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On call > Amanda C's notes > Flashcards

Amanda C's notes Flashcards

1
Q

what does obliquity do?

A

-increase side scatter at dmax
-shift dmax toward surface
-decrease depth of penetration

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2
Q

virtual electron source point

A

intersection of backprojections

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3
Q

limit on horns

A

5% for 40x40 cm2

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4
Q

what cancers spread to the brain?

A

-small cell lung (prophylactic brain irradiation is standard)
-breast cancer

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5
Q

most common sites of mets

A

-brain, liver, lungs

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6
Q

whole brain RT

A

-used for palliation of mets or prophylactically
-30/10
-treat down to foramen magnum or bottom of C1 or C2, typically use POP
-treat brain and brainstem
-can fail at cribiform plate, which is underdosed to spare eyes
-include orbital apex since field since CSF circulates around the optic nerve

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7
Q

time for total dose delivery for 103 Pd vs 125I

A

56 days vs 200 days

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8
Q

physicist responsisbility in brachy QA

A

-check daily QA
-perform annual QA

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9
Q

3 things: MP role in brachy per AAPM TG56

A
  1. design facility that meets clinical needs
  2. develop and implement treatment delivery procedures
    3.ensure accuracy and safety of each individual treatment
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10
Q

regulatory compliance vs adequate QA

A

they are not the same thing

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11
Q

goal of QA program

A

maximize likelihood that each tx is administered consistently, that it realizes RO intent, and is executed wrt safety of patient and others

QA endpoints:
safety
positional accuracy (2 mm)
temporal accuracy (2%)
dose delivery accuracy: 3 % relative to existing air kerma strength, 2 % for dose calcs

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12
Q

what is needed to calculate workload in brachy?

A

air kerma strength and max source activity

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13
Q

BNC vs TNC connectors

A

BNC: twist- has inncer conductor to cable core to shield to jacket
TNC: screw - has inner conductor to inner shield to inner jacket to outer shield to outer jacket

male: center conductor is pin
demale: center conductor is socket hole

triax= bettter BW and rejection of interference than coax but more expensive

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14
Q

challenge with measurement for TBI

A

-large amt of cable in tx field
-chamber leakage and saturation become more problematic at lower TBI dose rates

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15
Q

max dose delivered before MU verification per TG-40

A

3-4 Gy

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16
Q

4 things to check before using survey meter

A

-battery
-voltage
-source responde (functional check on all ranges of survey meter)
-calibration date within last 12 months

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17
Q

class II prescribed equipment

A

-irradiatior that uses > 10^15 Bq of a nuc
-irradiatior that requires shielding and delivers at rates > 1 cGy/min at 1 m
-teletherapy machine
-particle accelerator that produces enegy < 50 MeV for particles with amu </= 4 amu or <15 MeV for particles with amu >/= 4 amu
-remote afterloader

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18
Q

DVH for rectum in IMRT vs brachy prostate tx

A

-volume of rectum receiving high dose is very small for brachy
-volume receiving low dose may be larger for brachy
-bladder is same effect but less pronounced (ie effect is bigger in rectum)

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19
Q

radiation reaching maze door

A

-primary scattered off walls
-primary scattered off patient
-leakage scattered off walls
-leakage transmitted

-for > 10 MV, above is negligible
-consider neutron capture gamma rays from maze at door
-consider neutrons at door

-for neutrons, TVL = 4.5 cm (E = 100 kV)
-for photons, TVL = 6.1 cm (E = 3.6 MeV)

20
Q

what do acceptance tests accomplish?

A

-specs in purchase order are fulfilled
-environment is free of radiation
-radiotherapy equipment is free of electrical hazards to staff and patients

21
Q

pratical suggestions for water scanning

A

-increments for Fs should be < 5 cm but are typically 2 cm
-make measurements to depth of 35 or 40 cm

22
Q

HDR prostate planning objectives

A

V100%> 95%
V200%<11%
Urethra D10%< 118%
Rectum V80%<0.5cc

23
Q

wedge material

A

lead, brass, steel

24
Q

who does RSO report to?

A

RSO reports to licensee and licensee reports to CNSC

25
Q

replacement RSO

A

-temporary replacement can only replace RSO for up to 60 days in 365 day period. If absence is longer, replacement must be certified
-regardless of length of absence, notify CNSC in writing of change within 15 days of change
-If RSO gone > 60 days but < 13 months, must review material
-If RSO gone > 13 months, must recertify
-Absence > 60 d requires replacement to be certified

26
Q

TG 66 CTDI QA tolerance

A

+/- 20 % of manufacturer spec

27
Q

TG66 laser tolerance

A

2 mm
gantry and wall
gantry and imaging plane

28
Q

TG66 couch motion tolerance

A

1 mm, 1mm tolerance for couch indexing as well

29
Q

TG66 gantry tilt accuracy

A

1 degree

30
Q

TG 66 scan localization accuracy

A

< 1 mm

31
Q

TG66 CT number accuracy

A

0+/- 5 HU for water (daily)
monthly check more materials
annually check RED curve

32
Q

TG 66 fiel uniformity spec

A

within 5 HU

33
Q

TG66 spatial integrity tolerance

A

< 1 mm
checked daily and monthly

34
Q

typical measured dose rate outside a barrier

A

Gammas:
primary barrier: 20 uSv/h
secondary barrier: 2 uSv/h
door open: 50 uSv/h
door closed: 2 uSv/h

Neutrons
primary barrier: 10 uSv/h
secondary barrier: 10 uSv/h
door open: 600 uSv/h
door closed: 20 uSv/h

35
Q

typical dose rate allowed for wipe test for HDR source change

A

15 mRem

36
Q

positional accuracy for brachy HDR

A

1mm
source strength 1 %

37
Q

PDI vs PDD

A

PDI = ionization released in air
PDD= dose deposited to water

38
Q

isodose line bulding in electron beams

A

E > 15 MV- <30% bulges out and >80% constrict
E<15 MV- all isodose lines bulge out, especially < 30%

39
Q

what to consider for IGRT shifts

A

PTV margin
site
modality

40
Q

wedge factor range

A

0.6 to 0.3 for 15-60 degree wedge

41
Q

review tolerances in TG142

A
42
Q

OAR expected values at commissioning

A

within 0.02 (think symmetry)

43
Q

criteria for beam matched beams

A

dmax position +/- 1 mm
% PDD at 10 cm- +/- 0.5%
dose surrogate measured at or near surface +/- 5 %

44
Q

equivalent field for a shielded field

A

square root of (equivalent square field size ^2 * fraction unshielded)

45
Q

activity of old HDR source when removed

A

4 Ci

46
Q

equation to use to calculate surface contamination for wipe test

A

C= ((cpm(gross)-cpm(background))/efficiency)*100cm2/detector area

47
Q

when to do leak tests?

A

> 50 Mq
must be able to detect 200 Bq
-if stored > 12 months, check before use
every 2 years if stored
if damaged
every 12 months if inside class II equipment, every 6 months if not inside device

On call (23 decks)

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