Respiration-Induced Intraorgan Deformation of the Liver: Implications for Treatment Planning in Patients Treated With Fiducial Tracking.

Stereotactic body radiation therapy is a well-tolerated modality for the treatment of primary and metastatic liver lesions, and fiducials are often used as surrogates for tumor tracking during treatment. We evaluated respiratory-induced liver deformation by measuring the rigidity of the fiducial configuration during the breathing cycle. Seventeen patients, with 18 distinct treatment courses, were treated with stereotactic body radiosurgery using multiple fiducials. Liver deformation was empirically quantified by measuring the intrafiducial distances at different phases of respiration. Data points were collected at the 0%, 50%, and 100% inspiration points, and the distance between each pair of fiducials was measured at the 3 phases. The rigid body error was calculated as the maximum difference in the intrafiducial distances. Liver disease was calculated with Child-Pugh score using laboratory values within 3 months of initiation of treatment. A peripheral fiducial was defined as within 1.5 cm of the liver edge, and all other fiducials were classified as central. For 5 patients with only peripheral fiducials, the fiducial configuration had more deformation (average maximum rigid body error 7.11 mm, range: 1.89-11.35 mm) when compared to patients with both central and peripheral and central fiducials only (average maximum rigid body error 3.36 mm, range: 0.5-9.09 mm, P = .037). The largest rigid body errors (11.3 and 10.6 mm) were in 2 patients with Child-Pugh class A liver disease and multiple peripheral fiducials. The liver experiences internal deformation, and the fiducial configuration should not be assumed to act as a static structure. We observed greater deformation at the periphery than at the center of the liver. In our small data set, we were not able to identify cirrhosis, which is associated with greater rigidity of the liver, as predictive for deformation. Treatment planning based only on fiducial localization must take potential intraorgan deformation into account

A Novel Deep Learning Framework for Internal Gross Target Volume Definition from 4D Computed Tomography of Lung Cancer Patients

In this paper, we study the reliability of a novel deep learning framework for internal gross target volume (IGTV) delineation from four-dimensional computed tomography (4DCT), which is applied to patients with lung cancer treated by Stereotactic Body Radiation Therapy (SBRT). 77 patients who underwent SBRT followed by 4DCT scans were incorporated in a retrospective study. The IGTV_DL was delineated using a novel deep machine learning algorithm with a linear exhaustive optimal combination framework, for the purpose of comparison, three other IGTVs base on common methods was also delineated, we compared the relative volume difference (RVI), matching index (MI) and encompassment index (EI) for the above IGTVs. Then, multiple parameter regression analysis assesses the tumor volume and motion range as clinical influencing factors in the MI variation. Experimental results demonstrated that the deep learning algorithm with linear exhaustive optimal combination framework has a higher probability of achieving optimal MI compared with other currently widely used methods. For patients after simple breathing training by keeping the respiratory frequency in 10 BMP, the four phase combinations of 0%, 30%, 50% and 90% can be considered as a potential candidate for an optimal combination to synthesis IGTV in all respiration amplitudes

Dosimetric impact of gastrointestinal air column in radiation treatment of pancreatic cancer

OBJECTIVE: Dosimetric evaluation of air column in gastrointestinal (GI) structures in intensity modulated radiation therapy (IMRT) of pancreatic cancer. METHODS: Nine sequential patients were retrospectively chosen for dosimetric analysis of air column in the GI apparatus in pancreatic cancer using cone beam CT (CBCT). The four-dimensional CT (4DCT) was used for target and organs at risk (OARs) and non-coplanar IMRT was used for treatment. Once a week, these patients underwent CBCT for air filling, isocentre verification and dose calculations retrospectively. RESULTS: Abdominal air column variation was as great as ±80% between weekly CBCT and 4DCT. Even with such a large air column in the treatment path for pancreatic cancer, changes in anteroposterior dimension were minimal (2.8%). Using IMRT, variations in air column did not correlate dosimetrically with large changes in target volume. An average dosimetric deviation of mere -3.3% and a maximum of -5.5% was observed. CONCLUSION: CBCT revealed large air column in GI structures; however, its impact is minimal for target coverage. Because of the inherent advantage of segmentation in IMRT, where only a small fraction of a given beam passes through the air column, this technique might have an advantage over 3DCRT in treating upper GI malignancies where the daily air column can have significant impact. Advances in knowledge: Radiation treatment of pancreatic cancer has significant challenges due to positioning, imaging of soft tissues and variability of air column in bowels. The dosimetric impact of variable air column is retrospectively studied using CBCT. Even though, the volume of air column changes by ± 80%, its dosimetric impact in IMRT is minimum

Respiratory motion and its compensation possibilities in the modern external beam radiotherapy of lung cancer

