Can Post-radiosurgical Imaging Patterns Predict Long-term Results of Acoustic Tumor Radiosurger

Chih-Chun Wu1, Wan-Yuo Wayne GUO2, Hung-Chi Pan3, Wen-Yuh Chung3, Hsiu-Mei Wu4

1Pai-Tou, Taipei, Taiwan 2Taipei Veterans General Hospital and Yang-Ming University 3Neurological Institute, Taipei Veterans General Hospital 4Department of Radiology, Taipei Veterans General Hospital

Keywords: vestibular schwannoma, Imaging, gamma knife, outcome, radiosurgery

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     The imaging appearance of the tumor after radiosurgery may be predictive of the long-term result.
Our study was aimed to refine acoustic tumor radiosurgery by evaluating the long-term tumor morphological outcome based on sequential MR imaging, focusing on the post-radiosurgical tumor enhancing and volumetric change patterns.
     There were 104 females and 65 males, age 49, 11-79 y/o.
     We retrospectively reviewed 169 consecutive patients receiving Gamma Knife radiosurgery for acoustic tumors from 1993 to 2006, in our institute.  Radiosurgery was the primary treatment (NOP group) in 103 patients, and 66 patients received prior surgical tumor extirpation (OP group). The mean tumor volume, defined as the sum up of tumor segmentation on all tumor slices based on Gd-enhanced spin-echo T1-weighted MR images (3-mm slice thickness, no gap) was 4.32 (0.15-22.1) ml before radiosurgery, and the mean imaging follow-up period was 78 (36-177) months. Same imaging protocol and volumetric measurement were performed at every follow-up time point. We divided the post-radiosurgical tumor enhancing patterns into constant homogeneous enhancement and initial loss central enhancement. The post-radiosurgical volumetric changes was defined as transient tumor expansion if >10% volume larger than the baseline, or otherwise, as tumor stable or shrinkage. We used tumor volume ratio (TVR), tumor volume at follow-up divided by baseline tumor volume, to define radiosurgical outcome.
     Initial loss central enhancement was found in 128 (76%) patients. Transient tumor expansion was present in 91 (54%) patients. The irradiation dose and the previous treatment status showed no significant differences among the groups. Those tumors having larger baseline volume tended to exhibit initial loss central enhancement (p=0.005), and those had initial loss central enhancement tended to have transient tumor expansion (p=0.001). Those tumors showing transient tumor expansion had significantly larger residual TVR in both OP and NOP group (p= 0.02 and p<0.0001), but those exhibiting initial loss central enhancement had larger residual TVR only in the NOP group (p=0.005)
     This was a retrospective analysis.
     Initial loss central enhancement was common in post-radiosurgical acoustic tumors and usually associated with transient tumor expansion. 
     The presence of initial shrinkage or stable of the tumor might indicate better long-term tumor control, while presence of initial loss central enhancement did not indicate better long-term tumor shrinkage.


Project Roles:

C. Wu (), W. GUO (), H. Pan (), W. Chung (), H. Wu ()