Retrospective Analysis of Radiation-Induced Complications of Uveal Melanoma Patients Treated With Brachytherapy in the Era of Anti-VEGF

PURPOSE

To associate clinical factors and radiation doses delivered by iodine-125 plaque brachytherapy to visual outcomes and development of radiation-induced ocular complications in patients with uveal melanoma in the era of anti-vascular endothelial growth factor (anti-VEGF) injections.

DESIGN

Retrospective cohort study.

METHODS

A retrospective chart review was performed for 225 patients treated with iodine-125 brachytherapy for uveal melanoma. The effects of radiation doses (focal doses, average dose to the entire eye, and integral dose) on visual outcomes and development of radiation complications (radiation retinopathy, radiation optic neuropathy, vitreous hemorrhage, and neovascular glaucoma) were analyzed using multivariate Cox regression snalysis.

RESULTS

Median follow-up was 33.6 months (range, 12-105.6 months). Radiation retinopathy was associated with younger age, tumor distance to optic nerve <6 mm, and maximum radiation dose to fovea. Radiation optic neuropathy was associated with White race, tumor distance to optic nerve <6 mm, and integral radiation dose. Vitreous hemorrhage was associated with White race and integral radiation dose. Incidence of neovascular glaucoma was low in our study, with 2 patients (0.9%) developing the complication. Of the 123 patients who developed radiation retinopathy, 82 patients (66.7% of radiation retinopathy patients, 37.3% of total patients) received anti-VEGF injections.

CONCLUSIONS

Our study found multiple associations between radiation doses and complications as well as visual outcomes on multivariate analysis. Given that the majority of our patients who developed radiation retinopathy received anti-VEGF injections, our study helps to illustrate the course and progression of radiation-induced complications in the new era of anti-VEGF.

A feasibility study of utilizing a cadaveric training model for novel robotic bladder cancer brachytherapy techniques

PURPOSE

The current standard of care for muscle-invasive bladder cancer is neoadjuvant chemotherapy followed by radical cystectomy with lymph node dissection. Although this treatment provides therapeutic benefit, it is associated with notable morbidity. Bladder sparing techniques, such as concurrent chemo-radiation, are less invasive and prioritize organ preservation in individuals with invasive bladder cancer and offer comparable disease control. High-dose-rate brachytherapy is an emerging paradigm in the management of muscle-invasive bladder cancer. During high-dose-rate brachytherapy, radioactive sources are introduced to the area of the primary tumor through specialized catheters. The specific placement of brachytherapy catheters results in heightened effectiveness of the radiation treatment with less radiation damage to surrounding structures. For bladder-sparing therapies such as brachytherapy to rival radical cystectomy, these techniques need to be refined further by radiation oncologists.

PROCEDURE

One such modality for developing and practicing these techniques is the use of cadaveric models in innovation-focused clinical training facilities, which provide a simulated sterile surgical environment without the concern for extending intraoperative time.

FINDINGS AND CONCLUSIONS

The objective of this technical note is to demonstrate how clinical training facilities such as the Houston Methodist Institute for Technology, Innovation & Education are ideal for the development, testing, and training of novel brachytherapy techniques using cadaveric models. By utilizing a network of similarly innovative training centers, research and development of brachytherapy techniques can be expedited, and novel bladder-sparing treatment methods can be implemented as the standard of care for bladder cancer.

Enhancement of Long-Term External-Internal Correlation by Phase-Shift Detection and Correction Based on Concurrent External Bellows and Internal Navigator Signals

Purpose

The purpose of this study was to enhance the correlation between external and internal respiratory motions by dynamically determining and correcting the patient-specific phase shift between external and internal respiratory waveforms acquired concurrently during respiratory-correlated 4-dimensional magnetic resonance imaging scans.

Methods and Materials

Internal-navigator and external-bellows waveforms were acquired simultaneously during 6- to 15-minute respiratory-correlated 4-dimensional magnetic resonance imaging scans in 10 healthy participants under an institutional review board–approved protocol. The navigator was placed at the right lung–diaphragm interface, and the bellows were placed ∼5 cm inferior to the sternum. Three segments of each respiratory waveform, at the beginning, middle, and end of a scan, were analyzed. Three phase-domain methods were employed to estimate the phase shift, including analytical signal analysis, phase-space oval fitting, and principal component analysis. A robust strategy for estimating the phase shift was realized by combining these methods in a weighted average and by eliminating outliers (>2 σ) caused by breathing irregularities. Whether phase-shift correction affects the external-internal correlation was evaluated. The cross-correlation between the 2 waveforms in the time domain provided an independent check of the correlation enhancement.

Results

Phase-shift correction significantly enhanced the external-internal correlation in all participants across the entire 6- to 15-minute scans. On average, the correlation increased from 0.45 ± 0.28 to 0.85 ± 0.15 for the combined method. The combined method exhibited a 99.5% success rate and revealed that the phase of the external waveform leads that of the internal waveform in all 10 participants by 57 ^o ± 17^o (1.6 ± 0.5 bins) on average. Seven participants exhibited highly reproducible phase shifts over time, evidenced by standard deviations (σ) < 4^o, whereas 8^o < σ < 12^o in the remaining 3 participants. Regardless, phase-shift correction significantly improved the correlation in all participants.

