent 2 prone positioned computed tomography simulation scans utilizing free breathing and breath-hold. Separate treatment plans for each computed tomography simulation scan were created using tangential fields, and heart and left lung doses were compared between free breathing and breath-hold plans. The technique with the lower mean dose for the heart was used for treatment. All patients were treated with a hypofractionated regimen of 40 to 42 Gy in 15 to 16 fractions, followed by a lumpectomy cavity boost of 10 Gy in 5 fractions when indicated. Wilcoxon paired signed rank tests and paired t tests were performed for statistical analysis of dosimetric endpoints. ResultsThe median age of our patients was 58 years (range, 40-72 years). One patient was not able to tolerate prone positioning at simulation, leaving 14 patients with evaluable paired scans. The average mean heart dose with free breathing and with breath-hold was 0.93 Gy and 0.72 Gy, respectively (P = .0063). The average max heart dose with free breathing and with breath-hold was 15.70 Gy and 7.19 Gy, respectively (P = .001). The average mean left lung dose with free breathing and with breath-hold was 0.65 Gy and 0.88 Gy, respectively (P = .011). ConclusionsOur results indicate that breath-hold using the real-time position management system may provide additional cardiac dose reduction in patients receiving prone left-breast radiotherapy treated with tangential fields.

Technical Note: Evaluation of audiovisual biofeedback smartphone application for respiratory monitoring in radiation oncology.

Radiation dose delivered to targets located near the upper abdomen or thorax are significantly affected by respiratory motion, necessitating large margins, limiting dose escalation. Surrogate motion management devices, such as the Real-time Position Management (RPM™) system (Varian Medical Systems, Palo Alto, CA), are commonly used to improve normal tissue sparing. Alternative to current solutions, we have developed and evaluated the feasibility of a real-time position management system that leverages the motion data from the onboard hardware of Apple iOS devices to provide patients with visual coaching with the potential to improve the reproducibility of breathing as well as improve patient compliance and reduce treatment delivery time. The iOS application, coined the Instant Respiratory Feedback (IRF) system, was developed in Swift (Apple Inc., Cupertino, CA) using the Core-Motion library and implemented on an Apple iPhone® devices. Operation requires an iPhone®, a three-dimensional printed arm, and a radiolucent projector screen system for feedback. Direct comparison between IRF, which leverages sensor fusion data from the iPhone®, and RPM™, an optical-based system, was performed on multiple respiratory motion phantoms and volunteers. The IRF system and RPM™ camera tracking marker were placed on the same location allowing for simultaneous data acquisition. The IRF surrogate measurement of displacement was compared to the signal trace acquired using RPM™ with univariate linear regressions and Bland-Altman analysis. Periodic motion shows excellent agreement between both systems, and subject motion shows good agreement during regular and irregular breathing motion. Comparison of IRF and RPM™ show very similar signal traces that were significantly related across all phantoms, including those motion with different amplitude and frequency, and subjects' waveforms (all r>0.9, P<0.0001). We demonstrate the feasibility of performing four-dimensional cone beam computed tomography using IRF which provided similar image quality as RPM™ when reconstructing dynamic motion phantom images. Feasibility of an iOS application to provide real-time respiratory motion is demonstrated. This system generated comparable signal traces to a commercially available system and offers an alternative method to monitor respiratory motion.

Evaluation of patient specific quality assurance of gated field in field radiation therapy technique using two-dimensional detector array

Introduction: Gated tangential field-in-field (FIF) technique is used to lower the dose to organs at risk for breast cancer radiotherapy (RT). In this study, the authors investigated the accuracy of the delivered treatment plan with and without gating using a two-dimensional detector array for patient-specific verification purposes.Methods: In this study, a 6MV beams were used for the merged FIF RT (forward Intensity Modulated Radiation Therapy). The respiration signals for gated FIF delivery were obtained from the one-dimensional moving phantom using the real-time position management (RPM) system (Varian Medical Systems, Palo Alto, CA). RPM system used for four-dimensional computed tomography scanner light-speed, GE is based on an infrared camera to detect motion of external 6-point marker. The beams were delivered using a Clinac iX (Varian Medical Systems, Palo Alto, CA) with the multileaf collimator Millennium 120. The MapCheck2 (SunNuclear, Florida) was used for the evaluation of treatment plans. MapCheck2 was validated through a comparison with measurements from a farmer-type ion chamber. Gated beams were delivered using a maximum dose rate with varying duty cycles and analyzed the MapCheck2 data to evaluate treatment plan delivery accuracy.Results: Results of the gamma passing rate for relative and absolute dose differences for all ungated and gated beams were between 95.1% and 100%.Conclusion: Gated FIF technique can deliver an accurate dose to a detector during gated breast cancer RT. There is no significance between gated and ungated patient-specific quality assurance (PSQA); one can use ungated PSQA for verification of treatment plan delivery

A new respiratory monitor system for four-dimensional computed tomography by measuring the pressure change on the back of body.

