Planning 4D CT Research Articles

Assessing the adequacy of a 5-mm planning target volume margin for 4D-CT scan-based image-guided radiotherapy for locally advanced carcinoma of the lung

In developed nations, 4D-computed tomography (4D-CT)-based image-guided radiotherapy (IGRT) has become the standard for treating lung carcinoma patients, with the primary goal of achieving disease cure. However, its usage in India remains limited. Here, we compared target volume delineation for radical radiation planning in patients with locally advanced lung carcinoma using helical free-breathing CT (FBCT) and 4D-CT. In addition, we assessed the adequacy of a 5-mm planning target volume (PTV) margin with 4D-CT planning. Fifty patients with locally advanced lung cancer were enrolled in the study. Each patient underwent contouring based on 4D-CT to generate an internal target volume, and a 5-mm PTV margin (PTV_4D) was added for radical radiation. Subsequently, each patient underwent two intensity-modulated radiation therapy (IMRT) plans with comparable planning and optimization parameters. One plan was based on the FBCT-based volume (PTV_3D), while the other was based on the 4D-CT-based volume (PTV_4D). PTV, organ at risk (OAR) dose, and PTV coverage by 95% of the prescribed dose (PTVD 95_3D vs. PTVD 95_4D) were compared between the two schemes. Results revealed that 4D-CT-based planning reduced PTV (mean PTV volume: 539 cc vs. 782 cc) and lowered OAR doses (mean lung dose: 13 Gy vs. 15 Gy; mean esophagus dose: 18.5 Gy vs. 21.15 Gy; mean spinal cord max dose: 35.59 Gy vs. 37.39 Gy). At 3 months after treatment imaging, 40% of the patients showed a complete response, 48% showed a partial response, 4% showed stable disease, and 8% showed progressive disease. In conclusion, 4D-CT-based radiation planning for locally advanced lung carcinoma with a reduced PTV margin of 5 mm can dramatically decrease the PTV and OAR doses without sacrificing PTV coverage compared to FBCT-based planning. However, daily online image guidance or at least a well-defined offline image guidance protocol is recommended when employing such a small PTV margin.

Interobserver agreement on definition of the target volume in stereotactic radiotherapy for pancreatic adenocarcinoma using different imaging modalities

PurposeThe aim of this study was to evaluate interobserver agreement (IOA) on target volume definition for pancreatic cancer (PACA) within the Radiosurgery and Stereotactic Radiotherapy Working Group of the German Society of Radiation Oncology (DEGRO) and to identify the influence of imaging modalities on the definition of the target volumes.MethodsTwo cases of locally advanced PACA and one local recurrence were selected from a large SBRT database. Delineation was based on either a planning 4D CT with or without (w/wo) IV contrast, w/wo PET/CT, and w/wo diagnostic MRI. Novel compared to other studies, a combination of four metrics was used to integrate several aspects of target volume segmentation: the Dice coefficient (DSC), the Hausdorff distance (HD), the probabilistic distance (PBD), and the volumetric similarity (VS).ResultsFor all three GTVs, the median DSC was 0.75 (range 0.17–0.95), the median HD 15 (range 3.22–67.11) mm, the median PBD 0.33 (range 0.06–4.86), and the median VS was 0.88 (range 0.31–1). For ITVs and PTVs the results were similar. When comparing the imaging modalities for delineation, the best agreement for the GTV was achieved using PET/CT, and for the ITV and PTV using 4D PET/CT, in treatment position with abdominal compression.ConclusionOverall, there was good GTV agreement (DSC). Combined metrics appeared to allow a more valid detection of interobserver variation. For SBRT, either 4D PET/CT or 3D PET/CT in treatment position with abdominal compression leads to better agreement and should be considered as a very useful imaging modality for the definition of treatment volumes in pancreatic SBRT. Contouring does not appear to be the weakest link in the treatment planning chain of SBRT for PACA.

Clinical 3D/4D cumulative proton dose assessment methods for thoracic tumours with large motion

