Clinical implementation of electron energy changes of varian linear accelerators.

Modern dual photon energy linear accelerators often come with a few megavoltage electron beams. The megavoltage electron beam has limited range and relative sharp distal falloff in its depth dose curve compared to that of megavoltage photon beam. Its radiation dose is often delivered appositionally to cover the target volume to its distal 90% depth dose (d90), while avoiding the normal--sometimes critical--structure immediately distal to the target.

Erectile dysfunction and radiation dose to penile base structures: a lack of correlation.

Purpose: To evaluate the relationship between the dose and volume of radiation to proximal penile structures and the development of erectile dysfunction after external beam radiotherapy (RT) for localized prostate adenocarcinoma.

Methods And Materials: The study cohort comprised 28 patients who were enrolled our in-house three-dimensional conformal RT dose escalation protocol. The patients were treated to 78 Gy between 1995 and 1998.

Treatment planning for lung cancer: traditional homogeneous point-dose prescription compared with heterogeneity-corrected dose-volume prescription.

Purpose: To quantify the differences in doses to target volumes and critical thoracic structures calculated by traditional homogeneous point-dose prescription and heterogeneity-corrected volume-dose prescription.

Methods And Materials: Between 1998 and 2001, 30 patients with inoperable Stage I/II non-small-cell lung cancer underwent radiation treatment planning at our institution. A commercially available convolution/superposition- based algorithm was used.

Enhanced dynamic wedge factors at off-axis points in asymmetric fields.

Several recent reports have described methods for calculating enhanced dynamic wedge factors (EDWFs). Many of these reports use the monitor-unit (MU) fraction method to predict EDWFs as a function of field size. Although simple in approach, MU fraction methods do not produce accurate EDWFs in large or asymmetric fields.

On the need for monitor unit calculations as part of a beam commissioning methodology for a radiation treatment planning system.

This paper illustrates the need for validating the calculation of monitor units as part of the process of commissioning a photon beam model in a radiation treatment planning system. Examples are provided in which this validation identified subtle errors, either in the dose model or in the implementation of the dose algorithm. These errors would not have been detected if the commissioning process only compared relative dose distributions.

Beam-commissioning methodology for a three-dimensional convolution/superposition photon dose algorithm.

Commissioning beam data for the convolution/superposition dose-calculation algorithm used in a commercial three-dimensional radiation treatment planning (3D RTP) system (PINNACLE(3), ADAC Laboratories, Milpitas, CA) can be difficult and time consuming. Sixteen adjustable parameters, as well as spectral weights representing a discrete energy spectrum, must be fit to sets of central-axis depth doses and off-axis profiles for a large number of field sizes. This paper presents the beam-commissioning methodology that we used to generate accurate beam models.

Dosimetry of effective wedge fields produced by an internal wedge.

A procedure is described to calculate the monitor unit ratios required to produce effective wedge fields having a desired wedge angle by combining an internal 60 degrees wedge with an open field. Complementary procedures are derived and demonstrated for calculating the effective wedge dose distributions with wedge angles of 15 degrees, 30 degrees, and 45 degrees using the central axis depth dose data and off-axis ratios of the open field and the 60 degrees wedged field. Measurements at five points on and off the central axis within each field and measurements of the effective wedge factor demonstrated that the calculated wedge distributions were correctly delivered to within 2% in all cases.

Combined therapy as an alternative to exenteration for locally advanced vulvovaginal cancer. II. Results, complications, and dosimetric and surgical considerations.

We have introduced a therapeutic alternative to exenteration for locally advanced vulvovaginal cancer using surgery for the vulvar (external genital) phase of this disease presentation, combined with radiotherapy for the internal genital phase (with adequate overlap of fields to protect surgical margins). The rationale is that this approach treats the cancer and its dual regional spread patterns, while at the same time preserving the bladder and/or rectum, and should be associated with less morbidity and mortality than exenterative surgery. This report updates our experience with a total of 48 treated cases (37 primary cases and 11 cases of recurrent disease).