1. Radiotherapy uses ionizing radiation to kill tumor cells, with the goal of achieving permanent local tumor control or palliating symptoms. 2. External beam radiation is delivered via linear accelerators or cobalt-60 units and can treat deep or superficial tumors. Brachytherapy places radioactive sources close to the tumor. 3. Radiation damages DNA directly and indirectly via free radicals. This can lead to reproductive cell death and loss of clonogenicity. Fractionated low-dose delivery allows normal tissue recovery between fractions.

1. PRINCIPLES OF RADIOTHERAPY
ASWINI SIVAN G (M-6251)
MVSC SCHOLAR
IVRI

2. HISTORY
 1906-1912– Dr Richard Eberlien
 Not practiced in India –cost
 Specialty in radiation oncology -AVMA -American College of
Veterinary Radiology
 Recognized in 1994
 Orthovoltage x-ray machines -cobalt-60 and cesium-137.
 Cobalt and cesium -extremely dangerous and heavily regulated
 Linear accelerators – late 1960s

3. INDICATIONS
 Localised solid neoplasms
 Choice -brain tumors, nasal tumors, other neoplasms of the head
and neck
 Vertebral column & pelvic canal- only option
 Soft tissues of skin and subcutis
 Mediastinal cancers ,caudal abdomen and pelvic canal (thymoma,
prostatic carcinoma, and anal gland tumors)

4. Other indications
 When surgery has failed
 When radical surgery unable to remove whole of neoplasm
 Reduction in size for surgery
Not indication in neoplasia with high incidence of metastasis

5. External beam radiation therapy
 Patient evaluation- ability of patient to undergo GA , CBC ,
biochemical profile , urinalysis , thoracic radiography (3
views) ,regional lymph node biopsy ,USG.
 Tumor imaging &Treatment planning –radiography , CT,
USG, nuclear scintigraphy, MRI
 Tumor diagnosis and selection of therapy –histopathology
& grading determine prognosis and usefulness of therapy
Debilitated patients should not be subjected to radiotherapy

6. Nasal Tumor After Treatment, CT Scan
Nasal Tumor Before Treatment,
CT Scan

7. Cont…
 Post radiation evaluation- to evaluate animals for both
tumor response and side effects in normal tissue
 Evaluation at 2 nd and 4 th week after end of radiation
therapy , subsequent rechecks at 2,3,5,7,9 and 12 months and
then every 3 -6 months

8. Radio Therapy Planning
 Not given as single dose
 Given as divided dose spread over a period of time
(Fractioned therapy)
 10-12 fractions
 Each time 4-5 Gy

9. 4 r’s of Radiotherapy
Reoxygenation Repopulation
Redistribution Repair

10. Factors Influencing Radiosensitivity
 Oxygenation of tumor cell ,increase proportion of cell cycling
 Multiple daily treatments –reoxygenation , improve cell killing
 Stage of cell division – M & G2 Most sensitive
 Capacity to repair damage
 Repopulation–overcome by maximal dose of radiation in shortest
possible time

11. External Beam Radiation Equipment

External beam radiation sources include beams
of X-rays, gamma rays,
or electrons delivered by either orthovoltage or
megavoltage (e.g.,
cobalt 60 and linear accelerators) radiation
therapy equipment.
Megavoltage refers to the use of higher energy
radiation, which is
defined as ≥1 million volts (MV)

12. ORTHOVOLTAGE
 250–500 kV range
 X-rays that are generated by bombarding a metallic target
(i.e., tungsten) with high-energy electrons
 low energy radiation
 maximum radiation dose deposited at the skin surface
 Limited to lesions ≤2 to 3 cm in depth
 Differential absorption of radiation dose in bone compared
to soft tissue(2 to 4 times-risk of bone damage or necrosis.
 Short source-to-skin distance (usually 50 cm)

13. Cobalt 60
 Average energy 1.25 MV- Megavoltage radiation therapy
 gamma rays
 “Skin-sparing” effect (0.5 cm below skin surface)
 Deeply seated tumors
 Source-to-skin distance -80 cm, so larger field
sizes
 Thorax or abdomen- may result in unacceptable
toxicity and higher morbidity from the delivery of a radiation
dose

15. Linear Accelerator
 X-rays (also referred to as photons) or electron beams
 Greater flexibility in treating both deep and superficial tumors
 High-frequency electromagnetic waves to accelerate charged
particles
 Electron energies - 4 to 30 million electron volts (MeV)
 source-to-skin (or axis) distance -100 cm

