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All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Towards Adaptive Mesh Refinement for the Spectral Element Solver Nek5000

When performing computational fluid dynamics (CFD) simulations of complex flows, the a priori knowledge of the flow physics and the location of the dominant flow features are usually unknown. For this reason, the development of adaptive remeshing techniques is crucial for large-scale computational problems. Some work has been made recently to provide Nek5000 with adaptive mesh refinement (AMR) capabilities in order to facilitate the generation of the grid and push forward the limit in terms of problem size and complexity [10]. Nek5000 is an open-source, highly scalable and portable code based on the spectral element method (SEM) [4], which offers minimal dissipation and dispersion, high accuracy and exponential convergence. It is aimed at solving direct and large-eddy simulations of turbulent incompressible or low Mach-number flows with heat transfer and species transport. The approach chosen for adapting the mesh is the h-refinement method, where elements are split locally, which requires the relaxation of the conforming grid constraint currently imposed by Nek5000. Other challenges include the implementation of an efficient management of the grid as refinement is applied, the development of tools to localize the critical flow regions via error estimators and the extension of the current preconditioning strategy to non-conforming grids. In this paper, we present a new procedure to setup an algebraic multigrid solver used as part of the preconditioner for the pressure equation.

Offermans, N.↗
DOE OSTI2019

Porting Adaptive Ensemble Molecular Dynamics Workflows to the Summit Supercomputer

Molecular dynamics (MD) simulations must take very small (femtosecond) integration steps in simulation-time to avoid numerical errors. Efficient use of parallel programming models and accelerators in state-of-the art MD programs now is pushing Moore’s limit for time-per-MD step. As a result, directly simulating timescales beyond milliseconds will not be attainable directly, even at exascale. However, concepts from statistical physics can be used to combine many parallel simulations to provide information about longer timescales and to adequately sample the simulation space, while preserving details about the dynamics of the system. Implementing such an approach requires a workflow program that allows adaptable steering of task assignments based on extensive statistical analysis of intermediate results. Here we report the implementation of such an adaptable workflow program to drive simulations on the Summit IBM Power System AC922, a pre-exascale supercomputer at the Oak Ridge Leadership Computing Facility (OLCF). We compare to experiences on Titan, Summit’s predecessor, report the performance of the workflow and its components, and describe the porting process. We find that using a workflow program managed by a Mongo database can provide the fault tolerance, scalable performance, task dispatch rate, and reconfigurability required for robust and portable implementation of ensemble simulations such as are used in enhanced-sampling molecular dynamics. This type of workflow generator can also be used to provide adaptive steering of ensemble simulations for other applications in addition to MD.

Ossyra, John R.↗
DOE OSTI2013

Cross-validation based single response adaptive design of experiments for Kriging metamodeling of deterministic computer simulations

A new approach for single response adaptive design of deterministic computer experiments is presented. The approach is called SFCVT, for Space-Filling CrossValidation Tradeoff. SFCVT uses metamodeling to obtain an estimate of cross-validation errors, which are maximized subject to a constraint on space filling to determine sample points in the design space. The proposed method is compared, using a test suite of forty four numerical examples, with three DOE methods from the literature. The numerical test examples can be classified into symmetric and asymmetric functions. Symmetric examples refer to functions for which the extreme points are located symmetrically in the design space and asymmetric examples are those for which the extreme regions are not located in a symmetric fashion in the design space. Based upon the comparison results for the numerical examples, it is shown that SFCVT performs better than an existing adaptive and a non-adaptive DOE method for asymmetric multimodal functions with high nonlinearity near the boundary, and is comparable for symmetric multimodal functions and other test problems. The proposed approach is integrated with a multi-scale heat exchanger optimization tool to reduce the computational effort involved in the design of novel air-to-water heat exchangers. In conclusion, the resulting designs are shown to be significantly more compact than mainstream heat exchanger designs.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2013

