Quantification of coronary artery motion and internal risk volume from ECG gated radiotherapy planning scans

Cardiac substructure delineation in radiation therapy - A state-of-the-art review

Delineation of cardiac substructures is crucial for a better understanding of radiation-related cardiotoxicities and to facilitate accurate and precise cardiac dose calculation for developing and applying risk models. This review examines recent advancements in cardiac substructure delineation in the radiation therapy (RT) context, aiming to provide a comprehensive overview of the current level of knowledge, challenges and future directions in this evolving field. Imaging used for RT planning presents challenges in reliably visualising cardiac anatomy. Although cardiac atlases and contouring guidelines aid in standardisation and reduction of variability, significant uncertainties remain in defining cardiac anatomy. Coupled with the inherent complexity of the heart, this necessitates auto-contouring for consistent large-scale data analysis and improved efficiency in prospective applications. Auto-contouring models, developed primarily for breast and lung cancer RT, have demonstrated performance comparable to manual contouring, marking a significant milestone in the evolution of cardiac delineation practices. Nevertheless, several key concerns require further investigation. There is an unmet need for expanding cardiac auto-contouring models to encompass a broader range of cancer sites. A shift in focus is needed from ensuring accuracy to enhancing the robustness and accessibility of auto-contouring models. Addressing these challenges is paramount for the integration of cardiac substructure delineation and associated risk models into routine clinical practice, thereby improving the safety of RT for future cancer patients.

Quantitative analysis of the impact of respiratory state on the heartbeat-induced movements of the heart and its substructures

PURPOSE

This study seeks to examine the influence of the heartbeat on the position, volume, and shape of the heart and its substructures during various breathing states. The findings of this study will serve as a valuable reference for dose-volume evaluation of the heart and its substructures in radiotherapy for treating thoracic tumors.

METHODS

Twenty-three healthy volunteers were enrolled in this study, and cine four-dimensional magnetic resonance images were acquired during periods of end-inspiration breath holding (EIBH), end-expiration breath holding (EEBH), and deep end-inspiration breath holding (DIBH). The MR images were used to delineate the heart and its substructures, including the heart, pericardium, left ventricle (LV), left ventricular myocardium, right ventricle (RV), right ventricular myocardium (RVM), ventricular septum (VS), atrial septum (AS), proximal and middle portions of the left anterior descending branch (pmLAD), and proximal portion of the left circumflex coronary branch (pLCX). The changes in each structure with heartbeat were compared among different respiratory states.

RESULTS

Compared with EIBH, EEBH increased the volume of the heart and its substructures by 0.25-3.66%, while the average Dice similarity coefficient (DSC) increased by - 0.25 to 8.7%; however, the differences were not statistically significant. Conversely, the VS decreased by 0.89 mm in the left-right (LR) direction, and the displacement of the RV in the anterior-posterior (AP) direction significantly decreased by 0.76 mm (p < 0.05). Compared with EIBH and EEBH, the average volume of the heart and its substructures decreased by 3.08-17.57% and 4.09-20.43%, respectively, during DIBH. Accordingly, statistically significant differences (p < 0.05) were observed in the volume of the heart, pericardium, LV, RV, RVM, and AS. The average DSC increased by 0-37.04% and - 2.6 to 32.14%, respectively, with statistically significant differences (p < 0.05) found in the right ventricular myocardium and interatrial septum. Furthermore, the displacements under DIBH decreased in the three directions (i.e.,- 1.73 to 3.47 mm and - 0.36 to 2.51 mm). In this regard, the AP displacement of the heart, LV, RV, RVM, LR direction, LV, RV, and AS showed statistically significant differences (p < 0.05). The Hausdorff distance (HD) of the heart and its substructures under the three breathing states are all greater than 11 mm.

CONCLUSION

The variations in the displacement and shape alterations of the heart and its substructures during cardiac motion under various respiratory states are significant. When assessing the dose-volume index of the heart and its substructures during radiotherapy for thoracic tumors, it is essential to account for the combined impacts of cardiac motion and respiration.

