Early Outcomes of MR-Guided SBRT for Patients with Recurrent Pancreatic Adenocarcinoma

PURPOSE/OBJECTIVE(S)

Local treatment options for patients with locally recurrent pancreatic adenocarcinoma (L-PAC) are limited, with expected median survival time (MST) of 8-11 months (mo) following recurrence. MRI-guided radiation therapy (MRgRT) provides the ability to dose escalate while sparing normal tissue. The literature for MR-guided Stereotactic Body Radiotherapy (MRgSBRT) for L-PAC is sparse. Here we report on the early outcomes of MRgSBRT in patients with L-PAC.

MATERIALS/METHODS

Patients with prior resection of pancreatic adenocarcinoma with post-operative chemotherapy as indicated followed by local recurrence of disease at prior surgical site and treated with MRgSBRT at a single tertiary referral center from 5-2021 to 8-2022 for L-PAC were identified from our prospective database. MRgSBRT was delivered to 40-50 Gy in 4-5 fractions with target and OAR delineation per institutional standards. Descriptive analysis of the patient, disease, and treatment characteristics were performed. Endpoints included local control, defined as absence of tumor progression per RECIST criteria, distant failure, overall survival (OS), and acute and chronic toxicities per Common Terminology Criteria for Adverse Events (CTCAE), version 5.

RESULTS

Eleven patients with L-PAC were identified with median follow-up of 10.7 mo (3.2 - 22.3). Ten of those underwent surgical resection at the treating radiation facility and one patient underwent preoperative radiation for 50.4 Gy in 28 fractions followed by surgical resection at an outside hospital. MRgRT was delivered a median of 18.8 mo (3.5 - 48.0) following resection. There were 5 females and 6 males, with a median age of 72 years (52-83) and median KPS of 80 (60-100). OS rates following initial diagnosis at 12, 18 and 24 mo were 100%, 82%, and 61%, respectively, with an MST of 25.3 mo (12.4-53.1). OS rates following recurrence at 6 and 12 mo were 82% and 52%, respectively, with an MST of 10.7 mo (3.2 - 21.9). One patient experienced local failure at 7.8 mo, and 9 patients experienced distant failure at a median of 3.4 mo (0.3 - 21.9) following MRgSBRT. Five patients experienced distant failure less than 3 mo following radiation. Grade 1 or 2 acute GI toxicity was noted in 45% of patients and chronic GI toxicity, in 18% of patients. No Grade≥3 AEs were noted.

CONCLUSION

MRgSBRT for recurrent pancreatic adenocarcinoma demonstrates good local control with acceptable acute and chronic toxicity as well as reasonable overall survival. Distant failure remains a substantial problem with a significant number of patients demonstrating metastases immediately following radiation, suggesting the presence of micro-metastatic disease prior to local therapy. Adequate patient selection for MRgSBRT, and proper integration of systemic therapy in this patient population remains a topic of discussion that requires further exploration.

Deep-Learning Based Auto-Segmentation for Liver Yttrium-90 Selective Internal Radiation Therapy

PURPOSE/OBJECTIVE(S)

In resin Yttrium-90 (Y-90) selective internal radiation therapy (SIRT), liver volume sizes are needed for Y-90 activity calculations using the body-surface-area method, which are obtained from contours that are manually delineated in 3D images. The aim was to apply a deep-learning based auto-segmentation method for liver delineation for Y-90 SIRT.

MATERIALS/METHODS

A deep-learning-based liver segmentation method was applied using the U-Net3D architecture, which is a 3D convolutional neural network (CNN) extended from the original 2D U-Net architecture for 3D objects in medical imaging. The segmentation model was trained on the Liver Tumor Segmentation (LiTS) dataset. The training data set contained 130 CT scans, and the test data set contained 70 CT scans. The model was deployed in the clinic using DICOM communication. Auto-segmentation of liver in the CT images of 18 SIRT patients was studied. The CT images were exported from clinical database to the segmentation model's DICOM location, where a monitoring software detected the incoming data and automatically ran the liver segmentation. The results were then returned to the original DICOM location where the CT images were stored. Auto-segmented liver contours were compared with physician manually-delineated contours. Dice similarity coefficient (DSC), mean distance to agreement (MDA), ratio of volume (RV), and ratio of activity (RA, ratio of activity calculated using an auto-segmented liver contour to the accurate activity calculated using a manually-delineated contour), were assessed.

RESULTS

DSC, MDA, and RV are 0.942±0.014 (range: 0.908-0.959), 1.902±0.503 mm (range: 1.043-2.956 mm), and 0.988±0.039 (range: 0.901-1.045), respectively. RA is 1.001±0.003 (range: 0.993-1.007), which indicates that the activities calculated using the auto-segmented liver contours are close to the accurate activities.

CONCLUSION

The segmentation model was able to successfully identify and segment livers in the CT images, and provide accurate and reliable results. The proposed method is beneficial for clinical use as it can process large amounts of data quickly and efficiently, and can be easily deployed in a clinical environment using DICOM communication.

