Engineering topics

McNutt, Todd

Publications and source records attributed to McNutt, Todd.

14 records

DOE OSTI2018

Association of Neuronal Injury in the Genu and Body of Corpus Callosum After Cranial Irradiation in Children With Impaired Cognitive Control: A Prospective Study

Brain radiation is associated with functional deficits in children. The purpose of this study was to examine white matter integrity as measured by diffusion tensor imaging and associations with region-specific radiation dose and neuropsychological functioning in children treated with cranial irradiation.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2017

Consensus Contouring Guidelines for Postoperative Stereotactic Body Radiation Therapy for Metastatic Solid Tumor Malignancies to the Spine

Purpose: To develop consensus contouring guidelines for postoperative stereotactic body radiation therapy (SBRT) for spinal metastases. Methods and Materials: Ten spine SBRT specialists representing 10 international centers independently contoured the clinical target volume (CTV), planning target volume (PTV), spinal cord, and spinal cord planning organ at risk volume (PRV) for 10 representative clinical scenarios in postoperative spine SBRT for metastatic solid tumor malignancies. Contours were imported into the Computational Environment for Radiotherapy Research. Agreement between physicians was calculated with an expectation minimization algorithm using simultaneous truth and performance level estimation with κ statistics. Target volume definition guidelines were established by finding optimized confidence level consensus contours using histogram agreement analyses. Results: Nine expert radiation oncologists and 1 neurosurgeon completed contours for all 10 cases. The mean sensitivity and specificity were 0.79 (range, 0.71-0.89) and 0.94 (range, 0.90-0.99) for the CTV and 0.79 (range, 0.70-0.95) and 0.92 (range, 0.87-0.99) for the PTV), respectively. Mean κ agreement, which demonstrates the probability that contours agree by chance alone, was 0.58 (range, 0.43-0.70) for CTV and 0.58 (range, 0.37-0.76) for PTV (P<.001 for all cases). Optimized consensus contours were established for all patients with 80% confidence interval. Recommendations for CTV include treatment of the entire preoperative extent of bony and epidural disease, plus immediately adjacent bony anatomic compartments at risk of microscopic disease extension. In particular, a “donut-shaped” CTV was consistently applied in cases of preoperative circumferential epidural extension, regardless of extent of residual epidural extension. Otherwise more conformal anatomic-based CTVs were determined and described. Spinal instrumentation was consistently excluded from the CTV. Conclusions: We provide consensus contouring guidelines for common scenarios in postoperative SBRT for spinal metastases. These consensus guidelines are subject to clinical validation.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2016

Technical Note: SCUDA: A software platform for cumulative dose assessment

Purpose: Accurate tracking of anatomical changes and computation of actually delivered dose to the patient are critical for successful adaptive radiation therapy (ART). Additionally, efficient data management and fast processing are practically important for the adoption in clinic as ART involves a large amount of image and treatment data. The purpose of this study was to develop an accurate and efficient Software platform for CUmulative Dose Assessment (SCUDA) that can be seamlessly integrated into the clinical workflow. Methods: SCUDA consists of deformable image registration (DIR), segmentation, dose computation modules, and a graphical user interface. It is connected to our image PACS and radiotherapy informatics databases from which it automatically queries/retrieves patient images, radiotherapy plan, beam data, and daily treatment information, thus providing an efficient and unified workflow. For accurate registration of the planning CT and daily CBCTs, the authors iteratively correct CBCT intensities by matching local intensity histograms during the DIR process. Contours of the target tumor and critical structures are then propagated from the planning CT to daily CBCTs using the computed deformations. The actual delivered daily dose is computed using the registered CT and patient setup information by a superposition/convolution algorithm, and accumulated using the computed deformation fields. Both DIR and dose computation modules are accelerated by a graphics processing unit. Results: The cumulative dose computation process has been validated on 30 head and neck (HN) cancer cases, showing 3.5 ± 5.0 Gy (mean±STD) absolute mean dose differences between the planned and the actually delivered doses in the parotid glands. On average, DIR, dose computation, and segmentation take 20 s/fraction and 17 min for a 35-fraction treatment including additional computation for dose accumulation. Conclusions: The authors developed a unified software platform that provides accurate and efficient monitoring of anatomical changes and computation of actually delivered dose to the patient, thus realizing an efficient cumulative dose computation workflow. Evaluation on HN cases demonstrated the utility of our platform for monitoring the treatment quality and detecting significant dosimetric variations that are keys to successful ART.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2013

