OARs & Eval Flashcards
DVH for sarcoma. Showing 50% IDL covering the entire leg. what is the concern with this?
What is the OAR for bone?
We want a strip to spare of normal tissue (1-2cm or 25% of the limb circumference to max 30Gy). In this case, the 50% IDL should come off the leg a bit.
Bone mean <37Gy
Sarcoma limb, IMRT. What is the eval criteria for PTV coverage?
We want the PTV covered by the 95% IDL (not the 90% IDL!).
IE: PTV v95 = >99%
GBM near optic nerve, what is your CTV?
What do you do if optic nerve constraint
+1.5cm expansion, carve off optic nerve.
Compromise PTV, discuss patient potential risk of exceeding OAR dose tolerance (ie increased risk of blindness), reduce dose, use two phase technique (45Gy to region with large margins, 60 to smaller margins)
For linac treating with SRS, what are you looking for in terms of coverage?
V100>90%
Max dose 120%
CI for prescription IDL <1.3
IDL conformal to PTV
5 acute toxicity GBM treatment, 5 late
fatigue
alopecia
dermatitis
otitis media
headache
nausea
worsening neuro sc
TMZ:
- thrombocytopenia
- dizziness
- constipation
Late:
Radionecrosis
Neurocog decline
Decreaesed hearing
Increased risk of stroke
Panhypopituitarism
Late SKIN ortho/electron OARs
If near eye: cataract, glaucoma, excessive tearing, duct stenosis.
If near bone: #, ORN
Brain: RN
Nose: mucositis, dry nose, epistaxis, perforated septum
Hair: alopecia of beard/hairline
Lymphoma: when treating mediastinum, what are all the OARs? Name 3 dose constraints specific for XRT, perhaps for 30Gy/20#
Spinal cord
Small bowel
Kidney
Liver
Fertility/testes/ovary (not an issue in elderly)
Bone marrow
Skin, stomach, bone, spinal cord, nerves, lymphatics
NOTE: do not forget bone marrow!
Heart: ALARA, suggest mean <5Gy
Lung V20 <15% (half of quantac)
Mean breast dose <3Gy
Patient getting treatment for esophageal cancer. How would you manage esophagitis?
Esophagitis: avoidance of irritant foods – texture/temperature extremes; analgesia PRN systemic and topical (rinses/xylocaine)
What are the Kidney dose constraints?
V12< 55%, V20<32%, V23 < 30%, V28<20%
Cervix EBRT: what are OARs
With Dose 45/25;
Small bowel V45Gy < 195cc
Kidneys mean dose <15Gy
Ovaries Dmax < 8Gy
Everything else avoid hotspots
Cervix brachytherapy Rx dose and objectives:
Rx: 28Gy/4#
GTV: EQD2 95Gy
HRCTV (GTV+ entire cervix +grey zone of possible parametrial disease): EQD2 90Gy
IRCTV (HRCTV + 1cm, equivalent of point A): 60Gy
Coverage:
GTV D(98) > 95Gy
HRCTV D(90)> 90Gy
IRCTV D(98)> 60Gy
OARS;
- Bladder D2cc < 80
- Rectum D2cc < 65
- Sigmoid D2cc < 70
- Bowel D2cc < 70
Definition of point A?
What is the reason for packing?
Point A = 2cm superior to the intersection of tandem and ring (external cervical os) and 2cm lateral, it is the historical prescription point.
Point B = same but 5cm lateral
A: packing is to displace the vaginal walls so that they are further from the radioactive source and thus the dose to the mucosal surface is lower
Cervical cancer: how would you minimize excess dose to OARs?
Rectal retractor, rectal tube, custom balloon in vagina, fill bladder more.
Cervical cancer: Asked how you would come up with dose constraint for brachytherapy?
Take EQD2 limits for D2cc, IE rectum D2cc<65Gy, subtract EQD2 of 45Gy/25# (using alpha beta 3 for late effects of normal tissues), then divide by 4 to get per fraction EQd2 OAR.
What in SURGICAL report tell you it was a “good” SNLB
The number of sentinel lymph nodes should be reported: typically one but preferably two or more nodes should be identified to ensure adequate sampling.
The report should mention visualization of blue stained lymphatic vessels or radioactive uptake using a gamma probe. The report should identify if both methods were used, which leads to better results.
