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Flashcards in Radiotherapy Deck (23):



How does radiotherapy generally work?



Photons directed towards tumour cells knock electrons off atoms which are then damaging to DNA. The higher the energy the further the photons travel.




What are photons?


The smallest discrete amount or quantum of electromagnetic radiation. It is the basic unit of all light. Photons are always in motion and, in a vacuum, travel at a constant speed to all observers of 2.998 x 108 m/s. This is commonly referred to as the speed of light, denoted by the letter c.




What is ionizing radiation?


Radiation that carries enough energy to liberate electrons from atoms or molecules, thereby ionizing them.




What is a Gray?



The deposit of a joule of radiation energy in 1 Kg of matter or tissue





What is a Sievert?


1 joule/kg - biological effect of the deposit of a joule of radiaiton energy in a kg of human tissue. It is a measure of the health effect of low levels of ionizing radiation on human tissue

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What is the radiation weighting factor?



An estimate of the effectiveness per unit dose of the given radiation relative a to low-LET standard.




What is teletherapy?


External beam from a linear accelerator source produces X-rays. The energy is transmitted as photons and is the most commonly used form of radiotherapy. Cobalt-60 generators can also provide γ-rays and high-energy photons, but are being gradually phased out.

Most external beam treatments that are given with curative intent are delivered in 1.5–2 Gy fractions daily for 5 days per week.

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What is brachytherapy?


The use of radiation sources in close contact with the tissue to provide intense exposure over a short distance to a restricted volume. Such techniques have been used to treat localized breast, prostatic and cervical carcinoma.




What does the degree of free radical generation depend on in tissue?







What are acute side effects to radiotherapy?

  • Sore skin
  • Fatigue
  • Nausea
  • Loss of appetite
  • Diarrhoea
  • Hair loss
  • Dysphagia
  • Temporary distrubance of fertility
  • Loss of libido
  • Stiff joints and muscles




What is a general rule of thumb with radiotherapy side effects?



Only get side effects in the area that you are treating - if symtpoms occuring in another system this is not normally caused by radiotherapy




What are chronic/long term side effects of radiotherapy?

Depends on area treated

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What is fractionation?



Delivery of the radiation dose in increments separated by at least 4–6 hours to try to exploit any advantage in DNA repair between normal and malignant cells.




What is hyperfractionation?

When more than one fraction per day is given. The treatment can also be accelerated, i.e. the total dose is given in a shorter overall time. For example a standard curative treatment taking 6.5 weeks can be accelerated so that the same dose is delivered in 5.5 weeks. Radiation dose is thus described by three factors:

  • Total dose in Gy
  • Number of fractions
  • Time for completion.




Are those who recieve radiotherapy alone a danger to others (i.e "radioactive")?



No - only with seeds




Which cancers are treated with primary curative raditherapy?


  • Retina
  • CNS
  • Skin
  • Pharynx/Larynx
  • Cervix/Vagina
  • Prostate
  • Lymphoma


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What cancers are treated with radiotherapy as adjuvant to primary surgery?


  • Lung
  • Breast
  • Uterus
  • Bladder
  • Rectum
  • Testis-sarcoma
  • Sarcoma

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How is radiotherapy used in a palliative capacity?

  • Pain relief - bone metastases
  • Reduction of headache/vomiting in raised ICP - from CNS metastases
  • Relief of obstruction of bronchus, oesophagus, ureter and lymphatics
  • Preservation of skeletal integrity from mets in weight-bearing bones
  • Reversal of neurological impairment from spinal cord or optic nerve compression by metastases




How does chemotherapy aid radiotherapy effectiveness?



Can radiosensitize tumours by damaging DNA




When would you use radiotherapy in as an emergency treatment?


  • Cord compression
  • Superior Vena Cava syndrome
  • Total/large atelectasis
  • Acute diffuse bleeding




If someone presented with cord compression, what medication would you start them on?



Dexamethasone - 16mg OD




What is important in terms of time to treatment for cord compression?



Keep interval between first onset of symptoms and 1st RT as short as possible. If treated within 24hrs, chance of complete remission. If treated within 72 hrs, chance of partial remisson




When would you perform urgent radiotherapy?


  • Unstable/painful bone mets
  • Brain mets
  • Cord compression without neuro defects
  • Inferior vena cava syndrome
  • Chronic bleeding with effect on Hb
  • Threat of obstruction