K. Chao

Adjuvant Pelvic Radiation Therapy±Vaginal Brachytherapy in Patients With High-risk Stage I or Stage II Uterine Papillary Serous, Clear Cell, and High-grade Endometrioid Carcinoma.

Purpose:Radiation therapy (RT) for stages I-II uterine papillary serous carcinoma (UPSC), clear cell (CC), and high-grade endometrioid (HGE) carcinoma present a treatment challenge. Regimens include external beam radiotherapy (EBRT) with or without brachytherapy. We examine the use of these radiation modalities in these endometrial cancers (EC) with respect to cause-specific survival (CSS). Methods:The Surveillance, Epidemiology, and End Results (SEER) database was queried for patients with AJCC stages I-II UPSC, CC, or HGE cancer treated with hysterectomy and RT between 1998 and 2008. Patients who did not receive adjuvant RT or received brachytherapy alone were excluded. CSS was evaluated by the Kaplan-Meier survival analysis and the log-rank test was used to compare CSS. Multivariate analysis was performed using the Cox proportional hazards regression model. Adjusted hazard ratios (HR) were calculated for risk of EC death. Results:There were 1653 patients included in this analysis. The overall 100-month CSS for the entire cohort was 81.0%. The 100-month CSS was 85.3% for EBRT alone and 86.5% for EBRT+brachytherapy (P=0.72). Stage IC/IIA/IIB patients had a greater risk of EC death compared with stage IA/IB patients (adjusted HR=2.39; P<0.0001). Patients with UPSC and CC had a slightly higher risk of EC death compared with HGE (adjusted HR=1.01 [P=0.97] and 1.42 [P=0.02], respectively). On subset analysis, there was no difference in CSS with the addition of brachytherapy for UPSC (P=0.37), CC (P=0.27), or HGE cancer patients (P=0.42). Patients treated with brachytherapy in addition to EBRT did not demonstrate a reduced adjusted risk of EC death compared with EBRT alone (P=0.38). Conclusions:The addition of brachytherapy to adjuvant EBRT in stages I-II UPSC, CC, and HGE cancer did not demonstrate superior CSS. Thus, patients may not benefit from the addition of brachytherapy to EBRT.

Comparing outcomes in poorly-differentiated versus anaplastic thyroid cancers treated with radiation: a surveillance, epidemiology, and end results analysis.

PURPOSEnPoorly differentiated thyroid carcinoma (PDTC) and anaplastic thyroid carcinoma (ATC) are considered the most aggressive cancers of the head and neck. The aim of the study was to evaluate and compare survival outcomes in PDTC and ATC in a large population-based cohort.nnnMATERIALS AND METHODSnPatients with PDTC and ATC diagnosed from 1973 to 2008 were obtained from Surveillance, Epidemiology, and End RESULTS database. Kaplan-Meier survival analysis and log-rank analyses were performed to evaluate (1) The effect of histology on cause-specific survival (CSS) and (2) the influence of factors such as treatment, treatment sequence, race, sex, and age on CSS. Multivariate analysis was performed to assess the independent effect of these factors on CSS.nnnRESULTSnA total of 1352 patients with PDTC and ATC were identified. PDTC constituted 52.4% of patients versus 47.6% for ATC. Median CSS was similar in the two histology groups (P = 0.14). Both PDTC and ATC patients receiving radioisotopes showed a significantly better CSS compared to external beam radiation (P < 0.0001). PDTC and ATC Patients receiving radiation prior to surgery demonstrated a significantly lower CSS compared to patients receiving radiation postoperatively (P < 0.0001). Female gender and black/nonwhite race tended to improve CSS in PDTC and ATC patients (P = 0.29 and P = 0.03, for gender and race, respectively). However, multivariate analysis revealed only type of radiation treatment and age to be independently associated with CSS.nnnCONCLUSIONnThis is the first large population-based study evaluating PDTC and ATC outcomes in patients who received radiation treatment. Radioisotope use and timing of radiotherapy (postoperative vs. preoperative) were associated with improved CSS in both histologies.

Is there a cause-specific survival benefit of postmastectomy radiation therapy in women younger than age 50 with T3N0 invasive breast cancer? A SEER database analysis: outcomes by receptor status/race/age: analysis using the NCI Surveillance, Epidemiology, and End Results (SEER) database.

