Principles of Radiotherapy

Question 1

principles of radiation therapy

Answer 1

• minimize therapy
• minimize negative impact on quality of life
• improve quality of life
• maximize impact on quality of life (cure or remission)
• improve outcomes

Question 2

we do not want to overtreat patient because of ___

Answer 2

toxicity, time, and costs

Question 3

function of improving the quality of life

Answer 3

• for patients that need palliation

- organ and function preservation

Question 4

2 types of radiation

Answer 4

particulate radiation and electromagnetic radiation

Question 5

type of radiation dictates ___

Answer 5

how the radiation is used for treatment

how to protect the radiation workers

Question 6

2 subtypes of particulate radiation

Answer 6

alpha: can be stopped by a thin piece of paper
beta: need aluminum shielding to protect workers

Question 7

electromagnetic radiation used for treatment

Answer 7

gamma radiation (needs a thick concrete block for protection)
- shorter wavelength, higher frequency, higher energy

Question 8

radiations that come from machines

Answer 8

• linea accelerator (LINAC) !!!
• tomotherapy
• halcyon
• cyberknife
• proton machines

Question 9

types of radioactive materials

Answer 9

• cobalt: ebrt, bachytherapy, gamma knife
• iridium: brachy (gyne)
• iodine: brachy (prostate)

Question 10

classification of radiotherapy according to treatment type

Answer 10

• external beam radiotherapy

- brachytherapy

Question 11

most common machine used for radiotherapy

Answer 11

linear accelerator (linac)

Question 12

principle of linac

Answer 12

• can produce high energy photons (electromagnetic type of radiation, for deeper tumors)
• electrons (particulate type, for superficial tumors)

Question 13

benefits of linac

Answer 13

• more uniform beam characteristics
• more precise field shaping
• more precise delivery

Question 14

parts of the linac

Answer 14

• gantry + stand = where radiation is produced
• treatment couch
• table 1

Question 15

planning techniques for radiotherapy

Answer 15

• 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

Question 16

what is vmat

Answer 16

• radiation can be shut out of machine while moving in 360 degree arc
• quicker treatment delivery and improved dose homogeneity

Question 17

advantages of stereotactic techniques

Answer 17

• very high tumor dose
• almost negligible dose to organs at risk
• srs, sbrt or sabr
• gamma knife, linac, tomotherapy, cyberknife

Question 18

machines that use stereotactic techniques

Answer 18

gamma knife!!, linac, tomotherapy, cyberknife

Question 19

3 most common extracranial cancer primaries or locations

Answer 19

lung, liver, bone

Question 20

common uses of brachytherapy

Answer 20

body cavities (gyne, npca) or close to surface (prostate, sarcoma, tongue, lip, breast)

Question 21

two actions in radiation therapy

Answer 21

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

Question 22

radiation used in photon radiation

Answer 22

indirect action

Question 23

t/f cancer cells are better able to repair direct actions

Answer 23

false, indirect actions, due to more single stranded breaks of the dna compared to double strand breaks

Question 24

what is fractionation

Answer 24

• irradiating small doses over many treatments
• takes advantage of minimally improved survival of normal tissue at smaller doses
• amplified over many treatments

Question 25

4 rs of fractionated radiation

Answer 25

- repair - reassortment or redistribution - reoxygenation - repopulation

Question 26

principle of reassortment or redistribution

Answer 26

radiation causes cells to accumulate in certain phases of the cycle (g2 and m phase)

Question 27

principle of reoxygenation

Answer 27

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

Question 28

principle of repopulation

Answer 28

normal cells are better at repopulation after radiation

Question 29

type of radiosurgery that has very high radiation doses resulting in ablation

Answer 29

stereotactic / srs / sbrt / sabr

Question 30

what are radiation protectors

Answer 30

agents that allow normal tissues to tolerate radiation more

Question 31

what are radiation sensitizers

Answer 31

agents that make the cancer more sensitive to radiation

Question 32

most common radiation sensitizers

Answer 32

chemo: 5fu, platinum analogs (cisplatin), gemcitabine, taxanes targeted agents: egfr inhibitors!!, farnesyltransferase inhibitors, cox2 inhibitors, histone deacetylate inhibitors, hsp90 inhibitor

Question 33

ability of localized radiation to trigger systemic antitumor effects

Answer 33

abscopal effect | - molecules released after radiation improve defenses against cancer

Question 34

timing of toxicity

Answer 34

acute less/= 90 days of radiation | late >90 days

Question 35

radiotherapy can be curative for __

Answer 35

prostate cancer (and other urologic ca), breast ca, h&n ca, gyne ca (cervix), pediatric, cns, skin

Question 36

what is definitive rt

Answer 36

- radiotherapy is the main treatment with or without systemic agent - objective is cure

Question 37

what is concurrent rt

Answer 37

- rad given with systemic agent (chemo, targeted agent, immuno)

Question 38

what is neoadjuvant rt

Answer 38

- rad given prior to surg with/without systemic agent | - goal is to improve surgical results

Question 39

what is adjuvant rt

Answer 39

- rad given after surgery +/- systemic agent | - goal is to lower chance of recurrence

Question 40

methods to simulate and plan treatment

Answer 40

- ct scan - fusion of images (software) - contouring

Question 41

volumes in contouring

Answer 41

- 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)

Question 42

principle of proton therapy

Answer 42

- there is sudden increase in deposition then no more after | - ideal to have less dose to organs at risk after the dose is given