Response to neoadjuvant therapy in locally advanced rectal cancer: assessment with diffusion-weighted MR imaging and 18FDG PET/CT.

The aim of this study was to evaluate the correlation between the changes of SUV(max) and of apparent diffusion coefficient (ADC) before and after neoadjuvant therapy, to enable us predict the therapy response, in patients with locally advanced rectal cancer (LARC). A total of 30 patients with LARC who underwent CRT were recruited for our study. All the patients underwent a whole body 18F-FDG-PET/CT scan and a pelvic MR examination including DW imaging for staging (PET/CT1 and RM1), and after the chemoradiation therapy (PET/CT2, and RM2). Histopathologic analysis of rectal specimen, according to tumor regression grade (Mandard's criteria) was used as the standard reference. MR and PET-CT images were analyzed, and measurements of ADC values and SUV(max) were taken. Diagnostic performance for selection of complete responders (TRG1-2) and overall diagnostic accuracy for each item were calculated. After neoadjuvant therapy, all patients were submitted to surgery. According to Mandard's criteria, 21 tumors showed complete (TRG1) or subtotal regression (TRG2) and were classified as responders; nine tumors were classified as non responders (TRG3, 4, and 5). In all the patients, mean value of SUV(max) in PET/CT1 was higher than those in PET/CT2 (P < 0.001), whereas mean ADC value was lower in RM1 than RM2 (P < 0.001), with a significant percentage decrease of values after the treatment (P < 0.005).The best predictors cut-off values for TRG response were SUV(max) of 4.4 and ADC of 1.28 × 10(3) mm(2)/s with sensitivity, specificity accuracy, negative predictive value, and positive predictive values of 77.3%, 88.9%, 80.7%, 61.5%, and 94.4%, respectively. We conclude from the overall data of this study that the absolute values of SUV(max) and ADC of rectal lesion after CRT were the best parameters to define the response to treatment, by differentiating fibrosis from viable tumor tissue.

Set-up errors analyses in IMRT treatments for nasopharyngeal carcinoma to evaluate time trends, PTV and PRV margins.

INTRODUCTION: the aims of this study were to analyze the systematic and random interfractional set-up errors during Intensity Modulated Radiation Therapy (IMRT) in 20 consecutive nasopharyngeal carcinoma (NPC) patients by means of Electronic Portal Images Device (EPID), to define appropriate Planning Target Volume (PTV) and Planning Risk Volume (PRV) margins, as well as to investigate set-up displacement trend as a function of time during fractionated RT course. MATERIAL AND METHODS: before EPID clinical implementation, an anthropomorphic phantom was shifted intentionally 5 mm to all directions and the EPIs were compared with the digitally reconstructed radiographs (DRRs) to test the system's capability to recognize displacements observed in clinical studies. Then, 578 clinical images were analyzed with a mean of 29 images for each patient. RESULTS: phantom data showed that the system was able to correct shifts with an accuracy of 1 mm. As regards clinical data, the estimated population systematic errors were 1.3 mm for left-right (L-R), 1 mm for superior-inferior (S-I) and 1.1 mm for anterior-posterior (A-P) directions, respectively. Population random errors were 1.3 mm, 1.5 mm and 1.3 mm for L-R, S-I and A-P directions, respectively. PTV margin was at least 3.4, 3 and 3.2 mm for L-R, S-I and A-P direction, respectively. PRV margins for brainstem and spinal cord were 2.3, 2 and 2.1 mm and 3.8, 3.5 and 3.2 mm for L-R, A-P and S-I directions, respectively. Set-up error displacements showed no significant changes as the therapy progressed (p>0.05), although displacements >3 mm were found more frequently when severe weight loss or tumor nodal shrinkage occurred. DISCUSSION: these results enable us to choose margins that guarantee with sufficient accuracy the coverage of PTVs and organs at risk sparing. Collected data confirmed the need for a strict check of patient position reproducibility in case of anatomical changes.