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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Assessment of Uncertainties in Treatment Planning for Scanned Ion Beam Therapy of Moving Tumors

Purpose: To provide methods for quantification of uncertainties in 4-dimensional (4D) treatment during treatment planning. Methods and Materials: Uncertainty information was generated by multiple 4D treatment simulations with varying parameters. Sampled data were analyzed using uncertainty visualization methods that have been added to common treatment plan evaluation methods (eg, dose-volume histogram and dose distribution analysis). To illustrate the potential of the introduced methods, uncertainty analysis was completed for a single lung cancer case using 3 motion mitigation techniques: gating, slice-by-slice rescanning, and breath-controlled rescanning. Results: By repeating 4D dose calculations with varying parameters, we were able to show local uncertainties in dose distributions and to evaluate the stability of treatment setups. The new methods were found suitable for uncertainty evaluation in 4D treatment planning of moving tumors. Calculation time of the uncertainty base data was time consuming but contrivable overnight. Conclusions: Uncertainty analysis and visualization for 4D treatment planning provide an important tool in the decision process for an optimal treatment approach.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Probabilities of Radiation Myelopathy Specific to Stereotactic Body Radiation Therapy to Guide Safe Practice

Purpose: Dose-volume histogram (DVH) results for 9 cases of post spine stereotactic body radiation therapy (SBRT) radiation myelopathy (RM) are reported and compared with a cohort of 66 spine SBRT patients without RM. Methods and Materials: DVH data were centrally analyzed according to the thecal sac point maximum (Pmax) volume, 0.1- to 1-cc volumes in increments of 0.1 cc, and to the 2 cc volume. 2-Gy biologically equivalent doses (nBED) were calculated using an {alpha}/{beta} = 2 Gy (units = Gy{sub 2/2}). For the 2 cohorts, the nBED means and distributions were compared using the t test and Mann-Whitney test, respectively. Significance (P<.05) was defined as concordance of both tests at each specified volume. A logistic regression model was developed to estimate the probability of RM using the dose distribution for a given volume. Results: Significant differences in both the means and distributions at the Pmax and up to the 0.8-cc volume were observed. Concordant significance was greatest for the Pmax volume. At the Pmax volume the fit of the logistic regression model, summarized by the area under the curve, was 0.87. A risk of RM of 5% or less was observed when limiting the thecal sac Pmax volume doses to 12.4 Gy in a single fraction, 17.0 Gy in 2 fractions, 20.3 Gy in 3 fractions, 23.0 Gy in 4 fractions, and 25.3 Gy in 5 fractions. Conclusion: We report the first logistic regression model yielding estimates for the probability of human RM specific to SBRT.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Relationship of Imaging Frequency and Planning Margin to Account for Intrafraction Prostate Motion: Analysis Based on Real-Time Monitoring Data

Purpose: Correction for intrafraction prostate motion becomes important for hypofraction treatment of prostate cancer. The purpose of this study was to estimate an ideal planning margin to account for intrafraction prostate motion as a function of imaging and repositioning frequency in the absence of continuous prostate motion monitoring. Methods and Materials: For 31 patients receiving intensity modulated radiation therapy treatment, prostate positions sampled at 10 Hz during treatment using the Calypso system were analyzed. Using these data, we simulated multiple, less frequent imaging protocols, including intervals of every 10, 15, 20, 30, 45, 60, 90, 120, 180, and 240 seconds. For each imaging protocol, the prostate displacement at the imaging time was corrected by subtracting prostate shifts from the subsequent displacements in that fraction. Furthermore, we conducted a principal component analysis to quantify the direction of prostate motion. Results: Averaging histograms of every 240 and 60 seconds for all patients, vector displacements of the prostate were, respectively, within 3 and 2 mm for 95% of the treatment time. A vector margin of 1 mm achieved 91.2% coverage of the prostate with 30 second imaging. The principal component analysis for all fractions showed the largest variance in prostate position in the midsagittal plane at 54° from the anterior direction, indicating that anterosuperior to inferoposterior is the direction of greatest motion. The smallest prostate motion is in the left-right direction. Conclusions: The magnitudes of intrafraction prostate motion along the superior-inferior and anterior-posterior directions are comparable, and the smallest motion is in the left-right direction. In the absence of continuous prostate motion monitoring, and under ideal circumstances, 1-, 2-, and 3-mm vector planning margins require a respective imaging frequency of every 15, 60, and 240 to account for intrafraction prostate motion while achieving adequate geometric target coverage for 95% of the time.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2012

