Previously Untreated Childhood Rhabdomyosarcoma
For optimal care of pediatric patients undergoing radiation treatments, it is imperative to have available a radiation oncologist, radiation technicians, and nurses who are experienced in treating children. An anesthesiologist may be necessary to sedate and immobilize young patients. Computerized treatment planning with a 3-dimensional planning system should be available. Techniques to deliver radiation specifically to the tumor while sparing normal tissue (e.g., conformal radiation therapy, intensity-modulated radiation therapy [IMRT], proton-beam therapy [charged-particle radiation therapy], or brachytherapy) are appropriate.[13,14,15,16]
- Comparison of proton-beam and IMRT treatment plans has shown that proton-beam radiation can spare more normal tissue adjacent to the targeted volume than IMRT.[17,18] Follow-up remains relatively short, and there are no data available to determine if the reduction in dose to adjacent tissue will result in improved functional outcome or reduce the risk of secondary malignancy. Because patient numbers are small, it is not possible to determine if the risk of local recurrence might be increased by reducing radiation dose in tissue adjacent to the primary tumor.
- A retrospective review of patients with intermediate-risk rhabdomyosarcoma compared conformal RT and IMRT.[Level of evidence: 2B] IMRT improved the target coverage but did not show a difference in local failure rate or EFS.
Standard RT of children with rhabdomyosarcoma includes the following:
Table 5. Radiation Therapy (RT) Dose According to Rhabdomyosarcoma Group, Histology, and Site of Disease (Children's Oncology Group [COG])
|Group I|| |
|Alveolar||36 Gy to involved (prechemotherapy) site. The use of RT is under investigation.|
|Group II|| |
|N0 (microscopic residual disease after surgery)||36 Gy to involved (prechemotherapy) site.|
|N1 (resected regional lymph node involvement)||41.4 Gy to involved (prechemotherapy) site and nodes.|
|Group III|| |
|Orbital and nonorbital tumors||50.4 Gy with volume reduction after 36 Gy if excellent response to chemotherapy and noninvasive pushing tumors; no volume reduction for invasive tumors.|
|Group IV|| |
| ||As for other groups and including all metastatic sites, if safe and possible.Exception:lung (pulmonary metastases) treated with 15 Gy if aged 6 years or older, 12 Gy if younger than 6 years.|
- 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 36 Gy if they do not have involved lymph nodes and 41 Gy in the presence of involved nodes.[8,20,21] Low-risk patients (embryonal histology and favorable sites with microscopic residual disease) treated on a COG study had local control with 36 Gy, which was comparable to historic controls who received 41.4 Gy.IRS-II patients with gross residual disease (Group III) who received 40 Gy to more than 50 Gy had locoregional relapse rates greater than 30% but higher doses of radiation (>60 Gy) were associated with unacceptable long-term toxic effects.[23,24] Group III patients on the IRS-IV standard treatment arm received 50.4 Gy, with 5-year progression-free survival of 55% to 75%. Experience supports using a somewhat reduced dose of RT in patients with Group III disease who have delayed gross total resection with negative margins. In the recent COG-D9602 study, these patients had a greater than 85% likelihood of local control with 36 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. RT is usually given over 5 to 6 weeks (e.g., 1.8 Gy once per day), during which time chemotherapy is usually modified to avoid the radiosensitizing agents dactinomycin and doxorubicin.