WE-C-AUD C-03: Segmented Field Electron Conformal Therapy Planning Algorithm

Abstract

Purpose: To develop a clinically useful forward planning algorithm for determining the energy, shape, and weight of multiple abutted fields used in segmented‐field electron conformal therapy (SFECT) that conforms the 90% isodose to the PTV while minimizing the treatment of normal tissue. Method and Materials: An algorithm was developed that requires a beam's eye view (BEV) of depth of the distal PTV surface. First, the minimum energy for which R90 (10‐cm diameter field) exceeds the depth to the distal edge of the PTV is determined for each pixel of the BEV. Next, the minimum circular field size to treat R90 to the distal edge of the PTV is determined for each pixel and drawn around the pixel. Fields of the same energy are merged with higher energy fields taking precedence in areas of overlap, and the dose distribution is calculated. Finally, an iterative process is used to modify the fields to converge the 90% dose surface to the distal PTV surface. The algorithm was used on six hypothetical PTVs, and the dose distribution was compared to that of a single energy plan. A pencil‐beam algorithm calculated the dose distribution for both sets of plans. Results: The SFECT plans were able to deliver 90% of the dose to over 95% of the PTV, while irradiating an average of 16% less non‐PTV to 90% of the dose. Due to abutment dosimetry, SFECT plans increased dose range within the PTV by an average of 4.9%. Conclusion: The developed algorithm was useful for determining SFECT plans in a water phantom. SFECT plans irradiate significantly less non‐PTV volume than single energy therapy, but at the expense of increased dose range within the PTV (D90−10). Conflict of Interest: This work was funded in part by a research grant with Varian Medical Systems, Inc.

Planning tools for modulated electron radiotherapy

“…9 Modifying electron fields using low melting point alloy cutouts or an electron MLC is labor intensive and requires further technical development. 10 It was previously shown that using a photon MLC, electron fields can be shaped accurately and efficiently 11 with use of relatively short source-to-surface distances ͑SSDs͒. We have developed a treatment technique that relies on segmental delivered apertures provided by the photon MLC system.…”

SU‐FF‐T‐134: Segmented Field Electron Conformal Therapy with An Electron Multi‐Leaf Collimator

“…Segmented-field ECT has been defined by Hogstrom et al (2003) as "the utilization of multiple abutted electron fields, each having a common virtual source position but each having its own energy and weight, so as to conform the therapeutic dose surface (e.g., 90% of given dose) to the PTV." Treatment planning may be achieved through forward planning with a 3-D treatment planning system, or, preferably, with a computer based segmented-field ECT planning algorithm such as designed by Perrin (2008). shows a segmented field treatment plan created with forward planning (Richert 2006).…”

Potential of discrete Gaussian edge feathering method for improving abutment dosimetry in eMLC‐delivered segmented‐field electron conformal therapy

“…Segmented-field ECT, detailed by Zackrisson and Karlsson,8 should be useful for similar sites as bolus ECT; however, it is not easily used presently due to lack of treatment planning and delivery tools. Treatment planning tools for designing segmented-fields, such as those recently studied by Perrin, 16 are not available, hence, field segmentation must be done manually, which is slow and highly subjective. Also, automated dose delivery tools do not exist currently, although multiple Cerrobend inserts fabricated with diverging edges have been shown sufficiently accurate.…”