Skin

Skin

Key Points

The majority of skin carcinomas, the most common cancers in human, are treated with surgery.
Upfront radiotherapy is an appealing alternative for carcinomas on and around the nose, lower eyelids, and ear as it can yield better cosmetic outcome.
Postoperative radiotherapy is indicated in locally advanced skin carcinomas, particularly those with perineural spread along large nerves, invasion of bone, cartilage, and skeletal muscle, positive section margin, or nodal involvement with extracapsular extension (ECE).
Intensity Modulated Radiation Therapy is the preferred technique when target volumes include the cranial nerves such as the branches of the trigeminal or facial nerves.
Adjuvant radiotherapy is indicated for the treatment of malignant melanomas spreading to multiple lymph nodes, particularly in the presence of ECE.
Elective nodal irradiation is an alternative to nodal dissection in selected patients with thick melanoma.
Adjuvant radiotherapy plays a role in the treatment of rare skin cancers such as Merkel cell carcinoma or adnexal neoplasms.

I SQUAMOUS CELL CARCINOMA AND BASAL CELL CARCINOMA

Treatment Strategy

Surgery and radiotherapy are equally effective in curing most skin cancers. The choice of treatment modality is determined by several factors, such as functional and cosmetic results, patient age and occupation, treatment time, and cost. Surgery is preferred for most patients, particularly for younger patients who have years of exposure to sunlight ahead of them.

Primary radiotherapy is often indicated for lesions on and around the nose, lower eyelids, and ear, where it can usually attain better functional and cosmetic results than surgery. Extensive lesions of the cheek and oral commissures, which would require full-thickness resection, may also show better results on irradiation.

Postoperative radiotherapy is indicated for positive surgical margins, perineural invasion, and invasion of bone, cartilage, and skeletal muscle.

Rarely, patients have adenopathy at diagnosis. The choice of treatment of the nodal disease is determined by the type of therapy selected for the primary lesion and by the size of the node. A combination of surgery and radiotherapy is indicated when nodal disease is >3 cm or when ECE is present.

Primary Radiotherapy

Target Volume

The initial target volume encompasses primary tumor with 1- to 2-cm margins, depending on the size, location, and type of tumor (well-circumscribed vs. ill-defined border). Elective nodal irradiation is not indicated except when the primary is a large, infiltrative squamous cell carcinoma (SCC) or poorly differentiated.

The boost volume encompasses primary tumor with 0.5- to 1-cm margins, depending on the size, location, and type of tumor.

Setup and Field Arrangement

The patient is immobilized in a position that gives the best access to irradiate the tumor (preferably the plane of the skin to be treated is parallel to the surface of the treatment couch to avoid the need for gantry rotation) (see Fig. 16.1).

An appositional field is used in most cases. The borders of the field are chosen to include a 1- to 2-cm margin of normal skin around the tumor (up to 1 cm for lesions <l-cm tumor and 1 to 2 cm for larger tumors). Margins may be smaller when treating areas close to the eye. More generous margins are appropriate for lesions with an ill-defined border.

Radiation treatment is given with orthovoltage x-rays (usually 75 to 125 kilovolt potential [kVp]) or electrons (usually 6 to 12 MeV). The energy of x-rays or electrons is chosen on the basis of the thickness of tumor. The energy of electron beams should be selected so that the distal 90%-isodose line is a few millimeters deeper than the base of the tumor, including surface bolus.

The treatment distance for x-rays also depends on the thickness of the lesion. A 23-cm focus skin distance (FSD) cone is appropriate for superficial tumors, whereas a 50-cm FSD with open fields and skin collimation is preferable for thicker lesions to avoid a large dose gradient across the lesion. The FSD for electrons is usually 100 cm.

Case Study 15-1

A 59-year-old man sought medical attention because of a small ulcer at the left lateral dorsum of the nose that gradually increased in size over a 4-year period.