Considering the Influence of Coronary Motion on Artery-Specific Biomechanics Using Fluid-Structure Interaction Simulation

The endothelium in the coronary arteries is subject to wall shear stress and vessel wall strain, which influences the biology of the arterial wall. This study presents vessel-specific fluid-structure interaction (FSI) models of three coronary arteries, using directly measured experimental geometries and boundary conditions. FSI models are used to provide a more physiologically complete representation of vessel biomechanics, and have been extended to include coronary bending to investigate its effect on shear and strain. FSI both without- and with-bending resulted in significant changes in all computed shear stress metrics compared to CFD (p = 0.0001). Inclusion of bending within the FSI model produced highly significant changes in Time Averaged Wall Shear Stress (TAWSS) + 9.8% LAD, + 8.8% LCx, - 2.0% RCA; Oscillatory Shear Index (OSI) + 208% LAD, 0% LCx, + 2600% RCA; and transverse wall Shear Stress (tSS) + 180% LAD, + 150% LCx and + 200% RCA (all p < 0.0001). Vessel wall strain was homogenous in all directions without-bending but became highly anisotropic under bending. Changes in median cyclic strain magnitude were seen for all three vessels in every direction. Changes shown in the magnitude and distribution of shear stress and wall strain suggest that bending should be considered on a vessel-specific basis in analyses of coronary artery biomechanics.

Effects of respiratory and cardiac motion on estimating radiation dose to the left ventricle during radiotherapy for lung cancer

PURPOSE

Establish a workflow to evaluate radiotherapy (RT) dose variation induced by respiratory and cardiac motion on the left ventricle (LV) and left ventricular myocardium (LVM).

METHODS

Eight lung cancer patients underwent 4D-CT, expiratory T1-volumetric-interpolated-breath-hold-examination (VIBE), and cine MRI scans in expiration. Treatment plans were designed on the average intensity projection (AIP) datasets from 4D-CTs. RT dose from AIP was transferred onto 4D-CT respiratory phases. About 50% 4D-CT dose was mapped onto T1-VIBE (following registration) and from there onto average cine MRI datasets. Dose from average cine MRI was transferred onto all cardiac phases. Cumulative cardiac dose was estimated by transferring dose from each cardiac phase onto a reference cine phase following deformable image registration. The LV was contoured on each 4D-CT breathing phase and was called clinical LV (cLV); this structure is blurred by cardiac motion. Additionally, LV, LVM, and an American Heart Association (AHA) model were contoured on all cardiac phases. Relative maximum/mean doses for contoured regions were calculated with respect to each patient's maximum/mean AIP dose.

RESULTS

During respiration, relative maximum and mean doses on the cLV ranged from -4.5% to 5.6% and -14.2% to 16.5%, respectively, with significant differences in relative mean doses between inspiration and expiration (P < 0.0145). During cardiac motion at expiration, relative maximum and mean doses on the LV ranged from 1.6% to 59.3%, 0.5% to 27.4%, respectively. Relative mean doses were significantly different between diastole and systole (P = 0.0157). No significant differences were noted between systolic, diastolic, or cumulative cardiac doses compared to the expiratory 4D-CT (P > 0.14). Significant differences were observed in AHA segmental doses depending on tumour proximity compared to global LV doses on expiratory 4D-CT (P < 0.0117).

CONCLUSION

In this study, the LV dose was highest during expiration and diastole. Segmental evaluation suggested that future cardiotoxicity evaluations may benefit from regional assessments of dose that account for cardiopulmonary motion.

Cardiac computed tomographic imaging in cardio-oncology: An expert consensus document of the Society of Cardiovascular Computed Tomography (SCCT). Endorsed by the International Cardio-Oncology Society (ICOS)

Cardio-Oncology is a rapidly growing sub-specialty of medicine, however, there is very limited guidance on the use of cardiac CT (CCT) in the care of Cardio-Oncology patients. In order to fill in the existing gaps, this Expert Consensus statement comprised of a multidisciplinary collaboration of experts in Cardiology, Radiology, Cardiovascular Multimodality Imaging, Cardio-Oncology, Oncology and Radiation Oncology aims to summarize current evidence for CCT applications in Cardio-Oncology and provide practice recommendations for clinicians.

