Kilovoltage Rotational External Beam Radiotherapy on a Breast Computed Tomography Platform: A Feasibility Study

Abstract

Purpose To demonstrate the feasibility of a dedicated breast computed tomography (bCT) platform to deliver rotational kilovoltage external beam radiation therapy (kVEBRT) for partial breast irradiation (PBI), whole breast irradiation (WBI) and dose painting. Methods and Materials Rotational kV-EBRT using the geometry of a prototype bCT platform was evaluated via Monte Carlo simulator. A point source emitting 178 keV photons (approximating a 320 kVp spectrum with 4 mm copper filtration) was rotated around a 14 cm voxelized polyethylene disk (0.1 cm tall) or cylinder (9 cm tall) to simulate primary and primary plus scattered photon interactions, respectively. Simulations were also performed using voxelized bCT patient images. Beam collimation was varied in the x-y plane (1–14 cm) and in the z-direction (0.1–10 cm). Dose painting for multiple foci, line and ring distributions was demonstrated using multiple rotations with varying beam collimation. Simulations using the scanner’s native hardware (120 kVp filtered by 0.2 mm copper) were validated experimentally. Results As the x-y collimator was narrowed, the 2D dose profiles shifted from a cupped profile with high edge dose to an increasingly peaked central dose distribution with sharp dose fall-off. Using a 1 cm beam, the cylinder edge dose was less than 7% of dose deposition at the cylinder center. Simulations using 120 kVp x-rays showed distributions similar to experimental measurements. A homogeneous dose distribution (< 2.5% dose fluctuation) with a 20% decrease in dose deposition at the cylinder edge (i.e. skin sparing) was demonstrated by weighted summation of four dose profiles using different collimation widths. Simulations using patient bCT images demonstrated the potential for treatment planning and image-guided radiation therapy (IGRT). Conclusions Rotational kV-EBRT for PBI, dose painting, and WBI with skin sparing is feasible on a bCT platform with the potential for high-resolution IGRT.

Dedicated breast computed tomography: Basic aspects

“…The well-known excellent contrast resolution of x-ray CT imaging with respect to planar x-ray imaging for soft tissues is an additional plus of a BCT exam, since improved image quality may result in a better diagnosis. Additional advantages of BCT include its possible coupling with contrast-enhancement (CE) iodinated agents, [39][40][41] with positron emission tomography (PET) 40,42 or single photon emission computed tomography (SPECT) 43,44 for hybrid imaging, as well as with external beam x-ray radiation therapy 45 and with a robotic system for image-guided needle biopsy. 39 Karellas, Glick).…”

Feasibility of external beam radiation therapy to deep‐seated targets with kilovoltage x‐rays

“…Treatments of complex targets could be done with a CyberKnife‐ or Gamma Knife‐like approach of “packing spheres or shots.” As in the original version of the CyberKnife, where a number of fixed collimators were employed, the KVAT source could be designed with a number of varied collimator sizes in order to accommodate treatments of different target sizes. An analogous approach was implemented to generate a line distribution in the work by Prionas et al…”

Inverse optimization of low‐cost kilovoltage x‐ray arc therapy plans

“…used a modified CT scanner to treat contrast injected brain metastases and reported a reduction in the size of the metastases while maintaining safe brain doses. Prionas et al . demonstrated the feasibility of using a dedicated breast CT scanner for breast irradiation.…”