End Of Exhalation Research Articles

A Novel, Simplified Ex Vivo Method for Measuring Water Exchange Performance of Heat and Moisture Exchangers for Tracheostomy Application

Breathing through a tracheostomy results in insufficient warming and humidification of inspired air. This loss of air-conditioning can be partially compensated for with the application of a heat and moisture exchanger (HME) over the tracheostomy. In vitro (International Organization for Standardization [ISO] standard 9360-2:2001) and in vivo measurements of the effects of an HME are complex and technically challenging. The aim of this study was to develop a simple method to measure the ex vivo HME performance comparable with previous in vitro and in vivo results. HMEs were weighed at the end of inspiration and at the end of expiration at different breathing volumes. Four HMEs (Atos Medical, Hörby, Sweden) with known in vivo humidity and in vitro water loss values were tested. The associations between weight change, volume, and absolute humidity were determined using both linear and non-linear mixed effects models. The rating between the 4 HMEs by weighing correlated with previous intra-tracheal measurements (R(2) = 0.98), and the ISO standard (R(2) = 0.77). Assessment of the weight change between end of inhalation and end of exhalation is a valid and simple method of measuring the water exchange performance of an HME.

Airway exchange of highly soluble gases

Highly blood soluble gases exchange with the bronchial circulation in the airways. On inhalation, air absorbs highly soluble gases from the airway mucosa and equilibrates with the blood before reaching the alveoli. Highly soluble gas partial pressure is identical throughout all alveoli. At the end of exhalation the partial pressure of a highly soluble gas decreases from the alveolar level in the terminal bronchioles to the end-exhaled partial pressure at the mouth. A mathematical model simulated the airway exchange of four gases (methyl isobutyl ketone, acetone, ethanol, and propylene glycol monomethyl ether) that have high water and blood solubility. The impact of solubility on the relative distribution of airway exchange was studied. We conclude that an increase in water solubility shifts the distribution of gas exchange toward the mouth. Of the four gases studied, ethanol had the greatest decrease in partial pressure from the alveolus to the mouth at end exhalation. Single exhalation breath tests are inappropriate for estimating alveolar levels of highly soluble gases, particularly for ethanol.

Poster - Thur Eve - 53: Analysis of the distribution of dose delivery during respiratory-gated step-and-shoot IMRT for lung cancer radiotherapy.

Respiratory motion is a large source of dosimetric error when treating lung cancer with Intensity Modulated Radiation Therapy (IMRT). The asynchronicity of the tumour motion and the multileaf collimator (MLC) used to modulate the radiation beam intensity, leads to the interplay effect. One method to account for this effect is respiratory gating. Treatment planning optimization for gated IMRT is performed on a subset average 4D-CT which includes the phases surrounding end exhalation. However, this assumes that the beam delivery will be evenly distributed amongst those phases. This study investigates the distribution of beam delivery during gated step-and-shoot IMRT (SS-IMRT) for both early and late stage non-small cell lung cancer (NSCLC). Four Stage I NSCLC patients, prescribed a dose of 54 Gy in 3 fractions, and five Stage III NSCLC patients, prescribed a dose of 60 Gy in 30 fractions, were retrospectively planned with high and low modulation beams-IMRT, and delivered using the QUASAR™ Programmable Respiratory Motion Platform with 15 mm and 20 mm peak-to-peak sinusoidal motion and real patient breathing motion. The percent monitor units delivered at each phase were compared. For Stage I patients, the monitor units delivered were evenly distributed over the gating window due to a high number of monitor units delivered per control point. For Stage III patients, as the complexity of SS-IMRT increases, there were more monitor units delivered in the initial gating phase. This dose discrepancy could potentially lead to geographic miss of the tumour and should be taken into account during treatment planning.