The role of motion management and position verification in lymphoma radiotherapy

In the last decades, the substantial technical progress in radiation oncology offered the opportunity for more accurate planning and delivery of treatment. At the same time, the evolution of systemic treatment and the advent of modern diagnostic tools allowed for more accurate staging and consequently a safe reduction of radiotherapy (RT) target volumes and RT doses in the treatment of lymphomas. As a result, incidental irradiation of organs at risk was reduced, with a consequent reduction of severe late toxicity in long-term lymphoma survivors. Nevertheless, these innovations warrant that professionals pay attention to concurrently ensure precise planning and dose delivery to the target volume and safe sparing of the organs at risk. In particular, target and organ motion should be carefully managed in order to prevent any compromise of treatment efficacy. Several aspects should be taken into account during the treatment pathway to minimise uncertainties and to apply a valuable motion management strategy, when needed. These include: reliable image registration between diagnostic and planning radiologic exams to facilitate the contouring process, image guidance to limit positioning uncertainties and to ensure the accuracy of dose delivery and management of lung motion through procedures of respiratory gating and breath control. In this review, we will cover the current clinical approaches to minimise these uncertainties in patients treated with modern RT techniques, with a particular focus on mediastinal lymphoma. In addition, since uncertainties have a different impact on the dose deposition of protons compared to conventional x-rays, the role of motion management and position verification in proton beam therapy (PBT) will be discussed in a separate section.

First Asian population study of stereotactic body radiation therapy for ventricular arrhythmias

We report the first Asian series on stereotactic body radiation (SBRT) for refractory ventricular arrhythmia (VA) in Taiwanese patients. Three-dimensional electroanatomic maps, delayed-enhancement magnetic resonance imaging (DE-MRI), and dual-energy computed tomography (CT) were used to identify scar substrates. The main target volume was treated with a single radiation dose of 25 Gy and the margin volume received 20 Gy using simultaneous integrated boost delivered by the Varian TrueBeam system. Efficacy was assessed according to VA events recorded by an implantable cardioverter-defibrillator (ICD) or a 24-h Holter recorder. Pre- and post-radiation therapy imaging studies were performed. From February 2019 to December 2019, seven patients (six men, one woman; mean age, 55 years) were enrolled and treated. One patient died of hepatic failure. In the remaining six patients, at a median follow-up of 14.5 months, the VA burden and ICD shocks significantly decreased (only one patient with one ICD shock after treatment). Increased intensity on DE-MRI might be associated with a lower risk for VA recurrence, whereas dual-energy CT had lower detection sensitivity. No acute or minimal late adverse events occurred. In patients with refractory VA, SBRT is associated with a marked reduction in VA burden and ICD shocks, and DE-MRI might be useful for monitoring treatment effects.

The margin of internal risk volume on atrial septal and ventricular septal based on electrocardiograph gating 4DCT

Background

The aim of this study was to quantify the margin of internal risk volume (IRV) on the atrial septum (AS) and ventricular septum (VS) based on electrocardiograph gating (ECG-gating) 4DCT.

Methods

Twenty patients were enrolled and received an ECG-gating 4DCT scan performed in breath-hold, and CT images were reconstructed at 5% intervals of the cardiac cycle for a total of 20 phases (0-95%). The contouring of the AS and VS were delineated in each phase, and the displacements and margin of the AS and VS were calculated. We fused the total of the AS and VS (0-95% phase), which were recorded as AS₂₀ and VS₂₀. The margins were applied to the AS and VS in every phase and revised according to the cover rate of AS₂₀ and VS₂₀.

Results

(I) The margins of the AS and VS according to displacements in the left-right, cranio-caudal, and antero-posterior direction were 3 mm, 3 mm, and 3 mm; and 3 mm, 3 mm, and 2 mm, respectively. (II) The volume of AS₂₀ was (11.80±3.72) cm³, which was 2.9 times larger than the maximum volume of the AS. The volume of VS₂₀ was (60.45±12.92) cm³, which was 1.6 times larger than the maximum volume of the VS. (III) The emendatory margins of the AS and VS in the left-right, cranio-caudal, and antero-posterior direction were 7 mm, 10 mm, and 7 mm; and 5 mm, 3 mm, and 4 mm, respectively. The emendatory margins were added to the AS and VS, and the coverage rates were (95.88±3.29)% and (95.24±2.54)%, respectively.

Conclusions

The margin of IRV on the AS and VS could cover the movement of AS and VS induced by heartbeat in the left-right, cranio-caudal, and antero-posterior direction respectively during thoracic radiotherapy.

