Breath-hold CT Research Articles

Adequacy of inhale/exhale breathhold CT based ITV margins and image-guided registration for free-breathing pancreas and liver SBRT

PurposeTo evaluate use of breath-hold CTs and implanted fiducials for definition of the internal target volume (ITV) margin for upper abdominal stereotactic body radiation therapy (SBRT). To study the statistics of inter- and intra-fractional motion information.Methods and materials11 patients treated with SBRT for locally advanced pancreatic cancer (LAPC) or liver cancer were included in the study. Patients underwent fiducial implantation, free-breathing CT and breath-hold CTs at end inhalation/exhalation. All patients were planned and treated with SBRT using volumetric modulated arc therapy (VMAT). Two margin strategies were studied: Strategy I uses PTV = ITV + 3 mm; Strategy II uses PTV = GTV + 1.5 cm. Both CBCT and kV orthogonal images were taken and analyzed for setup before patient treatments. Tumor motion statistics based on skeletal registration and on fiducial registration were analyzed by fitting to Gaussian functions.ResultsAll 11 patients met SBRT planning dose constraints using strategy I. Average ITV margins for the 11 patients were 2 mm RL, 6 mm AP, and 6 mm SI. Skeletal registration resulted in high probability (RL = 69%, AP = 4.6%, SI = 39%) that part of the tumor will be outside the ITV. With the 3 mm ITV expansion (Strategy 1), the probability reduced to RL 32%, AP 0.3%, SI 20% for skeletal registration; and RL 1.2%, AP 0%, SI 7% for fiducial registration. All 7 pancreatic patients and 2 liver patients failed to meet SBRT dose constraints using strategy II. The liver dose was increased by 36% for the other 2 liver patients that met the SBRT dose constraints with strategy II.ConclusionsImage guidance matching to skeletal anatomy is inadequate for SBRT positioning in the upper abdomen and usage of fiducials is highly recommended. Even with fiducial implantation and definition of an ITV, a minimal 3 mm planning margin around the ITV is needed to accommodate intra-fractional uncertainties.

159 Towards validation of breath-hold ventilation CT for NSCLC radiotherapy planning

159 Towards validation of breath-hold ventilation CT for NSCLC radiotherapy planning

Multi-scale analysis of imaging features and its use in the study of COPD exacerbation susceptible phenotypes.

We propose a novel framework for exploring patterns of respiratory pathophysiology from paired breath-hold CT scans. This is designed to enable analysis of large datasets with the view of determining relationships between functional measures, disease state and the likelihood of disease progression. The framework is based on the local distribution of image features at various anatomical scales. Principal Component Analysis is used to visualise and quantify the multi-scale anatomical variation of features, whilst the distribution subspace can be exploited within a classification setting. This framework enables hypothesis testing related to the different phenotypes implicated in Chronic Obstructive Pulmonary Disease (COPD). We illustrate the potential of our method on initial results from a subset of patients from the COPDGene study, who are exacerbation susceptible and non-susceptible.

Motion-specific internal target volumes for FDG-avid mediastinal and hilar lymph nodes

Background and purposeTo quantify the benefit of motion-specific internal target volumes for FDG-avid mediastinal and hilar lymph nodes generated using 4D-PET, vs. conventional internal target volumes generated using non-respiratory gated PET and 4D-CT scans. Materials and methodsFive patients with FDG-avid tumors metastatic to 11 hilar or mediastinal lymph nodes were imaged with respiratory-correlated FDG-PET (4D-PET) and 4D-CT. FDG-avid nodes were contoured by a radiation oncologist in two ways. Standard-of-care volumes were contoured using conventional un-gated PET, 4D-CT, and breath-hold CT. A second, motion-specific, set of volumes were contoured using 4D-PET.Contours based on 4D-PET corresponded directly to an internal target volume (ITV4D), whereas contours based on un-gated PET were expanded by a series of exploratory isotropic margins (from 5 to 13mm) based on literature recommendations on lymph node motion to form internal target volumes (ITV3D). ResultsA 13mm expansion of the un-gated PET nodal volume was needed to cover the ITV4D for 10 of 11 nodes studied. The ITV3D based on a 13mm expansion included on average 45cm3 of tissue that was not included in the ITV4D. ConclusionsMotion-specific lymph-node internal target volumes generated from 4D-PET imaging could be used to improve accuracy and/or reduce normal-tissue irradiation compared to the standard-of-care un-gated PET based internal target volumes.