Predictor of Severe Gastroduodenal Toxicity After Stereotactic Body Radiotherapy for Abdominopelvic Malignancies

Purpose: To identify the predictors for the development of severe gastroduodenal toxicity (GDT) in patients treated with stereotactic body radiotherapy (SBRT) using 3 fractionations for abdominopelvic malignancies. Methods and Materials: From 2001 to 2011, 202 patients with abdominopelvic malignancies were treated with curative-intent SBRT. Among these patients, we retrospectively reviewed the clinical records of 40 patients with the eligibility criteria as follows: 3 fractionations, follow-up period {>=}1 year, absence of previous radiation therapy (RT) history or combination of external-beam RT and the presence of gastroduodenum (GD) that received a dose higher than 20% of prescribed dose. The median SBRT dose was 45 Gy (range, 33-60 Gy) with 3 fractions. We analyzed the clinical and dosimetric parameters, including multiple dose-volume histogram endpoints: V{sub 20} (volume of GD that received 20 Gy), V{sub 25}, V{sub 30}, V{sub 35}, and D{sub max} (the maximum point dose). The grade of GDT was defined by the National Cancer Institute Common Toxicity Criteria version 4.0, and GDT {>=}grade 3 was defined as severe GDT. Results: The median time to the development of severe GDT was 6 months (range, 3-12 months). Severe GDT was found in 6 patients (15%). D{sub max} was the best dosimetric predictor for severe GDT. D{sub max} of 35 Gy and 38 Gy were respectively associated with a 5% and 10% probability of the development of severe GDT. A history of ulcer before SBRT was the best clinical predictor on univariate analysis (P=.0001). Conclusions: We suggest that D{sub max} is a valuable predictor of severe GDT after SBRT using 3 fractionations for abdominopelvic malignancies. A history of ulcer before SBRT should be carefully considered as a clinical predictor, especially in patients who receive a high dose to GD.

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 OSTI2013

Dosimetric Analysis of Organs at Risk During Expiratory Gating in Stereotactic Body Radiation Therapy for Pancreatic Cancer

Purpose: To determine how the respiratory phase impacts dose to normal organs during stereotactic body radiation therapy (SBRT) for pancreatic cancer. Methods and Materials: Eighteen consecutive patients with locally advanced, unresectable pancreatic adenocarcinoma treated with SBRT were included in this study. On the treatment planning 4-dimensional computed tomography (CT) scan, the planning target volume (PTV), defined as the gross tumor volume plus 3-mm margin, the duodenum, and the stomach were contoured on the end-expiration (CT{sub exp}) and end-inspiration (CT{sub insp}) phases for each patient. A separate treatment plan was constructed for both phases with the dose prescription of 33 Gy in 5 fractions with 95% coverage of the PTV by the 100% isodose line. The dose-volume histogram (DVH) endpoints, volume of duodenum that received 20 Gy (V{sub 20}), V{sub 25}, and V{sub 30} and maximum dose to 5 cc of contoured organ (D{sub 5cc}), D{sub 1cc}, and D{sub 0.1cc}, were evaluated. Results: Dosimetric parameters for the duodenum, including V{sub 25}, V{sub 30}, D{sub 1cc}, and D{sub 0.1cc} improved by planning on the CT{sub exp} compared to those on the CT{sub insp}. There was a statistically significant overlap of the PTV with the duodenum but not the stomach during the CT{sub insp} compared to the CT{sub exp} (0.38 ± 0.17 cc vs 0.01 ± 0.01 cc, P=.048). A larger expansion of the PTV, in accordance with a Danish phase 2 trial, showed even more overlapping volume of duodenum on the CT{sub insp} compared to that on the CT{sub exp} (5.5 ± 0.9 cc vs 3.0 ± 0.8 cc, P=.0003) but no statistical difference for any stomach dosimetric DVH parameter. Conclusions: Dose to the duodenum was higher when treating on the inspiratory than on the expiratory phase. These data suggest that expiratory gating may be preferable to inspiratory breath-hold and free breathing strategies for minimizing risk of toxicity.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Treatment-Related Morbidity in Prostate Cancer: A Comparison of 3-Dimensional Conformal Radiation Therapy With and Without Image Guidance Using Implanted Fiducial Markers

