4 rs of radiobiology
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The document discusses key concepts in radiobiology related to the fractionation of radiotherapy. It summarizes the four R's of radiobiology: repair, reassortment, repopulation, and reoxygenation. It describes different types of radiation damage - lethal, potentially lethal, and sublethal damage. It also discusses different DNA repair pathways including base excision repair, nucleotide excision repair, and double strand break repair. The document notes that fractionating radiation doses allows cells to go through different phases of the cell cycle when subsequent doses are delivered, improving cancer cell killing. It also explains how tumor reoxygenation between fractions can overcome radiation resistance from tumor hypoxia.
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4 rs of radiobiology
This document discusses the radiobiological basis of fractionated radiation therapy. It covers the classic "4 R's" of radiobiology - repair, reassortment, repopulation and reoxygenation. Repair and reoxygenation make tumor cells more sensitive to radiation between fractions, while repopulation and reassortment make them more resistant. The document also proposes a "5th R" of radiossensitivity based on tissue maturity and metabolism. Finally, it briefly mentions the potential "6th R" of bystander effects and abscopal effects, where radiation triggers immune responses against distant tumor cells. Fractionation exploits repair in normal tissues while counteracting resistance mechanisms in tumors through its scheduling over multiple doses.
4 R's of radiobiology
This document discusses the 4 R's of radiobiology which form the basis of radiation fractionation in radiotherapy. The 4 R's are: repair of sublethal damage within hours allowing for fractionated doses; reassortment resulting in a partially synchronized cell population within hours; repopulation where tumor cells begin rapidly dividing about 5 weeks after treatment begins; and reoxygenation where hypoxic tumor cells become reoxygenated between fractions over hours to days. Understanding the 4 R's helps maximize tumor cell killing while minimizing damage to normal tissues from radiation treatment.
Time, dose and fractionation
This document discusses various aspects of fractionation in radiotherapy. It begins by describing early experiments by Regaud showing that fractionated doses achieved tumor sterilization without excessive skin damage, compared to single high doses. It then discusses the four R's of radiobiology - repair, repopulation, redistribution and reoxygenation - which form the basis for fractionated regimens. Various fractionation schedules are described, including conventional, hyperfractionation, accelerated fractionation and hypofractionation. The advantages and disadvantages of different approaches are summarized.
Time, dose & fractionation,
This document discusses fractionation in radiation therapy. It begins with a historical review of fractionation and discusses how proliferation is a factor for normal tissues. Early responding tissues like skin and mucosa proliferate within weeks of starting fractionated radiation, while late responding tissues like spinal cord and bladder proliferate far beyond the overall treatment time of most regimens. Prolonging overall treatment time has a large sparing effect on early reactions but little effect on late reactions. The document then discusses different tissue responses and rationales for fractionation including accelerated repopulation and different fractionation schedules like conventional, hyperfractionation, accelerated fractionation, concomitant boost, split-course, and hypofractionation.
4 rs of radiobiology
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.
Clinical response to normal tissue with radiation
The document discusses the clinical response of normal tissues to radiation. It makes three key points:
1) The response of normal tissues to radiation is determined by the inherent radiosensitivity of individual cells, the kinetics of the tissue as a whole, and how cells are organized structurally within the tissue.
2) Radiation effects are divided into early (acute) effects, which occur within days or weeks and result from cell death, and late effects, which appear months or years later and occur in slowly proliferating tissues.
3) Tissues can be classified based on their functional subunits (FSUs). Tissues with well-defined FSUs like the kidney have a low radiation tolerance, while tissues
4 R OF RADIOBIOLOGY.pptx
IT FORMS THE BASIS OF FRACTIONATION AND DETERMINES THE SUCCESS AND FAILURE OF RADIOTHERAPY. IT IS ALSO IMPORTANT FOR THE EXAM (MD OR DNB).
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4 rs of radiobiology
This document discusses the radiobiological basis of fractionated radiation therapy. It covers the classic "4 R's" of radiobiology - repair, reassortment, repopulation and reoxygenation. Repair and reoxygenation make tumor cells more sensitive to radiation between fractions, while repopulation and reassortment make them more resistant. The document also proposes a "5th R" of radiossensitivity based on tissue maturity and metabolism. Finally, it briefly mentions the potential "6th R" of bystander effects and abscopal effects, where radiation triggers immune responses against distant tumor cells. Fractionation exploits repair in normal tissues while counteracting resistance mechanisms in tumors through its scheduling over multiple doses.
