Composite planning to reduce the brain dose in primary CNS lymphoma
F. Ahmad, A-D. Durham, M. Zeverino, C. Zulliger, J. Bourhis, M. Ozsahin
Purpose/Objectives: Primary CNS Lymphoma is extremely sensitive to radiation therapy, however studies have failed to show a convincing survival benefit to consolidative whole brain radiation therapy after chemotherapy, with only an improvement in progression free survival. Moreover, patients who received WBRT had higher rates of delayed neurotoxicity.
We treated 2 patients with primary CNS lymphoma following chemotherapy at the dose of 23.4 Gy in 13 fractions of 1.8 Gy on the whole brain followed by a sequential boost of 45-50 Gy in 25 fractions of 1.8-2 Gy to the primary site/residual tumor. In order to limit the dose to the brain to the prescribed dose, we used composite planning (bias dose planning) and compared the plans to “standard” plans.
Materials/Methods: We analyzed plans from 2 patients treated in our clinic for brain radiation following chemotherapy for CNS primary lymphoma. Volumes were defined after rigid fusion of the pre- and post-chemotherapy MRIs using Velocity AI software (Varian). 2 plans were generated: - A standard plan where the WBRT dose was planned first for volumetric arc therapy (VMAT) using the Monoco TPS (Elekta), followed by the boost dose plan. A second plan was obtained by planning the sequential boost dose first and only thereafter planning the WBRT using the bias dose planning option with the Monaco TPS in order to have a final composite plan corresponding to the prescribed doses.
Results: Treatment plans resulting from the bias dose planning had a markedly reduced dose to the brain outside of the boost. Mean brain dose 25.94 Gy(Bias plan) vs 31.97 Gy(Standard plan) in one case, and a mean brain dose 25.06 Gy(Bias plan) vs 29.21Gy(Standard plan) in a second case.
Conclusions: Composite planning of the boost first and only thereafter planning the dose to the brain taking the boost plan into account produces better plans with a reduced brain dose. We recommend this procedure for CNS lymphoma irradiation.