prostate

Question 1

T2 values of cancerous and non-cancerous prostate

Answer 1

non-cancerous = 134 ms

cancerous ~ 80 ms

Question 2

what are typical prostate fractionations

Answer 2

60/20 (hypo)
36/6 over 6 weeks 9ultra-hypo)
44/20 with SIB of 60/20 to prostate and seminal vesicles
66/33 prostate bed only, 52/33 pelvic 
78/39 and 70/35- conventional
lymph nodes
HDR:
15 Gy HDR + 37.5/15 or 46/23

Question 3

PTV for prostate

Answer 3

7 mm

Question 4

how to deal with prosthetic hip?

Answer 4

• use MV energy images
• use avoidance structures so you don’t enter through prosthetis
• contour the artefact in the image- fill missing data with correct HU
• use lower energy as higher energy = more backscatter from prosthetic
• transmission through prosthetic increases with beam hardening- average transmission for titanium is ~ 80 %
• scattering from prosthesis can help compensate for increased attenuation; more significant for larger field size
• use TLDs to confirm exit dose (and potentially confirm assumptions made about the prosthesis)
• use compensators to push high intensity beams through prosthesis only

Question 5

uen/p and density of titanium

Answer 5

at 6 MV, uen/p is 0.02 cm2/g (similar to water), but density of titanium is 4.5 X that of water

Question 6

How is matching performed for intact prostate vs prostate bed?

Answer 6

• CTV for intact prostate

- clips for prostate bed

Question 7

How can you potentially reduce PTV margin on rectal side of prostate?

Answer 7

-Match to anterior rectal wall

Question 8

bladder/rectum status rules for prostate

Answer 8

• 2 of 2 and 3 of 5
• underfull bladder is less than 2/3 full in sagg view. At SIM, top of bladder should be 3 cm superior to top of femoral heads- more than 5 cm is overfull bladder.
• rectum is assessed on axial view - action taken if rectum diameter 10 mm larger than at time of SIM

Question 9

define location of pelvic nodes for prostate treatments

also where are seminal vesicles

Answer 9

distal common iliacs
internal and external iliacs
obturator
seminal vesicles sort of a pancake between prostate and bladder in axial view, between prostate and rectum in coronal view
(look at prostate treatment images for anatomy)

Question 10

describe ways to improve rectal sparing

Answer 10

• tuning structure
• intra-rectal balloon (keeps size and position of rectum consistent)
• Space Or- gel deposited between prostate and rectum to keep them separate
• match to anterior rectal wall so you can decrease PTV on post side

Question 11

what is CTV margin in prostate

Answer 11

CTV = GTV

Question 12

what is smallest PTV margin possible?

Answer 12

1 mm based on congruency of isocentres

also should probably consider some error in contouring

Question 13

explain calypso

Answer 13

uses implanted transponders- emit RF waves which are used to align the prostate area

Question 14

OAR constraints for prostate treatment, 2 Gy vs 3 Gy fractions

Answer 14

Structure	2 Gy fractions	3 Gy fractions
Rectum 50 %	50 Gy	43.5
Rectum 25 %	65 Gy	52.8 (30 %)
Rectum V 20%	70 Gy	
Rectum V15%	75 Gy	57 Gy
Rectum V 3%		60 Gy
Bladder Dmax	65 Gy	
Bladder V50%	65 Gy	40.8Gy
Bladder V35 %	70 Gy	
Bladder V25%	75 Gy	48.6 Gy
Bladder V15%	80 Gy	
Bladder V5%		60 GY
Small bowel 2 CC		46.2 Gy
Small bowel 120 cc	15 Gy	
Small bowel 195 cc	45 Gy	45 Gy
Penile bulb mean dose	50 Gy	52.5 Gy

Question 15

Bowel radiation toxicities and grades

Answer 15

Grade 2- diarrhea, bleeding
grade 3 - obstruction, alceration, necrosis
grade 4 - organ death

Question 16

describe TNM staging system

Answer 16

T = size and extent of main tumour (TX is main tumour cannot be measured, T0 is main tumour cannot be found)
N = regional lymph nodes (NX, N0, N1, N2, N3)
M = distant mets (MX, M0, M1- M1 is cancer has spread)

Question 17

describe different ways of normalizing a 3DCRT plan and how this would affect “heat” of plan

Answer 17

• to a point
• to dmax of each beam (this would reduce the hot spots on the lateral fields of a 4-field box for prostate)
• to target mean
• to max (makes plan cool)
• to min (makes plan hot)
• at field isocenter
• at reference point

Question 18

D’amico risk criteria for prostate

Answer 18

low risk = gleason score < 6, T1C - T2a, PSA < 10 mg/mL
intermediate = gleson 7, T2b, PSA 10-20
high =gleason > 8, T2C, PSA > 20

Question 19

different tumor stages in prostate cancer

Answer 19

T1c = tumor identified on biopsy
T2a = tumor on , 1/2 of one lobe
T2B = tumor on > 1/2 of one lobe
T2C = tumor on both lobes

Question 20

what is gleason score

Answer 20

grade based on how much the cells in cancerous tissue look like normal prostate tissue

• lower score is better
• 4+3 = 7 is higher risk than 3+ 4 = 7 because grade 4 is most common

Question 21

what is PSA

Answer 21

prostate specific antigen

-often elevated in prostate cancer

Question 22

what is PSMA?

Answer 22

specific PET tracer for prostate cells, specifically those that become resistant to hormone meds
Ga 68 PSMA 11

Question 23

what is meant by castrate resistant?

Answer 23

prostate cells become resistant to the testosterone suppressant hormone drugs after 3-5 years

Question 24

why do brachy? it can make urinary symptoms worse.

Answer 24

brachy + EBRT = better outcome than EBRT alone

Question 25

why doesn’t LDR need EBRT like HDR?

Answer 25

With seed LDR brachy- don’t need EBRT because it is over a longer period. With HDR, need EBRT. This is because with only 1 fraction, some of the cells will not be in the sensitive phase and thus will not be killed

Question 26

Prostate cancer and hypofractionation

Answer 26

• low alpha/beta

- use gold fiducials, calypso for hypofractionation

Question 27

where is penil bulb?

Answer 27

inferior to prostate

Question 28

pubic arch interference

Answer 28

if prostate > 50 cc, then brachy likely cannot be used due to pubic arch interference

Question 29

isodoses to keep out of bladder and rectum

Answer 29

50% for bladder

30% for rectum

Question 30

androgen deprivation therapy

Answer 30

block androgen receptors or production

Question 31

prostarte 4-field box- where would you use higher energy beams?

Answer 31

lat beams because the patient thickness is usually larger in that direction

Question 32

why 6 field box vs 4 field box?

Answer 32

better spare rectum and bladder

Question 33

typical PTV margin for prostate

Answer 33

7 mm- 1 cm

maybe 5 mm on rectal side since we can match to the rectal wall

Question 34

what does having more beams do to hot spots?

Answer 34

lowers them
-for example, for a 6 field plan, peripheral hot spot dose is POP hot spot dose divided by 3 since there are 3 times as many beams

Question 35

is there BID?

Answer 35

no