4 R's of radiobiology
This document discusses the 4 R's of radiobiology which form the basis of radiation fractionation in radiotherapy. The 4 R's are: repair of sublethal damage within hours allowing for fractionated doses; reassortment resulting in a partially synchronized cell population within hours; repopulation where tumor cells begin rapidly dividing about 5 weeks after treatment begins; and reoxygenation where hypoxic tumor cells become reoxygenated between fractions over hours to days. Understanding the 4 R's helps maximize tumor cell killing while minimizing damage to normal tissues from radiation treatment.
Time, dose and fractionation
This document discusses various aspects of fractionation in radiotherapy. It begins by describing early experiments by Regaud showing that fractionated doses achieved tumor sterilization without excessive skin damage, compared to single high doses. It then discusses the four R's of radiobiology - repair, repopulation, redistribution and reoxygenation - which form the basis for fractionated regimens. Various fractionation schedules are described, including conventional, hyperfractionation, accelerated fractionation and hypofractionation. The advantages and disadvantages of different approaches are summarized.
Time, dose & fractionation,
This document discusses fractionation in radiation therapy. It begins with a historical review of fractionation and discusses how proliferation is a factor for normal tissues. Early responding tissues like skin and mucosa proliferate within weeks of starting fractionated radiation, while late responding tissues like spinal cord and bladder proliferate far beyond the overall treatment time of most regimens. Prolonging overall treatment time has a large sparing effect on early reactions but little effect on late reactions. The document then discusses different tissue responses and rationales for fractionation including accelerated repopulation and different fractionation schedules like conventional, hyperfractionation, accelerated fractionation, concomitant boost, split-course, and hypofractionation.
4 rs of radiobiology
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.
Clinical response to normal tissue with radiation
The document discusses the clinical response of normal tissues to radiation. It makes three key points:
1) The response of normal tissues to radiation is determined by the inherent radiosensitivity of individual cells, the kinetics of the tissue as a whole, and how cells are organized structurally within the tissue.
2) Radiation effects are divided into early (acute) effects, which occur within days or weeks and result from cell death, and late effects, which appear months or years later and occur in slowly proliferating tissues.
3) Tissues can be classified based on their functional subunits (FSUs). Tissues with well-defined FSUs like the kidney have a low radiation tolerance, while tissues
4 R OF RADIOBIOLOGY.pptx
IT FORMS THE BASIS OF FRACTIONATION AND DETERMINES THE SUCCESS AND FAILURE OF RADIOTHERAPY. IT IS ALSO IMPORTANT FOR THE EXAM (MD OR DNB).
Radiobiology
This document discusses several key concepts in radiobiology including:
1. The interaction of radiation with cells is probabilistic, with damage occurring through direct and indirect action. Indirect action involves free radicals produced by radiation interacting with water molecules within cells.
2. Different phases of the cell cycle have differing radiosensitivities, with G2/M being most sensitive. Fractionated radiation can exploit this through redistribution effects.
3. The linear quadratic model describes cell survival curves and accounts for both single-hit and double-hit damage from radiation. It is used to calculate biologically equivalent doses.
4. Mechanisms like reoxygenation between fractions can improve the therapeutic ratio by making tumor cells
Fractionated radiation and dose rate effect
Fractionated radiation and the dose-rate effect can impact cell survival through mechanisms like sublethal damage (SLD) repair and cell cycle redistribution. SLD repair occurs as double-strand breaks are rejoined after radiation exposure. At lower dose rates, more SLD can be repaired between fractions, improving cell survival. However, very low dose rates may instead reduce survival if cells become frozen in radiosensitive phases of the cell cycle. The dose-rate effect varies between cell types and depends on factors like oxygenation and ability to progress through the cell cycle after radiation.