16. SYSTEMIC RADIATION THERAPY
 Direct injection of Isotopes into patient –
 I 131 ( thyroid tumors)
 Samarium 153 (bone neoplasia)
 P 32 (Polycythemia)

17. Units of radiation dose
 S.I. unit of absorbed radiation –gray (Gy)
 Gy is absorption of 1 joule / Kg
 1 Gy = 100 rad (Radiation absorbed dose)
Basic principle of radiotherapy -To kill tumor cells by ionizing
radiation

18. 4 main kVp ranges
1. Low voltage (50-120 kV)- superficial skin lesions
2. Intermediate voltage (130-150 kV)-lesions few cm beneath skin
3. Orthovoltage (160-300 kV)-deep lesion
4. Mega /Super voltage (300-1000 kV) deeper lesions

19. Therapeutic radiation delivery
Teletherapy
Brachytherapy
Nuclear oncology

20. TELETHERAPY
 General anaesthesia required
 Radiation source remain at a distance from lesion
 X -ray therapy units- Superficial & deep
 Supervoltage therapy
 Particulate beam therapy-electron , neutron/ proton beam
Radiation exposure range 50-300 centi Gy/min (400 cGy dose in 1-8 minutes)

21. BRACHYTHERAPY
 Radioactive isotopes placed very close to body as implant
 Surface applicators, needles , seeds or grains
 Low dose rate radiation used
 Surrounding tissue receives less of radiation
 Iridium 192 – primary isotope
Disadvantage –isolation of patient & risk of working with radioisotopes
Permanent – 198Au ,222Rn , 125K
Removable – 192Ir , 60Co, 137Cs

22. Specific methods
1. Interstitial brachytherapy-198Au, 60Co
2. Pleisotherapy- surface brachytherapy- 90Sr
3. Systemic brachytherapy-131I,
32 P

26. X ray therapy tube vs diagnostic X-ray
tubes
 Low tube current (5-20 mA); high kVp ; long
exposure time
 Stationary anode ,single large filament , large sized
focal spot(5-8mm)
 Target angle greater (30 °)
 Close focal object distance
 More efficient heat dissipation mechanism

27. Goals of Clinical Radiation therapy
RADICAL /CURATIVE THERAPY
 Decrease the number of tumor
cells to a level that achieves
permanent local tumor control
PALLIATIVE RADIOTHERAPY
 Decrease the symptoms of
malignant disease
 Includes all or only part of
demonstrated tumor
Staging of tumor is necessary to decide goal of therapy

28. Delivery of radiation
 Earlier weekly basis / Monday-Wednesday -Friday
 Current fractionation- Daily / mon-tue-wed-thur-fri
 Exception – malignant melanoma- weekly/ twice weekly treatment
 Palliative therapy- 3-4 weekly fractions/ 5 daily treatments during 1 week
 For each fraction patient is anesthetized
 Most patients 1-4 treatment fields – each taking 10-15 min

29. RADIOBIOLOGY

33. • DNA - primary target , single & double stranded breaks
• Direct damage (1/3rd) - DNA damage
• Indirect –Hydroxyl radical (-OH*)
Reproductive death of
cell
Clonogenicity is lost

34. RADIOSENSITIVITY
 Susceptibility of tumor or normal cell to a given dose of radiation
 Related to oxygen level, cell cycle position, repair mechanism, inherent radio
sensitivity
RADIORESPONSIVENESS
 Measurable reduction in size of tumor after radiation
 Manifestation of radiosensitivity
RADIATION CURABILITY
 Measure of ability of radiation to cure a patient of tumor
 Goal of therapy

35. Course Design
 Normal tissue tolerance dose( 200 rads –eyelens )
 Tumor lethal dose
 Therapeutic ratio
 Sensitive ( ratio ) -less dose required –regression 74% -( SCC)
 Moderately sensitive (ratio 1)-regression -54% (mast cell tumors)
 Resistant – regression 34% (fibrosarcoma)

36. Normal tissue response
 All irradiated cells are at risk of treatment related sequelae
 Radiation damage is a probability event
 Even at high doses tumor cell may escape radiation induced
death
 Even at low doses normal tissue may react in a dramatic
manner

37. DOSE RESPONSE CURVE
Dose response curve demonstrating
tumor control and normal tissue
complication

38. COMPLICATIONS
 ACUTE LATE
EFFECTS
Acute effects- proliferating
cells of body
During /within first 3-6
months
Factors –total dose, dose
intensity (duration),volume of
tissue irradiated.
Normal sequelae & short lived
effects
Slowly proliferating tissues – Nerve
& muscle
Damage is progressive and non
reversible
Fractionated radiation therapy can
reduce risk

39. complications