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Jonathan A. Borden, Jen-san Tsai and Anita Mahajan

their effect on the quality of radiosurgical dosimetry for small VSs. Magnetic resonance imaging and CT scanning data were compared for each patient. In addition the real accuracy of the studies was checked using a phantom. The goal of the study was to improve both the effectiveness of treatment and preservation of patients' hearing. Materials and Methods Fifteen mostly intracanalicular VSs were selected; all had a volume less than 1.5 cm 3 . In all cases the patients underwent evaluation in a Siemens Symphony 1.5-tesla MR imager to determine which spatial

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Jonathan A. Borden, Anita Mahajan and Jen-San Tsai

target. For each graph the QF is plotted as a function of V T . Particularly with gamma knife dosimetry, a significant inverse relationship exists between target complexity and QF 12 , as seen in Fig. 3 . This relationship is not so clear cut with IMRT or LINAC until complex targets are treated ( Fig. 4 ). Fig. 3. Graph showing the gamma knife QF 12 as a function of target complexity. The V T sets (0.5, 1.5, and 10 cm 3 ) are plotted individually. Fig. 4. Upper: The Beak IMRT QF 12 is plotted as a function of target complexity. The V T

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Marc Levivier, Rafael E. Carrillo, Rémi Charrier, André Martin and Jean-Philippe Thiran

T he Leksell Gamma Knife (LGK, Elekta AB) is a dedicated device for cranial radiosurgery using concomitant gamma rays emitted from 60 Co radiation sources focusing at an isocenter. This design provides unique dosimetry characteristics with a very steep gradient. 10 , 13 , 17 , 18 Usually, multiple isocenters are used to shape the desired irradiation to the target volume with a high conformity and selectivity. Manual forward planning (i.e., the user places each isocenter at specific stereotactic coordinates) is currently the standard, most frequent way to plan

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Richard D. Beegle, William A. Friedman and Frank J. Bova

treatment dose were found to have a statistically significant effect on subsequent new-onset facial numbness and on new-onset facial weakness. That study spanned more than a decade, during which time many improvements occurred in radiosurgical treatment planning, leading to significantly more conformal radiation shapes. In this study we examine two measures of treatment dosimetry quality: conformity of the radiation treatment isodose to the tumor shape and steepness of the radiation dose gradient. We attempt to answer this question: does the quality of treatment plan

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Stefan G. Scheib and Stefano Gianolini

S tereotactic radiosurgery relies on the accurate localization of target tissue for small radiation fields (diameters down to 4 mm) with steep dose gradients (up to 40%/mm). The total radiation dose in GKS is applied in a single session. Clinical indications for use are small benign and malignant brain tumors (typically < 25 cm 3 ), not infiltrating the surrounding healthy tissue, and arteriovenous malformations. Due to small field sizes, steep dose gradients, and highly conformal dose distributions, dosimetry and 3D dose verification are a challenging part

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Christian A. Taschner, Vianney Le Thuc, Nicolas Reyns, Juergen Gieseke, Jean-Yves Gauvrit, Jean-Pierre Pruvo and Xavier Leclerc

results in the literature support the radiosurgical treatment of a centrally located AVM with a nidus volume less than 10 mm 3 . 17 Most centers rely on intraarterial catheter angiography (that is, DS angiography) CT, and MR imaging performed under stereotactic conditions for the definition of radiosurgical target areas. The multimodal imaging data are processed using software dedicated to dosimetry planning such as the Leksell GammaPlan (Elekta). With that software, the radiosurgical target areas are displayed within the reference system of the stereotactic space

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Josef Novotný Jr., Josef Novotný, Václav Spĕvác˘ek, Pavel Dvor˘ák, Tomás˘ Cechák, Roman Lis˘c˘ák, Gustav Broz˘ek, Jaroslav Tintĕra and Josef Vymazal

satisfies this requirement. 3–6, 8, 9, 13–17, 19, 24 Polymer gel dosimetry is based on radiation-induced polymerization and cross-linking of acrylic monomers. The concentration of radiation-produced polymer and the degree of cross-linking in the irradiated regions of the gel are proportional to the applied dose. The concentration of the changes in the gel increases the NMR relaxation rates of neighboring water protons. 13–15 Consequently, 3D dose distributions can be measured and visualized using NMR dosimeter relaxometry. Because the dosimeter consists predominantly

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Thomas E. Merchant, Erin N. Kiehna, Larry E. Kun, Raymond K. Mulhern, Chenghong Li, Xiaoping Xiong, Frederick A. Boop and Robert A. Sanford

–Volume Effects Dosimetry for the total brain, supratentorial brain, infratentorial brain, and temporal lobe volumes (left and right) was portioned into three dose intervals (low, intermediate, and high) described as V 0–25 Gy or V 0–30 Gy , V 25–45 Gy or V 30–45 Gy , and V 45–60 Gy and represented as the percentage volume of the given normal tissue volume that received the dose over the specified intervals. With age as a covariate, the following IQ estimating equations were developed for the total brain, supratentorial brain, and left temporal lobe volumes. Equations

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Tatsuya Kobayashi, Naoki Kageyama and Ken Ohara

) intracystic corrosion of the cyst wall by a fixative solution or chemotherapeutic agents; 9 and 3) internal irradiation with radioisotopes. 2, 11, 13, 15, 18, 19 The former two methods have often been unsuccessful in controlling fluid secretion. However, internal irradiation has the theoretical potential of eradicating the tumor and alleviating fluid secretion with proper dosimetry. Summary of Cases Technique Before internal irradiation, the patients are subjected to craniotomy for identification of the cyst and placement of the Ommaya drainage system into the

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Maria Mamalui-Hunter, Thomas Jiang, Keith M. Rich, Colin P. Derdeyn and Robert E. Drzymala

-hardening artifacts on CT angiograms, necessitating the use of MR imaging as an alternate modality for radiosurgical dosimetry planning. 24 However, Onyx appears hypointense on T2-weighted MR images, making definition of the flow voids in the residual AVM nidus difficult. 24 One way to overcome this problem is to use time-of-flight MR angiography, which provides excellent contrast between Onyx and areas of residual flow. 15 Our results are not completely generalizable to other radiosurgical methods, such as LINAC. A recent paper from Andrade-Souza and colleagues 2 suggests