PurposeDespite the anticipated clinical benefits of intensity-modulated proton therapy (IMPT), plan robustness may be compromised due to its sensitivity to patient treatment uncertainties, especially for tumours with large motion. In this study, we investigated treatment course-wise plan robustness for intra-thoracic tumours with large motion comparing a 4D pre-clinical evaluation method (4DREM) to our clinical 3D/4D dose reconstruction and accumulation methods. Materials and methodsTwenty patients with large target motion (>10 mm) were treated with five times layered rescanned IMPT. The 3D-robust optimised plans were generated on the averaged planning 4DCT. Using multiple 4DCTs, treatment plan robustness was assessed on a weekly and treatment course-wise basis through the 3D robustness evaluation method (3DREM, based on averaged 4DCTs), the 4D robustness evaluation method (4DREM, including the time structure of treatment delivery and 4DCT phases) and 4D dose reconstruction and accumulation (4DREAL, based on fraction-wise information). ResultsBaseline target motion for all patients ranged from 11–17 mm. For the offline adapted course-wise dose assessment, adequate target dose coverage was found for all patients. The target volume receiving 95% of the prescription dose was consistent between methods with 16/20 patients showing differences < 1%. 4DREAL showed the highest target coverage (99.8 ± 0.6%, p < 0.001), while no differences were observed between 3DREM and 4DREM (99.3 ± 1.3% and 99.4 ± 1.1%, respectively). ConclusionOur results show that intra-thoracic tumours can be adequately treated with IMPT in free breathing for target motion amplitudes up to 17 mm employing any of the accumulation methods. Anatomical changes, setup and range errors demonstrated a more severe impact on target coverage than motion in these patients treated with fractionated proton radiotherapy.

How should we model and evaluate breathing interplay effects in IMPT?

Breathing interplay effects in Intensity Modulated Proton Therapy (IMPT) arise from the interaction between target motion and the scanning beam. Assessing the detrimental effect of interplay and the clinical robustness of several mitigation techniques requires statistical evaluation procedures that take into account the variability of breathing during dose delivery. In this study, we present such a statistical method to model intra-fraction respiratory motion based on breathing signals and assess clinical relevant aspects related to the practical evaluation of interplay in IMPT such as how to model irregular breathing, how small breathing changes affect the final dose distribution, and what is the statistical power (number of different scenarios) required for trustworthy quantification of interplay effects. First, two data-driven methodologies to generate artificial patient-specific breathing signals are compared: a simple sinusoidal model, and a precise probabilistic deep learning model generating very realistic samples of patient breathing. Second, we investigate the highly fluctuating relationship between interplay doses and breathing parameters, showing that small changes in breathing period result in large local variations in the dose. Our results indicate that using a limited number of samples to calculate interplay statistics introduces a bigger error than using simple sinusoidal models based on patient parameters or disregarding breathing hysteresis during the evaluation. We illustrate the power of the presented statistical method by analyzing interplay robustness of 4DCT and Internal Target Volume (ITV) treatment plans for a 8 lung cancer patients, showing that, unlike 4DCT plans, even 33 fraction ITV plans systematically fail to fulfill robustness requirements.

Incorporation of tumor motion directionality in margin recipe: The directional MidP strategy.

Planning target volume (PTV) definition based on Mid-Position (Mid-P) strategy typically integrates breathing motion from tumor positions variances along the conventional axes of the DICOM coordinate system. Tumor motion directionality is thus neglected even though it is one of its stable characteristics in time. We therefore propose the directional MidP approach (MidP dir), which allows motion directionality to be incorporated into PTV margins. A second objective consists in assessing the ability of the proposed method to better take care of respiratory motion uncertainty. 11 lung tumors from 10 patients with supra-centimetric motion were included. PTV were generated according to the MidP and MidP dir strategies starting from planning 4D CT. PTVMidP dir volume didn't differ from the PTVMidP volume: 31351mm3 IC95% [17242-45459] vs. 31003mm3 IC95% [ 17347-44659], p=0.477 respectively. PTVMidP dir morphology was different and appeared more oblong along the main motion axis. The relative difference between 3D and 4D doses was on average 1.09%, p=0.011 and 0.74%, p=0.032 improved with directional MidP for D99% and D95%. D2% was not significantly different between both approaches. The improvement in dosimetric coverage fluctuated substantially from one lesion to another and was all the more important as motion showed a large amplitude, some obliquity with respect to conventional axes and small hysteresis. Directional MidP method allows tumor motion to be taken into account more tightly as a geometrical uncertainty without increasing the irradiation volume.

Cardiac Motion and its Impact on Target Coverage During SBRT for Refractory Ventricular Tachycardia

