Investigations of different kilovoltage x‐ray energy for three‐dimensional converging stereotactic radiotherapy system: Monte Carlo simulations with CT data

Abstract

We are investigating three-dimensional converging stereotactic radiotherapy (3DCSRT) with suitable medium-energy x rays as treatment for small lung tumors with better dose homogeneity at the target. A computed tomography (CT) system dedicated for non-coplanar converging radiotherapy was simulated with BEAMnrc (EGS4) Monte-Carlo code for x-ray energy of 147.5, 200, 300, and 500 kilovoltage (kVp). The system was validated by comparing calculated and measured percentage of depth dose in a water phantom for the energy of 120 and 147.5 kVp. A thorax phantom and CT data from lung tumors (<20 cm3) were used to compare dose homogeneities of kVp energies with MV energies of 4, 6, and 10 MV. Three non-coplanar arcs (0 degrees and +/-25 degrees ) around the center of the target were employed. The Monte Carlo dose data format was converted to the XiO RTP format to compare dose homogeneity, differential, and integral dose volume histograms of kVp and MV energies. In terms of dose homogeneity and DVHs, dose distributions at the target of all kVp energies with the thorax phantom were better than MV energies, with mean dose absorption at the ribs (human data) of 100%, 85%, 50%, 30% for 147.5, 200, 300, and 500 kVp, respectively. Considering dose distributions and reduction of the enhanced dose absorption at the ribs, a minimum of 500 kVp is suitable for the lung kVp 3DCSRT system.

Optical imaging analysis of microscopic radiation dose gradients in Gafchromic EBT film using a digital microscope

“…Although we used lower energy photons and very small fields to test the ability of our microscope-film system to measure penumbra, the experimental measurement of penumbra for such fields and energies would be useful in verifying a number of recent theoretical publications. For example, Deloar et al, 41 using Monte Carlo simulations, describe a novel computed tomography stereotactic radio-therapy system capable of delivering more conformal doses to target volumes using kilovoltage x rays. Iwamoto et al 42 have reported on the treatment of canine brain tumors using kilovoltage x rays from a modified computed tomography scanner.…”

Converging Stereotactic Radiotherapy Using Kilovoltage X-Rays: Experimental Irradiation of Normal Rabbit Lung and Dose–Volume Analysis With Monte Carlo Simulation

“…(but lower than that used for current megavoltage photon therapies) is adequate for human applications (4). In addition, long irradiation time was needed in our study.…”

“…One rabbit did not undergo irradiation and served as a control. The irradiation doses were regulated by changing the beam-on duration based on a dose rate of 5 Gy/min at a depth of 3-cm in water-equivalent material (4,6). For each irradiation event, the X-ray tube was continuously rotated in one direction to achieve a rotational irradiation arc of 360 .…”

Design of a modulated orthovoltage stereotactic radiosurgery system

“…In general, the focal spot sizes for orthovoltage units are larger than those for standard 6 MV linear accelerators; however, the geometric penumbra may be minimized through the use of collimating cones near the surface of the volume to be irradiated. Multiple studies in SBRT and SRS have shown promise for the use of orthovoltage energy photons, with both theoretical and physical orthovoltage systems showing improvements in dose gradient, conformality, and homogeneity of stereotactic plans compared to standard megavoltage energy photons . In addition, orthovoltage energies have been noted as the ideal energy range for small animal irradiations .…”