Total skin electron radiation therapy for malignant lymphomaMedical editor Alexander Fosså MD
Oslo University Hospital
Irradiating the entire skin with electrons is used to treat certain malignant lymphomas that spread in large areas of the skin. Most patients appropriate for this treatment have mycosis fungoides. Oslo University Hospital has established a treatment arrangement for this demanding treatment form.
- Mycosis fungoides
- Other non-Hodgkin cutaneous lymphomas with diffuse spreading
|Target volume definitions from ICRU
(International Commission on Radiation Units and Measurements)
GTV (= Gross Tumor Volume)
|Palpable or visible/identifiable area of malignant growth.
CTV (= Clinical Target Volume)
Clinical target volume
Tissue volume containing GTV and subclinical microscopic malignant disease.
ITV (= Internal Target Volume)
Volume containing CTV and an internal margin taking into account internal movements and changes in CTV. This is the volume that should receive an optimal dose.
PTV (= Planning Target Volume)
Geometric volume containing ITV and one Setup margin taking into account assumed variation in patient movements, patient positioning, and field alignment.
Planning contour: Beams-Eye-View projection of PTV.
IM (= Inner margin) and SM (= Setup margin)
|IM and SM cannot be summed linearly. Total margin must be given specifically for different tumor localizations.
The field limit is defined as the area that 50% of the isodose curve outside the target volume must have to give a therapeutic isodose (90% isodose) which encircles the target volume to be treated. The distance from 90-50% of the isodose (penumbra) depends on multiple conditions and is typically 5-7 mm.
Definition of margins
The table below summarizes standards for use of the term GTV, for margins to CTV and ITV, as well as formulation of field limits for radiation therapy of malignant lymphomas.
Target volume for radiotherapy
||Tumor in indolent NHL stage I/II1, original tumor (before chemotherapy minus balloon effect) in aggressive NHL stage I/II1 and HL stage I/IIA
Residual tumor in aggressive NHL stage II2/IV and HL stage IIB/IV
||GTV + 2 cm craniocaudal to confined disease/short chemotherapy
GTV + 1 cm craniocaudal to residual tumor from advanced disease after full chemotherapy
GTV + 1 cm in the transversal plane
CTV should always include the entire lymph node region in the levels to be irradiated (limited in the lungs and bone, unless there is suspicion of infiltration).
CTV may for indolent NHL stage I/II1 include the nearest non-infiltrated lymph node region or parts of it.
||CTV if internal movement is negligent (CNS, ENH and others)
CTV + up to 1 cm craniocaudal and up to 0.5 cm transversal in the mediastinum
CTV + 2–3 cm in mesentary and stomach
CTV + up to 0.5 cm transversal retroperitoneally
Not routinely defined
Are set to 1 cm outside ITV for set-up margin and penumbra
Field limits should be arranged so that later junctions are as simple as possible (for example on one side of the spine, in invertebral discs)
The field of radiation surrounding macroscopically involved lymph nodes alone with margin. This definition is currently not widely used in Norway, but is emerging in international studies.
The involved field is the field of radiation surrounding the macroscopically involved lymph node region or organ with margin. After limited chemotherapy of localized lymphomas, the original macroscopically involved area is used as the foundation for field contouring (with the exception of the balloon effect). For residual lesions after full chemotherapy for advanced stages, the residual tumor is usually used as the foundation (with some exceptions). What determines an adequatemargin from the macrotumor to the field limit depends on multiple factors. For early stages of NHL and HL without previous chemotherapy or after chemotherapy (3–6 CHOP-based cycles, 2–4 ABVD or equivalent), the margins from the initial tumor to the field limit should be 3-4 cmin the direction of lymph drainage lengthwise from initial extent and 2 cm in the transversal plan (exception for balloon effect). With residual lesion have full chemotherapy for advanced NHL and HL and relatively little internal movement, then 2 cm from residualtumor to the field limit is used. Larger margins may be considered in areas for greater internal movement (abdomen, structures near diaphragm). As a general rule with nodal involvement, the target volume includes the entire lymph node region in the transversal plane for the levels included in the field.
