Respiratory-gated Radiotherapy Research Articles

Evaluation of breathing patterns for respiratory-gated radiation therapy using the respiration regularity index

Despite the considerable importance of accurately estimating the respiration regularity of a patient in motion compensation treatment, not to mention the necessity of maintaining that regularity through the following sessions, an effective and simply applicable method by which those goals can be accomplished has rarely been reported. The authors herein propose a simple respiration regularity index based on parameters derived from a correspondingly simplified respiration model. In order to simplify a patient’s breathing pattern while preserving the data’s intrinsic properties, we defined a respiration model as a cos4(ω(t) · t) wave form with a baseline drift. According to this respiration formula, breathing-pattern fluctuation could be explained using four factors: the sample standard deviation of respiration period (sf), the sample standard deviation of amplitude (sa) and the results of a simple regression of the baseline drift (slope as β, and standard deviation of residuals as σr) of a respiration signal. The overall irregularity (δ) was defined as \(\left\| {\vec \omega } \right\|\), where \(\vec \omega \) is a variable newly-derived by using principal component analysis (PCA) for the four fluctuation parameters and has two principal components (ω1, ω2). The proposed respiration regularity index was defined as ρ = ln(1 + (1/δ))/2, a higher ρ indicating a more regular breathing pattern. We investigated its clinical relevance by comparing it with other known parameters. Subsequently, we applied it to 110 respiration signals acquired from five liver and five lung cancer patients by using real-time position management (RPM; Varian Medical Systems, Palo Alto, CA). Correlations between the regularity of the first session and the remaining fractions were investigated using Pearson’s correlation coefficient. Additionally, the respiration regularity was compared between the liver and lung cancer patient groups. The respiration regularity was determined based on ρ; patients with ρ 0.7 was suitable for respiratory-gated radiation therapy (RGRT). Fluctuations in the breathing cycle and the amplitude were especially determinative of ρ. If the respiration regularity of a patient’s first session was known, it could be estimated through subsequent sessions. Notably, the breathing patterns of the lung cancer patients were more irregular than those of the liver cancer patients. Respiration regularity could be objectively determined by using a composite index, ρ. Such a single-index testing of respiration regularity can facilitate determination of RGRT availability in clinical settings, especially for free-breathing cases.

Pulmonary function tests – an easy selection method for respiratory-gated radiotherapy in patients with left-sided breast cancer

Purpose. The purpose of this study was to establish a feasible and convenient method for selection of the subset of patients with left-sided breast cancer for whom respiratory-gated radiotherapy (RT) would be necessary to meet the national recommendation regarding radiation dose to the heart.Material and methods. The volume of heart receiving a dose equal to or higher than 25 Gy (V25Gy), the mean heart dose (Dmean) and total lung volume (TLV-CT) were obtained from treatment plans based on computer tomography (CT) series recorded during free breathing (FB), and the correlation between dose to the heart and TLV-CT was studied. Second, the correlation between TLV-CT and TLV defined from three pulmonary function tests (PFTs); spirometry, gas diffusion and plethysmograhy, was evaluated.Results. Dose to the heart (V25Gy and Dmean) decreased with increasing TLV-CT. Pearson's correlation coefficient (r) for TLV-CT versus V25Gy and Dmean was equal (r = −0.809, p < 0.01) for patients planned for tangential breast RT only, and r = −0.853 and −0.861 (p < 0.01) for patients planned for loco-regional RT. Regression analysis showed good correlation between TLV-CT and TLV calculated from pulmonary function tests (R2 ≥ 0.717, p < 0.01).Conclusion. TLV defined by routine pulmonary function tests can be used to identify the subset of left-sided breast cancer patients who require respiratory-gated RT.

Effect of secondary particles on image quality of dynamic flat panels in carbon ion scanning beam treatment.

