In vivo measurements of change in tissue oxygen level during irradiation reveal novel dose rate dependence.

Background And Purpose: This study aimed to investigate the radiochemical oxygen depletion (ROD) in vivo by directly measuring oxygen levels in various mouse tissues during ultra-high dose rate (UHDR) irradiation at clinically relevant doses and dose rates.

Materials And Methods: Mice bearing subcutaneous human glioblastoma (U-87 MG) tumors were used for tumor and normal tissue (skin, muscle, brain) measurements. An oxygen-sensitive phosphorescent probe (Oxyphor PtG4) was injected into the tissues, and oxygen levels were monitored using a fiberoptic phosphorometer during UHDR irradiation with a 6 MeV electron linear accelerator (LINAC).

4Ddosimetry for a FLASH electron beam using radiation-induced acoustic imaging.

. The primary goal of this research is to demonstrate the feasibility of radiation-induced acoustic imaging (RAI) as a volumetric dosimetry tool for ultra-high dose rate FLASH electron radiotherapy (FLASH-RT) in real time. This technology aims to improve patient outcomes by accurate measurements ofdose delivery to target tumor volumes.

Multi-Institutional Audit of FLASH and Conventional Dosimetry With a 3D Printed Anatomically Realistic Mouse Phantom.

Purpose: We conducted a multi-institutional dosimetric audit between FLASH and conventional dose rate (CONV) electron irradiations by using an anatomically realistic 3-dimensional (3D) printed mouse phantom.

Methods And Materials: A computed tomography (CT) scan of a live mouse was used to create a 3D model of bony anatomy, lungs, and soft tissue. A dual-nozzle 3D printer was used to print the mouse phantom using acrylonitrile butadiene styrene (∼1.

Acute Hypoxia Does Not Alter Tumor Sensitivity to FLASH Radiation Therapy.

Purpose: Tumor hypoxia is a major cause of treatment resistance, especially to radiation therapy at conventional dose rate (CONV), and we wanted to assess whether hypoxia does alter tumor sensitivity to FLASH.

Methods And Materials: We engrafted several tumor types (glioblastoma [GBM], head and neck cancer, and lung adenocarcinoma) subcutaneously in mice to provide a reliable and rigorous way to modulate oxygen supply via vascular clamping or carbogen breathing. We irradiated tumors using a single 20-Gy fraction at either CONV or FLASH, measured oxygen tension, monitored tumor growth, and sampled tumors for bulk RNAseq and pimonidazole analysis.

Antitumor Effect by Either FLASH or Conventional Dose Rate Irradiation Involves Equivalent Immune Responses.

Purpose: The capability of ultrahigh dose rate FLASH radiation therapy to generate the FLASH effect has opened the possibility to enhance the therapeutic index of radiation therapy. The contribution of the immune response has frequently been hypothesized to account for a certain fraction of the antitumor efficacy and tumor kill of FLASH but has yet to be rigorously evaluated.

Methods And Materials: To investigate the immune response as a potentially important mechanism of the antitumor effect of FLASH, various murine tumor models were grafted either subcutaneously or orthotopically into immunocompetent mice or in moderately and severely immunocompromised mice.