283 - Radiation Oncology

Question 1

How does fractionating radiation allow for better cell kill and sparing of normal tissues?

Answer 1

• Spares normal tissue
  
  • Allows normal tissue to repair itself, re-populate
  • Often, malignant cells do not have these repair mechanisms
• Better cell kill
  
  • Reassortment: Allows cells in radio-resistant phase to get to a more sensitive phase before the next tx
  • Reoxygenation: Tumors that are hypoxic don’t respond as well; oxygenation is important for indirect killing (Ionizing radiaton -> free radical generation -> DNA damage)

Question 2

What is the mechanism by which radiation induces a biologic eent?

Answer 2

• Direct (~1/3 of damage)
  
  • Ionizing radiation causes DNA breaks
• Indirect (~2/3 of damage)
  
  • Ionizing radiation generates free radicals, which cause DNA breaks
  • Oxygen is important for this!

Question 3

What is brachytherapy?

When is it indicated?

Answer 3

Focal delivery of a radioactive isotope via implant for the purpose of cancer therapy

Example: curative therapy in locally advanced cervical cancer

Thank you @Lauren Smith and PJDJ deck!

Vs. external beam = shooting x-rays or gamma rays at the tumor from an external source

Question 4

What is “gamma knife” radiation?

When is it used?

Answer 4

Gama knife = stereotactic radiosurgery. Uses advanced image guidance

Used when there are small, well-defined targets (not for microscopic spread)

Often used for intra-cranial treatment (single fraction)