Mapping Patterns of Local Recurrence After Pancreaticoduodenectomy for Pancreatic Adenocarcinoma: A New Approach to Adjuvant Radiation Field Design

Purpose: To generate a map of local recurrences after pancreaticoduodenectomy (PD) for patients with resectable pancreatic ductal adenocarcinoma (PDA) and to model an adjuvant radiation therapy planning treatment volume (PTV) that encompasses a majority of local recurrences. Methods and Materials: Consecutive patients with resectable PDA undergoing PD and 1 or more computed tomography (CT) scans more than 60 days after PD at our institution were reviewed. Patients were divided into 3 groups: no adjuvant treatment (NA), chemotherapy alone (CTA), or chemoradiation (CRT). Cross-sectional scans were centrally reviewed, and local recurrences were plotted to scale with respect to the celiac axis (CA), superior mesenteric artery (SMA), and renal veins on 1 CT scan of a template post-PD patient. An adjuvant clinical treatment volume comprising 90% of local failures based on standard expansions of the CA and SMA was created and simulated on 3 post-PD CT scans to assess the feasibility of this planning approach. Results: Of the 202 patients in the study, 40 (20%), 34 (17%), and 128 (63%) received NA, CTA, and CRT adjuvant therapy, respectively. The rate of margin-positive resections was greater in CRT patients than in CTA patients (28% vs 9%, P=.023). Local recurrence occurred in 90 of the 202 patients overall (45%) and in 19 (48%), 22 (65%), and 49 (38%) in the NA, CTA, and CRT groups, respectively. Ninety percent of recurrences were within a 3.0-cm right-lateral, 2.0-cm left-lateral, 1.5-cm anterior, 1.0-cm posterior, 1.0-cm superior, and 2.0-cm inferior expansion of the combined CA and SMA contours. Three simulated radiation treatment plans using these expansions with adjustments to avoid nearby structures were created to demonstrate the use of this treatment volume. Conclusions: Modified PTVs targeting high-risk areas may improve local control while minimizing toxicities, allowing dose escalation with intensity-modulated or stereotactic body radiation therapy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2013

4D tumor centroid tracking using orthogonal 2D dynamic MRI: Implications for radiotherapy planning

Purpose: Current pretreatment, 4D imaging techniques are suboptimal in that they sample breathing motion over a very limited “snapshot” in time. Heretofore, long-duration, 4D motion characterization for radiotherapy planning, margin optimization, and validation have been impractical for safety reasons, requiring invasive markers imaged under x-ray fluoroscopy. To characterize 3D tumor motion and associated variability over durations more consistent with treatments, the authors have developed a practical dynamic MRI (dMRI) technique employing two orthogonal planes acquired in a continuous, interleaved fashion.Methods: 2D balanced steady-state free precession MRI was acquired continuously over 9–14 min at approximately 4 Hz in three healthy volunteers using a commercial 1.5 T system; alternating orthogonal imaging planes (sagittal, coronal, sagittal, etc.) were employed. The 2D in-plane pixel resolution was 2 × 2 mm{sup 2} with a 5 mm slice profile. Simultaneous with image acquisition, the authors monitored a 1D surrogate respiratory signal using a device available with the MRI system. 2D template matching-based anatomic feature registration, or tracking, was performed independently in each orientation. 4D feature tracking at the raw frame rate was derived using spline interpolation.Results: Tracking vascular features in the lung for two volunteers and pancreatic features in one volunteer, the authors have successfully demonstrated this method. Registration error, defined here as the difference between the sagittal and coronal tracking result in the SI direction, ranged from 0.7 to 1.6 mm (1σ) which was less than the acquired image resolution. Although the healthy volunteers were instructed to relax and breathe normally, significantly variable respiration was observed. To demonstrate potential applications of this technique, the authors subsequently explored the intrafraction stability of hypothetical tumoral internal target volumes and 3D spatial probability distribution functions. The surrogate respiratory information allowed the authors to show how this technique can be used to study correlations between internal and external (surrogate) information over these prolonged durations. However, compared against the gold standard of the time stamps in the dMRI frames, the temporal synchronization of the surrogate 1D respiratory information was shown to be likely unreliable.Conclusions: The authors have established viability of a novel and practical pretreatment, 4D tumor centroid tracking method employing a commercially available dynamic MRI sequence. Further developments from the vendor are likely needed to provide a reliably synchronized surrogate 1D respiratory signal, which will likely broaden the utility of this method in the pretreatment radiotherapy planning context.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2013

