Reproducibility of chestwall and heart position using surface-guided versus RPM-guided DIBH radiotherapy for left breast cancer.

This study compared the reproducibility of chestwall and heart position using surface-guided versus RPM (real-time position management)-guided deep inspiration breath hold (DIBH) radiotherapy for left sided breast cancer. Forty DIBH patients under either surface-guided radiotherapy (SGRT) or RPM guidance were studied. For patients treated with tangential fields, reproducibility was measured as the displacements in central lung distance (CLD) and heart shadow to field edge distance (HFD) between pretreatment MV (megavoltage) images and planning DRRs (digitally reconstructed radiographs). For patients treated with volumetric modulated arc therapy (VMAT), sternum to isocenter (ISO) distance (StID), spine to rib edge distance (SpRD), and heart shadow to central axis (CAX) distance (HCD) between pretreatment kV images and planning DRRs were measured. These displacements were compared between SGRT and RPM-guided DIBH. In tangential patients, the mean absolute displacements of SGRT versus RPM guidance were 0.19 versus 0.23 cm in CLD, and 0.33 versus 0.62 cm in HFD. With respect to planning DRR, heart appeared closer to the field edge by 0.04 cm with surface imaging versus 0.62 cm with RPM. In VMAT patients, the displacements of surface imaging versus RPM guidance were 0.21 versus 0.15 cm in StID, 0.24 versus 0.19 cm in SpRD, and 0.72 versus 0.41 cm in HCD. Heart appeared 0.41 cm further away from CAX with surface imaging, whereas 0.10 cm closer to field CAX with RPM. None of the differences between surface imaging and RPM guidance was statistically significant. In conclusion, the displacements of chestwall were small and were comparable with SGRT- or RPM-guided DIBH. The position deviations of heart were larger than those of chestwall with SGRT or RPM. Although none of the differences between SGRT and RPM guidance were statistically significant, there was a trend that the position deviations of heart were smaller and more favorable with SGRT than with RPM guidance in tangential patients.

Comparison of setup accuracy of optical surface image versus orthogonal x-ray images for VMAT of the left breast using deep-inspiration breath-hold.

To compare the setup accuracy of optical surface image (OSI) versus orthogonal x-ray images (2DkV) using cone beam computed tomography (CBCT) as ground truth for radiotherapy of left breast cancer in deep-inspiration breath-hold (DIBH). Ten left breast DIBH patients treated with volumetric modulated arc therapy (VMAT) were studied retrospectively. OSI, 2DkV, and CBCT were acquired weekly at treatment setup. OSI, 2DkV, and CBCT were registered to planning CT or planning DRR based on a breast surface region of interest (ROI), bony anatomy (chestwall and sternum), and both bony anatomy and breast surface, respectively. These registrations provided couch shifts for each imaging system. The setup errors, or the difference in couch shifts between OSI and CBCT were compared to those between 2DkV and CBCT. A second OSI was acquired during last beam delivery to evaluate intrafraction motion. The median absolute setup errors were (0.21, 0.27, 0.23 cm, 0.6°, 1.3°, 1.0°) for OSI, and (0.26, 0.24, 0.18 cm, 0.9°, 1.0°, 0.6°) for 2DkV in vertical, longitudinal and lateral translations, and in rotation, roll and pitch, respectively. None of the setup errors was significantly different between OSI and 2DkV. For both systems, the systematic and random setup errors were ≤0.6 cm and ≤1.5° in all directions. Nevertheless, larger setup errors were observed in some sessions in both systems. There was no correlation between OSI and CBCT whereas there was modest correlation between 2DkV and CBCT. The intrafraction motion in DIBH detected by OSI was small with median absolute translations <0.2 cm, and rotations ≤0.4°. Though OSI showed comparable and small setup errors as 2DkV, it showed no correlation with CBCT. We concluded that to achieve accurate setup for both bony anatomy and breast surface, daily 2DkV can't be omitted following OSI for left breast patients treated with DIBH VMAT.

Retrospective analysis of MV-kV imaging-based fiducial tracking in prostate SBRT treatment.

