Previously Untreated Childhood Rhabdomyosarcoma
Table 5. Radiation Therapy (RT) Dose According to Rhabdomyosarcoma Group, Histology, and Site of Disease (Children's Oncology Group [COG]) continued...
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.
Children who present with tumor cells in the CSF (Stage 4) may or may not have other evidence of diffuse meningeal disease and/or distant metastases. In a review of experience from IRSG Protocols II though IV, eight patients had tumor cells in the CSF at diagnosis; three of four without other distant metastases were alive at 6 to 16 years after diagnosis, as was one of four who had concomitant metastases elsewhere. Patients may also have multiple intraparenchymal brain metastases from a distant primary tumor. They may be treated with central nervous system-directed RT in addition to treatment with chemotherapy/RT for the primary tumor. Spinal RT may also be indicated.[46,47]