Previously Untreated Childhood Rhabdomyosarcoma
For optimal care of pediatric patients undergoing radiation treatments, it is imperative to have a radiation oncologist, radiation technicians, and nurses who are experienced in treating children. An anesthesiologist may be necessary to help sedate and immobilize young patients. The facility should be equipped with a linear accelerator and have the capabilities to administer electron beam therapy. Computerized treatment planning with a three-dimensional planning system should be available. Techniques to deliver radiation specifically to the tumor while sparing normal tissue (e.g., conformal radiation therapy, IMRT, proton-beam therapy [charged-particle radiation therapy], or brachytherapy) should be considered (see below).[96,97,98]
Standard treatment options
- The RT dose depends predominantly on the amount of residual disease, if any, following the primary surgical resection. In general, patients with microscopic residual disease (Group II) receive RT to approximately 41 Gy,[88,99] though doses from 30 Gy to 40 Gy may be adequate in patients receiving effective multiagent chemotherapy.IRS-II (POG-7898) study patients with gross residual disease (Group III) who received 40 Gy to more than 50 Gy had locoregional relapse rates greater than 30%; higher doses of radiation (>60 Gy) have been associated with unacceptable long-term toxic effects.[101,102] Group III patients on the IRS-IV-STAGE-1 standard treatment arm received 50.4 Gy.
- The treated volume should be determined by the extent of tumor at diagnosis prior to surgical resection and prior to chemotherapy. A margin of 2 cm is generally used, including clinically involved regional lymph nodes. While the volume irradiated may be modified on the basis of guidelines for normal tissue tolerance, gross residual disease at the time of radiation should receive full-dose treatment.
- The timing of RT generally allows for chemotherapy to be given for 1 to 3 months before RT is initiated. In COG protocols, patients with parameningeal disease who have evidence of intracranial extension start radiation therapy at the beginning of treatment.[61,104,105] A prospective trial of 26 patients with Group III parameningeal rhabdomyosarcoma achieved good local control and survival with RT administered at the conventional time. RT is usually given for 5 to 6 weeks (e.g., 1.8 Gy per day for 28 treatment days), during which time chemotherapy is usually modified to avoid the radiosensitizing agents dactinomycin and doxorubicin.
The IRSG conducted a randomized study within the IRS-IV-STAGE-1 protocol and showed that giving RT twice a day, 6 to 8 hours apart, at 1.1 Gy per dose (hyperfractionated schedule), 5 days per week was feasible but difficult to accomplish in small children who required sedation twice daily. Patients with localized, gross residual tumors were randomly assigned to receive conventional RT (50.4 Gy vs. 59.4 Gy) given by the twice-daily hyperfractionated schedule. There was no demonstrated advantage in terms of local control. Therefore, conventional RT remains the standard for treating patients with rhabdomyosarcoma and gross residual disease.