To investigate whether dose fall-off characteristics would be significantly different among intracranial radiosurgery modalities and the influence of these characteristics on fractionation schemes in terms of normal tissue sparing.
An analytic model was developed to measure dose fall-off characteristics near the target independent of treatment modalities. Variations in the peripheral dose fall-off characteristics were then examined and compared for intracranial tumors treated with Gamma Knife, Cyberknife, or Novalis LINAC-based system. Equivalent uniform biologic effective dose (EUBED) for the normal brain tissue was calculated. Functional dependence of the normal brain EUBED on varying numbers of fractions (1 to 30) was studied for the three modalities.
The derived model fitted remarkably well for all the cases (R(2) > 0.99). No statistically significant differences in the dose fall-off relationships were found between the three modalities. Based on the extent of variations in the dose fall-off curves, normal brain EUBED was found to decrease with increasing number of fractions for the targets, with alpha/beta ranging from 10 to 20. This decrease was most pronounced for hypofractionated treatments with fewer than 10 fractions. Additionally, EUBED was found to increase slightly with increasing number of fractions for targets with alpha/beta ranging from 2 to 5.
Nearly identical dose fall-off characteristics were found for the Gamma Knife, Cyberknife, and Novalis systems. Based on EUBED calculations, normal brain sparing was found to favor hypofractionated treatments for fast-growing tumors with alpha/beta ranging from 10 to 20 and single fraction treatment for abnormal tissues with low alpha/beta values such as alpha/beta = 2.
[Show abstract][Hide abstract] ABSTRACT: Existing dose guidelines for intracranial stereotactic radiosurgery (SRS) are primarily based on single-target treatment data. This study investigated dose guidelines for multiple targets treated with SRS.
A physical model was developed to relate the peripheral isodose volume dependence on an increasing number of targets and prescription dose per target. The model was derived from simulated and clinical multiple brain metastatic cases treated with the Leksell Gamma Knife Perfexion at several institutions, where the total number of targets ranged from 2 to 60. The relative increase in peripheral isodose volumes, such as the 12-Gy volume, was studied in the multitarget treatment setting based on Radiation Therapy Oncology Group 90-05 study dose levels.
A significant increase in the 12-Gy peripheral isodose volumes was found in comparing multiple target SRS to single-target SRS. This increase strongly correlated (R(2) = 0.92) with the total number of targets but not the total target volumes (R(2) = 0.06). On the basis of the correlated curve, the 12-Gy volume for multiple target treatment was found to increase by approximately 1% per target when a low target dose such as 15 Gy was used, but approximately 4% per target when a high dose such as 20-24 Gy was used. Reduction in the prescription dose was quantified for each prescription level in maintaining the 12-Gy volume.
Normal brain dose increases predictably with increasing number of targets for multitarget SRS. A reduction of approximately 1-2 Gy in the prescribed dose is needed compared with single target radiosurgery.
International journal of radiation oncology, biology, physics 10/2010; 78(2):605-8. DOI:10.1016/j.ijrobp.2009.11.055 · 4.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Acromegaly is a chronic insidious disease characterised by growth hormone (GH) hypersecretion, typically from a pituitary adenoma. Effective treatment of acromegaly is vital because it is associated with a mortality rate more than twice that of the general population, an increased prevalence of colonic malignancy and many significant co-morbidities. Transsphenoidal adenoma resection is still the best first-line treatment for acromegaly but persistence (43%) or recurrence (2% to 3%) of GH hypersecretion after surgery remains a problem. Treatment options for acromegaly after failed initial therapy or recurrence include further surgery, radiotherapy, radiosurgery or medical therapies, including somatostatin analogues, dopamine agonists and growth hormone receptor antagonists. There has been a progressive lowering of the accepted GH level defining cure in acromegaly. This article reviews the efficacy and safety of the various treatment options for persistent or recurrent acromegaly and the changing definition of cure.
[Show abstract][Hide abstract] ABSTRACT: Stereotactic body radiotherapy (SBRT) for spinal metastases is an emerging therapeutic option aimed at delivering high biologically effective doses to metastases while sparing the adjacent normal tissues. This technique has emerged following advances in radiation delivery that include sophisticated radiation treatment planning software, body immobilization devices, and capabilities of detecting and correcting patient positional deviations with image-guided radiotherapy. There are limited clinical data specifically supporting the role of SBRT as a superior alternative to conventional radiation in the postoperative patient. The focus of this review was to examine the evidence pertaining to spine SBRT in the treatment of spinal metastases and to provide a comprehensive analysis of published patterns of failure, with emphasis on the postoperative patient.
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