SALIVARY GLANDS: POSTOPERATIVE RADIOTHERAPY

INDICATIONS FOR PORT

Margins

* close margin
* positive margin
* residual tumor

Invasion into

* bone
* perineural space
* beyound the capsule of the gland with periglandular and soft tissue invasion

Surgical Factors

* tumor spillage during operation
* Large tumors (> 5 cm)
* deep lobed tumors requiring radical resection

Tumor Characteristics

* High-grade cancer
* Recurrent disease
* malignant transformation
* LN metastases

RADIATION TECHNIQUES

Target Volume

  • Initial target volume
    • Benign tumors and low-grade tumors without LN involvement: parotid bed only.
    • High-grade tumors: parotid and ipsilateral neck.
      • except acinic and adenoid cystic tumors
    • Tumors with LN involvement: parotid and ipsilateral neck.
    • Gross invasion of a named nerve: more generous coverage of nerve to base of skull.
      • 50% of adenoid cystic tumor have nerve invasion and should always have nerve coverage.
  • Boost: tumor bed.

Primary Treatment Volume

  • entire ipsilateral parotid gland
    • cover parapharyngeal space and infratemporal fossa
    • include ipsilateral subdigastric node as inferior pole of the parotid lies in this region

Dose

  • Pleomorphic Adenoma
    • 54-56 Gy in 1.8 to 2 Gy fractions for microscopic disease
    • 60-66 Gy for gross disease
  • Benign and low-grade tumors with negative resection margins: 50-54 Gy in 25-27 fractions
  • High-grade tumors and those with LN metastases: 60 Gy in 30 fractions after complete resection or 64-66 Gy in 32 to 33 fractions after incomplete resection. Field reductino is made after 50-54 Gy.
  • Elective neck irradiation: 50 Gy in 25 fractions.

Nodal Treatment

  • Indications
    • positive LN on a nodal dissection
    • > 4 cm tumors and/or high-grade tumors except
      • adenoid cystic
      • carcinoma ex pleomorphic adenoma
    • facial nerve dysfunction
    • recurrent disease
  • Field
    • at least Ib, II and III should be included
    • can include I-IV
  • Dose
    • 46-50 Gy for elective nodal irradiation
    • 60 Gy for positive node after dissection

FACIAL NERVE INVOLVEMENT

  • Facial nerve is generally preserved unless it is clearly involved with tumor.
  • Facial nerve sacrifice when nerve is grossly encased or involved with cancer
    • nerve grafting (cable facial nerve grafting with the greater auricular or sural nerve) can recover facial function in 2-13 months in majority of patients
    • Adjuvant postoperative radiotherapy had no negative effect on the graft.

Complications of Facial nerve resection

  • corneal exposure, ulceration, blindness
  • loss of sensation in the ear lobe and gustatory sweating (Frey's syndrome) in 5-25% of cases

SEQUELAE OF TREATMENT

NORMAL TISSUE EFFECTS

  • partial xerostomia
  • trismus
  • hearing loss if ≥ 60 Gy to cochlear (dose of ≤ 30 Gy should be attempted).

RADIATION EFFECT ON NORMAL SALIVARY FUNCTION

Acute

  • RT to serous cell expressed within 24 hours of irradiation
  • Apoptosis of serous cell and acute inflammatory response
  • Leads to swelling and dryness

Submandibular Gland

  • The submandibular glands are responsible for 70% of resting salivary flow.
  • Removal of the submandibular gland is most commonly performed for sialolithiasis, chronic sialoadenitis, or as part of a neck dissection.
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