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Dheerendra Prasad, Melita Steiner and Ladislau Steiner

heterogeneous-dose hypofractionation regimens in which some form of localization technique is used to guide the beams to the target. Although the relocatable localization techniques used by these groups are superior to those of conventional port-based radiation therapy, they do not achieve anywhere near the accuracy that is available using the LINAC radiosurgical systems, which use rigidly fixed frames, and certainly do not even approximate the accuracy of the Leksell gamma unit (0.3 mm). As long as such techniques are applied for treating large and regular lesions such as

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Mark E. Linskey

conventional multiport and wedge techniques. It can now be delivered more conformally by using multileaf collimators and inverse 3D dose planning. It can even be delivered stereotactically by using frame-based LINAC arc rotational systems, frame-based point-and-shoot mobile LINAC systems, or frameless stereotactic robotic point-and-shoot systems. Regardless of the delivery system used, fractionated radiotherapy, by definition, delivers a therapeutic radiation dose in more than one fraction. The terms “fractionation,” “hyperfractionation,” and “hypofractionation” refer to the

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Kazutoshi Hida, Hiroki Shirato, Toyohiko Isu, Toshitaka Seki, Rikiya Onimaru, Hidefumi Aoyama, Satoshi Ushikoshi, Kazuo Miyasaka and Yoshinobu Iwasaki

Object

Radiosurgical treatment of spinal arteriovenous malformations (AVMs) is becoming a practical therapeutic option as methodology improves, but no comparative study has yet been published on focal fractionated radiotherapy. The authors report their experience with conventional and hypofractionated radiotherapy for spinal AVM.

Methods

Candidates for this study were patients who experienced symptoms due to an intramedullary AVM but were ineligible for embolization or surgery. Of 21 patients with spinal AVMs, 10 cases in a 10-year period met this criterion. Angiography and contrast-enhanced computerized tomography scanning were used for treatment planning in all cases. Fractionated radiotherapy was performed using a linear accelerator, extracranial immobilization system, and frequent orthogonal linacographic verification. The starting radiation dose was 32 Gy in two, 36 Gy in three, and 40 Gy in two patients, in a regimen involving 1.8 to 2—Gy daily fractions; this was recently changed to a hypofractionation schedule of 30 Gy (in eight sessions) in one and 20 Gy (in four sessions) in two patients.

Results

The follow-up period ranged from 26 to 124 months (median of 49 months). There were no hemorrhages nor any adverse reactions attributable to irradiation. Of the seven patients who consented to undergo follow-up angiography, the nidus size decreased in five, but complete obliteration did not occur in any patient.

Conclusions

Because no patient experienced adverse effects, the maximum tolerable radiation dose for the spinal cord associated with an AVM could not be identified, although it presumably is higher than those administered. The lack of rebleeding in patients in whom complete angiographic occlusion was absent suggests that the natural history of spinal AVMs may be less aggressive than previously reported.

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Douglas Kondziolka, L. Dade Lunsford, Jay S. Loeffler and William A. Friedman

extended treatment course in which external-beam fractionated radiation is delivered, usually by an LINAC. Any treatment may or may not be relatively innocuous; it is the sum of the treatment sessions that leads to an effect. Stereotactic radiosurgery is no more radiation therapy than microsurgery is “microtherapy.” The adjective “fractionated” refers to the fact that treatment is divided into multiple fractions or sessions. A reduced number of fractions may be called hypofractionation and a greater number of fractions may be termed extended fractionation or

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Dennis C. Shrieve, Lisa Hazard, Kenneth Boucher and Randy L. Jensen

some investigators have recommended “hypofractionation,” the use of fewer, larger doses of radiation, usually 3 to 7 Gy per day when stereotactic radiotherapy is fractionated. 1, 2, 18 Several years of experience indicate that these regimens are efficacious and safe for acoustic tumors; 29 however, the use of such large fractions for parasellar tumors when optic nerve or chiasm are involved has been known for many years to increase the risk of optic neuropathy. 11, 20 In this paper we apply radiobiological principles to the treatment of parasellar tumors and

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Alessandra G. Pedroso, Antonio A. F. De Salles, Katayoun Tajik, Raymond Golish, Zachary Smith, Leonardo Frighetto, Timothy Solberg, Cynthia Cabatan-Awang and Michael T. Selch

. Maximal conformity and homogeneity may be valuable tools that allow an increased peripheral dose without a corresponding increase in complications. When not possible, strategies involving repeated radiosurgery, staged radiosurgery, or hypofractionation are being investigated. Hypofractionated Radiation Therapy Two patients were treated with hypofractionated radiation therapy (30 Gy in five fractions). A reduction in the AVM size was in both patients. In one patient virtually complete obliteration was achieved on the 5-month follow-up MR image ( Fig. 2

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Antonio A. F. De Salles, Alessandra G. Pedroso, Paul Medin, Nzhde Agazaryan, Timothy Solberg, Cynthia Cabatan-Awang, Dulce M. Espinosa, Judith Ford and Michael T. Selch

unchanged stable none 12 yes yes yes/no asymptomatic no MR imaging none 13 no no yes/yes pain improved, paresthesias unchanged no MR imaging none 14 no no yes/yes no pain no MR imaging none Dynamic shaped beams were used for irregularly shaped small lesions. Large irregular lesions not involving the spinal cord were better treated with static shaped beams. Lesions partially involving and compressing the spinal cord were treated with IMRS/IMRT to mostly spare the cord. Hypofractionation was necessary

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Michael T. Selch, Alessandro Pedroso, Steve P. Lee, Timothy D. Solberg, Nzhde Agazaryan, Cynthia Cabatan-Awang and Antonio A. F. Desalles

useful subjective hearing preservation to be 61% after stereotactic radiotherapy compared with 75% after stereotactic radiosurgery (p = 0.42). Both of these rates are inferior to the best results of stereotactic radiotherapy delivered by more protracted techniques. The statistical similarity of hearing preservation rates between hypofractionated stereotactic radiotherapy and low-dose stereotactic radiosurgery implies that hypofractionation does not sufficiently exploit the biological advantage of dose fractionation for protection of eighth cranial nerve function

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Mark E. Linskey, Stephen A. Davis and Vaneerat Ratanatharathorn

surgery, and patients with atypical or malignant meningiomas. Fractionated radiotherapy can now be delivered with standard port and wedge techniques, 3D conformal techniques, IMRT, or stereotactic radiotherapy. It can be delivered with conventional fractionation prescriptions, or with a two to five fraction (hypofractionation) technique. Fractionated radiotherapy clearly reduces the recurrence rate of subtotally resected meningiomas compared with subtotal resection alone. 8 The concerns for not favoring fractionated radiotherapy as a primary treatment modality for

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Bengt Karlsson, Ingmar Lax, Masaaki Yamamoto, Michael Söderman, Hidefumi Jokura, Charles Rosen and Julian Bailes

fractionation does increase the therapeutic window, 29 whereas others have disagreed with this statement. 9 The sparse literature in this field makes it difficult to support either position, and it is therefore still an open debate as to whether fractionated radiotherapy is superior to single-dose radiotherapy. In addition, it is not yet known whether hypofractionation with relatively high doses per fraction results in a more favorable risk–benefit ratio than more conventional fractionation schedules with daily doses of approximately 2 Gy. The articles we have found