Linear quadratic model ppt
This document summarizes key concepts regarding radiation-induced cell death and survival curves. It discusses how cell death is defined for differentiated and proliferating cells. The linear-quadratic model is then explained, which describes cell survival curves using alpha and beta coefficients. Various fractionation schemes and their resulting biological effective doses are calculated and compared for treating different head and neck cancers. The limitations of hypofractionation and importance of accounting for tumor proliferation are also covered.
Evolution of Fractionation and Conventional Fractionation in Radiotherapy
The document discusses the evolution of radiation fractionation in cancer treatment. Early radiation machines had low output, so delivering a tumoricidal dose as a single fraction would have caused unacceptable toxicity. Fractionation was used from the beginning. Over the following decades, two schools of thought emerged on fractionation - the Erlangen school believed single large doses were necessary, while the Paris school's experiments on animal models supported fractionation. Clinical results in the 1930s also showed fractionation produced better tumor control with less toxicity. The rationale for fractionation is based on the different cell kinetics of normal and tumor cells, allowing sparing of normal tissues. Mathematical models were later developed to quantify fractionation schedules, incorporating factors like overall time, dose per
Chap 5 fractionated radiation and the dose rate effect
This chapter discusses fractionated radiation and the dose-rate effect. It covers operational classifications of radiation damage including potentially lethal damage and sublethal damage. Fractionation allows for repair of sublethal damage through processes like reassortment and repopulation. The dose-rate effect results from increased repair at lower dose rates. Examples are provided for both in vitro and in vivo models. Brachytherapy techniques like intracavitary and interstitial brachytherapy are also summarized.
Oer , rbe & let
1) The document discusses various factors that affect radiation response, including linear energy transfer (LET), relative biological effectiveness (RBE), oxygen effect, and cell cycle phase.
2) It provides details on oxygen enhancement ratio (OER), describing how it ranges from 2.5-3.0 for x-rays and varies according to cell cycle phase and radiation type (higher for x-rays and neutrons vs. alpha particles).
3) LET is discussed in relation to radiation type (low for x-rays, medium for neutrons, high for alpha particles) and how it impacts ionization density and biological damage. An optimal LET of around 100 keV/μm is described.
craniospinal irradiation
The document discusses craniospinal irradiation (CSI), which delivers radiation to the entire cranial-spinal axis to treat intracranial tumors. It was pioneered in the 1950s and is commonly used to treat tumors that may spread through the cerebrospinal fluid such as medulloblastoma. The document outlines the techniques, challenges, indications, and evolving approaches for CSI such as reduced dose protocols and hyperfractionated regimens. It discusses topics like patient positioning, target volumes, critical structures, field arrangements, and the use of newer technologies like virtual simulation.
Sib.si
Simultaneously integrated boost (SIB) allows different doses to be delivered simultaneously to the planning target volume (PTV) and gross tumor volume (GTV), reducing the number of fractions needed. SIB provides a greater biological effective dose while allowing individual dose optimization to both targets in a single plan, overcoming limitations of conventional fractionation. An institutional study compared SIB to conventional 3D conformal radiation therapy in 30 patients with brain, breast, or bladder cancer, finding SIB reduced maximum doses to targets and organs at risk while shortening treatment duration by about a week.
Cell survival curve ppt.
Cell survival curves show the relationship between radiation dose and the proportion of cells that survive. For low linear energy transfer (LET) radiation like X-rays, the curve starts with a shoulder region followed by an exponential decrease in survival fraction. The linear-quadratic model describes cell survival as an exponential function of dose, with parameters α and β representing linear and quadratic components of cell killing. Fractionation reduces cell survival more than single high doses by allowing repair of sublethal damage between fractions. Hypoxic cells are less sensitive initially but may reoxygenate and become sensitive to later fractions. Mitotic cell death is the most common mode of radiation-induced cell death in tumor cells.
Cobalt & linac
This document provides information on teletherapy machines used to treat cancer with radiation. It discusses cobalt-60 teletherapy machines and linear accelerators. Cobalt-60 machines use a radioactive cobalt-60 source to generate gamma rays for treatment. Linear accelerators use microwave energy to accelerate electrons, which are then used to generate x-rays or electron beams for treatment. Both types of machines aim focused radiation beams at tumors while minimizing dose to surrounding healthy tissue using collimators and other targeting mechanisms. Linear accelerators have advantages over cobalt machines like more sharply defined beam edges and ability to vary dose rates.