Implications of simultaneously mitigating and adapting to climate change: Initial experiments using GCAM

Historically climate impacts research and climate mitigation research have been two separate and independent domains of inquiry. Climate mitigation research has investigated greenhouse gas emissions assuming that climate is unchanging. At the same time climate mitigation research has investigated the implications of climate change on the assumption that climate mitigation will proceed without affecting the degree of climate impacts or the ability of human and natural systems to adapt. The Global Change Assessment Model (GCAM) has largely been employed to study climate mitigation. Here we explore the development of capabilities to assess climate change impacts and adaptation within the GCAM model. These capabilities are being developed so as to be able to simultaneously reconcile the joint implications of climate change mitigation, impacts and adaptive potential. This is an important step forward in that it enables direct comparison between climate mitigation activities and climate impacts and the opportunity to understand interactions between the two.

Calvin, Katherine V↗
DOE OSTI2025

Robust Implicit Adaptive Low Rank Time-Stepping Methods for Matrix Differential Equations

In this work, we develop implicit rank-adaptive schemes for time-dependent matrix differential equations. The dynamic low rank approximation (DLRA) is a well-known technique to capture the dynamic low rank structure based on Dirac–Frenkel time-dependent variational principle. In recent years, it has attracted a lot of attention due to its wide applicability. Our schemes are inspired by the three-step procedure used in the rank adaptive version of the unconventional robust integrator (the so called BUG integrator) (Ceruti et al. in BIT Numer Math 62(4):1149–1174, 2022) for DLRA. First, a prediction (basis update) step is made computing the approximate column and row spaces at the next time level. Second, a Galerkin evolution step is invoked using an implicit solves for the small core matrix. Finally, a truncation is made according to a prescribed error threshold. Since the DLRA is evolving the differential equation projected on to the tangent space of the low rank manifold, the error estimate of the BUG integrator contains the tangent projection (modeling) error which cannot be easily controlled by mesh refinement. This can cause convergence issue for equations with cross terms. To address this issue, we propose a simple modification, consisting of merging the row and column spaces from the explicit step truncation method together with the BUG spaces in the prediction step. In addition, we propose an adaptive strategy where the BUG spaces are only computed if the residual for the solution obtained from the prediction space by explicit step truncation method, is too large. Here, we prove stability and estimate the local truncation error of the schemes under assumptions. We benchmark the schemes in several tests, such as anisotropic diffusion, solid body rotation and the combination of the two, to show robust convergence properties.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Data Assimilation in the ADAPT Photospheric Flux Transport Model

Global maps of the solar photospheric magnetic flux are fundamental drivers for simulations of the corona and solar wind and therefore are important predictors of geoeffective events. However, observations of the solar photosphere are only made intermittently over approximately half of the solar surface. The Air Force Data Assimilative Photospheric Flux Transport (ADAPT) model uses localized ensemble Kalman filtering techniques to adjust a set of photospheric simulations to agree with the available observations. At the same time, this information is propagated to areas of the simulation that have not been observed. ADAPT implements a local ensemble transform Kalman filter (LETKF) to accomplish data assimilation, allowing the covariance structure of the flux-transport model to influence assimilation of photosphere observations while eliminating spurious correlations between ensemble members arising from a limited ensemble size. We give a detailed account of the implementation of the LETKF into ADAPT. Advantages of the LETKF scheme over previously implemented assimilation methods are highlighted.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Insight into adaptive remodeling of the rotor ring complex of the bacterial flagellar motor