Real-time markerless tumour tracking using radiographic fluoroscopic imaging is one of the better solutions to improving respiratory-gated radiotherapy. However, particle beams cause secondary particles from patients, which could affect radiographs. Here, we evaluated the quality of radiographs during carbon ion pencil beam scanning (CPBS) irradiation for respiratory gating. A water phantom and chest phantom were used. The phantoms were irradiated with CPBS at 290 MeV n(-1) from orthogonal directions. Dose rates were 3.4 × 10(8), 1.14 × 10(8) and 3.79 × 10(7) particles per second. A dynamic flat panel detector (DFPD) was installed on the upstream (DFPD1) or downstream (DFPD2) side of the vertical irradiation port. DFPD images were acquired during CPBS at 15.00, 7.50 and 3.75 frames per second (fps). Charge on the DFPD was cleaned using fast readout technique every 30 fps. DFPD images were acquired during CPBS with radiographic exposure, and results with and without fast readout technique were compared. Secondary particles were visualized as spots or streak-like shapes. Capture of secondary particles from the horizontal beam direction was lower with fast readout technique than without it. With regard to beam irradiation direction dependency, CPBS from the horizontal direction resulted in a greater magnitude of secondary particles reaching DFPD2 than reaching DFPD1. When CPBS was delivered from the vertical direction, however, the magnitude of secondary particles on both DFPDs was very similar. Fast readout technique minimized the effect of secondary particles on DFPD images during CPBS. This technique may be useful for markerless tumour tracking for respiratory gating.

Evaluation of respiratory pattern during respiratory-gated radiotherapy.

The respiratory cycle is not strictly regular, and generally varies in amplitude and period from one cycle to the next. We evaluated the characteristics of respiratory patterns acquired during respiratory gating treatment in more than 300 patients. A total 331 patients treated with respiratory-gated carbon-ion beam therapy were selected from a group of patients with thoracic and abdominal conditions. Respiratory data were acquired for a total of 3,171 fractions using an external respiratory sensing monitor and evaluated for respiratory cycle, duty cycle, magnitude of baseline drift, and intrafractional/interfractional peak inhalation/exhalation positional variation. Results for the treated anatomical sites and patient positioning were compared. Mean±SD respiratory cycle averaged over all patients was 4.1±1.3s. Mean±SD duty cycle averaged over all patients was 36.5±7.3%. Two types of baseline drift were seen, the first decremental and the second incremental. For respiratory peak variation, the mean intrafractional variation in peak-inhalation position relative to the amplitude in the first respiratory cycle (15.5±9.3%) was significantly larger than that in exhalation (7.5±4.6%). Interfractional variations in inhalation (17.2±18.5%) were also significantly greater than those in exhalation (9.4±10.0%). Statistically significant differences were observed between patients in the supine position and those in the prone position in mean respiratory cycle, duty cycle, and intra-/interfractional variations. We quantified the characteristics of the respiratory curve based on a large number of respiratory data obtained during treatment. These results might be useful in improving the accuracy of respiratory-gated treatment.

Respiratory motion management using audio-visual biofeedback for respiratory-gated radiotherapy of synchrotron-based pulsed heavy-ion beam delivery.

To efficiently deliver respiratory-gated radiation during synchrotron-based pulsed heavy-ion radiotherapy, a novel respiratory guidance method combining a personalized audio-visual biofeedback (BFB) system, breath hold (BH), and synchrotron-based gating was designed to help patients synchronize their respiratory patterns with synchrotron pulses and to overcome typical limitations such as low efficiency, residual motion, and discomfort. In-house software was developed to acquire body surface marker positions and display BFB, gating signals, and real-time beam profiles on a LED screen. Patients were prompted to perform short BHs or short deep breath holds (SDBH) with the aid of BFB following a personalized standard BH/SDBH (stBH/stSDBH) guiding curve or their own representative BH/SDBH (reBH/reSDBH) guiding curve. A practical simulation was performed for a group of 15 volunteers to evaluate the feasibility and effectiveness of this method. Effective dose rates (EDRs), mean absolute errors between the guiding curves and the measured curves, and mean absolute deviations of the measured curves were obtained within 10%-50% duty cycles (DCs) that were synchronized with the synchrotron's flat-top phase. All maneuvers for an individual volunteer took approximately half an hour, and no one experienced discomfort during the maneuvers. Using the respiratory guidance methods, the magnitude of residual motion was almost ten times less than during nongated irradiation, and increases in the average effective dose rate by factors of 2.39-4.65, 2.39-4.59, 1.73-3.50, and 1.73-3.55 for the stBH, reBH, stSDBH, and reSDBH guiding maneuvers, respectively, were observed in contrast with conventional free breathing-based gated irradiation, depending on the respiratory-gated duty cycle settings. The proposed respiratory guidance method with personalized BFB was confirmed to be feasible in a group of volunteers. Increased effective dose rate and improved overall treatment precision were observed compared to conventional free breathing-based, respiratory-gated irradiation. Because breathing guidance curves could be established based on the respective average respiratory period and amplitude for each patient, it may be easier for patients to cooperate using this technique.

