Radiation Biology – 2 Dr Rupak Sethuraman

FORMAT INTRODUCTION DIRECT EFFECT INDIRECT EFFECT STOCHASTIC EFFECT DETERMINISTIC EFFECT

DIRECT EFFECT When the ionizing radiation directly interacts with the cell DNA,RNA,Chromosome the effect that occurs is called as Direct Effect.

Photon +H2O H+ + OH- HO 2- +H+ H2O 2 HO2 -+HO2- O2 + H2O2 INDIRECT EFFECT Photon +H2O H+ + OH- H+ + O2 HO2-(Hydroperoxyl) HO 2- +H+ H2O 2 HO2 -+HO2- O2 + H2O2

Accumulative Effect DIRECT EFFECT INDIRECT EFFECT ACCUMULATIVE EFFECT

Factors Affecting Effect of Radiation Radiation Factors Host Factors Type of radiation Total Dose Penetrating ability of radiation Acute/chronic exposure Threshold dose Type of tissue Sensitivity of the tissue Stochastic/deterministic effect Local area/whole body

Based on sensitivity: Vegetative inter mitotic cells eg – spermatogenic cells, erythroblastic, OMM Differentiating inter mitotic cells eg – Inner enamel epithelium of developing teeth, hematopoetic cells, Multi potent connective tissue cells – eg – vascular endothelial cells, fibroblasts, mesencymal cells Reverting post mitotic cells – eg – acinar cells, ductal cells, parenchymal tissue of organs Fixed post mitotic cells – eg – neurons, muscles,

Relative Radio sensitivity of Cells, Tissues and Organs Blood-forming Organs Reproductive Organs skin Vascular Organs Bone Teeth Muscles & Connective Tissue Nervous System Respiratory System Digestive Organs Extremely Radio sensitive Radio sensitive Moderately Radio sensitive Moderately Radio resistant Radio resistant Relatively Radio resistant Very Radio resistant Extremely Radio resistant

Stochastic Effect – Genetic Effect Definition – in which the probability (chances) of biologic damage increases with increasing absorbed dose but the severity (effect) in the affected individual does not depend on the magnitude (level) of absorbed dose.

Deterministic Effect – dose dependent Those effects which increases in severity with increasing absorbed dose in affected individuals.

Quiz – 21 – 09 – 14/26 – 11 - 1435 Radiation Physics – 1 Topics Covered Topics For Quiz Introduction to Radiology Radiation Physics – 1 Radiation Physics – 2 Practicals – Components of X ray Machine Radiation Protection X Ray Films Radiation Physics – 1 Radiation Physics – 2 Radiation Protection

Thank You Any Questions???