Clinical Implementation of Weak Magnetic Field Generator in Radiation Therapy

PURPOSE/OBJECTIVE(S)

The application of weak magnetic fields may improve radiation therapy efficacy by manipulating the free radical activity induced by radiation to optimize tumor death. Once the device is commercially available, we will conduct clinical trials to determine the clinical impact of the weak magnetic field. However, the magnetic field generator (MFG) restricts Linac gantry rotation to approximately 180° and this limitation may limit treatment plan quality. This work is a continuation of an ongoing study to determine if the gantry angle restrictions can be compensated for during treatment planning.

MATERIALS/METHODS

Previous work has demonstrated the feasibility for GBM cases. For this work, 10 prostate cancer treatment plans were retrospectively replanned using only coplanar arcs that spanned from 90° to 270° (half-arcs). The prescriptions were 60 Gy for 6 patients, 55.8 Gy for 2 patients, 54 Gy for 1 patient, and 40.05 Gy for 1 patient. The prescription doses were delivered to 95% of the planning target volume (PTV = GTV + 2 cm). The critical structure doses were compared to determine if clinically equivalent plans could be delivered using half-arcs.

RESULTS

The dose criteria that were met by the clinical plans were also met by the half-arc plans except for the cases shown in Table 1. Table 1: Doses that did not meet criteria CONCLUSION: The half-arc plans were able to deliver clinically equivalent dose distributions as the clinical treatment plans. This provides continuing evidence that clinical trials will be able to be developed to evaluate the use of weak magnetic fields for radiation therapy.

Surgical Outcomes in Patients Treated with 5-Day Preoperative Radiotherapy for Soft Tissue Sarcoma

PURPOSE/OBJECTIVE(S)

Treatment for high-risk soft tissue sarcoma (STS) of the extremity/trunk includes radiation therapy (RT) and surgical resection. Initial results of a phase 2 single arm trial of 5-day preoperative RT demonstrated acceptable safety and local control. Here we report an update of detailed surgical outcomes among patients treated with 5-day preoperative RT alone on the original phase 2 study, as well as an ongoing expansion cohort.

MATERIALS/METHODS

We conducted an updated analysis of surgical complications from a previously reported phase 2 trial of 50 patients with high-risk extremity/trunk STS treated with 5-day preoperative RT (30 Gy over 5 consecutive daily fractions) and surgery. The current analysis includes additional patients from an ongoing IRB-approved expansion cohort of the phase 2 study, which was designed to compare wound complication rates between patients receiving neoadjuvant chemotherapy and those receiving RT alone. However, given that the primary endpoint of this study has not matured, here we present only the data for patients treated with 5-day preoperative RT alone (n = 44; data cutoff date: February 17, 2022). We generated a secure prospective patient database and extracted data including demographic variables, cancer characteristics and surgical outcomes. Minimum post-operative follow-up was 90 days. Statistical analysis was performed using R (v4.2).

RESULTS

From a total of 94 patients, mean age was 57 (17-90), 40 (42.5%) were female, 10 (10.6%) were diabetic and 8 patients (8.5%) were active smokers or had a >10 pack-year smoking history. Median follow up was 24 months (IQR 10.6-41.8). The most common histologic diagnosis was undifferentiated pleomorphic sarcoma (n = 38, 40.4%). The most common location was the lower extremity (n = 57, 60.6%). Overall, 26 (27.7%) patients experienced surgical wound complications. In the lower extremity, wound complications occurred in 18 patients (31.6%). In all other sites, wound complications occurred in 8 patients (21.6%) (p = 0.41). Twenty-seven (28.7%) cases required local tissue advancement for primary closure and 12 of these patients (44.4%) experienced a wound complication (p = 0.04). Wound dehiscence occurred in 18 patients at a median duration of 43.5 days (IQR 40.3-85.3) from surgery, comprising 69.2% of all wound complications. Secondary surgical intervention was required in 28 patients (29.8%), of which 7 were oncologic re-excisions and 15 were irrigation and debridement. On multivariate analysis, the use of advancement flaps (OR = 5.39; p = 0.004) and diabetes (OR = 4.08; p = 0.07) were associated with wound complications.

CONCLUSION

Five-day preoperative RT for STS results in rates of wound complications comparable to standard fractionation. We identified local advancement flaps as the primary factor associated with wound complications. STS of the lower extremity that require complex closure warrant close attention for dehiscence.