SU‐E‐J‐155: Cardiac Dose Reduction in Left Sided Breast Using Breath Hold Tecnique

Purpose: In studies related to breast cancer and mortality, convincing evidence of an increased risk of cardiac morbidity following irradiation for leftsided breast cancer exists. The use of a breath hold technique enables a significant decrease of the dose to the heart as well as to the left anterior descending coronary artery (LAD). The purpose of deep inspiration Breath Hold (BH) is to expand the chest cavity during radiotherapy, which increases the distance between the breast to be treated and the heart. This allows for a lower heart dose as well as better PTV coverage. Methods: A study of 30 patients is showed. All patients underwent a free breathing (FB) and BH CT scan in supine treatment. Previously, the patient receives personal training to perform an adequate breathing and follows her own breathing cycle with glasses connected to the BH device. For simulation and treatment the same procedure as in the CT acquisition is performed. In the treatment, the patient placing includes daily image included in dosimetry. Results: The analysis compares the doses received in heart and LAD with FB and BH treatment. It presents data of medium dose with FB CT and BH CT and average and maximum dose (dose to 0.2 cm3) in LAD. The PTV coverage dose are between 95‐107 percentage of the prescribed dose is not present neither in the lung dose (V20) does not vary significantly.The DVH medium of LAD and heart (FB vs BH) is showed as well. Conclusion: The effects of radiation on the heart are late effects, which usually appear between 10 and 15 years after treatment. In young patients a dose reduction as drastic as that observed implies a reduced risk of heart disease a Result of radiation, which significantly increases the probability of survival over 10 years.

SU-E-T-568: Individualize the Treatment Plan with Anatomic Optimization for Lung Tumor Stereotactic Ablative Radiotherapy

Purpose: To demonstrate that an individualized anatomical optimized approach for each patient undergoing stereotactic ablative radiotherapy (SABR) for lung cancer will Result in a superior dosimetric treatment plan. Methods: Eleven patients were received 4DCT with both natural and extreme tidal volume breathing. The original treatments were planned on either natural end exhale (NEE) or deep inspiration breath hold (DIBH) CT image. For re-plan, all structures were deformed from the planned CT image to the opposite CT image. The dose was recalculated to meet the physician constraints. The dosimetric impact of the anatomically optimized approach was evaluated and compared for both plans. Results: From the 11 patients that were analyzed in this study, 8 patients were planned and treated on DIBH, whereas 3 patients were planned and treated on NEE. Two patients treated on NEE had a lower maximum dose to the great vessels compared to the plan on DIBH. One patient treated on DIBH had a higher dose to the great vessels compared to the plan on NEE, indicating that this patient would be benefited from the treatment on NEE. The dose reduction is due to the increased separation between the target and the OAR from 1.61cm to 2.77cm in average. Conclusion: In summary, anatomic optimization favored NEE rather than DIBH in 27% of patients. This study demonstrates proof of principle that an individualized anatomically optimized approach is feasible and could lead to lower doses to nearby organs at risk. While the majority of patients are benefited from treatment on DIBH, our data suggests that in order to maximize the efficacy of the treatment and minimize the toxicity to the nearby tissue, the separation between target and OAR should be evaluated individually for each patient. Funded through departmental Master Reseacrh Agreement with Varian Medical Systems, Inc

MO‐F‐WAB‐01: A Comparison of 20 Free Breathing Versus AlignRT Based DIBH Breast Treatments

Purpose: Deep inspiration breath hold (DIBH) for treatment of left breast cancer is a technique that is rapidly gaining acceptance due to the possibility of reducing heart dose, particularly dose to the left anterior descending coronary artery. We report on the treatment of twenty patients using AlignRT (VisionRT, London, UK) to monitor breath hold. Methods: Patients were simulated with a breath hold and free breathing CT scan. A treatment plan was created on each scan in the XiO treatment planning system (Elekta AB, Stockholm, Sweden). Plans consisted of two parent tangent fields and 1–2 reduced fields per side. The maximum point dose and volume receiving 30 Gy (V30) to the heart from each plan is compared. Patients were set‐up using an AlignRT reference surface generated from the breath hold scan with a 3 mm / 3 degree tolerance. Patient position was evaluated by comparing boney landmarks, breast tissue, and heart position on port images prior to the first treatment, then once per week. We examine the number of port images retaken as compared to free breathing set‐ups. Results: For DIBH plans the maximum heart dose was reduced by an average of 39% and the V30 was reduced by an average of 78%. For 16 patients that had completed treatment at this time the number of retaken port images was 9.6%, which is in line with 8.5% of retaken port images previously reported for our free breathing patients. Conclusion: Patients were generally able to complete each of the 4–6 fields in one breath hold per field. The number of port images was comparable to free breathing treatments. Treatment of left sided breast patients using DIBH is an effective way to reduce heart dose without impactful change in treatment time.

