Radiation therapy for Skin Cancers

RADIATION THERAPY FOR SKIN CANCERS

Mayur Mayank

SKIN CANCERS

MELANOMANON

MELANOMATOUS SKIN CANCERS

ANATOMY OF SKIN

MELANOMA

Cell of origin : Melanocyte

Present in all areas of the epidermis and in parts of the eye and upper respiratory, gastrointestinal, and genitourinary tracts.

Lesions occur most frequently in white adults

MELANOMA

High propensity for nodal metastasis

Histological subtypes : Superficial spreading Melanoma (SSM) Nodular melanoma (NM) Lentigo maligna melanoma (LMM) Acral lentiginous melanoma (ALM) Desmoplastic Melanoma (DM)

Treatment of choice is Surgery – Wide local excision

CLAKE’S LEVELS

SURVIVAL BASED ON LYMPH NODAL METASTASIS

RADIATION THERAPY FOR MELANOMA

Definitive Radiation Therapy Adjuvant Radiation Therapy Elective Nodal Irradiation Palliative Radiation Therapy


Relatively radio resistant tumor Low alpha/beta ratio -> Hypo fractionated

regimens have an advantage


Definitive Radiation Therapy Indicated only in selected instances

Lentigo melanoma of face Inoperable patients

Probability of control with radiation is related to lesion size

Regimens of 3 to 8 Gy per fraction are employed


Adjuvant Radiation Therapy Indications for primary disease :

Desmoplastic Melanoma histology Tumor thickness >4 mm with either ulceration or

satellite lesions Positive resection margins Primary or adjuvant treatment of locally recurrent

disease


Adjuvant Radiation Therapy Indications for nodal irradiation :

Extracapsular extension Four or more involved nodes Lymph node size >3 cm Cervical node location Recurrent nodal disease after initial resection


Elective Nodal Irradiation Risk of subclinical involvement of regional lymph

nodes is directly related to the depth of the primary lesion

BRESLOW’S TUMOR THICKNESS AND INCIDENCE OF LYMPH NODE METASTASIS


Elective node irradiation Head and neck melanomas of 1.50 mm Clark level IV (involvement of reticular dermis or

subcutis)

Palliative Radiation Therapy Unresectable loco regional disease Distant metastases


Radiation Time-Dose-Fractionation Schedules and Treatment Techniques

30 Gy in 5 fractions of 6 Gy per fraction during 2.5 weeks with treatment on a twice weekly schedule

Earlier studies had shown that fraction size > 4 Gy per fraction has better results

Studies done later showed that fraction sizes of 2.5 Gy per fraction leads to similar response in patients


In cases of nodal irradiation, conventional fractionation with 2 Gy per fraction has shown to give equivalent results with lesser incidence of lymph edema.

50 Gy in 20 fractions for primary disease 50-60 Gy in 25-30 fractions for nodal

irradiation


Adjuvant treatment of the primary tumor bed : 2 to 4 cm margins using electron beam with

appropriate bolus

Irradiation for a head and neck primary : Electron beam coverage of the primary site and

ipsilateral neck, including supraclavicular nodes


Electron energies : Determined by CT-guided treatment planning Appropriate bolus employed for prescription to Dmax Field junctions moved twice during treatment

Combination of photons and electrons or photons only can also be used if the depth to be treated is more


Axillary nodal irradiation includes : ipsilateral low cervical Supraclavicular axillary levels I through III

Inguinal lymph node treatment : Delivered to involved nodes only, without prophylaxis

of external or common iliac nodes To avoid late lymphedema


NON MELANOMA SKIN CANCERS

Basal Cell Carcinoma Squamous Cell Carcinoma Merkel cell carcinoma Dermatofibrosarcoma Protuberance

REGIONAL LYMPHATICS FOR SKIN CANCERS

BASAL CELL CARCINOMA

Represents ~80% of NMSC There is no precursor lesion Tumors are associated with mutations in the

tumor suppressor gene on chromosome 9q and p53

Also known as “Rodent ulcers” – as they burrow deeply, infiltrate vital areas, and cause marked deformity


Most tumors occur on the head and neck, especially above the line joining the earlobe to the angle of the mouth

Rarely metastasize Do not develop on mucous membranes Rare on palms and soles



Adverse prognostic factors for recurrence Tumor location : Face/Ears Tumor size : >2cms Pathology :

Poorly defined tumor borders Perineural invasion Aggressive histology : Morphaeform, Sclerosing,

Infiltrative, Micronodular Recurrent tumor Multifocality Tumor at site of prior Radiation Therapy

SQUAMOUS CELL CARCINOMA

Tumor of keratinizing cells of the epidermis that has invaded beyond the dermal-epidermal junction

Commonly associated with mutations in the p53 tumor suppressor gene

Associated with pre malignant lesions Nodal metastasis is seen Distant metastasis is common

SQUAMOUS CELL CARCINOMA

Adverse prognostic factors for recurrence Depth: >4 mm or invading the reticular dermis and subcutis Tumor size: >4 cm in diameter Treatment: resection margins of <6 mm Pathology: poorly differentiated tumors; perineural invasion

is an indicator for local and/or regional recurrence or distant metastasis

Location: head and neck area, genitalia, mucosal surfaces, ear

Locally recurrent SCC of the skin has an overall metastatic rate of 30%

INDICATIONS FOR RADIATION THERAPY

Radical : For lesions on face Older age patients Surgery is contraindicated

Adjuvant : Positive/Close margins Positive nodes Perineural invasion

Palliative

RADIATION THERAPY TECHNIQUES

Radiation therapy techniques used to treat skin cancer depends on Size of lesion Depth of lesion Anatomic location of the lesion

Quality of radiation is selected based on the best ratio between surface dose and ideal treatment depth

