Table 5. Radiation Therapy (RT) Dose According to Rhabdomyosarcoma Group, Histology, and Site of Disease (Children's Oncology Group [COG]) continued...
Brachytherapy, using either intracavitary or interstitial implants, is another method of local control and has been used in selected situations for children with rhabdomyosarcoma, especially those with primary tumors at vaginal or vulvar sites [28,29,30,31,32] and selected bladder/prostate sites.[Level of evidence: 3iiiA] In small series from one or two institutions, this treatment approach was associated with a high survival rate and with retention of a functional organ or tissue in most patients.[29,34] Other sites, especially head and neck, have also been treated with brachytherapy. Patients with initial Group III disease, who subsequently have microscopic residual disease following chemotherapy with or without delayed surgery are likely to achieve local control with RT at doses of 40 Gy or more.
Very young children (aged ≤36 months) diagnosed with rhabdomyosarcoma pose a therapeutic challenge because of their increased risk for treatment-related morbidity. As suggested above, in older children, reduced radiation doses may be appropriate if delayed surgery can provide negative margins. However, for infants who are unable to undergo surgical resection, higher doses of RT remain appropriate. Radiation techniques are designed to maximize normal tissue sparing, and should include conformal approaches, often with intensity-modulated techniques.
Local Control Management with Surgery and RT by Primary Sites of Disease
Head and neck
Rhabdomyosarcomas of the orbit should not undergo exenteration, but biopsy is needed for diagnosis.[38,39] Biopsy is followed by chemotherapy and RT, with orbital exenteration reserved for the small number of patients with locally persistent or recurrent disease.[40,41] RT and chemotherapy are the standard of care, with survival in excess of 90% to 95%. For patients with orbital tumors, precautions should be taken to limit the RT dose to the lens and cornea.
If the tumors are nonorbital and cranial parameningeal (arising in the middle ear/mastoid, nasopharynx/nasal cavity, paranasal sinus, parapharyngeal region, or pterygopalatine/infratemporal fossa), a magnetic resonance imaging (MRI) scan with contrast of the primary site and brain should be obtained to check for presence of base-of-skull erosion and possible extension onto or through the dura.[42,43,44] If skull erosion and/or transdural extension is equivocal, a computed tomography (CT) scan with contrast of the same regions is indicated. Also, if there is any suspicion of extension down the spinal cord, an MRI scan with contrast of the entire cord should be obtained. The cerebrospinal fluid (CSF) should be examined for malignant cells in all patients with parameningeal tumors. Because complete removal of these tumors is difficult, owing to their location, the initial surgical procedure for these patients is usually only a biopsy for diagnosis.
Nonorbital cranial parameningeal tumors are optimally managed by conformal RT and chemotherapy. Patients with parameningeal disease with intracranial extension in contiguity with the primary tumor, and/or cranial base bone erosion, and/or cranial nerve palsy do not require whole-brain irradiation or intrathecal therapy, unless tumor cells are present in the CSF at diagnosis. Patients should receive RT to the site of primary tumor with a 1.5 cm margin to include the meninges adjacent to the primary tumor and the region of intracranial extension, if present, with a 1.5 cm margin. In a retrospective trial, starting radiation therapy within 2 weeks of diagnosis for patients with signs of meningeal impingement was associated with lower rates of local failure. When no signs of meningeal impingement were present, delay of radiation therapy for more than 10 weeks did not impact local failure rates.