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David J. Schlesinger, Faisal T. Sayer, Chun-Po Yen, and Jason P. Sheehan

Object

Treatment planning for Gamma Knife surgery has traditionally been a forward planning (FP)–only approach with results that depend significantly on the experience of the user. Leksell GammaPlan version 10.0, currently in beta testing, introduces a new inverse planning (IP) engine that may allow more reproducible results across dosimetrists and individual institutions. In this study the authors compared the FP and IP approaches to Gamma Knife surgery.

Methods

Forty-three patients with pituitary adenomas were evaluated after dose planning was performed using FP and IP treatment approaches. Treatment plans were compared for target coverage, target selectivity, Paddick gradient index, number of isocenters, optic pathways dose, and treatment time. Differences between the forward and inverse treatment plans were evaluated in a statistical fashion.

Results

The IP software generated a dose plan within approximately 10 minutes. The FP approach delivered the prescribed isodose to a larger treatment volume than the IP system (p < 0.001). The mean (± SD) FP and IP coverage indices were 0.85 ± 0.23 and 0.85 ± 0.13, respectively (no significant difference). The mean FP and IP gradient indices were 2.78 ± 0.20 and 3.08 ± 0.37, respectively (p < 0.001). The number of isocenters did not appreciably differ between approaches. The maximum doses directed to the optic apparatus for the FP and IP methods were 8.67 ± 1.97 Gy and 12.33 ± 5.86 Gy, respectively (p < 0.001).

Conclusions

The Leksell GammaPlan IP system was easy to operate and provided a reasonable, first approximation dose plan. Particularly in cases in which there are eloquent structures at risk, experience and user-based optimization will be required to achieve an acceptable Gamma Knife dose plan.

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Arnaldo Neves Da Silva, Kazuki Nagayama, David J. Schlesinger, and Jason P. Sheehan

Object

Brain metastases from gastrointestinal cancers are rare. However, the incidence is increasing because patients with gastrointestinal carcinoma tend to live longer due to earlier diagnosis and more effective treatment of systemic disease. The purpose of this study was to evaluate the efficacy of Gamma Knife surgery (GKS) for the treatment of brain metastases from gastrointestinal cancers.

Methods

The authors performed a retrospective review of 40 patients (18 women and 22 men) who had undergone GKS to treat a total of 118 metastases from gastrointestinal cancers between January 1996 and December 2006. The mean patient age was 58.7 years, and the mean Karnofsky Performance Scale (KPS) score was 70. There were 7 patients with esophageal cancer, 25 with colon cancer, 5 with rectal cancer, 2 with pancreatic cancer, and 1 with gastric cancer. Nineteen patients were treated with whole-brain radiotherapy and/or local brain radiotherapy before GKS. Twenty-four patients had extracranial metastases, and 3 had an additional primary cancer. The mean metastatic brain tumor volume was 4.3 cm3, and the mean maximum tumor dose varied from 17.1 to 76.7 Gy (mean 41.8 Gy).

Results

Follow-up imaging studies were available in 25 patients with a total of 90 treated metastases. The results demonstrate a tumor control rate of 91%. The median survival time was 6.7 months, and the 6-month and 1-year survival rates were 55 and 25%, respectively. A univariate analysis revealed that the KPS score (≤ 70 vs ≥ 80) was significant (p = 0.018) for improved survival.

Conclusions

Results in this series suggest that GKS can be an effective tool for the treatment of brain metastases from gastrointestinal cancer.