Dosimetric impact from cardiac motion to heart substructures in thoracic cancer patients treated with a magnetic resonance guided radiotherapy system

Few studies have examined the cardiac volume and radiation dose differences among cardiac phases during radiation therapy (RT). Such information is crucial to dose reconstruction and understanding of RT related cardiac toxicity. In a cohort of nine patients, we studied the changes in the volume and doses of several cardiac substructures between the end-diastolic and end-systolic phases based on the clinical magnetic resonance-guided RT (MRgRT) treatment plans. Significant differences in the volume and dose between the two phases were observed. Onboard cardiac cine MRI holds promise for patient-specific cardiac sparing treatment designs.

Protecting the Heart: A Practical Approach to Account for the Full Extent of Heart Motion in Radiation Therapy Planning

PURPOSE

Emerging evidence suggests that the heart is more radiosensitive than previously assumed; therefore, accounting for heart motion in radiation therapy planning is becoming more critical. In this study, we determined how much heart delineations based on 3-dimensional (3D) computed tomography (CT), 4-dimensional (4D) average projection (AVG), and maximum intensity projection (MIP) images should be extended to represent the full extent of heart motion during 4D imaging acquisition.

METHODS AND MATERIALS

The 3D and 4D CT scans of 10 lung cancer patients treated with stereotactic ablative radiation therapy were used. Median surfaces were derived from heart delineations of 3 observers on the 3D CT, AVG, MIP, and 25% exhale scans. Per patient, the 25% exhale contour was propagated on every phase of the 4D scan. The union of all 4D phase delineations (U4D) represented the full extent of heart motion during imaging acquisition. Surface distances from U4D to 3D, AVG, and MIP volumes were calculated. Distances in the most extreme surface points (1.5 cm most superoinferior, 10% most right/left/anteroposterior) were used to derive margins accounting only for systematic (delineation) errors.

RESULTS

Heart delineations on the MIP were the closest to the full extent of motion, requiring only ≤2.5-mm margins. Delineations on the AVG and 3D scans required margins up to 3.4 and 7.1 mm, respectively. The largest margins were for the inferior, right, and anterior aspects for the delineations on the 3D, AVG, and MIP scans, respectively.

CONCLUSION

Delineations on 3D, AVG, or MIP scans required extensions for representing the heart's full extent of motion, with the MIP requiring the smallest margins. Research including daily imaging to determine the random components for the margins and dosimetric measurements to determine the relevance of creating a planning organ at risk volume of the heart is required.

Adoption of Expansion Margins to Reduce the Dose Received by the Coronary Arteries and the Risk of Cardiovascular Events in Lymphoma Patients

PURPOSE

Mediastinal radiation therapy (RT) in patients with lymphoma implies involuntary coronary artery (CA) exposure, resulting in an increased risk of coronary artery disease (CAD). Accurate delineation of CAs may spare them from higher RT doses. However, heart motion affects the estimation of the dose received by CAs. An expansion margin (planning organ at risk volume [PRV]), encompassing the nearby area where CAs displace, may compensate for these uncertainties, reducing CA dose and CAD risk. Our study aimed to evaluate if a planning process optimized on CA-specific PRVs, rather than just on CAs, could provide any dosimetric or clinical benefit.

METHODS AND MATERIALS

Forty patients receiving RT for mediastinal lymphomas were included. We contoured left main trunk, left anterior descending, left circumflex, and right coronary arteries. An isotropic PRV was then applied to all CAs, in accordance with literature data. A comparison was then performed by optimizing treatment plans either on CAs or on PRVs, to detect any difference in CA sparing in terms of maximum (D_max), median (D_med), and mean (D_mean) dose. We then investigated, through risk modeling, if any dosimetric benefit obtained with the PRV-related optimization process could translate to a lower risk of ischemic complications.

RESULTS

Plan optimization on PRVs demonstrated a significant dose reduction (range, 7%-9%) in D_max, D_med, and D_mean for the whole coronary tree, and even higher dose reductions when vessels were located 5- to 20-mm from PTV (range, 13%-15%), especially for left main trunk and left circumflex (range, 16%-21%). This translated to a mean risk reduction of developing CAD of 12% (P < .01), which increased to 17% when CAs were located 5- to 20-mm from PTV.

