3075 - Exploring the Potential of FLASH Proton Therapy in Medulloblastoma: Insights from Cerebellar and Tumor Organoids
Presenter(s)
H. Iwata1, I. S. Shimada2, C. Omachi3, T. Toshito3, K. Tanaka4, H. Kino4, M. Umezawa5, M. Yamada5, Y. Kato2, A. Hiwatashi6, and H. Ogino1; 1Department of Radiation Oncology, Nagoya Proton Therapy Center, Nagoya City University West Medical Center, Nagoya, Japan, 2Department of Cell Biology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan, 3Department of Proton Therapy Physics, Nagoya Proton Therapy Center, Nagoya City University West Medical Center, Nagoya, Japan, 4Department of Proton Therapy Technology, Nagoya Proton Therapy Center, Nagoya City University West Medical Center, Nagoya, Japan, 5Therapy System Business, Healthcare Business Group, Hitachi High-Tech Corporation, Kashiwa, Japan, 6Department of Radiology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan
Purpose/Objective(s):
Medulloblastoma is the most common malignant brain tumor in children. To minimize late toxicity and growth impairment caused by radiotherapy, the development of low-toxicity treatment strategies is strongly desired. This study aims to compare the effects of conventional dose-rate (Conv) and ultra-high dose rate (UHDR) proton irradiation (FLASH) on cerebellar and medulloblastoma organoids.Materials/Methods:
Human iPS cells were purchased from RIKEN BRC and used to generate cerebellar and medulloblastoma organoids. The Dual SMAD inhibition method was employed to induce neuroectoderm differentiation, followed by the addition of fibroblast growth factor 2 to promote cerebellum-specific differentiation. A three-dimensional suspension culture method was used for organoid formation. For medulloblastoma organoids, GPR161 knockout iPS cells were generated via gene editing to replicate the induction of SHH-type medulloblastoma. Radiation experiments were conducted with X-ray irradiation at doses of 1 Gy and 3 Gy to optimize irradiation conditions and analysis methods. Subsequently, the main experiments utilized a synchrotron accelerator to deliver proton irradiation at Conv (3 Gy/s) with doses of 3 Gy and 8 Gy, as well as UHDR proton irradiation (200 Gy/s) in both the 1-cm spread-out Bragg peak (SOBP) and plateau region at 3 Gy and 8 Gy. Organoids were fixed 24 hours post-irradiation, followed by immunostaining to analyze DNA damage (?H2AX staining), apoptosis (Cleaved Caspase 3 staining), and cell proliferation (pH3 staining).Results: The generated organoids exhibited ventricular-like structures with PAX6-positive stem cells and KIRREL2-positive cerebellum-specific GABAergic neurons. Medulloblastoma organoids demonstrated strong upregulation of NMYC in cancer stem cells, confirming that the generated organoids mimic normal cerebellum and Shh-type medulloblastoma. In cerebellar organoids, 3 Gy irradiation resulted in significant cell death, which was further exacerbated at 8 Gy. In contrast, medulloblastoma organoids exhibited resistance to high-dose irradiation, with viable cells persisting even at 8 Gy, suggesting the influence of radiation tolerance and hypoxic regions due to cell size. Notably, UHDR proton irradiation did not reduce cell death compared to Conv proton irradiation. In the case of 8 Gy peak irradiation, a stronger cytotoxic effect was observed. In cerebellar organoids, UHDR proton irradiation showed a trend toward reduced cell death at 3 Gy compared to Conv proton irradiation in both peak and plateau modes. At 8 Gy, only a slight reduction in cell death was observed, with no significant differences between irradiation modes.
Conclusion:
This study elucidated the differential cellular responses of cerebellar and medulloblastoma organoids to UHDR proton irradiation. The results suggest that FLASH proton therapy may contribute to reducing toxicity in normal cerebellar tissue while maintaining its efficacy against medulloblastoma.