Demonstration of bystander response in high dose technique of grid using theoretical calculation by linear quadratic model along with experimental investigations

Background: the linear quadratic (lq) equation as the most commonformula in radiotherapy has a debatable accuracy in modeling high-doseeffects. the purpose of this study was to demonstrate bystander response ofthe grid treatment in scc cell line, based on both theoretical calculations andexperimental investigations. materials and methods: the linear quadraticmodel was used to calculate the equivalent uniform dose (eud) of a grid-fieldwith the 10 gy maximum doses. according to the eud definition, the identicaltumor survival fraction (sf) was expected to obtain from both grid and openfieldsingle fraction. after observing the difference, the clonogenic andapoptosis assays were exerted to investigate bystander response via mediumtransfer strategy which was performed from 10gy-irradiated donors to 1.5gyirradiatedrecipients. results: the eud was equal to 4 gy and the sf of 4 gyeud and 10 gy grid-field were 0.1 ± 0.02 and 0.051 ± 0.008, respectively.these findings contradicted the theoretical expectations of their survivalsequality. moreover, the bystander clonogenic cells death enhancedapproximately by 2.91 times (statistically significant); highlighting thebystander response role. the apoptotic findings illustrated that the bystandercells experienced an approximately 10% increase and the apoptotic rateconfirmed the clonogenic survival result which was less in the eud than thegrid-field. conclusion: since the sf of the grid-field was less than the eud, itrevealed the grid therapeutic advantages plus bystander responsemanifestation; that was ignored in the lq equation and may not bedemonstrated by sheer theoretical calculations of the modulated- field.