Radiobiological effects of altering dose rate in filter-free photon beams.

To validate that altering radiotherapy dose rate through either changing pulse repetition frequency or instantaneous dose rate does not have an effect on cell survival, two human carcinoma and a hamster lung cell line were irradiated with various beam settings. Varian TrueBeam linac with a flattening filter free mode of operation was used for all experiments. The results obtained indicate that either method of changing dose rate has no effect on cell survival in the three cell lines studied. Filtered and filter free modes were also compared in treatments with protracted dose delivery which significantly increases overall treatment time. Cell survival indicated no difference between filter and filter free beam delivery in any of the protraction schemes. An increase in survival was seen in both modes upon protracting dose delivery to 15, 30 or 60 min rather than delivering acutely. Further, analysis of induced DNA double-strand breaks via the γH2AX assay showed no difference between filtered and unfiltered beams. The following study suggests that increasing dose rate is an acceptable manner of decreasing radiotherapy treatment time that does not have any detrimental effects on in vitro cell eradication.

SU-E-T-01: Applications of 6MV FFF Photon Beams in Optimizing Radiobiological Response for Respiratory-Gated Liver SBRT.

PURPOSE: To establish a radiobiological basis for gated stereotactic body radiotherapy of primary and metastatic liver cancers using volumetric arc radiotherapy in a flattening filter free (FFF) mode. METHODS: Human cervical carcinoma, SiHa, non-small cell lung carcinoma, H460, and Chinese hamster V79 cells were irradiated in a water bath with 6MV photons from a Varian TrueBeam linear accelerator. To establish dose-response and its sensitivity to dose rate following acute irradiation, doses of 2, 4, 6, 8 and 10 Gy were delivered in FFF mode at 400 and 1200 MU/min. To investigate whether removal of the flattening filter affects cell response, doses of 5 and 10 Gy were delivered to SiHa and H460 cells in FFF and filtered modes at 400 MU/min. Finally, to assess the effect of protracting dose delivery by gating, a dose of 10 Gy was delivered to SiHa and H460 cells acutely and also over 15, 30 and 60 min. RESULTS: Dose-response over doses examined was independent of dose rate in FFF mode. Differences in cell survival following irradiation in FFF and filtered modes were not significant. However a significant increase in survival for both H460 and SiHa cells was observed for 15 min split-dose irradiation compared to acute irradiation but further increase in irradiation time to 60 min did not affect cell survival. CONCLUSIONS: Dose rate and presence of a flattening filter showed no effect on cell survival, however, survival was significantly affected when dose delivery time was protracted to that typical of conformal field therapy. Volumetric arc based gated SBRT may be beneficial for tumor cell kill, though the gating window and duty cycle have to be balanced against the effect of dose delivery protraction. Research Support (Varian Medical Systems).

Relationship between sex roles and mental disorders.

The present study "Relationship between sex roles and mental disorders" analyses the various findings of research regarding the sex roles and mental problems. All these findings reveal that the women whether they work outside or not, face various mental problems especially functional psychosis and neurosis. This finding is also proved by the research of National Institute of Mental Health (NIMH) of U.S.A. They analysed the admissions and the treatment give for the psychologically affected persons in various hospitals and came across more women patients than the men. The research also formulates some possible suggestions to curb the mental disorders among the women.

Predictors and outcome of admission for invasive Streptococcus pneumoniae infections at a Canadian children's hospital.

Rates of admission for invasive Streptococcus pneumoniae infection in children vary considerably between institutions. We performed a retrospective study to investigate factors used in the decision to admit patients with invasive S. pneumoniae infection to Alberta Children's Hospital. Of 254 patients who were initially assessed in the emergency department, 38.2% were admitted to the hospital. Significant risk factors for admission as determined by a logistic regression model included murmur (odds ratio [OR], 18.98; 95% confidence interval [CI], 4.08-88.23), focal infection (OR, 11.41; 95% CI, 5.07-25.67), and older age (OR, 2.72; 95% CI, 1.03-7.17). Higher hemoglobin level (OR, 0.96; 95% CI, 0.93-0.99) and temperature of > 38.5 degrees C (OR, 0.39; 95% CI, 0.18-0.85) were associated with a lower risk of admission. Two patients died (case-fatality rate, 0.7%). Despite the low rate of admission for invasive S. pneumoniae infections at our hospital, the mortality rate was comparable with those at institutions with higher rates of admission, thus suggesting that the factors we identified may be useful in deciding whether to admit patients with (or who are at high risk for) invasive S. pneumoniae infections.