Physical examination showed a ulcerating lesion with raised borders, involving the left lateral dorsum of the nose, the medial aspect of the cheek, and the medial canthus (Fig. 15-1A). The thickest part of the tumor was close to the medial canthus. Biopsy revealed basal cell carcinoma. Computed tomography scans showed a small soft tissue mass in the medial canthus of the left orbit. The deepest point of this mass was 1.5 cm from the surface. Stage: T2 N0 M0. The lesion was treated with an appositional left anterior oblique field of 9-MeV electrons. Figure 15-1 shows a custom-made eye shield mounted on a contact lens used to protect the cornea and lens (Fig. 15-1B), a lead mask with extra layers over the contralateral eye for skin collimation (Fig. 15-1C), and a 1/4-inch scatter plate placed in the beam to eliminate the skin-sparing effect (Fig. 15-1D). A dose of 60 Gy, prescribed to 90% isodose line, was delivered in 2-Gy fractions, which resulted in local control with good cosmetic and functional outcome (Fig. 15-1E.F).

Figure 15.1A,B

A custom-made lead cutout is used for skin collimation. The cutout should be large enough so that the portal size for an electron beam is at least 4 × 4 cm.

Skin bolus or a perspex scatter plate is used with electrons to ensure full surface dose.

An internal eye shield is inserted when treating an eyelid lesion with orthovoltage x-rays or with electrons of 8 MeV or less. (Note: Eye shields should be individually calibrated with respect to the electron attenuating properties.)

Dose

Effective regimens for treating most skin cancers include a dose of 50 to 55 Gy in 20 fractions, a dose of 45 Gy in 15 fractions, or a dose of 40 Gy in 10 fractions. In general, protracted treatment provides better cosmetic results.

For large tumors close to crucial structures (e.g., eye), maximum tolerance is obtained with a dose of 60 to 70 Gy in 30 to 35 fractions (see Case Study 15-1).

If the patient is in poor general condition, hypofractionation (e.g., 4 fractions of 8 Gy) may be used.

Figure 15.1C-F

Dose Specification

x-Rays are prescribed at D_Mmax with electrons at the 90% line. This difference in prescription accounts for the relative biologic effectiveness difference between the two beam qualities.

Postoperative Radiotherapy

Most frequent indications are lymphatic spread to the parotid gland, upper neck nodes, or both, and perineural extension along the branches of the trigeminal nerves, facial nerves, or both.

Target Volume

The initial target volume encompasses the primary tumor bed and ipsilateral parotid and neck nodes, or trigeminal or facial nerve pathways, depending on the indication.

The boost volume encompasses areas of known disease with 1- to 2-cm margins.

Setup and Field Arrangement

For the treatment of parotid and neck nodes or branches of the facial nerve, the technique is similar to that for primary parotid tumors (see Chapter 13). The patient is immobilized in an open neck position. The anterior margin of the parotid portal can be slightly less generous because there is no need to encompass the parotid duct. Treatment is given with an electron beam of appropriate energy (e.g., 12 MeV for parotid and upper neck nodes and 9 MeV for lower neck nodes).

Background Data

Table 15.1 Control of Malignant Skin Lesions with Radiation Therapy: Hahnemann University Experience, 1960 to 1980

Diagnosis	No. Treated with Radiotherapy	No. of Treatment Failures	No. of Recurrences Controlled by Reirradiation	No Evidence of Disease 4 Yr or Longer (%)
Basal cell carcinoma	444	20	2	426/444 (95.9)
SCC	156	12	–	144/156(92.3)
Keratoacanthoma	12	0	–	12/12(100)
Modified from Solan MJ, Brady LW, Binnick SA, et al. Skin cancer. In: Perez CA, Brady LW, eds. Principles and practice of radiation oncology. 2nd ed. Philadelphia, PA: JB Lippincott, 1992:479-495.

Table 15.2 Clinical Experience with 1,166 Eyelid Tumors Treated by Radiotherapy (1958 To 1978)^a

Histologic Finding	Primary Tumors	Recurrent Tumors	Total	5-yr Control	%
Basal cell carcinoma	686	376	1,062	1,009	95.0
SCC	62	42	104	97	93.3
Total	748	418	1,166	1,106	94.8
^aMost of the primary tumors were controlled and the few failures were salvaged by surgery. Of the 1,166 tumors, 745 (64%) were <2 cm in diameter. Adapted from Fitzpatrick PJ. Skin cancer of the head—treatment by radiotherapy. Int J Radiat Oncol Biol Phys 1984; 10:450.