A motion-compensated image filter for low-dose fluoroscopy in a real-time tumor-tracking radiotherapy system.

In the real-time tumor-tracking radiotherapy system, a surrogate fiducial marker inserted in or near the tumor is detected by fluoroscopy to realize respiratory-gated radiotherapy. The imaging dose caused by fluoroscopy should be minimized. In this work, an image processing technique is proposed for tracing a moving marker in low-dose imaging. The proposed tracking technique is a combination of a motion-compensated recursive filter and template pattern matching. The proposed image filter can reduce motion artifacts resulting from the recursive process based on the determination of the region of interest for the next frame according to the current marker position in the fluoroscopic images. The effectiveness of the proposed technique and the expected clinical benefit were examined by phantom experimental studies with actual tumor trajectories generated from clinical patient data. It was demonstrated that the marker motion could be traced in low-dose imaging by applying the proposed algorithm with acceptable registration error and high pattern recognition score in all trajectories, although some trajectories were not able to be tracked with the conventional spatial filters or without image filters. The positional accuracy is expected to be kept within ±2 mm. The total computation time required to determine the marker position is a few milliseconds. The proposed image processing technique is applicable for imaging dose reduction.

SU‐E‐J‐67: Evaluation of Breathing Patterns for Respiratory‐Gated Radiation Therapy Using Respiration Regularity Index

Purpose:Despite the importance of accurately estimating the respiration regularity of a patient in motion compensation treatment, an effective and simply applicable method has rarely been reported. The authors propose a simple respiration regularity index based on parameters derived from a correspondingly simplified respiration model.Methods:In order to simplify a patient's breathing pattern while preserving the data's intrinsic properties, we defined a respiration model as a power of cosine form with a baseline drift. According to this respiration formula, breathing‐pattern fluctuation could be explained using four factors: sample standard deviation of respiration period, sample standard deviation of amplitude and the results of simple regression of the baseline drift (slope and standard deviation of residuals of a respiration signal. Overall irregularity (δ) was defined as a Euclidean norm of newly derived variable using principal component analysis (PCA) for the four fluctuation parameters. Finally, the proposed respiration regularity index was defined as ρ=ln(1+(1/ δ))/2, a higher ρ indicating a more regular breathing pattern. Subsequently, we applied it to simulated and clinical respiration signals from real‐time position management (RPM; Varian Medical Systems, Palo Alto, CA) and investigated respiration regularity. Moreover, correlations between the regularity of the first session and the remaining fractions were investigated using Pearson's correlation coefficient.Results:The respiration regularity was determined based on ρ; patients with ρ&lt;0.3 showed worse regularity than the others, whereas ρ&gt;0.7 was suitable for respiratory‐gated radiation therapy (RGRT). Fluctuations in breathing cycle and amplitude were especially determinative of ρ. If the respiration regularity of a patient's first session was known, it could be estimated through subsequent sessions.Conclusions:Respiration regularity could be objectively determined using a respiration regularity index, ρ. Such single‐index testing of respiration regularity can facilitate determination of RGRT availability in clinical settings, especially for free‐breathing cases.This work was supported by a Korea Science and Engineering Foundation (KOSEF) grant funded by the Korean Ministry of Science, ICT and Future Planning (No. 2013043498).