<h3>Purpose/Objective(s)</h3> Refractory ventricular tachycardia (VT) is a common cause of death and morbidity in the heart failure population. Stereotactic body radiation therapy (SBRT) is a new and promising approach to treating VT, but there are practical concerns about SBRT delivery to the heart, which undergoes motion from both cardiac and respiratory cycles. In this study, we investigate motion magnitudes from both cycles and their impact on treatment margins and target coverage for VT SBRT. <h3>Materials/Methods</h3> Twenty-one patients were treated with SBRT for VT at our institution between April 2018 and December 2020 under an IRB-approved registry protocol. All patients had respiratory-correlated 4DCT for treatment planning and 7 patients had diagnostic cardiac-gated CT scans taken less than two weeks prior to treatment. Target structures were delineated on free-breathing CT and transferred to respiratory average (RAVG) CT via rigid registration. Dose was initially calculated on the RAVG per current institutional standard of care. For this retrospective study, deformable image registration (DIR) was applied between RAVG and the cardiac average CT (CAVG), systolic, and diastolic CTs from the cardiac dataset. Target contours were transferred to the registration target image. Motion magnitudes and distributions from the deformation vector fields were analyzed. Internal target volumes (ITVs) were created on the respiratory average images for quantitative analysis of target motion and coverage changes. From these 7 patients, 11 distinct target volumes were treated, with 8 being epicardial and 3 endocardial. Motion and dosimetry for all 11 targets were analyzed separately. <h3>Results</h3> The average (SD) target shift magnitudes (in mm) from the RAVG to CAVG CTs were 2.0 ± 1.0, 2.0 ± 1.3, and 4.0 ± 2.0 in the left-right (LR), anterior/posterior (AP), and superior/inferior (SI) directions. Endocardial targets had greater motion magnitude than epicardial targets, with mean shifts of 2.2 ± 1.0, 2.3 ± 1.9, and 4.2 ± 2.4 in the LR, AP, and SI directions versus 1.4 ± 0.9, 1.3 ± 0.8, and 3.6 ± 0.5. Cardiac cycle motion showed more variability for epicardial targets with shifts of 1.4 ± 2.5, 2.4 ± 3.0, and 2.5 ± 3.7 in the LR, AP and SI directions, versus 2.0 ± 0.6, 2.1 ± 0.8, and 1.6 ± 0.7 for endocardial targets. Creation of motion encompassing ITVs led to an average target size increase of 100% (25 cm³). V95 for initial target volumes was 99.9 ± 0.4% while the average V95 for ITVs was 84.1 ± 15.6%. Similarly, D95 for the target dropped from 108.2 ± 5.7% to 75.3 ± 28.4%. <h3>Conclusion</h3> In this cohort of patients undergoing SBRT for VT, cardiac shifts were location-dependent and were largest in the SI direction. These shifts typically exceeded the 1-5 mm margins used for SBRT treatment planning and ITV generation to encompass all target motion led to a doubling in target size. Our data suggest that cardiac-gated delivery may be helpful to minimize treatment volumes and spare cardiac tissue.

B-AB04-01 STEREOTACTIC BODY RADIOTHERAPY FOR REFRACTORY SCAR RELATED VENTRICULAR TACHYCARDIA: A SINGLE CENTER EXPERIENCE

Stereotactic body radiation therapy (SBRT) is an emerging treatment option for ventricular tachycardia (VT) refractory to catheter ablation (CA). To describe experience with SBRT for refractory VT with acute and mid-term outcomes. This is a single-center experience of patients who underwent SBRT for VT. The target for therapy was defined based on all available data including 12-lead ECG VT morphology, cardiac imaging, and electroanatomic mapping data. 25 Gy was delivered with 4D CT planning and conebeam CT guidance. All patients were placed on anticoagulation post and had follow up echocardiography and chest CT. A 4-week blanking period was used for VT outcomes. Ten patients with significant scar on cardiac imaging or electroanatomic mapping underwent SBRT; 6 (60%) for VT refractory to treatment, 2 with contraindication to CA, and 2 patients with inaccessible epicardial substrate. 8 (80%) had VT storm. Patients were 62.6±7.8 years, with mean LVEF of 33±14%. All failed antiarrhythmic therapy and amiodarone in 9 (90%) and had 2.2±0.9 prior CA. 9 (90%) had one or more CA at our institution. During a median follow-up of 6.5 months, VT episodes decreased from 44 ± 108 6 months prior to therapy to 4 ± 7 (p = 0.02). ICD shocks decreased from 4.8 ± 3.4 to 0 (p=0.002). 3 (30%) of patients had VT in the first 3 weeks post treatment with no VT after. Two patient deaths occurred in the follow-up period that were unlikely related to SBRT. No short-term complications or changes on ECHO were noted. In patients with VT refractory to medications and CA, SBRT was associated with a marked reduction in VT burden and ICD shocks. Long term outcomes and complications are unknown.

Geometric and dosimetric accuracy of deformable image registration between average-intensity images for 4DCT-based adaptive radiotherapy for non-small cell lung cancer.