PURPOSE: Motion management is critical for prostate stereotactic body radiotherapy (SBRT) due to its high fractional dose and proximity to organs at risk. This study seeks to quantify the advantages of MV-kV tracking over kV imaging alone through a retrospective analysis of over 300 patients who underwent prostate SBRT treatment using MV-kV tracking. METHODS: An MV-kV imaging-based fiducial tracking technique has been developed at our institute and become a standard clinical practice. This technique calculates three-dimensional (3D) fiducial displacement in real time from orthogonal kV and MV images acquired simultaneously. The patient will be repositioned if for two consecutive MV-kV data points, the motion is larger than a tolerance of 1.5 mm in any of the lateral, superior-inferior, and/or anterior-posterior directions. This study retrospectively analyzed detected 3D motions using an MV-kV approach of 324 patients who recently underwent prostate SBRT treatments. An algorithm was developed to recover the 2D motion components as if they were detected by kV or MV imaging alone. RESULTS: Our results indicated that out-of-tolerance motions were primarily limited to the range of 1.5-3 mm (>95%). The motions are primarily anterior-posterior and superior-inferior, with less than 14.8% of the occurrences in the lateral direction. Compared to out-of-tolerance occurrences detected by MV-kV approach, kV alone caught 46.6% of motions in all three directions, and MV alone caught 46.7%. kV alone shows an overall missing rate of 45.8% for superior-inferior motions and 38.6% for lateral motions. It is also demonstrated that the detectability of motion in specific directions greatly depends on gantry angles, as does the missing rate. CONCLUSIONS: Our study demonstrated that MV-kV imaging-based intrafraction motion tracking is superior to single kV imaging for prostate SBRT in clinical practice.

Femoral Fracture in Primary Soft Tissue Sarcoma Treated with Intensity-Modulated Radiation Therapy with and Without Dose Constraints.

BACKGROUND: We previously reported that the cumulative risk of femoral fracture in patients treated with intensity-modulated radiation therapy (IMRT) for thigh and groin soft tissue sarcoma (STS) is low. In the current study, we sought to evaluate the effect of radiation dose constraints on the rate of femoral fracture in a more contemporary cohort. METHODS: All patients treated with IMRT for STS of the thigh or groin from 2004 to 2016 were included (n = 145). Beginning in 2011, radiation dose was constrained to a mean dose of < 37 Gy, volume of bone receiving ≥ 40 Gy (V40Gy) < 64%, and maximum dose < 59 Gy to limit the dose to the femur. RESULTS: Sixty-one patients were treated before dose constraints were implemented, and 84 patients were treated after. Median follow-up for patients treated before and after constraints were implemented was 6.1 and 5.7 years, respectively, and the two groups were demographically and clinically similar. On univariate analysis, the 5-year cumulative incidence of femoral fracture among patients treated with and without dose constraints was 1.8% (95% confidence interval [CI] 0.3-12.2%) versus 7.4% (95% CI 3.1-17.6%) [p = 0.11, p = non-significant, respectively]. On multivariable analysis, only age ≥ 60 years was significantly associated with increased risk of fracture. CONCLUSIONS: The risk of femoral fracture after IMRT for STS of the thigh/groin is low, and with the implementation of radiation dose constraints, the risk is < 2%. Although longer follow-up is needed, our results support the utilization of extremity sarcoma IMRT-specific dose constraints for fracture prevention.

Efficiency and safety increases after the implementation of a multi-institutional automated plan check tool at our institution.

PURPOSE: The plan check tool (PCT) is the result of a multi-institutional collaboration to jointly develop a flexible automated plan checking framework designed with the versatility to be shared across collaborating facilities while supporting the individual differences between practices. We analyze the effect that PCT has had on the efficiency and effectiveness of initial chart checks at our institution. METHODS AND MATERIALS: Data on errors identified during initial chart checks were acquired during two time periods: before the introduction of PCT in the clinic (6/24/2015 to 7/31/2015, 187 checks) and post-clinical release (4/14/2016 to 5/2/2016, 186 checks). During each time period, human plan checkers were asked to record all issues that they either manually detected or that were detected by PCT as well as the amount of time, less breaks, or interruptions, it took to check each plan. RESULTS: After the clinical release of PCT, there was a statistically significant decrease in the number of issues recorded by the human plan checkers both related to checks explicitly performed by PCT (13 vs 50, P < 0.001) and in issues identified overall (127 vs 200, P < 0.001). The mean and medium time for a plan check decreased by 20%. CONCLUSIONS: The use of a multi-institutional, configurable, automated plan checking tool has resulted in both substantial gains in efficiency and moving error detection to earlier points in the planning process, decreasing their likelihood that they reach the patient. The sizeable startup effort needed to create this tool from scratch was mitigated by the sharing, and subsequent co-development, of software code from a peer institution.

A phantom study to evaluate three different registration platform of 3D/3D, 2D/3D, and 3D surface match with 6D alignment for precise image-guided radiotherapy.