CONCLUSIONS

Integration of CA-related PRVs in the optimization process reduces the dose received by CAs and translates to a meaningful prevention of CAD risk in patients with lymphoma treated with mediastinal RT.

Fondazione Italiana Linfomi (FIL) expert consensus on the use of intensity-modulated and image-guided radiotherapy for Hodgkin's lymphoma involving the mediastinum

Aim

Advances in therapy have resulted in improved cure rates and an increasing number of long-term Hodgkin's lymphoma (HL) survivors. However, radiotherapy (RT)-related late effects are still a significant issue, particularly for younger patients with mediastinal disease (secondary cancers, heart diseases). In many Centers, technological evolution has substantially changed RT planning and delivery. This consensus document aims to analyze the current knowledge of Intensity-Modulated Radiation Therapy (IMRT) and Image-Guided Radiation Therapy (IGRT) for mediastinal HL and formulate practical recommendations based on scientific evidence and expert opinions.

Methods

A dedicated working group was set up within the Fondazione Italiana Linfomi (FIL) Radiotherapy Committee in May 2018. After a first meeting, the group adopted a dedicated platform to share retrieved articles and other material. Two group coordinators redacted a first document draft, that was further discussed and finalized in two subsequent meetings. Topics of interest were: 1) Published data comparing 3D-conformal radiotherapy (3D-CRT) and IMRT 2) dose objectives for the organs at risk 3) IGRT protocols and motion management.

Results

Data review showed that IMRT might allow for an essential reduction in the high-dose regions for all different thoracic OAR. As very few studies included specific dose constraints for lungs and breasts, the low-dose component for these OAR resulted slightly higher with IMRT vs. 3D-CRT, depending on the technique used. We propose a set of dose objectives for the heart, breasts, lungs, and thyroid. The use of IGRT is advised for margin reduction without specific indications, such as the use of breath-holding techniques. An individual approach, including comparative planning and considering different risk factors for late morbidity, is recommended for each patient.

Conclusions

As HL therapy continues to evolve, with an emphasis on treatment reduction, radiation oncologists should use at best all the available tools to minimize the dose to organs at risk and optimize treatment plans. This document provides indications on the use of IMRT/IGRT based on expert consensus, providing a basis for clinical implementation and future development.

Cardiac substructure segmentation with deep learning for improved cardiac sparing

PURPOSE

Radiation dose to cardiac substructures is related to radiation-induced heart disease. However, substructures are not considered in radiation therapy planning (RTP) due to poor visualization on CT. Therefore, we developed a novel deep learning (DL) pipeline leveraging MRI's soft tissue contrast coupled with CT for state-of-the-art cardiac substructure segmentation requiring a single, non-contrast CT input.

MATERIALS/METHODS

Thirty-two left-sided whole-breast cancer patients underwent cardiac T2 MRI and CT-simulation. A rigid cardiac-confined MR/CT registration enabled ground truth delineations of 12 substructures (chambers, great vessels (GVs), coronary arteries (CAs), etc.). Paired MRI/CT data (25 patients) were placed into separate image channels to train a three-dimensional (3D) neural network using the entire 3D image. Deep supervision and a Dice-weighted multi-class loss function were applied. Results were assessed pre/post augmentation and post-processing (3D conditional random field (CRF)). Results for 11 test CTs (seven unique patients) were compared to ground truth and a multi-atlas method (MA) via Dice similarity coefficient (DSC), mean distance to agreement (MDA), and Wilcoxon signed-ranks tests. Three physicians evaluated clinical acceptance via consensus scoring (5-point scale).

RESULTS

The model stabilized in ~19 h (200 epochs, training error <0.001). Augmentation and CRF increased DSC 5.0 ± 7.9% and 1.2 ± 2.5%, across substructures, respectively. DL provided accurate segmentations for chambers (DSC = 0.88 ± 0.03), GVs (DSC = 0.85 ± 0.03), and pulmonary veins (DSC = 0.77 ± 0.04). Combined DSC for CAs was 0.50 ± 0.14. MDA across substructures was <2.0 mm (GV MDA = 1.24 ± 0.31 mm). No substructures had statistical volume differences (P > 0.05) to ground truth. In four cases, DL yielded left main CA contours, whereas MA segmentation failed, and provided improved consensus scores in 44/60 comparisons to MA. DL provided clinically acceptable segmentations for all graded patients for 3/4 chambers. DL contour generation took ~14 s per patient.