PurposeRe‐planning for four‐dimensional computed tomography (4DCT)‐based lung adaptive radiotherapy commonly requires deformable dose mapping between the planning average‐intensity image (AVG) and the newly acquired AVG. However, such AVG‐AVG deformable image registration (DIR) lacks accuracy assessment. The current work quantified and compared geometric accuracies of AVG‐AVG DIR and corresponding phase‐phase DIRs, and subsequently investigated the clinical impact of such AVG‐AVG DIR on deformable dose mapping.Methods and MaterialsHybrid intensity‐based AVG‐AVG and phase‐phase DIRs were performed between the planning and mid‐treatment 4DCTs of 28 non‐small cell lung cancer patients. An automated landmark identification algorithm detected vessel bifurcation pairs in both lungs. Target registration error (TRE) of these landmark pairs was calculated for both DIR types. The correlation between TRE and respiratory‐induced landmark motion in the planning 4DCT was analyzed. Global and local dose metrics were used to assess the clinical implications of AVG‐AVG deformable dose mapping with both DIR types.ResultsTRE of AVG‐AVG and phase‐phase DIRs averaged 3.2 ± 1.0 and 2.6 ± 0.8 mm respectively (p < 0.001). Using AVG‐AVG DIR, TREs for landmarks with <10 mm motion averaged 2.9 ± 2.0 mm, compared to 3.1 ± 1.9 mm for the remaining landmarks (p < 0.01). Comparatively, no significant difference was demonstrated for phase‐phase DIRs. Dosimetrically, no significant difference in global dose metrics was observed between doses mapped with AVG‐AVG DIR and the phase‐phase DIR, but a positive linear relationship existed (p = 0.04) between the TRE of AVG‐AVG DIR and local dose difference.ConclusionsWhen the region of interest experiences <10 mm respiratory‐induced motion, AVG‐AVG DIR may provide sufficient geometric accuracy; conversely, extra attention is warranted, and phase‐phase DIR is recommended. Dosimetrically, the differences in geometric accuracy between AVG‐AVG and phase‐phase DIRs did not impact global lung‐based metrics. However, as more localized dose metrics are needed for toxicity assessment, phase‐phase DIR may be required as its lower mean TRE improved voxel‐based dosimetry.

P20.06 Dosimetric Comparison of the Real and Virtual Plans in Non-Small Cell Lung Cancer Patients Treated With Respiratory Motion Management

We conducted a prospective study to increase tumor control, reducing side effects and dosimetric comparison of the real and virtual plans by using motion management in 40 patients with locally advanced non-small cell lung cancer. The study was approved by the ethics (2018-7/7) and scientific committee (OUAP (T) 2019/2) as scientific research project in our university. Simulation images were obtained using free breathing in the treatment position using axial cine mode 16-slice 4D-CT scanner and RPM in 10 respiratory phases. In the MIP phase, PTV with a 5 mm border in each direction was created for the ITV including the tumor and involved nodes. A volumetric arc treatment plan was established by taking the 98% of prescription dose to 95% of PTV and also taking into account the risky organ doses. Patients were treated with CBCT imaging on LINAC device every other day. For virtual plan, GTV for tumor and involved nodes and CTV according to ICRU83 were created in the free respiratory phase. PTV was created with a 5 mm margin to CTV and virtual treatment plan was created with the same prescribed dose. 10 patients were treated till December 2019. The median age was 59 years (49-72) and the M/F ratio was 8/2. Histopathological diagnosis were SCC (4), adenocarcinoma (5), LCNEC (1). AJCC18 staging were listed as IA2 (1), IIIA (2), IIIB (4), IIIC (2) and IVB (1). The median RT dose was 6300 cGy (5940-6400) with 32 fractions (30-35). In the third month, 2 complete, 3 partial responses and 1 locoregonal progression were detected by PET/CT. ITVtm was 46.98 and GTVtm was 31.27 cc (p = 0.66), while PTV volumes were 173.53 and 494.50 cc (p = 0.008) in treatment and virtual plans, respectively. The tumor volume was higher but PTV volume was lower in the treatment plans. D95 for ITVtm and GTVtm were found 6311 and 6326 cGy (p = 0.72) whereas D95 for PTV 6297 and 6051 cGy (p = 0.13), respectively. The mean lung dose, V5, V20 and V30 were 15.14 vs 16.07 Gy (p = 0.077), 55.95% vs 63.8% (p = 0.087), 26.44% vs 31.55% (p = 0.23) and 17.44% vs 20.64 (p = 0.085), median heart dose was 6.03 and 10.36 Gy (p = 0.043), heart V50 was 8.2% vs 33.9% (p = 0.007), median esophageal dose was 18.94 vs 21.43 Gy (p = 0.35) and esophagus V50 11.39% vs 18% (p = 0.69), the median and maximum spinal cord dose was 8.11 vs 8.22 Gy (p = 0.61) and 33.15 vs 37.39 Gy, respectively (p = 0.22), in treatment and virtual plans. It was observed that all risky organ doses were less in treatment plans than virtual plans with statistical significance in heart doses. In this study, it was shown that the target volume did not increase, the target was covered with 95% accuracy and the risky organ doses were lower in 10 patients who were treated with 4D-CT planning and respiratory motion management.

