The 4 Rs of radiobiology are repair, reoxygenation, redistribution, and repopulation. Repair refers to the ability of cells to repair radiation damage over hours through pathways like base excision repair. Redistribution occurs as cells in different phases of the cell cycle are irradiated, with some phases being more radioresistant. Repopulation is the regrowth of cells after irradiation, with tumors potentially repopulating faster than normal tissues. Reoxygenation occurs as hypoxic tumor cells reoxygenate over hours to days, allowing radiation to better damage them in subsequent fractions. Understanding the 4 Rs helps explain fractionated radiotherapy dosing.
The 4 Rs of radiobiology are repair, reoxygenation, redistribution, and repopulation. Repair refers to the ability of cells to repair radiation damage over hours through pathways like base excision repair. Redistribution occurs as cells in different phases of the cell cycle are irradiated, with some phases being more radioresistant. Repopulation is the regrowth of cells after irradiation, with tumors potentially repopulating faster than normal tissues. Reoxygenation occurs as hypoxic tumor cells reoxygenate over hours to days, allowing radiation to better damage them in subsequent fractions. Understanding the 4 Rs helps explain fractionated radiotherapy dosing.
Wilhelm Conrad Roentgen discovered X-rays in 1895 while experimenting with cathode rays. He noted a new type of ray coming from the cathode tube that could pass through materials and photographed his wife's hand. X-rays are produced when high-speed electrons collide with a metal target in a vacuum tube. This produces bremsstrahlung X-rays of varying energies and characteristic X-rays of specific energies related to the target material. Factors like target material, voltage, current, and filtration determine the quantity, quality, and efficiency of the X-ray beam produced.
The four R's of radiobiology are repair, repopulation, redistribution, and reoxygenation. Repair refers to cells' ability to fix radiation-induced DNA damage through pathways like base excision repair. Redistribution occurs as cells in different phases of the cell cycle have differing radiosensitivities. Repopulation is the regrowth of cells after irradiation. Repopulation can reduce the effectiveness of fractionated radiotherapy if it accelerates in tumors. Reoxygenation describes how hypoxic tumor cells may reoxygenate between fractions, increasing their sensitivity to subsequent doses. Fractionating radiation therapy exploits these four R's to better kill tumor cells while allowing normal tissues to recover.
This document discusses the cell cycle and its relevance to cancer. It begins by describing the basic components and organelles of the cell. It then explains the different phases of the cell cycle, including interphase (G1, S, G2 phases) and mitosis. Key control mechanisms like cyclin-dependent kinases and checkpoints are described. Alterations in cell cycle pathways and genes can lead to uncontrolled cell proliferation and cancer. Understanding the cell cycle provides opportunities to target specific phases with chemotherapy or radiotherapy to treat cancer.
The document summarizes key factors related to radiation pathology of tissues, tissue radiosensitivity, and the effects of time, dose, and fractionation of radiation therapy. It discusses how the sensitivity of tissues depends on the type of cells, their proliferation rate, and how they are organized. It also describes Casarett's and Michalowski's classifications of tissue radiosensitivity. Finally, it explains the rationale for fractionating radiation doses, such as allowing for repair of sublethal damage and reoxygenation of tumors.
Radiation can cause ionization or excitation of atoms in biological material. Ionizing radiation directly or indirectly causes damage by ionizing atoms. Directly ionizing radiation like electrons or alpha particles directly cause ionization, while indirectly ionizing radiation like X-rays produce fast moving particles that cause damage. Radiation can directly interact with targets in cells or indirectly via free radicals produced from interacting with water. Radiation damages DNA, especially double-strand breaks which can lead to chromosomal aberrations and cell death if unrepaired. Cells have several DNA repair pathways like base excision repair, nucleotide excision repair, and double-strand break repair via homologous recombination or non-homologous end joining to repair radiation
Wilhelm Conrad Roentgen discovered X-rays in 1895 while experimenting with cathode rays. He noted a new type of ray coming from the cathode tube that could pass through materials and photographed his wife's hand. X-rays are produced when high-speed electrons collide with a metal target in a vacuum tube. This produces bremsstrahlung X-rays of varying energies and characteristic X-rays of specific energies related to the target material. Factors like target material, voltage, current, and filtration determine the quantity, quality, and efficiency of the X-ray beam produced.
The four R's of radiobiology are repair, repopulation, redistribution, and reoxygenation. Repair refers to cells' ability to fix radiation-induced DNA damage through pathways like base excision repair. Redistribution occurs as cells in different phases of the cell cycle have differing radiosensitivities. Repopulation is the regrowth of cells after irradiation. Repopulation can reduce the effectiveness of fractionated radiotherapy if it accelerates in tumors. Reoxygenation describes how hypoxic tumor cells may reoxygenate between fractions, increasing their sensitivity to subsequent doses. Fractionating radiation therapy exploits these four R's to better kill tumor cells while allowing normal tissues to recover.
This document discusses the cell cycle and its relevance to cancer. It begins by describing the basic components and organelles of the cell. It then explains the different phases of the cell cycle, including interphase (G1, S, G2 phases) and mitosis. Key control mechanisms like cyclin-dependent kinases and checkpoints are described. Alterations in cell cycle pathways and genes can lead to uncontrolled cell proliferation and cancer. Understanding the cell cycle provides opportunities to target specific phases with chemotherapy or radiotherapy to treat cancer.
The document summarizes key factors related to radiation pathology of tissues, tissue radiosensitivity, and the effects of time, dose, and fractionation of radiation therapy. It discusses how the sensitivity of tissues depends on the type of cells, their proliferation rate, and how they are organized. It also describes Casarett's and Michalowski's classifications of tissue radiosensitivity. Finally, it explains the rationale for fractionating radiation doses, such as allowing for repair of sublethal damage and reoxygenation of tumors.
Radiation can cause ionization or excitation of atoms in biological material. Ionizing radiation directly or indirectly causes damage by ionizing atoms. Directly ionizing radiation like electrons or alpha particles directly cause ionization, while indirectly ionizing radiation like X-rays produce fast moving particles that cause damage. Radiation can directly interact with targets in cells or indirectly via free radicals produced from interacting with water. Radiation damages DNA, especially double-strand breaks which can lead to chromosomal aberrations and cell death if unrepaired. Cells have several DNA repair pathways like base excision repair, nucleotide excision repair, and double-strand break repair via homologous recombination or non-homologous end joining to repair radiation