CONCLUSIONS

These promising results suggest DL poses major efficiency and accuracy gains for cardiac substructure segmentation offering high potential for rapid implementation into RTP for improved cardiac sparing.

Comparison of the dose on specific 3DCT images and the accumulated dose for cardiac structures in esophageal tumors radiotherapy: whether specific 3DCT images can be used for dose assessment?

BACKGROUND

Cardiac activity could impact the accuracy of dose assessment for the heart, pericardium and left ventricular myocardium (LVM). The purpose of this study was to explore whether it is possible to perform dose assessment by contouring the cardiac structures on specific three-dimensional computed tomography (3DCT) images to reduce the impact of cardiac activity.

METHODS

Electrocardiograph-gated 4DCT (ECG-gated 4DCT) images of 22 patients in breath-hold were collected. MIM Maestro 6.8.2 (MIM) was used to reconstruct specific 3DCT images to obtain the Maximal intensity projection (MIP) image, Average intensity projection (AIP) image and Minimum intensity projection (Min-IP) image. The heart, pericardium and LVM were contoured in 20 phases of 4DCT images (0, 5%... 95%) and the MIP, AIP and Min-IP images. Then, a radiotherapy plan was designed at the 0% phase of the 4DCT images, and the dose was transplanted to all phases of 4DCT to acquire the dose on all phases, the accumulated dose of all phases was calculated using MIM. The dose on MIP, AIP and Min-IP images were also obtained by deformable registration of the dose. The mean dose (D_mean), V₅, V₁₀, V₂₀, V₃₀ and V₄₀ for the heart, pericardium and LVM in MIP, AIP and Min-IP images were compared with the corresponding parameters after dose accumulation.

RESULTS

The mean values of the difference between the D_mean in the MIP image and the D_mean after accumulation for the heart, pericardium and LVM were all less than 1.50 Gy, and the dose difference for the pericardium and LVM was not statistically significant (p > 0.05). For dose-volume parameters, there was no statistically significant difference between V₅, V₁₀, and V₂₀ of the heart and pericardium in MIP, AIP, and Min-IP images and those after accumulation (p > 0.05). For the LVM, only in the MIP image, the differences of V₅, V₁₀, V₂₀, V₃₀ and V₄₀ were not significant compared to those after dose accumulation (p > 0.05).

CONCLUSIONS

There was a smallest difference for the dosimetry parameters of cardiac structures on MIP image compared to corresponding parameters after dose accumulation. Therefore, it is recommended to use the MIP image for the delineation and dose assessment of cardiac structures in clinical practice.

Intrafractional Displacement of Cardiac Substructures Among Patients With Mediastinal Lymphoma or Lung Cancer

Purpose

The radiation dose to specific substructures of the heart may be more critical than the dose to the whole heart. Yet, these substructures are sensitive to intrafractional motion from breathing and cardiac motion, which can affect their dose-volume histograms. We sought to investigate intrafractional motion of the heart and its substructures among free-breathing patients undergoing radiation for mediastinal lymphoma or lung cancer.

Methods and materials

After institutional review board approval, the medical records of 20 patients (12 with mediastinal lymphoma; 8 with lung cancer) were retrospectively reviewed. Patients underwent 4-dimensional computed tomography simulation and a contrasted scan for treatment planning. Using MIMVista software, the heart, coronary arteries, chambers, and valves were contoured on the 50% phase, and these contours were propagated to the other phases and edited. Each substructure was graded on the basis of its ease of contouring across all phases (1 = no difficulty; 2 = minor difficulty; 3 = moderate difficulty; and 4 = very difficult). The centroid position and volume of each substructure for all phases were exported to Excel to calculate basic statistics and the independent t test.