The use of tumour markers in oesophageal cancer to quantify setup errors and baseline shifts during treatment

PurposeTo prospectively evaluate the feasibility of solid gold marker placement in oesophageal cancer patients and to quantify inter-fractional and intra-fractional (baseline shift) marker motion during radiation treatment. Radiotherapy target margins and matching strategies were investigated. Materials/methodsThirty-four markers were implanted by echo-endoscopy in 10 patients. Patients received a planning 4D CT, daily pre-treatment cone-beam CT (CBCT) and a post-treatment CBCT for at least five fractions. For fractions with both pre- and post-treatment CBCT, marker displacement between planning CT and pre-treatment CBCT (inter-fractional) and between pre-treatment and post-treatment CBCT (intra-fractional; only for fractions without rotational treatment couch correction) were calculated in left–right (LR), cranio-caudal (CC) and anterior-posterior (AP) direction after bony-anatomy and soft-tissue matching. Systematic/random setup errors were estimated; treatment margins were calculated. ResultsNo serious adverse events occurred. Twenty-three (67.6%) markers were visible during radiotherapy (n = 3 middle oesophagus, n = 16 distal oesophagus, n = 4 proximal stomach). Margins for inter-fractional displacement after bony-anatomy match depended on the localisation of the primary tumour and were 11.2 mm (LR), 16.4 mm (CC) and 8.2 mm (AP) for distal markers. Soft-tissue matching reduced the CC margin for these markers (16.4 mm to 10.5 mm). The mean intra-fractional shift of 12 distal markers was 0.4 mm (LR), 2.3 mm (CC) and 0.7 mm (AP). Inclusion of this shift resulted in treatment margins for distal markers of 12.8 mm (LR), 17.3 mm (CC) and 10.4 mm (AP) after bony-anatomy matching and 12.4 mm (LR), 11.4 mm (CC) and 9.7 mm (AP) after soft-tissue matching. ConclusionThis study demonstrated that the implantation of gold markers was safe, albeit less stable compared to other marker types. Inter-fractional motion was largest cranio-caudally for markers in the distal oesophagus, which was reduced after soft-tissue compared to bony-anatomy matching. The impact of intra-fractional baseline shifts on margin calculation was rather small.

Dose-escalated volumetric modulated arc therapy for total marrow irradiation: A feasibility dosimetric study with 4DCT planning and simultaneous integrated boost.

To evaluate the planning feasibility of dose-escalated total marrow irradiation (TMI) with simultaneous integrated boost (SIB) to the active bone marrow (ABM) using volumetric modulated arc therapy (VMAT), and to assess the impact of using planning organs at risk (OAR) volumes (PRV) accounting for breathing motion in the optimization. Five patients underwent whole-body CT and thoraco-abdominal 4DCT. A planning target volume (PTV) including all bones and ABM was contoured on each whole-body CT. PRV of selected OAR (liver, heart, kidneys, lungs, spleen, stomach) were determined with 4DCT. Planning consisted of 9-10 full 6 MV photon VMAT arcs. Four plans were created for each patient with 12Gy prescribed to the PTV, with or without an additional 4Gy SIB to the ABM. Planning dose constraints were set on the OAR or on the PRV. Planning objective was a PTV Dmean<110% of the prescribed dose, a PTV V110%<50%, and OAR Dmean≤50-60%. PTV Dmean<110% was accomplished for most plans (n=18/20), while all achieved V110%<50%. SIB plans succeeded to optimally cover the boost volume (median ABM Dmean=16.3Gy) and resulted in similar OAR sparing compared to plans without SIB (median OAR Dmean=40-54% of the ABM prescribed dose). No statistically significant differences between plans optimized with constraints on OAR or PRV were found. Adding a 4Gy SIB to the ABM for TMI is feasible with VMAT technique, and results in OAR sparing similar to plans without SIB. Setting dose constraints on PRV does not impair PTV dosimetric parameters.

Comparative Dosimetric Analysis and Normal Tissue Complication Probability Modelling of Four-Dimensional Computed Tomography Planning Scans Within the UK NeoSCOPE Trial

AimsNeoSCOPE is a trial of two different neoadjuvant chemoradiotherapy regimens for resectable oesophageal cancer and was the first multicentre trial in the UK to incorporate four-dimensional computed tomography (4D-CT) into radiotherapy planning. Despite 4D-CT being increasingly accepted as a standard of care for lower third and junctional oesophageal tumours, there is limited evidence of its benefit over standard three-dimensional computed tomography (3D-CT). MaterialsUsing NeoSCOPE 4D-CT cases, we undertook a dosimetric comparison study of 3D-CT versus 4D-CT plans comparing target volume coverage and dose to organs at risk. We used established normal tissue complication probability models to evaluate the potential toxicity reduction of using 4D-CT plans in oesophageal cancer. Results4D-CT resulted in a smaller median absolute PTV volume and lower dose levels for all reported constraints with comparable target volume coverage. NTCP modelling suggests a significant relative risk reduction of cardiac and pulmonary toxicity endpoints with 4D-CT. ConclusionOur work shows that incorporating 4D-CT into treatment planning may significantly reduce the toxicity burden from this treatment.

