Dose conformity and falloff in single-lesion intracranial SRS with DCA and VMAT methods.

Background: Intracranial stereotactic radiosurgery (SRS) aims at achieving highly conformal dose distribution and, at the same time, attaining rapid dose falloff outside the treatment target. SRS is performed using different techniques including dynamic conformal arcs (DCA) and volumetric modulated arc therapy (VMAT).

Purpose: In this study, we compare dose conformity and falloff in DCA and VMAT plans for SRS with a single target.

Toward an improved assessment of dose conformity in radiotherapy.

Background: Evaluation of dose conformity is important to ensure minimum dose to normal tissue and sufficient dose coverage of the planning target volume (PTV). The existing conformity indices depend on the PTV volume and do not differentiate between two different scenarios: overdosing normal tissue and underdosing PTV.

Purpose: In this study, we introduce a novel index to assess conformity of dose distributions in radiotherapy.

Novel approach for the evaluation of dose conformity in radiotherapy.

Purpose: We describe a new approach to evaluate conformity of dose distributions in radiotherapy.

Methods: The suggested conformity factor λ is defined by using existing conformity indices and expansion of the planning target volume (PTV). If the average distance ( ) between the PTV and reference isodose surface and an arbitrarily selected PTV expansion margin ( ) are both much smaller than the size of the PTV, then λ approximately equals the ratio .

Impact of target dose inhomogeneity on BED and EUD in lung SBRT.

Purpose: To evaluate the effect of dose heterogeneity in the treatment target on biologically effective dose (BED) for frequently used hypofractionation regimens in stereotactic body radiation therapy (SBRT).

Methods: In the case of non-uniform target dose, BED in the planning target volume (PTV) is determined by using the linear-quadratic model. An expression for BED is obtained for an arbitrary dose distribution in the PTV in the case of small variance of the target dose.

Technical Note: New similarity index for radiotherapy and medical imaging.

Purpose: To describe a new similarity index and consider its biomedical applications.

Methods: Similarity index for a pair of objects is defined by the number of shared features and total number of features in these objects. Similarity measure for more than two objects is commonly defined by using pairwise similarity indices.

Effect of radiation protraction in hypofractionated radiotherapy.

Purpose: To evaluate how protracted delivery of radiation affects radiobiological properties of hypofractionated radiotherapy.

Methods: The utilized approach is based on the concept of biologically effective dose (BED). The linear-quadratic model replete with a protraction factor is used to describe changes in biologically effective dose in normal tissue (BED ) caused by varying number of fractions under the condition of fixed BED in the treatment target (BED ).

Cell kill by megavoltage protons with high LET.

The aim of the current study is to develop a radiobiological model which describes the effect of linear energy transfer (LET) on cell survival and relative biological effectiveness (RBE) of megavoltage protons. By assuming the existence of critical sites within a cell, analytical expression for cell survival S as a function of LET is derived. The obtained results indicate that in cases where dose per fraction is small, [Formula: see text] is a linear-quadratic (LQ) function of dose while both alpha and beta radio-sensitivities are non-linearly dependent on LET.

Effect of variable dose rate on biologically effective dose.

Purpose: To investigate the effect of variable dose rate on biologically effective dose (BED).

Materials And Methods: By using the linear-quadratic (LQ) model with bi-exponential repair, we analytically determine the time-dependent dose rate [Formula: see text] which minimizes the effective protraction factor (Geff) and BED under the condition of fixed fraction time and dose per fraction. Because normal tissue complication probability (NTCP) monotonically decreases with decreasing BED, the dose rate [Formula: see text] also minimizes NTCP.

Analytical representation for varian EDW factors at off-center points.

The purpose of this study is to describe and evaluate a new analytical model for Varian enhanced dynamic wedge factors at off-center points. The new model was verified by comparing measured and calculated wedge factors for the standard set of wedge angles (i.e.

A new analytical model for Varian enhanced dynamic wedge factors.

Dynamic and physical (hard) wedges are used in 3D conformal radiotherapy in order to improve dose distribution in patients. Unlike wedge factors for physical wedges that depend on wedge material and thickness, wedge factors for Varian dynamic wedges depend on the relationship between the position of the moving jaw and the number of delivered monitor units. In this study, we describe a new analytical model for dynamic wedge factors.

On the usefulness of portal monitor unit subtraction in radiation therapy.

In order to avoid additional dose to patients caused by portal imaging with megavoltage x-rays, portal monitor units (MUs) are frequently subtracted from the actual treatment MUs. This study examines the usefulness of portal MU subtraction in radiation therapy. For 11 prostate cancer patients treated with 23 MV photons, dose to prostate due to portal filming with 6 MV photons was determined.