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Since the dose delivery pattern in high-precision radiotherapy is different from that in conventional radiation, radiobiological assessment of the physical dose used in stereotactic irradiation and intensity-modulated radiotherapy has become necessary. In these treatments, the daily dose is usually given intermittently over a time longer than that used in conventional radiotherapy. During prolonged radiation delivery, sublethal damage repair takes place, leading to the decreased effect of radiation. This phenomenon is almost universarily observed in vitro. In in vivo tumors, however, this decrease in effect can be counterbalanced by rapid reoxygenation, which has been demonstrated in a laboratory study. Studies on reoxygenation in human tumors are warranted to better evaluate the influence of prolonged radiation delivery. Another issue related to radiosurgery and hypofractionated stereotactic radiotherapy is the mathematical model for dose evaluation and conversion. Many clinicians use the linear-quadratic (LQ) model and biologically effective dose (BED) to estimate the effects of various radiation schedules, but it has been suggested that the LQ model is not applicable to high doses per fraction. Recent experimental studies verified the inadequacy of the LQ model in converting hypofractionated doses into single doses. The LQ model overestimates the effect of high fractional doses of radiation. BED is particularly incorrect when it is used for tumor responses in vivo, since it does not take reoxygenation into account. For normal tissue responses, improved models have been proposed, but, for in vivo tumor responses, the currently available models are not satisfactory, and better ones should be proposed in future studies.

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BackgroundBleeding negatively impacts quality of life in patients with unresectable advanced gastric cancer and has the potential to be lethal. When blood transfusion and endoscopic hemostasis are unsuccessful to stop bleeding, radiation to stomach is selected in patients with unsuitable condition for surgery. We performed a retrospective cohort study to clarify the utility of radiotherapy in treating gastric bleeding, particularly for patients with limited life expectancy.MethodsWe evaluated the efficacy and safety of palliative radiotherapy in patients with advanced gastric cancer between January 2007 and December 2012 in Aichi Cancer Center Hospital. All patients had gastric bleeding requiring blood transfusion. We defined hemostasis as an increase in hemoglobin level to more than 7.0 g/dL together with the cessation of melena or hematemesis for at least 1 week.ResultsDuring the study period, 313 advanced gastric cancer patients treated in our institution. Of these 17 patients received gastric radiotherapy to stop bleeding. Two patients were excluded from analysis due to combined treatment of intravascular embolization. Eleven out of 15 patients (73 %) had undergone two or more previous chemotherapy regimens. Ten patients (67 %) had an Eastern Cooperative Oncology Group performance status of 3 and 14 patients (93 %) were in palliative prognostic index group B or C. The median total planned radiation dose was 30 Gy in 10 fractions. At a median interval of 2 days after initiation of radiotherapy, 11 patients (73 %) achieved hemostasis; rebleeding was observed in four patients (36 %). The median hemoglobin level before radiotherapy was significantly increased from 6.0 to 9.0 g/dL (p < 0.0001). The median volume of red blood cell transfusion was significantly decreased from 1120 to 280 mL (p = 0.007). The median rebleeding-free survival interval was 27 days, with a median overall survival of 63 days. The cause of death was bleeding in 1 patient (7 %) and cancer progression without bleeding in 12 patients (80 %). There were no severe adverse events attributable to radiotherapy.ConclusionsPalliative radiotherapy for gastric bleeding achieves hemostasis within a short time frame. This appears to be a useful treatment option, especially for patients with end-stage, unresectable advanced gastric cancer.

Respiratory tumor movement was modestly suppressed by the BodyFIX system, while the SpO2 level did not decrease. It was considered a simple and effective method for SBRT of lung tumors. Preliminary results were encouraging.