Field size is determined by lesion size and histopathology

TDF schedule depends on cosmetic and functional considerations


Quality of Radiation Superficial X rays Orthogonal X rays Electron beam therapy Photon beam therapy : For depths >5-6 cms, with

the use of a bolus Combination therapy : Electrons and Photons Surface mould therapy

Superficial therapy machine Orthovoltage therapy machine


Field size Depends on

Lesion size Site treated Quality of radiation employed

Choo et al : Microscopic tumor extension varied from 1 to 15 mm (mean, 5.2

mm). They determined a margin of 10 mm around gross tumor was

necessary for 95% likelihood of margin negativity and that larger tumors were associated with greater microscopic extension


Low-energy electron beam dosimetry requires larger lateral field margins for small fields because of constriction of high isodose lines at depth, and a wider field margin is required for electron beam than superficial or orthovoltage fields

Megavoltage photon beams have better flatness and sharper penumbra than electron beams

ELECTRON BEAM ISODOSE CHARTS


For tumors up to 2 cm Photon margins of 0.5 to 1 cm Electron margins of 1 to 1.5 cm

For tumors >2 to 7 cm Photon margins of 1.5 to 2 cm Electron margins of 2 to 2.5 cm


Depth of tumor extension : CT and MRI are helpful in assessing deep tissue penetration

For lesions of the eyelid, pinna, or nasal ala : Tissue thickness is readily measured Full-thickness treatment is recommended


For tumors up to 4 cm : Treatment depth should be about 5 mm below the

expected tumor depth Typically at least 1 cm

Larger, recurrent, and high-grade lesions Higher risk of occult deep extension Treatment depths of at least 2 cm are required


Time-Dose fractionation The relative biologic effectiveness (RBE) is 10% to 20%

less for megavoltage than for superficial or orthovoltage beams

Treatment with megavoltage photons or electrons requires 10% to 20% dose increase for similar biologic effect

Dose adjustment for RBE entails either prescription to the 80% to 90% depth or dose increase of 10% to 20% and prescription to Dmax for megavoltage treatment when converting from orthovoltage schedules


Patient positioning and shielding The region treated is immobilized to achieve stability

and maximize setup reproducibility

The machine gantry is angled so the treated surface is perpendicular to the beam axis when using electrons

When treating with electrons, the thickness of lead in millimeters required to reduce transmission to <5% of maximum is approximately E/2 (E = electron beam energy)


A lead cut-out placed in the head of the machine cone avoids a high-dose zone under the shield edge when treating with high-energy electrons

Secondary beam collimation with a lead cut-out placed directly on the skin surface generally is preferred because the dose at the beam margins is lower than at the center


Special shielding devices are required when treating lesions involving the eye, nose, mouth, and ear

Eyes : Tungsten Eye shield An alternative method involves rotation of the lens and

cornea out of the beam by having the patient stare away from the beam source during treatment : Difficult to reproduce every day


Exit beam blocking is necessary when treating tumors involving the nose, mouth, or ear

The nasal septum and canal are shielded by lead strips coated with either wax or dental acrylic placed directly in the nose

Similar shields are placed under the lip when treating tumors around the mouth to protect the gingiva and oral mucosa

An exit beam shield can be placed at the junction of the posterior surface of the pinna with the scalp over the mastoid to treat auricle lesions


Doses and fractionation : Basal Cell carcinoma

Doses depend on the size of the tumor and the intent of treatment (Radical/Adjuvant)

Mostly, in Radical setting, 2.5 Gy per fraction is used for better results.

In postoperative setting, doses of 2 Gy per fraction are employed – 60 Gy in 30 fractions for close margins

66-70 Gy in 33 to 35 fractions in cases of positive margins

MERKEL CELL CARCINOMA

Neuroendocrine carcinoma of the skin Aggressive and potentially lethal behavior Local recurrence after surgical excision (25%

to 75%) Frequent involvement of regional lymph

nodes (30% to 80%) Distant metastatic spread (20% to 75%) Mortality rates of 20% to 55%


Mainstay of management is surgery Has a high propensity of local recurrence Adjuvant radiation therapy is indicated Surgical resection should be followed by

wide-field irradiation to the primary tumor site, surgical bed and scar, and draining lymphatics


3 to 5 cm field margins are recommended : because of propensity for in-transit metastasis and marginal

recurrence

Primary tumor site 56 to 60 Gy for subclinical disease with negative margin 60 to 66 Gy for microscopically positive margins 66 to 70 Gy for gross residual disease at conventional fractionation

Nodal doses 46 to 50 Gy are employed for prophylaxis of subclinical disease 56 to 60 Gy for gross disease


For medically or surgically inoperable patients, radiation therapy can be employed in a definitive attempt with elective treatment of clinically uninvolved nodes.

DERMATOFIBROSARCOMA PROTUBERANS Dermal sarcoma of fibroblast origin Low grade Characterized by

Indolent growth Frequent local recurrence Rare lymphatic or hematogenous metastasis

DERMATOFIBROSARCOMA PROTUBERANS

Surgery is the mainstay of treatment Clear resection margins of 3 cm down to and

including muscle or fascia result in a local recurrence rate <10%


Role of Radiation therapy : Pre operative : patients at high risk for positive

resection margins based on large tumor size or location where critical structures preclude optimal resection

Post operative : close or positive margins because of recurrence risk >50%


Dose and fractionation : Pre operative :

3-5 cm margin throughout the lesion 50 Gy in 1.8-2 Gy per fraction

Post operative : Close resection margins - 60 Gy Microscopic positive margins - 60 to 65 Gy Gross residual disease - 65 to 75 Gy with field

reductions after 50 Gy All recurrent or high-grade lesions regardless of margin

status

THANK YOU !!!

Healthcare

Radiation therapy for Skin Cancers