Treatment planning for the layer‐stacking irradiation system for three‐dimensional conformal heavy‐ion radiotherapy

Abstract

We have upgraded a heavy-ion radiotherapy treatment-planning system to adapt for the layer-stacking irradiation method, which is to conform a variable SOBP to a target volume by means of dynamic control of the conventional beam-modifying devices. The biophysical model, the beam-setup logic, and the dose-calculation algorithm implemented for the layer-stacking method are described and the expected clinical usability is discussed.The layer-stacking method was integrated in perfect accordance with the ongoing conventional treatments so that the established protocols, which are the clinically optimized dose fractionation schemes, will still be valid. On the other hand, a simulation study indicated a substantial improvement of dose distribution with the 3 layer-stacking method though the significance may depend on the size, shape, and location of the tumor. The completed treatment system will provide an option for improved conformal radiotherapy without interfering with the conventional method and we expect a gradual expansion of the clinical cases applicable to the layer-stacking method.

Effects of a difference in respiratory cycle between treatment planning and irradiation for phase-controlled rescanning and carbon pencil beam scanning

“…This is because a large number of rescannings increased scanning speed and decreased dose rate, with the result that the beam could be configured close to a broad shape. This situation is similar to layer-stacking rather than passive scattering beam irradiation [23]. Dose conformation with 8XPCR showed no particular degradation, even though the irradiation respiratory cycle was changed fiom the planning respiratory cycle.…”

Four-Dimensional Lung Treatment Planning in Layer-Stacking Carbon Ion Beam Treatment: Comparison of Layer-Stacking and Conventional Ungated/Gated Irradiation

“…To solve this problem, we used both a PTC to shape the beam field to the target and an MLC to change the beam field to the respective layers. Other details, such as biophysical modeling and beam weight optimization, have been described elsewhere (11).…”

“…Kanai et al proposed layer-stacking irradiation, which uses passive proton beams to achieve higher dose conformation and thereby provide similar dose conformity to scanning irradiation (10). They were followed by Kanematsu et al, who extended this idea to carbon ion beams and integrated it into the Heavy Ion Medical Accelerator in Chiba (HMAC) at the NIRS (11), and the NIRS has now been upgraded to provide layer-stacking irradiation. This advance represents a relatively easy means of upgrading treatment centers currently using passive beams.…”

Secondary range shifting with range compensator for reduction of beam data library in heavy‐ion radiotherapy

“…For example, beam data 3 and 4 in Table I will be excluded because their primary range shifts always exceed S max = 6 cm H2O and that of beam data 2 needs to be modified from [5,8) to [5,6] cm H2O .…”