Clinical practice - Prostate Flashcards
external beam RT treatment
volumetric modulated arc therapy (VMAT)
justification for VMAT
-Precision: VMAT focuses the radiation on the tumor while sparing healthy tissue.
-Speed: takes around 2 mins. Faster treatments improve the accuracy of radiation delivery
– Improved sparing with OAR doses
– Consistent and significant reduction in Monitor Units
features of VMAT
– Either single or double arc
– Can also be partial arc
– 6MV is standard
IGRT @ the linac: DEFINITIVE
Possible match structures
– Fiducials
– Sof tissue (prostate gland)
– Bone – Used but not recommended practice
IGRT @ the linac: POST PROSTATECTOMY
Possible match structures
-Bone
– Surgical clips – area of current research
target volumes
Prostate CTV-The entire prostate gland as defined on planning CT with aid of MRI
Target Dose: Post Op Radiotherapy
– Adjuvant 60-64Gy
Target Dose: Lymph Node Irradiation
- 80Gy in 40fx to prostate and SVs @ 2Gy/fx
- 60Gy in 40fx to LN @ 1.5Gy/fx
dose volume constraints =
Bladder= V65<50%, V70<35%, V75<25%, V80<15%
Femoral Heads= V50<5% (NB: this was taken from RTOG not QUANTEC)
Small Bowel = When contoured as a bowel bag V45<195cc
VERIFICATION
-
imaging verification protocol
Daily online IGRT – matching to the prostate
if matching to prostate -3D (CBCT)
if matching to Fiducials (2D KV orthogonal or 3D (CBCT)
2D KV orthogonal field Matching to Fiducials
- Orthogonal KV images to match in all three directions
- “Best fit” may be required
- Placement of fiducials is important – at least 3 inserted
KV imaging limitation
-not possible to assess rectal or bladder volumes , but if rectum is inconsistent there should be larger discrepancy between bone and fiducal
Post prostatectomy with implanted fiducials
CBCT match to bone initially then manually adjust to match fiducials
features of 2D KV orthogonal imaging
-prostate cant be seen
-imaging dose lower
-image acquisition quicker