SU‐E‐T‐343: Respiratory‐Gated Volumetric Modulated Arc Therapy for Lung SBRT with an Elekta Digital Accelerator: A Pre‐Clinical Evaluation

Purpose: To evaluate the machine‐delivery capabilities and dosimetric accuracy of respiratory‐gated VMAT delivered with an Elekta digital accelerator. Method and Materials: Three lung patients previously treated with SBRT using un‐gated 6 MV VMAT were used for this evaluation. The treatment plans were created in Monaco treatment planning system (ver. 3.0). For each case, one un‐gated and two gated deliveries were delivered to a static ion‐chamber‐array phantom. Surface motion was used as a surrogate for breathing motion and was simulated using a moving chest plate driven by a motor with a constant amplitude range of +/− 3 mm and a period of 4 seconds using a cos6ωt waveform. Two gating windows (GWs), 77% and 66% around the end of exhalation were used for the gated deliveries. An ion chamber array was used and comparisons were made between the measured and the planned coronal dose distributions. The dosimetric accuracy of gated VMAT plans was determined using gamma‐index analyses (3 mm/3% passing rate criteria). Results: There were insignificant differences between the two gated deliveries and the un‐gated delivery. For the planar dose comparisons between the measured and the planned, the gamma passing rates were all higher than 99.0%. For the two gated deliveries, the true duty cycles were calculated as 57% and 39%, as against the corresponding GWs 77% and 66%. This was mainly due to the beam‐on latencies, which were estimated as 0.25 second and 0.40 second for GWs 77% and 66%, respectively. Conclusions: Respiratory‐gated VMAT was demonstrated for the first time using an Elekta digital accelerator with a pre‐clinical gating interface provided by Elekta and a novel surface imaging system as a respiratory input. High dosimetric accuracy was demonstrated in three SBRT lung cases for as many as 213 beam interruptions during a single 360°‐arc delivery. This work is sponsored by a research grant from Elekta AB.

Reproducibility of registration-based measures of lung tissue expansion

Lung function depends on lung expansion and contraction during the respiratory cycle. Respiratory-gated CT imaging and 3D image registration can be used to locally estimate lung tissue expansion and contraction (regional lung volume change) by computing the determinant of the Jacobian matrix of the image registration deformation field. In this study, the authors examine the reproducibility of Jacobian-based measures of lung tissue expansion in two repeat 4DCT acquisitions of mechanically ventilated sheep and free-breathing humans. 4DCT image data from three white sheep and nine human subjects were used for this analysis. In each case, two 4DCT studies were acquired for each subject within a short time interval. The animal subjects were anesthetized and mechanically ventilated, while the humans were awake and spontaneously breathing based on respiratory pacing audio cues. From each 4DCT data set, an image pair consisting of a volume reconstructed near end inspiration and a volume reconstructed near end exhalation was selected. The end inspiration and end exhalation images were registered using a tissue volume preserving deformable registration algorithm and the Jacobian of the registration deformation field was used to measure regional lung expansion. The Jacobian map from the baseline data set was compared to the Jacobian map from the followup data by measuring the voxel-by-voxel Jacobian ratio. In the animal subjects, the mean Jacobian ratio (baseline scan Jacobian divided by followup scan Jacobian, voxel-by-voxel) was 0.9984±0.021 (mean ± standard deviation, averaged over the entire lung region). The mean Jacobian ratio was 1.0224±0.058 in the human subjects. The reproducibility of the Jacobian values was found to be strongly dependent on the reproducibility of the subject's respiratory effort and breathing pattern. Lung expansion, a surrogate for lung function, can be assessed using two or more respiratory-gated CT image acquisitions. The results show that good reproducibility can be obtained in anesthetized, mechanically ventilated animals, but variations in respiratory effort and breathing patterns reduce reproducibility in spontaneously-breathing humans. The global linear normalization can globally compensate for breathing effort differences, but a homogeneous scaling does not account for differences in regional lung expansion rates. Additional work is needed to develop compensation procedures or normalization schemes that can account for local variations in lung expansion during respiration.

Double CT imaging can measure the respiratory movement of small pulmonary tumors during stereotactic ablative radiotherapy.