4D CT image artifacts affect local control in SBRT of lung and liver metastases

Background and purpose:4D CT images often contain artifacts that are suspected to affect treatment planning quality and clinical outcome of lung and liver SBRT. The present study investigates the correlation between the presence of artifacts in SBRT planning 4D CT data and local metastasis control.Materials and methods:The study includes 62 patients with 102 metastases (49 in the lung and 53 in the liver), treated between 2012 and 2016 with SBRT for mainly curative intent. For each patient, 10-phase 4D CT images were acquired and used for ITV definition and treatment planning. Follow-up intervals were 3 weeks after treatment and every 3–6 months thereafter. Based on the number and type of image artifacts, a strict rule-based two-class artifact score was introduced and assigned to the individual 4D CT data sets. Correlation between local control and artifact score (consensus rating based on two independent observers) were analyzed using uni- and multivariable Cox proportional hazards models with random effects. Metastatic site, target volume, metastasis motion, breathing irregularity-related measures, and clinical data (chemotherapy prior to SBRT, target dose, treatment fractionation) were considered as covariates.Results: Local recurrence was observed in 17/102 (17%) metastases. Significant univariable factors for local control were artifact score (severe CT artifacts vs. few CT artifacts; hazard ratio 8.22; 95%-CI 2.04–33.18) and mean patient breathing period (>4.8 s vs. ≤4.8 s; hazard ratio 3.58; 95%-CI 1.18–10.84). Following multivariable analysis, artifact score remained as dominating prognostic factor, although statistically not significant (hazard ratio 10.28; 95%-CI 0.57–184.24).Conclusion: The results support the hypothesis that image artifacts in 4D CT treatment planning data negatively influence clinical outcome in SBRT of lung and liver metastases, underlining the need to account for 4D CT artifacts and improve image quality.

Dosimetric Correlation Between The Depth of Chest Wall Expansion and Heart Dose in Left Breast Cancer Irradiation Using Deep Inspiratory Breath Hold Technique

Introduction and Objective: In adjuvant radiotherapy for left breast cancer, a significant heart volume may be included in the radiation field leading to long-term cardiac toxicities. Deep inspiratory breath hold technique (DIBH) leads to chest wall separation away from the heart and thus can reduce the heart dose compared to free breathing technique. The aim of this study is to correlate dosimetrically the degree of chest wall expansion measured on planning 4D-CT scan to the heart dose in left breast cancer irradiation using DIBH technique. Materials and Methods: Thirty four patients with left breast cancer planned for adjuvant radiotherapy were included. All patients were scanned by Varian RPM (Real Time Position Managment) respiratory gating system using infrared reflecting markers and a video camera to detect the respiratory motion. IMRT or VMAT plans were done for all patients with a prescribed dose 50Gy/25fr/5w with or without operative bed boost dose 10Gy/5fr/1w. The degree of chest wall expansion was identified by measuring the amplitude of DIBH breathing curve from baseline in planning 4D-CT scan in centimeters. The depth of expansion was correlated dosimetrically with the heart V20, V30, and mean heartdose. Results: The mean distance of chest wall expansion was 2.9cm. The mean left lung dose was 8.6Gy. The mean left lung V20 was 13.8%. The mean heart dose was 1.8Gy. The mean heart V30 was 0.6%. A statistically significant reduction of the mean heart dose and V30 was observed with chest wall expansion of 1.4cm or higher (p&lt;0.05). Conclusion: In DIBH technique, the depth of chest wall expansion in 4DCT planning is dosimetrically correlated with the cardiac dose reduction during adjuvant irradiation of left breast cancer. Further clinical studies are needed to translate this dosimetric advantage into clinical benefit.

Organ sparing potential and inter-fraction robustness of adaptive intensity modulated proton therapy for lung cancer

Background: The aim of this study was to compare adaptive intensity modulated proton therapy (IMPT) robustness and organ sparing capabilities with that of adaptive volumetric arc photon therapy (VMAT).Material and methods: Eighteen lung cancer patients underwent a planning 4DCT (p4DCT) and 5 weekly repeated 4DCT (r4DCT) scans. Target volumes and organs at risk were manually delineated on the three-dimensional (3D) average scans of the p4DCT (av_p4DCT) and of the r4DCT scans (av_r4DCT). Planning target volume (PTV)-based VMAT plans and internal clinical target volume (ICTV)-based robust IMPT plans were optimized in 3D on the av_p4DCT and re-calculated on the av_r4DCTs. Re-planning on av_r4DCTs was performed when indicated and accumulated doses were evaluated on the av_p4DCT.Results: Adaptive VMAT and IMPT resulted in adequate ICTV coverage on av_r4DCT in all patients and adequate accumulated-dose ICTV coverage on av_p4DCT in 17/18 patients (due to a shrinking target in one patient). More frequent re-planning was needed for IMPT than for VMAT. The average mean heart dose reduction with IMPT compared with VMAT was 4.6 Gy (p = .001) and it was >5 Gy for five patients (6, 7, 8, 15, and 22 Gy). The average mean lung dose reduction was 3.2 Gy (p < .001). Significant reductions in heart and lung V5 Gy were observed with IMPT.Conclusion: Robust-planned IMPT required re-planning more often than VMAT but resulted in similar accumulated ICTV coverage. With IMPT, heart and lung mean dose values and low dose regions were significantly reduced. Substantial cardiac sparing was obtained in a subgroup of five patients (28%).