The aim of this paper is to present a systematic review of the current characteristics and recent development of commercially available respiratory motion solutions and their compensation possibilities in the external beam radio­therapy treatment of lung cancer. The most commonly used X-ray and radiotherapeutic technologies are presented, as well as their division into pre-treatment methods and intra-treatment verification. The article discusses the most important technological achievements that allow radiation to be safely applied in the lung region and reports the potential advantages and limitations of each. Finally, it presents details concerning selected research trends and problems related to motion compensation

Dynamic-arc respiratory-gated stereotactic radiotherapy — technique presentation

Main advancements in radiation treatment in recent years have included the introduction of dynamic techniques and 4D radiotherapy. The treatment of movable tumors relies on two important techniques: gating and tracking. The limitation of the former is the relatively short duration of the respiratory phase during which the radiation can be delivered and the need to teach the patient to breathe in accordance with the correct pattern. At the same time, certain clinical situations require the use of dynamic techniques. Intensity modulated radiotherapy (IMRT), combined with gantry rotation, forms the basis for the VMAT technique. The procedure usually takes a shorter time to complete than other dynamic techniques, which considerably improves patient comfort. The recently introduced True BeamTM accelerator employs all the latest innovations in terms of dose-rate modeling and respiratory gating

Patient’s respiratory curve synchronization by visual feedback application

In radiation therapy, irradiation systems are focused to target using a CT scan. In the case of target which is moving by breathing, the CT scan is performed in the patient's inhale or exhale. However, ensuring that the patient is breathing same way as during the CT scan is really problematic. This project deals with the issue by using special respiratory sensor and software application, which presents respiratory curve to patient via video goggles. During the planning CT scan, the patient's breathing curve is captured by a special sensor and is displayed using a software application that allows insertion of the limit markers, which are represented by stripes, which indicate how much the patient inhaled. The application has possibilities to store the location of stripes during CT scan and retrieve it again during a scheduled radiotherapy, when patient can surely breathe the same way as during a planning CT scan. The application was developed, implemented and successfully tested at the Oncology Clinic of the Faculty Hospital Ostrava

Effect of MLC tracking latency on conformal volumetric modulated arc therapy (VMAT) plans in 4D stereotactic lung treatment

AbstractBackground and purposeThe latency of a multileaf collimator (MLC) tracking system used to overcome respiratory motion causes misalignment of the treatment beam with respect to the gross tumour volume, which may result in reduced target coverage. This study investigates the magnitude of this effect.Material and methodsSimulated superior–inferior breathing motion was used to construct histograms of isocentre offset with respect to the gross tumour volume (GTV) for a variety of tracking latencies. Dose distributions for conformal volumetric modulated arc therapy (VMAT) arcs were then calculated at a range of offsets and summed according to these displacement histograms. The results were verified by delivering the plans to a Delta4 phantom on a motion platform.ResultsIn the absence of an internal target margin, a tracking latency of 150ms reduces the GTV D95% by approximately 2%. With a margin of 2mm, the same drop in dose occurs for a tracking latency of 450ms. Lung V13Gy is unaffected by a range of latencies. These results are supported by the phantom measurements.ConclusionsAssuming that internal motion can be modelled by a rigid translation of the patient, MLC tracking of conformal VMAT can be effectively accomplished in the absence of an internal target margin for substantial breathing motion (4s period and 20mm peak–peak amplitude) so long as the system latency is less than 150ms

Navigator channel adaptation to reconstruct three dimensional heart volumes from two dimensional radiotherapy planning data

BACKGROUND: Biologically-based models that utilize 3D radiation dosimetry data to estimate the risk of late cardiac effects could have significant utility for planning radiotherapy in young patients. A major challenge arises from having only 2D treatment planning data for patients with long-term follow-up. In this study, we evaluate the accuracy of an advanced deformable image registration (DIR) and navigator channels (NC) adaptation technique to reconstruct 3D heart volumes from 2D radiotherapy planning images for Hodgkin's Lymphoma (HL) patients. METHODS: Planning CT images were obtained for 50 HL patients who underwent mediastinal radiotherapy. Twelve image sets (6 male, 6 female) were used to construct a male and a female population heart model, which was registered to 23 HL "Reference" patients' CT images using a DIR algorithm, MORFEUS. This generated a series of population-to-Reference patient specific 3D deformation maps. The technique was independently tested on 15 additional "Test" patients by reconstructing their 3D heart volumes using 2D digitally reconstructed radiographs (DRR). The technique involved: 1) identifying a matching Reference patient for each Test patient using thorax measurements, 2) placement of six NCs on matching Reference and Test patients' DRRs to capture differences in significant heart curvatures, 3) adapting the population-to-Reference patient-specific deformation maps to generate population-to-Test patient-specific deformation maps using linear and bilinear interpolation methods, 4) applying population-to-Test patient specific deformation to the population model to reconstruct Test-patient specific 3D heart models. The percentage volume overlap between the NC-adapted reconstruction and actual Test patient's true heart volume was calculated using the Dice coefficient. RESULTS: The average Dice coefficient expressed as a percentage between the NC-adapted and actual Test model was 89.4 ± 2.8%. The modified NC adaptation technique made significant improvements to the population deformation heart models (p = 0.01). As standard evaluation, the residual Dice error after adaptation was comparable to the volumetric differences observed in free-breathing heart volumes (p = 0.62). CONCLUSIONS: The reconstruction technique described generates accurate 3D heart models from limited 2D planning data. This development could potentially be used to retrospectively calculate delivered dose to the heart for historically treated patients and thereby provide a better understanding of late radiation-related cardiac effects

