Modified X-ray tube for high dose rate FLASH radiotherapy research

FLASH radiotherapy (FLASH-RT) has been demonstrated to achieve comparable tumor control to conventional radiotherapy (CONV-RT) while reducing radiation-induced damage to normal tissues. However, current FLASH experiments primarily rely on particle accelerators (e.g., linear electron accelerators or proton synchrotrons), which are expensive, scarce, and technically challenging to install, thereby hindering the widespread adoption and fundamental research of FLASH technology. In contrast, kV X-ray tubes offer a compact structure, low cost, and easy accessibility. By modifying their structure, they can be adapted into a simplified FLASH-RT experimental platform.

Ultra-high dose rate kilovoltage X-rays generated from rotating anode X-ray tubes at short source-to-surface distances (SSD) offer a cost-effective alternative for FLASH radiotherapy research in basic laboratory settings, compared to advanced proton and electron accelerators. However, the direct use of rotating anode X-ray tubes to achieve ultra-high dose rates is limited by housing constraints. This study presents a housing modification that shortens the SSD with higher flux for a higher dose rate, and expand beam exit port providing more space for sample placement.

A high-capacity X-ray tube was modified to enhance dose rate capabilities and expand the beam exit port. Dose rate measurements were performed using kV-compatible solid water phantoms to assess the effects of SSD and field size on dose rates and depth-dose characteristics before and after the modification using radiochromic EBT4 film.

The modification shortened the SSD by 5 mm from the original design, enabling a maximum surface dose rate of 200 Gy/s at a minimum SSD of 29.5 mm, 1.6 times higher than the original configuration. Additionally, the beam exit port was expanded to a 127 mm × 96 mm rectangular area, providing ample space for sample placement. FLASH dose rates exceeding 40 Gy/s were achieved at depths up to 25 mm into solid water. A nonuniform high-to-low dose gradient was observed due to the anode heel effect. The dose flatness within a 10 mm diameter field of view was evaluated by incorporating a collimator, and the attenuation characteristics of the radiation beam after traversing biological tissue were approximated using a water-equivalent film phantom. This experimental setup ensured that both the lateral and depth-dose profiles remained within the FLASH dose range throughout the investigation.

Modifying the housing of rotating anode X-ray tubes enhances the efficient delivery of ultra-high dose rate radiation by shortening the SSD and expanding the beam exit port. Although the use of tubes for FLASH experiments will have problems such as uneven dose depth and shortened tube life, this improved tube configuration enables high-dose-rate irradiation, providing an accessible platform for laboratory-based FLASH studies.