4 r's of radiobiology and dose rate effects
1) The four Rs of radiobiology are repair, re-assortment, repopulation, and re-oxygenation. They influence how tumors and normal tissues respond to fractionated radiation treatment.
2) When radiation is delivered in two fractions separated by time, cell survival increases due to repair of sublethal damage between fractions. The increase peaks at 2-3 hours and then levels off due to repopulation.
3) Lowering the radiation dose rate generally decreases biological effects because it allows more time for repair of sublethal damage.
Altered fractionation kiran
The document discusses various radiation fractionation schedules used in cancer treatment. It begins with an overview of conventional fractionation, which divides the total radiation dose into smaller daily doses to allow healthy cells to repair sublethal damage between fractions. It then explores the radiobiological rationale of the 5 R's of fractionation - repair, redistribution, reoxygenation, repopulation, and radiosensitivity. The document discusses various altered fractionation schedules including hyperfractionation, accelerated fractionation, split-course, and hypofractionation, explaining how each schedule aims to improve the therapeutic ratio for cancer patients.
Cell survival curve
Cell survival curves describe the relationship between radiation dose and the fraction of cells that survive that dose. The shape of the curve is influenced by many factors including:
1) The proliferative capacity of cells, with rapidly dividing cells being more radiosensitive.
2) The presence of oxygen, with hypoxic cells being more radioresistant.
3) Fractionation, with fractionated doses allowing more time for repair between exposures and resulting in a higher surviving fraction compared to a single dose.
4) Dose rate, with low dose rate irradiation resembling continuous fractionation and having less cell killing compared to an acute high dose rate.
Cell survival curves take different shapes for early-responding normal tissues dominated
Beam modification devices
This document discusses various beam modification devices used in radiation therapy to modify the spatial distribution of radiation within the patient. It defines beam modification and lists some common reasons for its use, such as irregular patient contours or tissue deficits. The main types of beam modification discussed are shielding, compensation, wedge filtration, and flattening. Specific devices covered include field blocking devices, compensators, wedge filters, bolus, and multi-leaf collimators. The document provides details on the purpose, design considerations, advantages, and disadvantages of several common beam modification devices.
TSET
Total skin electron therapy (TSET) is used to treat cutaneous T-cell lymphoma by delivering a uniform dose of radiation to the entire skin surface while sparing underlying organs. It requires large electron fields over the entire body and precise dosimetry. The most common technique uses six electron beams arranged at 60 degree intervals to provide circumferential coverage. Proper field design and calibration are needed to achieve uniform dose across irregular body surfaces and minimize dose from bremsstrahlung x-rays.
5 Rs OF RADIOBIOLOGY.pptx
The document discusses the key concepts of radiobiology known as the "5 R's of Radiobiology". It describes radiobiology as the branch of science combining physics and biology to study the effects of ionizing radiation on tissues and living organisms. The 5 R's are: repair, repopulation, reoxygenation, redistribution, and reassortment. The document provides details on the law of Bergonie and Tribondeau which established that immature cells are more radiosensitive. It also discusses the history of fractionation in radiotherapy and mechanisms such as sublethal damage, potentially lethal damage, and accelerated repopulation that provide rationale for fractionating radiation doses.
Fractionation in Radiotherapy
Fractionation in radiotherapy refers to dividing the total radiation dose into smaller doses given over multiple treatment sessions. This allows healthy cells to repair sublethal damage between fractions while maximizing cancer cell kill through mechanisms like redistribution and reoxygenation. The "5 R's" of radiobiology explain fractionation: repair of sublethal damage in normal cells; redistribution of tumor cells to sensitive phases; reoxygenation of hypoxic tumor cells; repopulation of tumor cells during prolonged treatment; and intrinsic radiosensitivity differences between cell types. Fractionation schedules are tailored based on these factors to improve the therapeutic ratio for different cancers and patients.