Highlights: • Adaptive remodeling of the flagellar motor ring is responsible for motor switching. • Helix{sub MC} connecting FliG{sub M} and FliG{sub C} is responsible for the switching. • A CW-locked deletion of FliG suppresses the oligomerization of FliG in solution. • The CW-locked deletion reduces the binding affinity of FliG for FliM. • We provide an insight into structural remodeling of the flagellar motor. The bacterial flagellar motor rotates in both counterclockwise (CCW) and clockwise (CW) directions. FliG, FliM and FliN form the C ring on the cytoplasmic face of the MS ring made of a transmembrane protein, FliF. The C ring acts not only as a rotor but also as a switch of the direction of motor rotation. FliG consists of three domains: FliG{sub N}, FliG{sub M} and FliG{sub C}. FliG{sub N} directly binds to FliF. Intermolecular interactions between FliG{sub M} and FliG{sub C} drive FliG ring formation. FliG{sub M} is responsible for the interaction with FliM. FliG{sub C} is involved in the interaction with the stator protein MotA. Adaptive remodeling of the C ring occurs when the motor switches between the CCW and CW states. However, it remained unknown how. Here, we report the effects of a CW-locked deletion mutation (ΔPEV) in FliG of Thermotaoga maritia (Tm-FliG) on FliG–FliG and FliG–FliM interactions. The PEV deletion stabilized the intramolecular interaction between FliG{sub M} and FliG{sub C}, thereby suppressing the oligomerization of Tm-FliG{sub MC} in solution. This deletion also induced a conformational change of Helix{sub MC} connecting FliG{sub M} and FliG{sub C} to reduce the binding affinity of Tm-FliG{sub MC} for FliM. We will discuss adaptive remodeling of the C ring responsible for flagellar motor switching.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Adaptive simulations enable computational design of electron beam processing of nanomaterials with supersonic micro-jet precursor

Focused Electron Beam Induced Processing (FEBIP) is a powerful tool for the “direct-write” of nanomaterials with the possibility of atomistic control on suspended 2D material substrates. FEBIP capabilities have been significantly expanded by using a localized jet-based delivery of precursors, and especially when a thermally energized supersonic micro-jet enhances the delivery of mass flux along with controlling the far-from-equilibrium thermodynamic state of adsorbed adatoms. The possibilities of growing nanomaterials with “dialed-in” composition with ultra-high growth rates and aspect ratios up to 100:1 have been demonstrated using the supersonic micro-jet-FEBIP. Bringing this scientific discovery to the level of maturity required for practical applications in additive nanomanufacturing requires simulation tools that are capable of capturing the complex flow physics of micro-jet-substrate interactions that bridge a wide range of flow regimes from the high-density gas micro-jet expanding into the vacuum environment of FEBIP. To address this significant computational challenge, a new approach has been developed and described in this work for a multiscale adaptive DSMC (Direct Simulation Monte Carlo) algorithm to predict the micro-jet gas dynamics in an FEBIP environment, spanning the full range of flow regimes from low Knudsen (Kn) number O(0.01) continuum flow to high Kn of O(10) for the molecular flow within a unified computational framework. Here, the fundamental principles of the adaptive DSMC algorithm are described, its viability as a DSMC technique is demonstrated, and computational improvements for the benchmark cases are discussed in the context of advancing 3D nanofabrication with FEBIP. Ultimately, combining the first principle simulations via adaptive DSMC with the complementary experimental data will enable the creation of the powerful CAD tools for in silico design and optimal operation of micro-jet-FEBIP.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Accounting for adaptation and intensity in projecting heat wave-related mortality

Highlights: • We propose novel models for intensity of and adaptation to heat waves in projections of heat wave- mortality. • The modeling used a large national dataset and the projections used a rich set of climate models and scenarios. • Future heat wave-related mortality would be substantially overestimated, if adaptation were ignored. • The time trend of future heat wave-related mortality will vary substantially across climate regions. How adaptation and intensity of heat waves affect heat wave-related mortality is unclear, making health projections difficult.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

Limiter-aware adaptive excitation control for hydropower generators with legacy voltage regulation systems

