ABSTRACT
Single photon avalanche diode (SPAD) is the new generation of Geiger-Muller (GM) detectors, developed with semiconductor technology, and able to detect single photons, mainly in visible range. In this work we study the signal generation process and the dead time (DT) mechanisms of the device under a constant light regime. According to our results, it is possible to discriminate low rate signals from afterpulse and noise production and, moreover, to overcome the saturation effect due to the dead time losses. Starting from hybrid DT model [S. H. Lee and R. P. Gardner, Appl. Radiat. Isot. 53, 731 (2000)] we have been able to evaluate the real amount of incident photon rate up to 10(7) cps using a passive quenched device with 0.97 mus total dead time. In this way the passive quenched SPAD achieves the same performance of the active quenched one showing that relatively complex data analysis and complex device implementation are comparable solutions for constant light measurement. We also analyze some effects, lacking in GM counter, which should be introduced in the analysis of semiconductor device, as afterpulse, reduced photon detection efficiency, and noise production.
ABSTRACT
PURPOSE: To evaluate the therapeutic activity and toxicity of gemcitabine in the treatment of metastatic urothelial carcinoma. PATIENTS AND METHODS: Twenty-four consecutive patients with recurrent- and/or metastatic urothelial carcinoma pretreated with first line cisplatin-based chemotherapy were treated with gemcitabine 1000 mg/m2/week intravenously diluted in 250 cc of normal saline as 20 minutes infusion for 3 consecutive weeks followed by a 1 week rest period. Chemotherapy was repeated every 28 days. RESULTS: All enrolled patients were evaluable for objective response accordingly to an intent-to-treat analysis. A complete response was achieved in 1 patient (4%) and a partial response in 6 cases (25%) for an overall response rate of 29% (confidence limits 18%-39%). The median duration of objective responses was 7.4+ months (range 3.0+/12.8). Six patients showed no changes (25%) with a median duration of 4.0 months. A subjective improvement in tumor-related symptoms was reported by all responding patients, and in 3 patients with no change. Six out of 9 patients with symptomatic bone lesions had a subjective improvement with reduction in analgesic drugs consumption. Objective responses were observed at all sites of disease. The median overall survival was 13.0+ months (range 4.0/16.2+). Over a total of 76 cycles (a mean of 3.1 cycles/patient), grade 1-2 leukopenia was seen in 9 patients (37%), grade 1-2 thrombocytopenia in 4 patients (17%), and grade 1 anemia in only 2 cases (8%). Grade 3 leukopenia was seen in 3 cases (12.5%). Grade 4 leukopenia or grade 3-4 thrombocytopenia were not seen. Gastrointestinal toxicity was very mild. CONCLUSIONS: Single agent gemcitabine at the dose of 1000 mg/m2 on a weekly schedule is active, at least in terms of objective response rate and tumor-related symptoms palliation, against pretreated urothelial carcinoma with good tolerability. These results compare favorably with those achieved with the most active drugs such as cisplatin and methotrexate.