TIME DOSE & FRACTIONATION
Introduction
Time dose & fractionation
Therapeutic index
Four R’s Of Radiobiology
Radiation response
Survival Curves Of Early & Late Responding Cells
Various fractionation schedules
Clinical trials of altered fractionation
Late effects of Radiotherapy on Normal Tissues
This document summarizes the acute and late effects of radiation therapy on normal tissues. It discusses the differences between early and late effects, which depend on the tissue kinetics. Early effects occur within weeks in rapidly proliferating tissues, while late effects take months or years to appear in slowly proliferating tissues. It also describes various models for classifying tissue radiosensitivity and explores factors like dose, volume, and fractionation that determine normal tissue tolerance. Specific sections are dedicated to discussing the effects of radiation on brain, spinal cord, optic nerves and other organs.
Cell Survival Curves by Dr.Abhilash.pptx
Cell survival curves relate the fraction of cells retaining reproductive integrity to radiation dose. Mammalian curves have an initial curved portion then become exponential. This shoulder represents sublethal damage repair. The linear-quadratic model is clinically used, describing cell kill as proportional to dose (αD) and dose-squared (βD2). α measures intrinsic radiosensitivity and β repair capacity. Their ratio determines curve shape and tissue type. Factors like oxygen level, proliferation, and fractionation influence survival curves. Cell survival curves are important for understanding radiation effects and optimizing fractionation schemes.
Time , Dose & Fractionationrevised
The document discusses key concepts in radiation oncology including dose fractionation, tumor lethal dose, normal tissue tolerance, and factors that affect radiosensitivity. Fractionating the total radiation dose into smaller daily doses allows time for repair of sublethal damage in normal tissues, improving the therapeutic ratio by reducing side effects while still effectively treating the tumor.
Altered Fractionation Radiotherapy in Head-Neck Cancer
Altered fractionation radiotherapy has been shown to improve outcomes for head and neck cancer patients compared to conventional fractionation. Meta-analyses demonstrate significant benefits including improved 5-year locoregional control and overall survival. However, most modern trials do not address fractionation. Hypofractionation shows promise with comparable tumor control and toxicity but reduced treatment time. Ongoing research combines altered fractionation with chemotherapy and radiosensitizers to further improve outcomes while minimizing toxicity.
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This document discusses several key concepts in radiobiology including:
1. The interaction of radiation with cells is probabilistic, with damage occurring through direct and indirect action. Indirect action involves free radicals produced by radiation interacting with water molecules within cells.
2. Different phases of the cell cycle have differing radiosensitivities, with G2/M being most sensitive. Fractionated radiation can exploit this through redistribution effects.
3. The linear quadratic model describes cell survival curves and accounts for both single-hit and double-hit damage from radiation. It is used to calculate biologically equivalent doses.
4. Mechanisms like reoxygenation between fractions can improve the therapeutic ratio by making tumor cells
Fractionated radiation and dose rate effect
Fractionated radiation and the dose-rate effect can impact cell survival through mechanisms like sublethal damage (SLD) repair and cell cycle redistribution. SLD repair occurs as double-strand breaks are rejoined after radiation exposure. At lower dose rates, more SLD can be repaired between fractions, improving cell survival. However, very low dose rates may instead reduce survival if cells become frozen in radiosensitive phases of the cell cycle. The dose-rate effect varies between cell types and depends on factors like oxygenation and ability to progress through the cell cycle after radiation.
Linear quadratic model ppt
This document summarizes key concepts regarding radiation-induced cell death and survival curves. It discusses how cell death is defined for differentiated and proliferating cells. The linear-quadratic model is then explained, which describes cell survival curves using alpha and beta coefficients. Various fractionation schemes and their resulting biological effective doses are calculated and compared for treating different head and neck cancers. The limitations of hypofractionation and importance of accounting for tumor proliferation are also covered.
Evolution of Fractionation and Conventional Fractionation in Radiotherapy
The document discusses the evolution of radiation fractionation in cancer treatment. Early radiation machines had low output, so delivering a tumoricidal dose as a single fraction would have caused unacceptable toxicity. Fractionation was used from the beginning. Over the following decades, two schools of thought emerged on fractionation - the Erlangen school believed single large doses were necessary, while the Paris school's experiments on animal models supported fractionation. Clinical results in the 1930s also showed fractionation produced better tumor control with less toxicity. The rationale for fractionation is based on the different cell kinetics of normal and tumor cells, allowing sparing of normal tissues. Mathematical models were later developed to quantify fractionation schedules, incorporating factors like overall time, dose per
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This chapter discusses fractionated radiation and the dose-rate effect. It covers operational classifications of radiation damage including potentially lethal damage and sublethal damage. Fractionation allows for repair of sublethal damage through processes like reassortment and repopulation. The dose-rate effect results from increased repair at lower dose rates. Examples are provided for both in vitro and in vivo models. Brachytherapy techniques like intracavitary and interstitial brachytherapy are also summarized.