A novel respiratory monitoring method based on the periodical pressure change on the patient's back was proposed and assessed by applying to four-dimensional CT (4DCT) scanning. A pressure-based respiratory monitoring system is developed and validated by comparing to real-time position management (RPM) system. The pressure change and the RPM signal are compared with phase differences and correlations calculated. The 4DCT images are reconstructed by these two signals. Internal and skin artifacts due to mismatch between CT slices and respiratory phases are evaluated. The pressure and RPM signals shows strong consistency (R = 0.68±0.19 (1SD)). The time shift is 0.26 ± 0.51 (1SD) s and the difference of breath cycle is 0.02 ± 0.17 (1SD) s. The quality of 4DCT images reconstructed by two signals is similar. For both methods, the number of patients with artifacts is eight and the maximum magnitudes of artifacts are 20 mm (internal) and 10 mm (skin). The average magnitudes are 8.8 mm (pressure) and 8.2 mm (RPM) for internal artifacts, and 5.2 mm (pressure) and 4.6 mm (RPM) for skin artifacts. The mean square gray value difference shows no significant difference (p = 0.52). The pressure signal provides qualified results for respiratory monitoring in 4DCT scanning, demonstrating its potential application for respiration monitoring in radiotherapy. Pressure change on the back of body is a novel and promising method to monitor respiration in radiotherapy, which may improve treatment comfort and provide more information about respiration and body movement.

A Qualitative Analysis of Human Error During the DIBH Procedure

IntroductionThis quality assurance study analyzed human errors that occurred during the radiation treatment delivery of the deep-inspiration breath hold (DIBH) technique at a tertiary cancer centre. The intention is to recommend solutions and system changes that have the potential to decrease the frequency of errors based on human factors principles. MethodsEighty-two incident reports from January 2012 to July 2017 were retrieved and analysed to determine theme bins of performance-influencing factors contributing to the error. Performance-influencing factors were generated from the incident reports and from focus group discussions with volunteer radiation therapists in the department. Potential solutions to mitigate the error were sought from incident reports, focus groups, literature search, and an interview with a human factors specialist. The solutions were ranked based on the hierarchy of effectiveness, and recommendations were classified using a priority matrix. ResultsEighty-nine percent of the errors captured in the incident reports were defined as a slip or lapse error type, and 11% of the remaining errors were defined as a mistake error type. Treatment-related problem solving and distractions/interruptions were the highest frequency causative factors that contributed to the observed error. Potential solutions that were suggested across sources included implementing a forcing function, such as the real-time position management system, adding reminders, such as a console sign-off, and updating the current task checklist. DiscussionThe potential solutions generated were summarized into four recommendations that have varying degrees of association with known causative factors. The four recommendations include investing in (1) a forcing function, (2) updating/reinforcing the procedure, (3) managing workload, and (4) updating the checklist. A priority matrix was used to assess both potential effectiveness and cost/effort of each recommendation. Ideally, recommendation 1 would be implemented; however, it is understood that there would be an associated cost. It is therefore suggested that recommendations 2, 3, and 4 are implemented together to increase the effectiveness of the intervention until recommendation 1 can be achieved. ConclusionThis qualitative study introduced a method that analyzed human factors in a specialized procedure used in the treatment of a specific population of patients with cancer. Recommendations were formulated and proposed to the radiation therapy department in hopes of potentially decreasing the frequency of this specific error in the future.

Clinical implementation of respiratory-gated spot-scanning proton therapy: An efficiency analysis of active motion management.