The purpose of this study was to investigate the application of double CT imaging to measuring the respiratory movement of small pulmonary tumors during stereotactic ablative radiotherapy (SABR). A total of 122 small pulmonary tumors were measured in 45 patients. CT scans were conducted twice in all 122 tumors, once at the end of quiet inhalation and once at the end of exhalation. CT scans were conducted three times including at the end of quiet inhalation, at the end of exhalation and at free breathing in 36 tumors of 17 patients. The displacement of the tumor center in three directions was measured. The 3D motion of 122 tumors was 10.10±7.16 mm. On average, the tumors moved 1.96±2.03 mm (rang, 0-9 mm) in the X direction, 5.19±4.69 mm (rang, 0-19 mm) in the Y direction, and 7.38±6.48 mm (rang, 0-26 mm) in the Z direction. The 3D motion of tumors in the lower lung (13.00±7.64 mm) was significantly greater than that in the upper lung (7.15±5.14 mm), P<0.01. The 3D motion of the lower left lung was 16.35±7.31 mm, which was significantly greater than that of the lower right lung (11.40±7.04 mm), P<0.05. Movement in the anterior lung in the Y direction was significantly larger than in the posterior lung. The motion was 7.49±5.43 mm and 4.04±3.82 mm respectively, P<0.01. Double CT imaging provides accurate data for determining the outline of each target area during stereotactic ablative radiotherapy plane. The location of small pulmonary tumor foci was significantly affected by respiratory and cardiac motion.

Changes in lung tumor shape during respiration

Evidence that some lung tumors change shape during respiration is derived from respiratory gated CT data by statistical shape modeling and image manipulation. Some tumors behave as rigid objects while others show systematic shape changes. Two views of lung motion are presented to allow analysis of the results. In the first, lung motion is viewed as a wave motion in which inertial effects arising from mass are present and in the second it is a quasistatic motion in which the mass of the lung tissues is neglected. In the first scenario, the extremes of tumor compression and expansion are expected to correlate with maximum upward and downward velocity of the tumor, respectively. In the second, they should occur at end exhale and end inhale, respectively. An observed correlation between tumor strain and tumor velocity provides more support for the first view of lung motion and may explain why previous attempts at observing tumor shape changes during respiration have largely failed. The implications for the optimum gating of radiation therapy are discussed.

Mass preserving image registration for lung CT

This paper presents a mass preserving image registration algorithm for lung CT images. To account for the local change in lung tissue intensity during the breathing cycle, a tissue appearance model based on the principle of preservation of total lung mass is proposed. This model is incorporated into a standard image registration framework with a composition of a global affine and several free-form B-Spline transformations with increasing grid resolution. The proposed mass preserving registration method is compared to registration using the sum of squared intensity differences as a similarity function on four groups of data: 44 pairs of longitudinal inspiratory chest CT scans with small difference in lung volume; 44 pairs of longitudinal inspiratory chest CT scans with large difference in lung volume; 16 pairs of expiratory and inspiratory CT scans; and 5 pairs of images extracted at end exhale and end inhale phases of 4D-CT images. Registration errors, measured as the average distance between vessel tree centerlines in the matched images, are significantly lower for the proposed mass preserving image registration method in the second, third and fourth group, while there is no statistically significant difference between the two methods in the first group. Target registration error, assessed via a set of manually annotated landmarks in the last group, was significantly smaller for the proposed registration method.

Dosimetric investigation of breath-hold intensity-modulated radiotherapy for pancreatic cancer