SU-E-J-253: Evaluation of 4DCT Images with Correlation of RPM Signals to Tumor Motion for Respiratory-Gated Radiotherapy

Purpose: The amplitudes of lung tumor target motion and RPM signals are different from each other. Also, RPM system does not have in-depth RPM signal analysis tool. We have developed an algorithm that analyzes RPM signals for its stability as well as correlativity to the tumor motion. Methods: We used a Philips Big Bore CT scanner with a Varian Real-Time Position Management™ (RPM) system attached. 4DCT images were reviewed and tumor motion amplitudes of full breathing in superior-inferior, anterior-posterior, and left-right directions were measured. RPM signals were analyzed with the algorithm developed with Matlab. Average signal period, amplitude and statistical stability of the full breathing pattern as well as the pattern around full expiration were calculated. RPM signal amplitudes were normalized to measured tumor motion amplitudes so that selected gating phases (30%–70% or 40%–60%) allow tumor motion under 5.0mm. Results: Twelve patient cases were analyzed in this study with GTV sizes ranged from 1.0cm to 3.0cm diameter. The periods and amplitudes of RPM signal ranged from 3.1seconds to 6.5seconds and from 0.2cm to 1.7cm, respectively. RPM signals were most stable at full expiration. The standard deviation of the RPM signal peaks at full expiration was <0.11cm, and that of gatedmore » amplitudes was <0.25cm. Tumor motion amplitudes were primary in superior-inferior direction and minor (<=0.2cm) in other directions on all analyzed cases, ranged from 0.2cm to 2.5cm. The amplitudes increases with the tumor located toward the diaphragm. The gated phases were selected so that the average gated tumor motion amplitude as well as that plus deviation became under 0.5cm in superior-inferior direction. Conclusion: We were able to determine the respiratory-gated phases in RPM signals employing measured tumor motion amplitudes as well as developed RPM signal analyzer through correlation process. The RPM signal amplitudes do not represent tumor motion because of its location.« less

Suitability of markerless EPID tracking for tumor position verification in gated radiotherapy

To maximize the benefits of respiratory gated radiotherapy (RGRT) of lung tumors real-time verification of the tumor position is required. This work investigates the feasibility of markerless tracking of lung tumors during beam-on time in electronic portal imaging device (EPID) images of the MV therapeutic beam. EPID movies were acquired at ∼2 fps for seven lung cancer patients with tumor peak-to-peak motion ranges between 7.8 and 17.9 mm (mean: 13.7 mm) undergoing stereotactic body radiotherapy. The external breathing motion of the abdomen was synchronously measured. Both datasets were retrospectively analyzed in PortalTrack, an in-house developed tracking software. The authors define a three-step procedure to run the simulations: (1) gating window definition, (2) gated-beam delivery simulation, and (3) tumor tracking. First, an amplitude threshold level was set on the external signal, defining the onset of beam-on/-off signals. This information was then mapped onto a sequence of EPID images to generate stamps of beam-on/-hold periods throughout the EPID movies in PortalTrack, by obscuring the frames corresponding to beam-off times. Last, tumor motion in the superior-inferior direction was determined on portal images by the tracking algorithm during beam-on time. The residual motion inside the gating window as well as target coverage (TC) and the marginal target displacement (MTD) were used as measures to quantify tumor position variability. Tumor position monitoring and estimation from beam's-eye-view images during RGRT was possible in 67% of the analyzed beams. For a reference gating window of 5 mm, deviations ranging from 2% to 86% (35% on average) were recorded between the reference and measured residual motion. TC (range: 62%-93%; mean: 77%) losses were correlated with false positives incidence rates resulting mostly from intra-/inter-beam baseline drifts, as well as sudden cycle-to-cycle fluctuations in exhale positions. Both phenomena can lead to considerable deviations (with MTD values up to a maximum of 7.8 mm) from the intended tumor position, and in turn may result in a marginal miss. The difference between tumor traces determined within the gating window against ground truth trajectory maps was 1.1 ± 0.7 mm on average (range: 0.4-2.3 mm). In this retrospective analysis of motion data, it is demonstrated that the system is capable of determining tumor positions in the plane perpendicular to the beam direction without the aid of fiducial markers, and may hence be suitable as an online verification tool in RGRT. It may be possible to use the tracking information to enable on-the-fly corrections to intra-/inter-beam variations by adapting the gating window by means of a robotic couch.

