IMPROVEMENT OF LOCAL TUMOR-CONTROL IN PRI MARY NONRESECTABLE RHABDOMYOSARCOMA IN CHILDREN BY EARLY, RISKADAPTED RADIOTHERAPY - REPORT OF THE GERMAN COOPERATIVE SOFT-TISSUE SARCOMA STUDIES CWS-81 AND 86

Since the lack of local tumor control was a major cause of therapy fai lure in the CWS-81 Study, the concept of the definitive local tumor co ntrol in patients with primary non-resectable RMS has been changed. In the CWS-81 Study RT was stratified according to the results of SL sur gery at week 16-20 (after 2 cycles of CT), given only to patients who at this time stage had still microscopic or macroscopic tumor residual s. In the CWS-86 Study irradiation was given prior to SL surgery after one cycle of CT (7-10 weeks). The cumulative dose was stratified acco rding to the degree of tumor volume reduction (32 Gy and 54.4 Gy) and given simultanous to the second CT. The single dose was reduced (1.6 G y) and given twice a day (accelerated hyperfractionation). This analys is excluded patients with parameningeal and extremity primaries since this group had special RT recommendation in both studies. 62% of patie nts had been irradiated in the CWS 81 Study and 70% in the CWS 86. The local tumor control improved dramatically in the CWS-86 Study in the group of patients who had been irradiated prior to SL surgery and stil l had macroscopic residues at the start of RT (rate of local tumor con trol 25% vs. 95%, p < .001). The average RT dose for this group was ev en lower in the CWS-86 Study (38.8 vs. 40 Gy). In the patients who wer e irradiated in clinical remission, no major change in local tumor con trol between studies was observed (CWS 81 82% vs. 75% CWS 86). The ave rage RT dose in the CWS 86 Study has been dramatically reduced: 34 Gy vs. 44.4 Gy. It is noteworthy that 25 patients in the CWS-86 were irra diated with 32 Gy, the local tumor control in this group was 88%. Loca l failure rate was 14% (CWS 86) vs. 35% (CWS 81) in patients irradiate d with < 40 Gy, in patients irradiated with > 40 Gy it was 0% (CWS 86) vs. 43% (CWS 81). The following factors should be considered as poten tial influencing for the improvement of local tumor control in the CWS -86 Study: earlier, preoperative application of RT, acceleration and h yperfractionation, simultaneous RT-CT.