Stereotactic radiosurgery: Dose‐volume analysis of linear accelerator techniques

Abstract

Stereotactic radiosurgery of the brain may be accomplished with a linear accelerator by performing several noncoplanar arcs of a highly collimated beam focused at a point. The shape of the radiation distribution produced by this technique is affected by the beam energy, field size, and the number and size of the arcs. The influence of these parameters on the resulting radiation distributions was analyzed by computing dose volume histograms for a typical brain. Dose volume functions were computed for: (a) the energy range of 4-24 MV x rays; (b) target sizes of 1-4 cm; and (c) 1-11 arcs and dynamic rotation. The dose volume histograms were found to be dependent on the number of arcs for target sizes of 1-4 cm. However, these differences were minimal for techniques with 4 arcs or more. The influence of beam energy on the dose volume histogram was also found to be minimal.

Viability of an isocentric cobalt‐60 teletherapy unit for stereotactic radiosurgery

“…Radiosurgical treatment plans were devised using the cobalt-60 and 10 MV beams. The arc geometries were based on treatment plan optimization criteria described by Schell et al 15 and Serago et al, 16 who compared the cumulative dose volume histograms for different noncoplanar and dynamic radiosurgical arc techniques, and reported that the normal tissue dose is minimized when ͑a͒ the arc planes are distributed evenly; ͑b͒ individual arc lengths are less than 180°; and ͑c͒ the total arc traversal is greater than 400°per isocenter. In accordance with these guidelines, the radiosur-gical techniques used in our work consisted of four, six, eight, or ten noncoplanar converging arcs, distributed evenly over the coronal plane between the couch angle limits of Ϯ75°, with each arc traversing 120°for a total minimum arc traversal of 480°.…”

Dose-volume Analysis of Different Stereotactic Radiotherapy Mono-isocentric Techniques

“…Serago (19) uses arcs technique for most radiosurgical cases: 'Although the dose volume histogram for 4 vs. 6 arcs is essentially identical, we feel, there is a minor safety advantage of using more arcs.' He also adds that the differences between techniques are only appreciated at the lower isodose levels that are not generally clinically significant.…”

“…Several authors argue that the DVH is an effective tool in evaluating 3-D plans (11)(12)(13)(14). The use of DVH as a basis for comparison between three-dimensional dose distributions provided by different stereotactic radiotherapy techniques has been reported in the literature (10,(15)(16)(17)(18)(19)(20). In this study a DVH analysis of radiosurgical techniques, based on Linac and Gamma Knife, will be reported.…”

Verification of radiosurgery target point alignment with an electronic portal imaging device (EPID)

“…A technique using a target point simulator to verify the stereotactic coordinates prior to treatment has been described by Lutz et al 2 and was used by others in a number of studies. [3][4]8,10 However, the alignment verification of the target simulator has usually been done by visual inspection of portal films, which is slow and usually qualitative. By using the electronic portal imaging device ͑EPID͒, digital images can be quickly acquired and quantitative alignment errors may be calculated by analyzing the digital portal images.…”

“…Many investigators have studied the accuracy and precision requirements for this treatment technique. [1][2][3][4][5][6][7][8][9][10] The Brown-Roberts-Wells ͑BRW͒ neurosurgical stereotactic system 11,12 uses computed tomography, angiography, magnetic resonance imaging, or a combination of these to relate the target position to the BRW coordinate system. An important quality assurance step is to verify the alignment of the target center in the BRW coordinate system with the radiation center of a linac.…”