Potential Dosimetric Predictors of Patient-Reported Quality of Life for Head and Neck Cancer Following Chemoradiation IMRT

PURPOSE/OBJECTIVE(S)

This study aims to identify both acute and late patient patient-reported salivary quality of life outcomes in patients with head and neck cancer treated with chemoradiation therapy on a prospective trial.

MATERIALS/METHODS

A cohort of 40 patients with head and neck cancers were included in the study. All patients underwent concurrent chemoradiation therapy using IMRT delivery (1 patient on one Linac, 24 patients on a different Linac, and 15 on a helical delivery machine). All patients were asked to complete the University of Washington Quality of Life (UOW-QOL) questionnaire at baseline, immediately after treatment, as well as at 1 month, 3 months, 6 months, 12 month and 18 months post-treatment. For the salivary quality of life (QOL) outcome scores, the possible responses were scored on a discreet scale of 100, 70, 30, and 0, with 100 as normal and 0 as dysfunctional. Dosimetric endpoints achieved based on the treatment plan, such as maximum/mean/minimum doses, V30 (percent volume receiving 30 Gy dose), and Dy (dose received to y percent volume) were collected for the bilateral salivary glands, bilateral temporomandibular joint and bilateral submandibular glands. The associations between these dosimetric parameters and the corresponding salivary QOL scores at each time point were analyzed. A Wilcoxon test was performed to identify any differences in the dosimetry and salivary QOL scores among the four different responses.

RESULTS

At short-term follow-up including 1- and 6-month, the distribution of the mean dose received by the right parotid was significantly different between the patients that reported a salivary QOL score of 30 and those that reported 100, with p-values of 0.007 for the 1-month comparison and 0.006 for the 6-month comparison. This was also seen for the V30, with p-values of 0.027 for the 1-month comparison and 0.013 for the 6-month comparison. At 3 months, the maximum dose received by the left temporomandibular joint was significantly different between the patients that reported 30 and those that reported 70, with a p-value of 0.038. At 6 months, the average dose distribution of the right submandibular gland received between the patients that reported a score of 30 and 100 was also significantly different, with a p-value of 0.006. At the long-term follow-up time points of 12 and 18 months, no significant differences were found.

CONCLUSION

The significant differences seen in the data suggest that the dosimetry may have effects on patient reported salivary QOL at short-term follow-up but not long-term. This provides a new perspective into how a patient's QOL over a period of time could be affected by the amount of dose to critical organs. These results also serve as the basis for further investigation into the actual delivered dose, which could differ from the planned dose due to daily anatomic changes over the course of head and neck radiotherapy delivery. These daily volumetric and dosimetric changes may guide early adaptive treatment to improve patient-reported QOL outcomes.

Developing an Online Interactive Volumetric Surface Viewer for Visualizing Spatial Distribution of Intracranial Lesions

PURPOSE/OBJECTIVE(S)

The exact location of intracranial neoplasms and metastatic lesions within the cortex may provide key insights into predicting treatment effectiveness and toxicities. Modern neuroimaging approaches have enabled precise, rapid diffeomorphic alignment from individual brains to an atlas, allowing the registration of contours and dose distributions onto a common template. However, there is a paucity of intuitive tools to perform such functions. Here, we developed an online interactive volumetric surface viewer that displays distribution of brain lesions of specific clinical features within the context of prior radiation treatment in populations of patients on a common atlas.

MATERIALS/METHODS

Data from 647 patients treated at our institution with radiotherapy for intracranial lesions were analyzed with FreeSurfer to perform intensity normalization, skull-stripping, and affine registration to Talairach coordinates. A custom-built VoxelMorph model was trained to register T1 MRIs to a common atlas. Radiation dose maps and contours on underlying CT simulation scans were rigidly aligned to the T1 MRIs. The diffeomorphic warps were then applied to the radiation dose maps and contours, including the gross tumor volumes. Surface rendering of the template atlas was performed using FreeSurfer and visualized using PyCortex. Clinical information including primary sites for brain metastases, lesion size, survival, recurrence, use of anti-epileptic medications, radiation necrosis, and neuro-cognitive toxicity was embedded into the PyCortex viewer.

RESULTS

The custom-trained VoxelMorph model enabled rapid normalization of the T1MRIs to the atlas brain. PyCortex allows for interactive visualization of the spatial distribution of lesions on the cortical surface across a rich array of clinical parameters. Initial maps have qualitatively revealed a predilection for metastases in the right hemisphere. This WebGL viewer allows intuitive clinical interrogation on a visual surface enabling population inferences. For example, one can visualize the distribution of brain metastases of a large patient cohort based on their primary tumor sites, propensity for seizure and risk for radionecrosis.