Clinical Significance of Pulmonary Nodules Missed on Non-Breath-Hold PET/CT

Objective: In clinical practice, PET images are acquired during shallow breathing and CT images of the PET/ CT during shallow breathing or at near end-expiration. We determined the clinical significance of pulmonary nodules that were missed on PET/CT acquired during non-breath-hold (NBH) imaging in patients with proven non-thoracic solid malignancies. Methods: 200 consecutive cancer patients who underwent both PET/CT and diagnostic breath-hold (BH) chest CT within 30 days, and who had a follow-up with BH CT at least 2 years after these baseline studies, were evaluated. NBH CT of the PET/CT was analyzed first, followed by the baseline BH CT. Missed nodules were defined as nodules not detected on NBH PET/CT, but detected on BH CT. Missed nodules were then evaluated on BH CT performed at least 2 years later. A second radiologist was used to evaluate inter observer variability for a subset of 50 patients. Results: 343 nodules were identified in 121 patients. 166 nodules from 86 patients were classified as missed nodules. Seven of these 166 nodules were excluded due to interval surgery or development of consolidation. When a change in size was counted only if it was ≥2 mm, only 11 of the 159 nodules (6.9%) grew, 113 nodules (71.1%) did not change, and the remaining 35 nodules (22.0%) were not present at follow-up. Malignancy was deemed the most likely diagnosis in only 6 of the original 159 missed nodules. Conclusion: Although the incidence of pulmonary nodules missed on NBH PET/CT was high, most of these nodules did not show any growth on follow-up and few were proven to be metastatic. Current clinical practice of PET/CT, with acquisition during shallow breathing or at near end expiration is sufficient; performing additional deep inspiration BH CT does not appear warranted.

Accuracy Evaluation of a 3-Dimensional Surface Imaging System for Guidance in Deep-Inspiration Breath-Hold Radiation Therapy

To investigate the applicability of 3-dimensional (3D) surface imaging for image guidance in deep-inspiration breath-hold radiation therapy (DIBH-RT) for patients with left-sided breast cancer. For this purpose, setup data based on captured 3D surfaces was compared with setup data based on cone beam computed tomography (CBCT). Twenty patients treated with DIBH-RT after breast-conserving surgery (BCS) were included. Before the start of treatment, each patient underwent a breath-hold CT scan for planning purposes. During treatment, dose delivery was preceded by setup verification using CBCT of the left breast. 3D surfaces were captured by a surface imaging system concurrently with the CBCT scan. Retrospectively, surface registrations were performed for CBCT to CT and for a captured 3D surface to CT. The resulting setup errors were compared with linear regression analysis. For the differences between setup errors, group mean, systematic error, random error, and 95% limits of agreement were calculated. Furthermore, receiver operating characteristic (ROC) analysis was performed. Good correlation between setup errors was found: R(2)=0.70, 0.90, 0.82 in left-right, craniocaudal, and anterior-posterior directions, respectively. Systematic errors were ≤0.17 cm in all directions. Random errors were ≤0.15 cm. The limits of agreement were -0.34-0.48, -0.42-0.39, and -0.52-0.23 cm in left-right, craniocaudal, and anterior-posterior directions, respectively. ROC analysis showed that a threshold between 0.4 and 0.8 cm corresponds to promising true positive rates (0.78-0.95) and false positive rates (0.12-0.28). The results support the application of 3D surface imaging for image guidance in DIBH-RT after BCS.

