Evaluating changes in tumor volume using magnetic resonance imaging during the course of radiotherapy treatment of high-grade gliomas: Implications for conformal dose-escalation studies.
OBJECTIVE
To determine whether changes in tumor volume occur during the course of conformal 3D radiotherapy of high-grade gliomas by use of magnetic resonance imaging (MRI) during treatment and whether these changes had an impact on tumor coverage.


METHODS
Between December 2000 and January 2004, 21 patients with WHO Grades 3 to 4 supratentorial malignant gliomas treated with 3D conformal radiotherapy (median dose, 70 Gy) were enrolled in a prospective clinical study. All patients underwent T1-weighted contrast-enhancing and T2-weighted and fluid-attenuated inversion recovery (FLAIR) imaging at approximately 1 to 2 weeks before radiotherapy, during radiotherapy (Weeks 1 and 3), and at routine intervals thereafter. All MRI scans were coregistered to the treatment-planning CT. Gross tumor volume (GTV Pre-Rx) was defined from a postoperative T1-weighted contrast-enhancing MRI performed 1 to 2 weeks before start of radiotherapy. A second GTV (GTV Week 3) was defined by use of an MRI performed during Week 3 of radiotherapy. A uniform 0.5 cm expansion of the respective GTV, PTV (Pre-Rx), and PTV (Week 3) was applied to the final boost plan. Dose-volume histograms (DVH) were used to analyze any potential adverse changes in tumor coverage based on Week 3 MRI.


RESULTS
All MRI scans were reviewed independently by a neuroradiologist (DGH). Two patients were noted to have multifocal disease at presentation and were excluded from analysis. In 19 cases, changes in the GTV based on MRI at Week 3 during radiotherapy were as follows: 2 cases had an objective decrease in GTV (> or =50%); 12 cases revealed a slight decrease in the rim enhancement or changes in cystic appearance of the GTV; 2 cases showed no change in GTV; and 3 cases demonstrated an increase in tumor volume. Both cases with objective decreases in GTV during treatment were Grade 3 tumors. No cases of tumor progression were noted in Grade 3 tumors during treatment. In comparison, three of 12 Grade 4 tumors had tumor progression, based on MRI obtained during Week 3 of radiotherapy. Median increase in GTV (Week 3) was 11.7 cc (range, 9.8-21.3). Retrospective DVH analysis of PTV (Pre-Rx) and PTV (Week 3) demonstrated a decrease in V(95%)(PTV volume receiving 95% of the prescribed dose) in those 3 cases.


CONCLUSIONS
Routine MR imaging during radiotherapy may be essential in ensuring tumor coverage if highly conformal radiotherapy techniques such as stereotactic boost and intensity-modulated radiotherapy are used in dose-escalation trials that utilize smaller treatment margins.
Tsien
Christina
C
Department of Radiation Oncology, University of Michigan, Ann Arbor, MI 48109, USA. ctsien@umich.edu
Gomez-Hassan
Diana
D
Ten Haken
Randall K
RK
Tatro
Daniel
D
Junck
L
L
Chenevert
T L
TL
Lawrence
T
T
D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D005260:Female; D005910:Glioma / Q000473:pathology* / Q000532:radiotherapy*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D020266:Radiotherapy, Conformal; D047368:Tumor Burden