verfication

Question 1

two types of verification

Answer 1

dosimetric
geometric

Question 2

what is the aim of geometric verification

Answer 2

to deliver RT as it was planned

Question 3

how is geometric verification achieved

Answer 3

comparing images acquired in treatment with images of treatment planning position(references images)

Question 4

Gross Tumour Volume

Answer 4

gross palpable or visible extent of the tumour

• NO GTV if patient has had surgery

Question 5

Clinical Target Volume

Answer 5

tissue volume that contains the GTV and subclinical microscopic malignant lesions.

Question 6

Internal Target Volume (ITV)

Answer 6

-CTV plus a margin taking into account changes in shape size and position of CTV of patient

-Lung and cervix uses ITV

Question 7

SET UP MARGIN:
accounts for

Answer 7

uncertainties in patient positioning and position of beams during tx planning and tx sessions. (geometric uncertainties)

Question 8

Image Guided Radiotherapy

Answer 8

-starts before treatment
-fusion of added diagnostic or simulated scans to the planning CT to facilitate target definition
-ideally carried out in tx position

Question 9

CTV-PTV MARGIN:
too tight
too generous

Answer 9

-risk of geometric risk
-risk of irradiating excess normal tissue

margin is critical for understanding the precision required at verification

Question 10

what is a set up error

Answer 10

any geometric displacement in the patients position compared to the reference image.

calculated as a shift in the tx position when the tx image is being compared to the reference image.

Question 11

how to reduce PTV margin

Answer 11

eliminate geometric uncertainties as much as possible before delivering your beam

Question 12

eliminating geometric uncertainties by

Answer 12

-ITV = bladder filling protocols and motion management techniques
-Robust immobilisation= reduces set up errors
-IGRT=daily imaging of tx volume (IGRT has the potential to remove nearly all geometric uncertainties)

Question 13

interfraction definition

Answer 13

motion observed between fractions.

quantified and corrected by online daily imaging

Question 14

-intrafraction defintion
-how does it happen
-treatment planning approach

Answer 14

-motion observed during a single tx fraction
-due contracting muscles and organ motion
-real time imaging needed to account for it

Question 15

Gross Errors:
-what is it
-which can cause

Answer 15

-unaccepatly large set up error (more than 1cm)
-underdose of GTV/CTV and over dose of OARS

planning margins do not account for gross errors and must be corrected before tx.

Question 16

Gross errors can be caused by

Answer 16

-incorrect patient, site or ortentaion
-incorrect immobilisation or shifts implemeneted
-incorrect plan

Question 17

definition of systematic set up errors(SSE)

Answer 17

deviation from the planned position that occurs in the same direction and similar magnitude for each traction throughout the course

pattern detected when imaging trends are assessed

Question 18

systematic error issues

Answer 18

-data transfer issues=immobolisation details , shifts from tx plan, couch sag

-patient issues=positioning , bladder/rectal volumes

Question 19

Random Errors definition

Answer 19

deviations that vary from direction and mangitude from every tx fraction. daily fluctuations

Question 20

how do random errors occur

Answer 20

variations of positioning or organ motion and can be attributed to patients anatomy and compliance

Question 21

Random and Systematic Error & Dose Impact

Answer 21

systematic errors cause a shift in a cumulative dose distribution

random errors cause a blurring in dose distribution

dosimetric impact will entirely depend on magnitude of shift

Question 22

What are the target volumes in prostate RT?

Answer 22

-prostate only
-prostate +/- sv
-prostate + sv +/- lymph nodes
-prostate beds

Question 23

What lymph nodes do we treat in high risk patients?

Answer 23

-common iliac nodes (starting at L5-S1),
-internal and external iliac nodes,
-pre-sacral (sub-aortic nodes )
-obturator nodes

Question 24

nodal coverage and imaging

Answer 24

when imaging never comprise treating the prostate and sv to mantain nodal coverage !!

Question 25

Prostate Motion

Answer 25

prostate moves independently of bone (must be imaged correctly using 3D imaging or a apt surrogate.

Question 26

Target Motion

Answer 26

-SV larger motion than prostate but motion can be independent to prostate
-bone is a reasonable surrogate for nodes