Potentials of robust intensity modulated scanning proton plans for locally advanced lung cancer in comparison to intensity modulated photon plans

Background and purposeThe potentials of lung sparing, dose escalation, and the robustness of intensity modulated proton plans (IMPTrobust), obtained by minimax optimization on multiple scenarios, were studied. Materials and methodsIMPTrobust optimization as described by Fredriksson et al. [23] was evaluated by means of comparative treatment planning using breath hold CT data from 6 non-small cell lung cancer (NSCLC) patients. IMPTrobust and single field uniform dose (SFUD) proton plans were compared to Tomotherapy and 7-field intensity modulated photon therapy (IMXT). Plan robustness against set-up errors, range uncertainties, and between field motions were analyzed as well as lung exposure quantified by the mean lung dose (MLD) and the partial lung volumes receiving at least 20, 10, and 5GyRBE (V20, V10, V5). Robustness was analyzed with regard to stability of the effective uniform dose (EUD) and the dose level reached or exceeded in 95% of the CTV (D95). ResultsMLD by IMPTrobust was less than by SFUD, and Tomotherapy in each patient, on average by 14.8% and 28.5% (p<0.05, Friedman test). V20–V5 were higher with Tomotherapy compared to both proton therapy techniques, on average by a factor of >1.8. Robustness of IMPTrobust was high. EUD and D95 values were maintained above 96% and 94% of the reference plan values for all tested scenarios. With dose escalation to 86GyRBE lung tissue tolerances were maintained. ConclusionsIMPTrobust proved advantageous in terms of lung exposure and possible dose escalation while being also markedly robust. However, motion during delivery of a field remains a major problem of IMPTrobust to be mitigated by high scanning speed and variable spot size.

Classifying geometric variability by dominant eigenmodes of deformation in regressing tumours during active breath-hold lung cancer radiotherapy

The purpose of this study is to develop and evaluate a lung tumour interfraction geometric variability classification scheme as a means to guide adaptive radiotherapy and improve measurement of treatment response. Principal component analysis (PCA) was used to generate statistical shape models of the gross tumour volume (GTV) for 12 patients with weekly breath hold CT scans. Each eigenmode of the PCA model was classified as ‘trending’ or ‘non-trending’ depending on whether its contribution to the overall GTV variability included a time trend over the treatment course. Trending eigenmodes were used to reconstruct the original semi-automatically delineated GTVs into a reduced model containing only time trends. Reduced models were compared to the original GTVs by analyzing the reconstruction error in the GTV and position. Both retrospective (all weekly images) and prospective (only the first four weekly images) were evaluated. The average volume difference from the original GTV was 4.3% ± 2.4% for the trending model. The positional variability of the GTV over the treatment course, as measured by the standard deviation of the GTV centroid, was 1.9 ± 1.4 mm for the original GTVs, which was reduced to 1.2 ± 0.6 mm for the trending-only model. In 3/13 cases, the dominant eigenmode changed class between the prospective and retrospective models. The trending-only model preserved GTV and shape relative to the original GTVs, while reducing spurious positional variability. The classification scheme appears feasible for separating types of geometric variability by time trend.

Respiratory-gated 18F-FDG PET imaging in lung cancer: effects on sensitivity and specificity

Respiratory motion is known to deteriorate positron emission tomography (PET) images and may lead to potential diagnostic errors when a standardized uptake value (SUV) cut-off threshold is used to discriminate between benign and malignant lesions. To evaluate and compare ungated and respiratory-gated 18F-fluorodeoxyglucose PET/computed tomography (CT) methods for the characterization of pulmonary nodules. The list-mode acquisition during respiratory-gated PET was combined with a short breath-hold CT scan to form the CT-based images. We studied 48 lesions in 43 patients. PET images were analyzed in terms of the maximum SUV (SUV(max)) and the lesion location. Using receiver-operating characteristic (ROC) curves, the optimal SUV cut-off thresholds for the ungated and CT-based methods were calculated to be 2.0 and 2.2, respectively. The corresponding sensitivity values were 83% and 92%, respectively, with a specificity of 67% for both methods. The two methods gave equivalent performance levels for the upper and middle lobes (sensitivity 93%, specificity 62%). They differed for the lower lobes, where the CT-based method outperformed the ungated method (sensitivity values of 90% and 70%, respectively, and a specificity of 73% with both methods) - especially for lesions smaller than 15 mm. The CT-based method increased sensitivity and did not diminish specificity, compared with the ungated method. It was more efficient than the ungated method for imaging the lower lobes and smallest lesions, which are most affected by respiratory motion.

