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Head and Neck > Radiation Oncology > Flashcards

Radiation Oncology Flashcards

1
Q

How does RT work?

A

Causes cell death by DNA damage

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2
Q

How does RT cause DNA damage?

A
  1. Damages DNA through direct interaction

2. Creates free radicals by hitting a water molecule that then damage DNA

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3
Q

What is RT dosed in fractions?

A
  • This allows time for normal tissue to repair its DNA

- Caveat is that tumor cells can also repair its DNA during the break

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4
Q

What determines whether a tumor is radiosensitive or radioresistant?

A
  1. Capacity for DNA repair

2. Oxygenation (under hypoxic conditions, free radicals can be scavenged by the hypoxia-induced acidic environment)

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5
Q

What is the most commonly used form of RT?

A

Photons

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6
Q

What is electron RT good for?

A

Skin cancer bc it has short depth of penetration (90% deposits energy w/in 2 cm)

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7
Q

How is RT produced?

A

Linear accelerator

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8
Q

What is 1 gray (Gy)

A
  • The amount of energy dose absorbed per unit mass
  • 1 J/kg
  • Equal to 100 rad
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9
Q

What is the typical total dose for adjuvant RT for HNC

A

60-66 Gy

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10
Q

What is the typical total dose for definitive RT for HNC

A

70-74 Gy

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11
Q

What is “radiobiologically equivalent dose”

A

It is the total dose of RT tolerated and is dependent on the fractionation chosen
-e.g. may be 30 Gy at 3 Gy fractions vs 45 Gy at 2 Gy fractions

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12
Q

What are the different fractionation patterns available?

A
  • Conventional/standard: QD Mon-Fri
  • Hypofractionation: QD
  • Accelerated fractionation or concomitant boost: once daily until last 12 days of Tx, then >QD
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13
Q

Which fractionation pattern results in the best local control?

A
  • Hyperfractionation or accelerated

- Risk is increased acute toxicity (but no significant increase in late toxicity)

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14
Q

What are the 2 ways to improve RT outcome?

A
  1. Hyperfractionation

2. Chemotherapy

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15
Q

When should you choose chemotherapy or hyperfractionation?

A
  • Only use hyperfractionation for pts who can’t get chemo and must be treated with RT alone
  • Chemo + hyperfractionation vs Hyperfractionation alone –> 70% vs 44% locoregional control
  • Chemo + standard fractionation had no difference in outcome vs chemo + hyperfractionation
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16
Q

Why should treatment breaks be avoided during RT?

A

Local failure increases when total treatment time (from surgery to completion of RT) exceeds 11 wks

17
Q

How does one reduce setup error between and during treatment?

A

Pts have a plastic mask to reproduce positioning

18
Q

What is the difference between

  • Gross tumor volume (GTV)
  • Clinical tumor volume (CTV)
  • Planning tumor volume (PTV)
A
  • GTV: The areas of actual tumor (this should be zero for adjuvant RT bc it follows surgery)
  • CTV: Areas at risk for harboring microscopic dz
  • PTV: an extra 3-10mm expansion on the CTV or GTV to account for errors in daily setup
19
Q

What is an “organ at risk (OAR)”?

A

-Normal tissue not involved w/ cancer that needs to be protected from RT (spine, parotid, mandible, pharyngeal constrictors)

20
Q

How much radiation can normal parotids take?

A

25 Gy to 50% of the gland

21
Q

How much radiation can the mandible take b4 getting ORN

A

70 Gy

22
Q

What is a dose volume histogram (DVH)?

A
  • A plot of percent volume of a structure vs the radiation dose.
  • Used to evaluate a radiation plan and determine if its safe for normal structures (OARs)
23
Q

Indications for adjuvant RT

A
    • margins
  • nodal dz
  • Large tumor size (T3, T4)
  • PNI
24
Q

Indications for adjuvant chemo

A
  • ECS

- + margins

25
Q

What is IMRT?

A
  • Intensity-modulated radiation therapy
  • Uses multiple radiation beams (beamlets) from different directions all of which can have different intensities of radiation
  • Allows radiation dose to “bend” around nl structures
  • Requires a multileaf collimator (MLC) but its cheap and easy to implement
26
Q

Advantage of IMRT?

A
  • Protect OARs whereas all structures in the 3D plans path would get high dose
  • Thus, reduces likelihood of late radiation-induced toxicity (xerostomia 39% vs 82% in conventional RT)
  • Reported improved QOL
27
Q

Disadvantages of IMRT?

A
  • Lot of planning required (not ideal for rapidly growing or bleeding tumors that need plans quickly)
  • More expensive
  • While the high-dose RT is very focused, a much broader area gets low-dose RT in comparison to 3D planning (can result in nausea from RT through the brainstem)
  • ?higher chance of radiation-induced cancer since broad low-dose volume
28
Q

When does acute toxicity from RT typically appear? plateau?

A
  • At the 2 wk mark

- Plateaus at 5-6 wk mark

29
Q

Acute toxicity from RT

A
  • PAIN (sore throat/mouth) from mucositis
  • Taste change
  • Loss of facial hair (in the field)
  • Skin irritation
  • Thick mucous
  • Dry mouth
30
Q

When do the acute toxicities from RT abate?

A
  • Skin breakdown heals in about 2 wks
  • Thick mucus resolves around 3-4 wks
  • Pain improves around 8-12 wks
  • Most can return to work at 8 wks post-RT
31
Q

What are the late toxicities from RT

A
  • Xerostomia
  • Taste change (resolves by 3 months usu)
  • Hypothyroidism
  • Neck fibrosis
  • Carotid artery stenosis
  • ORN
  • Dysphagia and aspiration
32
Q

What is the role of PET with RT

A

PET-based contouring allows for a significantly smaller target volume with good survival rates

33
Q

Why is proton radiation better than photon radiation?

A
  • Photons lose energy slowly as they travel through tissue so energy gets deposited in nl tissue in front of and behind tumor
  • Protons have very low energy loss until reach specific depth at which point all their energy is released (thus don’t affect nl tissue as bad)
34
Q

What is “Bragg peak”

A

The sudden peak in dose at a specific depth seen with proton radiation

35
Q

What is radiosurgery?

A
  • Requires very stringent immobilization and alignment techniques allowing for high doses of RT to be delivered in a highly conformal manner
  • Much higher doses over much fewer fractions

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