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Emphasizing conformal avoidance versus target definition for IMRT planning in head-and-neck cancer
Paul M Harari1, Shiyu Song, Wolfgang A Tomé
1Department of Human Oncology, University of Wisconsin Medical School, Madison, WI 53792, USA.
Purpose:
To describe a method for streamlining the process of elective nodal volume definition for head-and-neck (H&N) intensity-modulated radiotherapy (IMRT) planning.
Methods And Materials:
A total of 20 patients who had undergone curative-intent RT for H&N cancer underwent comprehensive treatment planning using three distinct, plan design techniques: conventional three-field design, target-defined IMRT (TD-IMRT), and conformal avoidance IMRT (CA-IMRT). For each patient, the conventional three-field design was created first, thereby providing the "outermost boundaries" for subsequent IMRT design. In brief, TD-IMRT involved physician contouring of the gross tumor volume, high- and low-risk clinical target volume, and normal tissue avoidance structures on consecutive 1.25-mm computed tomography images. CA-IMRT involved physician contouring of the gross tumor volume and normal tissue avoidance structures only. The overall physician time for each approach was monitored, and the resultant plans were rigorously compared.
Results:
The average physician working time for the design of the respective H&N treatment contours was 0.3 hour for the conventional three-field design plan, 2.7 hours for TD-IMRT, and 0.9 hour for CA-IMRT. Dosimetric analysis confirmed that the largest volume of tissue treated to an intermediate (50 Gy) and high (70 Gy) dose occurred with the conventional three-field design followed by CA-IMRT and then TD-IMRT. However, for the two IMRT approaches, comparable results were found in terms of salivary gland and spinal cord protection.
Conclusion:
CA-IMRT for H&N treatment offers an alternative to TD-IMRT. The overall time for physician contouring was substantially reduced (approximately threefold), yielding a more standardized elective nodal volume. Because of the complexity of H&N IMRT target design, CA-IMRT might ultimately prove a safer and more reliable method to export to general radiation oncology practitioners, particularly those with limited H&N caseload experience.