WE‐C‐BRA‐04: Left Breast Deep Inspiration Breath Hold Treatment Based on 3D Surface Matching

Deep inspiration breath hold (DIBH) is a cardiac sparing technique to treat left‐sided breast cancer. By supervising a patient holding her breath at the deep inspiration level, we can deliver tangent radiation beams to effectively treat tumors while reducing the dose to the heart. Research has confirmed both the effectiveness of this treatment, and the reduction in cardiac toxicity. Most clinics in the US are treating DIBH through external surrogate. However, for breast irradiation, the ideal way to implement DIBH would be through direct breast surface matching. This lecture will use AlignRT Beam Hold system (VisionRT Ltd., London, UK) as an example to provide an overview of breast surface matching based DIBH. Clinical implementation will be addressed.Each DIBH patient will have a breath hold CT scan. Patient will also have conventional tattoos. The skin rendering of the breath hold CT is generated and transferred to the AlignRT Beam Hold system. Region‐Of‐Interest (ROI) is selected, and the ROI is the reference image to be matched on during the treatment. There are two criteria for the ROI selection. First, the ROI needs to cover the treatment area. Second, it is important to include some computer vision distinguishable features to assure the accuracy of the surface matching result.On the treatment day, the patient is first setup based on the conventional tattoos. Then, she will be guided to take a deep breath and hold. The AlignRT Beam Hold system will obtain real‐time patient surface images and register it to the reference image. The registration result includes the six degree (translational vertical, longitudinal, and lateral, and rotational vertical, longitudinal, and lateral) displacements and the magnitude displacement. The magnitude displacement is the Euclidian norm of the three translational displacements. All seven displacements are called real‐time deltas. While the patient is still holding her breathe, therapist can adjust the table so that all the real‐time deltas are within pre‐selected tolerances. Now, patient will be instructed to breath normally for a moment followed by another breath hold for verification purpose. If all the real‐time deltas are still within tolerances, the treatment can start.The translational real‐time delta tolerance is selected as follows. On the DRR in the beam eyeˈs view (BEV) with the tangent beam shape and the heart contour, we can measure the shortest distance between the beam edge to the heart. Any number smaller than that shortest distance can be the real‐ time delta tolerance. Rotational tolerance is selected empirically.Either audio or video coaching will be used during the treatment to guide patient breathing in and out to bring the breast surface to the planed level. AlignRT Beam Hold again will report the real‐time deltas. Radiation beam will be turned on automatically when real‐time deltas are within the tolerance and off otherwise.The Learning Objectives of this lecture are:1. Understand the principal of surface matching on left breast DIBH treatment2. Get familiar with the clinical flow of left breast DIBH treatment

MO-F-BRC-04: Is the External Point/marker a Good Surrogate for the Breast Surface Motion during the Left Breast DIBH Treatment?

Purpose: The ideal way of treating left breast DIBH is through direct breast surface matching. Many DIBH techniques, however, rely on a surrogate—external point/marker motion. We try to quantify the predictability of the breast surface motion using external point/marker. Methods: AlignRT Beam Hold system is applied to perform real‐time surface matching and the external point/marker tracking simultaneously. The skin rendering of breath hold CT scan is served as the reference. During the treatment, the patient surface is monitored and registered to the reference to calculate the corresponding distance (S(t)). Radiation beam is turned on when this distance is within a preselected threshold. The external point/marker tracking is implemented by tracking the vertical amplitude of a point in the center part of the left breast skin. The real‐time distance (P(t)) of the selected point to the corresponding reference point is calculated. A model is built to predict S(t) using P(t). Statistical and computational complexityanalyses are conducted. Results: 5 patients are included in this study. Based on our statistical analysis, S(t) can be modeled as a proportioned P(f). For each patient, the ratio is calculated for the first treatment day and applied on the subsequent days. The difference between the prediction and the true S(t) is calculated. The average standard deviations of the difference over all the treatment days are 1.69–2.85mm for different patient, which corresponds to 3.8%–14.6% error rate for 3mm threshold. The biggest standard deviation is from the patient with the largest breast. The computational complexity of the fast ICP based surface matching algorithm is O(N), and of the point/marker tracking is O(1). Conclusions: The breast surface motion and external point/marker tracking result do have strong correlation. Surface matching is more accurate at the price of higher computational complexity.

