Total skin irradiation is a unique treatment reserved for particular stages of mycosis fungoides. Due to the special set up and treatment required I am including it in the 'special techniques' section as well.
Mycosis fungoides is the only conventional indication, and then only when the tumour is involving > 10 % of the body surface area as patches, plaques or tumours. Due to the availability of other treatments such as topical retinoid creams, topical steroid creams, or PUVA, total skin irradiation is now reserved for patients with plaques or tumours that are extensive.
Less extensive plaques or tumours are best treated with local therapy (e.g. eternal electron beam or AP/PA photon beams).
Informed consent must be obtained, focussing on the early and late toxicities. Early toxicity includes:
- Generalised erythema of the skin and areas of moist desquamation may occur but are uncommon
- Hair loss
- Reduced sweating
- Nose bleeds
- Skin infection
Simulation and Treatment
There are almost as many ways to deliver TSI as there are centres that deliver it. The objectives are:
- To deliver relatively homogenous dose to the entire skin surface
- Avoid dose to deep structures
- Avoid toxicity to the eyes and thin parts of the body (digits)
The techniques to deliver treatment to the entire skin surface are:
- 6 field Stanford technique, where the patient stands in three of six positions per day
- Rotational technique, where the patient is treated on a rotating platform.
The patient stands behind a beam spoiler which increases the skin dose by scattering electrons prior to them entering the skin.
Each position is treated by two beams, with the central beam axis angled above and below the patient to reduce bremsstrahlung contribution which is greatest along the central axis. The two beams are junctioned at the umbilicus.
The ideal dose distribution is:
- dmax at 1 mm
- d80 at 9 mm
- d20 < 20 mm
This should ensure the skin receives adequate dose and the underlying structures are spared.
Multiple TLDs are used to provide dosimetry on the first day of treatment. These allow detection of inhomogeneities which may require boosting with additional fields during therapy. Sites that always require boosting are the perineum, the axillae, the scalp and the soles of the feet; in large breasted women the inframammary fold may also need a boost field.
Shielding of the eyes is essential; if the eyelids are involved then internal eye shields are used, otherwise external eye shields suffice. The scalp may be shielded after 20 Gy to reduce the risk of permanent alopecia. The fingers and toes should be shielded once they reach the prescribed dose, which often happens more rapidly due to the increased dose from all angles at these sites. The foot should be shielded after 20 Gy to prevent hot spots forming at the junction between the total skin field and the sole field.