Impact of respiratory motion on IMRT (Intensity Modulated Radiation Therapy) of the chest wall in post-mastectomy breast cancer patients: A Dosimetric comparison with 3D conformal radiotherapy

INTRODUCTION: Radiotherapy forms an essential part of breast cancer treatment. The technology of radiotherapy has developed to give very precise dose to target region with sparing of critical organs. But irradiation of thorax is always influenced by respiratory motion. The influence of respiratory motion on breast cancer radiotherapy and choice of technology based on this has not been studied in detail. We intend to study the effect of respiration on IMRT and 3D conformal radiotherapy of breast cancer. AIM AND OBJECTIVES: To study the dosimetric effect of respiratory motion on intensity modulated radiotherapy to the chest wall in patients with carcinoma breast and compare it with the respiratory motion effect on 3D conformal tangents based plan. MATERIALS AND METHODS: The respiratory parameters of 10 study participants and their dosimetric data on target coverage and dose to organs at risk with IMRT (intensity modulated radiotherapy) and 3D CRT (3D conformal radiotherapy) plans in free breathing, normal inspiration and normal expiration were compared and analysed. RESULTS: Respiratory motion resulted in a significant fall in target coverage (V95) with IMRT when compared to 3D-DRT to chest wall (p=0.007&0.002 vs. 0.174&0.063 with inspiration and expiration respectively) by about 4-5%. Dose inhomogeneity increased in the target volume with respiration, and its minimal dose was decreased by 28% with IMRT in comparison to 14% with 3D-CRT. An analysis of the impact of chest wall movement during IMRT demonstrated that respiration increased the volume of target receiving high radiation dose (11.79% & 20.07% in inspiration and expiration respectively). Evaluation of the dose to organs at risk revealed that there was an overall increasein dose with respiration in IMRT more than 3D-CRT. However, the mean cardiac dose in left sided breast cancer patients crossed the limit of V25 0.68 L and chest wall expansion of >0.5 cm had a poor target coverage with respiration in IMRT (though not significant statistically). The difference in target under-coverage between 3D CRT and IMRT was 11.2% & 5.08% with inspiration and expiration respectively, when tidal volume was >0.68 L. CONCLUSIONS: The dose delivered to target volume is dependent on respiratory movement of chest wall in IMRT technique. It is important to consider the respiratory parameters of a patient prior to choosing the technique of post- mastectomy radiotherapy

Comparison of four dimensional computed tomography and magnetic resonance imaging in abdominal radiotherapy planning

Background and Purpose: Four-dimensional (4D) computed tomography (CT) is widely used in radiotherapy (RT) planning and remains the current standard for motion evaluation. We assess a 4D magnetic resonance imaging (MRI) sequence in terms of motion and image quality in a phantom, healthy volunteers and patients undergoing RT. Materials and Methods: The 4D-MRI sequence is a prototype T1-weighted 3D gradient echo with radial acquisition with self-gating. The accuracy of the 4D-MRI respiratory sorting based method was assessed using a MRICT compatible respiratory simulation phantom. In volunteers, abdominal viscera were evaluated for artefact, noise, structure delineation and overall image quality using a previously published four-point scoring system. In patients undergoing abdominal RT, the tumour (or a surrogate) was utilized to assess the range of motion on both 4D-CT and 4D-MRI. Furthermore, imaging quality was evaluated for both 4D-CT and 4D-MRI. Results: In phantom studies 4D-MRI demonstrated amplitude of motion error of less than 0.2mm for five, seven and ten bins. 4D-MRI provided excellent image quality for liver, kidney and pancreas. In patients, the median amplitude of motion seen on 4D-CT and 4D-MRI was 11.2mm (range 2.8-20.3 mm) and 10.1mm (range 0.7-20.7 mm) respectively. The median difference in amplitude between 4D-CT and 4D-MRI was −0.6mm (range −3.4-5.2 mm). 4D-MRI demonstrated superior edge detection (median score 3 versus 1) and overall image quality (median score 2 versus 1) compared to 4D-CT. Conclusions: The prototype 4D-MRI sequence demonstrated promising results and may be used in abdominal targeting, motion gating, and towards implementing MRI-based adaptive RT