Increased Subventricular Zone Radiation Dose Correlates With Survival in Glioblastoma Patients After Gross Total Resection

Purpose: Neural progenitor cells in the subventricular zone (SVZ) have a controversial role in glioblastoma multiforme (GBM) as potential tumor-initiating cells. The purpose of this study was to examine the relationship between radiation dose to the SVZ and survival in GBM patients. Methods and Materials: The study included 116 patients with primary GBM treated at the Johns Hopkins Hospital between 2006 and 2009. All patients underwent surgical resection followed by adjuvant radiation therapy with intensity modulated radiation therapy (60 Gy/30 fractions) and concomitant temozolomide. Ipsilateral, contralateral, and bilateral SVZs were contoured on treatment plans by use of coregistered magnetic resonance imaging and computed tomography. Multivariate Cox regression was used to examine the relationship between mean SVZ dose and progression-free survival (PFS), as well as overall survival (OS). Age, Karnofsky Performance Status score, and extent of resection were used as covariates. The median age was 58 years (range, 29-80 years). Results: Of the patients, 12% underwent biopsy, 53% had subtotal resection (STR), and 35% had gross total resection (GTR). The Karnofsky Performance Status score was less than 90 in 54 patients and was 90 or greater in 62 patients. The median ipsilateral, contralateral, and bilateral mean SVZ doses were 48.7 Gy, 34.4 Gy, and 41.5 Gy, respectively. Among patients who underwent GTR, a mean ipsilateral SVZ dose of 40 Gy or greater was associated with a significantly improved PFS compared with patients who received less than 40 Gy (15.1 months vs 10.3 months; P=.028; hazard ratio, 0.385 [95% confidence interval, 0.165-0.901]) but not in patients undergoing STR or biopsy. The subgroup of GTR patients who received an ipsilateral dose of 40 Gy or greater also had a significantly improved OS (17.5 months vs 15.6 months; P=.027; hazard ratio, 0.385 [95% confidence interval, 0.165-0.895]). No association was found between SVZ radiation dose and PFS and OS among patients who underwent STR or biopsy. Conclusion: A mean radiation dose of 40 Gy or greater to the ipsilateral SVZ was associated with a significantly improved PFS and OS in patients with GBM after GTR.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2012

Fully Automated Simultaneous Integrated Boosted-Intensity Modulated Radiation Therapy Treatment Planning Is Feasible for Head-and-Neck Cancer: A Prospective Clinical Study

Purpose: To prospectively determine whether overlap volume histogram (OVH)-driven, automated simultaneous integrated boosted (SIB)-intensity-modulated radiation therapy (IMRT) treatment planning for head-and-neck cancer can be implemented in clinics. Methods and Materials: A prospective study was designed to compare fully automated plans (APs) created by an OVH-driven, automated planning application with clinical plans (CPs) created by dosimetrists in a 3-dose-level (70 Gy, 63 Gy, and 58.1 Gy), head-and-neck SIB-IMRT planning. Because primary organ sparing (cord, brain, brainstem, mandible, and optic nerve/chiasm) always received the highest priority in clinical planning, the study aimed to show the noninferiority of APs with respect to PTV coverage and secondary organ sparing (parotid, brachial plexus, esophagus, larynx, inner ear, and oral mucosa). The sample size was determined a priori by a superiority hypothesis test that had 85% power to detect a 4% dose decrease in secondary organ sparing with a 2-sided alpha level of 0.05. A generalized estimating equation (GEE) regression model was used for statistical comparison. Results: Forty consecutive patients were accrued from July to December 2010. GEE analysis indicated that in APs, overall average dose to the secondary organs was reduced by 1.16 (95% CI = 0.09-2.33) with P=.04, overall average PTV coverage was increased by 0.26% (95% CI = 0.06-0.47) with P=.02 and overall average dose to the primary organs was reduced by 1.14 Gy (95% CI = 0.45-1.8) with P=.004. A physician determined that all APs could be delivered to patients, and APs were clinically superior in 27 of 40 cases. Conclusions: The application can be implemented in clinics as a fast, reliable, and consistent way of generating plans that need only minor adjustments to meet specific clinical needs.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2012

Effect of Radiotherapy and Chemotherapy on the Risk of Mucositis During Intensity-Modulated Radiation Therapy for Oropharyngeal Cancer

