Biomedical subjects

Per H Halvorsen

Publications and source records attributed to Per H Halvorsen.

3 recordsLinked to original sources

PubMed2005

AAPM Task Group 103 report on peer review in clinical radiation oncology physics.

This report provides guidelines for a peer review process between two clinical radiation oncology physicists. While the Task Group's work was primarily focused on ensuring timely and productive independent reviews for physicists in solo practice, these guidelines may also be appropriate for physicists in a group setting, particularly when dispersed over multiple separate clinic locations. To ensure that such reviews enable a collegial exchange of professional ideas and productive critique of the entire clinical physics program, the reviews should not be used as an employee evaluation instrument by the employer. Such use is neither intended nor supported by this Task Group. Detailed guidelines are presented on the minimum content of such reviews, as well as a recommended format for reporting the findings of a review. In consideration of the full schedules faced by most clinical physicists, the process outlined herein was designed to be completed in one working day.

Health Physics↗

PubMed2005

Dosimetric evaluation of a new design MOSFET in vivo dosimeter.

A single-use dosimeter, designed for in vivo patient dosimetry, has been evaluated. Key dosimetric characteristics of the dosimetry system have been measured for high-energy photon and electron beams commonly used in external beam therapy. Under the measurement conditions utilized, dose accuracy was within 5% for all data points, and inter-batch uniformity was acceptable, with a standard deviation of 1.7%. Dose linearity was confirmed for doses ranging from 2 to 400 cGy. The dosimeter readings were independent of dose rate for rates ranging from 80 to 480 cGy/min. When used as instructed, the dosimeter readings were accurate across the tested range of energy and modality. These measurements show that the dosimetry system's performance may be acceptable for in vivo dosimetry of entrance d(max) doses.

Algorithms↗

PubMed2002

Dose optimization via index-dose gradient minimization.

This paper presents an iterative optimization algorithm based on gradient minimization of index dose, defined as the product of physical dose and a numerical index. Acting as a template the index distribution is designed to represent the dosimetry that meets the dose volume histogram-based optimization objectives. The treatment dosimetry is optimized when the uniformity of the index-dose distribution is maximized. Prior to optimization the user can select all or only some of the beams to be intensity modulated. The remaining unmodulated beams can be either open or wedged photon beams, electron beams, or beams of previous treatments. The optimization result and treatment delivery efficiency can often be enhanced by including not only the IM photon beams but also all suitable fixed-beams available on the linac in the treatment plan. In addition, the doses from previous treatments can also be considered in the optimization of current treatment. Five clinical examples with different complexities in optimization objective are presented. The effects of two nonoptimization variables, beam setup and initial beam weights, on the quality of the dose optimization are also presented. The results are analyzed in terms of isodose distribution, dose volume histograms, and a dose optimization quality factor. The optimization algorithm, implemented in our in-house TPS PLanUNC, has been used in clinical application since 1996. The primary advantages of our optimization algorithm include computational efficiency, intensity modulation selection choice, and performance reliability for a wide range of clinical beam setups and optimization objectives.

Algorithms↗