Objective:Postmastectomy radiation therapy (PMRT) remains controversial for patients with pathologic stage T3N0 (pT3N0) breast cancer. A Surveillance, Epidemiology, and End Results (SEER) database analysis suggested that PMRT might benefit patients older than age 50. However, the relevance between estrogen receptor (ER), progesterone receptor (PR), race, and PMRT in patients younger than age 50 is unknown. Methods:The impact of PMRT treatment on cause-specific survival (CSS) and overall survival (OS) were analyzed for women in the SEER database from 1998 to 2007. Approximately half (47%) of the 1104 patients who met the study requirements received PMRT. We performed univariate analysis to compare CSS between the PMRT and no-PMRT groups for all patients and further stratified by age, race, tumor size, tumor grade, and ER/PR status. Results:No difference in CSS or OS was detected between women treated with or without PMRT. Black/other race, ER−, and PR−, all suggested a trend toward decreased CSS. In univariate analysis, PMRT seems to be beneficial in patients younger than age 40 (hazard ratio=0.65; P=0.25; a nonsignificant trend in favor of PMRT). Conclusions:This SEER database analysis of patients younger than age 50 and with pT3N0 breast cancer showed that PMRT did not significantly affect CSS at 5 years; however, it implied a trend of benefit for patients younger than 40. The findings that patients with African heritage and negative ER/PR status showing decreased CSS warrant further investigation to determine the role of personalized PMRT in these high-risk cohorts.

Management of single malignant lung nodules in elderly patients (70 years or older) who are not candidates for lobectomy.

PurposeThe aim of this study was to evaluate and compare sublobar resection plus intraoperative seed implant (IOS) versus stereotactic body radiation therapy (SBRT) in patients with single malignant lung nodules in patients 70 years of age or older. Materials and MethodsA retrospective chart review was performed and 47 patients with adequate information were selected for analysis. Thirty patients with single malignant lung nodules received SBRT. Seventeen patients received limited surgical resection plus radioactive seed implantation for solitary malignant lung nodules. Univariate statistical analysis showed a significant difference only for the age in the 2 groups: the mean age in the radioactive seed group, 78.8 years versus 76.1 years in the SBRT group (2-sided, P=0.05). ResultsThere was high local control and minimal toxicity with either treatment modality and no significant difference among the 2 groups in terms of local control, survival, and toxicity. However, the distant failure was higher but not statistically significant in the SBRT group (9 of 30 patients in SBRT vs. 0 of 17 in IOS, P=0.1). ConclusionsOur study has shown excellent outcomes and limited toxicity in both IOS and SBRT for treatment of single malignant lung nodules in patients who are not candidates for lobectomy. However, a randomized trial is needed in this group of elderly patients to determine the most appropriate treatment.

SU‐E‐J‐72: Shift Invariant Feature Transform (SIFT) Based Image Stitching for Panoramic Cone Beam CT (CBCT)

PURPOSEnPanoramic CBCT is a novel imaging technique that stitches together projection images from multiple views to increase the imaging volume to as large as practically needed using half (200 degree gantry rotation) scans only. In this study, we investigated a SIFT-based method to improve the accuracy of image stitching for panoramic CBCT.nnnMETHODSnPanoramic CBCT data were acquired for a torso phantom using two half scans: (A) the detector at the center position and (B) the detector shifted 148mm toward the right side of the phantom. For each projection image of scan A, a corresponding projection image of the same gantry angle was interpolated for scan B using images of two neighboring gantry angles. The SIFT method was applied to extract matching feature points in the overlapping region of the projection images of the same gantry angle from each scan. The rigid (translation and rotation) transform matrix derived from this analysis was then used to stitch together the two projection images for CBCT reconstruction using the simultaneous algebraic reconstruction technique (SART) method. Three overlapping (5-cm, 3-cm and 2-cm) sizes were used for the SIFT analysis to determine the optimal imaging parameters.nnnRESULTSnThe CBCT reconstructions using the SIFT stitching method showed significant artifact reduction compared with the direct stitching method. The success rate of matching (less than 0.5 degrees rotation and 2 pixels horizontal/vertical shifts) was close to 100% for 5-cm overlapping and gradually reduced as the overlapping size decreased. The minimum overlapping size we could reliably apply our method was 2 cm (93.8% success rate) below which significant operator involvement was required to determine the applicable rigid transform parameters.nnnCONCLUSIONnWe have demonstrated the effectiveness of the SIFT stitching method for panoramic CBCT reconstruction. We are currently improving the registration technique to further reduce the required overlapping size. This work was partially supported by a DOD grant DOD W81XWH1010862.

