***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: It is now well established that most animal solid tumors contain oxygen-deficient hypoxic cells and that these cells will influence the response of those tumors to radiation . Identifying hypoxic cells in human tumors has proven more difficult , primarily because most of the direct procedures used in animals are not applicable to humans . However , substantial indirect evidence , which goes back to as early as 1909 , clearly indicates the presence of hypoxia in human tumors , although with a considerable heterogeneity among individual tumors . Experimental studies during the last 30 years have shown that this source of radiation resistance can be effectively eliminated by a variety of procedures that include high oxygen-content gas breathing , nitrometric radiation sensitizers , blood transfusions , hemoglobin-oxygen affinity modifiers , and nicotinamide . A number of these procedures have also been tested clinical ly such that by 1995 over 10,000 patients in 83 r and omized trials had undergone treatment design ed to modify tumor hypoxia before radiation therapy . Although a number of these trials showed no benefit , an overview analysis showed that modification of tumor hypoxia significantly improved the locoregional tumor control after radiotherapy with an odds ratio of 1.21 ( 95 % confidence interval 1.12 - 1.30 ) . The treatment benefit could mostly be related to an improved response in head and neck with odds ratio 1.31 ( 1.19 - 1.43 ) and to a lesser extent in bladder tumors ; no significant effect was observed in other tumor sites ( cervix , lung and esophagus ) . Similar to the local control benefit , the overall survival rate improved with an overall odds ratio of 1.13 ( 1.05 - 1.21 ) . The overall results thus showed that the biological issue related to hypoxia appears to be a sound rationale , which may impact the outcome of radiotherapy , especially with head and neck carcinoma . However , despite this wealth of positive data , " hypoxic modification " still has no impact on general clinical practice Abstract The Radiation Therapy Oncology Group ( RTOG ) Study , in which 254 patients were analyzed , adjunctive carbogen breathing in irradiation of carcinomas of the oral cavity , oropharynx , nasopharynx , hypopharynx , and larynx failed to bring about a gain in survival at any of these sites . In only two of the five regional subgroups did results show any improvement with respect to patients in the Carbogen group as compared to those in the Air group , i.e. , the larynx and hypopharynx subgroups . Since both of these subgroups contained relatively small numbers of patients ( 42 larynx , 39 hypopharynx ) , it was not possible to declare these improvements as definitely due to carbogen breathing . In the case of the larynx subgroup , improvement might have been due to the slightly unequal distribution with respect to T-stage ; in either subgroup , the possibility that apparent improvement was due to nothing more than r and om variation could not be ruled out . In the subgroups with larger numbers of patients , i.e. , the oral cavity and oropharynx groups , there was no demonstrated improvement accompanying carbogen breathing 
    Output:
    
We found evidence that HBOT improves local tumour control , mortality , and local tumour recurrence for cancers of the head and neck .
These benefits may only occur with unusual fractionation schemes .
Hyperbaric oxygenation therapy is associated with severe tissue radiation injury .
There is little evidence available concerning malignancies at other anatomical sites