CONCLUSION

We successfully built an online interactive viewer to visualize the spatial distribution of intracranial lesions on a common reference. Our approach extends prior work allowing visual interaction of lesions and real-time generation of inference maps by combining a front-end viewer and back-end database of clinical data. This viewer may represent a critical step towards uncovering the location-dependent breakdown of the blood-brain-barrier, differentiating the propensity of primary lesions metastasizing to brain regions, and allowing the discovery of associations of previously understudied spatial neighborhoods. We plan to release a publicly available web-based viewer to further explore, interrogate, and inform future radiation treatments.

Treatment Delivery Gating of MRI-Guided Stereotactic Radiotherapy for Prostate Cancer: An Exploratory Analysis of a Phase III Randomized Trial of CT-Vs. MR-Guided Radiotherapy (MIRAGE)

PURPOSE/OBJECTIVE(S)

Compared to CT-guided radiotherapy, MRI-guided radiotherapy (MRgRT) has been shown to reduce acute physician-scored and patient-reported gastrointestinal and genitourinary (GU) toxicities associated with prostate stereotactic body radiotherapy (SBRT) in the MIRAGE randomized trial (NCT04384770). We hypothesize that real-time intrafraction tracking/gating is important and is a critical enabler of aggressive margin reduction with MRgRT.

MATERIALS/METHODS

79 patients received MRgRT on the MIRAGE trial with a planning margin of 2mm around the prostate and proximal seminal vesicles, which were treated to 40 Gy in five fractions on an MR-Linac. Tracking was performed at 4 frames/second in the sagittal plane during treatment with a gating boundary of 3mm for automatic beam hold. An in-house tool was developed to extract treatment time and beam gating status based on treatment logs and real-time cine images. The ratio of the time that the target was within the gating window/total time of target inside or outside the gating boundary was defined as the duty cycle (DC). Target contours were extracted from each frame of tracking and overlaid to create a motion-convolved target occupancy map. Minimum isotropic expansions of the prostate to cover 85%, 90% and 95% of the intrafraction motion were calculated with and without gating.

RESULTS

Median treatment time per fraction including image guidance procedure and beam delivery was 24.3 min (IQR: 22.2-27.7 min). The median time for image guidance 5.4 min (IQR: 4.2-6.7 min). A total of 391 treatment fractions were analyzed and the median DC per fraction was 0.974 (IQR: 0.926 -0.983). 89 (22.8%) and 35 (9.0%) of fractions had DC<90% and <80%, respectively, corresponding to 50/79 (62.3%) and 24/79 (30.4%) of patients having at least one fraction with a DC<90% and <80%, respectively. The minimum duty cycle of all fractions was lower among patients with grade ≥2 GU toxicity compared to those with grade 0-1 GU toxicity (mean 79.8% vs. 85.9%, p = 0.06). The proportion of patients with grade ≥2 GU toxicity was also greater in patients with a minimum gating cycle <80% (37.5% vs. 18.2%, p = 0.06). Gating significantly decreased the minimum isotropic expansion of the prostate to cover 85%, 90% and 95% of the intrafraction motion (p<0.0001 for all). Prostate intrafraction motion tended to be along the bladder-rectum axis secondary to bladder filling, rectal gas and bulk motion. Fractions with large prostate motion were mostly stochastic.

CONCLUSION

A large fraction (30%) of patients had at least of one treatment fraction with DC<80%, which correlated with increased acute GU toxicity. Gating effectively reduces the expansion needed to cover prostate intrafraction motion, and is necessary for real-time motion management given the unpredictable nature of prostate motion.

Use of Postoperative PET/CT in Altering Management in Adjuvant Head and Neck Radiation Therapy

PURPOSE/OBJECTIVE(S)

Routine clinical practice does not include postoperative positron emission tomography (PET)/CT prior to postoperative radiation therapy (PORT) for head and neck cancer. Besides logistical challenges in obtaining postoperative PET/CT within six weeks after surgery, interpreting PET/CT findings in the postoperative setting can also be difficult. However, given the potential for residual or rapidly recurrent disease, postoperative PET/CT may help identify the need for additional diagnostic evaluation or alter adjuvant therapy. There are limited data evaluating the utility of postoperative PET/CT prior to PORT for head and neck cancer. We sought to evaluate the use and clinical relevance of postoperative PET/CT prior to PORT.