Evaluating Utility of 4D PET-CT Motion Freeze Imaging for Lung SABR

In Lung stereotactic ablative radiotherapy (SABR), 4D PET-CT gives an edge over static 3D PET-CT in target volume delineation given its ability to reduce motion artifacts. Motion Freeze (MF) PET imaging combines the quantitative benefits of 100% counts of 4D phase-matched PET-CT imaging into a single static image by collecting CT & PET data at each phase of the breathing cycle, then matching the data for attenuation consistency. This provides further robustness of biologic target volume delineation with reduced image noise. The authors evaluated the utility of 4D PET-CT MF imaging in lung SABR treatments & the consequent dosimetric impact when either motion inclusive (retrospective imaging) technique or gating technique were to be used. Five patients of lung SABR were included for purpose of this dosimetric study (1 Ca lung and 4 lung oligo-metastasis). All patients underwent 4D CT /PET scan with the RPM system on 16 slice PET-CT scanner. The 4D CT and 4D PET data were binned in 10 phases of respiratory cycle. The Motion match software was utilized to create a MF image of all the 10 PET bins (MF-10) and 3 bins corresponding to end expiratory phase 40%,50%,60% (MF-3) in which tumor position was relatively stable. For study purpose we analyzed 3 clinical scenarios for target delineation (a) target volume generated using 4D CT alone (b) 4D CT all bins deformably registered with MF-10 (c) 4D-CT 3 bins deformably registered with corresponding MF-3, using gradient based intensity based registration algorithm. Three VMAT 6 MV FFF plans were generated for all the above all 3 volumes. The dosimetric parameters analysed included Target volume coverage, dose spillage (high, intermediate and low dose) & OAR doses as per RTOG protocol. Statistical comparison was done using paired sample t test in statistical analysis software. The target volume was reduced using 4D PET MF 10 & MF 3 as compared to 4D CT alone though the values were statistically insignificant [P=0.75(MF10), P=0.68 (MF3)]. There was statistically insignificant difference in target volume coverage parameters i.e. Conformity index, Heterogeneity index, dose spillage (high, intermediate and low dose) among all the plans. However the trend towards reduced OAR doses was seen in MF 10 plan & MF 3 plan as compared to 4D CT plan {Lungs V20 [P=0.06(MF10), P=0.08(MF3)], Heart Dmax [P=0.02(MF10), P=0.03(MF3)], Spinal cord Dmax [P=0.08(MF10), P=0.07(MF3)], Chest wall Dmax [P=0.001(MF10), P=0.037(MF3)], Great Vessel Dmax [P=0.03(MF10), P=0.045 (MF3)]}. Inclusion of 4D PET-CT MF scan 10 bins (non gated delivery) or 3 bins (gated delivery) can improvise the robustness of Lung SABR in terms of better target volume delineation, OAR doses & estimation of SUV values helping in better treatment response evaluation in follow up. While this study, first of its kind for Lung SABR, gives proof-of-concept & integration into workflow, a larger sample size evaluating 4D PET-CT MF would address the target delineation issue.

Use of 4D-CT for radiotherapy planning and reality in France: Data from a national survey

PurposeLung and some digestive tumours move during a respiratory cycle. Four-dimensional scanography (4D-CT) is commonly used in treatment planning to account for respiratory motion. Although many French radiotherapy centres are now equipped, there are no guidelines on this subject to date. We wanted to draw up a description of the use of the 4D-CT for the treatment planning in France. Methods and materialWe conducted a survey in all French radiotherapy centres between March and April 2017. ResultsOne hundred and seventy-two were contacted. The participation rate was 88.37%. The use of the 4D-CT seems to be common and concerned planning for 15.28% of kidney and adrenal cancers, 19.72% of pancreatic cancers, 27.78% of oesophageal cancers and 73.24% of lung cancers in case of normofractionated treatments. The use of the 4D-CT was also widespread in the case of stereotactic body radiation therapy: with 61.11% in the case of pulmonary irradiation and 34.72% in the case of hepatic irradiation. Many centres declared they carried out several 4D-CT for treatment planning (29, 55% in case of stereotactic body radiation therapy for lung tumours and 20% for liver tumours). Private centres tend to repeat 4D-CT more. ConclusionAlthough the use of the 4D-CT appears to be developing, it remains very heterogeneous. To date, the repetition of the 4D-CT has been very poorly studied and could be the subject of clinical studies, allowing to define in which indications and for which populations there is a real benefit.