Oer , rbe & let
1) The document discusses various factors that affect radiation response, including linear energy transfer (LET), relative biological effectiveness (RBE), oxygen effect, and cell cycle phase.
2) It provides details on oxygen enhancement ratio (OER), describing how it ranges from 2.5-3.0 for x-rays and varies according to cell cycle phase and radiation type (higher for x-rays and neutrons vs. alpha particles).
3) LET is discussed in relation to radiation type (low for x-rays, medium for neutrons, high for alpha particles) and how it impacts ionization density and biological damage. An optimal LET of around 100 keV/μm is described.
craniospinal irradiation
The document discusses craniospinal irradiation (CSI), which delivers radiation to the entire cranial-spinal axis to treat intracranial tumors. It was pioneered in the 1950s and is commonly used to treat tumors that may spread through the cerebrospinal fluid such as medulloblastoma. The document outlines the techniques, challenges, indications, and evolving approaches for CSI such as reduced dose protocols and hyperfractionated regimens. It discusses topics like patient positioning, target volumes, critical structures, field arrangements, and the use of newer technologies like virtual simulation.
Sib.si
Simultaneously integrated boost (SIB) allows different doses to be delivered simultaneously to the planning target volume (PTV) and gross tumor volume (GTV), reducing the number of fractions needed. SIB provides a greater biological effective dose while allowing individual dose optimization to both targets in a single plan, overcoming limitations of conventional fractionation. An institutional study compared SIB to conventional 3D conformal radiation therapy in 30 patients with brain, breast, or bladder cancer, finding SIB reduced maximum doses to targets and organs at risk while shortening treatment duration by about a week.
Cell survival curve ppt.
Cell survival curves show the relationship between radiation dose and the proportion of cells that survive. For low linear energy transfer (LET) radiation like X-rays, the curve starts with a shoulder region followed by an exponential decrease in survival fraction. The linear-quadratic model describes cell survival as an exponential function of dose, with parameters α and β representing linear and quadratic components of cell killing. Fractionation reduces cell survival more than single high doses by allowing repair of sublethal damage between fractions. Hypoxic cells are less sensitive initially but may reoxygenate and become sensitive to later fractions. Mitotic cell death is the most common mode of radiation-induced cell death in tumor cells.
Cobalt & linac
This document provides information on teletherapy machines used to treat cancer with radiation. It discusses cobalt-60 teletherapy machines and linear accelerators. Cobalt-60 machines use a radioactive cobalt-60 source to generate gamma rays for treatment. Linear accelerators use microwave energy to accelerate electrons, which are then used to generate x-rays or electron beams for treatment. Both types of machines aim focused radiation beams at tumors while minimizing dose to surrounding healthy tissue using collimators and other targeting mechanisms. Linear accelerators have advantages over cobalt machines like more sharply defined beam edges and ability to vary dose rates.
4 r's of radiobiology and dose rate effects
1) The four Rs of radiobiology are repair, re-assortment, repopulation, and re-oxygenation. They influence how tumors and normal tissues respond to fractionated radiation treatment.
2) When radiation is delivered in two fractions separated by time, cell survival increases due to repair of sublethal damage between fractions. The increase peaks at 2-3 hours and then levels off due to repopulation.
3) Lowering the radiation dose rate generally decreases biological effects because it allows more time for repair of sublethal damage.
Altered fractionation kiran
The document discusses various radiation fractionation schedules used in cancer treatment. It begins with an overview of conventional fractionation, which divides the total radiation dose into smaller daily doses to allow healthy cells to repair sublethal damage between fractions. It then explores the radiobiological rationale of the 5 R's of fractionation - repair, redistribution, reoxygenation, repopulation, and radiosensitivity. The document discusses various altered fractionation schedules including hyperfractionation, accelerated fractionation, split-course, and hypofractionation, explaining how each schedule aims to improve the therapeutic ratio for cancer patients.