PurposeThe aim of this work is to describe the clinical implementation of respiratory‐gated spot‐scanning proton therapy (SSPT) for the treatment of thoracic and abdominal moving targets. The experience of our institution is summarized, from initial acceptance and commissioning tests to the development of standard clinical operating procedures for simulation, motion assessment, motion mitigation, treatment planning, and gated SSPT treatment delivery.Materials and methodsA custom respiratory gating interface incorporating the Real‐Time Position Management System (RPM, Varian Medical Systems, Inc., Palo Alto, CA, USA) was developed in‐house for our synchrotron‐based delivery system. To assess gating performance, a motion phantom and radiochromic films were used to compare gated vs nongated delivery. Site‐specific treatment planning protocols and conservative motion cutoffs were developed, allowing for free‐breathing (FB), breath‐holding (BH), or phase‐gating (Ph‐G). Room usage efficiency of BH and Ph‐G treatments was retrospectively evaluated using beam delivery data retrieved from our record and verify system and DICOM files from patient‐specific quality assurance (QA) procedures.ResultsMore than 70 patients were treated using active motion management between the launch of our motion mitigation program in October 2015 and the end date of data collection of this study in January 2018. During acceptance procedures, we found that overall system latency is clinically‐suitable for Ph‐G. Regarding room usage efficiency, the average number of energy layers delivered per minute was <10 for Ph‐G, 10‐15 for BH and ≥15 for FB, making Ph‐G the slowest treatment modality. When comparing to continuous delivery measured during pretreatment QA procedures, the median values of BH treatment time were extended from 6.6 to 9.3 min (+48%). Ph‐G treatments were extended from 7.3 to 13.0 min (+82%).ConclusionsActive motion management has been crucial to the overall success of our SSPT program. Nevertheless, our conservative approach has come with an efficiency cost that is more noticeable in Ph‐G treatments and should be considered in decision‐making.

Intrafraction tumor motion during deep inspiration breath hold pancreatic cancer treatment.

PurposeBeam gating with deep inspiration breath hold (DIBH) has been widely used for motion management in radiotherapy. Normally it relies on some external surrogate for estimating the internal target motion, while the exact internal motion is unknown. In this study, we used the intrafraction motion review (IMR) application to directly track an internal target and characterized the residual motion during DIBH treatment for pancreatic cancer patients through their full treatment courses.Methods and MaterialsEight patients with pancreatic cancer treated with DIBH volumetric modulated arc therapy in 2017 and 2018 were selected for this study, each with some radiopaque markers (fiducial or surgical clips) implanted near or inside the target. The Varian Real‐time Position Management (RPM) system was used to monitor the breath hold, represented by the anterior‐posterior displacement of an external surrogate, namely reflective markers mounted on a plastic block placed on the patient's abdomen. Before each treatment, a cone beam computed tomography (CBCT) scan under DIBH was acquired for patient setup. For scan and treatment, the breath hold reported by RPM had to lie within a 3 mm window. IMR kV images were taken every 20° or 40° gantry rotation during dose delivery, resulting in over 5000 images for the cohort. The internal markers were manually identified in the IMR images. The residual motion amplitudes of the markers as well as the displacement from their initial positions located in the setup CBCT images were analyzed.ResultsEven though the external markers indicated that the respiratory motion was within 3 mm in DIBH treatment, significant residual internal target motion was observed for some patients. The range of average motion was from 3.4 to 7.9 mm, with standard deviation ranging from 1.2 to 3.5 mm. For all patients, the target residual motions seemed to be random with mean positions around their initial setup positions. Therefore, the absolute target displacement relative to the initial position was small during DIBH treatment, with the mean and the standard deviation 0.6 and 2.9 mm, respectively.ConclusionsInternal target motion may differ from external surrogate motion in DIBH treatment. Radiographic verification of target position at the beginning and during each fraction is necessary for precise RT delivery. IMR can serve as a useful tool to directly monitor the internal target motion.

Optimal Gating Window for Respiratory-Gated Radiotherapy with Real-Time Position Management and Respiration Guiding System for Liver Cancer Treatment

Respiratory-gated radiotherapy is one of the most effective approaches to minimise radiation dose delivery to normal tissue and maximise delivery to tumours under patient’s motion caused by respiration. We propose a respiration guiding system based on real-time position management with suitable gating window for respiratory-gated radiotherapy applied to liver cancer. Between August 2016 and February 2018, 52 patients with liver cancer received training in real-time position management and respiration guiding. Respiration signals were statistically analysed during unguided respiration and when applying the respiration guiding system. Phases of 30–60% and 30–70% retrieved the lowest respiration variability among patients, and 47 patients exhibited significant differences in terms of respiration reproducibility between unguided and guided respiration. The results suggest that either of these phases can establish suitable windows for gated radiotherapy applied to liver cancer, especially regarding respiration reproducibility.

