Pulsed Reduced Dose-Rate Radiotherapy Ruduce Tissue Damage And Clinical Efficacy Analysis

Part I Study on pulsed reduced dose-rate radiotherapy for normal tissue injury of re-irradiation ObjectiveTo establish a re-irradiation model of mouse and investigate the in vivo effects of PRDR on normal mouse tissues which accepted re-irradiation.Materials and MethodsTwenty five female BALB/c nude mice,8 weeks of age,were randomly assigned into a PRDR group(n=10),a CRT group(n=10),and a untreated control group(n=5).Whole body irradiation(TBI)was performed on CRT group and PRDR group mice using a 6 Mv X-ray linear accelerator.The mice received a total of 14 Gy in 2 fractions with a 20 day interval.The CRT group received the 7Gy dose continuously at a dose rate of 300 MU/min,which was given once every 20 days for a total of 2 times of 14 Gy;the PRDR group was irradiated with 0.2Gy×35 pulses with a 3min interval between the pulses,with an effective dose rate of 6.7 cGy/min,and the total dose of 7 Gy;PRDR irradiation was performed again at intervals of 20 days,with a cumulative total of 14 Gy.No radiotherapy was administered to the control group.The mice were weighed thrice weekly.After the death of the last mouse in the CRT group,the number of surviving mice in the other two groups was recorded;at the same time,3 mice were randomly selected from the PRDR group and the Control group respectively to be sacrificed for tissue extraction,the tissues were fixed,paraffin-embedded and stained with H&E.Morphological changes were observed under a microscope.Results1.The mouse model of re-irradiation was successfully established.2.After 2 TBIs,mice in the CRT group began to experience a death(40%).All mice died in the CRT group 19 days after the last radiotherapy,and the mean body weight of the mice gradually decreased,while the mice of PRDR group did not die during the entire experiment,and no significant weight loss was observed.There was a statistically significant difference in body weight changes and survival time between the CRT group and the PRDR group(p<0.001).3.H&E staining showed that the spleen and bone marrow of the irradiated mice were damaged to varying degrees compared to thenon-irradiated mice.Compared with the CRT mice,the spleen and bone marrow damage of the PRDR mice were significantly reduced.ConclusionOur results showed that PRDR induced less toxicity in the normal mouse tissues than conventional radiotherapy for the same dose and regimen when receiving re-irradiotherapy.Part II Clinical effect of pulsed reduced dose-rate radiotherapy for local recurrence of head and neck tumor after radiotherapyObjective To observe the clinical efficacy of pulsed reduced dose-rate radiotherapy for patients with local recurrence of head and neck cancer after radiotherapy and their damage to normal tissues.Materials and MethodsUsing pulsed reduced dose-rate radiotherapy for patients with local recurrence of head and neck cancer after radiotherapy,magnetic resonance imaging of the head and neck was performed before,during,and after radiotherapy,the clinical curative effect of reradiation therapy was evaluated according to the evaluation criteria of solid tumor efficacy(RECIST version 1.1);the common adverse event evaluation criteria(CTCAE version 4.0)was used to assess the incidence of side effects of radiotherapy in patients undergoing radiotherapy and during half a year after radiotherapy.Results1.For patients with local recurrence of head and neck cancer after radiotherapy used by IMRT pulsed reduced dose-rate radiotherapy,tumor shrinkage can be clearly observed from magnetic resonance images,and three patients had complete response(CR)and one patient achieved Partial response(PR).2.In the course of treatment and within half a year after the treatment,1 case of grade 2 skin lesions occurred,and none of the 4 patients experienced grade 3 or higher severe radiotherapy side effects.Conclusion IMRT pulsed reduced dose-rate radiotherapy may be another effective mode of treatment for locally recurring head and neck tumors.