Friday, April 17, 2009

Cutaneous Topics in Radiation Oncology

Dr. Oleson speaks today about non-melanoma skin cancers and other cutaneous topics.

 Incidence of non-melanoma skin cancer is around 1,000,000

 Basal cell cancer 75%.
On the face usually these occur above the line from the earlobe to the angle of the mouth.
node mets in 0.1%. 5yr OS in LN + is around 10%
Nodular-ulcerative 50%
Superficital 33%
Morpheaform has poorer prognosis incidence around 15%

 Squamous cell carcinoma incidence around 20% LN incidence <5%
5 yr survival around 25% in LN+ patients.
Below the line from earlobe to angle of mouth

 NCCN has a good table for risk factors in non-melanoma skin cancer.
Lesion size and location play into risk category.
H shaped area around the face is a higher risk area, eyes/nose/mouth/ears/jawline, not the cheeks or forehead or scalp.
H zone cancers tend to have vertical invasion, high nerve density, and the area is highly cosmetically important.

 Remember that with electrons, higher energies have less skin sparing, thus with low energies, bolus is ofter needed for skin cancers. Recall the rule of thumb that the Energy/3 is roughly the 80% PDD. Also recall that the drop off in bone, attenuation is approximately double that of water equivalent tissue. Penumbra is also an issue, particularly with small field size, and for a 5x5 field, the 80% line may not build up till 5mm into the field edge (Larger fields have less of this build up effect on the field edge).

 For head and neck skin cancers, try to immobilize with a mask. Due to gaps in the cone to skin distance, often times additional shielding can be placed directly on the skin for better collimation. Many of these issues can be avoided with the use of orthovoltage when available (which is the case at Duke University Medical Center). Recall that orthovoltage has approximately 20% greater biological effect and adjust all doses accordingly.

 CTV Margins (from the Mohs data)
SCC for diam <2cm, margin should be 4mm
SCC >2cm use 6mm
BCC <2cm use 4mm
BCC >2cm use 7mm
for morpheaform consider adding additional margin due to the indeterminant margins of this disease.

 So for CTV expansion of 4-7mm plus 5-10mm for penumbra to get to PTV, thus allow for 1–2cm around the lesion to the field edge.

Small Lesions (<5cm square)
2000 in 1-2 fx
3000 in 5-10fx
4000 in 10-16fx

Larger lesions
4500 in 15-18fx
5000 in 20-25fx
6000 in 20-30fx

Indications for RT in non-melanoma skin cancer:
Morrison, et al. Clin Plas Surgery 1997;24:719
H region- eyelids, nose, auricle
avoid in young patients due to development of telangectasias, and other long term cosmetic effects (though LP disputes that this is a big problem)
5y ST necrosis 34% for 5 x 10Gy
5y ST necrosis 3% for 45-54Gy in 9-18fx

Perineural invasion is a risk factor for failure in the first echelon nodes.

  Cartilage necrosis is probably over sold as a late effect – both JO and LP have only rarely seen this in their experience, including treatment of noses and ears.

  Locke IJROBP 2001;51:748
local control of 89%, less for recurrent lesions on the order of 80%. recommend 2.5Gy/day of 40-60Gy depending on lesion size.
Finizio Tumori 2002;88:48
96% local control    
Pinna – Silva IJROBP 2000;47:451
2y LC 87%, 5y LC 79%
limit dose/fx below 4gy to avoid cartilage necrosis
Nose - Tsao IJROBP 2002;52:973
2yr LC 90, 5yr LC 85%
<2cm 35Gy in 5fx
2-5cm 45Gy in 10fx
>5cm 50Gy in 25fx
good cosmesis

  long term toxicity should be on the order of 2% with modern treatment.

definitive RT has poor results
recurrence after surgery is 50-80%
recurrence with postop RT 12-28%
BED goal of >30Gy per: Sakamoto, Rad Onc 2009 (in press)
8Gy x 2 or 6 Gy x 3
should start RT within 48hr
Freedom from recurrence with BED>30 at 10%, vs 40% for BED <30.

  Previous treatment doses were around 4Gy x 3, though perhaps given this data, we may consider increasing daily dose, in selected individuals.

  No reports of radiation induced cancers.

  Merkel Cell Carcinoma
Neuroendocrine tumor of the skin. Higher incidence in immuno-suppressed patients. High rates of LN and DM, intransit mets often seen. May have an association with the polyomavirus. 30% mortality

  LF seems to be improved with adjuvant RT after surgery compared to surgery alone. SLNB also recommended.

  CDDP + etoposide is often used, however data is lacking right now.
Poulsen IJROBP 2006;64:114 – prosepective study of S-RT-Cis/VP16. On MVA there was no benefit to the addition of CDDP/VP16, though the trial was likely underpowered to make any definitive conclusions.
Dose Recommendations: 66Gy gross disease, 60Gy microscopic disease, 50-56 for lymph nodes basins at risk

  Mycosis Fungoides/CTCL
TSE (total skin electron beam) is very useful, however is a specialized technique. Six positions described by Stanford group, then treated at extended distance with two different beams treating with the central ray off the patient superiorly and then inferiorly. A Lucite degrader is used just in front of the patient. May refer to EORTC consensus.

  Kaposis Sarcoma
8Gy x 1 offers good palliation to AIDS related KS. 40Gy in 20fx is more appropriate of endemic KS.


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