Hydropower units often rely on legacy excitation systems with fixed automatic voltage regulator (AVR) settings, but parameter drift, changing operating conditions, and evolving grid-service demands can degrade terminal-voltage regulation over time. This problem should be addressed because poor voltage regulation affects reactive-power support, system stability, and reliable plant operation, and replacing installed AVR and limiter logic is costly and disruptive in practice. To address this issue, this paper proposes a retrofit-friendly enhancement for hydropower generator excitation systems that combines adaptive tuning of the AVR middle lead–lag branch with a small proportional-integral correction for removing steady bias and slow drift. The adaptive laws are normalized, projection-bounded, and equipped with leakage, while adaptation is enabled only in the middle branch. Thus, the intent of the underexcitation and overexcitation limiters, as well as legacy current and rate limits, remains unchanged. Stability is analyzed under incremental performance assumptions, yielding boundedness and asymptotic tracking in the absence of saturation. The method is evaluated using real operational data from a utility-scale hydropower unit at Rocky Reach Dam, Unit C-8. Compared with the fixed AVR baseline, the proposed method reduces terminal-voltage mean squared error by about 70%, removes long periods of steady-state bias, and improves transient tracking while coexisting with limiter actions. These results show that substantial voltage-control improvement can be achieved on existing hydropower units with minimal integration effort and without replacing the installed AVR structure.

ESST5B model↗
DOE OSTI2012

Adaptive Image-Guided Radiotherapy (IGRT) Eliminates the Risk of Biochemical Failure Caused by the Bias of Rectal Distension in Prostate Cancer Treatment Planning: Clinical Evidence

Purpose: Rectal distension has been shown to decrease the probability of biochemical control. Adaptive image-guided radiotherapy (IGRT) corrects for target position and volume variations, reducing the risk of biochemical failure while yielding acceptable rates of gastrointestinal (GI)/genitourinary (GU) toxicities. Methods and Materials: Between 1998 and 2006, 962 patients were treated with computed tomography (CT)-based offline adaptive IGRT. Patients were stratified into low (n = 400) vs. intermediate/high (n = 562) National Comprehensive Cancer Network (NCCN) risk groups. Target motion was assessed with daily CT during the first week. Electronic portal imaging device (EPID) was used to measure daily setup error. Patient-specific confidence-limited planning target volumes (cl-PTV) were then constructed, reducing the standard PTV and compensating for geometric variation of the target and setup errors. Rectal volume (RV), cross-sectional area (CSA), and rectal volume from the seminal vesicles to the inferior prostate (SVP) were assessed on the planning CT. The impact of these volumetric parameters on 5-year biochemical control (BC) and chronic Grades {>=}2 and 3 GU and GI toxicity were examined. Results: Median follow-up was 5.5 years. Median minimum dose covering cl-PTV was 75.6 Gy. Median values for RV, CSA, and SVP were 82.8 cm{sup 3}, 5.6 cm{sup 2}, and 53.3 cm{sup 3}, respectively. The 5-year BC was 89% for the entire group: 96% for low risk and 83% for intermediate/high risk (p < 0.001). No statistically significant differences in BC were seen with stratification by RV, CSA, and SVP in quartiles. Maximum chronic Grades {>=}2 and 3 GI toxicities were 21.2% and 2.9%, respectively. Respective values for GU toxicities were 15.5% and 4.3%. No differences in GI or GU toxicities were noted when patients were stratified by RV. Conclusions: Incorporation of adaptive IGRT reduces the risk of geometric miss and results in excellent biochemical control that is independent of rectal volume/distension while maintaining very low rates of chronic GI toxicity.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2012

A 5-Year Investigation of Children's Adaptive Functioning Following Conformal Radiation Therapy for Localized Ependymoma

