FLASH photons @ Sapienza

The challenge

To date, a robust clinical approach for delivering photon treatments at UHDR remains undefined. The existing conventional radiotherapy techniques present significant limitations:

  • VMAT: Cannot be used. The continuous gantry rotation required makes the overall irradiation time per treatment too long, fundamentally incompatible with UHDR requirements.
  • IMRT: This is the most viable approach, requiring a fixed number of fields (typically 4–9) and Multi-Leaf Collimators (MLCs) for both tumor shaping and intensity modulation. However, MLCs move during irradiation to dynamically shape and attenuate the photon beam, with a speed (3-5 cm/s) incompatible with the required ~ms delivery times necessary to trigger the FLASH effect. Consequently, even if we assume the FLASH effect survives fractionation, standard, dynamic MLC operation cannot be relied upon for UHDR modulation.

Given that the VMAT limitation is not resolvable, the core idea is to find an alternative to standard, dynamic IMRT. Our approach is to replace the function of the dynamic MLCs for intensity modulation with passive, high-Z patient specific beam attenuators. In this view, Photon FLASH treatments could be realized by adopting an approach based on the Sapienza SAFEST linac, attached to the TRIUMF converter  and using fixed fields and a passive beam attenuator.

The SAFEST + TRIUMF converter setup in FLUKA

 

To start the study of a possible irradiation scenario, pancreatic cancer patients will be studied.

For internal users

Some useful material can be found here

Bibliography