There were some clinical trials done several years ago to determine whether re-irradiation was feasible see:

http://linkinghub.elsevier.com/retrieve/pii/S0167814006003975

http://jco.ascopubs.org/cgi/content/abstract/24/17/2653

http://www.amjclinicaloncology.com/pt/re/ajco/abstract.00000421-200808000-00015.htm;jsessionid=JmFWBZ4n1cyz0TsR13M2Ycf8kdJzvtKJxDQy0L0mNkBh17fkvy2P!1173332523!181195629!8091!-1

http://www.mskcc.org/mskcc/html/2270.cfm?IRBNO=08-050

Here is a list of current clinical trials:

http://clinicaltrials.gov/ct2/results?cond=%22Head+and+Neck+Cancer%22

Gary Allsebrook
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Dx 11/22/02, SCC, 6 x 3 cm Polypoid tumor, rt tonsil, Stage III/IVA, T3N0M0 G1/2
Tx 1/28/03 - 3/19/03, Cisplatin ct x2, IMRT, bilateral, with boost, x35(69.96Gy)
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"You are a mist that appears for a little while and then vanishes" (James 4:14 NIV)