Purpose: Conformal and intensity modulated radiation therapies have the potential to preserve cognitive outcomes in children with ependymoma; however, functional behavior remains uninvestigated. This longitudinal investigation prospectively examined intelligence quotient (IQ) and adaptive functioning during the first 5 years after irradiation in children diagnosed with ependymoma. Methods and Materials: The study cohort consisted of 123 children with intracranial ependymoma. Mean age at irradiation was 4.60 years (95% confidence interval [CI], 3.85-5.35). Serial neurocognitive evaluations, including an age-appropriate IQ measure and the Vineland Adaptive Behavior Scales (VABS), were completed before irradiation, 6 months after treatment, and annually for 5 years. A total of 579 neurocognitive evaluations were included in these analyses. Results: Baseline IQ and VABS were below normative means (P<.05), although within the average range. Linear mixed models revealed stable IQ and VABS across the follow-up period, except for the VABS Communication Index, which declined significantly (P=.015). Annual change in IQ (-.04 points) did not correlate with annual change in VABS (-.90 to +.44 points). Clinical factors associated with poorer baseline performance (P<.05) included preirradiation chemotherapy, cerebrospinal fluid shunt placement, number and extent of surgical resections, and younger age at treatment. No clinical factors significantly affected the rate of change in scores. Conclusions: Conformal and intensity modulated radiation therapies provided relative sparing of functional outcomes including IQ and adaptive behaviors, even in very young children. Communication skills remained vulnerable and should be the target of preventive and rehabilitative interventions.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2012

Tumor Volume-Adapted Dosing in Stereotactic Ablative Radiotherapy of Lung Tumors

Purpose: Current stereotactic ablative radiotherapy (SABR) protocols for lung tumors prescribe a uniform dose regimen irrespective of tumor size. We report the outcomes of a lung tumor volume-adapted SABR dosing strategy. Methods and Materials: We retrospectively reviewed the outcomes in 111 patients with a total of 138 primary or metastatic lung tumors treated by SABR, including local control, regional control, distant metastasis, overall survival, and treatment toxicity. We also performed subset analysis on 83 patients with 97 tumors treated with a volume-adapted dosing strategy in which small tumors (gross tumor volume <12 mL) received single-fraction regimens with biologically effective doses (BED) <100 Gy (total dose, 18-25 Gy) (Group 1), and larger tumors (gross tumor volume {>=}12 mL) received multifraction regimens with BED {>=}100 Gy (total dose, 50-60 Gy in three to four fractions) (Group 2). Results: The median follow-up time was 13.5 months. Local control for Groups 1 and 2 was 91.4% and 92.5%, respectively (p = 0.24) at 12 months. For primary lung tumors only (excluding metastases), local control was 92.6% and 91.7%, respectively (p = 0.58). Regional control, freedom from distant metastasis, and overall survival did not differ significantly between Groups 1 and 2. Rates of radiation pneumonitis, chest wall toxicity, and esophagitis were low in both groups, but all Grade 3 toxicities developed in Group 2 (p = 0.02). Conclusion: A volume-adapted dosing approach for SABR of lung tumors seems to provide excellent local control for both small- and large-volume tumors and may reduce toxicity.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Predictive Models for Regional Hepatic Function Based on 99mTc-IDA SPECT and Local Radiation Dose for Physiologic Adaptive Radiation Therapy

Purpose: High-dose radiation therapy (RT) for intrahepatic cancer is limited by the development of liver injury. This study investigated whether regional hepatic function assessed before and during the course of RT using 99mTc-labeled iminodiacetic acid (IDA) single photon emission computed tomography (SPECT) could predict regional liver function reserve after RT. Methods and Materials: Fourteen patients treated with RT for intrahepatic cancers underwent dynamic 99mTc-IDA SPECT scans before RT, during, and 1 month after completion of RT. Indocyanine green (ICG) tests, a measure of overall liver function, were performed within 1 day of each scan. Three-dimensional volumetric hepatic extraction fraction (HEF) images of the liver were estimated by deconvolution analysis. After coregistration of the CT/SPECT and the treatment planning CT, HEF dose–response functions during and after RT were generated. The volumetric mean of the HEFs in the whole liver was correlated with ICG clearance time. Three models, dose, priori, and adaptive models, were developed using multivariate linear regression to assess whether the regional HEFs measured before and during RT helped predict regional hepatic function after RT. Results: The mean of the volumetric liver HEFs was significantly correlated with ICG clearance half-life time (r=−0.80, P<.0001), for all time points. Linear correlations between local doses and regional HEFs 1 month after RT were significant in 12 patients. In the priori model, regional HEF after RT was predicted by the planned dose and regional HEF assessed before RT (R=0.71, P<.0001). In the adaptive model, regional HEF after RT was predicted by regional HEF reassessed during RT and the remaining planned local dose (R=0.83, P<.0001). Conclusions: 99mTc-IDA SPECT obtained during RT could be used to assess regional hepatic function and helped predict post-RT regional liver function reserve. This could support individualized adaptive radiation treatment strategies to maximize tumor control and minimize the risk of liver damage.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

