What is the optimal treatment approach for a patient with mycosis fungoides, considering the size and extent of the disease, and when is local electron therapy versus total skin electron beam therapy (TSEB) indicated?

Treatment Selection: Local Electron Therapy vs Total Skin Electron Beam Therapy in Mycosis Fungoides

For solitary or few localized lesions, use local electron therapy with 20-30 Gy in 2-Gy fractions; for large areas (trunk, limbs, whole scalp) or extensive cutaneous disease (stage T2b), use total skin electron beam therapy (TSEB) with 32-36 Gy. 1

Local Electron Therapy: Size and Extent Criteria

Solitary or minimal disease is the primary indication for local electron therapy rather than TSEB 1:

• Unilesional mycosis fungoides (rare presentation of solitary patch or plaque) can be treated with curative intent using local radiotherapy at 20-30 Gy in 2-Gy fractions 1
• One or few infiltrated plaques or tumors (stage IIB) are appropriate for local radiotherapy 1
• Small plaques and tumors respond to relatively low doses such as 8 Gy in two fractions for palliative intent 1

Treatment field specifications for local therapy 1:

• Radiotherapy field margins on the skin should extend ≥2 cm beyond visible disease 1
• The treatment depth is determined by tumor thickness and depth of invasion, which may require assessment using ultrasound, CT, or MRI 1
• Energy selection (orthovoltage X-rays, electrons, or photons) depends on the depth of invasion 1

Dosing Algorithms for Local Electron Therapy

For palliative treatment of localized disease 1:

• Single lesions or small areas: 7-8 Gy in single fraction is effective and convenient, though this limits re-treatment options and may not be suitable for areas with poor skin tolerance (e.g., lower legs) 1
• Alternative palliative approach: 8 Gy in 2 fractions for plaques and small/large tumors 1
• Stage IIB tumors: 12 Gy in 3 fractions is very effective for palliative treatment 1

For tumors involving large areas requiring local (not total skin) treatment 1:

• Use smaller doses per fraction: 20-30 Gy in 10-15 fractions 1
• This approach is necessary when the treatment area is large but does not warrant TSEB

For curative intent in solitary lesions 1:

• Dose: 20-30 Gy in 2-Gy fractions 1
• Alternatively, 24-36 Gy total dose with appropriate fractionation 1
• This achieves excellent local control with minimal toxicity 2

Total Skin Electron Beam Therapy: Indications

TSEB is indicated when the treatment area is extensive 1:

• Large areas of skin such as trunk, limbs, or whole scalp require TSEB with smaller doses per fraction (e.g., 20 Gy in 10 fractions) 1
• Stage IB disease with extensive cutaneous involvement (stage T2b) should be considered for first-line TSEB 1
• Stage IB disease that has relapsed or is refractory to other skin-directed therapies warrants second-line TSEB 1

High-dose TSEB regimen (Stanford protocol) 1:

• Dose: 32-36 Gy delivered with six dual-field technique over 9 weeks, 2-Gy fractions per 2-day cycle 1
• Higher skin-surface dose (32-36 Gy) and higher energy (4-6 MeV electrons) are associated with higher complete response rates and reasonable 5-year relapse-free survival in early-stage disease 1
• Stage IA achieves 97% complete response with 50-month median relapse-free survival 1

Low-dose TSEB regimen (increasingly popular) 1:

• Dose: 10-12 Gy total dose 1
• Advantages include shorter treatment duration, fewer side-effects, and opportunity for re-treatment 1
• Overall response rate of 88% with 18% complete response rate and median duration of clinical benefit of 132 months for stage IB-IV disease 1
• Particularly useful for patients requiring multiple courses of TSEB during their disease course 3

Critical Decision Points and Pitfalls

Avoid these common errors when selecting between local and TSEB:

• Do not use high-dose radiotherapy unnecessarily for localized disease—minimum effective dose facilitates repeat treatment if needed 1
• Do not use single-fraction regimens (7-8 Gy) for areas with poor skin tolerance such as lower legs, as this limits re-treatment options 1
• Do not overlook the need for smaller doses per fraction when treating large surface areas, even with local therapy (not TSEB), to limit acute and long-term toxicity 1

Special anatomic considerations 1:

• Eyelids may benefit from very small doses per fraction (4 Gy in 2 fractions) to limit acute and long-term toxicity 1
• Extensive involvement of hands and feet can be treated with local radiotherapy even in the context of erythrodermic disease (stage III-IVA1) 1

Concurrent therapy considerations 1:

• Localized radiotherapy can be used simultaneously with other skin-directed therapies, including phototherapy 1
• This allows for a multimodal approach without compromising either treatment modality