Tx planning - techniques

Question 1

Factors that affect hot spots for parallel opposed beam

Answer 1

1. as Pt thickness increases, hot spot increases
2. as E decreases, hot spot increases
3. as FS increases, hot spot decreases

Question 2

What energies are optimal for 15cm separation

Answer 2

Co-60 and 4-6 MV

Question 3

What energies are optimal for 20cm separation

Answer 3

10 MV or higher

Question 4

Where are the hot spots of a POP beam found?

Answer 4

at the surface of each beam entry point

Question 5

What is Integral Dose

Answer 5

Measure of total energy absorbed in the treated volume

Question 6

Define Integral Dose mathematically

Answer 6

ID = mass(kg) x dose(rad)

Question 7

Integral Dose relationship to energy for parallel opposed beams

Answer 7

As E increases, Integral dose decreases

Question 8

List from tx techniques from highest to lowest in terms of how much integral dose is produced:

Answer 8

in general - VMAT > IMRT > 3D > Proton

Question 9

Between a physical and dynamic wedge, which type of gives more dose, why?

Answer 9

Physical; more scatter due to being in path of beam longer

Question 10

Advantages of IMRT: Forward Planning over Inverse Panning:

Answer 10

1. simpler intensity patterns
2. Easier to deliver
3. Easier to verify
4. Easier to calculate MU’s (able to use standard 3D TPS)

Question 11

Advantages of IMRT: Inverse Planning over Forward Planning:

Answer 11

1. Intensity Patterns (better distribution - not necessarily more uniform)
2. Less dose to critical structures

Question 12

For IMRT planning, what is the typical number of fields used?

Answer 12

5, 7, or 9

Question 13

What energies should be used for IMRT, why?

Answer 13

6 MV or 10 MV - tighter penumbra, better coverage, no neutron shielding, no neutron pt dose

Question 14

What energies should not be used for IMRT why?

Answer 14

energies over 10 MV - neutron production

Question 15

IMRT causes more or less dose heterogeneity?

Answer 15

More

Question 16

Advantages of Compensator based IMRT:

Answer 16

1. better resolution than MLC
2. Less MU required
3. Less pt dose (outside field)
4. Larger FS
5. Tx planning may be easier

Question 17

Disadvantages of Compensator based IMRT:

Answer 17

1. Slower delivery (RTTs enter room for each field)
2. Must be fabricated
3. Accounting for transmission

Question 18

What factors influence dose to contralateral breast?

Answer 18

1. distance away from beam edge
2. Use of HPP (increased dose if Cerro)
3. Use of wedge (Medial get 3x more than lat)
4. Alignment of Tangents
5. Port film

Question 19

What factors do not influence dose to contralateral breast?

Answer 19

1. Gantry angle
2. lung density
3. breast volume

Question 20

Ways to limit dose to contralateral breast

Answer 20

1. Don’t use Cerro HBB,
2. align tangents,
3. decrease wedge angle (or only use lateral wedge;
4. Use 2.5cm thick Pb shield
5. Limit collimator for port films

Question 21

Contralateral breast dose limit to women < 45 years old

Answer 21

200 cGy

Question 22

When is TBI utilizied

Answer 22

as a radioimmuno-suppressant prior to bone marrow transplant

Question 23

Common TBI Rx

Answer 23

1. 5-8 fx
2. 1000 - 1200cGy
3. Rx to umbilicus
4. Lung blocks used post 600-800cGy
5. Dose Rate of 5 - 10 cGy/min
6. SSD = 350cm and 450cm

Question 24

Common TBI techniques:

Answer 24

1. AP/PA
2. Laterals
3. Sliding tables

Question 25

Physics goals of TBI:

Answer 25

1. TPR: +-4% 2. ISL: +-6% 3. OAR: +-5%

Question 26

For TBI inhomogeneity worsens with:

Answer 26

1. Lateral technique 2. Decreased E 3. Increased Pt thickness 4. Decreased distance (SSD)

Question 27

For TBI, skin dose increases with:

Answer 27

1. FS 2. Distance (increased SSD) 3. Spoilers (**want this for pediatric pts)

Question 28

When is IORT(e') typically used?

Answer 28

originally for pancreas, now breasts

Question 29

Typical Rx for IORT(e')

Answer 29

1. Single fx 2. 1000 - 2000 rad 3. 6 MeV - 20 MeV

Question 30

For IORT(e'), use high or low Z material to collimate beam?

