The impact of imaging modality (CT vs MRI) and patient position (supine vs prone) on tangential whole breast radiotherapy planning

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Publication date: Available online 14 July 2017
Source:Practical Radiation Oncology
Author(s): Kylie Dundas, Elise M Pogson, Vikneswary Batumalai, Geoff P Delaney, Miriam M Boxer, Mei Ling Yap, Verity Ahern, Christine Chan, Steven David, Marion Dimigen, Jennifer A Harvey, Eng-Siew Koh, Karen Lim, George Papadatos, Elizabeth Lazarus, Joseph Descellar, Peter Metcalfe, Lois Holloway
PurposeTo evaluate the impact of MRI vs CT derived planning target volumes (PTVs), in both supine and prone positions, for whole breast (WB) radiotherapy.Methods and MaterialsFour WB radiotherapy plans were generated for 28 patients, where PTVs were generated based on CT or MRI data alone in both supine and prone positions. A 6MV tangential IMRT technique was used, with plans designated as ideal, acceptable or non-compliant. Dose metrics for PTVs and OARs were compared to analyse any differences based on imaging modality (CT vs MRI) or patient position (supine vs prone).ResultsWith respect to imaging modality 2/11 WB_PTV dose metrics (V90% and V110%) displayed statistically significant differences, however these differences did not alter the average plan compliance rank. With respect to patient positioning, the odds of having an ideal plan vs a non-compliant plan were higher for the supine position compared to the prone position (p=0.026). The minimum distance between the seroma cavity (SC)_PTV and the chest-wall was increased with prone positioning, (p<0.001, supine and prone values 1.1mm and 8.7mm respectively). Heart volume was greater in the supine position (p=0.005). Heart doses were lower in the supine position than prone (p<0.01, mean doses 3.4±1.55Gy vs 4.4±1.13Gy for supine vs prone respectively). Mean lung doses met ideal dose constraints in both positions, however best spared in the prone position. The contra-lateral breast D1cc showed significantly lower doses in the supine position, (p<0.001, 4.64Gy vs 9.51Gy).ConclusionsPlanning with PTVs generated from MRI data showed no clinically significant differences to planning with PTVs generated from CT with respect to PTV and OAR doses. Prone positioning within this study reduced mean lung dose and whole heart volumes but increased mean heart and contra-lateral breast doses, compared to supine.

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