PRINCIPLE AND PRACTICE OF RADIOTHERAPY .ppt

I. Introduction & Purpose

Radiotherapy = use of ionizing radiation to kill cancer cells.

Goal: local tumour control while reducing damage to normal tissues.

Radiotherapy may be used alone or with surgery / chemotherapy / immunotherapy.

Key balance = therapeutic ratio (tumour control vs normal tissue toxicity).

Radiotherapy is tech‑intensive; requires multidisciplinary team (oncologists, physicists, therapists).
IAEA
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PubMed
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Keywords: ionizing radiation, therapeutic ratio, local control, normal tissue, multidisciplinary

II. Physics & Types of Radiation
A. Radiation Types & Sources

Electromagnetic: X‑rays and γ (gamma) rays.

Particulate: electrons, protons, ions, neutrons (less common).
Obgyn Key
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Linear accelerators (linacs) generate high‑energy X‑rays / electrons.
Obgyn Key
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OUP Academic
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Radioisotopes (e.g. Ir‑192, Co‑60, I‑125) used in brachytherapy / sealed sources.
IAEA
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oncohemakey.com
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Keywords: X‑ray, gamma ray, electron, proton, linac, radioisotope, Co‑60, Ir‑192

B. Radiation Interaction with Tissue

Ionization: radiation deposits energy, ejects electrons.

Photoelectric effect, Compton scattering, pair production (depending on energy).

Depth dose curves: energy deposition vs depth in tissue.

Electrons: good for superficial lesions (rapid falloff).
Obgyn Key
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OUP Academic
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Protons/ions: Bragg peak enables sparing of distal normal tissue.
Obgyn Key
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Keywords: ionization, depth‑dose, photoelectric, Compton, Bragg peak

III. Radiobiology: How Radiation Kills Cells
A. Biological Effects & Damage Phases

Physical → chemical → biological phases.
arXiv
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Radiation causes DNA damage: single‑strand breaks, double‑strand breaks.

Double‑strand breaks often irreparable → cell death or mutation.

Also induces free radicals, oxidative damage.

Keywords: DNA break, single strand, double strand, free radical

B. The “4 (or 5) R’s” of Radiobiology

Repair: normal cells repair sublethal damage between fractions.

Redistribution: cells move through cell cycle phases (some more radiosensitive).

Reoxygenation: hypoxic (low‑oxygen) tumour cells become reoxygenated → more radiosensitive.

Repopulation: surviving tumour cells may divide during treatment.

Radiosensitivity: inherent sensitivity of cell type to radiation.
arXiv
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ebook.sts.org
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OUP Academic
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Keywords: repair, redistribution, reoxygenation, repopulation, radiosensitivity

C. Dose–Response Models & Fractionation

Linear–quadratic (LQ) model describes cell survival vs dose.

Fractionation: splitting total dose into many small doses (fractions).

Conventional: ~1.8–2 Gy per fraction, daily over weeks.

Hyperfractionation: smaller doses, more fractions.

Hypofractionation: larger dose per fraction, fewer sessions.

Purpose: spare normal tissue (repair), maximize tumour kill.
oncohemakey.com
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Sumathi Publications
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OUP Academic
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Keywords: linear‑quadratic, fractionation, conventional, hypofractionation, hyperfractionation

D. Tumour Control

1. PRINCIPLE AND PRACTICE OF RADIOTHERAPY
 
MILE STONES IN THE HISTORY OF RADIOTHERAPY
1895—Wilhem Conrad Roentgen discovered x-rays
1896---X-rays used to treat cancer
-- Becquerel discovered Radioactivity
 1898----Pierre and Marie Curie discovered Radium
1934 ----Frederick Johot and his wife produce artificial radioactivity by bombarding alluminium with &
particles
----- Neutron beam first used to treat cancer
 1951----First CO-60 Teletherapy unit installed in Canada
 1952---First Linear Accellerator designed for RT
1960 Computerised RTP
1991----CT developed

2. MILESTONES CONTD
 1991 --- Stereostatic RT
---Conformal RT
1993 --Radio-surgery[gamma-knife]
2000 --Image guided Rt (IGRT)
2002 Intensity modulated Rt(IMRT)
2010 True Beam Rt

3. PRODUCTION
Extra- Nuclear eg X-rays from an X- ray tube
Electron from Linear Accellerators
Protons ,Neutron from Betatron
and Cyclotron
 Intra- Nuclear eg, Gamma from Radioactive
sources eg, 137 Cs, 60 CO, 226R a,
198Au,125Iodine

4. PRINCIPLE OF RADIOTHERAPY
Definition: Radiotherapy is the use of Ionising
Radiation in the management of tumours
Types of Radiations
1, Sparely ionising R eg, X-rays, Gamma , Betta
rays
2,Intermediate ionising R eg, Electron,
3,Densely ionising R eg, Neutron, &particles,
Negative pi-mesons.