Traditionally, the entire inolved lymph node area has been included completely in the craniocaudal direction (direction of lymph drainage). This provides a recognizeable geometric field (parts of mantle or inverted Y field) which is advantageous for standardization, reproduciblity, later junctioning etc. The lymph node regions as defined in the Ann Arbor classification then do not represent any biologically functional entitites and are not considered a base for radiation therapy. Thus, it is natural to see the regions coherently length-wise inthe direction of lymph drainage and use margins to involved lymph nodes to avoid irradiation of entire regions (for example in the neck, supreclavicular region, mediastinum, and retroperitoneum). Parts of neighboring organs are included to satisfy the minimum margins given above. Field modeling should still be geometric shapes as much as possible to make later joining of fields easier and to avoid border recurrences in areas difficult to irradiate again.
For extranodal lymfomas/organ manifestations, it is sometimes natural to include the entire organ (thyroid gland, stomach, brain, spinal cord). In such cases, it is also necessary to take internal movement into consideration, for example, stomach movement and movement of lung borders etc.. With multiple organ localizations, it is not possible to give full doses to the entire organ due to the tolerance for ionizing radiation (lungs, liver, kidneys) and the fields and doses must be adapted accordingly.
This type of field includes macroscopically involved regions/organs and lymph node regions that are assumed to have diseased cells. This may be the nearest macroscopically normal region or multiple, more distant areas. This technique was developed for Hodgkin's lymphoma when radiation therapy was used as the only treatment modality and was given to large areas with assumed microscopic disease on one or both sides of the diaphragm (mantle field, paraaortal field, inverted Y-field). In today's practice, the term 'extended field' is not widely used. For localized stages of low-grade NHL, where radiotherapy is given alone to cure the disease, we have chosen to include the nearest uninvolved regions in the field of radiation, a type of "minimally extended field". This is not, however, practiced by all radiation therapy centers in Norway.
- If the disease has not spread to the scalp, fingers and toes, it is sensible to consider shielding these areas with customized lead shields.
- Use of supplementary fields toward the vertex, pelvic floor, and soles of the feet should be determined before starting treatment.
- An eye shield of lead is molded in wax or gold-plated mesh blocks. These are placed under the eyelids for each treatment, which requires use of eyedrops and local anesthetic. If the skin around the eyes will also be shielded, customized lead shields are taped to the skin.
- In men, the testicles will receive a relevant amount of the skin dose, therefore sperm banking should be considered before radiation therapy.
- Contacting a dermatologist for supplementary skin care during treatment may be beneficial.
An electron field is used which is at a significant distance from the source to the patient, and the fields are angles with nearly horizontal rays diagonal from below and above. The fields will then add to each other to give a relatively even dose distribution for the entire length of the patient. The field angled from below gives primarily the dose to the upper body, while the field angled from below gives the dose primarily to the lower body.
- By rotating the patient on a stool during irradiation, the dose will be evenly distributed to the skin. Irradiation should start at different points under rotation every day.
The patient should stand centered on a stool with their feet apart and supporting with one hand (or both if necessary) using the support device from the ceiling. The patient alternates between fractions by holding the right or left hand up. The other hand is held 10-15 cm away from the body.
The field will not cover the pelvic floor, sole of the feet, and crown. An additional field to these areas may be necessary. These areas are usually treated with an electron field with 2 Gy per fraction in the last part of treatment. To achieve adequate skin coverage, a bolus is necessary for these fields.
Any plaque or tumorous lesions requiring treatment with greater doses in depth than the skin should be evaluated for a local supplementary field with higher electron energies.
The target dose of 1.2 Gy per fraction is given as five fractions per week. It is recommended to give 30–36 Gy measured as the dose in the surface of the skin, which is in compliance with international recommendations. The electron energy from the source (6MeV) is lower in the surface of the skin to the patient with depth dose curves following. Eighty percent isodose is at a depth of 4 mm. Because large amounts of the dose are given as tangential irradiation, the dose maximum is in the surface of the skin contrary to skin irradiation with electrons perpendicular to the surface.
Skin, nails, hair
The nearest obligate side effects are:
- Erythema of the skin
- Edema of the hands and feet which may last for some time after treatment.
- Halt of nail growth. Loss of nails is uncommon.
- Reversible complete alopecia
- Sores on the hands and feet may occur and sometimes with superinfection.
Eyes and lenses
Sore eyes possibly with superinfection may occur. Eye shields prevent cataracts.