radiation therapy for skin cancers
DESCRIPTION
Role of Radiation TherapyTRANSCRIPT
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RADIATION THERAPY FOR SKIN CANCERS
Mayur Mayank
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SKIN CANCERS
MELANOMANON
MELANOMATOUS SKIN CANCERS
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ANATOMY OF SKIN
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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
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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
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CLAKE’S LEVELS
SURVIVAL BASED ON LYMPH NODAL METASTASIS
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RADIATION THERAPY FOR MELANOMA
Definitive Radiation Therapy Adjuvant Radiation Therapy Elective Nodal Irradiation Palliative Radiation Therapy
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RADIATION THERAPY FOR MELANOMA
Relatively radio resistant tumor Low alpha/beta ratio -> Hypo fractionated
regimens have an advantage
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RADIATION THERAPY FOR MELANOMA
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
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RADIATION THERAPY FOR MELANOMA
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
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RADIATION THERAPY FOR MELANOMA
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
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RADIATION THERAPY FOR MELANOMA
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
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RADIATION THERAPY FOR MELANOMA
Elective node irradiation Head and neck melanomas of 1.50 mm Clark level IV (involvement of reticular dermis or
subcutis)
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Palliative Radiation Therapy Unresectable loco regional disease Distant metastases
RADIATION THERAPY FOR MELANOMA
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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
RADIATION THERAPY FOR MELANOMA
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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
RADIATION THERAPY FOR MELANOMA
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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
RADIATION THERAPY FOR MELANOMA
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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
RADIATION THERAPY FOR MELANOMA
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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
RADIATION THERAPY FOR MELANOMA
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NON MELANOMA SKIN CANCERS
Basal Cell Carcinoma Squamous Cell Carcinoma Merkel cell carcinoma Dermatofibrosarcoma Protuberance
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REGIONAL LYMPHATICS FOR SKIN CANCERS
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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
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BASAL CELL CARCINOMA
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
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BASAL CELL CARCINOMA
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BASAL CELL CARCINOMA
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
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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
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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%
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INDICATIONS FOR RADIATION THERAPY
Radical : For lesions on face Older age patients Surgery is contraindicated
Adjuvant : Positive/Close margins Positive nodes Perineural invasion
Palliative
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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
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RADIATION THERAPY TECHNIQUES
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
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Superficial therapy machine Orthovoltage therapy machine
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RADIATION THERAPY TECHNIQUES
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
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RADIATION THERAPY TECHNIQUES
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
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ELECTRON BEAM ISODOSE CHARTS
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RADIATION THERAPY TECHNIQUES
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
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RADIATION THERAPY TECHNIQUES
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
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RADIATION THERAPY TECHNIQUES
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
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RADIATION THERAPY TECHNIQUES
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
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RADIATION THERAPY TECHNIQUES
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)
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RADIATION THERAPY TECHNIQUES
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
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RADIATION THERAPY TECHNIQUES
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
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RADIATION THERAPY TECHNIQUES
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
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RADIATION THERAPY TECHNIQUES
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
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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%
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MERKEL CELL CARCINOMA
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
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MERKEL CELL CARCINOMA
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
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MERKEL CELL CARCINOMA
For medically or surgically inoperable patients, radiation therapy can be employed in a definitive attempt with elective treatment of clinically uninvolved nodes.
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DERMATOFIBROSARCOMA PROTUBERANS Dermal sarcoma of fibroblast origin Low grade Characterized by
Indolent growth Frequent local recurrence Rare lymphatic or hematogenous metastasis
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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%
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DERMATOFIBROSARCOMA PROTUBERANS
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%
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DERMATOFIBROSARCOMA PROTUBERANS
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
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