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Perez_chap1

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arunmp's version from 2017-04-07 05:50

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Radiation oncology is that discipline of human medicine concerned with thegeneration, conservation, and dissemination of knowledge concerning the causes,prevention, and treatment of cancer and other diseases involving special expertise in the therapeuticapplications of ionizing radiation.
Radiation therapy is a clinical modality dealing withthe use of ionizing radiations in the treatment of patients with malignant neoplasias (and occasionally benign diseases).
In 1962, Buschke defined a radiotherapistas a physician whose practice is limited to radiation therapy.
Roentgen xraynov8 1895
Curie Radium1898
Palliative radiation therapy isdesigned to ameliorate a specific symptom such aspain, obstruction, or bleeding.
Interstitialcervix ,breast,sarcoma
Intracavitrycervix ,npx
Mouldskin
the dose rate(i.e., the number of cGy per minute)
TUMOR control probability (TCP, or local control) is proportional to the logarithm of the number of clonogenic cells in the tumor
a rational approach to the problem of heterogeneous tumor distribution (ie centre needs more dose since its more hypoxic)A shrinking field technique
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Recommended definitions of terms and concepts for radiation therapy treatment volumes and margins in(ICRU) 50
Because the PTV does not account for treatment machine characteristics, the actual treated volume is that volume enclosed by an isodose surface that is selected and specified by the radiation oncologist as being appropriate to achieve the goal of treatment
The treated volume almost always ----- than the PTVlarger ( usually has a somewhat simpler shape).
The irradiated volume is that volume of tissue that receivesa dose considered significant in relationship to tissue tolerance.
Irradiated volume includetissues in the exit region of unopposed photon beams or in the penumbra region of a beam.
The planning organ at risk volume refers to thedefinition of margins around organs at risk for injury by radiation(PRV SPINE AND BRAINSTEM)
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Uncertainites in RT is divided into one related to DELIVERY OF DOSE other is SPATIAL UNCERTAINITES

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Five example of uncertainties related to DELIVERY OF DOSE1. inhomogeneities in the beam,2.problems related to dose calculations, 3.variables in the output of treatment machines,4.instability of the beam monitoring technique, and 5. problemsrelated to beam flatness
2 Spatial Uncertainity includesMechanical Uncertanites of machine and Patient related inaccuracies
Mechanical Uncertanites of machineField size setting +Rotational setting+Cross hair+Light beam congruence+Allignment system+Couch topsag+Beam shaping blocks+Isocenter
Patient related inaccuraciesTarget delineation+Organ motion+Skin mark+Repositioning+Patient motion
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Two types of hypoxia are Diffusion limited hypoxia and perfusion limited hypoxia

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Diffusion limited hypoxiainadequate angiogenesis,
perfusion limited hypoxia is associatedwith intermittent closure of tumor vessels, leading to acute hypoxic conditions for tumor cells downstream from the obstruction
Diffusion limited hypoxiaPermanent
perfusion limited hypoxiaTransient till obstruction relieved
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Radiosensitivity(Bergonie and Tribondeau) and Radiocurability

Radiocurability refers to the eradication of tumor at the primary or regional site and reflects a direct effect of the irradiation;this does not necessarily equatewith the patient’s cure from cancer
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radiosensitivity is a measure of tumor–radiation response, thus describing the degree and speed of regression during and immediately after radiotherapy
Radiosensitivity IS DIRECTLY PROPOTIONAL TOability of cell todivide or reproduce
Radiosensitivity IS inversly PROPOTIONAL TOdegree of differentiation
Radiosensitivity IS DEPEND ONHYPOXIA+ Proportion of clonogenic cells+ Repair of radiation damage.+Inherent radiosensitivity of cell
Paterson divided tumors into three groupsradiosensitive (germ cell tumors and reticuloses ) +intermediate(squamous cell and adenocarcinomas) and radioresistant soft-tissue and bone sarcomas and melanomas.
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This shrinking field technique administers higher radiation doses to the entiregross tumor where more clonogenic cells (including hypoxiccells) reside, relative to lower doses to tissues in the immediate proximity of the clinically apparent (gross) tumor.
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acute(first 3 months)
late effects(more than 3 months after irradiation),
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The farther the
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TCP and NTCP curves divergethe more favorable is the therapeutic ratio or therapeutic gain
Short overall treatment times are required for tumors with alow α/β ratio or fast proliferation.
For median potential doubling times of 5 days and intermediate radiosensitivity, overall times of 2.5 to 4 weeks would be optimal.
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Continuous hyperfractionated accelerated radiotherapy

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Chart1.5 Gy three times per day, 7 days per week. so 54Gy in 36 fraction over 12 days
Continuouswithout any weekend breaks
hyperfractionatedFraction size smaller than 1.8 Gy , Usually more than one treatment sitting per day, at least 6 hours apart
acceleratedoverall treatment duration without a comparable reduction in total dose
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In ca cervix prolongation of overall treatment time resulted in an increased failure rate of 0.59% per day in stage IB and IIA and 0.86% per day in stage IIB disease.