Quality Assurance for Respiratory-Gated Radiotherapy Using the Real-Time Tumor-Tracking Radiotherapy System

Purpose: Respiratory-gated radiation therapy (RT) using the real-time tumor-tracking radiotherapy (RTRT) system is an effective technique for managing tumor motion. High dosimetric and geometric accuracy is needed; however, quality assurance (QA) for respiratory-gated RT using the RTRT system has not been reported. The purpose of this study was to perform QA for respiratorygated RT using the RTRT system. Materials and Methods: The RTRT system detected the position of the fiducial marker and radiation delivery gated to the motion of the marker was performed. The dynamic anthropomorphic thorax phantom was positioned at the isocenter using the fiducial marker in the phantom. The phantom was irradiated only when the fiducial marker was within a three-dimensional gating window of ±2 mm from the planned position. First, the absolute doses were measured using anionization chamber inserted in the phantom under the stationary, gating and non-gating state for sinusoidal (nadir-to-peak amplitude [A]: 20 - 40 mm, breathing period [T]: 2 - 4 s) and the basic respiratory patterns. Second, the dose profiles were measured using Gafchromic films in the phantom under the same conditions. Differences between dose profiles were calculated to evaluate the dosimetric and geometric accuracy. Finally, differences between the actual and measured position of the fiducial marker were calculated to evaluate the tracking accuracy for sinusoidal and basic respiratory patterns. Results: For the sinusoidal patterns, the relative doses were 0.93 for non-gating and 0.99 for gating (A = 20 mm, T = 2 s), 0.94 for non-gating and 1.00 for gating (A = 20 mm, T = 4 s), 0.55 for non-gating and 1.00 for gating (A = 40 mm, T = 4 s), respectively. For the basic respiratory pattern, the relative doses were 1.00 for non-gating and 1.00 for gating, respectively. Compared to the stationary conditions, the differences in lateral distance between the 90% dose of dose profiles were 6.23 mm for non-gating and 0.36 mm for gating (A = 20 mm, T = 2 s), 8.79 mm for non-gating and 1.73 mm for gating (A = 20 mm, T = 4 s), 18.37 mm for non-gating and 0.67 mm for gating (A = 40 mm, T = 4 s), respectively. For the basic respiratory pattern, those were 5.23 mm for non-gating and 0.35 mm for gating. The root mean square (RMS) values of the tracking error were 0.18 mm (A = 20 mm, T = 2 s), 0.14 mm (A = 20 mm, T = 4 s), and 0.21 mm (A = 40 mm, T = 4 s) for sinusoidal and 0.79 mm for the basic respiratory pattern, respectively. Conclusion: We conducted QA for respiratory-gated RT using the RTRT system. The respiratory-gated RT using the RTRT system reduced the blurring effects on dose distribution with high dosimetric and geometric accuracy.

Establishment of quality assurance for respiratory-gated radiotherapy using a respiration-simulating phantom and gamma index: Evaluation of accuracy taking into account tumor motion and respiratory cycle

The purpose of this study is to present a new method of quality assurance (QA) in order to ensure effective evaluation of the accuracy of respiratory-gated radiotherapy (RGR). This would help in quantitatively analyzing the patient’s respiratory cycle and respiration-induced tumor motion and in performing a subsequent comparative analysis of dose distributions, using the gamma-index method, as reproduced in our in-house developed respiration-simulating phantom. Therefore, we designed a respiration-simulating phantom capable of reproducing the patient’s respiratory cycle and respiration-induced tumor motion and evaluated the accuracy of RGR by estimating its pass rates. We applied the gamma index passing criteria of accepted error ranges of 3% and 3 mm for the dose distribution calculated by using the treatment planning system (TPS) and the actual dose distribution of RGR. The pass rate clearly increased inversely to the gating width chosen. When respiration-induced tumor motion was 12 mm or less, pass rates of 85% and above were achieved for the 30–70% respiratory phase, and pass rates of 90% and above were achieved for the 40–60% respiratory phase. However, a respiratory cycle with a very small fluctuation range of pass rates failed to prove reliable in evaluating the accuracy of RGR. Therefore, accurate and reliable outcomes of radiotherapy will be obtainable only by establishing a novel QA system using the respiration-simulating phantom, the gamma-index analysis, and a quantitative analysis of diaphragmatic motion, enabling an indirect measurement of tumor motion.

