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Intensity-modulated radiotherapy for craniospinal irradiation: target volume considerations, dose constraints, and
William Parker1, Edith Filion, David Roberge
1Department of Medical Physics, McGill University Health Centre, Montréal, QC, Canada. william@medphys.mcgill.ca
Purpose:
To report the results of an analysis of dose received to tissues and organs outside the target volume, in the setting of spinal axis irradiation for the treatment of medulloblastoma, using three treatment techniques.
Methods And Materials:
Treatment plans (total dose, 23.4 Gy) for a standard two-dimensional (2D) technique, a three-dimensional (3D) technique using a 3D imaging-based target volume, and an intensity-modulated radiotherapy (IMRT) technique, were compared for 3 patients in terms of dose-volume statistics for target coverage, as well as organ at risk (OAR) and overall tissue sparing.
Results:
Planning target volume coverage and dose homogeneity was superior for the IMRT plans for V(95%) (IMRT, 100%; 3D, 96%; 2D, 98%) and V(107%) (IMRT, 3%; 3D, 38%; 2D, 37%). In terms of OAR sparing, the IMRT plan was better for all organs and whole-body contour when comparing V(10Gy), V(15Gy), and V(20Gy). The 3D plan was superior for V(5Gy) and below. For the heart and liver in particular, the IMRT plans provided considerable sparing in terms of V(10Gy) and above. In terms of the integral dose, the IMRT plans were superior for liver (IMRT, 21.9 J; 3D, 28.6 J; 2D, 38.6 J) and heart (IMRT, 9 J; 3D, 14.1J; 2D, 19.4 J), the 3D plan for the body contour (IMRT, 349 J; 3D, 337 J; 2D, 555 J).
Conclusions:
Intensity-modulated radiotherapy is a valid treatment option for spinal axis irradiation. We have shown that IMRT results in sparing of organs at risk without a significant increase in integral dose.
