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.

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.

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.

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.

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.

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.

Use of a constrained hierarchical optimization dataset enhances knowledge-based planning as a quality assurance tool for prostate bed irradiation.

PURPOSE: To investigate whether building a knowledge-based planning (KBP) model with prostate bed plans constructed from constrained hierarchical optimization (CHO) would result in more efficient model construction with more consistent output than a model built using plans from a traditional, trial-and-error-based optimization (TEO) technique. METHODS: Three KBP models were constructed from plans from subsets of 58 post-prostatectomy patients treated with intensity-modulated radiation therapy. TEO54 was built from 54 TEO plans, selected to represent typical clinical variations in target and organ-at-risk sizes and shapes. CHO30 and TEO30 were built from the same 30 patients populated with CHO and TEO plans, respectively. The three models were each applied to a new set of 18 patient scans and dose-volume histogram estimates (DVHEs) were generated for rectal and bladder walls and compared for each patient. RESULTS: CHO30 resulted in a significantly tighter range in DVHEs (P < 0.01) for both the rectal and bladder walls compared with either of the TEO models, indicating less uncertainty in the dose estimation. Plans resulting from KBP optimization using each model were very similar. CONCLUSION: Populating a KBP model with CHO data resulted in a high quality model. Since CHO plans can be generated automatically offline in a process that necessitates little to no user interaction, a CHO-KBP model can quickly adapt to changes in plan evaluation criteria or planning techniques without the need to wait to accrue sufficient numbers of clinical TEO plans. This may facilitate the use of KBP approaches for initial or ongoing quality assurance procedures and plan quality audits.

Five years' experience with a customized electronic checklist for radiation therapy planning quality assurance in a multicampus institution.

INTRODUCTION: An electronic checklist has been designed with the intention of reducing errors while minimizing user effort in completing the checklist. We analyze the clinical use and evolution of the checklist over the past 5 years and review data in an incident learning system (ILS) to investigate whether it has contributed to an improvement in patient safety. METHODS AND MATERIALS: The checklist is written as a standalone HTML application using VBScript. User selection of pertinent demographic details limits the display of checklist items only to those necessary for the particular clinical scenario. Ten common clinical scenarios were used to illustrate the difference between the maximum possible number of checklist items available in the code versus the number displayed to the user at any one time. An ILS database of errors and near misses was reviewed to evaluate whether the checklist influenced the occurrence of reported events. RESULTS: Over 5 years, the number of checklist items available in the code nearly doubled, whereas the number displayed to the user at any one time stayed constant. Events reported in our ILS related to the beam energy used with pacemakers, projection of anatomy on digitally reconstructed radiographs, orthogonality of setup fields, and field extension beyond match lines, did not recur after the items were added to the checklist. Other events related to bolus documentation and breakpoints continued to be reported. CONCLUSION: Our checklist is adaptable to the introduction of new technologies, transitions between planning systems, and to errors and near misses recorded in the ILS. The electronic format allows us to restrict user display to a small, relevant, subset of possible checklist items, limiting the planner effort needed to review and complete the checklist.

Intensity-modulated radiation therapy (IMRT) for nasopharynx cancer: update of the Memorial Sloan-Kettering experience.

PURPOSE: We previously demonstrated that intensity-modulated radiation therapy (IMRT) significantly improves radiation dose distribution over three-dimensional planning for nasopharynx cancer and reported positive early clinical results. We now evaluate whether IMRT has resulted in improved outcomes for a larger cohort of patients with longer follow-up. METHODS AND MATERIALS: Since 1998, all 74 patients with newly diagnosed, nonmetastatic nasopharynx cancer were treated with IMRT using accelerated fractionation to 70 Gy; 59 received a hyperfractionated concomitant boost, and more recently 15 received once-daily treatment with dose painting. With the exception of Stage I disease (n = 5) and patient preference (n = 1), 69 patients received concurrent and adjuvant platinum-based chemotherapy similar to that in the Intergroup 0099 trial. PATIENT CHARACTERISTICS: median age 45; 32% Asian; 72% male; 65% World Health Organization III; 6% Stage I, 16% Stage II, 30% Stage III, 47% Stage IV. Median follow-up is 35 months. The 3-year actuarial rate of local control is 91%, and regional control is 93%; freedom from distant metastases, progression-free survival, and overall survival at 3 years are 78%, 67%, and 83%, respectively. There was 100% local control for Stage T1/T2 disease, compared to 83% for T3/T4 disease (p = 0.01). Six patients failed at the primary site, with median time to local tumor progression 16 months; 5 were exclusively within the 70 Gy volume, and 1 was both within and outside the target volume. There is a trend for improved local control with IMRT when compared to local control of 79% for 35 patients treated before 1998 with three-dimensional planning and chemotherapy (p = 0.11). Six months posttherapy, 21%, 13%, 15%, and 0% of patients with follow-up audiograms (n = 24 patients) had Grade 1, 2, 3, and 4 sensorineural hearing loss, respectively. For patients with >1 year follow-up (n = 59), rates of long-term xerostomia were as follows: 26% none, 42% Grade 1, 32% Grade 2, and zero Grade 3. CONCLUSIONS: The pattern of primary site failure within the target volume suggests locally advanced T stage disease may require a higher biologic dose to gross tumor. Rates of severe (Grade 3-4) ototoxicity and xerostomia are low with IMRT as a result of normal-tissue protection. Distant metastases are now the dominant form of failure, emphasizing the need for improved systemic therapy.

