Parapharyngeal extension of nasopharyngeal carcinoma: still a significant factor in era of modern radiotherapy?

PURPOSE: To retrospectively analyze the prognostic value of parapharyngeal space (PPS) extension after conformal radiotherapy for nasopharyngeal carcinoma. PATIENTS AND METHODS: Between 1998 and 2005, 700 patients were treated with conformal radiotherapy at 2 Gy/fraction daily to a total of 70 Gy. All patients underwent staging with magnetic resonance imaging. The incidence of PPS was determined, and the extent of involvement was further subclassified regarding the presence or absence of carotid space (CS) involvement. The prognostic parameters, including age, gender, stage, chemotherapy, additional boosting, and extent of PPS involvement, were analyzed by univariate and multivariate analyses. RESULTS: The median duration of follow-up was 51 months, and the 5-year overall survival rate for the whole group was 73%. The overall incidence of PPS extension was high (74%), and 29% had additional extension to the CS. Multivariate analysis showed age, gender, chemotherapy, T stage, and N stage to be significant prognostic factors, but not PPS involvement with or without CS extension. In the subgroup of patients with Stage T2 disease (n = 242), the presence of PPS involvement alone or PPS plus CS extension had no statistically significant effect in terms of local control (p = 0.68), distant metastases (p = 0.34), or overall survival (p = 0.24) compared with those without PPS involvement (Stage T2a). CONCLUSIONS: With better tumor delineation by magnetic resonance imaging and improved coverage using modern radiotherapy techniques, PPS extension per se no longer predicts for disease outcome. Hence, subcategorizing Stage T2 disease is no longer important in future International Union Against Cancer/American Joint Committee on Cancer classifications.

N-staging by magnetic resonance imaging for patients with nasopharyngeal carcinoma: pattern of nodal involvement by radiological levels.

BACKGROUND AND PURPOSE: To study the pattern of lymphatic spread for patients with nasopharyngeal carcinoma (NPC), the significance of retropharyngeal node (RP-LN) involvement, and the possibility of replacing the supraclavicular fossa (SCF) by Levels IV and Vb (LL) as a demarcating criterion for N3-category. PATIENTS AND METHODS: The magnetic resonance imagings (MRI) of 202 consecutive patients with NPC treated during 2001-2002 were retrospectively reviewed. Distribution in terms of radiological level (using the same criteria as other head and neck cancers) was mapped, and the size of individual node measured. Prognostic significance of RP-LN and LL was analyzed. RESULTS: Only 4% of patients were node-negative on presentation. The nodal involvement occurred predominately at II (94%), III (85%) and RP-LN (80%). The presence of RP-LN affected the N-category in 3.5% of patients, and had no significant impact on tumor control. Replacing SCF by LL as one of the criteria for defining N3 is predictive for both distant control and overall survival. CONCLUSIONS: With sensitive detection by MRI, the incidence of nodal involvement was very high for patients with NPC. It was difficult to isolate the prognostic significance of RP-LN. The current criterion for defining N3-category by extension into SCF or nodal size > 6 cm is the recommended standard, however replacing SCF with LL could be potentially useful and further validation is warranted.

Magnetic Resonance for T-staging of nasopharyngeal carcinoma--the most informative pair of sequences.

OBJECTIVE: To evaluate the most informative pair of sequences in magnetic resonance (MR) for T-staging of nasopharyngeal carcinoma (NPC). METHODS: The MR images of 134 patients with newly diagnosed NPC, from 1996 to 2002, were retrospectively reviewed. All the patients were scanned using 1.5 Tesla MR systems. The images of the nasopharynx were reviewed by two qualified radiologists to determine the positive findings and the T-stage by UICC (6th edition) System, using each sequence separately. The T-stage derived from a single MR sequence was then compared with the T-stage based on the five selected sequences to assess the number and percentage of patients who were being understaged. Therefore, the overall percentage accuracy of each single sequence could be determined. A pair of sequences providing information to achieve almost 100% diagnostic accuracy was then derived. RESULTS: The overall percentage accuracy of five individual sequences of the nasopharynx is as follows: contrast-enhanced (CE) fat suppression (FS) axial T1 (94.8%), CE FS coronal T1 (88.1%), FS axial T2 (85.8%), non-contrast enhanced (NE) axial T1 (78.4%) and non-contrast enhanced (NE) coronal T1 (77.6%). CE FS axial T1 has the best accuracy. All the structures that are missed in CE FS axial T1, which lead to apparent understaging, are appreciated in NE axial T1-weighted images. CONCLUSION: Individual sequences supplement each other in the NPC staging. CE FS axial T1 is the most informative individual sequence. Combination of CE FS axial T1 and NE axial T1 of the nasopharynx provides sufficient information to achieve almost 100% diagnostic accuracy in T-staging; therefore, both should be included in the MR-staging protocol.

Minimization of acquisition time in short-range free-space optical communication.

We consider short-range (1-3-km) free-space optical communication between moving parties when covertness is the overriding system performance requirement. To maximize covertness, it is critical to minimize the time required for the acquisition phase, during which the party initiating contact must conduct a broad-field scan and so risks revealing his position. Assuming an elliptical Gaussian beam profile, we show how to optimize the beam divergence angles, scan speed, and design of the raster scan pattern so as to minimize acquisition time. In this optimization, several constraints are considered, including signal-to-noise ratio, required for accurate bearing detection and reliable decoding; limited receiver bandwidth; limited scanner speed; and beam divergence as limited by the scanner mirror dimensions. The effects of atmospheric turbulence are also discussed.