Effect of a Device-Free Compressed Shell Fixation Method on Hepatic Respiratory Movement

Various abdominal compression methods using some mechanical devices have been reported to suppress tumor and organ motions during irradiation. In particle therapy, however, it is desirable not to place such a device near the irradiation field to prevent deterioration of dose distribution due to scattering. Therefore, we developed a device-free compressed shell fixation method and have treated liver tumors using this system. This study examined the effect of suppressing respiratory motion of the liver by this method. This was a part of clinical studies for primary hepatocellular carcinoma and metastatic liver tumor using proton beam therapy based on protocols elaborated at Nagoya Proton Therapy Center and approved by the institutional review board. 146 patients (102 males and 44 females) with fiducial markers placed in the vicinity of the target tumor prior to proton beam therapy were included in this study. The patients were fixed to the couch using a thermoplastic shell made of polycaprolactone resin (ESFORM; Engineering System Co., Ltd., Nagano, Japan). When this shell was shaped to fit the patient’s body, a beanbag weighing 2, 3, or 5 kg was placed on the epigastrium of the patient for the purpose of suppressing the respiratory movement of the liver. After the shell cooled down and the beanbag was removed, the device-free compressed shell was completed. After making the shell, the patient was instructed to breathe about 14 times per minute, and finally 4D-CT for treatment planning was taken. The magnitude of respiratory movement of the liver was calculated by analyzing the coordinates in the cranio-caudal direction of the fiducial marker from the X-ray fluoroscopic images at the time of shell molding and 4DCT for treatment planning. The magnitude of suppression indicating the overall effect of the shell fixation and breathing method instruction was calculated by subtracting the magnitude of respiratory movement at the 4D-CT from the value before making the shell for each patient. The median respiratory movement before making the shell, after fixing with the shell, and after instructing the breathing method were 14.2 mm (interquartile range (IQR), 10.7-19.8), 11.5 mm (IQR, 8.6-17.5), and 10.4 mm (IQR, 7.3-15.8), respectively. These values were significantly different in Kruskal-Wallis test. The median magnitude of suppression was 3.9 mm (IQR, 1.3-7.8). There was no significant difference in the magnitude of suppression according to the weight of the beanbag, sex, and BMI. The patient group wearing a shell made with the 5-kg beanbag had a significant variability in the value in Mann-Whitney U-test. The device-free compressed shell fixation method was efficient in suppressing respiratory movement of the liver. This method requires no device for abdominal compression, so compatibility may be good, especially for particle beam therapy.

Radiothérapie guidée par l’image dans le cancer du poumon

Image-guided radiotherapy takes place at every step of the treatment in lung cancer, from treatment planning, with fusion imaging, to daily in-room repositioning. Managing tumoral and surrounding thoracic structures motion has been allowed since the routine use of 4D computed tomography (4DCT). The integration of respiratory motion has been made with “passive” techniques based on reconstruction images from 4DCT planning, or “active” techniques adapted to the patient's breathing. Daily repositioning is based on regular images, weekly or daily, low (kV) or high (MV) energy. MRI and functional imaging also play an important part in lung cancer radiation and open the way for adaptative radiotherapy.

Influence of deformable image registration on 4D dose simulation for extracranial SBRT: A multi-registration framework study

To evaluate the influence of deformable image registration approaches on correspondence model-based 4D dose simulation in extracranial SBRT by means of open source deformable image registration (DIR) frameworks. Established DIR algorithms of six different open source DIR frameworks were considered and registration accuracy evaluated using freely available 4D image data. Furthermore, correspondence models (regression-based correlation of external breathing signal measurements and internal structure motion field) were built and model accuracy evaluated. Finally, the DIR algorithms were applied for motion field estimation in radiotherapy planning 4D CT data of five lung and five liver lesion patients, correspondence model formation, and model-based 4D dose simulation. Deviations between the original, statically planned and the 4D-simulated VMAT dose distributions were analyzed and correlated to DIR accuracy differences. Registration errors varied among the DIR approaches, with lower DIR accuracy translating into lower correspondence modeling accuracy. Yet, for lung metastases, indices of 4D-simulated dose distributions widely agreed, irrespective of DIR accuracy differences. In contrast, liver metastases 4D dose simulation results strongly vary for the different DIR approaches. Especially in treatment areas with low image contrast (e.g. the liver), DIR-based 4D dose simulation results strongly depend on the applied DIR algorithm, drawing resulting dose simulations and indices questionable.