To experimentally investigate the effects of variations in respiratory motion during breath-holding (BH) at end-exhalation (EE) on intensity-modulated radiotherapy (BH-IMRT) dose distribution using a motor-driven base, films, and an ionization chamber. Measurements were performed on a linear accelerator, which has a 120-leaf independently moving multileaf collimator with 5-mm leaf width at the isocenter for the 20-cm central field. Polystyrene phantoms with dimensions of 40 × 40 × 10 cm were set on a motor-driven base. All gantry angles of seven IMRT plans (a total of 35 fields) were changed to zero, and doses were then delivered to a film placed at a depth of 4 cm and an ionization chamber at a depth of 5 cm in the phantom with a dose rate of 600 MU/min under the following conditions: pulsation from the abdominal aorta and baseline drift with speeds of 0.2 mm/s (BD(0.2mm/s)) and 0.4 mm/s (BD(0.4mm/s)). As a reference for comparison, doses were also delivered to the chamber and film under stationary conditions. In chamber measurements, means ± standard deviations of the dose deviations between stationary and moving conditions were -0.52% ± 1.03% (range: -3.41-1.05%), -0.07% ± 1.21% (range: -1.88-4.31%), and 0.03% ± 1.70% (range: -2.70-6.41%) for pulsation, BD(0.2mm/s), and BD(0.4mm/s), respectively. The γ passing rate ranged from 99.5% to 100.0%, even with the criterion of 2%/1 mm for pulsation pattern. In the case of BD(0.4mm/s), the γ passing rate for four of 35 fields (11.4%) did not reach 90% with a criterion of 3%/3 mm. The differences in γ passing rate between BD(0.2mm/s) and BD(0.4mm/s) were statistically significant for each criterion. Taking γ passing rates of > 90% as acceptable with a criterion of 3%/3 mm, large differences were observed in the γ passing rate between the baseline drift of ≤5 mm and that of >5 mm (minimum γ passing rate: 92.0% vs 82.7%; p < 0.01). This study suggested that the baseline drift of >5 mm should be avoided in the BH-IMRT.

Ultrasound-assisted translaryngeal block for awake fibreoptic intubation

To the Editor, The difficulty of identifying landmarks can preclude the success of airway blocks and awake tracheal intubation in patients with challenging airways. We describe a case wherein the use of ultrasound made it possible to perform a translaryngeal block successfully by injection of local anesthetic into the tracheal lumen. This technique allowed subsequent awake intubation in a super morbidly obese patient. Informed consent was obtained from the patient prior to submission of this correspondence. The patient was a 38-yr-old female with a body mass index of 57.4 kg m who was scheduled to undergo a Roux-en-Y gastric bypass. Due to a potential difficult airway, the anesthetic plan was to perform an awake fibreoptic intubation. Preoperatively, the patient’s pharynx was sprayed with a combination of 14% benzocaine and 2% tetracaine. In the operating room, the patient was sedated with midazolam 3 mg iv and ketamine 20 mg iv. She was positioned with her neck extended. An attempt was made to identify the cricothyroid membrane by palpating the space between the cricoid and thyroid cartilages. The midline of the membrane was also located by visual inspection and lidocaine was applied subcutaneously. A 20G catheter over a needle attached to a syringe was slowly advanced through the skin while simultaneously attempting to aspirate air. No air could be aspirated, but a small amount of blood (\1 mL) was obtained. At this point, we reassessed the patient’s anatomy and made another attempt (approximately 1.5 cm below the initial attempt) without success. The translaryngeal block was abandoned and fibreoptic intubation was attempted. Even after injection of 4% lidocaine 4 mL through the side port of the fibrescope, the patient still had a prominent cough reflex which precluded the advancement of the fibrescope below the vocal cords. A portable ultrasound machine, Logiq e, (GE Healthcare, Chalfont, St. Giles, UK) was then brought to the operating room, and the patient’s neck was scanned in an attempt to identify landmarks and the midline. A transverse scan was performed at the level of the thyroid and cricoid cartilages (Figure), and the space immediately below the midline of the thyroid cartilage was marked with a pen. The thyroid cartilage had a hypoechoic inverted V-shape appearance, and the cricoid cartilage had a hypoechoic arch-like appearance. A 20G angiocath was inserted through the patient’s skin and air could then be aspirated into the syringe. The catheter of the angiocath was advanced into the larynx and the metal needle was removed. The patient was asked to exhale; 4% lidocaine 4 mL was injected through the catheter at the end of exhalation and the patient coughed profusely. The fibrescope was then advanced through the patient’s mouth, and the vocal cords were easily visualized. The fibrescope was then inserted below the vocal cords without triggering a cough reflex, and a size 7.0-mm endotracheal tube was passed easily through the vocal cords. Correct placement of the endotracheal tube was confirmed with the fibrescope. Examination of the patient’s neck revealed that the first two attempts were made lateral to the midline. In this case, the use of ultrasound made it possible to perform a translaryngeal block in a patient whose landmarks could not be identified correctly using traditional palpation. This case illustrates a potential clinical application for ultrasound assistance in regional anesthesia G. S. De Oliveira Jr, MD (&) P. Fitzgerald, MS M. Kendall, MD Northwestern University, Chicago, USA e-mail: g-jr@northwestern.edu

