Review Note
Last Update: 02/18/2024 05:30 AM
Current Deck: Part 2::6. High Yield Questions::Skin
PublishedCurrently Published Content
Front
b. He
has a 4cm horizontal scar over the right lateral forehead 2cm above the eye
with no signs of local recurrence. There is no altered sensation and no
lymphadenopathy. Histology shows a 2.0cm x 1cm x 7mm thick poorly
differentiated SCC. Peripheral margins are well clear, the deep margin is
0.3mm. There is evidence of perineural spread involving several nerves up to
0.2mm in diameter at the deep margin. There are no signs of further disease on
examination or imaging. A decision is made to proceed with adjuvant radiation
therapy.
Describe a suitable radiation therapy technique and dose fractionation
schedule. Your answer should include a detailed description and justification
for your choice of target volumes and what potential complications you would
discuss with this patient. (5 marks)
Back
I will treat this patient with curative intent using orthovoltage
radiotherapy (DXR).
Prescription: 45Gy in 15 fractions, 5 fractions/week. Dosed to skin surface
Clinical mark up:
-
Identify surgical scar under
good lighting +/- magnification. Involve dermatologist if the scar margins are
not easily identified.
-
Mark up treatment field to
include 1.5cm margin around the surgical scar
-
treatment template and set up
parameters to be accurately documented.
Technique:
-
DXR 125kVp HVL 7.0mm AL. FSD 20cm. 90% isodose line to
a depth of at least 5mm from the surface.
Shielding:
-
Right external eye shield. Lead
mask cut-out shaped to treatment field.
Target verification:
-
Ensure accurate set up on Day 1
treatment
-
Set up parameters to be
documented
Justification:
-
non-melanoma skin cancers are
radio-responsive and excellent local control rates can be expected
-
In older patients (70yo in this
case), late effects are less of a concern. Hypofractionation can achieve
similar outcomes.
-
Reasonable alternative
treatment techniques include the use of electron beam or MV photons with VMAT
technique. DXR was chosen due to its simplicity of set up, sharper penumbra as
compared to electron beam especially with the lesion’s proximity to the lacrimal
gland and globe. DXR is less deeply penetrating as compared to MV photons hence
reducing dose to the brain. Bolus required for both electrons and MV photons,
which is not required in DXR.
Potential complications:
Acute
-
Skin reaction/dermatitis
-
Alopecia especially when lesion
is close to the hairline/eyebrow
-
Fatigue
-
Ocular --> keratitis sicca,
lacrimal duct stenosis/epiphora
Late:
-
Atrophy, telangiectasia,
hypopigmentation and sclerosis of the skin
-
Rare risk of cataract formation
-
Keratitis sicca
Further information, not for memorising (no card)
Exam
Current Tags:
Pending Suggestions
No pending suggestions for this note.