Purpose: To estimate the prevalence of rectal and urinary dysfunctional symptoms using image guided radiation therapy (IGRT) with fiducials and magnetic resonance planning for prostate cancer. Methods and Materials: During the implementation stages of IGRT between September 2008 and March 2010, 367 consecutive patients were treated with prostatic irradiation using 3-dimensional conformal radiation therapy with and without IGRT (non-IGRT). In November 2010, these men were asked to report their bowel and bladder symptoms using a postal questionnaire. The proportions of patients with moderate to severe symptoms in these groups were compared using logistic regression models adjusted for tumor and treatment characteristic variables. Results: Of the 282 respondents, the 154 selected for IGRT had higher stage tumors, received higher prescribed doses, and had larger volumes of rectum receiving high dosage than did the 128 selected for non-IGRT. The follow-up duration was 8 to 26 months. Compared with the non-IGRT group, improvement was noted in all dysfunctional rectal symptoms using IGRT. In multivariable analyses, IGRT improved rectal pain (odds ratio [OR] 0.07 [0.009-0.7], P=.02), urgency (OR 0.27 [0.11-0.63], P=<.01), diarrhea (OR 0.009 [0.02-0.35], P<.01), and change in bowel habits (OR 0.18 [0.06-0.52], P<.010). No correlation was observed between rectal symptom levels and dose-volume histogram data. Urinary dysfunctional symptoms were similar in both treatment groups. Conclusions: In comparison with men selected for non-IGRT, a significant reduction of bowel dysfunctional symptoms was confirmed in men selected for IGRT, even though they had larger volumes of rectum treated to higher doses.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Quality Research in Radiation Oncology Analysis of Clinical Performance Measures in the Management of Gastric Cancer

Background: The specific aim was to determine national patterns of radiation therapy (RT) practice in patients treated for stage IB-IV (nonmetastatic) gastric cancer (GC). Methods and Materials: A national process survey of randomly selected US RT facilities was conducted which retrospectively assessed demographics, staging, geographic region, practice setting, and treatment by using on-site record review of eligible GC cases treated from 2005 to 2007. Three clinical performance measures (CPMs), (1) use of computed tomography (CT)-based treatment planning; (2) use of dose volume histograms (DVHs) to evaluate RT dose to the kidneys and liver; and (3) completion of RT within the prescribed time frame; and emerging quality indicators, (i) use of intensity modulated RT (IMRT); (ii) use of image-guided tools (IGRT) other than CT for RT target delineation; and (iii) use of preoperative RT, were assessed. Results: CPMs were computed for 250 eligible patients at 45 institutions (median age, 62 years; 66% male; 60% Caucasian). Using 2000 American Joint Committee on Cancer criteria, 13% of patients were stage I, 29% were stage II, 32% were stage IIIA, 10% were stage IIIB, and 12% were stage IV. Most patients (43%) were treated at academic centers, 32% were treated at large nonacademic centers, and 25% were treated at small to medium sized facilities. Almost all patients (99.5%) underwent CT-based planning, and 75% had DVHs to evaluate normal tissue doses to the kidneys and liver. Seventy percent of patients completed RT within the prescribed time frame. IMRT and IGRT were used in 22% and 17% of patients, respectively. IGRT techniques included positron emission tomography (n=20), magnetic resonance imaging (n=1), respiratory gating and 4-dimensional CT (n=22), and on-board imaging (n=10). Nineteen percent of patients received preoperative RT. Conclusions: This analysis of radiation practice patterns for treating nonmetastatic GC indicates widespread adoption of CT-based planning with use of DVH to evaluate normal tissue doses. Most patients completed adjuvant RT in the prescribed time frame. IMRT and IGRT were not routinely incorporated into clinical practice during the 2005-2007 period. These data will be a benchmark for future Quality Research in Radiation Oncology GC surveys.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Lack of a Dose-Effect Relationship for Pulmonary Function Changes After Stereotactic Body Radiation Therapy for Early-Stage Non-Small Cell Lung Cancer