A Fully Automated Method for CT-on-Rails-Guided Online Adaptive Planning for Prostate Cancer Intensity Modulated Radiation Therapy

Purpose: This study was designed to validate a fully automated adaptive planning (AAP) method which integrates automated recontouring and automated replanning to account for interfractional anatomical changes in prostate cancer patients receiving adaptive intensity modulated radiation therapy (IMRT) based on daily repeated computed tomography (CT)-on-rails images. Methods and Materials: Nine prostate cancer patients treated at our institution were randomly selected. For the AAP method, contours on each repeat CT image were automatically generated by mapping the contours from the simulation CT image using deformable image registration. An in-house automated planning tool incorporated into the Pinnacle treatment planning system was used to generate the original and the adapted IMRT plans. The cumulative dose–volume histograms (DVHs) of the target and critical structures were calculated based on the manual contours for all plans and compared with those of plans generated by the conventional method, that is, shifting the isocenters by aligning the images based on the center of the volume (COV) of prostate (prostate COV-aligned). Results: The target coverage from our AAP method for every patient was acceptable, while 1 of the 9 patients showed target underdosing from prostate COV-aligned plans. The normalized volume receiving at least 70 Gy (V{sub 70}), and the mean dose of the rectum and bladder were reduced by 8.9%, 6.4 Gy and 4.3%, 5.3 Gy, respectively, for the AAP method compared with the values obtained from prostate COV-aligned plans. Conclusions: The AAP method, which is fully automated, is effective for online replanning to compensate for target dose deficits and critical organ overdosing caused by interfractional anatomical changes in prostate cancer.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Adaptive Liver Stereotactic Body Radiation Therapy: Automated Daily Plan Reoptimization Prevents Dose Delivery Degradation Caused by Anatomy Deformations

Purpose: To investigate how dose distributions for liver stereotactic body radiation therapy (SBRT) can be improved by using automated, daily plan reoptimization to account for anatomy deformations, compared with setup corrections only. Methods and Materials: For 12 tumors, 3 strategies for dose delivery were simulated. In the first strategy, computed tomography scans made before each treatment fraction were used only for patient repositioning before dose delivery for correction of detected tumor setup errors. In adaptive second and third strategies, in addition to the isocenter shift, intensity modulated radiation therapy beam profiles were reoptimized or both intensity profiles and beam orientations were reoptimized, respectively. All optimizations were performed with a recently published algorithm for automated, multicriteria optimization of both beam profiles and beam angles. Results: In 6 of 12 cases, violations of organs at risk (ie, heart, stomach, kidney) constraints of 1 to 6 Gy in single fractions occurred in cases of tumor repositioning only. By using the adaptive strategies, these could be avoided (<1 Gy). For 1 case, this needed adaptation by slightly underdosing the planning target volume. For 2 cases with restricted tumor dose in the planning phase to avoid organ-at-risk constraint violations, fraction doses could be increased by 1 and 2 Gy because of more favorable anatomy. Daily reoptimization of both beam profiles and beam angles (third strategy) performed slightly better than reoptimization of profiles only, but the latter required only a few minutes of computation time, whereas full reoptimization took several hours. Conclusions: This simulation study demonstrated that replanning based on daily acquired computed tomography scans can improve liver stereotactic body radiation therapy dose delivery.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Manifestation Pattern of Early-Late Vaginal Morbidity After Definitive Radiation (Chemo)Therapy and Image-Guided Adaptive Brachytherapy for Locally Advanced Cervical Cancer: An Analysis From the EMBRACE Study