Purpose: To define the roles of radiotherapy and chemotherapy on the risk of Grade 3+ mucositis during intensity-modulated radiation therapy (IMRT) for oropharyngeal cancer. Methods and Materials: 164 consecutive patients treated with IMRT at two institutions in nonoverlapping treatment eras were selected. All patients were treated with a dose painting approach, three dose levels, and comprehensive bilateral neck treatment under the supervision of the same radiation oncologist. Ninety-three patients received concomitant chemotherapy (cCHT) and 14 received induction chemotherapy (iCHT). Individual information of the dose received by the oral mucosa (OM) was extracted as absolute cumulative dose-volume histogram (DVH), corrected for the elapsed treatment days and reported as weekly (w) DVH. Patients were seen weekly during treatment, and peak acute toxicity equal to or greater than confluent mucositis at any point during the course of IMRT was considered the endpoint. Results: Overall, 129 patients (78.7%) reached the endpoint. The regions that best discriminated between patients with/without Grade 3+ mucositis were found at 10.1 Gy/w (V10.1) and 21 cc (D21), along the x-axis and y-axis of the OM-wDVH, respectively. On multivariate analysis, D21 (odds ratio [OR] = 1.016, 95% confidence interval [CI], 1.009-1.023, p < 0.001) and cCHT (OR = 4.118, 95% CI, 1.659-10.217, p = 0.002) were the only independent predictors. However, V10.1 and D21 were highly correlated (rho = 0.954, p < 0.001) and mutually interchangeable. cCHT would correspond to 88.4 cGy/w to at least 21 cc of OM. Conclusions: Radiotherapy and chemotherapy act independently in determining acute mucosal toxicity; cCHT increases the risk of mucosal Grade 3 toxicity Almost-Equal-To 4 times over radiation therapy alone, and it is equivalent to an extra Almost-Equal-To 6.2 Gy to 21 cc of OM over a 7-week course.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2012

A method for deriving a 4D-interpolated balanced planning target for mobile tumor radiotherapy

Purpose: Tumor control and normal tissue toxicity are strongly correlated to the tumor and normal tissue volumes receiving high prescribed dose levels in the course of radiotherapy. Planning target definition is, therefore, crucial to ensure favorable clinical outcomes. This is especially important for stereotactic body radiation therapy of lung cancers, characterized by high fractional doses and steep dose gradients. The shift in recent years from population-based to patient-specific treatment margins, as facilitated by the emergence of 4D medical imaging capabilities, is a major improvement. The commonly used motion-encompassing, or internal-target volume (ITV), target definition approach provides a high likelihood of coverage for the mobile tumor but inevitably exposes healthy tissue to high prescribed dose levels. The goal of this work was to generate an interpolated balanced planning target that takes into account both tumor coverage and normal tissue sparing from high prescribed dose levels, thereby improving on the ITV approach. Methods: For each 4DCT dataset, 4D deformable image registration was used to derive two bounding targets, namely, a 4D-intersection and a 4D-composite target which minimized normal tissue exposure to high prescribed dose levels and maximized tumor coverage, respectively. Through definition of an ''effective overlap volume histogram'' the authors derived an ''interpolated balanced planning target'' intended to balance normal tissue sparing from prescribed doses with tumor coverage. To demonstrate the dosimetric efficacy of the interpolated balanced planning target, the authors performed 4D treatment planning based on deformable image registration of 4D-CT data for five previously treated lung cancer patients. Two 4D plans were generated per patient, one based on the interpolated balanced planning target and the other based on the conventional ITV target. Plans were compared for tumor coverage and the degree of normal tissue sparing resulting from the new approach was quantified. Results: Analysis of the 4D dose distributions from all five patients showed that while achieving tumor coverage comparable to the ITV approach, the new planning target definition resulted in reductions of lung V{sub 10}, V{sub 20}, and V{sub 30} of 6.3% {+-} 1.7%, 10.6% {+-} 3.9%, and 12.9% {+-} 5.5%, respectively, as well as reductions in mean lung dose, mean dose to the GTV-ring and mean heart dose of 8.8% {+-} 2.5%, 7.2% {+-} 2.5%, and 10.6% {+-} 3.6%, respectively. Conclusions: The authors have developed a simple and systematic approach to generate a 4D-interpolated balanced planning target volume that implicitly incorporates the dynamics of respiratory-organ motion without requiring 4D-dose computation or optimization. Preliminary results based on 4D-CT data of five previously treated lung patients showed that this new planning target approach may improve normal tissue sparing without sacrificing tumor coverage.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2011

SmartArc-Based Volumetric Modulated Arc Therapy for Oropharyngeal Cancer: A Dosimetric Comparison With Both Intensity-Modulated Radiation Therapy and Helical Tomotherapy