Purpose: To evaluate the influence of tumor size, prescription dose, and dose to the lungs on posttreatment pulmonary function test (PFT) changes after stereotactic body radiation therapy (SBRT) for early-stage non-small cell lung cancer (NSCLC). Methods and Materials: The analysis is based on 191 patients treated at 5 international institutions: inclusion criteria were availability of pre- and post-SBRT PFTs and dose-volume histograms of the lung and planning target volume (PTV); patients treated with more than 1 SBRT course were excluded. Correlation between early (1-6 months, median 3 months) and late (7-24 months, median 12 months) PFT changes and tumor size, planning target volume (PTV) dose, and lung doses was assessed using linear regression analysis, receiver operating characteristics analysis, and Lyman's normal tissue complication probability model. The PTV doses were converted to biologically effective doses and lung doses to 2 Gy equivalent doses before correlation analyses. Results: Up to 6 months after SBRT, forced expiratory volume in 1 second and carbon monoxide diffusion capacity changed by −1.4% (95% confidence interval [CI], −3.4% to 0) and −7.6% (95% CI, −10.2% to −3.4%) compared with pretreatment values, respectively. A modest decrease in PFTs was observed 7-24 months after SBRT, with changes of −8.1% (95% CI, −13.3% to −5.3%) and −12.4% (95% CI, −15.5% to −6.9%), respectively. Using linear regression analysis, receiver operating characteristic analysis, and normal tissue complication probability modeling, all evaluated parameters of tumor size, PTV dose, mean lung dose, and absolute and relative volumes of the lung exposed to minimum doses of 5-70 Gy were not correlated with early and late PFT changes. Subgroup analysis based on pre-SBRT PFTs (greater or equal and less than median) did not identify any dose-effect relationship. Conclusions: This study failed to demonstrate a significant dose-effect relationship for changes of pulmonary function after SBRT for early-stage non-small cell lung cancer.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Small Bowel Dose Parameters Predicting Grade ≥3 Acute Toxicity in Rectal Cancer Patients Treated With Neoadjuvant Chemoradiation: An Independent Validation Study Comparing Peritoneal Space Versus Small Bowel Loop Contouring Techniques

Purpose: To determine whether volumes based on contours of the peritoneal space can be used instead of individual small bowel loops to predict for grade ≥3 acute small bowel toxicity in patients with rectal cancer treated with neoadjuvant chemoradiation therapy. Methods and Materials: A standardized contouring method was developed for the peritoneal space and retrospectively applied to the radiation treatment plans of 67 patients treated with neoadjuvant chemoradiation therapy for rectal cancer. Dose-volume histogram (DVH) data were extracted and analyzed against patient toxicity. Receiver operating characteristic analysis and logistic regression were carried out for both contouring methods. Results: Grade ≥3 small bowel toxicity occurred in 16% (11/67) of patients in the study. A highly significant dose-volume relationship between small bowel irradiation and acute small bowel toxicity was supported by the use of both small bowel loop and peritoneal space contouring techniques. Receiver operating characteristic analysis demonstrated that, for both contouring methods, the greatest sensitivity for predicting toxicity was associated with the volume receiving between 15 and 25 Gy. Conclusion: DVH analysis of peritoneal space volumes accurately predicts grade ≥3 small bowel toxicity in patients with rectal cancer receiving neoadjuvant chemoradiation therapy, suggesting that the contours of the peritoneal space provide a reasonable surrogate for the contours of individual small bowel loops. The study finds that a small bowel V15 less than 275 cc and a peritoneal space V15 less than 830 cc are associated with a less than 10% risk of grade ≥3 acute toxicity.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Dosimetric Evaluation and Treatment Outcome of Intensity Modulated Radiation Therapy After Doxorubicin-Based Chemotherapy for Primary Mediastinal Large B-Cell Lymphoma

