The cluster model of ultraviolet disinfection explains tailing kinetics.

AIMS: To develop a new mathematical model derived from first principles to define the kinetics of ultraviolet disinfection and to explain the phenomenon known as tailing. The theory presented interprets tailing as the result of photoprotection due to cumulative Mie scattering effects in clustered populations of micro-organisms. METHODS AND RESULTS: Mie scattering effects at ultraviolet wavelengths are used to compute a shielding constant for each micro-organism based on the average projected diameter. An intrinsic rate constant, hypothesized to be a characteristic property of the microbial genome alone, is computed. The cluster model is fitted to tailing data from 30 ultraviolet inactivation studies and results are compared with the classic two stage multihit model. CONCLUSIONS: The cluster model demonstrates a statistically significant improvement in the mean adjusted R2 values of the tested data sets (P < 0·0001). Tailing in survival curves is the direct consequence of the Gaussian distribution of cluster sizes and the intrinsic rate constant is a real and critical parameter that defines ultraviolet susceptibility. SIGNIFICANCE AND IMPACT OF THE STUDY: The ultraviolet dose-response behaviour of micro-organisms can now be explained in terms of parameters that have physical meaning and provide deep insight into the disinfection process.

Global quality of life during the acute toxicity phase of multimodality treatment for patients with head and neck cancer: can we identify patients most at risk of profound quality of life decline?

PURPOSE: Treatment intensification has improved outcomes for patients with head and neck cancer (HNC), but little has been reported on health-related quality of life (QoL) consequences. We investigated changes in QoL after (chemo)radiotherapy to identify patient characteristics that predict those whose QoL deteriorates most profoundly in the acute post-treatment period. MATERIALS AND METHODS: Patients with locally advanced HNC treated with curative intent received intensity-modulated radiotherapy (60-70 Gy) in this prospective study. (Chemo)radiotherapy was either definitive or adjuvant. Induction chemotherapy consisted of three cycles of docetaxel, cisplatin, and 5-fluorouracil; responders received (chemo)radiotherapy; nonresponders underwent salvage surgery followed by (chemo)radiotherapy if appropriate. Patients completed the EORTC QLQ-C30 and HNC-specific HN35 module before and at the end of (chemo)radiotherapy and 6-8 weeks after therapy completion. RESULTS: Ninety-five patients participated. At baseline, patients reported significantly lower Global health status, functioning, and symptom scale scores than a reference German population (all p<0.001). At the end of (chemo)radiotherapy, patients had significantly lower QoL scores vs. baseline on all functioning scales (p<0.05). Most symptom and HN35 scores worsened during (chemo)radiotherapy but many recovered 6-8 weeks post-treatment. QoL deteriorated more in patients with high vs. low baseline QoL; no clinical or sociodemographic characteristics of patients most likely to experience a significant deterioration in QoL during treatment were identified. CONCLUSION: These standard QoL instruments did not predict patients at risk of profound global QoL impairments during acute treatment. Other than baseline QoL, no patient characteristics associated with significant QoL deterioration were identified.