Background and Purpose: Brachytherapy in the treatment of locally advanced cervical cancer has changed substantially because of the introduction of combined intracavitary/interstitial applicators and an adaptive target concept, which is the focus of the prospective, multi-institutional EMBRACE study ( (www.embracestudy.dk)) on image-guided adaptive brachytherapy (IGABT). So far, little has been reported about the development of early to late vaginal morbidity in the frame of IGABT. Therefore, the aim of the present EMBRACE analysis was to evaluate the manifestation pattern of vaginal morbidity during the first 2 years of follow-up. Methods and Materials: In total, 588 patients with a median follow-up time of 15 months and information on vaginal morbidity were included. Morbidity was prospectively assessed at baseline, every 3 months during the first year, and every 6 months in the second year according to the Common Terminology Criteria for Adverse Events, version 3, regarding vaginal stenosis, dryness, mucositis, bleeding, fistula, and other symptoms. Crude incidence rates, actuarial probabilities, and prevalence rates were analyzed. Results: At 2 years, the actuarial probability of severe vaginal morbidity (grade ≥3) was 3.6%. However, mild and moderate vaginal symptoms were still pronounced (grade ≥1, 89%; grade ≥2, 29%), of which the majority developed within 6 months. Stenosis was most frequently observed, followed by vaginal dryness. Vaginal bleeding and mucositis were mainly mild and infrequently reported. Conclusion: Severe vaginal morbidity within the first 2 years after definitive radiation (chemo)therapy including IGABT with intracavitary/interstitial techniques for locally advanced cervical cancer is limited and is significantly less than has been reported from earlier studies. Thus, the new adaptive target concept seems to be a safe treatment with regard to the vagina being an organ at risk. However, mild to moderate vaginal morbidity is still pronounced with currently applied IGABT, and it needs further attention.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Dosimetrically Triggered Adaptive Intensity Modulated Radiation Therapy for Cervical Cancer

Purpose: The widespread use of intensity modulated radiation therapy (IMRT) for cervical cancer has been limited by internal target and normal tissue motion. Such motion increases the risk of underdosing the target, especially as planning margins are reduced in an effort to reduce toxicity. This study explored 2 adaptive strategies to mitigate this risk and proposes a new, automated method that minimizes replanning workload. Methods and Materials: Thirty patients with cervical cancer participated in a prospective clinical study and underwent pretreatment and weekly magnetic resonance (MR) scans over a 5-week course of daily external beam radiation therapy. Target volumes and organs at risk (OARs) were contoured on each of the scans. Deformable image registration was used to model the accumulated dose (the real dose delivered to the target and OARs) for 2 adaptive replanning scenarios that assumed a very small PTV margin of only 3 mm to account for setup and internal interfractional motion: (1) a preprogrammed, anatomy-driven midtreatment replan (A-IMRT); and (2) a dosimetry-triggered replan driven by target dose accumulation over time (D-IMRT). Results: Across all 30 patients, clinically relevant target dose thresholds failed for 8 patients (27%) if 3-mm margins were used without replanning. A-IMRT failed in only 3 patients and also yielded an additional small reduction in OAR doses at the cost of 30 replans. D-IMRT assured adequate target coverage in all patients, with only 23 replans in 16 patients. Conclusions: A novel, dosimetry-triggered adaptive IMRT strategy for patients with cervical cancer can minimize the risk of target underdosing in the setting of very small margins and substantial interfractional motion while minimizing programmatic workload and cost.

62 RADIOLOGY AND NUCLEAR MEDICINE↗