SU‐E‐T‐291: How Many Sets of Four‐Dimensional Computed Tomography (4DCT) Images Are Needed to Determine the Internal Target Volume (ITV) for Lung Radiation Therapy?

Purpose: For the treatment of patients with lung cancer, internal target volume (ITV) is frequently determined by contouring of gross tumor volumes (GTV) on 10 phases of a four‐dimensional computed tomography (4DCT) scan. This study investigated the possibility of generating ITV by using selective phases of a 4DCT scan. Methods: The 4DCT scans of 20 patients with lung cancer were included in this study. GTVs were contoured on all 10 phases in Focal4D (CMS, St. Louis, MO). Different ITVs were derived by encompassing volumes of contours from selective phases. ITV10 was derived from contouring GTV on all 10 phases and served as the gold standard. All the other ITVs were smaller and within ITV10. The ratios of the volume of ITVs to ITV10 were calculated and used as a criterion to determine the similarity of ITVs to ITV10. ITV2 represented the ITV derived by using end of inhalation and end of exhalation (0%+50%). ITV3E was derived from contouring the three phases at end‐inhalation, mid‐exhalation, end‐exhalation (0%+20%+50%). ITV3I was derived from contouring the three phases at end‐inhalation, mid‐inhalation, end‐exhalation (0%+70%+50%). ITV4 was created by contouring the fours phases at end‐inhalation, mid‐inhalation, end‐exhalation, mid‐exhalation (0%+20%+50%+70%). ITV6E was derived from contouring the six consecutive phases during exhalation (0%+10%+20%+30%+40%+50%). ITV6I was derived from contouring the six consecutive phases during inhalation (50%+60%+70%+80%+90%+0%). Results: ITV6I showed excellent agreement with ITV10 (Volume ratio ITV6I/ITV10=0.975). ITV4 and ITV6E showed good agreement with ITV10 (ITV6E/ITV10=0.939, ITV4/ITV10=0.944). The volume ratio ITV3I/ITV10 and ITV3E/ITV10 was 0.927 and 0.906 respectively. ITV2 did not agree well with ITV10 (ITV2/ITV10 =0.888). Conclusions: Contouring all phases during inhalation will give a good estimate of the internal target volume, while helping to minimize the clinical load and work time during treatment planning. However, the ITV will be underestimated if only contouring on two extreme phases.

SU‐E‐J‐119: Development of Voxel‐by‐Voxel Respiratory Lung Motion Simulation Model

Purpose: 1. To justify the respiratory induced lung tumor motion is correlated to volume change in lung 2.To show that such motion is a hysteresis type of motion, i.e. the inspiration and expiration paths the tumor follows are different. Methods: The model equation was generated based on the data obtained from the axial displacement versus volume plot of the lung by Verschakelen et al (1989). The time variation of the lung volume change was introduced using linear and non‐linear functions. After comparison with literature (Lu et al, 2006), we verified the non‐linear time variation is more reliable. The lung motion amplitude as a function of time was then plotted and fitted with sinusoidal function. The dynamic 3D lung motion was simulated as a function of time based on the model equation. Two independent simulations were performed and compared: 1. Independent tumor motion amplitude and lung volume change. 2. Lung tumor motion dependent on the lung volume change. Results: 1.The model function generated from the fitting curve is periodic function with even power. This agrees with the periodic nature of respiration induced lung motion and also with the fact that longer time is spent at the end of exhalation than at the end of inhalation, which is proven by other researchers too. 2.Based on the simulated dynamic lung motion, we observe that the lung tumor motion is well correlated to the lung volume change. Conclusions: Clinically, chest wall as well as diaphragm amplitude measurements are used to provide lung motion gating window. In this study, we observe that respiration induced motion of the lung tumor is correlated to the lung volume change, and this can give a good prediction of: 1. The 3D location of the lung tumor. 2. Density change of the lung.