PURPOSE: To evaluate two three-dimensional (3D)/3D registration platforms, one two-dimensional (2D)/3D registration method, and one 3D surface registration method (3DS). These three technologies are available to perform six-dimensional (6D) registrations for image-guided radiotherapy treatment. METHODS: Fiducial markers were asymmetrically placed on the surfaces of an anthropomorphic head phantom (n = 13) and a body phantom (n = 8), respectively. The point match (PM) solution to the six-dimensional (6D) transformation between the two image sets [planning computed tomography (CT) and cone beam CT (CBCT)] was determined through least-square fitting of the fiducial positions using singular value decomposition (SVD). The transformation result from SVD was verified and was used as the gold standard to evaluate the 6D accuracy of 3D/3D registration in Varian's platform (3D3DV), 3D/3D and 2D/3D registration in the BrainLab ExacTrac system (3D3DE and 2D3D), as well as 3DS in the AlignRT system. Image registration accuracy from each method was quantitatively evaluated by root mean square of target registration error (rmsTRE) on fiducial markers and by isocenter registration error (IRE). The Wilcoxon signed-rank test was utilized to compare the difference of each registration method with PM. A P < 0.05 was considered significant. RESULTS: rmsTRE was in the range of 0.4 mm/0.7 mm (cranial/body), 0.5 mm/1 mm, 1.0 mm/1.5 mm, and 1.0 mm/1.2 mm for PM, 3D3D, 2D3D, and 3DS, respectively. Comparing to PM, the mean errors of IRE were 0.3 mm/1 mm for 3D3D, 0.5 mm/1.4 mm for 2D3D, and 1.6 mm/1.35 mm for 3DS for the cranial and body phantoms respectively. Both of 3D3D and 2D3D methods differed significantly in the roll direction as compared to the PM method for the cranial phantom. The 3DS method was significantly different from the PM method in all three translation dimensions for both the cranial (P = 0.003-P = 0.03) and body (P < 0.001-P = 0.008) phantoms. CONCLUSION: 3D3D using CBCT had the best image registration accuracy among all the tested methods. 2D3D method was slightly inferior to the 3D3D method but was still acceptable as a treatment position verification device. 3DS is comparable to 2D3D technique and could be a substitute for X-ray or CBCT for pretreatment verification for treatment of anatomical sites that are rigid.

Femoral Fracture in Primary Soft-Tissue Sarcoma of the Thigh and Groin Treated with Intensity-Modulated Radiation Therapy: Observed versus Expected Risk.

PURPOSE: This study was designed to compare the observed risk of femoral fracture in primary soft-tissue sarcoma (STS) of the thigh/groin treated with intensity-modulated radiation therapy (IMRT) to expected risk calculated using the Princess Margaret Hospital (PMH) nomogram. METHODS: Expected femoral fracture risk was calculated by using the PMH nomogram. Cumulative risk of fracture was estimated by using Kaplan-Meier statistics. Prognostic factors were assessed with univariate and multivariate analysis using Cox's stepwise regression. RESULTS: Between February 2002 and December 2010, 92 consecutive eligible patients were assessed. Median follow-up was 73 months (106 months in surviving patients). IMRT was delivered preoperatively (50 Gy) in 13 (14%) patients and postoperatively in 79 (86%) patients (median dose, 63 Gy; range, 59.4-66.6 Gy). The observed crude risk of fractures was 6.5% compared with 25.6% expected risk from the nomogram; the cumulative risk of fracture using IMRT at 5 years was 6.7% (95% CI 2.8-16.0%). The median time to fracture was 23 months (range, 6.9-88.6). Significant predictors of fracture on univariate analysis were age ≥ 60 years (p = 0.03), tumor location in the anterior thigh (p = 0.008), and periosteal stripping to > 20 cm (p < 0.0001). On multivariate analysis, age ≥ 60 years and periosteal stripping > 20 cm retained significance (p = 0.04 and p = 0.009, respectively). CONCLUSIONS: In this study, the cumulative risk of femur fracture in patients treated with IMRT (6.7%) is less than the expected risk using the PMH nomogram (25.6%). Established predictors of femur fracture, such as gender, tumor size, and dose of RT, seem to have less impact on fracture risk when using IMRT.

A Simulation-Free Replacement Solution for Radiation Therapy Immobilization Devices Using Computer Numerical Control (CNC) -Milled Polystyrene Molds.

