Respiratory Management Techniques Research Articles

Clinical Outcomes of Stereotactic Body Radiation Therapy across Treatment Platforms Employing Varied Approaches to Respiratory Management at a Single Institution

<h3>Purpose/Objective(s)</h3> Stereotactic Body Radiation Therapy (SBRT) has been the standard of care for early-stage non-small cell lung cancer patients who do not undergo surgery since soon after the publication of RTOG 0236. Since then, various linear accelerator platforms have been employed with a variety of approaches to respiratory management, treatment planning and treatment delivery. Comparisons of local control and survival end points using a variety of treatment platforms in addition to respiratory management techniques have not been reported. Here, we present the results of our analysis of clinical outcomes at a single institution across multiple treatment platforms representative of the available technology since the widespread adoption of SBRT for early-stage lung cancer. <h3>Materials/Methods</h3> Consecutive patients who underwent SBRT for early-stage lung cancer between 2011 and 2018 at a single institution were retrospectively analyzed. Treatments were planned and delivered with standardized simulation, dose and fractionation per institutional guidelines. Overall Survival (OS), Local Control (LC), Distant Metastasis Free Survival (DMFS), and Progression Free Survival (PFS) were calculated for the entire cohort. Log rank comparisons of all survival endpoints were then calculated by treatment platform: stereoscopic orthogonal kV x-ray localization with conventional Linac (Linac1), volumetric cone beam CT localization with conventional Linac (Linac2), and megavoltage CT with helical tomotherapy (Linac3). Comparisons were also performed by respiratory management technique: free breath (FB), breath hold (BH) or end expiration respiratory gating (RG). <h3>Results</h3> A total of 240 patients were included in the analysis. Treatment platform utilization was well balanced in the group: 28% on Linac1, 32% on Linac2, and 40% on Linac3. The majority of patients were treated with FB, 72%. Median OS for the entire cohort was 50 months. The crude rate of local recurrence was 7%. Kaplan-Meier estimate of LC for the entire cohort was 94% at 3 years. The median time to local recurrence was not reached. LC was not impacted by treatment platform, p = 0.897, or respiratory management technique, p = 0.623. Comparisons by treatment platform and respiratory management technique revealed no significant differences in OS, DMFS, and PFS. <h3>Conclusion</h3> Irrespective of treatment platform or approach to respiratory management, SBRT remains highly effective at providing durable LC in patients with early-stage lung cancer. Differences in treatment delivery platform and respiratory management do not significantly influence other disease control and survival outcomes.

Evaluation of delivered dose to a moving target by 4D dose reconstruction in gated volumetric modulated arc therapy.

PurposeTo develop a 4D dose reconstruction method and to evaluate the delivered dose in respiratory-gated volumetric modulated arc therapy (VMAT).Materials and methodsA total 112 treatment sessions of gated VMAT for 30 stereotactic body radiotherapy (SBRT) patients (10 lung, 10 liver, and 10 pancreas) were evaluated. For respiratory-gated SBRT, 4DCT was acquired, and the CT data at the end-exhale phase was used for a VMAT plan. The delivered dose was reconstructed using a patient’s respiratory motion and machine motion acquired during the beam delivery. The machine motion was obtained from the treatment log file, while the target position was estimated from an external respiratory marker position. The target position was divided into 1-mm position bins, and sub-beams with beam isocenters corresponding to each position bin were created in a motion mimicking plan, reflecting motion data including MLC leaf positions and gantry angle and target position data during beam treatment. The reconstructed 4D dose was compared with the dose of the original plan using these dosimetric parameters; the maximum dose (Dmax) and mean dose (Dmean) of gross target volume (GTV) or organs at risk (spinal cord, esophagus, heart, duodenum, kidney, spinal cord, and stomach). The minimum dose (Dmin) to GTV was also calculated to verify cold spots in tumors.ResultsThere was no significant difference of dose parameters regard to the GTV in all tumors. For the liver cases, there were significant differences in the Dmax of duodenum (-4.2 ± 1.4%), stomach (-3.5 ± 4.2%), left kidney (-4.1 ± 2.8%), and right kidney (-3.2 ± 1.3%), and in the Dmean of duodenum (-3.8 ± 1.4%), stomach (-3.9 ± 2.2%), left kidney (-3.1 ± 2.8%), and right kidney (-4.1 ± 2.6%). For the pancreas cases, there were significant differences in the Dmax of stomach (2.1 ± 3.0%), and in the Dmean of liver (1.5 ± 0.6%), duodenum (-1.0 ± 1.4%), stomach (2.1 ± 1.6%), and right kidney (-1.3 ± 0.9%). The average gamma pass rates were 97.6 ± 4.8% for lung cases, 99.6 ± 0.5% for liver cases, and 99.5 ± 0.5% for pancreas cases. Most cases showed insignificant dose variation, with gamma pass rates higher than 98%, except for two lung cases with gamma pass rates of 86.9% and 90.6%. The low gamma pass rates showed larger global motion ranges resulting from the baseline shift during beam delivery.ConclusionThe actual delivered dose in thoracic and abdominal VMAT under breathing motion was verified by 4D dose reconstruction using typical treatment equipment and software. The proposed method provides a verification method for the actual delivered dose and could be a dosimetric verification QA tool for radiation treatment under various respiratory management techniques.