SU‐E‐T‐206: Improving Radiotherapy Toxicity Based On Artificial Neural Network (ANN) for Head and Neck Cancer Patients

PURPOSE/OBJECTIVE(S)nThe aim of this study is to build the estimator of toxicity using artificial neural network (ANN) for head and neck cancer patients MATERIALS/METHODS: An ANN can combine variables into a predictive model during training and considered all possible correlations of variables. We constructed an ANN based on the data from 73 patients with advanced H&N cancer treated with external beam radiotherapy and/or chemotherapy at our institution. For the toxicity estimator we defined input data including age, sex, site, stage, pathology, status of chemo, technique of external beam radiation therapy (EBRT), length of treatment, dose of EBRT, status of post operation, length of follow-up, the status of local recurrences and distant metastasis. These data were digitized based on the significance and fed to the ANN as input nodes. We used 20 hidden nodes (for the 13 input nodes) to take care of the correlations of input nodes. For training ANN, we divided data into three subsets such as training set, validation set and test set. Finally, we built the estimator for the toxicity from ANN output.nnnRESULTSnWe used 13 input variables including the status of local recurrences and distant metastasis and 20 hidden nodes for correlations. 59 patients for training set, 7 patients for validation set and 7 patients for test set and fed the inputs to Matlab neural network fitting tool. We trained the data within 15% of errors of outcome. In the end we have the toxicity estimation with 74% of accuracy.nnnCONCLUSIONnWe proved in principle that ANN can be a very useful tool for predicting the RT outcomes for high risk H&N patients. Currently we are improving the results using cross validation.

SU‐E‐T‐702: Performance of Multiple Conformity, Homogeneity and Dose Gradient Indices in SRS and SBRT Treatment Planning of the Spinal, Pelvic and Lung Lesions

Purpose: Presently, various forms of quality indices (QI) are used to compare and evaluate stereotactic treatment plans with no single QI accepted as universal. In this work we evaluate and compare the performance of 11 previously reported QI: 5 conformity (CI), 5 homogeneity (HI), and 1 dose gradient (DGI) indices as a function of target size, site, and mode of treatment. A novel unified quality function (UQF) which combines conformity, homogeneity and dose gradient is presented and investigated. Methods: 27 spine SRS, 8 pelvic SBRT and 34 lung SBRT cases were analyzed using an in‐house wxPython program which imports treatment plan data and calculates various quality indices, dose volume tables, displays 3D dose/CT images, cumulative and differential DVHs. Results: Mean spine, pelvis and lung coverages were 0.91, 0.93, 0.85 respectively. Mean maximum target dose was best for pelvis (108%), followed by the lung (115%) and the spine (118%). Mean minimum target dose was best for the lung (95%), followed by pelvis (94%) and spine (88%). Mean DGI were 4.6, 5.2 and 7.54 for the pelvis, spine and lung. UQF scores the best for pelvis (0.2), followed by spine (0.28) and the lung (0.42). IMRT spine plans had better mean coverages (0.94), and lower maximum target dose (114%), while VMAT plans had better minimum target dose (89%). Conclusion: Mean CI, HI and DGI show various sensitivities to the treatment site, size and the delivery type (VMAT or IMRT). All CI except coverage show large variations with volume < 130 cc while all 5 HI show little dependence on the PTV volume. DGI values fall sharply for the lung (from 15 to 6) and spine (from 10 to 5) as the PTV increases to about 100 cc, while pelvic DGI stays about 5 for all PTV sizes.

SU‐E‐T‐259: Dosimetric Comparison of Cs‐131 Vs. I‐125 Vs. Pd‐103 Intraoperative Brachytherapy in Patients with Resected Brain Metastasis

Purpose: Cs‐131, I‐125 and Pd‐103, have been used for permanent implant brachytherapy. Cs‐131 has shorter half‐life — 9.7 days as compared to I‐125 and Pd‐103 — 59.4 and 17.0 days, respectively. It is likely more biologically efficient for tumor cell kill as the initial dose rate from Cs‐131(23.9 cGy/h) is 4 times higher than that of I‐125(5.8 cGy/h) and twice of Pd‐103(13.62 cGy/h). These isotopes differ in their average gamma‐ray energies (30.4keV, 28.5keV and 20.8keV, respectively). This study examines the dosimetric differences amongst these isotopes when used as a permanent implant for patients with resected brain metastasis with regard to exposure of normal brain tissue and the potential for developing radiation necrosis (RN). Methods: 24 patients with a single newly diagnosed and resected brain metastasis were implanted with Cs‐131. Post‐op dosimetry plans were generated for Cs‐131, I‐125 model #6711 and Pd‐103 model #200. The prescription dose was 80 Gy to 5mm depth from the surface cavity. The mean air kerma strength for the Cs‐131, I‐125 and Pd‐103 seeds were 2.4U, 0.6985U and 2.11U respectively. The volume of brain tissue exposed to radiation at 100%, 80% and 50% isodose lines were compared for each isotope. Results: Significantly larger volume of brain tissue exposed to radiation, with the use of I‐125 when compared to both Cs‐131 (p less than 0.00005) and Pd‐103 (p less than 0.00004). There is no significant difference when comparing Cs‐131 to Pd‐103 (p=0.26605). Conclusion: In this analysis, we report that Cs‐131 and Pd‐103 expose less normal brain tissue to radiation when compared to I‐125, thus providing a dosimetric superiority and subjecting less tissue to RN. In addition, Cs‐131 has the shortest T1/2 and in our trial with a median follow up of 10 months, all 24 patients have 100% local control while experiencing 0% incidence of RN.