Purpose: In radiation therapy (RT), if an immobilization device is lost or damaged, the patient may need to be brought back for resimulation, device fabrication, and treatment planning, causing additional imaging radiation exposure, inconvenience, cost, and delay. We describe a simulation-free method for replacing lost or damaged RT immobilization devices. Methods and Materials: Replacement immobilization devices were fabricated using existing simulation scans as design templates by computer numerical control (CNC) milling of molds made from extruded polystyrene (XPS). XPS material attenuation and bolusing properties were evaluated, a standard workflow was established, and 12 patients were treated. Setup reproducibility was analyzed postfacto using Dice similarity coefficient (DSC) and mean distance to agreement (MDA) calculations comparing onboard treatment imaging with computed tomography (CT) simulations. Results: Results showed that XPS foam material had less dosimetric impact (attenuation and bolusing) than materials used for our standard immobilization devices. The average direct cost to produce each replacement mold was $242.17, compared with over $2000 for standard resimulation. Hands-on time to manufacture was 86.3 minutes, whereas molds were delivered in as little as 4 hours and mostly within 24 hours, compared with a week or more required for standard resimulation. Each mold was optically scanned after production and was measured to be within 2-mm tolerance (pointwise displacement) of design input. All patients were successfully treated using the CNC-milled foam mold replacements, and pretreatment imaging verified satisfactory clinical setup reproduction for each case. The external body contours from the setup cone beam CT and the original CT simulation with matching superior-inferior extent were compared by calculating the DSC and MDA. DSC average was 0.966 (SD, 0.011), and MDA average was 2.694 mm (SD, 0.986). Conclusions: CNC milling of XPS foam is a quicker and more convenient solution than traditional resimulation for replacing lost or damaged RT immobilization devices. Satisfactory patient immobilization, low dosimetric impact compared with standard immobilization devices, and strong correlation of onboard contours with CT simulations are shown. We share our clinical experience, workflow, and manufacturing guide to help other clinicians who may want to adopt this solution.

Implementation of a knowledge-based decision support system for treatment plan auditing through automation.

BACKGROUND: Independent auditing is a necessary component of a comprehensive quality assurance (QA) program and can also be utilized for continuous quality improvement (QI) in various radiotherapy processes. Two senior physicists at our institution have been performing a time intensive manual audit of cross-campus treatment plans annually, with the aim of further standardizing our planning procedures, updating policies and guidelines, and providing training opportunities of all staff members. PURPOSE: A knowledge-based automated anomaly-detection algorithm to provide decision support and strengthen our manual retrospective plan auditing process was developed. This standardized and improved the efficiency of the assessment of our external beam radiotherapy (EBRT) treatment planning across all eight campuses of our institution. METHODS: A total of 843 external beam radiotherapy plans for 721 lung patients from January 2020 to March 2021 were automatically acquired from our clinical treatment planning and management systems. From each plan, 44 parameters were automatically extracted and pre-processed. A knowledge-based anomaly detection algorithm, namely, "isolation forest" (iForest), was then applied to the plan dataset. An anomaly score was determined for each plan using recursive partitioning mechanism. Top 20 plans ranked with the highest anomaly scores for each treatment technique (2D/3D/IMRT/VMAT/SBRT) including auto-populated parameters were used to guide the manual auditing process and validated by two plan auditors. RESULTS: The two auditors verified that 75.6% plans with the highest iForest anomaly scores have similar concerning qualities that may lead to actionable recommendations for our planning procedures and staff training materials. The time to audit a chart was approximately 20.8 min on average when done manually and 14.0 min when done with the iForest guidance. Approximately 6.8 min were saved per chart with the iForest method. For our typical internal audit review of 250 charts annually, the total time savings are approximately 30 hr per year. CONCLUSION: iForest effectively detects anomalous plans and strengthens our cross-campus manual plan auditing procedure by adding decision support and further improve standardization. Due to the use of automation, this method was efficient and will be used to establish a standard plan auditing procedure, which could occur more frequently.

Clinical Experience and Feasibility of Using 2D-kVimage Online Intervention in the Ultrafractionated Stereotactic Radiation Treatment of Prostate Cancer.

PURPOSE: This study reports clinical experience and feasibility of using a 2-dimensional (2D)-kV image system with online intervention in the ultrafractionated stereotactic body radiation treatment (UF-SBRT) of prostate cancer. METHODS AND MATERIALS: Fifteen patients with prostate cancer who had a low- to intermediate-risk marker implanted received UF-SBRT with online 2D-kV image tracking and a manual beam interruption strategy with a 2-mm motion threshold. A total of 180 kV paired setup images and 1272 intrabeam 2D-kV images were analyzed to evaluate the setup deviation and intratreatment target deviation. Correlation of expected treatment interruptions with a set of parameters (eg, image and treatment time; direction of deviation) was performed (Spearman test). A subset of the data from 22 fractions was re-evaluated to check the differences in analysis results between using the planning position and using the pretreatment setup position as a reference. Margins based on the derived system and random errors were calculated to evaluate the feasibility of the workflow in ensuring prostate coverage during treatment. RESULTS: Mean target motion in 3D propagated from 1.0 mm (setup at 0 minutes) to 2.0 mm (beam on at 7 minutes) to 2.4 mm (end at 13.5 minutes). Out of 75 fractions, 50 were found to require beam interruption. Interruption had a strong correlation with prostate motion along the longitudinal direction and had moderate correlation with prostate motion along the vertical direction and the prostate's treatment starting position along vertical and longitudinal directions. Using the pretreatment position as a reference for intrabeam monitoring, the magnitude of motion deviation from the reference position was reduced by 0.3 mm at a vertical direction and 0.4 mm at lateral and longitudinal directions. The calculated 3D margin to ensure target coverage was 3.7 mm, 4.6 mm, and 5.0 mm in lateral, vertical, and longitudinal directions, respectively. CONCLUSIONS: Prostate motion propagated over time. It is feasible to use a 2D-kV online intrabeam monitoring system with a proper intervention scheme to perform UF-SBRT for prostate cancer.

