Direct energy spectrum measurement of X-ray from a clinical linac.

A realistic X-ray energy spectrum is essential for accurate dose calculation using the Monte Carlo (MC) algorithm. An energy spectrum for dose calculation in the radiation treatment planning system is modeled using the MC algorithm and adjusted to obtain acceptable agreement with the measured percent depth dose (PDD) and off-axis ratio. The simulated energy spectrum may not consistently reproduce a realistic energy spectrum.

Contrast enhancement for portal images by combination of subtraction and reprojection processes for Compton scattering.

For patient setup of the IGRT technique, various imaging systems are currently available. MV portal imaging is performed in identical geometry with the treatment beam so that the portal image provides accurate geometric information. However, MV imaging suffers from poor image contrast due to larger Compton scatter photons.

Bremsstrahlung and photoneutron production in a steel shield for 15-22-MeV clinical electron beams.

The physical data regarding bremsstrahlung and neutrons produced in a steel shield by high-energy electron beams from a medical linear accelerator were investigated. These data are required to allow the accurate prediction of shielding performance for high-energy electron beams and in the design of radiotherapy facilities. A Monte Carlo code was used to develop Monte Carlo beam models for clinical electron beams and to directly simulate bremsstrahlung and secondary neutron production in a steel shield.

Depth scaling of solid phantom for intensity modulated radiotherapy beams.

To reduce the uncertainty of absorbed dose for high energy photon beams, water has been chosen as a reference material by the dosimetry protocols. However, solid phantoms are used as media for absolute dose verification of intensity modulated radiotherapy (IMRT). For the absorbed dose measurement, the fluence scaling factor is used for converting an ionization chamber reading in a solid phantom to absorbed dose to water.

Bremsstrahlung and Photoneutron leakage from steel shielding board impinged by 12-24 MeV electrons beams.

Many medical linear accelerators generate not only high-energy photons, but also high-energy electrons, and they are no longer equipped with beam stoppers. Therefore, shields might be necessary against bremsstrahlung and photoneutron generated by high-energy electron beams. However, there are few physical studies, and no recommendations are made about shields nowadays.

Reference dosimetry condition and beam quality correction factor for CyberKnife beam.

This article is intended to improve the certainty of the absorbed dose determination for reference dosimetry in CyberKnife beams. The CyberKnife beams do not satisfy some conditions of the standard reference dosimetry protocols because of its unique treatment head structure and beam collimating system. Under the present state of affairs, the reference dosimetry has not been performed under uniform conditions and the beam quality correction factor kQ for an ordinary 6 MV linear accelerator has been temporally substituted for the kQ of the CyberKnife in many sites.

[Evaluation of relative electrometer calibration factor with user beam.].

To establish traceability of absorbed dose to water, a cobalt calibration coefficient is transferred to a reference ionization chamber by the standard dosimetry laboratory in the radiotherapy field. In Japan, the calibration is done against a set of an ionization chamber and an electrometer as a system. Nowadays, solely electrometer calibration is desirable to measure absorbed dose with more than one combination of ionization chamber and electrometer.

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

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).

Dose calculation system for remotely supporting radiotherapy.

The dose calculation system IMAGINE is being developed keeping in mind remotely supporting external radiation therapy using photon beams. The system is expected to provide an accurate picture of the dose distribution in a patient body, using a Monte Carlo calculation that employs precise models of the patient body and irradiation head. The dose calculation will be performed utilising super-parallel computing at the dose calculation centre, which is equipped with the ITBL computer, and the calculated results will be transferred through a network.

Effects of density changes in the chest on lung stereotactic radiotherapy.

To experimentally and theoretically evaluate dose distribution during lung stereotactic radiotherapy, we investigated the relative electron densities in lung and tumor tissues using X-ray computed tomography images obtained from 30 patients in three breathing states: free breathing, inspiration breath-hold, and expiration breath-hold. We also calculated dose distribution using Monte Carlo simulation for lung tissue with two relative electron densities. The effect of changes in relative electron density on dose distribution in lung tissue was evaluated using calculated differential and integral dose volume histograms.