Target volume definition

Question 1

What is contoured?

Answer 1

GTV
CTV
PTV
OARS

Question 2

What are the OARS and their tol?

Answer 2

Small bowel - V45<250cm3

Femoral Heads - V50<50%

Urinary Bladder - V50<50%

Rectum - V60<50%

Question 3

What are the volumes for Pre-op?

Answer 3

GTV - prostate

CTV - High risk involvement = prostate + SVs with 5mm margin
Low risk = prostate and proximal 2cm of SV with 5mm margin

PTV - multiple PTVs With different prescriptions to reduce dose to rectum

Question 4

What are the volumes for Post-OP (prostate bed)?

Answer 4

GTV - None

CTV - Borders
INF - 5mm cranial to sup border of penile bulb
ANT - post aspect of pubic symphysis
POST - Ant rectal wall
LATERAL - Medial border of Obturator internus
SUP - Base of SV

PTV - 5mm - 1cm margin

Question 5

What is the beam energy and type?

Answer 5

Photons - high energy (10-15MV)

VMAT - 6MV photons

Question 6

IMRT

Answer 6

Inversely planned as there is better sparing of bowel and bladder

Fixed 5-7 fields and dynamic MLCs which are uniformally distributed to improve dose distribution

Question 7

Explain 3DCRT for prostate.

Answer 7

3/4 field technique - POST LTLAT RTLAT (RPO/LPO - not less than 45 degrees to prevent overlap with post field.

If ANT abdominal wall involvement: 4 field to increase dose anteriorly

Question 8

VMAT for prostate

Answer 8

Single rotation up to 360