Implementation and experimental results of 4D tumor tracking using robotic couch

PURPOSE

This study presents the implementation and experimental results of a novel technique for 4D tumor tracking using a commercially available and commonly used treatment couch and evaluates the tumor tracking accuracy in clinical settings.

METHODS

Commercially available couch is capable of positioning the patient accurately; however, currently there is no provision for compensating physiological movement using the treatment couch in real-time. In this paper, a real-time couch tracking control technique is presented together with experimental results in tumor motion compensation in four dimensions (superior-inferior, lateral, anterior-posterior, and time). To implement real-time couch motion for tracking, a novel control system for the treatment couch was developed. The primary functional requirements for this novel technique were: (a) the treatment couch should maintain all previous∕normal features for patient setup and positioning, (b) the new control system should be used as a parallel system when tumor tracking would be deployed, and (c) tracking could be performed in a single direction and∕or concurrently in all three directions of the couch motion (longitudinal, lateral, and vertical). To the authors' best knowledge, the implementation of such technique to a regular treatment couch for tumor tracking has not been reported so far. To evaluate the performance of the tracking couch, we investigated the mechanical characteristics of the system such as system positioning resolution, repeatability, accuracy, and tracking performance. Performance of the tracking system was evaluated using dosimetric test as an endpoint. To investigate the accuracy of real-time tracking in the clinical setting, the existing clinical treatment couch was replaced with our experimental couch and the linear accelerator was used to deliver 3D conformal radiation therapy (3D-CRT) and intensity modulated radiation therapy (IMRT) treatment plans with and without tracking. The results of radiation dose distribution from these two sets of experiments were compared and presented here.

RESULTS

The mechanical accuracies were 0.12, 0.14, and 0.18 mm in X, Y, and Z directions. The repeatability of the desired motion was within ±0.2 mm. The differences of central axis dose between the 3D-CRT stationary plan and two tracking plans with different motion trajectories were 0.21% and 1.19%. The absolute dose differences of both 3D tracking plans comparing to the stationary plan were 1.09% and 1.20%. Comparing the stationary IMRT plan with the tracking IMRT plan, it was observed that the central axis dose difference was -0.87% and the absolute difference of both IMRT plans was 0.55%.

CONCLUSIONS

The experimental results revealed that the treatment couch could be successfully used for real-time tumor tracking with a high level of accuracy. It was demonstrated that 4D tumor tracking was feasible using existing couch with implementation of appropriate tracking methodology and with modifications in the control system.

Racial disparity trends in clinical presentation and outcomes in colorectal cancer: Findings from an urban university hospital

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Background: African Americans (AA) have a higher incidence and lower survival rates from colon and rectal cancer than Caucasian Americans (C). This disparity has been attributed to many factors, including diagnosis at later stage, unfavorable histopathologic features, inadequate treatment, and socioeconomic factors. The multidisciplinary management setting ensures similarity in management and treatment planning. In this study, we assessed the pathological features and evaluated survival outcomes in patients with CRC in AA and CA using a large single institutional database.

Methods: We compiled data from 3,826 patients with colon and rectal cancer treated at Thomas Jefferson University Hospital from 1988-2009 and used Surveillance Epidemiology and End Results registry data from 1988-2004 to compare survival rates. Independent variables included age, racial background, site of primary tumor, degree of differentiation, stage at presentation, recurrence-free survival and overall survival rates for colon and rectal cancer and for each stage of disease. We compared survival rates using statistical modeling to account for differences in patient and disease characteristics between the two groups.

Results: At diagnosis, AA pts presented with more advanced stage of disease (p < 0.0001), were more likely to have proximal disease (p < 0.000000528), had worse overall 5-year survival, and worse survival stage-by-stage than C patients. Data also showed that the odds ratio for risk of nodal involvement was greater for AA pts than C pts with lower T tumors. AA pts were more likely to have less well differentiated colon tumors, but more well differentiated rectal tumors, younger age and worse survival stage-by stage than C pts. Although C pts were more likely to have rectal cancer (p < 0.0001), they were less likely to have stage IV disease at presentation.

Conclusions: AA pts with CRC are more likely to present at a younger age with later stage, more proximal tumors, have higher nodal involvement with lower T lesions, and less well differentiated tumors than C. Additional studies on biological feature sand molecular markers are ongoing to and will be presented.

No significant financial relationships to disclose.