Interfractional Dose Variations in Intensity-Modulated Radiotherapy With Breath-Hold for Pancreatic Cancer

To investigate the interfractional dose variations for intensity-modulated radiotherapy (RT) combined with breath-hold (BH) at end-exhalation (EE) for pancreatic cancer. A total of 10 consecutive patients with pancreatic cancer were enrolled. Each patient was fixed in the supine position on an individualized vacuum pillow with both arms raised. Computed tomography (CT) scans were performed before RT, and three additional scans were performed during the course of chemoradiotherapy using a conventional RT technique. The CT data were acquired under EE-BH conditions (BH-CT) using a visual feedback technique. The intensity-modulated RT plan, which used five 15-MV coplanar ports, was designed on the initial BH-CT set with a prescription dose of 39 Gy at 2.6 Gy/fraction. After rigid image registration between the initial and subsequent BH-CT scans, the dose distributions were recalculated on the subsequent BH-CT images under the same conditions as in planning. Changes in the dose-volume metrics of the gross tumor volume (GTV), clinical target volume (CTV = GTV+ 5 mm), stomach, and duodenum were evaluated. For the GTV and clinical target volume (CTV), the 95th percentile of the interfractional variations in the maximal dose, mean dose, dose covering 95% volume of the region of structure, and percentage of the volume covered by the 90% isodose line were within ±3%. Although the volume covered by the 39 Gy isodose line for the stomach and duodenum did not exceed 0.1 mL at planning, the volume covered by the 39 Gy isodose line for these structures was up to 11.4 cm(3) and 1.8 cm(3), respectively. Despite variations in the gastrointestinal state and abdominal wall position at EE, the GTV and CTV were mostly ensured at the planned dose, with the exception of 1 patient. Compared with the duodenum, large variations in the stomach volume receiving high-dose radiation were observed, which might be beyond the negligible range in achieving dose escalation with intensity-modulated RT combined with BH at EE.

Origin of Exhaled Breath Particles from Healthy and Human Rhinovirus-Infected Subjects

Exhaled breath studies suggest that humans exhale fine particles during tidal breathing, but little is known of their physical origin in the respiratory system during health or disease. Particles generated by 3 healthy and 16 human rhinovirus (HRV)-infected subjects were counted using an optical particle counter with nominal diameter-size bins ranging between 0.3 and 10 μm. Data were collected from HRV-infected subjects during tidal breathing. In addition, data from healthy subjects were collected during coughs, swallows, tidal breathing, and breathing to total lung capacity (TLC) and residual volume (RV). Using general additive models, we graphed exhaled particle concentration versus airflow during exhalation. Exhaled particles were collected from expired air on gelatin filters and analyzed for HRV via quantitative PCR. HRV-infected subjects exhaled from 0.1 to 7200 particles per liter of exhaled air during tidal breathing (geometric mean = 32 part/L). A small fraction (24%) of subjects exhaled most (81%) of the particles measured and 82% of particles detected were 0.300-0.499 μm. Minute ventilation, maximum airflow during exhalation, and forced expiratory volume 1 second (FEV(1) % predicted) were positively correlated with particle production. No human rhinovirus was detected in exhaled breath samples. Three healthy subjects exhaled less than 100 particles per liter of exhaled air during tidal breathing and increased particle concentrations more with exhalation to RV than with coughing, swallowing, or rapid exhalation. Submicron particles were detected in the exhaled breath of healthy and HRV-infected subjects. Particle concentrations were correlated with airflow during the first half of exhalation, and peaked at the end of exhalation, indicating both lower and upper airways as particle sources. The effect of breathing maneuver suggested a major contribution from lower airways, probably the result of opening collapsed small airways and alveoli.