Purpose: The value of intensity-modulated radiation therapy (IMRT) after doxorubicin-based chemotherapy in primary mediastinal large B-cell lymphoma (PMBCL) is unknown. We assessed the dosimetric parameters, treatment outcomes, and toxicity of IMRT in PMBCL. Methods and Materials: Forty-one PMBCL patients underwent mediastinal IMRT after doxorubicin-based chemotherapy. Thirty-eight patients had stage I-II disease, and 3 patients had stage III-IV disease. Most patients presented with bulky mediastinal disease (65.9%) and local invasion (82.9%). The dose-volume histograms of the target volume and critical normal structures were evaluated. Results: The average planning target volume (PTV) mean dose was 39 Gy. Only 0.5% and 1.4% of the PTV received <90% and <95% of the prescribed dose, respectively, indicating excellent target coverage. The median mean lung dose and percentage lung volume receiving 20 Gy (V20) were 16.3 Gy and 30.6%. The 5-year overall survival (OS) and local control (LC) were 95.1% and 89.8%. After chemotherapy, consolidation radiation therapy in patients with complete/partial response resulted in significantly better survival than salvage radiation therapy in patients with stable/progressive disease (3-year OS 100% vs 75%; 3-year LC 96.6% vs 62.5%). No grade 4 or 5 acute or late toxicities occurred. Conclusions: Mediastinal IMRT after doxorubicin-based chemotherapy can be safely and efficiently delivered, and it provides favorable outcomes in PMBCL patients with a large target volume and high-risk features.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

The Residual Setup Errors of Different IGRT Alignment Procedures for Head and Neck IMRT and the Resulting Dosimetric Impact

Purpose: To assess residual setup errors during head and neck radiation therapy and the resulting consequences for the delivered dose for various patient alignment procedures. Methods and Materials: Megavoltage cone beam computed tomography (MVCBCT) scans from 11 head and neck patients who underwent intensity modulated radiation therapy were used to assess setup errors. Each MVCBCT scan was registered to its reference planning kVCT, with seven different alignment procedures: automatic alignment and manual registration to 6 separate bony landmarks (sphenoid, left/right maxillary sinuses, mandible, cervical 1 [C1]-C2, and C7-thoracic 1 [T1] vertebrae). Shifts in the different alignments were compared with each other to determine whether there were any statistically significant differences. Then, the dose distribution was recalculated on 3 MVCBCT images per patient for every alignment procedure. The resulting dose-volume histograms for targets and organs at risk (OARs) were compared to those from the planning kVCTs. Results: The registration procedures produced statistically significant global differences in patient alignment and actual dose distribution, calling for a need for standardization of patient positioning. Vertically, the automatic, sphenoid, and maxillary sinuses alignments mainly generated posterior shifts and resulted in mean increases in maximal dose to OARs of >3% of the planned dose. The suggested choice of C1-C2 as a reference landmark appears valid, combining both OAR sparing and target coverage. Assuming this choice, relevant margins to apply around volumes of interest at the time of planning to take into account for the relative mobility of other regions are discussed. Conclusions: Use of different alignment procedures for treating head and neck patients produced variations in patient setup and dose distribution. With concern for standardizing practice, C1-C2 reference alignment with relevant margins around planning volumes seems to be a valid option.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Early-Stage Breast Cancer Treated With 3-Week Accelerated Whole-Breast Radiation Therapy and Concomitant Boost

Purpose: To report early outcomes of accelerated whole-breast radiation therapy with concomitant boost. Methods and Materials: This is a prospective, institutional review board-approved study. Eligibility included stage TisN0, T1N0, and T2N0 breast cancer. Patients receiving adjuvant chemotherapy were ineligible. The whole breast received 40.5 Gy in 2.7-Gy fractions with a concomitant lumpectomy boost of 4.5 Gy in 0.3-Gy fractions. Total dose to the lumpectomy site was 45 Gy in 15 fractions over 19 days. Results: Between October 2004 and December 2010, 160 patients were treated; stage distribution was as follows: TisN0, n=63; T1N0, n=88; and T2N0, n=9. With a median follow-up of 3.5 years (range, 1.5-7.8 years) the 5-year overall survival and disease-free survival rates were 90% (95% confidence interval [CI] 0.84-0.94) and 97% (95% CI 0.93-0.99), respectively. Five-year local relapse-free survival was 99% (95% CI 0.96-0.99). Acute National Cancer Institute/Common Toxicity Criteria grade 1 and 2 skin toxicity was observed in 70% and 5%, respectively. Among the patients with ≥2-year follow-up no toxicity higher than grade 2 on the Late Effects in Normal Tissues–Subjective, Objective, Management, and Analytic scale was observed. Review of the radiation therapy dose–volume histogram noted that ≥95% of the prescribed dose encompassed the lumpectomy target volume in >95% of plans. The median dose received by the heart D{sub 05} was 215 cGy, and median lung V{sub 20} was 7.6%. Conclusions: The prescribed accelerated schedule of whole-breast radiation therapy with concomitant boost can be administered, achieving acceptable dose distribution. With follow-up to date, the results are encouraging and suggest minimal side effects and excellent local control.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Hippocampal Dosimetry Predicts Neurocognitive Function Impairment After Fractionated Stereotactic Radiotherapy for Benign or Low-Grade Adult Brain Tumors

