Previously Untreated Childhood Rhabdomyosarcoma
Among the modifications of RT for specific primary sites recommended for IRS-IV-STAGE-1 patients were the following:[37,103]
- For patients with orbital tumors, precautions should be taken to limit the dose to the lens, cornea, lacrimal gland, and optic chiasm.
- Patients with bladder/prostate primary tumors who present with a large pelvic mass resulting from a distended bladder caused by outlet obstruction receive treatment to a volume defined by imaging studies following initial chemotherapy.
- Girls with genitourinary primary tumors should have their ovaries shielded or possibly moved, in an effort to preserve fertility when they are receiving RT to the lower abdomen and pelvis. In the COG-ARST0331 study, there has been an unacceptably high rate of local recurrence in girls with Group III vaginal tumors who did not receive RT. The COG-STS is now recommending that RT be administered to subsequent patients with residual viable vaginal tumor, beginning at week 24.
- 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 2-cm margin to include the meninges adjacent to the primary tumor  and the region of intracranial extension, if present, again with a 2-cm margin. Patients with intracranial extension should begin receiving RT within 2 weeks after diagnosis.
- Rarely, children can present with tumor cells in the CSF, have other evidence of diffuse meningeal disease, and/or have multiple intraparenchymal brain metastases from a distant primary tumor. They should be treated with central nervous system-directed irradiation in addition to chemotherapy/RT for the primary tumor. Spinal irradiation may also be indicated.
Very young children (age <36 months or younger) diagnosed with rhabdomyosarcoma pose a therapeutic challenge because of their increased risk for treatment-related morbidity. Recent experience  supports using a somewhat reduced dose of RT in settings where surgery alone is insufficient to provide a high likelihood of local control. For children with initially unresectable tumors, delayed gross total resection followed by 36 Gy beam RT provides an excellent likelihood of local control. For infants with unresectable tumors, 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.
Treatment options under clinical evaluation
The following are examples of national and/or institutional clinical trials involving RT that are currently being conducted. Information about ongoing clinical trials is available from the NCI Web site.
- Brachytherapy: 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,[109,110,111,112,113] and selected bladder/prostate sites. 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.[110,114] Other sites, especially head and neck, have also been treated with brachytherapy. Patients with initial Group III disease who later have microscopic residual disease after chemotherapy with or without delayed surgery are likely to achieve local control with RT at doses of 40 Gy or more.