Hyperfractionated radiation in children with rhabdomyosarcoma--results of an Intergroup Rhabdomyosarcoma Pilot Study

The Intergroup Rhabdomyosarcoma Study (IRS) Group initiated a pilot study (IRS IV-P) of hyperfractionated radiation (HF XRT) with chemotherapy to test the feasibility and toxicity of this combined modality approach in children with localized but nonresected (group III) and metastatic (group IV) rhabdomyosarcoma.

Using the linear quadratic equation, and an alpha/beta ratio of 10 Gy for acute reacting tumor effect and 3 Gy for late reacting normal tissue effect, a HF XRT protocol was developed giving a total radiation dose of 59.4 Gy, in 1.10 Gy fractions, twice daily at 6-8 h intervals. All patients received chemotherapy in addition to irradiation. The radiation scheme was calculated to increase the biologically effective dose to the tumor by 10% without increasing late effects, when compared to a conventional schedule of 50.4 Gy in 1.8 Gy daily fractions. This protocol also was predicted to cause an increase in acute normal tissue effects.

Four hundred forty-nine children age 21 years and younger were eligible for the hyperfractionated radiation study of whom 297 had Group III disease and 152 had Group IV disease. A total of 117 patients were excluded from the feasibility and toxicity analysis because of progressive disease or death prior to scheduled irradiation, surgical resection, major protocol violation, treatment with brachytherapy, or missing data. Thus, 332 children were evaluable for the HF XRT protocol. Twenty-eight of the 332 (8%) were given conventional radiation because of physician preference or young age. Twenty of the 332 (6%) were not irradiated because of young age, anesthesia, or transportation problems. All nonirradiated children were < or = 3 years of age. Thus, 284 children, 86% of the evaluable population, received HF XRT. The radiation dose, number of fractions, number of days, and interfractional interval were scored as appropriate in 93% of cases. Review of radiation portals revealed that in 230 of 284 cases (81%) the radiation fields were appropriate, as per protocol. Thus, the HF XRT was feasible treatment in a multiinstitutional study. Analysis of toxicity revealed that 152 of 204 (75%) of Group III and 52 of 80 (65%) of Group IV patients experienced severe or life-threatening toxicity, explained by the addition of chemotherapy with the radiation. The majority of this toxicity was hematopoietic. Observed organ toxicity, which was potentially explained by the radiation treatment, was greatest at the end of radiation, and improved at the 6-week and 3-month evaluation periods. There were no deaths attributed to radiation toxicity and no instance of toxicity that required alteration of the radiation protocol. Thus, the treatment was not associated with toxicity that was considered excessive or unusual.

The IRS IV-P study confirms that HF XRT combined with chemotherapy is both feasible and tolerable in children with rhabdomyosarcoma. A prospective randomized trial is underway to test its efficacy as compared to conventional radiation among children also receiving concurrent chemotherapy for rhabdomyosarcoma.