Cell survival curve
Cell survival curves describe the relationship between radiation dose and the fraction of cells that survive that dose. The shape of the curve is influenced by many factors including:
1) The proliferative capacity of cells, with rapidly dividing cells being more radiosensitive.
2) The presence of oxygen, with hypoxic cells being more radioresistant.
3) Fractionation, with fractionated doses allowing more time for repair between exposures and resulting in a higher surviving fraction compared to a single dose.
4) Dose rate, with low dose rate irradiation resembling continuous fractionation and having less cell killing compared to an acute high dose rate.
Cell survival curves take different shapes for early-responding normal tissues dominated
Beam modification devices
This document discusses various beam modification devices used in radiation therapy to modify the spatial distribution of radiation within the patient. It defines beam modification and lists some common reasons for its use, such as irregular patient contours or tissue deficits. The main types of beam modification discussed are shielding, compensation, wedge filtration, and flattening. Specific devices covered include field blocking devices, compensators, wedge filters, bolus, and multi-leaf collimators. The document provides details on the purpose, design considerations, advantages, and disadvantages of several common beam modification devices.
TSET
Total skin electron therapy (TSET) is used to treat cutaneous T-cell lymphoma by delivering a uniform dose of radiation to the entire skin surface while sparing underlying organs. It requires large electron fields over the entire body and precise dosimetry. The most common technique uses six electron beams arranged at 60 degree intervals to provide circumferential coverage. Proper field design and calibration are needed to achieve uniform dose across irregular body surfaces and minimize dose from bremsstrahlung x-rays.
5 Rs OF RADIOBIOLOGY.pptx
The document discusses the key concepts of radiobiology known as the "5 R's of Radiobiology". It describes radiobiology as the branch of science combining physics and biology to study the effects of ionizing radiation on tissues and living organisms. The 5 R's are: repair, repopulation, reoxygenation, redistribution, and reassortment. The document provides details on the law of Bergonie and Tribondeau which established that immature cells are more radiosensitive. It also discusses the history of fractionation in radiotherapy and mechanisms such as sublethal damage, potentially lethal damage, and accelerated repopulation that provide rationale for fractionating radiation doses.
Fractionation in Radiotherapy
Fractionation in radiotherapy refers to dividing the total radiation dose into smaller doses given over multiple treatment sessions. This allows healthy cells to repair sublethal damage between fractions while maximizing cancer cell kill through mechanisms like redistribution and reoxygenation. The "5 R's" of radiobiology explain fractionation: repair of sublethal damage in normal cells; redistribution of tumor cells to sensitive phases; reoxygenation of hypoxic tumor cells; repopulation of tumor cells during prolonged treatment; and intrinsic radiosensitivity differences between cell types. Fractionation schedules are tailored based on these factors to improve the therapeutic ratio for different cancers and patients.
TIME DOSE & FRACTIONATION
Introduction
Time dose & fractionation
Therapeutic index
Four R’s Of Radiobiology
Radiation response
Survival Curves Of Early & Late Responding Cells
Various fractionation schedules
Clinical trials of altered fractionation
Late effects of Radiotherapy on Normal Tissues
This document summarizes the acute and late effects of radiation therapy on normal tissues. It discusses the differences between early and late effects, which depend on the tissue kinetics. Early effects occur within weeks in rapidly proliferating tissues, while late effects take months or years to appear in slowly proliferating tissues. It also describes various models for classifying tissue radiosensitivity and explores factors like dose, volume, and fractionation that determine normal tissue tolerance. Specific sections are dedicated to discussing the effects of radiation on brain, spinal cord, optic nerves and other organs.
Cell Survival Curves by Dr.Abhilash.pptx
Cell survival curves relate the fraction of cells retaining reproductive integrity to radiation dose. Mammalian curves have an initial curved portion then become exponential. This shoulder represents sublethal damage repair. The linear-quadratic model is clinically used, describing cell kill as proportional to dose (αD) and dose-squared (βD2). α measures intrinsic radiosensitivity and β repair capacity. Their ratio determines curve shape and tissue type. Factors like oxygen level, proliferation, and fractionation influence survival curves. Cell survival curves are important for understanding radiation effects and optimizing fractionation schemes.