Purpose: To investigate the roles of volumetric modulated arc therapy with SmartArc (VMAT-S), intensity-modulated radiation therapy (IMRT), and helical tomotherapy (HT) for oropharyngeal cancer using a simultaneous integrated boost (SIB) approach. Methods and Materials: Eight patients treated with IMRT were selected at random. Plans were computed for both IMRT and VMAT-S (using Pinnacle TPS for an Elekta Infinity linac) along with HT. A three-dose level prescription was used to deliver 70 Gy, 63 Gy, and 58.1 Gy to regions of macroscopic, microscopic high-risk, and microscopic low-risk disease, respectively. All doses were given in 35 fractions. Comparisons were performed on dose-volume histogram data, monitor units per fraction (MU/fx), and delivery time. Results: VMAT-S target coverage was close to that achieved by IMRT, but inferior to HT. The conformity and homogeneity within the PTV were improved for HT over all strategies. Sparing of the organs at risk (OAR) was achieved with all modalities. VMAT-S (along with HT) shortened delivery time (mean, -38%) and reduced MU/fx (mean, -28%) compared with IMRT. Conclusion: VMAT-S represents an attractive solution because of the shorter delivery time and the lower number of MU/fx compared with IMRT. However, in this complex clinical setting, current VMAT-S does not appear to provide any distinct advantage compared with helical tomotherapy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2011

A Treatment Planning Method for Sequentially Combining Radiopharmaceutical Therapy and External Radiation Therapy;External beam therapy; Radiopharmaceutical therapy; Three-dimensional dosimetry; Treatment planning

Purpose: Effective cancer treatment generally requires combination therapy. The combination of external beam therapy (XRT) with radiopharmaceutical therapy (RPT) requires accurate three-dimensional dose calculations to avoid toxicity and evaluate efficacy. We have developed and tested a treatment planning method, using the patient-specific three-dimensional dosimetry package 3D-RD, for sequentially combined RPT/XRT therapy designed to limit toxicity to organs at risk. Methods and Materials: The biologic effective dose (BED) was used to translate voxelized RPT absorbed dose (D{sub RPT}) values into a normalized total dose (or equivalent 2-Gy-fraction XRT absorbed dose), NTD{sub RPT} map. The BED was calculated numerically using an algorithmic approach, which enabled a more accurate calculation of BED and NTD{sub RPT}. A treatment plan from the combined Samarium-153 and external beam was designed that would deliver a tumoricidal dose while delivering no more than 50 Gy of NTD{sub sum} to the spinal cord of a patient with a paraspinal tumor. Results: The average voxel NTD{sub RPT} to tumor from RPT was 22.6 Gy (range, 1-85 Gy); the maximum spinal cord voxel NTD{sub RPT} from RPT was 6.8 Gy. The combined therapy NTD{sub sum} to tumor was 71.5 Gy (range, 40-135 Gy) for a maximum voxel spinal cord NTD{sub sum} equal to the maximum tolerated dose of 50 Gy. Conclusions: A method that enables real-time treatment planning of combined RPT-XRT has been developed. By implementing a more generalized conversion between the dose values from the two modalities and an activity-based treatment of partial volume effects, the reliability of combination therapy treatment planning has been expanded.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2011

Volumetric Change of Selected Organs at Risk During IMRT for Oropharyngeal Cancer

Purpose: To assess volumetric changes of selected organs at risk (OAR) during intensity-modulated radiotherapy (IMRT) for oropharyngeal carcinoma. Materials and Methods: Twenty-six consecutive patients that were treated with definitive IMRT {+-} chemotherapy between November 2007 and November 2008 were selected for the present study. As part of an internal quality assurances program, a repeat kilovolt (KV) computed tomography was planned weekly during the 7-week treatment course. On each available scan, a single observer contoured the parotid submandibular, and thyroid glands (PG/SMG/TG), larynx (L), and constrictor, masticatory, and sternocleidomastoid muscles (CM/MM/SCM) as appropriate. The volume at each scan was compared with the one at planning CT in a pair-wise fashion. p values <0.05 after correction for multiple testing were considered significant. Results: A total of 159 scans was obtained during treatment for a total of 185 scans, including the baseline imaging. All OARs showed statistically significant changes over baseline by week 5. At week 7, the PG showed the largest absolute change with an average reduction of {approx}10 mL followed by both the SCM and MM ({approx}-5 mL). The largest ({approx}-30%) relative change was observed for the salivary glands. L and CM showed a {approx}15% increase in volume during treatment. Conclusion: All selected OAR undergo significant volumetric changes during a course of IMRT for oropharyngeal squamous cell carcinoma.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2011

