RADIOBIOLOGY 

þ The Law of Bergonie and Tribondeau (1906) 
 - states that 
   1) the more differentiated a cell is, the less sensitive it is, 
   2) actively proliferating cells are most radiosensitive and 
   3) radiosensitivity is proportional to duration of mitotic and
      developmental activity. 
 - Two notable exceptions to the Law of Bergonie and Tribondeau is the
   observation that there are also is some significant radiosensitivity in
   some cells with large nuclei. The best known examples of this phenomenon
   are the lymphocyte and the oocyte. Both cell have large nuclei and
   relatively small amounts of cytoplasm, and the nuclei pose a significant
   target for radiation. 

þ Deterministic (Threshold, Direct) and Stochastic Effects 
 - Deterministic effects 
  + have a threshold dose which must be exceeded for the effect to be seen. 
  + Effect severity is a function of dose (commonly associated with threshold) 
  + Inflammatory response 
  + Organ failure	
  + Fibrosis
 - stochastic
  + "AII-or-Nothing" effect occurrence 
  + probability is function of dose 
  + Increased Risk of Developing Cancer 
  + Inheritable Mutations

þ Acute Radiation Syndrome 
 - Systemic effects from acute radiation exposure 
 - Multi faceted spectrum of disease 
 - Involvement of one or more organ systems 
 - Radiation skin injury
  .75 Gy - Hair Follicles Change 
     3Gy - Epilation 
     6Gy - Erythema 
   10 Gy - Dry Desquamation 
   20 Gy - Wet Desquamation 

þ Delayed Deterministic/Direct
 - Typical Expression (Organ/Tissue Dependent) of Direct Effects 
   at 5 Years Postexposure 
  + Ulceration 
  + Fibrosis 
  + Sclerosis 
  + Sterilization 
  + Atrophy 
  + Cataract 
  + Hypoplasia 

þ Prompt vs. Protracted Doses 
 - Divide a protracted / fractionated dose by 2 - 3 to obtain an estimate
   for an equivalent prompt dose. 
 - The reason for this distinction between prompt and
   protracted/fractionated radiation doses is that in the case of
   protracted/fractionated doses, there is some time in which cells might
   be able to undertake some degree of interval repair between doses. 

þ Prodromal Symptoms 
 - Vomiting: 50 rads (0.5 Gy) for brief, 150 rads (1.5 Gy) for protracted
 - Diarrhea: 100 rads (1 Gy) for brief, 250 rads (2.5 Gy) for protracted

þ Lymphocytes
 - Lymphocytes most susceptible. Can use lymphocyte count to estimate dose. 
   If goes to 0 in 36 hours, that's really, really bad.

þ Deposition: along route of entry
 - Translocation:
 - Incorporation:
 - Decorporation:
 - Clearance: 

þ Clearance Times

Respiratory Tract Clearance Time:
Segment 		Time (hours)
Anterior nare		1.0 
Nasopharynx		0-1 (10 mm/min) 
Trachea		0.1 
Bronchi		1.0 
Terminal Bronchioles	10.0 
Alveoli			100+ days 

Gastrointestinal Tract Residence Times
Portion	Residence Time (hours) 
stomach	6 / 24 
Small Intestine	14 / 24 
Upper Colon	18/24 
Lower Colon	24 / 24