Conclusions

Correcting the phase shift estimated by the phase-domain methods provides a new approach for enhancing the correlation between external and internal respiratory motions. This strategy holds promise for improving the accuracy of respiratory-gated radiation therapy.

Direct Comparison of Respiration-Correlated Four-Dimensional Magnetic Resonance Imaging Reconstructed Using Concurrent Internal Navigator and External Bellows

PURPOSE

To compare the image quality of amplitude-binned 4-dimensional magnetic resonance imaging (4DMRI) reconstructed using 2 concurrent respiratory (navigator and bellows) waveforms.

METHODS AND MATERIALS

A prospective, respiratory-correlated 4DMRI scanning program was used to acquire T2-weighted single-breath 4DMRI images with internal navigator and external bellows. After a 10-second training waveform of a surrogate signal, 2-dimensional MRI acquisition was triggered at a level (bin) and anatomic location (slice) until the bin-slice table was completed for 4DMRI reconstruction. The bellows signal was always collected, even when the navigator trigger was used, to retrospectively reconstruct a bellows-rebinned 4DMRI. Ten volunteers participated in this institutional review board-approved 4DMRI study. Four scans were acquired for each subject, including coronal and sagittal scans triggered by either navigator or bellows, and 6 4DMRI images (navigator-triggered, bellows-rebinned, and bellows-triggered) were reconstructed. The simultaneously acquired waveforms and resulting 4DMRI quality were compared using signal correlation, bin/phase shift, and binning motion artifacts. The consecutive bellows-triggered 4DMRI scan was used for indirect comparison.

RESULTS

Correlation coefficients between the navigator and bellows signals were found to be patient-specific and inhalation-/exhalation-dependent, ranging from 0.1 to 0.9 because of breathing irregularities (>50% scans) and commonly observed bin/phase shifts (-1.1 ± 0.6 bin) in both 1-dimensional waveforms and diaphragm motion extracted from 4D images. Navigator-triggered 4DMRI contained many fewer binning motion artifacts at the diaphragm than did the bellows-rebinned and bellows-triggered 4DMRI scans. Coronal scans were faster than sagittal scans because of the fewer slices and higher achievable acceleration factors.

CONCLUSIONS

Navigator-triggered 4DMRI contains substantially fewer binning motion artifacts than bellows-rebinned and bellows-triggered 4DMRI, primarily owing to the deviation of the external from the internal surrogate. The present study compared 2 concurrent surrogates during the same 4DMRI scan and their resulting 4DMRI quality. The navigator-triggered 4DMRI scanning protocol should be preferred to the bellows-based, especially for coronal scans, for clinical respiratory motion simulation.

A Novel Respiratory Motion Perturbation Model Adaptable to Patient Breathing Irregularities

PURPOSE

To develop a physical, adaptive motion perturbation model to predict tumor motion using feedback from dynamic measurement of breathing conditions to compensate for breathing irregularities.

METHODS AND MATERIALS

A novel respiratory motion perturbation (RMP) model was developed to predict tumor motion variations caused by breathing irregularities. This model contained 2 terms: the initial tumor motion trajectory, measured from 4-dimensional computed tomography (4DCT) images, and motion perturbation, calculated from breathing variations in tidal volume (TV) and breathing pattern (BP). The motion perturbation was derived from the patient-specific anatomy, tumor-specific location, and time-dependent breathing variations. Ten patients were studied, and 2 amplitude-binned 4DCT images for each patient were acquired within 2 weeks. The motion trajectories of 40 corresponding bifurcation points in both 4DCT images of each patient were obtained using deformable image registration. An in-house 4D data processing toolbox was developed to calculate the TV and BP as functions of the breathing phase. The motion was predicted from the simulation 4DCT scan to the treatment 4DCT scan, and vice versa, resulting in 800 predictions. For comparison, noncorrected motion differences and the predictions from a published 5-dimensional model were used.

RESULTS

The average motion range in the superoinferior direction was 9.4 ± 4.4 mm, the average ΔTV ranged from 10 to 248 mm³ (-26% to 61%), and the ΔBP ranged from 0 to 0.2 (-71% to 333%) between the 2 4DCT scans. The mean noncorrected motion difference was 2.0 ± 2.8 mm between 2 4DCT motion trajectories. After applying the RMP model, the mean motion difference was reduced significantly to 1.2 ± 1.8 mm (P=.0018), a 40% improvement, similar to the 1.2 ± 1.8 mm (P=.72) predicted with the 5-dimensional model.

CONCLUSIONS

A novel physical RMP model was developed with an average accuracy of 1.2 ± 1.8 mm for interfraction motion prediction, similar to that of a published lung motion model. This physical RMP was analytically derived and is able to adapt to breathing irregularities. Further improvement of this RMP model is under investigation.