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Intro to Medical Dosimetry > Hand Calc > Flashcards

Hand Calc Flashcards

1
Q

How does MU change when TMR change

A

as TMR decreases, MU increases

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2
Q

How does TMR change when calc point depth changes

A

as depth increases, TMR decreases

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3
Q

Whole brain irradiation- patient selection

A

metastatic diseases: frequent breast, lungs, melanoma, sarcoma, CNS

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4
Q

Goal of treatment (whole brain)

A

palliation of symptoms
quality of life
prolonging survival
could be prophylactically (PCI)

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5
Q

what us treating prophylactically

A

PCI given to small cell lung cancer a head of time because patients have brain cancer frequently. when treating prophylactically, we treat the areas that we think will develop cancer later on, so we treat in advance with lower dose (24 Gy in 12 fx)

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6
Q

whole brain immobilization

A

supine, exact bar, reg.h. “B”, pad on table, mask, arms across chest holding A-bar, knee wedge

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7
Q

where is the isocenter placed for whole brain

A

mid- separation

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8
Q

why is isocenter placed at mid separation

A

for homogeneous dose distribution, if the isocenter is off, we will have a hot and cold plan

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9
Q

Conventional Whole brain sim

A
  1. Fluoroscopic x-ray will be taken of treatment field
  2. Doctor draw field (wax pencil in scan or digitally)
  3. Blocking created (cerrobend or MLC)
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10
Q

Virtual whole brain sim (more realistic)

A
  1. Pt receives CT scan
  2. Axial slices imported into treatment planning computer
  3. Dr draws field on TPS
  4. MLCs for blocking
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11
Q

Whole Brain Fields gantry angles

A

Opposed laterals

tilted anterior

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12
Q

why do we set beam angles tilted anterior and opposed laterals (obliged) for whole brain

A

TO LIMIT DIVERGENCES TO THE LENSES

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13
Q

How to change gantry angles to limit divergence for whole brain

A

ex: if beam 1 is at 278 (270+8), beam 2 will be at 82 (90-8)

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14
Q

where is interior border usually placed for whole brain

A

below C1, or could be below C2 as well but rare

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15
Q

why is the interior border always placed at C1 or C2

A

patients are usually here for metastatic cancer, chances are they will come back for more treatment. When that happens, we want to know where we stopped at the previous irradiation so that we can avoid overlapping and overtreating that area

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16
Q

Superior and lateral borders incorporate flash for whole brain, why?

A

patient’s set up can be different each day. flash ensures we have the whole skull covered every treatment. Also, if the field borders are against the head, we do not have adequate dmax to tissue

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17
Q

critical structures to consider when treating whole brain

A

face

lenses

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18
Q

what happens if we dont consider face and lenses for whole brain irradiation

A

radiation induced cataract that can develop in 20 years

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19
Q

block position for whole brain

A

“one thumb length” away from target

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20
Q

Whole brain palliative prescription

A

30 Gy for 10 fx

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21
Q

Whole Brain PCI fractionation

A

24 Gy in 12 fx

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22
Q

whole brain calculation

A

heterogeneous calculation if imported into TPS

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23
Q

what is the normalization of whole brain

A

100% to iso, no further optimization needed

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24
Q

what happens when you normalize down

A

plan gets hotter

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25
Q

what happens when you normalize up

A

plan gets cooler

26
Q

what do you do when you want to increase coverage

A

normalize down (hotter)

27
Q

what is MDACC normalization percentage allowed

A

95-105%

whole number or 0.5

28
Q

no simulation?