Tempos máximos de fonação de vogais em mulheres adultas com nódulos vocais

Maximum phonation times (MPT) of vowels in adult women with vocal nodules. To verify and to correlate the values of MPT of vowels in young and middle-aged adult women with vocal nodules. Database records from a speech therapy school-clinic were used, making up a total of 38 subjects. female adults, aged between 20 and 53 years, with otorhinolaryngology diagnosis of vocal nodules. to present a laryngeal pathology other than vocal nodules; hearing loss ; oral breathing; history of neurological, psychiatric, endocrine or gastric disorders; flu or allergy history; drinking and/or smoking habits; previous speech therapy and/or otorhinolaryngology treatments. Anamnesis data, the otorhinolaryngology diagnosis, and the MPT measurements of vowels /a, i, u/ were verified for each subject. MPT evaluation consisted of the duration measurement of three emissions of the vowels, using habitual tone and intensity, until the end of exhalation, with the patient in a standing position, considering the highest value of each vowel. The results were statistically analyzed with a significance level of 5%. Representative age range; less representative MPT and mean, below normality and with a strong positive and meaningful correlation; moderate, positive and significant correlation between MPTs and their means. For the group of adult women with vocal nodules, the MPT values were reduced and positively correlated; the MPT of vowel /a/ presented a lower value when compared to the other investigated vowels.

Positional Reproducibility of Pancreatic Tumors Under End-Exhalation Breath-Hold Conditions Using a Visual Feedback Technique

To assess positional reproducibility of pancreatic tumors under end-exhalation (EE) breath-hold (BH) conditions with a visual feedback technique based on computed tomography (CT) images. Ten patients with pancreatic cancer were enrolled in an institutional review board-approved trial. All patients were placed in a supine position on an individualized vacuum pillow with both arms raised. At the time of CT scan, they held their breath at EE with the aid of video goggles displaying their abdominal displacement. Each three-consecutive helical CT data set was acquired four times (sessions 1-4; session 1 corresponded to the time of CT simulation). The point of interest within or in proximity to a gross tumor volume was defined based on certain structural features. The positional variations in point of interest and margin size required to cover positional variations were assessed. The means ± standard deviations (SDs) of intrafraction positional variations were 0.0 ± 1.1, 0.1 ± 1.2, and 0.1 ± 1.0 mm in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions, respectively (p = 0.726). The means ± SDs of interfraction positional variations were 0.3 ± 2.0, 0.8 ± 1.8, and 0.3 ± 1.8 mm in the LR, AP, and SI directions, respectively (p = 0.533). Population-based margin sizes required to cover 95th percentiles of the overall positional variations were 4.7, 5.3, and 4.9 mm in the LR, AP, and SI directions, respectively. A margin size of 5 mm was needed to cover the 95th percentiles of the overall positional variations under EE-BH conditions, using this noninvasive approach to motion management for pancreatic tumors.

SU‐GG‐J‐07: Respiratory Phase Effect on Tumor Shrinkage Analysis

Purpose: Despite recent advances in image‐guided techniques, radiation treatment outcomes of lung cancer patients remains relatively poor. One of the main challenges is the change in tumor position due to breathing motion, which may lead to inaccurate tumor volume estimates. We are investigating the possibility of differences in measured tumor volumes at different breathing phases. Accurate quantification of these volume differences and identification of an “ideal” respiratory phase for volume measurement would likely improve prediction of tumor response. Methods and Materials: We evaluated the shrinking tumor volume at four specific respiratory phases for 7 NSCLC patients. The corresponding 3D‐CT image for a specific respiratory phase was reconstructed from 4D‐CT acquisition data. For each phase, the mid‐treatment and end of treatment scans were fused to the treatment planning CT using rigid registration. Pre‐treatment GTV and PTV contours were copied to the mid‐treatment and end of treatment scans, and further used for tumor segmentation using a registration‐assisted approach based on the level‐set deformable algorithm. After segmentation, the tumor volume was calculated for the two time‐points during the course of RT. The differences in measured tumor volumes for four respiratory phases (mid‐inhalation (MI), end‐of‐inhalation (EI), mid‐exhalation (ME), end‐of‐exhalation (EE)) at two time‐points in treatment were investigated. Results: Our preliminary analysis show that tumor volume measurements can differ at different respiratory phases, however, effects on tumor shrinkage analysis is small. Relatively, it is noted that volumes reconstructed at EI and ME phases tend to underestimate the shrinkage effect while MI and EE tend to overestimate the shrinkage effect. Conclusions: Our preliminary results show differences in volume measurements at different respiratory phases. A larger patient population would be required to select the ideal respiratory phase to provide accurate tumor volume changes. This will be a step further towards better understanding of radiation treatment efficacy.