SU-E-T-516: Evaluation of the Effects of Total Lung Volume, Age, and Body Mass Index on Breath-Hold Level for Left Breast Cancer Patients

Purpose: To determine if abdominal height displacement between free- breathing and breath-hold correlates with change in total lung volume (TLV). Correlation between abdominal height during breath-hold versus patient age and body mass index (BMI) was also investigated. Methods: The study involved 35 patients, each with free-breathing and breath-hold CT scans. The RPM System (Varian Oncology Systems, Palo Alto, Ca) was used to measure abdominal height. Abdominal height displacement was defined as the distance from end of normal inspiration to the average breath- hold level during simulation. Breathing data for each patient was exported from the RPM system and analyzed. Free-breathing and breath-hold scans were fused by matching the field borders, scar, excision cavity, and left breast skin. One physician performed all contouring and image fusions. TLV was calculated by the planning system. Box displacement was plotted against change in TLV, patient age, and BMI. Correlation coefficients (r) were calculated for each comparison. Results: An r-value of 0.59 was calculated for TLV versus breath-hold level. The relationship showed larger TLV changes with greater abdominal height displacement. Comparing box displacement against all ages the r-value was 0.48. Separating by age, patients 70 years and older had an r-value of 0.91 with box displacement decreasing with age. For the remaining age groups (30–49, 50–59, and 60– 69), r-values were 0.30, 0.33, and 0.07, respectively. For BMI, the r-value was 0.35. Conclusions: The data in this investigation was plotted between patients, therefore only inter-patient trends can be described. Younger patients generally achieve deeper breath-holds as measured by abdominal motion than older patients. It can be concluded that abdominal height carries a moderate predictive value for change in TLV for patients under age 70, regardless of BMI. However, a strong correlation exists for patients over age 70.

Regional nodal staging with 18F-FDG PET–CT in non-small cell lung cancer: Additional diagnostic value of CT attenuation and dual-time-point imaging

[Fluorine-18]-fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG PET-CT) is widely performed in the regional nodal staging of non-small cell lung cancer (NSCLC). However, the uptake of (18)F-FDG by tubercular granulomatous tissues may lead to false-positive diagnosis. This is of special concern in China, where tubercular granulomatous disease is epidemic. Herein, we evaluated the efficacy of an additional CT attenuation and a dual-time-point scan in determining the status of lymph nodes. Eighty NSCLC patients underwent curative surgical resection after (18)F-FDG PET-CT and separate breath-hold CT examinations. The initial images were analyzed by two methods. In method 1, nodal status was determined by (18)F-FDG uptake only. In Method 2, nodal status was determined by (18)F-FDG uptake associated with CT attenuation. For dual-time-point imaging, the retention index (RI) of benign and malignant nodal groups with positive uptake in the initial scan was examined. A total of 265 nodal groups were documented. On a per-nodal-group basis, the diagnostic sensitivity, specificity, and accuracy of Method 1 were 66.7%, 89.7%, and 85.3%, respectively, whereas those of Method 2 were 64.7%, 96.7%, and 90.6%, respectively. The improvement in diagnostic specificity and accuracy associated with the addition of CT attenuation in Method 2 as compared to Method 1 was statistically significant (p<0.01). Thirty-nine nodal groups with positive uptake in the initial scan underwent dual-time-point imaging and the difference in the RI between benign and malignant groups showed no statistical significance (p>0.05). (18)F-FDG PET-CT has high diagnostic value for preoperative lymph-node (N) staging of NSCLC patients. We show that (18)F-FDG uptake combined with CT attenuation improves the diagnostic specificity and accuracy of nodal diagnosis in NSCLC. For the lymph nodes with positive uptake in the initial scan, dual-time-point imaging has limited effect in differentiation.

Abstract P4-11-21: Dosimetric Comparison of Radiotherapy for Left Sided Breast Cancer: Breath-Hold Versus Free-Breathing

