Multimodality functional imaging using DW-MRI and 18F-FDG-PET/CT during radiation therapy for human papillomavirus negative head and neck squamous cell carcinoma: Meixoeiro Hospital of Vigo Experience

AIMTo noninvasively investigate tumor cellularity measured using diffusion-weighted magnetic resonance imaging (DW-MRI) and glucose metabolism measured by 18F-labeled fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG-PET/CT) during radiation therapy (RT) for human papillomavirus negative (HPV-) head and neck squamous cell carcinoma (HNSCC).METHODSIn this prospective study, 6 HPV- HNSCC patients underwent a total of 34 multimodality imaging examinations DW-MRI at 1.5 T Philips MRI scanner [(n = 24) pre-, during- (2-3 wk), and post-treatment (Tx), and 18F-FDG PET/CT pre- and post-Tx (n = 10)]. All patients received RT. Monoexponential modeling of the DW-MRI data yielded the imaging metric apparent diffusion coefficient (ADC) and the mean of standardized uptake value (SUV) was measured from 18F-FDG PET uptake. All patients had a clinical follow-up as the standard of care and survival status was documented at 1 year.RESULTSThere was a strong negative correlation between the mean of pretreatment ADC (ρ = -0.67, P = 0.01) and the pretreatment 18F-FDG PET SUV. The percentage (%) change in delta (∆) ADC for primary tumors and neck nodal metastases between pre- and Wk2-3 Tx were as follows: 75.4% and 61.6%, respectively, for the patient with no evidence of disease, 27.5% and 32.7%, respectively, for those patients who were alive with disease, and 26.9% and 7.31%, respectively, for those who were dead with disease.CONCLUSIONThese results are preliminary in nature and are indicative, and not definitive, trends rendered by the imaging metrics due to the small sample size of HPV- HNSCC patients in a Meixoeiro Hospital of Vigo Experience.

Multicomponent Assessment of the Geometrical Uncertainty and Consequent Margins in Prostate Cancer Radiotherapy Treatment Using Fiducial Markers

The aim is to compute all sources of geometrical uncertainty in prostate radiotherapy using fiducial markers and determine the safety treatment margins. Based on the markers position, correlations between prostate rotation/deformation and rectal and bladder fillings as well as changes in prostate volume during the treatment course are analyzed. The study includes 375 pre-treatment CBCT images from 15 prostate cancer patients treated with hypofractionated radiotherapy. The position coordinates of the markers were obtained from each image acquisition. In addition, rectum and bladder were outlined on CBCTs. The intrafractional error was estimated by an additional post-treatment CBCT acquired on alternate days. Tau-Kendall analysis was performed to correlate organ fillings with prostate rotation/deformation. Delineation uncertainty was assessed from contours of 10 patients performed by two radiation oncologists and repeated twice. The CT contouring was assisted by a multiparametric MR approach combining a T2-weighted with diffusion-weighted imaging, and a gradient recalled echo for fiducial marker identification. Uncertainty associated to treatment unit was estimated from phantom measurements. The obtained clinical margins were 4.4, 7.3, 5.1 mm in the Left-Right, Superior-Inferior, and Anterior-Posterior directions, respectively, being the contouring the most important contribution. The mechanical limitations of the beam delivery system and the associated imaging device entailed errors of the same order as prostate motion, rotation or deformation. Weak correlations between variation of the rectal volume and the presence of rotations/deformations were found (correlation coefficient 0.182, p = 0.001 for rotations around lateral axis;correlation coefficients 0.1, p < 0.05 for deformations). The distance between markers decreased with session number, becoming more pronounced from fraction 13 and reaching 1 - 1.8 mm at the end of the treatment. In summary we have determined the optimal treatment margins based on geometrical uncertainty assessment using van Herk formalism. An appropriate preparation of rectum and bladder involves minimizing the effect of prostate rotations/deformations. The prostate tends to decrease in size during the treatment which could influence treatment re-planning strategies.