Impact of Respiratory Waveform on Gate Signal Generation on Respiratory Gated Irradiation and Evaluation Method of Respiratory Waveform to Be Used

The respiratory gated irradiation using the real-time position management system (RPM) was used to clarify the generation of the gated signal when the respiration waveform changed, and also the evaluation method of the respiration waveform was also examined. The respiratory waveform was changed using a moving phantom. Respiratory waveform was analyzed from the data recorded in RPM, and the out-of-phase gated rate was examined. Analysis was made by focusing on the coefficient of variation of the respiratory wavelength in the evaluation of respiratory waveform. Immediately after the change of respiratory wavelength from the short cycle to the long cycle, a gated signal was generated at a phase before the set gated phase, and a maximum advance of 1.259 ± 0.212 s occurred. Immediately after the change of respiratory wavelength from the long cycle to the short cycle, the gated signal was generated at the phase exceeding the set gated phase, and a delay of 0.997 ± 0.180 s occurred at the maximum. As the value of the coefficient of variation increased, the gated rate which was out of setting also increased. In respiratory gated irradiation using RPM, it became clear that the gated signal is generated out of the phase set by the respiratory waveform change. Coefficient of variation of the respiratory wavelength is considered to be an indicator for evaluating the respiratory waveform to be used in the respiratory gated irradiation.

A Novel 4D-CT Sorting Method Based on Combined Mutual Information and Edge Gradient

Although mutual information is a general method usually being used to measure the similarity of two images, the robustness is questionable due to the absence of spatial information. The purpose of this study is to develop a feasible sorting technique for 4D-CT. A novel sorting algorithm named mutual information and edge gradient (MIEG), which includes spatial information by combining mutual information with a term based on the edge gradient of the image, was proposed to sort sequential CT images. The edge of image was extracted by calculating the wavelet transform modulus maxima, and the gradient similarity coefficient of the edge image was calculated and used to multiply by mutual information to form the final similarity metric. This sorting technique was validated by comparing the 4D-CTs reconstructed using MIEG and Real-time Position Management system (Varian Medical Systems, Inc., Palo Alto, CA). Tumor motion trajectories derived from 4D-CTs were analyzed in three orthogonal directions. Their correlation coefficients (CC) and differences in tumor motion magnitude (Ds) were determined. In addition, Dice similarity coefficient (DSC) was used to measure how well the tumor volumes segmented from the two 4D datasets overlapped with each other. For all patients, the mean CC values were >0.95 in all directions. The mean Ds were <0.64 mm in all directions. In addition, good overlapping was achieved between the segmented volumes with the mean DSC = 0.97 at end- and median-inspiration phases, respectively. This study proposed a feasible sorting method for 4D-CT, and its usefulness in imaging accurate tumor motion has been demonstrated.

Performance Validation of In-House Developed Four-dimensional Dynamic Phantom.

Objective:The objective of this study was to validate the performance characteristics of in-house developed four-dimensional (4D) dynamic phantom (FDDP).Materials and Methods:There are three target inserts of 1.0, 1.5 and 2.0 cm diameter. The targets were driven in sinusoidal pattern in the longitudinal direction, using the combinations of amplitudes of 0.5, 1.0, and 1.5 cm with frequencies of 0.2 and 0.25 Hz. The amplitude and frequency of motion were measured manually, and by using Real-Time Position Management (RPM) system also. The static, free-breathing, and 4D computed tomography (CT) scans of the phantom were acquired with 1.0 mm slice thickness. The 4DCT scans were sorted into 0%–90% phase, and the maximum intensity projection (MIP) images were also generated. The static, free-breathing, and 4DCT data sets and MIP images were contoured to get VStatic, VFB, V00......V90, and internal target volume ITV MIP, respectively. The individual phase volumes were summed to obtain V4D. The length of the target in the motion was measured using MIP image and compared with theoretical length (TL). The variation of 3D displacement vector of individual phase volume with respect to V00 with the phase of motion was studied at amplitude and frequency of 1.0 cm and 0.25 Hz, respectively. The degree of similarity between VFB and V4D and VFB and ITVMIP was also studied for all the target sizes at amplitude and frequency of 1.0 cm and 0.2 Hz and 1.0 cm and 0.25 Hz, respectively.Results:The amplitude and frequency of motion agreed within the limits of uncertainty with the manually and RPM measured values. The length of target in the motion matched within 1.0 mm with TL. The 3D displacement of individual phase volume showed no target size dependence, and the degree of similarity between VFB and V4D and VFB and ITVMIP decreases with increase in the displacement between the two volumes.Conclusions:The mechanical and imaging performances of FDDP were found within the acceptable limits. Therefore, this phantom can be used for quality assurance of 4D imaging process in radiotherapy.