Changes in the planning target volume and liver volume dose based on the selected respiratory phase in respiratory-gated radiation therapy for a hepatocellular carcinoma

The aim of this study was to quantitatively analyze the changes in the planning target volume (PTV) and liver volume dose based on the respiratory phase to identify the optimal respiratory phase for respiratory-gated radiation therapy for a hepatocellular carcinoma (HCC). Based on the standardized procedure for respiratory-gated radiation therapy, we performed a 4-dimensional computed tomography simulation for 0 ∼ 90%, 30 ∼ 70%, and 40 ∼ 60% respiratory phases to assess the respiratory stability (SR) and the defined PTVi for each respiratory phase i. A treatment plan was established, and the changes in the PTVi and dose volume of the liver were quantitatively analyzed. Most patients (91.5%) passed the respiratory stability test (SR = 0.111 ± 0.015). With standardized respiration training exercises, we were able to minimize the overall systematic error caused by irregular respiration. Furthermore, a quantitative analysis to identify the optimal respiratory phase revealed that when a short respiratory phase (40 ∼ 60%) was used, the changes in the PTV were concentrated inside the center line; thus, we were able to obtain both a PTV margin accounting for respiration and a uniform radiation dose within the PTV.

Dose Verification of 2D and 3D Intrafractional Tumor Motion for Patient-Specific Quality Assurance of Respiratory-Gated Radiation Therapy

The commercial programmable motion phantoms/platforms for patient specific quality assurance (QA) in respiratory-gated radiation therapy (RGRT) supported to deliver only limited motion. The simulation of two-dimensional motion (left-right and superior-inferior direction) or one-dimensional motion (superior-inferior direction) with sinusoidal motion could not deliver real tumor motion because tumor moves in the three-dimension. Developed platform supported full three-dimensional tumor motion with external marker motion.

Evaluation of the Reproducibility of Lung Tumor Position in Respiratory-Gated Stereotactic Body Radiation Therapy (SBRT) Using Fluoroscopy of an On-Board Imager (OBI) System

Evaluation of the Reproducibility of Lung Tumor Position in Respiratory-Gated Stereotactic Body Radiation Therapy (SBRT) Using Fluoroscopy of an On-Board Imager (OBI) System

Detectability of the Position of the Diaphragm in the Exhale CBCT for Patient Positioning in Respiratory-Gated Stereotactic Body Radiation Therapy

Detectability of the Position of the Diaphragm in the Exhale CBCT for Patient Positioning in Respiratory-Gated Stereotactic Body Radiation Therapy

Minimal benefit of respiratory‐gated radiation therapy in the management of thoracic malignancy

Respiratory-gated radiotherapy (RGRT) is used in several centres around the world. However, there is continuing controversy regarding the benefit of this technique. The aims of this study are to quantify the dosimetric benefits and the potential predictive factors. Thirty-four consecutive patients were planned using the RGRT and the Free Breathing (FB) approach and compared with regard to target volume coverage and normal tissue parameters. Potential predictive factors were also evaluated. Tumour coverage was similar 94.4% versus 95.5%. Use of RGRT was not associated with a significant reduction in spinal cord, oesophagus or cardiac dosimetric parameters. However, it did reduce the lung mean dose by 1.33 Gy (P < 0.001) and V20 by 2.2% (P < 0.001). Only superior/inferior displacement of >1 cm was predictive of a >5% reduction in lung V20 parameter, and these patients all had a gross tumour volume (GTV) of <100 cm(3). The dosimetric benefit of applying RGRT is small when applied in an unselected population of patients. Superior/inferior displacement of >1 cm for tumours with GTV less than 100 cm(3) may be used to select patients who may derive a >5% reduction in lung V20 parameters.