Purpose: To prospectively evaluate the association between hippocampal dose and long-term neurocognitive function (NCF) impairment for benign or low-grade adult brain tumors treated with fractionated stereotactic radiotherapy (FSRT). Methods and Materials: Adult patients with benign or low-grade adult brain tumors were treated with FSRT per institutional practice. No attempt was made to spare the hippocampus. NCF testing was conducted at baseline and 18 months follow-up, on a prospective clinical trial. Regression-based standardized z scores were calculated by using similar healthy control individuals evaluated at the same test-retest interval. NCF impairment was defined as a z score {<=}-1.5. After delineation of the bilateral hippocampi according to the Radiation Therapy Oncology Group contouring atlas, dose-volume histograms were generated for the left and right hippocampi and for the composite pair. Biologically equivalent doses in 2-Gy fractions (EQD{sub 2}) assuming an {alpha}/{beta} ratio of 2 Gy were computed. Fisher's exact test and binary logistic regression were used for univariate and multivariate analyses, respectively. Dose-response data were fit to a nonlinear model. Results: Of 29 patients enrolled in this trial, 18 completed both baseline and 18-month NCF testing. An EQD{sub 2} to 40% of the bilateral hippocampi >7.3 Gy was associated with impairment in Wechsler Memory Scale-III Word List (WMS-WL) delayed recall (odds ratio [OR] 19.3; p = 0.043). The association between WMS-WL delayed recall and EQD{sub 2} to 100% of the bilateral hippocampi >0.0 Gy trended to significance (OR 14.8; p = 0.068). Conclusion: EQD{sub 2} to 40% of the bilateral hippocampi greater than 7.3 Gy is associated with long-term impairment in list-learning delayed recall after FSRT for benign or low-grade adult brain tumors. Given that modern intensity-modulated radiotherapy techniques can reduce the dose to the bilateral hippocampi below this dosimetric threshold, patients should be enrolled in ongoing prospective trials of hippocampal sparing during cranial irradiation to confirm these preliminary results.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

A Knowledge-Based Approach to Improving and Homogenizing Intensity Modulated Radiation Therapy Planning Quality Among Treatment Centers: An Example Application to Prostate Cancer Planning

Purpose: Intensity modulated radiation therapy (IMRT) treatment planning can have wide variation among different treatment centers. We propose a system to leverage the IMRT planning experience of larger institutions to automatically create high-quality plans for outside clinics. We explore feasibility by generating plans for patient datasets from an outside institution by adapting plans from our institution. Methods and Materials: A knowledge database was created from 132 IMRT treatment plans for prostate cancer at our institution. The outside institution, a community hospital, provided the datasets for 55 prostate cancer cases, including their original treatment plans. For each “query” case from the outside institution, a similar “match” case was identified in the knowledge database, and the match case’s plan parameters were then adapted and optimized to the query case by use of a semiautomated approach that required no expert planning knowledge. The plans generated with this knowledge-based approach were compared with the original treatment plans at several dose cutpoints. Results: Compared with the original plan, the knowledge-based plan had a significantly more homogeneous dose to the planning target volume and a significantly lower maximum dose. The volumes of the rectum, bladder, and femoral heads above all cutpoints were nominally lower for the knowledge-based plan; the reductions were significantly lower for the rectum. In 40% of cases, the knowledge-based plan had overall superior (lower) dose–volume histograms for rectum and bladder; in 54% of cases, the comparison was equivocal; in 6% of cases, the knowledge-based plan was inferior for both bladder and rectum. Conclusions: Knowledge-based planning was superior or equivalent to the original plan in 95% of cases. The knowledge-based approach shows promise for homogenizing plan quality by transferring planning expertise from more experienced to less experienced institutions.