Intrafraction esophageal motion in patients with clinical T1N0 esophageal cancer.

To investigate the intrafraction movement of the esophagus using fiducial markers. Studies on intrafraction esophageal motion using the fiducial markers are scarce. We retrospectively analyzed patients with clinical T1N0 esophageal cancer who had received fiducial markers at our hospital between July 2007 and December 2013. Real-Time Position Management System to track the patient's respiration was used, and each patient underwent three-dimensional computed tomography of the resting expiratory and inspiratory level. We used the center of the marker to calculate the distance between the expiratory and inspiratory breath-holds, which were measured with the radiotherapy treatment planning system in three directions: left-right (LR), superior-inferior (SI), and anterior-posterior (AP). The movements at each site were compared with the Kruskal-Wallis analysis and Wilcoxon rank sum test with a Bonferroni correction. A total of 101 patients with 201 fiducial markers were included. The upper, middle and lower thoracic positions had 40, 77, and 84 markers, respectively. The mean absolute magnitudes of the shifts (standard deviation) were 0.18 (0.19) cm, 0.68 (0.46) cm, and 0.24 (0.24) cm in the LR, SI, and AP directions, respectively. From the cumulative frequency distribution, we assumed that 0.35 cm LR, 0.8 cm SI, and 0.3 cm AP in the upper; 0.5 cm LR, 1.55 cm SI, and 0.55 cm AP in the middle; and 0.75 cm LR, 1.9 cm SI, and 0.95 cm AP in the lower thoracic esophagus covered 95% of the cases. The internal margin based on the site of esophagus was estimated.

P256] The effect of different breathing stages on treatment plans prepared using VMAT technique in early stage left breast irradiation

Purpose Volumetric Arc Therapy (VMAT) has become one of the most frequently used techniques in the treatment of left breast cancer radiotherapy due to its ability to reduce critical organ doses.In patients with left breast cancer, it is very important to reduce the amount of irradiated heart dose-volume in order to prevent possible cardiovascular morbidity associated with radiotherapy. Deep inspiration breath-hold (DIBH) is a technique that delivered the radiotherapy to the left breast patients in a deep breath hold position.In this study, VMAT plans on computed tomography (CT) images taken at different breath phases for left sided breast cancer patients were compared in terms of plan quality and risky organ doses. Methods In the study, VMAT plans were prepared on the CT images taken both free-breathing (FB) and DIBH modes. Eclipse treatment planning system (TPS) was used in order to prepare radiotherapy plans. The Varian Real Time Position Management System (RPM) was used for the DIBH technique.The dose was defined as 50 Gy/25 fractions. For all plans, 95% of the CTV breast volume was targeted to receive 46 Gy. In both techniques, target volume homogeneity index (HI) and conformity index (CI), critical organ doses and MU values were compared. Result CI values of VMAT plans prepared for both FB and DIBH CT images was found as 1.02 ± 0.04 and 1.014 ± 0.03; HI was found as 0.101 ± 0.018 and 0.113 ± 0.016, respectively. In terms of dose homogeneity, DIBH-VMAT plans were found to be better than FB-VMAT plans; the difference is statistically significant. The LAD mean doses were found to be lower in the DIBH-VMAT technique (p Conclusion DIBH-VMAT technique should be preferred instead of FB-VMAT technique for early stage left breast cancer irradiation. This work was supported by Scientific Research Projects Coordination Unit of Istanbul University (Project Number: I.U.BAP-23057).

P136] The correlation of infrared reflecting marker movement and lung expansion with deep inspiration breath-hold technique for left-sided breast cancer radiotherapy