SU‐E‐J‐143: Improvement in Accuracy of Respiratory Gated Radiation Therapy Using Respiratory Training System

Purpose: The accuracy of respiratory gated radiation therapy (RGRT) depends on the respiratory regularity because external respiratory signals are used for gating the radiation beam at particular phases. Many studies have applied a respiratory guiding system to improve the respiratory regularity. This study aims to evaluate the effect of an in‐house developed respiratory guiding system to improve the respiratory regularity for RGRT. Methods: To verify the effectiveness of this system, respiratory signals were acquired from 5 volunteers. The improvement in respiratory regularity was analyzed by comparing the standard deviations of amplitudes and periods between free and guided breathing. The reduction in residual motion at each phase was analyzed by comparing the standard deviations of sorted data within each corresponding phase bin as obtained from free and guided breathing. Results: The results indicate that the respiratory guiding system improves the respiratory regularity, and most volunteers show significantly lesser average residual motion at each phase. The average residual motion measured at phases of 40, 50, and 60%, which showed lower variation than other phases, were respectively reduced by 41, 45, and 44% during guided breathing. Conclusion: The results show that the accuracy of RGRT could be improved using the in‐house developed respiratory guiding system. Furthermore, this system should reduce artifacts caused by respiratory motion in 4D CT imaging. This program was supported by the program of Basic Atomic Energy Research Institute (BAERI) which is a part of the Nuclear R and D programs (No. 20120004886) funded by the Ministry of Education, Science and Technology (MEST) and a grant (2012‐007883) from the Mid‐career Researcher Programfunded by the Ministry of Education, Science and Technology (MEST) and Leading Foreign Research Institute Recruitment Program through the National Research Foundation of Korea(NRF)(Grant No.2009‐00420) funded by the Ministry of Education, Science &amp; Technology (MEST) of Korea.

0SU-E-T-326: Assessment of 2D / 3D Intra-Fractional Tumor Motion for Respiratory-Gated Radiotherapy

Purpose: This study aims to develop and evaluate the effectiveness of full 3-dimensional motion platform in respiratory-gated radiotherapy (RGRT) quality assurance (QA). For this study, a motion platform had been developed to simulate the patient specific QA in RGRT. Commercial motion platforms have the limited freedom of movement : lateral-longitudinal or vertical movement for tumor motion, and vertical movement for the external marker motion. Addition to these, the developed platform has the freedom of full 3-dimensional movement: simultaneous lateral, longitudinal as well as vertical motion for tumor motion. Methods: 3-dimensional tumor motions of ten abdomen cancer patients treated RGRT with no-motion, 2-dimensional 0motion, and 3-dimensional motion were extracted in phase sorted 4D-CT images. After deformable registration based on contoured image in 50% respiratory phase, the center of voxel was defined as the tumor position to trace its motion. Varian RPM log files were used to trace external markers. 3-dimensional tumor motions were simulated using the developed motion platform. On its polycarbonate panel, a radio-chromic film attached on 10 cm solid water slabs was placed for the dose verification. 2-dimensional and 3-dimensional tumor motions were performed with gated beam delivery to compare their dosimetric differences. The gating window was 35-65%. Gamma-index method was adopted to compare dose distributions of the measurement using radio-chromic film with those of treatment planning system. Results: The average gamma pass rates (2%/2 mm) were 96.11%, 89.69%, and 88.86% for static-continuous, 2D-gated, and 3D-gated, respectively. Excepting one case, static-continuous showed results over 94%. Some of 3D-gated resulted in pass rates larger than those of 2D-gated. Conclusion: 3-dimensional tumor motions showed lower gamma pass rates than those of 2-dimensional tumor motions during treatment. These imply the requirement of tools that provide the 3-dimensional tumor motion for QA in RGRT.