Implementation of EPID transit dosimetry based on a through-air dosimetry algorithm.

PURPOSE: A method to perform transit dosimetry with an electronic portal imaging device (EPID) by extending the commercial implementation of a published through-air portal dose image (PDI) prediction algorithm Van Esch et al. [Radiother. Oncol. 71, 223-234 (2004)] is proposed and validated. A detailed characterization of the attenuation, scattering, and EPID response behind objects in the beam path is used to convert through-air PDIs into transit PDIs. METHODS: The EPID detector response beyond a range of water equivalent thicknesses (0-35 cm) and field sizes (3×3 to 22.2×29.6 cm(2)) was analyzed. A constant air gap between the phantom exit surface and the EPID was utilized. A model was constructed that accounts for the beam's attenuation along the central axis, the presence of phantom scattered radiation, the detector's energy dependent response, and the difference in EPID off-axis pixel response relative to the central pixel. The efficacy of the algorithm was verified by comparing predicted and measured PDIs for IMRT fields delivered through phantoms of increasing complexity. RESULTS: The expression that converts a through-air PDI to a transit PDI is dependent on the object's thickness, the irradiated field size, and the EPID pixel position. Monte Carlo derived narrow-beam linear attenuation coefficients are used to model the decrease in primary fluence incident upon the EPID due to the object's presence in the beam. This term is multiplied by a factor that accounts for the broad beam scatter geometry of the linac-phantom-EPID system and the detector's response to the incident beam quality. A 2D Gaussian function that models the nonuniformity of pixel response across the EPID detector plane is developed. For algorithmic verification, 49 IMRT fields were repeatedly delivered to homogeneous slab phantoms in 5 cm increments. Over the entire set of measurements, the average area passing a 3%∕3mm gamma criteria slowly decreased from 98% for no material in the beam to 96.7% for 35 cm of material in the beam. The same 49 fields were delivered to a heterogeneous slab phantom and on average, 97.1% of the pixels passed the gamma criteria. Finally, a total of 33 IMRT fields were delivered to the anthropomorphic phantom and on average, 98.1% of the pixels passed. The likelihood of good matches was independent of anatomical site. CONCLUSIONS: A prediction of the transit PDI behind a phantom or patient can be created for the purposes of treatment verification via an extension of the Van Esch through-air PDI algorithm. The results of the verification measurements through phantoms indicate that further investigation through patients during their treatments is warranted.

Bayesian estimation of extropy and goodness of fit tests.

Extropy, a complementary dual of entropy, is considered in this paper. A Bayesian approach based on the Dirichlet process is proposed for the estimation of extropy. A goodness of fit test is also developed. Many theoretical properties of the procedure are derived. Several examples are discussed to illustrate the approach.

Nested block self-attention multiple resolution residual network for multiorgan segmentation from CT.