Abstract Background: Radiotherapy for left sided breast cancer potentially increases risk for late toxicity to the heart. The simple technique of breath-hold (BH) can be instituted in an attempt to reduce volume of lung and heart irradiated in tangential fields. We report on patients with left sided breast cancer that were planned both with conventional free-breathing (FB) and BH radiation techniques from a single institution. Methods: From 10/2006 to 5/2010, 20 patients with node-negative, early stage breast cancer underwent CT simulation for left sided breast cancer and were selected for analysis in this report. FB and BH CT scans were obtained and treatment plans using opposed tangential fields were created to compare various dosimetric indices. Results: BH plans resulted in lower doses to the heart (max dose 1774 vs. 4560cGy, P&amp;lt;0.0001; mean dose 175 vs. 296cGy, p=0.0178; V25 0 vs. 1.85%, P&amp;lt;0.0001; volume in tangential field 0 vs. 10.11cc p=0.0002) compared to FB. The ipsilateral lung received lower doses but a larger volume of lung was encompassed in the tangential fields (V20 13.32 vs. 20.32%, P&amp;lt;0.0001; mean dose 741 vs. 1025cGy, p=0.0003; volume in tangential field 198.8 vs. 256.8cc P&amp;lt;0.0001) compared to FB. Conclusions: Treatment of early stage left sided breast cancer with BH technique is a simple method for minimizing cardiac and ipsilateral lung dose. Long term follow-up is necessary to demonstrate if these dosimetric differences translate into clinically meaningful differences. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-11-21.

Variations in GTV Size in Free Breathing 4D-CT, Breathhold CT and Conventional CT Scans of Patients with Lung Tumors

Variations in GTV Size in Free Breathing 4D-CT, Breathhold CT and Conventional CT Scans of Patients with Lung Tumors

Attenuation correction of emission PET images with average CT: Interpolation from breath-hold CT

Misregistration resulting from the difference of temporal resolution in PET and CT scans occur frequently in PET/CT imaging, which causes distortion in tumor quantification in PET. Respiration cine average CT (CACT) for PET attenuation correction has been reported to improve the misalignment effectively by several papers. However, the radiation dose to the patient from a four-dimensional CT scan is relatively high. In this study, we propose a method to interpolate respiratory CT images over a respiratory cycle from inhalation and exhalation breath-hold CT images, and use the average CT from the generated CT set for PET attenuation correction. The radiation dose to the patient is reduced using this method. Six cancer patients of various lesion sites underwent routine free-breath helical CT (HCT), respiration CACT, interpolated average CT (IACT), and 18F-FDG PET. Deformable image registration was used to interpolate the middle phases of a respiratory cycle based on the end-inspiration and end-expiration breath-hold CT scans. The average CT image was calculated from the eight interpolated CT image sets of middle respiratory phases and the two original inspiration and expiration CT images. Then the PET images were reconstructed by these three methods for attenuation correction using HCT, CACT, and IACT. Misalignment of PET image using either CACT or IACT for attenuation correction in PET/CT was improved. The difference in standard uptake value (SUV) from tumor in PET images was most significant between the use of HCT and CACT, while the least significant between the use of CACT and IACT. Besides the similar improvement in tumor quantification compared to the use of CACT, using IACT for PET attenuation correction reduces the radiation dose to the patient.

Anatomic and Pathologic Variability During Radiotherapy for a Hybrid Active Breath-Hold Gating Technique

To evaluate intra- and interfraction variability of tumor and lung volume and position using a hybrid active breath-hold gating technique. A total of 159 repeat normal inspiration active breath-hold CTs were acquired weekly during radiotherapy for 9 lung cancer patients (12-21 scans per patient). A physician delineated the gross tumor volume (GTV), lungs, and spinal cord on the first breath-hold CT, and contours were propagated semiautomatically. Intra- and interfraction variability of tumor and lung position and volume were evaluated. Tumor centroid and border variability were quantified. On average, intrafraction variability of lung and GTV centroid position was <2.0 mm. Interfraction population variability was 3.6-6.7 mm (systematic) and 3.1-3.9 mm (random) for the GTV centroid and 1.0-3.3 mm (systematic) and 1.5-2.6 mm (random) for the lungs. Tumor volume regressed 44.6% +/- 23.2%. Gross tumor volume border variability was patient specific and demonstrated anisotropic shape change in some subjects. Interfraction GTV positional variability was associated with tumor volume regression and contralateral lung volume (p < 0.05). Inter-breath-hold reproducibility was unaffected by time point in the treatment course (p > 0.1). Increases in free-breathing tidal volume were associated with increases in breath-hold ipsilateral lung volume (p < 0.05). The breath-hold technique was reproducible within 2 mm during each fraction. Interfraction variability of GTV position and shape was substantial because of tumor volume and breath-hold lung volume change during therapy. These results support the feasibility of a hybrid breath-hold gating technique and suggest that online image guidance would be beneficial.