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

Novel Parameter Predicting Grade 2 Rectal Bleeding After Iodine-125 Prostate Brachytherapy Combined With External Beam Radiation Therapy

Purpose: To propose a novel parameter predicting rectal bleeding on the basis of generalized equivalent uniform doses (gEUD) after {sup 125}I prostate brachytherapy combined with external beam radiation therapy and to assess the predictive value of this parameter. Methods and Materials: To account for differences among radiation treatment modalities and fractionation schedules, rectal dose–volume histograms (DVHs) of 369 patients with localized prostate cancer undergoing combined therapy retrieved from corresponding treatment planning systems were converted to equivalent dose-based DVHs. The gEUDs for the rectum were calculated from these converted DVHs. The total gEUD (gEUD{sub sum}) was determined by a summation of the brachytherapy and external-beam radiation therapy components. Results: Thirty-eight patients (10.3%) developed grade 2+ rectal bleeding. The grade 2+ rectal bleeding rate increased as the gEUD{sub sum} increased: 2.0% (2 of 102 patients) for <70 Gy, 10.3% (15 of 145 patients) for 70-80 Gy, 15.8% (12 of 76 patients) for 80-90 Gy, and 19.6% (9 of 46 patients) for >90 Gy (P=.002). Multivariate analysis identified age (P=.024) and gEUD{sub sum} (P=.000) as risk factors for grade 2+ rectal bleeding. Conclusions: Our results demonstrate gEUD to be a potential predictive factor for grade 2+ late rectal bleeding after combined therapy for prostate cancer.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Effect of Normal Lung Definition on Lung Dosimetry and Lung Toxicity Prediction in Radiation Therapy Treatment Planning

Purpose: This study aimed to compare lung dose–volume histogram (DVH) parameters such as mean lung dose (MLD) and the lung volume receiving ≥20 Gy (V20) of commonly used definitions of normal lung in terms of tumor/target subtraction and to determine to what extent they differ in predicting radiation pneumonitis (RP). Methods and Materials: One hundred lung cancer patients treated with definitive radiation therapy were assessed. The gross tumor volume (GTV) and clinical planning target volume (PTV{sub c}) were defined by the treating physician and dosimetrist. For this study, the clinical target volume (CTV) was defined as GTV with 8-mm uniform expansion, and the PTV was defined as CTV with an 8-mm uniform expansion. Lung DVHs were generated with exclusion of targets: (1) GTV (DVH{sub G}); (2) CTV (DVH{sub C}); (3) PTV (DVH{sub P}); and (4) PTV{sub c} (DVH{sub Pc}). The lung DVHs, V20s, and MLDs from each of the 4 methods were compared, as was their significance in predicting radiation pneumonitis of grade 2 or greater (RP2). Results: There are significant differences in dosimetric parameters among the various definition methods (all Ps<.05). The mean and maximum differences in V20 are 4.4% and 12.6% (95% confidence interval 3.6%-5.1%), respectively. The mean and maximum differences in MLD are 3.3 Gy and 7.5 Gy (95% confidence interval, 1.7-4.8 Gy), respectively. MLDs of all methods are highly correlated with each other and significantly correlated with clinical RP2, although V20s are not. For RP2 prediction, on the receiver operating characteristic curve, MLD from DVH{sub G} (MLD{sub G}) has a greater area under curve of than MLD from DVH{sub C} (MLD{sub C}) or DVH{sub P} (MLD{sub P}). Limiting RP2 to 30%, the threshold is 22.4, 20.6, and 18.8 Gy, for MLD{sub G}, MLD{sub C}, and MLD{sub P}, respectively. Conclusions: The differences in MLD and V20 from various lung definitions are significant. MLD from the GTV exclusion method may be more accurate in predicting clinical significant radiation pneumonitis.

62 RADIOLOGY AND NUCLEAR MEDICINE↗