BACKGROUND: Fast and accurate multiorgans segmentation from computed tomography (CT) scans is essential for radiation treatment planning. Self-attention(SA)-based deep learning methodologies provide higher accuracies than standard methods but require memory and computationally intensive calculations, which restricts their use to relatively shallow networks. PURPOSE: Our goal was to develop and test a new computationally fast and memory-efficient bidirectional SA method called nested block self-attention (NBSA), which is applicable to shallow and deep multiorgan segmentation networks. METHODS: A new multiorgan segmentation method combining a deep multiple resolution residual network with computationally efficient SA called nested block SA (MRRN-NBSA) was developed and evaluated to segment 18 different organs from head and neck (HN) and abdomen organs. MRRN-NBSA combines features from multiple image resolutions and feature levels with SA to extract organ-specific contextual features. Computational efficiency is achieved by using memory blocks of fixed spatial extent for SA calculation combined with bidirectional attention flow. Separate models were trained for HN (n = 238) and abdomen (n = 30) and tested on set aside open-source grand challenge data sets for HN (n = 10) using a public domain database of computational anatomy and blinded testing on 20 cases from Beyond the Cranial Vault data set with overall accuracy provided by the grand challenge website for abdominal organs. Robustness to two-rater segmentations was also evaluated for HN cases using the open-source data set. Statistical comparison of MRRN-NBSA against Unet, convolutional network-based SA using criss-cross attention (CCA), dual SA, and transformer-based (UNETR) methods was done by measuring the differences in the average Dice similarity coefficient (DSC) accuracy for all HN organs using the Kruskall-Wallis test, followed by individual method comparisons using paired, two-sided Wilcoxon-signed rank tests at 95% confidence level with Bonferroni correction used for multiple comparisons. RESULTS: MRRN-NBSA produced an average high DSC of 0.88 for HN and 0.86 for the abdomen that exceeded current methods. MRRN-NBSA was more accurate than the computationally most efficient CCA (average DSC of 0.845 for HN, 0.727 for abdomen). Kruskal-Wallis test showed significant difference between evaluated methods (p=0.00025). Pair-wise comparisons showed significant differences between MRRN-NBSA than Unet (p=0.0003), CCA (p=0.030), dual (p=0.038), and UNETR methods (p=0.012) after Bonferroni correction. MRRN-NBSA produced less variable segmentations for submandibular glands (0.82 ± 0.06) compared to two raters (0.75 ± 0.31). CONCLUSIONS: MRRN-NBSA produced more accurate multiorgan segmentations than current methods on two different public data sets. Testing on larger institutional cohorts is required to establish feasibility for clinical use.

Automated Plan Checking Software Demonstrates Continuous and Sustained Improvements in Safety and Quality: A 3-year Longitudinal Analysis.

PURPOSE: This study aimed to perform a longitudinal analysis of the performance of our automated plan checking software by retrospectively evaluating the number of errors identified in plans delivered to patients in 3, month-long, data collection periods between 2017 and 2020. METHODS AND MATERIALS: Eleven automated checks were retrospectively run on 1169 external beam radiation therapy treatment plans identified as meeting the following criteria: planning target volume-based multifield photon plans receiving a status of treatment approved in March 2017, March 2018, or March 2020. The number of passes (true positives) and flags were recorded. Flags were subcategorized into false negatives, false negatives due to naming conventions, and true negatives. In addition, 2 × 2 contingency tables using a 2-tailed Fisher's exact test were used to determine whether there were nonrandom associations between the output of the automated plan checking software and whether the check was manual or automated at the original time of treatment approval. RESULTS: A statistically significant decrease in flags between the pre- and postautomation data sets was observed for 4 contour-based checks, namely adjacent structures overlap, empty structures and missing slices, overlap between body and couch, and laterality, as well as a check that determined whether the plan's global maximum dose was within the planning target volume. A review of the origins of false negatives was fed back into the design of the checks to improve the reliability of the system and help avoid warning fatigue. CONCLUSIONS: Periodic and longitudinal review of the performance of automated software was essential for monitoring and understanding its impact on error rates, as well as for optimization of the tool to adapt to regular changes of clinical practice. The automated plan checking software has demonstrated continuous contributions to the safe and effective delivery of external beam radiation therapy to our patient population, an impact that extends beyond its initial implementation and deployment.

Radiation therapy for de novo anorectal cancer in patients with a history of prostate radiation therapy.

Introduction: Radiation therapy (RT) for anorectal cancer after prior prostate cancer RT is usually avoided due to concern for complications. Data on this topic is scarce. Our aim was to evaluate tolerability, toxicity, and clinical outcomes associated with a second course of pelvic radiation in men with de novo anorectal cancers previously treated with RT for prostate cancer. Materials/methods: We conducted a single-institution retrospective study of men treated with RT for rectal or anal cancer after prior prostate RT. Toxicity data were collected. Treatment plans were extracted to assess doses to organs at risk and target coverage. Cumulative incidence was calculated for local and distant progression. Kaplan-Meier curves were used to estimate overall survival (OS) and progression-free survival (PFS). Results: We identified 26 patients who received anorectal RT after prostate cancer RT: 17 for rectal cancer and 9 for anal cancer. None had metastatic disease. Prior prostate RT was delivered using low dose rate brachytherapy (LDR), external beam RT (EBRT), or EBRT + LDR. RT for rectal cancer was delivered most commonly using 50.4Gy/28 fractions (fr) or 1.5 Gy twice-daily to 30-45 Gy. The most used RT dose for anal cancer was 50Gy/25 fr. Median interval between prostate and anorectal RT was 12.3 years (range:0.5 - 25.3). 65% and 89% of rectal and anal cancer patients received concurrent chemotherapy, respectively. There were no reported ≥Grade 4 acute toxicities. Two patients developed fistulae; one was urinary-cutaneous after prostate LDR and 45Gy/25fr for rectal cancer, and the other was recto-vesicular after prostate LDR and 50Gy/25fr for anal cancer. In 11 patients with available dosimetry, coverage for anorectal cancers was adequate. With a median follow up of 84.4 months, 5-yr local progression and OS were 30% and 31% for rectal cancer, and 35% and 49% for anal cancer patients, respectively. Conclusion: RT for anorectal cancer after prior prostate cancer RT is feasible but should be delivered with caution since it poses a risk of fistulae and possibly bleeding, especially in patients treated with prior LDR brachytherapy. Further studies, perhaps using proton therapy and/or rectal hydrogel spacers, are needed to further decrease toxicity and improve outcomes.

