T2 weighted MRI in assessment of volume changes during radiotherapy of high grade gliomas.

Aim: To determine whether any changes in gross tumor volume occur between pre treatment MRI and week 5 MRI in high grade gliomas treated by conformal radiotherapy.

Methods And Materials: Between July 2003-July 2005, 17 patients with WHO grades 3 and 4 malignant gliomas treated with conformal radiotherapy to a total dose of 60 Gy were included in this retrospective study. All patients had undergone T2 weighted MRI a day before treatment and then again at end of week 5 of treatment for definition of initial and boost fields respectively. Gross tumor volumes were delineated on the two MRI's of each patient and the differences were noted. Two patients with multifocal disease were excluded from the final analysis.

Results: Of the 15 patients with unifocal disease, 12/15 cases (80%) showed a reduction in tumor volumes (median 54.85 cc). Of these, 4/15 (26.6%) cases (two each of grade 3 and grade 4 gliomas) had an objective reduction in GTV (> or = 50%) and 3/15 (20%) cases (two of grade 4 and one of grade 3 gliomas) demonstrated an increase in tumor volume (median 14 cc).

Conclusions: This study has shown that a change in gross tumor volume occurred in almost all patients on week 5 MRI. The likelihood of treatment success would appear to be decreased if the tumour is not within the treatment field and hence it may be worthwhile to do a mid treatment MRI for definition of boost volumes especially in dose escalation trials employing highly conformal radiotherapy fields.