Poster - Thur Eve - 11: A realistic respiratory trace generator and its application to respiratory management techniques.

Respiratory motion complicates radiotherapy treatment of thoracic and abdominal tumours. Simplified respiratory motions such as sinusoidal and single patient traces are often used to determine the impact of motion on respiratory management techniques in radiotherapy. Such simplifications only accurately model a small portion of patients, as most patients exhibit variability and irregularity beyond these models. We have preformed a comprehensive analysis of respiratory motion and developed a software tool that allows for explicit inclusion of variability. We utilize our realistic respiratory generator to customize respiratory traces to test the robustness of the estimate of internal gross target volumes (IGTV) by 4DCT and CBCT. We confirmed that good agreement is found between 4DCT and CBCT for regular breathing motion. When amplitude variability was introduced the accuracy of the estimate slightly, but the absolute differences were still < 3 mm for both modalities. Poor agreement was shown with the addition of baseline drifts. Both modalities were found to underestimate the IGTV by as much as 30% for 4DCT and 25% for CBCT. Both large and small drifts deteriorated the estimate accuracy. The respiratory trace generator was advantageous for examining the difference between 4DCT and CBCT IGTV estimation under variable motions. It provided useful implementation abilities to test specific attributes of respiratory motion and detected issues that were not seen with the regular motion studies. This is just one example of how the respiratory trace generator can be utilized to test applications of respiratory management techniques.

Perioperative Complications in Patients with End-Stage Renal Disease Undergoing Pulmonary Resection

Introduction: Among the perioperative complications encountered in patients with renal failure, there is a high risk of events such as heart failure and increased susceptibility to infection. Herein, we report the results of our investigation of perioperative management in patients with chronic renal failure who underwent a pulmonary resection. Methods: The subjects were 21 hemodialysis patients with renal failure who underwent pulmonary resection for lung cancer. We retrospectively investigated their clinical characteristics and perioperative management. The patients were classified into two groups; those with and without symptoms of postoperative acute heart failure. Intergroup comparisons of preoperative examinations and management were performed. Results: The most common preoperative comorbidity was cardiac complications, which occurred at a high incidence of 38%. There were no serious perioperative complications. In contrast, postoperative complications associated with renal failure were numerous, including acute heart failure in 3 (14%) and hyperkalemia in 2 (9.5%). We concluded that preoperative respiratory function, intraoperative fluid infusion volume, and preoperative cardiac comorbidities are potential risk factors for postoperative heart failure in such patients. Conclusion: Although there were no cases with perioperative mortality, postoperative complications were encountered, including heart failure and hyperkalemia, suggesting that more stringent cardiovascular and respiratory management techniques are necessary.