Ablative radiation therapy for hepatocellular carcinoma is associated with reduced treatment- and tumor-related liver failure and improved survival.

BACKGROUND: More than 70% of patients with hepatocellular carcinoma (HCC) are not candidates for curative therapy or recur after curative-intent therapy. There is growing evidence on the use of ablative radiation therapy (RT) for liver tumors. We aimed to analyze outcomes of HCC patients treated with conventional versus ablative RT. METHODS: We retrospectively analyzed medical records of HCC patients treated with liver RT from 2001 to 2019. We defined ablative RT as biologically effective dose (BED) ≥80 Gy. RECIST 1.1 was used to define early responses at 3-6 months after RT, and local control (LC) at last follow-up (FU). Data was analyzed using Fisher exact test, Kaplan-Meier, cumulative incidence rates, Cox proportional hazards model and Fine-Gray competing risks. RESULTS: Forty-five patients were identified, of whom 14 (31.1%) received ablative RT using a stereotactic technique. With median FU of survivors of 10.1 months, 1-year cumulative incidence of LC was 91.7% for ablative and 75.2% for BED <80 Gy. At early FU, patients treated with ablative RT had better responses compared to BED <80 Gy, with 7% progressing versus 19%, and 21.4% with complete response versus none (P=0.038). On univariate analysis (UVA), Child-Pugh (CP) score [hazard ratio (HR): 3 for CP-B, HR: 16 for CP-C] and BED (HR: 7.69 for BED <80 Gy) correlated with deterioration of liver function, leading to liver failure. Most liver failure cases were due to disease progression. No RT-related liver failure occurred in the ablative RT group. On UVA, only BED ≥80 Gy was associated with improved overall survival (OS) (HR: 0.4; P=0.044). Median OS (mOS) and 1-year OS were 7 months and 35% respectively for BED <80 Gy compared to 28 months and 66% for BED ≥80 Gy. No grade 3+ bowel toxicity was reported in either group. CONCLUSIONS: Greater than 90% LC was achieved after stereotactic ablative RT, which was associated with minimized tumor- and treatment-related liver failure and improved survival for highly selected inoperable HCC patients.

A field size specific backscatter correction algorithm for accurate EPID dosimetry.

PURPOSE: Portal dose images acquired with an amorphous silicon electronic portal imaging device (EPID) suffer from artifacts related to backscattered radiation. The backscatter signal varies as a function of field size (FS) and location on the EPID. Most current portal dosimetry algorithms fail to account for the FS dependence. The ramifications of this omission are investigated and solutions for correcting the measured dose images for FS specific backscatter are proposed. METHODS: A series of open field dose images were obtained for field sizes ranging from 2 x 2 to 30 x 40 cm2. Each image was analyzed to determine the amount of backscatter present. Two methods to account for the relationship between FS and backscatter are offered. These include the use of discrete FS specific correction matrices and the use of a single generalized equation. The efficacy of each approach was tested on the clinical dosimetric images for ten patients, 49 treatment fields. The fields were evaluated to determine whether there was an improvement in the dosimetric result over the commercial vendor's current algorithm. RESULTS: It was found that backscatter manifests itself as an asymmetry in the measured signal primarily in the inplane direction. The maximum error is approximately 3.6% for 10 x 10 and 12.5 x 12.5 cm2 field sizes. The asymmetry decreased with increasing FS to approximately 0.6% for fields larger than 30 x 30 cm2. The dosimetric comparison between the measured and predicted dose images was significantly improved (p << .001) when a FS specific backscatter correction was applied. The average percentage of points passing a 2%, 2 mm gamma criteria increased from 90.6% to between 96.7% and 97.2% after the proposed methods were employed. CONCLUSIONS: The error observed in a measured portal dose image depends on how much its FS differs from the 30 x 40 cm2 calibration conditions. The proposed methods for correcting for FS specific backscatter effectively improved the ability of the EPID to perform dosimetric measurements. Correcting for FS specific backscatter is important for accurate EPID dosimetry and can be carried out using the methods presented within this investigation.

Addressing brain injury in health care for the homeless settings: A pilot model for provider training.

