Intensity-modulated radiotherapy planning from limited anatomical information: Is Sim-CT sufficient for planning women with breast cancer receiving intensity-modulated radiotherapy?

Aims: To investigate intensity-modulated radiotherapy (IMRT) plans for women with carcinoma of the breast, using a small number of Sim-CT slices, thus avoiding changing the patient's position and potential problems with CT capacity. Materials and methods: Ten CT scans of women with breast cancer were obtained for use in the study. IMRT plans based on an open tangent pair and additional top-up segment fields were created using the full CT scan, and represented the gold standard treatment plan for comparison purposes. Five-slice CT simulator scans were artificially created by omitting intermediate slices from the full CT scans. Additionally, the intermediate CT slices were recreated via interpolation of the five slices using a standard interpolation algorithm. IMRT plans were created in the same way as for the full CT scans. To allow a suitable plan comparison to be made, the beam segments and monitor units were transferred to the full CT scans, and the dose distribution calculated. Results: The interpolated five-slice plans showed no significant differ ence in the volume of tissue receiving dose outside the range 95-105%, compared with the IMRT plans created using the full CT data set (1.3 ± 2.2%, P = 0.092). In contrast, the discrete slice CT simulator plans increased by 6.3 ± 5.4%, P = 0.0054, showing a statistically significant difference in the dose distribution produced and a clinically inferior plan. Conclusions: Plans created using five discrete slice CT scans were inferior to full CT-derived IMRT treatment plans, and are therefore not acceptable for IMRT. However, interpolating five CT simulator slices provides adequate anatomical information to produce comparable IMRT plans to those created by full CT scans of the patient. This allows the introduction of IMRT for this patient group without the need to change treatment position to accommodate CT scanning. © 2005 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.