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. 2013 May;40(5):051703.
doi: 10.1118/1.4798961.

GammaPod-a new device dedicated for stereotactic radiotherapy of breast cancer

Cedric X Yu  1 , Xinyu Shao, Jin Zhang, William Regine, Mike Zheng, Ying S Yu, Jianchun Deng, Zhengcheng Duan
Affiliations

GammaPod-a new device dedicated for stereotactic radiotherapy of breast cancer

Cedric X Yu et al. Med Phys. 2013 May.

Abstract

Purpose: This paper introduces a new external beam radiotherapy device named GammaPod that is dedicated for stereotactic radiotherapy of breast cancer.

Methods: The design goal of the GammaPod as a dedicated system for treating breast cancer is the ability to deliver ablative doses with sharp gradients under stereotactic image guidance. Stereotactic localization of the breast is achieved by a vacuum-assisted breast immobilization cup with built-in stereotactic frame. Highly focused radiation is achieved at the isocenter due to the cross-firing from 36 radiation arcs generated by rotating 36 individual Cobalt-60 beams. The dedicated treatment planning system optimizes an optimal path of the focal spot using an optimization algorithm borrowed from computational geometry such that the target can be covered by 90%-95% of the prescription dose and the doses to surrounding tissues are minimized. The treatment plan is intended to be delivered with continuous motion of the treatment couch. In this paper the authors described in detail the gamma radiation unit, stereotactic localization of the breast, and the treatment planning system of the GammaPod system.

Results: A prototype GammaPod system was installed at University of Maryland Medical Center and has gone through a thorough functional, geometric, and dosimetric testing. The mechanical and functional performances of the system all meet the functional specifications.

Conclusions: An image-guided breast stereotactic radiotherapy device, named GammaPod, has been developed to deliver highly focused and localized doses to a target in the breast under stereotactic image guidance. It is envisioned that the GammaPod technology has the potential to significantly shorten radiation treatments and even eliminate surgery by ablating the tumor and sterilizing the tumor bed simultaneously.

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Figures

Figure 1
Figure 1
(a) The GammaPod radiation unit without the cover showing the treatment couch at its near upright position with the breast cup locked in the opening. Also shown are the treatment doors, the support columns, and the base frame the unit rests on; (b) break-up view of the central section of the radiation unit showing the major inner components including the collimator, the source carrier, and the shielding body, all concentrically mounted.
Figure 2
Figure 2
(a) Shielding around the uppermost source at 18° when the beam is at the “off” position; (b) the cone angles of the collimators are designed to encompass the entire active source inside the cone.
Figure 3
Figure 3
(a) Vacuum assisted breast cup, showing the outer cup, inner cup, silicone flange, the cup-locking feature, and the localization frame. (b) The stereotactic localization frame detected from a set of CT images (square dots) and the theoretical locations by design.
Figure 4
Figure 4
Dose distribution of a single 25 mm shot around the isocenter. Upper panel shows the isodose distributions on the vertical and horizontal planes (patient's axial and coronal planes). Lower panel depicts the vertical (patient's PA direction) and lateral (patient's LR direction) dose profiles.
Figure 5
Figure 5
(a) Planned dose distributions on axial and coronal planes of a GammaPod treatment delivering 16 Gy to a 2.4 cm3 target. (b) DVHs of the target and normal breast tissues.
Figure 6
Figure 6
(a) Planned dose distributions on axial and coronal planes of a GammaPod APBI treatment delivering 8 Gy to a 151 cm3 target. (b) DVHs of the target and normal breast tissues.
Figure 7
Figure 7
(a) Planned dose distributions on axial and coronal planes of a GammaPod treatment simultaneously delivering 18 Gy to a 2.4 cm3 GTV and 9 Gy to the tumor bed, a 3D expansion from the GTV by 15 mm. (b) DVHs for GTV, tumor bed, and normal breast tissues.
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