횡격막의 움직임을 이용한 최적화된 호흡 위상의 선택: 폐암의 호흡 동기 방사선치료 중심

본 연구는 각 호흡 위상에 따른 계획용표적체적(planning target volume. PTV)의 움직임 및 체적(PTV volume)의 변화를 횡격막(diaphragm)의 움직임을 이용하여 정량적으로 분석함으로써 폐암의 호흡 동기 방사선치료를 위한 최적화된 호흡 위상을 알아보고자 하였다. 비특이적 호흡이나 불규칙적인 호흡에 의한 체계적 오류(system error)를 화하기 위하여 모의 호흡 훈련을 시행하였다. 정규화된 호흡 동기 방사선치료 절차에 따라 각 호흡 위상 i에 따른 4차원 전산화치료계획(4-dimensional computed tomography. 4DCTi)을 시행하였으며 0~90%, 30~70%, 40~60% 호흡 위상으로 재구성된 4DCTi 영상에서 PTV를 정의하고 PTVi의 움직임 및 체적의 변화를 정략적으로 분석하였다. 모의호흡 훈련에 의한 평균 호흡 주기는 <TEX>$3.4{\pm}0.5$</TEX>초로 나타났으며 임상적으로 유도되는 예상 값과 실제 측정값의 일치 정도를 나타내는 R-제곱 값은 1에 근접하여 유의하였다. 또한 각 호흡 위상 i에 따른 PTVi의 움직임은 0~90% 호흡 위상의 경우 <TEX>$13.4{\pm}6.4mm$</TEX>, 30~70% 호흡 위상의 경우 <TEX>$6.1{\pm}2.9mm$</TEX>, 40~60% 호흡 위상의 경우 <TEX>$4.0{\pm}2.1mm$</TEX> 이었으며 PTVi의 체적 변화는 30~70% 호흡 위상의 경우 <TEX>$32.6{\pm}8.7%$</TEX>, 40~60% 호흡 위상의 경우 <TEX>$41.6{\pm}6.2%$</TEX> 감소되었다. 결론적으로 짧은 호흡 위상(40~60%: 30% duty cycle) 폭을 적용하였을 때 PTV의 움직임 및 체적의 변화가 감소되어 호흡을 고려한 PTV 마진이 4mm 이내이면서 PTV 내 선량의 균일성을 얻을 수 있었다. This study was to analyze quantitatively movement of planning target volume (PTV) and change of PTV volume through movement of diaphragm according to breathing phase. The purpose of present study was to investigate optimized respiration phase for radiation therapy of lung cancer. Simulated breathing training was performed in order to minimize systematic errors which is caused non-specific or irregular breathing. We performed 4-dimensional computed tomography (4DCTi) in accordance with each respiratory phase in the normalized respiratory gated radiation therapy procedures, then not only defined PTVi in 0 ~ 90%, 30 ~ 70% and 40 ~ 60% in the reconstructed 4DCTi images but analyzed quantitatively movement and changes of volume in PTVi. As a results, average respiratory cycle was <TEX>$3.4{\pm}0.5$</TEX> seconds by simulated breathing training. R2-value which is expressed as concordance between clinically induced expected value and actual measured value, was almost 1. There was a statistically significant. And also movement of PTVi according to each respiration phase 0 ~ 90%, 30 ~ 70% and 40 ~ 60% were <TEX>$13.4{\pm}6.4mm$</TEX>, <TEX>$6.1{\pm}2.9mm$</TEX> and <TEX>$4.0{\pm}2.1mm$</TEX> respectively. Change of volume in PTVi of respiration phase 30 ~ 70% was decreased by <TEX>$32.6{\pm}8.7%$</TEX> and 40 ~ 60% was decreased by <TEX>$41.6{\pm}6.2%$</TEX>. In conclusion, PTVi movement and volume change was reduced, when we apply a short breathing phase (40 ~ 60%: 30% duty cycle) range. Furthermore, PTVi margin considered respiration was not only within 4mm but able to get uniformity of dose.

Respiratory Gating for Radiotherapy: Main Technical Aspects and Clinical Benefits

Respiratory-gated radiotherapy offers a significant potential for improvement in the irradiation of tumor sites affected by respiratory motion such as lung, breast, and liver tumors. An increased conformality of irradiation fields leading to decreased complication rates of organs at risk is expected. Five main strategies are used to reduce respiratory motion effects: integration of respiratory movements into treatment planning, forced shallow breathing with abdominal compression, breath-hold techniques, respiratory gating techniques, and tracking techniques. Measurements of respiratory movements can be performed either in a representative sample of the general population, or directly on the patient before irradiation. Reduction of breathing motion can be achieved by using either abdominal compression, breath-hold techniques, or respiratory gating techniques. Abdominal compression can be used to reduce diaphragmatic excursions. Breath-hold can be achieved with active techniques, in which airflow of the patient is temporarily blocked by a valve, or passive techniques, in which the patient voluntarily breath-holds. Respiratory gating techniques use external devices to predict the phase of the breathing cycle while the patient breathes freely. Another approach is tumor-tracking technique, which consists of a real-time localization of a constantly moving tumor. This work describes these different strategies and gives an overview of the literature.