SU‐GG‐T‐543: The Effect of Respiratory Motion on the Dose Distribution of Free‐Breathing Stereotactic Body Radiation Therapy for Spinal Tumors

Purpose: Stereotactic Body Radiation Therapy (SBRT) has been used increasingly for the management of spinal lesions. This study was performed to investigate the effect of respiratory motion on the dose distributions of spine SBRT patients. Method: 4D CT and treatment planning data for thoracic spinal lesions (T5 and T8) in two linac‐based SBRT patients was studied retrospectively. Bony structures of the spine were visually inspected in all 10 phases of the 4D CT images and there was no spinal motion observed. Tumors were contoured by radiation oncologists on the 50% phase of the 4D CT images, which corresponded to end exhalation. A single‐fraction dose of 20Gy and 14Gy was prescribed to CTV20 (gross tumor) and CTV14 (contiguous marrow cavity) respectively. Intensity modulated treatment plans were constructed on the 50% 4DCT phase and copied to all other phases of the 4D data set for comparative dose calculations. The DVHs of CTV20, CTV14, and the spinal cord were compared between actual dose, which is the sum of dose from all phases, and planned dose, which was done on 50% phase of 4D CT images. Results: The impacts of chest wall and diaphragm motion on the dose distribution were analyzed. Treatment plans that incorporated all respiratory phases resulted in improved CTV20 coverage less than 2% but the maximum dose within spinal cord was increased 3∼4%. Conclusion: Respiratory motion has a modest impact on the dose distribution of spine SBRT treatments including a 3–4% increase in cord dose. Motion control methods should be considered to reduce the uncertainties of dose delivery when motion amplitude is large.

SU‐GG‐I‐157: Phase Correlated Image Registration to 4D CT for Liver Stereotactic Radiosurgery with Image Guidance CT

Purpose: Stereotactic radiosurgery (SRS) is characterized by high doses delivered to small targets in a few fractions. Image guidance systems, cone beam computed tomography (CBCT), that yield volume imaging and sufficient soft‐tissue contrast have permitted daily imaging of bony anatomy and target permitting online correction of tumor position prior to treatment delivery, but CBCT is not perfectly support in phase correlated image guidance for targeting. The main objective was to overcome breathing induced uncertainties in the process of image guided RT using phase correlated image registration both the planning CT scan and CBCT for verification imaging scan. Methods and materials: For 20 patients with liver SRS, respiratory correlated 4D CT scan and CBCT for image guidance was acquired. Internal target volume (ITV) is determined utilizing 50% phase end exhalation reconstructed images by 4DCT, In order to check the accuracy of maximum intensity projection for various target motion, especially for target moving irregularly with three implanted gold seed. The data analyzed were respiratory‐induced peak‐to‐trough distance, 3D motion from LR, AP and SI directions and motion nonlinearity and hysteresis. Motion hysteresis occurs when three seed follows different paths between inhale and exhale phases during a respiratory cycle. Results: The overall mean respiratory‐induced peak‐to‐trough distance is 0.48 cm, with individual treatment fraction means ranging from 0.02 to 1.44 cm. The overall mean respiratory period is 3.8 s, with individual treatment fraction means ranging from 2.2 to 6.4 s. Conclusions: The motion nonlinearity and hysteresis are important characteristics of respiratory tumor motion. From 3D tumor trajectories, they showed that the hysteresis ranged from 0.1 to 0.6 cm for 20 tumors.

Keeping Patients Safe During Intrahospital Transport

Keeping Patients Safe During Intrahospital Transport