A
  • pt could be seen on weekend by physician
  • therapist turns collimator to block critical structures or hand block
  • homogeneous calculation done
  • calc verified by dosimetrist/physics on monday
29
Q

MU tolerance

A

3% or 2 MUs

30
Q

what does homogeneous calculation mean

A

not considering different materials, treating as if were treating water

31
Q

heterogeneous

A

considering different kinds of materials such as tissues bones, etc…

32
Q

purpose of wedge

A

wedges are designed for breasts
they compensate for missing tissue/ manipulate the iso line to make it look like it pushes dose heel to toe (they dont actually push dose)

33
Q

why do we have MLC on superior part of field border

A

to make the superior border nondivergent, if not, the border would diverse out

34
Q

what is displacement

A

how far the calc point is from central axis in y-direction

35
Q

why should electron be at 90 degree (appositional) to skin surface in breast

A

if at an oblique angle, can have hot spots and cold spots

36
Q

4 calc point rules

A
  1. inside the field
  2. at least 2 cm from jaw edge
  3. must be tissue equivalent material
  4. cannot be in build up region (really close to surface)
37
Q

why does the calc point have to be inside the field

A

if not, TPS will push MU to that point

38
Q

why does calc point have to be at least 2cm from jaw edge

A

oe else, we dont have full buildup, dose is not accurately reflected

39
Q

why must calc point be in tissue equivalent material

A

cant be in bone or air, or else we dont have adequate buildup

40
Q

why cant calc point be in buildup region

A

cant have dmax

pinnacle doesnt model the buildup region well

41
Q

4 rad onc emergencies

A
  1. spinal cord compression
  2. uncontrolled bleeding
  3. extreme cases of pain due to bone mets
  4. Superior vena cava syndrome (if tumor compressses on SVC, pt can die)
42
Q

Palliative Spine irradiation goal of treatment

A
  • palliation of symptoms
  • quality of life
  • could be one of the rad onc emerg
43
Q

Palliative Spine irradiation patient selection

A

metastatic diseases (breast, lung, melanoma, CNS)

44
Q

when would a patient receive no sim for palliative spine treatment

A

if they come on the weekend

45
Q

can you use MLCs without sim

A

yes, you can digitize in Mosaiq

46
Q

Vertebral column anatomy

A

C1-C7
T1-T12
L1-L5
S1-S5

47
Q

where is T12

A

floating rib

48
Q

palliative spine single PA field benefits

A

reproducible
efficient to calc, set up, and treat
cost efficient for palliative care

49
Q

palliative spine single PA field negatives

A

high surface dose

not optimized dose distribution

50
Q

palliative spine AP/PA fields benefits

A

reproducible
efficient to calc, set up, and treat
cost efficient for palliative care

51
Q

palliative spine AP/PA field negatives

A

not fully optimized dose distribution

possible excessive dose from entrance from AP beam

52
Q

palliative spine AP/PA field energy choice

A

AP/Pa- both 6X
AP/PA- both 18X
PA-6X and AP-18X- very prevalent

53
Q

why is PA-6X and AP-18X the optimal energy choice for AP/PA spine treatment

A

higher energy, higher penetration

54
Q

palliative spine Rt and Lt Laterals benefits

A

reproducible

efficient to calc, set up, and treat

55
Q

palliative spine Rt and Lt Laterals negatives

A

suboptimal dose distribution

possibly added complication and cost of wedges

56
Q

where in the body would you treat the spine with opposed laterals instead of AP/PA

A

cervical spine- spare mandible

57
Q

palliative spine wedge pair benefits

A

reproducible
efficient to calc, set up, and treat
slightly optimized dose distribution

58
Q

palliative spine wedge pair negatives

A

added complications of wedges in calc and treatment

added cost of wedges

59
Q

Palliative Spine prescription

A

usually 30 Gy in 10 fx

60
Q

Palliative spine that deliver one large dose to a bone met that is causing extreme pain (8 Gy or 12 Gy)

A

“rapid” or “one shot”

61
Q

what is the difference between heterogeneous and homogeneous calc

A

heterogeneous: looks at effective depth
homogeneous: looks at reference depth (physical/ geometric depth)

62
Q

Palliative Spin optimization

A

based on doctor reference

Intro to Medical Dosimetry (1 decks)

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