Answer 30

low, to not produce bremsstrahlung

Question 31

A decrease in width will improve/worsen flatness of beam for IORT(e')

Answer 31

worsen

Question 32

When is Total Skin Irradiation used (TSCT)?

Answer 32

for Mycosis Fungoides, and t-cell lymphoma

Question 33

Common Rx for TSCT?

Answer 33

1. 3-7 Mev 2. SSD = 300 to 400cm 3. 6-field tx 4. dose prescribed to 1cm 5. Do not exceed bone marrow tolerance

Question 34

For SRS, a large volume gets a smaller/larger dose?

Answer 34

smaller

Question 35

At what isodose line is Gamma Knife Rx'd?

Answer 35

50%...want a 200% hot spot

Question 36

At what isodose line is SRS on LINACs Rx'd

Answer 36

90%

Question 37

For SRS is penumbra better with Gamma Knife or LINAC

Answer 37

Gamma Knife

Question 38

For SRS, additional field/arcs will effect penumbra how?

Answer 38

worsens

Question 39

For SRS, what will an overlap of beams cause?

Answer 39

inhomogeneities (hot spots)

Question 40

How are dose profiles measured for SRS

Answer 40

Radiochromatic film

Question 41

How is output measured for SRS

Answer 41

small ion chamber or film

Question 42

For SRS, what is a shortcoming in regards to output measurements with chambers?

Answer 42

volume averaging

Question 43

What kind and how many sources are present on a gamma knife unit

Answer 43

201 Co-60 Sources - 6000Ci

Question 44

What is the size of the isocenter for a gamma knife unit

Answer 44

.3mm

Question 45

What is the gold standard of radiosurgery

Answer 45

Gamma Knife

Question 46

Gamma Knife is governed by what body

Answer 46

NRC

Question 47

Daily tests of Gamma Knife include:

Answer 47

1. Interlocks 2. Intercom 3. Radiation Monitors - Geiger Muller

Question 48

Monthly Gamma Knife tests:

Answer 48

1. Timer reproducibility 2. Timer linearity 3. Timer Accuracy 4. Timer Error 5. Mechanical Alignment 6. Output (for 18mm collimator)

Question 49

Semi-Annual Gamma Knife tests:

Answer 49

Leak tests

Question 50

Annual Gamma Knife tests:

Answer 50

1. Output for all Helmets 2. Mechanical Iso - Rad iso 3. Dose profiles

Question 51

Most accurate SRS delivery by LINAC is ____

Answer 51

cones, especially for lesions < 1mm

Question 52

Range of SRS cone diameters:

Answer 52

2.5mm to 50mm

Question 53

Typical number of arcs for LINAC SRS:

Answer 53

4-6

Question 54

Energies used for LINAC SRS:

Answer 54

< 10MV

Question 55

Typical Rx isodose line for CyberKnife:

Answer 55

70-80%

Question 56

SADs used for brain and body with CyberKnife:

Answer 56

80 SAD for brain; 90-100 SAD for body

Question 57

What is the name used to describe the fixed ranged of heavy charged particles?

Answer 57

Bragg Peak

Question 58

E range of Proton machines

Answer 58

30-250 MeV

Question 59

How is the Bragg Peak spread out (SOBP)

Answer 59

using multiple energies, or by a modulator

Question 60

Whats the purpose of an aperture in Proton therapy

Answer 60

to shape the beam

Question 61

Features of the Proton Head design:

Answer 61

Double Scattering Head: uniform scan or pencil beam scan

Question 62

How are protons accelerated

Answer 62

Cyclotrons or Acclerators

Question 63

What is the RBE of a proton, where is it largest?

Answer 63

1.1; can vary with E (depth) - larger at distal end of Bragg Peak

Question 64

Largest inhomogeneity corrections are for what kind of energy

Answer 64

Proton Energy

Question 65

How is Neutron Contamination associated with Proton Energy

Answer 65

1. Increases with use of Modulator 2. Increases with use of collimator 3. Increases with higher E 4. Increases if Mod/Coll is closer to pt

Question 66

Skin dose of Proton Beam is _____ than 15X or 18X

Answer 66

slightly higher

Question 67

For proton beam lateral dose penumbra is ______ than 15X or 18X

Answer 67

Larger