Poster Presentations

involvement and bowel wall invasion of the tumor. There was considerable upstaging of both T and N staging using MRI versus CT scans. Also, MRI provides consistency in T and N stage assessment compared to clinical evaluation where subjective variation exists. We support routine use of MRI for initial local staging of anal canal cancers.

Practical Radiation Oncology: April-June Supplement 2013 over time was observed, a blinded revision of the original PET/CT scans is currently in progress. Author Disclosure Block: H. Hansen: None. A. Loft: None. A.K. Berthelsen: None. S. Lassen: None. C. Høgdall: None. S.A. Engelholm: None.

Author Disclosure Block: V.G. Swami: None. K. Joseph: None. D. Severin: None. K. Tankel: None. N. Usmani: None. T. Nijjar: None. 114 112 Withdrawn

Quantifying Tumor Aggressiveness Using Diffusion-Weighted MRI for Prostate Cancer M. Sanders 1, K. Nandalur 2, N. Tyagi 2, D. Schulze 2, D. Yan 2, D. Krauss 2, 1 William Beaumont Hospital, Royal Oak, MI, 2Beaumont Hospital, Royal Oak, MI

113 Hilgh Sensitivity and Specificity of PET/CT and Laparoscopic Diagnostic Lymph Node Excision for Lymph Node Metastases in Cervical Cancer Patients H. Hansen 1, A. Loft 2, A.K. Berthelsen 1, 2, S. Lassen 1, C. Høgdall 3, S.A. Engelholm 1, 1Department of Radiation Oncology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark, 2Department of Clinical Physiology, Nuclear Medicine & PET, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark, 3Department of Gynecology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark Purpose/Objectives: In cancer of the uterine cervix, lymph node (LN) metastases are associated with poor prognosis. The purpose of this study was to evaluate the efficacy of PET/CT to guide and verify laparoscopic diagnostic lymph node excision in cervical cancer patients. Materials/Methods: A single institution retrospective analysis of procedure efficacy and survival in cervical cancer patients with PET/ CT positive LN as well as identifying possible sources of error. Patient inclusion criteria: Histopathological diagnosis of cervical cancer, LN metastases at PET/CT prior to staging, laparoscopic diagnostic lymph node excision, control PET/CT after surgery. Missed Lesion (ML) was a lesion seen on the staging PET/CT with no sign of tumor tissue at histological analysis and a subsequent planning PET/CT revealing the same lesion as before laparoscopy. False Positive Lesion (FPL) was a lesion seen on the staging PET/CT with no sign of tumor tissue at histological analysis and verified by the planning PET/CT. Kaplan Meier plots and log-rank tests were performed. Histopathology of removed LN number of FPL over time was registered. Results: Sixty-five patients were included. Laparoscopy confirmed metastatic spread to LN in 39 patients. In 4 of 26 patients with negative laparoscopic results, post-operative PET/CT showed ML. Of these, three patients were re-operated of which two had LN metastases confirmed, and one continued having no evidence of metastatic disease. Of the total 23 patients with twice verified negative LN pathology, one patient died of metastatic breast cancer. Of the 42 patients with metastatic disease, 15 died. For the entire staging procedure sensitivity and specificity were calculated to 0.98 and 1.00 respectively. Positive and negative predictive values were 1.00 and 0.96. Of the 23 patients with FPL, histopathology of removed LN showed nonspecific changes of reactive origin in 65% (C.I. 43-84%), fibrosis in 17% (5-39%), calcifications in 13% (3-34%), histiocytosis in 35% (16-57%), follicular hyperplasia in 9% (128%) and necrosis in 4% (0-21%) (some showed more than one type). Completely normal architecture was observed in 17% (5-39%) of the patients. No change in frequency of FPL was observed over time. Conclusions: PET/CT as control of laparoscopic diagnostic lymph node excision provides high sensitivity and specificity as well as high positive and negative predictive values, for lymph node staging in cervical cancer patients. However, a high number of FPL was observed at PET/CT, mainly due to inflammation. Although no change in frequency

Purpose/Objectives: To quantify tumor aggressiveness based on apparent diffusion coefficient (ADC) in prostate cancer for therapy assessment. Materials/Methods: 42 patients (median age: 68 yrs, median serum prostatic specific antigen [PSA]:6.9) with biopsy-proven prostate cancer underwent diffusion weighted images of the prostate using an optimized single-shot echo planar imaging sequence at 3T with an endorectal coil. Quantitative apparent diffusion coefficient (ADC) maps were generated via a mono-exponential fit using three b-values (50, 400 and 800s/ mm2). Anatomical images include high resolution axial, sagittal and coronal T2-weighted images. T2, DWI and ADC maps were imported into our clinical treatment planning system and rigidly registered using manual registration. Tumor foci in peripheral zone (pz), central gland (cg) and seminal vesicles (sv) were delineated on ADC maps at the sites of visible tumor on T2, DW images and ADC maps using T2weighted images as a reference. Statistical parameters and tumor volumes extracted from tumor foci were used as a measure of tumor aggressiveness. Multivariate linear regression models were estimated to test for associations between mean ADC and age, tumor volume (TV), histology grade Gleason score (GS) and PSA. The multivariate regression model was also used to generate predictions for mean ADC. Results: A total of 63 MR lesions (42 in pz, 18 in cg and 3in sv) were identified. Both GS (ρ = − 0.57, pb0.0001) and TV (ρ = 0.47, p = 0.0014) were significantly correlated with the mean ADC for the tumors in entire prostate gland. For tumors located in PZ, the correlation was even stronger for GS (ρ = − 0.63, p b 0.0001) and TV (ρ = 0.5, p b 0.0001). When age, GS, PSA and TV were all included as predictors in a multivariate regression model for pz tumors, only GS (p = 0.002) had a statistically significant effect but not PSA (p = 0.532), age (p = 0.297) or TV (p = 0.558). The model is able to explain a fairly significant amount of the variation in the mean ADC (adjusted R-squared = 0.337). The correlation between the predicted and observed values of mean tumor ADC is 0.638 (p b 0.001).Central gland tumors did not show statistically significant association with any of the clinical parameters. Conclusions: Increased tumor cellularity in high GS tumors results in a negative correlation between mean tumor ADC and GS. Quantifying tumor aggressiveness based on ADC values has a potential to further improve the clinical risk models that are currently based on only GS and PSA. Author Disclosure Block: M. Sanders: None. K. Nandalur: None. N. Tyagi: None. D. Schulze: None. D. Yan: None. D. Krauss: None.

115 Absolute Lymphocyte Count: A Novel Prognostic Factor for Merkel Cell Carcinoma M.E. Johnson, A. Turaka, F. Zhu, T. Galloway, J. Farma, C. Perlis, Fox Chase Cancer Center, Philadelphia, PA

Quantifying tumor aggressiveness using diffusion-weighted MRI for prostate cancer.

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