Results

The heart, 4 chambers, and atrioventricular valves were easily identified with a mean score of 1 to 1.2, and the pulmonic valve, left anterior descending artery, aortic valve, circumflex, and right coronary artery were minor-to-moderately difficult with a mean score of 2.1 to 3.2. The smallest centroid displacement was seen in the 4 chambers and mitral and pulmonic valves (0.7-1.1 cm). Greater displacement was seen in the coronary vessels and tricuspid and aortic valves (1.2-1.5 cm). The greatest displacement was in the Z direction (craniocaudal) for all substructures; however, the displacement was significantly greater among patients with lymphoma for the right ventricle, aortic valve, and left anterior descending artery (P < .05). However, patients with lung cancer had more displacement in the X and Y directions, which was statistically significant for the right atrium, tricuspid valve, right ventricle, and heart. When calculating overall displacement, no statistically significant difference was observed between patients with lymphoma and patients with lung cancer.

Conclusions

Intrafractional motion of the cardiac substructures ranged from 0.7 to 1.5 cm, mostly in the Z direction. Further investigation of the respiratory motion effect on the dose-volume histogram of the substructures is needed for patients treated with contemporary radiation techniques.

Impact of deformable image registration on dose accumulation applied electrocardiograph-gated 4DCT in the heart and left ventricular myocardium during esophageal cancer radiotherapy

Background

The deformable image registration (DIR) technique has the potential to realize the dose accumulation during radiotherapy. This study will analyze the feasibility of evaluating dose-volume parameters for the heart and left ventricular myocardium (LVM) by applying DIR.

Methods

The electrocardiograph-gated four-dimensional CT (ECG-gated 4DCT) data of 21 patients were analyzed retrospectively. The heart and LVM were contoured on 20 phases of 4DCT (0%, 5%,…,95%). The heart and LVM in the minimum volume/dice similarity coefficient (DSC) phase (Volume _min/DSC _min) were deformed to the maximum volume/DSC phase (Volume _max/ DSC _max), which used the intensity-based free-form DIR algorithm of MIM software. The dose was deformed according to the deformation vector. The variations in volume, mean dose (D_mean), V₂₀, V₃₀ and V₄₀ for the heart and LVM before and after DIR were compared, and the reference phase was the Volume _max/DSC _max phase.

Results

For the heart, the difference between the pre- and post-registration Volume _min and Volume _max were reduced from 13.87 to 1.72%; the DSC was increased from 0.899 to 0.950 between the pre- and post-registration DSC _min phase relative to the DSC _max phase. The post-registration D_mean, V₂₀, V₃₀ and V₄₀ of the heart were statistically significant compared to those in the Volume _max/DSC _max phase (p < 0.05). For the LVM, the difference between the pre- and post-registration Volume _min and Volume _max were only reduced from 18.77 to 17.38%; the DSC reached only 0.733 in the post-registration DSC _min phase relative to the DSC _max phase. The pre- and post-registration volume, D_mean, V₂₀, V₃₀ and V₄₀ of the LVM were all statistically significant compared to those in the Volume _max/DSC _max phase (p < 0.05).

Conclusions

There was no significant relationship between the variation in dose-volume parameters and the variation in the volume and morphology for the heart; however, the inconsistency of the variation in the volume and morphology for the LVM was a major factor that led to uncertainty in the dose-volume evaluation. In addition, the individualized local deformation registration technology should be applied in dose accumulation for the heart and LVM.

Definition of the margin of major coronary artery bifurcations during radiotherapy with electrocardiograph-gated 4D-CT

PURPOSE

The aim was to measure the cardiac motion-induced displacements of major coronary artery bifurcations utilizing electrocardiography (ECG)-gated four-dimensional computed tomography (4D-CT) and to determine the margin of coronary artery bifurcations.

METHODS

Thirty-seven female patients who underwent retrospective ECG-gated 4D-CT in inspiratory breath hold (IBH) were enrolled. The left main coronary artery bifurcation (LM), the obtuse marginal branch bifurcation (OM), the first diagonal branch bifurcation (D₁), the second diagonal branch bifurcation (D₂), the caudal portion of the left anterior descending branch (APX), the first right ventricular artery bifurcation (V) and the acute marginal branch bifurcation (AM) were contoured. The center of the contour of the coronary arterial bifurcations at end systole was defined as the standard, and the margin were then calculated.