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I'll delete the file immediately, if it is illegal to upload the file.
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Management Of Early Stage Ca Cervix [Autosaved]
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1) Anal cancer is uncommon, comprising 2.4% of digestive system cancers in the US, with an estimated 7,060 new cases and 880 deaths in 2013.
2) The median age at diagnosis of anal cancer is 60, younger than the median age of 66 for all cancers.
3) The majority of anal cancers are squamous cell carcinomas caused by HPV infection, while adenocarcinomas are rare. Treatment typically involves chemotherapy and radiation.
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4 rs of radiobiology
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- 3. Four R’s of radiobiology explains the rationale behind the fractionation of radiotherapy. REPAIR REASSORTMENT REPOPULATION REOXYGENATION
- 5. Single strand break Double strand break
- 7. LETHAL DAMAGE:irreversible,irreparable and leads to cell death. POTENTIALLY LETHAL DAMAGE: Radiation damage that can be modified by postirradiation environmental conditions. SUBLETHAL DAMAGE:Repaired in hours unless additional sublethal damage is addded.
- 8. If cells are prevented from dividing by creating suboptimal growth condition for 6 hrs after irradiation,damage can be repair Invitro:by keeping cells in saline
- 9. Operatinal term for increase in cell survival if given radiation dose in split into two fractions separated by time interval
- 10. Base Excision Repair(BER) Nucleotide Excision Repair(NER) DNA Double–strand Break Repair Nonhomologous End joining Homologous Recombination Repair Others Single strand annealing Cross link repair Mismatch Repair
- 11. Single base mutation that is first removed by a glycosylase/DNA lyase Removal of the sugar residue by an AP endonuclease Replacement with the correct nucleotide by DNA polymerase Completed by DNA ligase III-XRCC –mediated ligation
- 12. Nucleotide excision repair removes bulky adducts in the DNA such as pyrimidine dimers. The process can be subdivided into pathways Global genome repair(GER) Transcription coupled repair(TER)
- 14. Occurs in late S/G2 phase Undamage sister chromatid as template Error free
- 15. Occurs in G1 phase No template Fast but error prone Accounts for premutagenic lesion in DNA of human cell by ionizing radiation
- 16. Cells may be in different phases of cell cycle during irradiation Cells in M phase most radiosensitive and S phase radioresistant Cells surviving in first dose of radiation may reach sensitive phase in second dose Sensitization due to reassortment causes therapeutic gain,
- 18. Process of increase in cell division seen in normal and malignant cells after irradiation In normal tissues. Acute Responding tissue:stem cells,GI epithelium,skin,oropharyngeal mucosa Late Responding tissue:renal tubular epithelium,oligodendrocytes,schwann cells,endothelium
- 19. Some tumors exhibit accelerated repopulation,a marked increase in their growth fraction,doubling time and decrease in cell cycle time. Dangerous phenomenon that is present when treatment exceeds over 5 weeks.
- 20. Tumor less than 1mm are fully oxic Over 1 mm develops region of hypoxia. Hypoxia in tumor results from Acute hypoxia Chronic hypoxia
- 21. Temporary closing or blockage of particular blood vessels When dose of radiation is delivered,a propotion of tumor cells become hypoxic,but if radiation is delayed different grp of cells become hypoxic.
- 22. Results from limited diffusion distance of oxygen in respiring tissues Distance oxygen can diffuse in respiring tissue is about 70 micrometer
- 24. Process by which hypoxic cells become oxygenated after a dose of radiation. Tumor contains the mixture of aerated and hypoxic cells Dose of radiation kills greater proportion of aerated than hypoxic cells Radiation if given in series of fractions separated in time sufficient for reoxygenation to occur,the presence of hypoxic cell doesnot greatly influence the response of tumors.
- 26. Reoxygenation in tumors have : Fast component • Seen in acute hypoxia • Occurs within hours • Temporary closed vessels reopen Slow component • Seen in chronic hypoxia • Occurs within days • Tumor shrink in size .surviving cells previously beyond the range of oxygen diffusion come closer to blood supply.
- 27. THANK YOU