Radiation Therapy as Primary and Adjuvant Treatment for Local and Regional Melanoma

Lawrence B. Berk, MD, PhD

Disclosures

Cancer Control. 2008;15(3):233-238. 

In This Article

Technical Aspects of Radiation Therapy

Modern radiation therapy techniques allow high-precision treatment of the areas at risk with maximal sparing of normal tissues. This increased precision necessitates accurate definition of the nodal regions. The following descriptions of the nodal risk areas are based on the surgical approach to nodal dissections.

Lower Extremity. The inguinal nodes lie along the femoral artery. They spread laterally along the circumflex vessels and medially along the external pudendal arteries. The lateral border of the nodal basin is the medial edge of the sartorius muscle. The medial border is the lateral edge of the adductor longus muscle. The superior border is above the inguinal ligament, at a line from the anterior superior iliac crest towards the umbilicus, stopping medially at the level of the pubic tubercle. The deep margin of the supra-inguinal ligament extent is the external oblique aponeurosis. The inferior border, or apex, is where the sartorius muscle crosses over the femoral artery, as the muscle comes superior-laterally to inferior-medially.[39]

The nodes continue into the pelvis along the femoral artery as it goes under the inguinal ligament and becomes the external iliac artery. Both the external iliac nodes and the obturator nodes should be included in the field. The external iliac nodes are along the iliac vessels and are found within the area bounded by the inguinal ligament inferiorly, pelvic sidewall laterally, the lateral border of the bladder medially, and the iliac bifurcation superiorly. The obturator nodes extend along the obturator artery, which arises from the internal iliac artery near the iliac vein bifurcation, running along the pelvic wall. It exits at the upper aspect of the obturator foramen.[39]

For treatment planning purposes, one set of recommendations to encompass the external iliac nodes is to include a 7-mm margin around the external iliac vessels; extending the anterior border by an additional 10 mm anterolaterally along the iliopsoas muscle to include lateral external iliac nodes.[40] An 18-mm strip encompassing the external and internal iliac regions with an 18-mm-wide strip along the pelvic sidewall will encompass the obturator nodes. Another source recommends a 2-cm radial expansion around the external iliac vessels to encompass the iliac nodes.[41]

Upper Extremity. The axillary node compartment can be described as an eccentrically shaped pyramid. In the axial plane the compartment is triangular. The chest wall is the medial border, the subscapularis muscle is the posterior border, the latissimus muscle is the posteriorlateral border, and the pectoralis muscle is the anterior border. A coronal section through the axillary compartment is bounded by the axillary vein superiorly, the chest wall medially,and the latissimus laterally.[42] Dijkema et al[43] reviewed CT delineation of the nodes, based on a cadaveric dissection. Their review, as well as that of Mansur et al,[44] compared the location of the axillary nodes in abduction and adduction. Mansur et al[44] noted that the lymph nodes are medial to the humeral head when the arm is adducted (arm akimbo) whereas they overlie the humeral head when the arm is abducted (raised 180°). Therefore, in contrast to axillary irradiation during breast irradiation, treating with the arm akimbo may be more appropriate during radiation for melanoma. Madu et al[45] reviewed the location of the infraclavicular and supraclavicular nodes. The supraclavicular fossa is described as being divided into two compartments: the lesser supraclavicular fossa, which is between the two heads of the sternocleidomastoid muscle, and the greater supraclavicular fossa at the base of the posterior triangle of the neck. The authors defined the entire supraclavicular fossa as:

  • medial = lateral edge of the trachea, excluding the thyroid and thyroid cartilage

  • anterior = deep surface of the sternocleidomastoid muscle and deep cervical fascia

  • posterolateral = anterior and medial borders of anterior scalene muscle

  • posteromedial = carotid artery and jugular vein

The infraclavicular fossa was defined as:

  • inferior = subclavian artery

  • inferior = most superior border of pectoralis minor muscle at the level of the insertion of the clavicle into the manubrium

  • anterior = deep surface of the pectoralis major muscle

  • posterior = subclavian-axillary artery

Head and Neck. Delman and Lee[46] describe the technique for a neck dissection for melanoma. A modified radical neck dissection is the standard operation, clearing the nodes of levels II–V and sparing the spinal accessory nerve, sternocleidomastoid muscle, and the internal jugular vein. Some aspects of their dissection are determined by the results of the sentinel lymph node biopsy. For example, they do not perform a parotid resection unless it is involved clinically or radiographically.

Several radiographic head and neck nodal atlases are available. Poon et al[46] developed an atlas based on MRI scans of 35 patients with head and neck cancer. They defined 12 neck levels that were more specific to a CT evaluation than are the classical levels I–VI. These levels were based on structures identifiable within the axial CT slices,such as the nasopharynx,thyroid cartilage,ascending ramus of mandible, and inferior to the mandible.

Generally, levels II–V should be included within the radiation portal. However, alterations can be made depending on the location of the primary and expected nodal drainage. A sentinel lymph node biopsy and a PET scan can help direct the definition of the areas at potential risk.

There is no consensus on dose and fractionation. Preclinical studies on the inherent radiosensitivity of melanoma cells led Ang et al[28] at The University of Texas M. D. Anderson Cancer Center to employ a high-doseper- fractionation regimen for adjuvant head and neck irradiation of 6 Gy twice a week for a total of 30 Gy. Other centers followed suit.[48] However, clinical studies found no advantage for larger per-fraction doses for nodal irradiation,[27] including studies that found an advantage for hypofractionation at the primary site.[14] The policy at our center is to use 2 Gy fractions for nodal irradiation in order to reduce the risk of edema and myelopathy. Usually 50 to 60 Gy total dose is given.

Prior to 3-dimensional treatment planning, lymph nodes were frequently treated to arbitrary volumes and depths, often using electrons for the supraclavicular and inguinal nodes. CT- or MRI-based treatment planning allows precise treatment planning based on the relation of the nodes to the vascular supply.

Intensity-modulated radiation therapy (IMRT) and other highly conformal treatment methods allow treatment of the complex nodal structures while minimizing the risk of damage to normal structures and, hopefully, reducing the risk of edema. No prospective studies have been done to confirm this. Nonetheless, it is probably advantageous to use IMRT for inguinal/pelvic and head and neck nodes. There can also be advantage in some patients during treatment of the axillary nodes. This can be determined on a case-by-case basis.

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