RESULTS

The margin in the left-right (LR), cranio-caudal (CC), and anterior-posterior (AP) coordinates were as follows: LM 3, 3, and 3 mm; D₁ 6, 3, and 3 mm; D₂ 3, 3, and 3 mm; APX 4, 4, and 4 mm; OM 4, 6, and 5 mm; V 6, 8, and 7 mm; and AM 6, 8, and 7 mm, respectively.

CONCLUSION

Coronary artery bifurcations should be considered a separate organ at risk (OAR), and different margin should be provided due to the differences resulting from motion displacement. The maximum margin in the LR, CC, and AP coordinates of left coronary artery bifurcations were 6, 6, and 5 mm, and those of the right coronary artery bifurcations were 6, 8, and 7 mm, respectively.

Quantification of heart, pericardium, and left ventricular myocardium movements during the cardiac cycle for thoracic tumor radiotherapy

Purpose

The purpose of this study was to quantify variations in the heart, pericardium, and left ventricular myocardium (LVM) caused by cardiac movement using the breath-hold technique.

Patients and methods

In this study, the electrocardiography-gated four-dimensional computed tomography (CT) images of 22 patients were analyzed, which were sorted into 20 phases (0-95%) according to the cardiac cycle. The heart, pericardium, and LVM were contoured on each phase of the CT images. The positions, volume, dice similarity coefficient (DSC) in reference to 0% phase, and morphological parameters (max 3D diameter, roundness, spherical disproportion, sphericity, and surface area) in different phases of the heart, pericardium, and LVM were analyzed, which were presented as mean ± standard deviation.

Results

The mean values of displacements along the X, Y, and Z axes respectively were as follows: 1.2 mm, 0.6 mm, and 0.6 mm for the heart; 0.5 mm, 0.4 mm, and 0.8 mm for the pericardium; and 1.0 mm, 4.1 mm, and 1.9 mm for the LVM. The maximum variations in volume and DSC respectively were 16.49%±3.85% and 10.08%±2.14% for the heart, 12.62%±3.94% and 5.20%±1.54% for the pericardium, and 24.23%±11.35% and 184.33%±128.61% for the LVM. The differences in the morphological parameters between the maximum and minimum DSC phases for the heart and pericardium were not significantly different (p>0.05) but were significantly different for the LVM (p<0.05).

Conclusion

The volumetric and morphological variations of the heart were similar to those of pericardium, and all were significantly smaller than those of the LVM. This inconsistency in the volumetric and morphological variations between the LVM and the heart and pericardium indicates that special protection of the LVM should be considered.

Quantification of radiation dose reduction by reducing z-axis coverage in 320-detector coronary CT angiography

OBJECTIVE

To quantify the radiation dose reduction achievable by minimizing z-axis coverage in 320-detector coronary CT angiography (CCTA).

METHODS

We retrospectively reviewed 130 CCTAs performed on 320-detector CT that offers up to 16 cm z-axis coverage (adjustable in 2-cm increments), allowing complete coverage of the heart in a single gantry rotation. For each CT, we obtained the radiation dose [CT dose index and dose-length product (DLP)], measured the z-axis field of view and measured the craniocaudal cardiac size (distance from the left main coronary artery to the cardiac apex). We calculated the radiation dose savings achievable by reducing the z-axis coverage to the minimum necessary to cover the heart using 320 × 0.5-mm (maximum 16 cm) and 256 × 0.5-mm (maximum 12.8 cm) detector collimations.

RESULTS

Results are expressed as mean ± standard deviation. The mean craniocaudal cardiac size was 10.5 ± 1.0 cm, with 85% (n = 112) of CCTAs performed with 16 cm of z-axis coverage. The mean DLP was 417.6 ± 182.4 mGy cm, with the mean DLP saving achievable using the minimum z-axis coverage required to completely image the heart being 96.2 ± 47.4 mGy cm, an average dose reduction of 26.9 ± 7.0%. z-axis coverage of ≤12 cm was adequate for 92% and 12.8 cm for 98% of subjects.

CONCLUSION

Using the minimal z-axis coverage to adequately image the heart is a simple step that can reduce the DLP in 320-detector CCTA by approximately 27%. z-axis coverage of ≤12 cm is adequate for 92%, 12.8 cm for 98% and 14 cm for 100% of patients undergoing CCTA. Advances in knowledge: Reducing z-axis coverage in 320-detector CCTA can reduce DLP by approximately 27%.