Dosimetric comparison of IMRT rectal and anal canal plans generated using an anterior dose avoidance structure |
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| Affiliation: | 2. Drexel University College of Medicine, Allegheny Campus, Philadelphia, PA;2. Department of Radiology, Baylor College of Medicine, Houston, TX;3. Department of Radiation Oncology, University of Colorado, Denver, CO;4. Department of Radiation Oncology, Duke University, Durham, NC;2. Department of Radiation Oncology, HIA du Val de Grâce, Paris, France;3. Department of Radiation Oncology, Centre Antoine Lacassagne, Nice, France;4. Department of Physics, Institut de Cancérologie de la Loire, St Priest en Jarez, France;2. Institute of Medical Physics, School of Physics, University of Sydney, New South Wales, Australia;3. Northern Clinical School, University of Sydney, New South Wales, Australia;2. Department of Radiation Oncology, Acibadem University, Istanbul, Turkey;3. Institute of Biomedical Engineering, Bogazici University Istanbul, Turkey;4. Istanbul University, Institute of Oncology, Istanbul, Turkey;2. Optimization and Systems Theory, KTH Royal Institute of Technology, Stockholm, Sweden;3. RaySearch Laboratories, Stockholm, Sweden;4. Centre for Cancer Research and Cell Biology, Queen’s University Belfast, Belfast, Northern Ireland, UK |
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| Abstract: | To describe a dosimetric method using an anterior dose avoidance structure (ADAS) during the treatment planning process for intensity-modulated radiation therapy (IMRT) for patients with anal canal and rectal carcinomas. A total of 20 patients were planned on the Elekta/CMS XiO treatment planning system, version 4.5.1 (Maryland Heights MO) with a superposition algorithm. For each patient, 2 plans were created: one employing an ADAS (ADAS plan) and the other replanned without an ADAS (non-ADAS plan). The ADAS was defined to occupy the volume between the inguinal nodes and primary target providing a single organ at risk that is completely outside of the target volume. Each plan used the same beam parameters and was analyzed by comparing target coverage, overall plan dose conformity using a conformity number (CN) equation, bowel dose-volume histograms, and the number of segments, daily treatment duration, and global maximum dose. The ADAS and non-ADAS plans were equivalent in target coverage, mean global maximum dose, and sparing of small bowel in low-dose regions (5, 10, 15, and 20 Gy). The mean difference between the CN value for the non-ADAS plans and ADAS plans was 0.04 ± 0.03 (p < 0.001). The mean difference in the number of segments was 15.7 ± 12.7 (p < 0.001) in favor of ADAS plans. The ADAS plan delivery time was shorter by 2.0 ± 1.5 minutes (p < 0.001) than the non-ADAS one. The ADAS has proven to be a powerful tool when planning rectal and anal canal IMRT cases with critical structures partially contained inside the target volume. |
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| Keywords: | Dose avoidance structures Conformal dose Normal tissue sparing IMRT |
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