Principles of Radiotherapy Flashcards
principles of radiation therapy
- minimize therapy
- minimize negative impact on quality of life
- improve quality of life
- maximize impact on quality of life (cure or remission)
- improve outcomes
we do not want to overtreat patient because of ___
toxicity, time, and costs
function of improving the quality of life
- for patients that need palliation
- organ and function preservation
2 types of radiation
particulate radiation and electromagnetic radiation
type of radiation dictates ___
how the radiation is used for treatment
how to protect the radiation workers
2 subtypes of particulate radiation
alpha: can be stopped by a thin piece of paper
beta: need aluminum shielding to protect workers
electromagnetic radiation used for treatment
gamma radiation (needs a thick concrete block for protection) - shorter wavelength, higher frequency, higher energy
radiations that come from machines
- linea accelerator (LINAC) !!!
- tomotherapy
- halcyon
- cyberknife
- proton machines
types of radioactive materials
- cobalt: ebrt, bachytherapy, gamma knife
- iridium: brachy (gyne)
- iodine: brachy (prostate)
classification of radiotherapy according to treatment type
- external beam radiotherapy
- brachytherapy
most common machine used for radiotherapy
linear accelerator (linac)
principle of linac
- can produce high energy photons (electromagnetic type of radiation, for deeper tumors)
- electrons (particulate type, for superficial tumors)
benefits of linac
- more uniform beam characteristics
- more precise field shaping
- more precise delivery
parts of the linac
- gantry + stand = where radiation is produced
- treatment couch
- table 1
planning techniques for radiotherapy
- 2d/conventional (xray): most simple
- conventional ct = uniform intensity, square or rectangular
- 3d conformal radiotherapy (3dcrt) = uniform intensity, irregular shapes
- imrt = varying intensity, irregular shapes, higher conformity
- igrt = changes per change in size, shape, and location of tumor
what is vmat
- radiation can be shut out of machine while moving in 360 degree arc
- quicker treatment delivery and improved dose homogeneity
advantages of stereotactic techniques
- very high tumor dose
- almost negligible dose to organs at risk
- srs, sbrt or sabr
- gamma knife, linac, tomotherapy, cyberknife
machines that use stereotactic techniques
gamma knife!!, linac, tomotherapy, cyberknife
3 most common extracranial cancer primaries or locations
lung, liver, bone
common uses of brachytherapy
body cavities (gyne, npca) or close to surface (prostate, sarcoma, tongue, lip, breast)
two actions in radiation therapy
direct action: radiation itself breaks the dna bonds
indirect action: radiation interacts with water to form hydroxyl groups, oxygen is important to make the damage more permanent
radiation used in photon radiation
indirect action
t/f cancer cells are better able to repair direct actions
false, indirect actions, due to more single stranded breaks of the dna compared to double strand breaks
what is fractionation
- irradiating small doses over many treatments
- takes advantage of minimally improved survival of normal tissue at smaller doses
- amplified over many treatments
4 rs of fractionated radiation
- repair
- reassortment or redistribution
- reoxygenation
- repopulation
principle of reassortment or redistribution
radiation causes cells to accumulate in certain phases of the cycle (g2 and m phase)
principle of reoxygenation
tumors reoxygenate after radiation but when tumors reach a certain size, those cells farther away from the vessels are poorly oxygenated because diffusion of oxygen is limited
principle of repopulation
normal cells are better at repopulation after radiation
type of radiosurgery that has very high radiation doses resulting in ablation
stereotactic / srs / sbrt / sabr
what are radiation protectors
agents that allow normal tissues to tolerate radiation more
what are radiation sensitizers
agents that make the cancer more sensitive to radiation
most common radiation sensitizers
chemo: 5fu, platinum analogs (cisplatin), gemcitabine, taxanes
targeted agents: egfr inhibitors!!, farnesyltransferase inhibitors, cox2 inhibitors, histone deacetylate inhibitors, hsp90 inhibitor
ability of localized radiation to trigger systemic antitumor effects
abscopal effect
- molecules released after radiation improve defenses against cancer
timing of toxicity
acute less/= 90 days of radiation
late >90 days
radiotherapy can be curative for __
prostate cancer (and other urologic ca), breast ca, h&n ca, gyne ca (cervix), pediatric, cns, skin
what is definitive rt
- radiotherapy is the main treatment with or without systemic agent
- objective is cure
what is concurrent rt
- rad given with systemic agent (chemo, targeted agent, immuno)
what is neoadjuvant rt
- rad given prior to surg with/without systemic agent
- goal is to improve surgical results
what is adjuvant rt
- rad given after surgery +/- systemic agent
- goal is to lower chance of recurrence
methods to simulate and plan treatment
- ct scan
- fusion of images (software)
- contouring
volumes in contouring
- gross tumor volume: seen or palpable tumor
- clinical target volume: areas where there can be microscopic ca extension
- planning target volume: isotopic margin or expansion to compensate for the possible setup uncertainty
- internal target volume: not always done, but for when tumor moves (lung or liver)
principle of proton therapy
- there is sudden increase in deposition then no more after
- ideal to have less dose to organs at risk after the dose is given
