Present and future developments in radiotherapy treatment units

Radiotherapeutical innovations in pediatric solid tumors

There have been considerable technical improvements in radiation therapy for the past two decades. In children affected with cancer, these have been likely overshadowed by concommittant major chemotherapy-based advances, and at least in part ignored and misused. This article outlines principles, technological requirements, and clinical applications of innovations that aim at improving ballistical selectivity (such as conformal, intensity modulation, stereotactic photons, charged particles, and intraoperative therapies), as well as at influencing tumors and normal tissues sensitivity to radiations (such as high LET particles, and altered fractionations).

Exploring the limits of spatial resolution in radiation dose delivery

Flexibility and complexity in patient treatment due to advances in radiotherapy techniques necessitates a simple method for evaluating spatial resolution capabilities of the dose delivery device. Our purpose in this investigation is to evaluate a model that describes the ability of a radiation therapy device to deliver a desired dose distribution. The model is based on linear systems theory and is analogous to methods used to describe resolution degradation in imaging systems. A qualitative analysis of spatial resolution degradation using the model is presented in the spatial and spatial frequency domains. The ability of the model to predict the effects of geometric dose conformity to treatment volumes is evaluated by varying multileaf collimator leaf width and magnitude of dose spreading. Dose distributions for three clinical treatment shapes, circular shapes of varying diameter and one intensity modulated shape are used in the evaluation. We show that the model accurately predicts the dependence of dose conformity on these parameters. The spatial resolution capabilities of different radiation therapy devices can be quantified using the model, providing a simple method for comparing different treatment machine characteristics. Also, as different treatment sites have different resolution requirements this model may be used to tailor machine characteristics to the specific site.

Body CT and oncologic imaging

The most commonly used imaging modality in patients with cancer is computed tomography (CT). Whether to evaluate primary tumor or metastases to the neck, chest, abdomen, or pelvis, oncologic body CT has become invaluable to medical, gynecologic, and radiation oncologists. CT is the principal tool used to stage tumor, assess response, and guide radiation therapy. This review provides a discussion of how we optimize oncologic CT to best meet the needs of the patient with cancer.

A simple model for examining issues in radiotherapy optimization

Convolution/superposition software has been used to produce a library of photon pencil beam dose matrices. This library of pencil beams is designed to serve as a tool for both education and investigation in the field of radiotherapy optimization. The elegance of this pencil beam model stems from its cylindrical symmetry. Because of the symmetry, the dose distribution for a pencil beam from any arbitrary angle can be determined through a simple rotation of a pre-computed dose matrix. Rapid dose calculations can thus be performed while maintaining the accuracy of a convolution/superposition based dose computation. The pencil beam data sets have been made publicly available. It is hoped that the data sets will facilitate a comparison of a variety of optimization and delivery approaches. This paper will present a number of studies designed to demonstrate the usefulness of the pencil beam data sets. These studies include an examination of the extent to which a treatment plan can be improved through either an increase in the number of beam angles and/or a decrease in the collimator size. A few insights into the significance of heterogeneity corrections for treatment planning for intensity modulated radiotherapy will also be presented.