MO-F-108-10: Implementation of 4Pi Non-Coplanar Converging (4PiNC) Beams Using a Conical Delivery Geometry

PURPOSEnTo study the feasibility of a proposed conical delivery system for implementing 4PiNC beams.nnnMETHODSnIn the proposed novel 4PiNC beam delivery system, the x-ray source aims at the isocenter but rotates around a point on the superior-inferior axis in a conical fashion. Mathematically, each rotation forms a cone where the vertex is the isocenter and the base is the area bounded by the circular trajectory of the x-ray source. By changing the cone angle (90 - vertex angle), the proposed 4PiNC system allows hundreds of non-coplanar beams to be delivered without couch rotation. We developed a simple treatment planning system to investigate the dosimetry for an elliptic cylinder phantom. The planning target volume was a sphere inside the phantom. The three-dimensional dose calculation was calculated using the TMR table, off-axis ratios and output factors of a 6 x-ray beam commissioned for radiosurgery cones. Planning parameters (depth, off-axis distance…) were calculated analytically. The dose grid contained 100×100×100 voxels with a voxel size of 2×2×2 mm^ 3.nnnRESULTSnDose distributions were calculated for (A) 263 beams using cone angles 0, ±20, ±40, ±60, ±80 degree, (B) 153 beam using cone angles 0, 20, 40, 60, 80 degree and (C) 179 beams using cone angles 0, ±20, ±40 degree. Highly conformed dose distributions were achieved with conformity indexes 1.12, 1.11 and 1.19 for case (A), (B) and (C), respectively. The dose falloff (80%-20% of the central dose profile) was 8 mm, 8 mm and 11 mm, respectively.nnnCONCLUSIONnWe proved in principle that the proposed 4PiNC beam delivery system can provide excellent dose distribution (low conformity index and fast dose falloff) without couch rotation. The proposed system can significantly improve the treatment plan quality and avoid couch-gantry collisions, a common patient safety concern of c-arm linear accelerators, when delivering non-coplanar beams. This work was partially supported by a DOD grant DOD W81XWH1010862.

SU‐E‐J‐02: GPU‐Accelerated Polyenergetic DRR Generation Based On Data Parallelism and Task Parallelism with a Dispatcher Using OpenCL: Effect of the Numbers of Tasks and Energies

PURPOSEnTo improve the performance of parallel processing of multi-energetic digitally reconstructed radiograph (DRR) generation using a task-overlap strategy on heterogeneous platforms.nnnMETHODSnA segmented 512 ×512 ×223 head-neck phantom was used to generate 512 ×512 polyenergetic DRR based on Mohan4 and Mohan6 spectrums containing 16 and 24 energy bins, respectively. The DRR formation for each energy bin comprises three steps: (1) phantom conversion, (2) line integral and (3) exponential and weighting of projection. The parallel computing ecosystem consisted of one 8-core CPU and one general purpose graphics processing unit (GPGPU). We used Open Computing Language (OpenCL) to decompose the low-degree parallel and serial workloads into multiple tasks on CPU using task parallelism, and partition the high-degree parallel workloads on GPGPU using data parallelism. Two sequential task partitions for the first DRR formation were tested: (A) Step1 as Task1 on CPU, Step2 as Task2 on GPU and Step3 as Task3 on CPU; and (B) Step1 as Task1 on CPU and Step2 and Step3 as Task2 on GPU. The subsequent DRR generation does not need Step 1 so Step1 as Task1 was excluded in each partition. A task-overlap method driven by a dispatcher was also implemented using regular single-threaded host program to further improve the performance.nnnRESULTSnFor the first DRR formation and Partition A, the task-overlap strategy was 5.8 and 6.5 times faster than sequential method for 16-energy-bin Mohan4 and 24-energy-bin Mohan6 spectrums, respectively. For Partition B, the speedup of the task-overlap strategy was 5.2 and 5.5 times for Mohan4 and Mohan6 spectrums, respectively. For the following DRR formation, the speedups were 1.16 and 1.165 times in two-task scenario for Mohan4 and Mohan6 spectrums.nnnCONCLUSIONnThe task-overlap strategy significantly improves the performance for parallel processing of multi-energetic DRR generation. The parallelism is increased when more energies and tasks are driven by the dispatcher.