Physical Mechanisms in Radiation Biology

Three general m e t h o d s w h e r e b y we can i m p r o v e o u r u n d e r s t a n d i n g o f the b i o p h y s i c a l e f fect o f a phys i ca l agent are : (1 ) A t t e m p t t o f o l l o w t h e series o f processes t a k i n g place b e g i n n i n g w i t h the i n t e r a c t i o n o f the agent a n d t h e b i o l o g i ca l s ys t em. (2 ) T r y t o unrave l t h e causal cha in b a c k w a r d b e g i n n i n g w i t h t h e e f fec t . (3 ) Search f o r basic rules t h a t govern t h e overa l l process. A f ew years ago Rossi , c ons ide r ing these approaches in an even ing l e c tu re t o the R a d i a t i o n Research Soc i e ty , c o n c l u d e d t h a t i n r a d i o b i o l o g y o n l y the t h i r d l ine o f a t t a ck ho lds any real p romise , at least at th i s t i m e . A m o d i f i e d c o p y o f his address makes u p the f i r s t sec t i on o f t h i s paper t o deve lop th i s a r g u m e n t and t o f u r n i s h a s imp l e i n t r o d u c t i o n t o the sub jec t . M i c r o d o s i m e t r y p rov ides some o f the phys i ca l concepts r equ i r ed f o r w h a t we t e r m the " t h e o r y o f dua l r a d i a t i o n a c t i o n . " I n the second sec t i on we summar i z e the c u r r e n t status o f th i s t h e o r y . INTRODUCTION TO MICRODOSIMETRY* I somet imes w o n d e r h o w the R a d i a t i o n Research Soc ie ty has been so successful despite the fac t t h a t b o t h physic is ts and b io log is ts be long t o i t . T h e y have rather d i f f e r en t sc ient i f i c t emperaments . T h e phys ic i s t , b y and large an ana l y t i ca l f e l l ow, prefers t o f i n d s i m p l i c i t y i n the c omp l i ca t ed , say, b y r educ ing the universe t o a d i f f e r en t i a l e qua t i on . T h e b io log i s t is mo r e l i k e l y t o f i n d c o m p l e x i t y i n the s imp l e ; f o r example , w h e n c o n t e m p l a t i n g a b a c t e r i u m or even a bacter iophage, he discovers enough t o f i l l a t least a m o n o g r a p h . The t w o persona l i t y types rare ly in te rac t . A t a un i v e r s i t y they are l i k e l y t o encoun t e r * O u d i n e o f an address presented b y Hara ld Η. Rossi at the 1 8 t h A n n u a l M e e t i n g o f t h e R a d i a t i o n Research Soc i e ty , M a r c h 1 5 , 1 9 7 0 , i n Dal las.