BACKGROUND: Brain injury has been recently understood to be a common occurrence among adults experiencing homelessness, resulting in the need for modifications to clinical practice in agencies serving this population. OBJECTIVE: A health care agency for adults experiencing homelessness initiated a pilot training for mental health providers to address the issues of brain injury. METHODS: Providers attended eight training sessions which focused on: screening for a history of brain injury, treatment planning, and specific strategies to implement with individuals with a history of brain injury. Strategies taught were based on current literature and therapeutic methods, adapted specifically for the clinic's population of adults experiencing homelessness. RESULTS: Screening for a history of brain injury at the clinic indicated a high prevalence of a history of brain injury that was previously unidentified, indicating need for provider training. Providers reported increased ability to screen for and address the needs of individuals with brain injury within their clinical setting. Providers reported benefit from sessions tailored to address various cognitive functions which incorporated evidence-based practice and familiar therapeutic methods. CONCLUSION: Providers who engage individuals experiencing homelessness benefit from structured training in order to increase ability to screen for and modify interventions for a history of brain injury to better address their clients' needs.

PSIGAN: Joint Probabilistic Segmentation and Image Distribution Matching for Unpaired Cross-Modality Adaptation-Based MRI Segmentation.

We developed a new joint probabilistic segmentation and image distribution matching generative adversarial network (PSIGAN) for unsupervised domain adaptation (UDA) and multi-organ segmentation from magnetic resonance (MRI) images. Our UDA approach models the co-dependency between images and their segmentation as a joint probability distribution using a new structure discriminator. The structure discriminator computes structure of interest focused adversarial loss by combining the generated pseudo MRI with probabilistic segmentations produced by a simultaneously trained segmentation sub-network. The segmentation sub-network is trained using the pseudo MRI produced by the generator sub-network. This leads to a cyclical optimization of both the generator and segmentation sub-networks that are jointly trained as part of an end-to-end network. Extensive experiments and comparisons against multiple state-of-the-art methods were done on four different MRI sequences totalling 257 scans for generating multi-organ and tumor segmentation. The experiments included, (a) 20 T1-weighted (T1w) in-phase mdixon and (b) 20 T2-weighted (T2w) abdominal MRI for segmenting liver, spleen, left and right kidneys, (c) 162 T2-weighted fat suppressed head and neck MRI (T2wFS) for parotid gland segmentation, and (d) 75 T2w MRI for lung tumor segmentation. Our method achieved an overall average DSC of 0.87 on T1w and 0.90 on T2w for the abdominal organs, 0.82 on T2wFS for the parotid glands, and 0.77 on T2w MRI for lung tumors.

Dynamic multiatlas selection-based consensus segmentation of head and neck structures from CT images.

PURPOSE: Manual delineation of head and neck (H&N) organ-at-risk (OAR) structures for radiation therapy planning is time consuming and highly variable. Therefore, we developed a dynamic multiatlas selection-based approach for fast and reproducible segmentation. METHODS: Our approach dynamically selects and weights the appropriate number of atlases for weighted label fusion and generates segmentations and consensus maps indicating voxel-wise agreement between different atlases. Atlases were selected for a target as those exceeding an alignment weight called dynamic atlas attention index. Alignment weights were computed at the image level and called global weighted voting (GWV) or at the structure level and called structure weighted voting (SWV) by using a normalized metric computed as the sum of squared distances of computed tomography (CT)-radiodensity and modality-independent neighborhood descriptors (extracting edge information). Performance comparisons were performed using 77 H&N CT images from an internal Memorial Sloan-Kettering Cancer Center dataset (N = 45) and an external dataset (N = 32) using Dice similarity coefficient (DSC), Hausdorff distance (HD), 95th percentile of HD, median of maximum surface distance, and volume ratio error against expert delineation. Pairwise DSC accuracy comparisons of proposed (GWV, SWV) vs single best atlas (BA) or majority voting (MV) methods were performed using Wilcoxon rank-sum tests. RESULTS: Both SWV and GWV methods produced significantly better segmentation accuracy than BA (P < 0.001) and MV (P < 0.001) for all OARs within both datasets. SWV generated the most accurate segmentations with DSC of: 0.88 for oral cavity, 0.85 for mandible, 0.84 for cord, 0.76 for brainstem and parotids, 0.71 for larynx, and 0.60 for submandibular glands. SWV's accuracy exceeded GWV's for submandibular glands (DSC = 0.60 vs 0.52, P = 0.019). CONCLUSIONS: The contributed SWV and GWV methods generated more accurate automated segmentations than the other two multiatlas-based segmentation techniques. The consensus maps could be combined with segmentations to visualize voxel-wise consensus between atlases within OARs during manual review.