Dosimetric comparison between gamma knife plans and intensity-modulated radiotherapy plans for benign intracranial tumors

Nakazawa, H.; Mori, Y.; Tsugawa, T.; Hagiwara, M.; Komori, M.; Uchiyama, Y.; Kobayashi, T.; Hashizume, C.
March 2013
Journal of Radiosurgery & SBRT;2013 Supplement 2.1, Vol. 2, p71
Academic Journal
Purpose: Excellent clinical treatment results for various brain lesions by stereotactic irradiation, including both Gamma Knife (GK) stereotactic radiosurgery (SRS) and linear accelerator-based (LINAC) fractionated stereotactic radiotherapy (SRT) such as Novalis, have been reported. Novalis is equipped with sophisticated patient setup system and LINAC radiation delivery system, including intensity modulation (IM), useful for SRT. On the other hand, recent GK Perfexion(PFX) features composite collimator shots, besides multi-isocenter technique, for better target conformality. In addition, Extend system for GK-SRT, without invasive skull frame fixation, was developed. In this study, the dosimetric results of these two modalities were compared from the viewpoint of conformity, heterogeneity, and gradient in target covering. Methods: Fourteen patients (skull base meningioma [9], craniopharyngiomas [4] and pituitary adenoma [1]) were originally treated by Novalis IM-SRT from April 2011 through June 2012. Treatment planning was made on iPlan workstation. Five- to 7-beam IM-SRT in 14 to 18 fractions with fraction dose of 2.5 or 3 Gy was performed. With these patients' data, additional treatment planning simulation using GammaPlan workstation for PFX-SRT was performed. Reference CT images with planning structure contour set including planning target volume (PTV) and those of organs at risk (OAR), which had been used on iPlan for actual Novalis treatment, were exported to GammaPlan in DICOM-RT (digital communications in medicine-radiation therapy) format. Dosimetric results in both Novalis IM-SRT and PFX-SRT were evaluated using indices including target coverage, CI (conformity index), HI (homogeneity index), and GI (gradient index), while the same prescription dose would be used. Results: The PTV volume ranged from 2.3 to 102.2 cc and isocenter number of PFX was between 12 and 50 at the isodose contour of 45% to 60%. The PTV coverage ranged from 95% to 99% for Novalis and from 94% to 98% for PFX. The CI was 1.11-1.61 and 1.04-1.15, the HI was 1.1-3.62 and 2.3-3.25, and the GI was 3.72-7.97 and 2.54-3.39 in Novalis and PFX respectively. Conclusions: PTV coverage by both Novalis and PFX was almost equivalent. However, CI, HI, and GI for the PTV had significant differences. PFX was superior in CI and GI, and Novalis was better in HI. The outcome of this study showed that better conformality would be achieved by multi-isocenter PFX, if we don't mind the homogeneity inside the tumors. Disclosure: No significant relationships.


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