skin Flashcards
What genetic condition predisposes to non-melanoma skin cancer and for which RT is contraindicated
What is the defect
Xeroderma pigmentosa
Defect in nucleotide excision repair
What should be assessed for skin cancer on examination
Size & depth of tumour, fixation to underlying structures, bony involvement
Margins
Regional LN involvement
When is surgery preferred for a skin cancer
Young age < 60yrs – cancer risk, RT effect on cosmesis worsens with time
Poor Vascular supply: lower leg – shin/malleoli, dorsum of hand
Large lesions involving cartilage / bone - RT may cause osteoradionecrosis
Upper eyelid (overlying lacrimal gland) - risk of dry eye if gave RT
Prior burns / previous RT
DNA defect syndrome: Gorlin’s, XP, Ataxia telangiectasia - RT could induce tumours
When is RT preferred for skin cancer
Provides better cosmesis / functional outcome - nose, lower eyelid, ear, lower lip/commissure
Sites with potential for deep infiltration: inner canthus, nasolabial fold, ala nasi, tragus, post auricular area
Large superficial lesions
Elderly or unfit for surgery
Multiple lesions
When is adjuvant RT indicated for a skin cancer
R1 margin and no further surgery possible (6-10mm margin ideally)
Extensive or large PNI
Multiple risk factors - infiltrative growth pattern, poorly differentiated
How is a skin cancer best treated with kV
BCC - 5mm margin
SCC - 1cm margin
Deep margin the same - receiving at least 90% of the dose
Protective - Eye shield, mouthguard
What radical dose should a skin cancer receive
SCC - 45Gy/10# (if small can hypo fractionate to 35Gy/5#; if large, hyperfractionate to 60Gy/30#)
BCC - 40.5Gy/9#
How are margins altered when treating with electrons
What is the minimal lateral size
Need wider margins as dose distribution narrows with depth
40mm min lateral size
What protection is needed when treating eg a lip with electrons
lead mouthguard covered in wax due to backscatter of electrons
How does the depth dose depend on energy for electrons
Dx2 = Dmax
Dx3 = D90
dx4 = D50
dx5 = practical range (tail)
What thickness of lead shielding is needed depending on electron energy
Energy / 2 = thickness in mm
For photons, where is Dmax in relation to energy
Energy/4 = Dmax in mm
How is a low risk BCC best treated
How is a high risk BCC best treated
Low risk - surgical curettage or cautery, topical imiquimod or 5FU
High risk - surgical excision (WLE, Moh’s) or RT
What margin is given for a BCC treated with primary RT
Well defined - 5mm margin
Poorly defined or morphoiec - 10mm
If treating with electrons, allow an extra 5mm margin
What percentage of actinic keratosis will transform to SCC per year
1%
What radical primary RT dose would be given to an SCC
What margin should be included
45Gy/10#
Can consider 18-20Gy/1# if elderly & lesion <3cm
35Gy/5# if >4cm
If >5cm - 55Gy/20#
If >6cm - 60Gy/30#
Well defined SCC - 1cm
poorly defined or large (>4cm) - 2cm margin
1cm deep margin
For electrons, add an extra 1cm margin to these
When should electrons be chosen as treatment modality
Over bone and cartilage due to the photoelectric effect
Lesions >4cm
Scalp - drop off of dose minimises dose to brain
When should orthovoltage XRs be chosen as treatment modality
<1cm depth and <4cm lesion
What systemic treatments can be used for metastatic SCC
Cisplatin & 5FU (capecitabine) – like head & neck
Cemiplimab – PDL1 inhibitor
What is a Merkel cell carcinoma
Aggressive neuroendocrine cancer with high risk of spread, typically occurring within H&N area
What is the treatment for a Merkel cell carcinoma
If operable, surgical resection with 3cm margin and SLNB
If positive LN -> nodal dissection
Adjuvant RT (50Gy/25#) if node positive, >2cm or positive margins
If inoperable - primary RT (60Gy/30#) with 3-5cm margin
What are the indications for adjuvant RT for a Merkel cell carcinoma
What dose RT is given adjuvantly
Positive margins
Primary tumour >2cm
Node positive
Dose: 50Gy/25#
What is the treatment for a metastatic Merkel cell carcinoma
avelumab first line
+/- RT to neck nodes
Carboplatin/etoposide 2nd line
What is the prognosis for a Merkel cell carcinoma
High rate of local recurrence
