Aim: Thallium-201 (Tl-201) scintigraphy in patients with malignant soft tissue tumours was evaluated to determine whether the images correlated with histological response to preoperative radiotherapy.
Methods: We studied 54 patients, median age 32 (range 17-84) years, with non-metastatic, malignant soft tissue tumours diagnosed between 1996 and 2001. Thirty-eight patients had unoperated tumours and 16 patients had previous incomplete excisions. All patients received preoperative radiotherapy followed by surgery. No patient received chemotherapy as part of their initial management. Qualitative analyses of early phase (30 min) and late phase (4 h) Tl-201 scintigraphic images before and after preoperative radiotherapy were compared with the degree of tumour necrosis determined histologically.
Results: In the previously unoperated group, all 38 patients had increased TL-201 uptake in the late phase of scanning prior to radiotherapy suggesting metabolically active tissue. In the previously excised group 11 patients had increased Tl-201 uptake in the late phase of scanning prior to radiotherapy. Following radiotherapy, patients with Tl-201 retention on late phase scans had a lower rate of necrosis than patients with minimal retention, p<0.0001. Following radiotherapy, 28 of 29 patients with minimal uptake on the late phase had 80% or more necrosis, while 24 of 25 patients with increased uptake on the late phase had less than 80% necrosis (p<0.0001). Patients with previously excised tumours who had thallium retention following radiotherapy demonstrated evidence of residual disease at surgery. All patients with incompletely excised tumours who had no thallium retention on late phase scanning after radiotherapy demonstrated no evidence of residual disease at surgery.
Conclusion: Thallium scintigraphy is a readily available investigative tool, which when used in conjunction with other imaging modalities in the assessment of primary and incompletely excised malignant soft tissue tumours, may predict histological tumour response to preoperative radiotherapy.