MATERIALS/METHODS

In this retrospective, single-institution cohort study, we identified patients with head and neck cancer between 2013 and 2020 who received a postoperative PET/CT prior to PORT. We extracted electronic medical record data supplemented with manual chart review to collect patient and disease-related information. We measured the rates of additional diagnostic workup and treatment alterations as a result of postoperative PET/CT findings.

RESULTS

The cohort included 29 patients who received a postoperative PET/CT prior to PORT. The mean age at diagnosis was 60.8 years (standard deviation: 15.0 years) and 20 (69.0%) were male. Regarding primary site, 10 (34.5%) were oropharynx, 7 (24.1%) were salivary gland, and 6 (20.7%) were oral cavity. The mean time from surgery to postoperative PET was 40.9 days (standard deviation: 27.7 days), and the mean time from postoperative PET/CT to start of PORT was 22.4 days (standard deviation: 20.3 days). A total of 9 (31.0%) patients experienced a change in management as a result of the PET/CT findings. Six (66.7%) patients received a biopsy. All 9 patients had a change in their radiation treatment plan, either dose escalation, target change, or in one case, converting to palliative dosing. Six (66.7%) patients were recommended addition of chemotherapy as a result of additional workup, with 4 (44.4%) of those patients ultimately receiving chemotherapy. Three (33.3%) patients underwent re-resection prior to PORT.

CONCLUSION

In patients with head and neck cancer who received postoperative PET/CT prior to PORT, a meaningful proportion underwent additional diagnostic evaluation and/or experienced an alteration in adjuvant therapy as a result of the imaging findings. Interestingly, all patients with abnormal postoperative PET findings had changes in their radiation treatment plan, including at least boosting gross disease for patients in whom re-resection or chemotherapy was not pursued. Future work will seek to expand this cohort through 2022 when postoperative PET/CT became more routine at our institution and include oncologic outcomes. Additional studies are needed to identify appropriate candidates for postoperative PET/CT and determine the clinical impact of postoperative PET/CT.

Validation of a Fast-Helical Free-Breathing CT-Based Ventilation Technique Using Ventilation/Perfusion SPECT Imaging

PURPOSE/OBJECTIVE(S)

In radiotherapy, the lung is considered one homogenous organ at risk during planning. However, avoiding dose to functional lung could help preserve lung function after treatment. This could be possible with ventilation mapping, which is traditionally done with SPECT imaging. Having an accurate, CT-based approach could allow for ventilation mapping within the radiotherapy workflow. In this study, we aim to compare a novel, CT-based ventilation mapping approach to SPECT-based ventilation images.

MATERIALS/METHODS

We acquired both CT-based and SPECT-based ventilation scans for one patient. For the SPECT-based images, the patient inhaled 8.8 mCi Tc-99m DTPA aerosol before scan acquisition with a dual headed SPECT/CT. For the CT-based approach, we acquired 25 fast-helical free-breathing CTs as part of our 5DCT protocol with simultaneous monitoring of the breathing pattern using a respiratory bellows surrogate. We chose one scan as the reference scan, and deformably registered the other 24 scans to it. The Jacobian expansion of each registration was calculated for each voxel and linearly related to the bellows amplitude. The slope of the linear fit, dJ/dA, represented the ventilation for each voxel. To compare the resulting ventilation maps from each method, we first calculated the normalized cross-correlation (NCC) and Spearman correlation coefficient. We also created masks of ventilation greater than various thresholds to see how we could accurately define high and low functioning lung. For example, greater than 50th percentile ventilation being 1 (high functioning) and less than 50th percentile being 0 (low functioning). We calculated Dice scores to compare these threshold masks between the CT-based and SPECT-based ventilation images.

RESULTS

The NCC between the ventilation images was 0.810, and the Spearman correlation between them was 0.587. When comparing volumes of ventilation greater than 50th percentile, the Dice score was 0.730. However, when the threshold was increased, the Dice scores were reduced. Qualitatively, we noted that the lobar ventilation agreed in general, but there was more detail throughout the CT-based image, as opposed to the more precisely defined, high ventilating areas in the SPECT image.

CONCLUSION

We were able to compare our novel, CT-based ventilation approach against a more conventional technique in ventilation SPECT imaging. The resulting ventilation images were qualitatively similar. Analyzing different thresholds showed that we can reasonably separate high and low functioning tissue into greater than or less than 50th percentile ventilation, respectively. In future work, we will aim to expand this study over a larger cohort of patients and also examine longitudinal changes to ventilation after SBRT and lung brachytherapy.