Dosimetric comparison of axilla and groin radiotherapy techniques for high-risk and locally advanced skin cancer.

PURPOSE: Radiation therapy targeting axilla and groin lymph nodes improves regional disease control in locally advanced and high-risk skin cancers. However, trials generally used conventional two-dimensional radiotherapy (2D-RT), contributing towards relatively high rates of side effects from treatment. The goal of this study is to determine if three-dimensional conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT), or volumetric-modulated arc therapy (VMAT) may improve radiation delivery to the target while avoiding organs at risk in the clinical context of skin cancer regional nodal irradiation. MATERIALS AND METHODS: Twenty patients with locally advanced/high-risk skin cancers underwent computed tomography simulation. The relevant axilla or groin planning target volumes and organs at risk were delineated using standard definitions. Paired t-tests were used to compare the mean values of several dose-volumetric parameters for each of the 4 techniques. RESULTS: In the axilla, the largest improvement for 3D-CRT compared to 2D-RT was for homogeneity index (13.9 vs. 54.3), at the expense of higher lung V20 (28.0% vs. 12.6%). In the groin, the largest improvements for 3D-CRT compared to 2D-RT were for anorectum Dmax (13.6 vs. 38.9 Gy), bowel D200cc (7.3 vs. 23.1 Gy), femur D50 (34.6 vs. 57.2 Gy), and genitalia Dmax (37.6 vs. 51.1 Gy). IMRT had further improvements compared to 3D-CRT for humerus Dmean (16.9 vs. 22.4 Gy), brachial plexus D5 (57.4 vs. 61.3 Gy), bladder D5 (26.8 vs. 36.5 Gy), and femur D50 (18.7 vs. 34.6 Gy). Fewer differences were observed between IMRT and VMAT. CONCLUSION: Compared to 2D-RT and 3D-CRT, IMRT and VMAT had dosimetric advantages in the treatment of nodal regions of skin cancer patients.

Interobserver variability in radiation therapy plan output: Results of a single-institution study.

PURPOSE: We investigated the sources of variability in radiation therapy treatment plan output between planners within a single institution. METHODS AND MATERIALS: Forty treatment planners across 5 campuses of an institution created a plan on the same thoracic esophagus patient computed tomography scan and structure set. Plans were scored and ranked based on the planner's adherence to an ordered list of target dose coverage and normal tissue evaluation criteria. A runs test was used to identify whether any of the studied planner qualities influenced the ranking. Spearman rank correlation was used to investigate whether plan score correlated with years of experience or planned monitor units. RESULTS: The distribution of scores, ranging from 80.24 to 135.89, was negatively skewed (mean, 128.7; median, 131.5). No statistically significant relationship between plan score and campus (P = .193), job title (P = .174), previous outside experience (P = .611), or number of gantry angles (P = .156) was discovered. No statistical correlation between plan score and monitor unit or years of experience was found. CONCLUSIONS: Despite clear and established critical organ dose criteria and well-documented planning guidelines, planning variation still occurs, even among members of the same institution. Because plan consistency does not seem to significantly correlate with experience, career path, or campus, investigation into alternate methods beyond additional education and training to reduce this variation, such as knowledge-based planning or advanced optimization techniques, is necessary.