Median OS – 9 months in metastatic disease
What are the 4 types of Kaposi sarcoma
How is it treated
HIV related
Immunosuppressed
Classical - indolent, lower limbs
Endemic - sub-saharan africa - aggressive and occurs in children with fulminant lymphadenopathy
Treatment:
HAART
Palliative RT to symptomatic lesions - 8Gy/1#, 20Gy/10# pop
If severe disease - systemic treatment with caelyx or paclitaxel
How is a cutaneous angiosarcoma treated
Resection with wide margin then 50Gy/25# adj RT
If inoperable, caelyx in combination with RT (60Gy/30#)
How is a low grade cutaneous follicular or marginal-zone (MALT) lymphoma treated
Superficial RT or electrons
PTV = GTV + 2-3 cm margin
24Gy in 12# or 15Gy in 5#
How are cutaneous T cell lymphomas classified
Indolent:
Mycosis fungoides / Sezary syndrome – erythroderma, poor prognosis (32m)
Aggressive:
Anaplastic large cell / NK cell lymphoma
How are cutaneous T cell lymphomas treated
Observe until symptomatic, then PUVA or topical steroids
Palliative RT for symptomatic lesions - 8Gy/2# or 12Gy/3#
Systemic treatment - No benefit of combination treatment (eg CHOP) over single agents: methotrexate, liposomal doxorubicin, gemcitabine
What is the treatment for mycosis fungoides
Total body electron therapy - 30Gy in 20#
How is T staging defined for skin SCC
T1 - <2cm
T2 - 2-4 cm
T3 - >4cm or bone invasion or perineural invasion
T4a - gross cortical bone or marrow invasion
T4b - Skull base or axial skeleton involvement
How is nodal staging defined for skin SCC
N1 - single node and <3cm
N2a - single node 3-6cm
N2b - multiple ipsilateral nodes all <6cm
N2c - bilateral or contralateral nodes ≤6cm
N3 - ECS or LN >6cm
What histological markers would suggest melanoma
HMB 45, S100
What is the Van Herk recipe
used to calculate CTV-PTV margin to allow for setup error for EBRT photons
What is the 10yr local control rate of BCC
<2cm - 95%
>2cm - 90%
deep invasion 50%
What are the indications for adjuvant RT for BCC
T3 (>4cm)
T4
Positive margins
Perineural invasion
Recurrence
First line mx of SCC
Outcomes
Surgery - aiming 4mm margin at least
<2cm - 95% 5yr control
2-5cm - 65-85%
>5cm 50-60%
Indications for adjuvant RT for SCC
What dose should be given for adjuvant RT
Positive margins
Inadequate margins:
<4mm margin for low risk (<2cm)
<6mm for high risk (>2cm or >6mm depth, perineurial invasion)
Recurrent disease
Nodal mets
Perineural invasion and LVI
completely excised T3 (>4cm) tumours, where there are multiple high-risk factors (>6 mm in thickness (depth) and invasion beyond subcutaneous fat)
Dose: 50Gy/25# or 60Gy/30# or 66Gy/33# for high risk H&N SCC
What defines a high risk BCC
> 2 cm
Morphoeic or infiltrative
Poor margin
Recurrent
Immunosuppressed or Gorlin
Sites – face and scalp, over critical structures
primary surgical closure difficult
When is RT preferred
Facial triangle - better cosmesis
Large superficial lesions, with no bone involvement
When is surgery preferred
Large lesions, involving cartilage, bone, tendons or joints (risk of necrosis and lower cure rate)
Young pts - cosmesis and 2nd cancer risk
Areas with poor vascular supply / healing problems / problems with function - lower leg, feet, dorsum of hand and genitalia
Areas likely to result in repeated trauma - elbow
Gorlin’s, xeroderma
When is Moh’s surgery preferred
Ill defined tumour (ie indistinct clinical margins) or tumour arising in unhealthy or damaged skin
H-zone of the face
Ensures 100% clear margin with minimal tissue resection
When is adjuvant RT given to a nodal site for SCC
≥3 cm node (n2)
Parotid node metastasis
Multiple involved nodes
Extranodal extension (n3)
What is gorlin’s syndrome
Autosomal dominant familial cancer = PTCH (patched gene) on Chr 9: q22-31
Multiple BCC at an early age
Mandible bone cysts, rib abnormalities, short 4th metacarpal, coloboma (gap in eye structure), cataracts, fused vertebrae, polydactyly, cleft lip, cardiac tumours
Increased risk of medulloblastoma, meningioma, ovarian fibromas
Skull x-ray shows calcification of falx cerebri in patients >12 years in 90% of cases
Treatment: surgical excision – avoid RT if possible
consider vismodegib