MO‐FF‐A2‐06: Effects of Lung Tumor Motion On Rapid Arc Treatment Technique

Purpose/Objective: To determine the error due to lung tumor motion on dose distribution delivered by Rapid Arc (RA) treatment technique, a procedure also known as volumetric modulated arc therapy. Materials/Methods: An indigenously developed dynamic phantom was set in linear sinusoidal motion in cranio‐caudal direction with amplitude of 2cm and at a frequency of 15 cycles/minute. A RA treatment plan was optimized for and delivered to the phantom containing a simulated target and critical organs. The treatment plan was executed for 30 fractions to the dynamic phantom, started at random initial breathing phases. GAF‐Chromic films embedded in the moving phantom in the coronal plane at the isocenter level were used to capture the dose distribution. Results: (i) ROI as PTV: When the daily dose distributions were compared against the static distribution, dose variation of 10% to 20% was observed near the field edges and 5% to 10% dose difference was observed elsewhere. Similar results were observed when comparing the dose distribution averaged for 30 fractions against the static distribution. (ii) ROI as CTV (simulated target): It is observed that on a day‐to‐day basis the standard deviation of the dose to a given pixel could be as high as 4.5% to 6.5%. Also, the mean, median, and modal dose varies inter‐fractionally with a standard deviation of 5.62%, 5.61%, and 5.73% respectively. When comparing the averaged dose distribution with the static distribution, dose variation ranging from 5% to 10% was observed. Also, the mean, median and modal doses were reduced by 6.35%, 6.45% and 6.87% respectively, compared with static distribution. Conclusion: Our study indicates that, if respiratory management techniques were not implemented, RA procedures for lung cancer treatment can result in underdosage, so this error should be measured and accounted for as part of the patient specific quality assurance.

SU‐GG‐J‐183: The Use of Video Feedback for the Improvement of Respiratory Gating Radiation Treatments

Purpose: Breath‐hold respiratory gating is currently being used to improve the quality of radiotherapy, especially for sites subject to internal motion. One technical challenge that exists is patient regulation of respiration. Typically, the radiation therapist verbally coaches the patient during treatment. This may not be the most efficient or accurate practice, since the patient is receiving delayed commands based on secondary cues. As such, a video feedback system has been implemented. During treatment, a live plot of breathing amplitude versus time is displayed to the patient for first‐hand adjustments. Method and Materials: Varian's RPM system was used to track the patient's respiratory motion. i‐O Display Systems' i‐Glasses, a headset displaying video feed, was worn by the patient for visual feedback. The RPM software interface was displayed in this headset. Patients with treatment sites in the abdomen and thorax, such as lung, liver, and breast cancer, were of interest in this study. Those who were candidates for breath‐hold gating treatment were selected for either video feedback or verbal coaching respiratory management techniques, based on the patient's physical and mental condition. Results: The accuracy and efficiency of the video feedback system, using i‐Glasses, was compared to the more conventional system of audio commands given by the therapist. Accuracy was based on the magnitude of motion within the threshold, while efficiency was based on beam‐on time during a particular field of treatment. Conclusion: Video feedback proved better accuracy and efficiency of treatment compared to audio coaching. However, not all patients were candidates for the video feedback system. Some patients did not understand what the plot of amplitude versus time meant. Some patients could not resolve the plot, due to poor eye sight. Other patients found the headset to be uncomfortable during treatment. These problems are currently being taken into consideration for future studies.

MO‐A‐T‐6C‐01: Managing Respiratory Motion in Radiation Oncology

Intrafraction motion is an issue that is becoming increasingly important in the era of image‐guided radiotherapy. Intrafraction motion can be caused by the respiratory, skeletal muscular, cardiac and gastrointestinal systems. Of these three systems, much research and development to date has been directed towards accounting for respiratory motion. Respiratory motion causes deleterious effects during the imaging, planning and delivery of radiation therapy. The management of respiratory motion in radiation oncology is the subject of this continuing education class which aims to advise medical physicists involved in the external beam radiation therapy of patients with thoracic and abdominal tumors that move due to respiratory motion. This session will describe the magnitude of respiratory motion, discuss radiotherapy‐specific problems caused by respiratory motion, explain techniques that explicitly manage respiratory motion during radiotherapy and give recommendations in the application of these techniques for patient care, including quality assurance guidelines for these devices. The techniques to be described include respiratory gating, breath‐hold techniques, forced shallow breathing and respiration‐synchronized radiotherapy. This session intends to reflect the current state of the scientific understanding and technical methodology in imaging, treatment planning and radiation delivery for radiation oncology patients with tumors affected by respiratory motion. Issues requiring further study will also be raised. The educational objectives of this course include:1. Appreciate the effects of respiratory motion during the imaging, planning and delivery of radiotherapy.2. Learn the various techniques that have been clinically applied to manage respiratory motion.3. Understand the general and specific quality assurance requirements for different respiratory management techniques.4. Describe the clinical process for managing patients with tumors affected by respiratory motion.