Use of ionising radiation to damage DNA to prevent cell replication




Most rapidly replicating cells affected the most


Radiosensitive tissue

- high turnover tissue

- high blood supply


Give DXRT in incremental radiation


Produce free radical by breakup of H2O

- H2O -> H+ + OH-

- free radicals denature DNA

- damage DNA so that cell can't divide 

- cell then dies without dividing



- bigger particle produces greater damage

- different particles have different RBE (Radiobiological effectiveness)

- each particle works the same way- free radical production


Both tumour & normal cells injured

- normal cells recover

- tumour dies


Need O2 for DXRT to work

- hyperbaric better

- unoperated bed better




1.  Photons


2.  Gamma Rays 


Go through body / not absorbed as particles

- Cobolt 60 - Almost obsolete

- Iridium - Occasionally used in Brachytherapy

- Caesium - Used for Gynaecology tumours

- Radium - Now obsolete


3.  X-Rays 

- diagnostic 50-150 kv

- deep X-Ray Therapy - 300 kv

- linear accelerators - 4-24 mv


4. Particle beams


Electrons - Linear Accelerators

- particle beams via linear accelerator

- produce electron beams -> absorbed as particles

- depending on energy of beam can dial up depth of beam 

- 6MeV - 20MeV 


5.  Beta - Rays

- electrons given off by ionised substance

- injected locally

- Strontium, Yttrium & Samarium


6.  Neutron beams 

- very damaging

- experimentally are producing heavy particle beams via cyclotrons as neutron beams





- 1 large dose vs 60 small doses

- curative / fractionation

- palliative / minimal fractionation


100 Centigray = 100 Rad = 1 Gy



- 1000 Centigray in 10 doses


Bone Tumour

- 6000 Centigray in 30 doses




Maximum possible dose with acceptable damage to normal tissue

- 60 Gy in 30 fractions over 6/52

- equivalent to 18 Gy in one dose

- fractionation decreases late effects on normal tissue

- increased differential between tumour & tissue damage

- allows repair between treament


Usually given 3/52 postoperatively

- allows wound healing

- minimum delay as tumour interference activates cells in arrest phase


Careful planning

- multiple fields

- minimum normal tissue damage




Short course with lower total dose

- 30 Gy in 10 fractions

- 3 CentiGy or 3 Rad or 0.03 mRad


Simple field set ups

- late morbidity less of an issue

- delays callus formation if pathogical fracture

- slows chondroid formation at fracture but not with osteogenesis 

- 96% local remission


Method of Delivery


External Beam



- old method

- place radioactive agent down tube 

- high risk to doctor giving treatment

- now use remote brachytherapy


Intrapoerative radiotherapy

- give dose to site at time of surgery

- give high dose with minimal local effects


Remote Afterloading

- pour radio-active agent down into tube




6 Week Rule

- start radiotherapy < 6/52 after OT



- better blood supply 

- needs oxygen to effect cell kill

- shrinks tissue from neurovascular bundle

- may allow limb salvage



- impairs healing



- usually preferred

- wait for wound to heal

- start within 6/52 otherwise repopulates with tumour cells

- also easier to identify site of tumour




100% side effects




Erythema / Dry desquamation / Ulceration skin






GIT effects




Skin Fibrosis

Joint Contracture

Muscle Atrophy


Hair loss


Chronic bone changes / fracture


Post Radiotherapy Changes With Stress Fracture


Osteoradionecrosis - eg AVN Femoral head


Transverse myelitis


Lung fibrosis


ST & bony hypoplasia in kids

- physeal arrest


Endocrine suppression




Skin cancers


Sarcomatous change


Specific tumours




No indication for preoperative treatment


May be used for

- unresectable 

- palliation for metastasis


Ewing's Sarcoma


Very high radioresponsiveness 

- but low curability

- effective if combined with chemotherapy

- surgery & chemotherapy  have better results




Relatively radioresistant


May be used for

- recurrence

- inoperable disease




Effective for Plasmocytoma

Combined with chemotherapy for Multiple Myeloma


Soft Tissue Sarcomas



- doubt about surgical margins

- NV structures close to tumour

- 50 Gy DXRT  preoperatively

- 10 Gy Brachytherapy postoperatively


Useful to give radiotherapy preoperatively for sarcomas

- because it develops a rind around the tumour 

- makes it a lot easier to excise

- operate at about 6 weeks post radiotherapy