2606 - The Association of Linear Energy Transfer and Dose with Late Radiation-Induced Contrast-Enhancement after Proton Therapy in CNS Malignancy
Presenter(s)
E. Huang1, S. Puri2, P. Sriya3, A. Li4, Y. Tarui5, B. R. Page1, V. J. Croog1, K. J. Redmond1, H. Li1, and L. R. Kleinberg1; 1Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, 2Oregon Health Science University, Portland, OR, 3Johns Hopkins University, Baltimore, MD, 4Department of Psychology, Johns Hopkins University, Baltimore, MD, 5Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD
Purpose/Objective(s): Proton radiation therapy (PRT) is an emerging modality for CNS malignancies because of its improvement in normal tissue sparing outside the target by the Bragg peak compared with photon radiation but which may also lead to increase of some toxicities in the high dose region. This study is to investigate if there is a relationship between the risk of late radiation-induced contrast-enhancement (RICE), relative biological effectiveness (RBE) and linear energy transfer (LET).
Materials/Methods: 150 consecutive adult patients, with a histopathologic diagnosis of CNS malignancy and underwent at one institution between 2019 – 2023, were analyzed. Patients with at least 1 year of follow-up imaging were included. We contoured RICEs identified on follow-up T1 post contrast MRI scans and computed RBE dose and dose-averaged LET distributions for all patients using the Monte Carlo method in TPS. RICE was diagnosed based on new contrast enhancement with low clinical suspicion of tumor progression and evaluation of additional follow-up images. The control group of 8 patients were selected to match with RICE group-based on age, gender, follow-up, tumor diagnosis and location. The computed RBE dose and dose-averaged LET distributions of target and organs at risk (OARs) are performed for Rice and control groups using the Monte Carlo Method in Treatment planning system. Maximum, minimum and average RBE dose of OARs and RICEs and LET of RICEs were extracted.
Results: RICE was identified in 10 cases including diagnosis as 5 astrocytoma, 2 meningioma, 1 oligodendroglioma, 1 tectal glioma and 1 high-grade glioma. The mean age was 45.5 year. 6 of 10 in RICE group treated with concurrent chemotherapy (Temozolomide) while 6 of 8 in control group treated with the concurrent chemotherapy (5 with Temozolomide, 1 with ICE). Median prescription dose was 54.6 Gy (RBE) (range, 45.0-60.0) with the fraction dose 1.8Gy or 2Gy. The p value of univariate regression of maximum, minimum and average dose of OARs of the presence of RICEs was not significant. The mean doses with RICEs are in the range of 45.01 to 61.37 Gy of RBE (median, 54.48 Gy). Mean LET values with the RICEs are in the range of 2.3 keV/µm to 4.7 keV/ µm (median, 2.8 keV/ µm). Mean LET values with the GTV are in the range of 2.16 keV/ µm to 2.90 keV/ µm (median, 2.45 keV/ µm). The mean LET values to RICEs were higher than to GTV or boost GTV volume in 7 of 10 cases.
Conclusion: Our study suggested the occurrence of RICEs appears in the region of high RBE dose and high LET such as at the distal end of beams and the study was limited. We plan to explore more dose parameters if any of them is important for the occurrence of RICEs and explore any association with late clinical toxicity.