5. BIOLOGICAL BASIS
The critical target in the mamallian cells is the DNA, when this is damaged the cells loose their reproductive
integrity. Depending on the Linear Energy Transfer (LET) there are two types of Interactions
1,Indirect Interaction – the photon reacts with water
e- + H2O = H2O+
H2O+ + e- = OH’, H’ [Free Radicals]
The free radicals react with DNA to cause damage, this represents 2/3 of damage done by X-rays and & rays
with the resultant inability of the cells to replicate and attempts by the cells to divide lead to cell death.This
process is amenable to modification by precence or absence of O2
2,
Direct Interaction—This is true of radiation with high LET , the energy of the radiation is high enough to
directly damage the DNA in the cell nucleus The critical target in the mamallian cells is the DNA, when this is
damaged the cells loose their reproductive integrity. Depending on the Linear Energy Transfer (LET) there
are two types of Interactions
1,Indirect Interaction – the photon reacts with water
e- + H2O = H2O+
H2O+ + e- = OH’, H’ [Free Radicals]
The free radicals react with DNA to cause damage, this represents

6. FRACTIONATION IN RT
This is repeated, brief application of
irradiation to produce profound effects on
tumours with less injury to normal tissue
rationale for fractionation is based on
4Radiobiological effects 4Rs
---Repair of sub lethal damage
----Re-assortment
----Repopulation
---Re –oxygenation

7. MODIFIERS OF RT
---Oxygen, this enhances the effect of
the free radicals
--Hypoxic cell sensitizer eg,
Misonidazol, Etanidazol,Pimonidazol
--Haloginated Pyrimidine
--Protectors eg,
Cysteine,Cysteamine,WR2721 given IV

8. INDICATION FOR COMBINING RT
WITH SURGERY
1, To improve local control in a locally advanced
cancer for which RT or SURGERY alone could not
prevent a recurrence
2,Used in efforts for organ preservation for
aethetic or functional reasons
3,Used sometimes to convert a locally non-
resectable tumour to a resectable one
4,Surgery sometimes is done to expose the lesion
as done in Intra-operative RT for retroperitonial
lesion.

9.  
SAND WITCH RT
This is combination of pre-op and
post-op RT. This is not commonly
done because if for any reason the
post-op RT is delayed the advantage
is lost.

10. CONSEQUENCES OF DELAYED RT POST-OP
1, The mass of cancer cells will have become
much larger and spread over a wider
volume.
2, Increase chance of metastasis
3,There is decrease chance of local control
when recurrence is clinically present, if for
any reason the post-op RT is delayed the
advantage is lost.

11. INDICATION FOR POST-OP RT
1,When there are known or suspected residual
lesion post-op
2,Anatomic sites and clinical stages of high risk of
post-op recurrence eg, Head and Neck cancers
3,Pathologic findings post-op associated with
increasing risk of local recurrence eg, status of
surgical margins,vascular invasions, nodal
involvement,pathologic grade.
4,post-op RT is indicated among group of
patients with 15%-20% incidence of loco-regional
recurrence

12.  
TYPES OF RADIOTHERAPY MACHINES
TELETHERAPY

Machines---Megavoltage eg, 60 CO machine
Linear Acellerator 6MV,15-20MV
Orthovoltage
eg, 100KV 300KV
BRACHYTHERAPY
Intracavitary – RALS., MALS
Interstitial [implant]

13.  
PALLIATIVE ROLES OF RT
To prevent Fungation
For Heamostatis
Pain control
Tumour debulking
For decompresion in Spinal cord mets
For decompression in Sup vena cava
obstruction secondary to lung ca

14. RT for Benign Lesion
Keloid Post Excision 12 Gy in 2
fractions
Pterygium post excision
Haemangioma 25GY 6 fractions

15. THANK YOU