Selective internal radiation therapy (SIRT) as salvage therapy for uveal melanoma (UM) hepatic metastases

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Background: The liver is the first site of metastasis in >80% of patients with UM. Transarterial chemoembolization (TACE) has been used to control hepatic metastases, however, patients eventually progress through or experience complications related to TACE. We report our results using SIRT as salvage therapy for patients with UM liver metastases who are no longer candidates for TACE. Methods: Patients with UM liver metastases previously treated with TACE were treated with SIRT. Patients were followed 1-month post-SIRT for acute toxicity then every 3 months for tumor response evaluation and for complications of delayed toxicity. Common Toxicity Criteria 3.0 (CTC) was used for toxicity assessment. Best radiographic tumor response was determined by MRI using RECIST criteria. Results: Five men and 7 women, ages 48–81 (median 65) with UM liver metastases were treated with SIRT after tumor progression post-TACE (n=9), complications of TACE (n=1) or patient preference (n=2). Pretreatment whole liver tumor burdens were as follows: <25% (n=10), 25–50% (n=1) and >50% (n=1). Patients had both hepatic lobes treated on separate occasions (n=7), one lobe (n=3) or whole liver (n=2) therapy. Treatment dose per patient was reduced by 25% due to prior TACE procedures. The mean total SIRT dose delivered was 1.0 GBq (0.62–1.47 GBq). Five patients had an increase in hepatic enzymes (Grade 1–4) at 1-month follow-up. No procedure related deaths or serious adverse events were experienced. Best tumor response was as follows: CR (n=0), PR (n=0), SD (n=8), PD (n=4), with a median follow-up of 7.8 months (1.0–16.0). The median time to liver progression was 7.0 months (1.0- 15.5). Nine of the 12 patients, including 2 patients with >25% pretreatment tumor burden, died due to progression of liver disease (n=6), extrahepatic disease (n=1) or both (n=2). Post-SIRT, median overall patient survival was 10.8 months (1.0–19.0). Three patients (ECOG 0 performance status) are still alive at 13.5–19.0 months (median 16.2 months) following SIRT. Conclusions: SIRT was safely used and showed a potential clinical benefit for patients previously treated with TACE. Further investigation is warranted to determine if SIRT should be employed as a first line therapy for patients with UM liver metastases.

No significant financial relationships to disclose.

Variation of clinical target volume definition in three-dimensional conformal radiation therapy for prostate cancer

PURPOSE

Currently, three-dimensional conformal radiation therapy (3D-CRT) planning relies on the interpretation of computed tomography (CT) axial images for defining the clinical target volume (CTV). This study investigates the variation among multiple observers to define the CTV used in 3D-CRT for prostate cancer.

METHODS AND MATERIALS

Seven observers independently delineated the CTVs (prostate +/- seminal vesicles [SV]) from the CT simulation data of 10 prostate cancer patients undergoing 3D-CRT. Six patients underwent CT simulation without the use of contrast material and serve as a control group. The other 4 had urethral and bladder opacification with contrast medium. To determine interobserver variation, we evaluated the derived volume, the maximum dimensions, and the isocenter for each examination of CTV. We assessed the reliability in the CTVs among the observers by correlating the variation for each class of measurements. This was estimated by intraclass correlation coefficient (ICC), with 1.00 defining absolute correlation.

RESULTS

For the prostate volumes, the ICC was 0.80 (95% confidence interval [CI]: 0.56-0.96). This changed to 0.92 (95% CI: 0.75-0.99) with the use of contrast material. Similarly, the maximal prostatic dimensions were reliable and improved. There was poor agreement in defining the SV. For this structure, the ICC never exceeded 0.28. The reliability of the isocenter was excellent, with the ICC exceeding 0.83 and 0.90 for the prostate +/- SV, respectively.

CONCLUSIONS

In 3D-CRT for prostate cancer, there was excellent agreement among multiple observers to define the prostate target volume but poor agreement to define the SV. The use of urethral and bladder contrast improved the reliability of localizing the prostate. For all CTVs, the isocenter was very reliable and should be used to compare the variation in 3D dosimetry among multiple observers.

A dosimetry system for 192IR interstitial breast implants performed at the time of lumpectomy

PURPOSE

192Ir interstitial breast implants performed at the time of lumpectomy present a unique problem because they cannot be preplanned, and yet they are expected to produce a treatment dose rate (TDR) from 0.3 to 0.5 Gy/h using sources already procured. The purpose of this work is to describe a system of dosimetry that works within these constraints and has been used to perform more than 600 such implants.

METHODS AND MATERIALS

The underlying principle is to fix the ribbon spacing, the interplaner separation, and the linear activity (1 mCi/cm) so that the TDR will depend only on the area (L x W) implanted. The ribbons are spaced 1.5 cm and 2.0 cm apart in single plane and double implants, respectively. Idealized implants were used to study the TDR as a function of the implant dimensions, and to study the effects of varying the ribbon spacing and interplanar separation. Volume-dose histograms were generated to study the homogeneity of dose.

RESULTS

The TDRs of single plane implants range from 0.3 Gy/h for small 4 x 4 cm2 implants to 0.4 Gy/h for large 10 x 10 cm2 implants. The TDRs for double plane implants are similar for the same range of dimensions.

CONCLUSIONS

Implants with a TDR between 0.3 and 0.5 Gy/h can be performed for a wide range of geometries without preplanning using fixed ribbons spacings of 1.5 and 2.0 cm for single and double plane implants, respectively, and a linear activity of 1 mCi/cm.