Data-Driven Approach to Generating Achievable Dose-Volume Histogram Objectives in Intensity-Modulated Radiotherapy Planning

Purpose: To propose a method of intensity-modulated radiotherapy (IMRT) planning that generates achievable dose-volume histogram (DVH) objectives using a database containing geometric and dosimetric information of previous patients. Methods and Materials: The overlap volume histogram (OVH) is used to compare the spatial relationships between the organs at risk and targets of a new patient with those of previous patients in a database. From the OVH analysis, the DVH objectives of the new patient were generated from the database and used as the initial planning goals. In a retrospective OVH-assisted planning demonstration, 15 patients were randomly selected from a database containing clinical plans (CPs) of 91 previous head-and-neck patients treated by a three-level IMRT-simultaneous integrated boost technique. OVH-assisted plans (OPs) were planned in a leave-one-out manner by a planner who had no knowledge of CPs. Thus, DVH objectives of an OP were generated from a subdatabase containing the information of the other 90 patients. Those DVH objectives were then used as the initial planning goals in IMRT optimization. Planning efficiency was evaluated by the number of clicks of the 'Start Optimization' button in the course of planning. Although the Pinnacle{sup 3} treatment planning system allows planners to interactively adjust the DVH parameters during optimization, planners in our institution have never used this function in planning. Results: The average clicks required for completing the CP and OP was 27.6 and 1.9, respectively (p <.00001); three OPs were finished within a single click. Ten more patient's cord + 4 mm reached the sparing goal D{sub 0.1cc} <44 Gy (p <.0001), where D{sub 0.1cc} represents the dose corresponding to 0.1 cc. For planning target volume uniformity, conformity, and other organ at risk sparing, the OPs were at least comparable with the CPs. Additionally, the averages of D{sub 0.1cc} to the cord + 4 mm decreased by 6.9 Gy (p <.0001); averages of D{sub 0.1cc} to the brainstem decreased by 7.7 Gy (p <.005). The averages of V(30 Gy) to the contralateral parotid decreased by 8.7% (p <.0001), where V(30 Gy) represents the percentage volume corresponding to 30 Gy. Conclusion: The method heralds the possibility of automated IMRT planning.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2011

Real-time dose computation: GPU-accelerated source modeling and superposition/convolution

Purpose: To accelerate dose calculation to interactive rates using highly parallel graphics processing units (GPUs). Methods: The authors have extended their prior work in GPU-accelerated superposition/convolution with a modern dual-source model and have enhanced performance. The primary source algorithm supports both focused leaf ends and asymmetric rounded leaf ends. The extra-focal algorithm uses a discretized, isotropic area source and models multileaf collimator leaf height effects. The spectral and attenuation effects of static beam modifiers were integrated into each source's spectral function. The authors introduce the concepts of arc superposition and delta superposition. Arc superposition utilizes separate angular sampling for the total energy released per unit mass (TERMA) and superposition computations to increase accuracy and performance. Delta superposition allows single beamlet changes to be computed efficiently. The authors extended their concept of multi-resolution superposition to include kernel tilting. Multi-resolution superposition approximates solid angle ray-tracing, improving performance and scalability with a minor loss in accuracy. Superposition/convolution was implemented using the inverse cumulative-cumulative kernel and exact radiological path ray-tracing. The accuracy analyses were performed using multiple kernel ray samplings, both with and without kernel tilting and multi-resolution superposition. Results: Source model performance was <9 ms (data dependent) for a high resolution (400{sup 2}) field using an NVIDIA (Santa Clara, CA) GeForce GTX 280. Computation of the physically correct multispectral TERMA attenuation was improved by a material centric approach, which increased performance by over 80%. Superposition performance was improved by {approx}24% to 0.058 and 0.94 s for 64{sup 3} and 128{sup 3} water phantoms; a speed-up of 101-144x over the highly optimized Pinnacle{sup 3} (Philips, Madison, WI) implementation. Pinnacle{sup 3} times were 8.3 and 94 s, respectively, on an AMD (Sunnyvale, CA) Opteron 254 (two cores, 2.8 GHz). Conclusions: The authors have completed a comprehensive, GPU-accelerated dose engine in order to provide a substantial performance gain over CPU based implementations. Real-time dose computation is feasible with the accuracy levels of the superposition/convolution algorithm.

60 APPLIED LIFE SCIENCES↗