Purpose This study was to quantify the correlation of the infrared reflecting marker movement and deep inspiration breath-hold (DIBH) lung expansions by setting the infrared reflecting marker below the xiphoid process on the abdominal wall. Methods Ten patients with left breast cancer post operation underwent free-breathing (FB) and DIBH computed tomography (CT) using infrared reflecting marker on the abdominal wall. Therapists coached patient breathing maneuvers before CT scans. The breath-hold level (BHL) was recorded by infrared reflecting marker in the anteroposterior (AP) direction by Real-time Position Management system (RPM) system during CT procedure. Lung diameter in AP direction on both free-breathing (FB) and DIBH images were measured at 4 levels: half upper, upper border of heart, half lower and diaphragm levels of lung. The first CT slice with visible lung tissue and diaphragm level were identified for lung diameter in superioinferior (SI) direction corresponding Z values (slice position). Pearson correlation test was used to examine the correlation significance among BHL, lung AP diameter, lung SI diameter, heart dose, and left lung dose. Results The BHL had strongly positive correlation with lung expansion in SI direction (Pearson correlation r = 0.770). When BHL increased 1.0 cm, the lung expansion in SI direction increased 2.6 cm. Also, moderately positive correlation was revealed between BHL and total lung volume (Pearson correlation r = 0.596). When BHL increased 1.0 cm, the total lung volume increased 414.1c.c. Heart mean dose and maximum dose were strongly negative correlated to BHL according to inverse square law. Weak or no correlation was noted between BHL and lung expansion in AP direction at 4 levels (Pearson correlation r = 0.318, 0.009, −0.105 and −0.238). DIBH plans had lower heart dose (2.64 vs. 1.32 Gy; P = 0.005) and ipsilateral lung V20 (%) relative volume (13.6 vs. 10.9 %; P = 0.007) than FB plans as previous studies. Conclusions Setting infrared reflecting marker below the xiphoid process on the abdominal wall is sufficient for DIBH technique to detect lung expansion in SI direction and decrease the heart dose significantly. Patient couching before CT scans is recommended.

Target position reproducibility in left-breast irradiation with deep inspiration breath-hold using multiple optical surface control points.

The aim of this study was to investigate the use of 3D optical localization of multiple surface control points for deep inspiration breath‐hold (DIBH) guidance in left‐breast radiotherapy treatments. Ten left‐breast cancer patients underwent whole‐breast DIBH radiotherapy controlled by the Real‐time Position Management (RPM) system. The reproducibility of the tumor bed (i.e., target) was assessed by the position of implanted clips, acquired through in‐room kV imaging. Six to eight passive fiducials were positioned on the patients' thoraco‐abdominal surface and localized intrafractionally by means of an infrared 3D optical tracking system. The point‐based registration between treatment and planning fiducials coordinates was applied to estimate the interfraction variations in patients' breathing baseline and to improve target reproducibility. The RPM‐based DIBH control resulted in a 3D error in target reproducibility of 5.8 ± 3.4 mm (median value ± interquartile range) across all patients. The reproducibility errors proved correlated with the interfraction baseline variations, which reached 7.7 mm for the single patient. The contribution of surface fiducials registration allowed a statistically significant reduction (p < 0.05) in target localization errors, measuring 3.4 ± 1.7 mm in 3D. The 3D optical monitoring of multiple surface control points may help to optimize the use of the RPM system for improving target reproducibility in left‐breast DIBH irradiation, providing insights on breathing baseline variations and increasing the robustness of external surrogates for DIBH guidance.

Multileaf Collimator Position Accuracy of Respiratory Gated VMAT

Respiratory gated VMAT (volumetric modulated arc therapy) repeats rapid stop and go operations of a MLC (multileaf collimator) by turning the beam on and off by respiratory gating. The rapid stop and go operations of the MLC during respiratory gated irradiation may induce position error of the MLC and may affect output error and dose distribution. The purpose of this study was to clarify the relationship between the MLC position accuracy of the respiratory gated VMAT and the VMAT parameters. In the method, 1 arc, 2 arcs, and 4 arcs plan were created for the virtual target and irradiation was performed without the gated respiration and with the gated respiration. The respiratory gated system used a RPM (real-time position management system). The MLC position error, gap size error, and the MLC leaf speed were calculated from a log-file. In the histogram of the gap size error, the frequency of falling within the error range up to 0.2 mm was about 12 percentage points higher for the gated respiration. The MLC position error increased with increasing the MLC leaf speed. The correlation coefficient between the MLC leaf speed and the MLC position error exceeded 0.96, showing a strong correlation. Dose rate of VMAT parameters decreased with increasing arc number with the gated respiration and without the gated respiration. Gated irradiation was temporarily stopped, and it decreased by about 27% with respect to the dose rate without the gated respiration. The gantry rotation speed repeated the stop and re-rotation operations when gated irradiation was performed. For all arcs, the rotation speed decreased by about 30% compared with the rotation speed without the gated respiration. The pass rate of gamma analysis for each arc plan was about 95%. No effect on gated irradiation dose distribution was observed. Respiratory gated irradiation reduced dose rate change and gantry rotation speed of the VMAT. Reduction of the MLC leaf speed occurred, and the MLC position error and gap size error decreased. The MLC positional accuracy was secured, and it was confirmed that there was no effect on dose distribution by the respiratory gated VMAT.