Flash Therapy
Flash Therapy, also called Flash Radiotherapy (Flash-RT) is an emerging innovative technique to treat cancers. As the name suggests, Flash-RT delivers an extremely high dose of radiation (>40 Gy/s) to the tumor in just a fraction of a second. Thus, Flash-RT differs from conventional radiotherapy, which is given over a longer time of a few weeks and tumour may start re-population if there are delays in treatment.
Current sophisticated radiotherapy techniques utilize highly conformal radiation beams that can be delivered precisely to target tumor tissue and minimize damage to surrounding healthy tissues. However, radiation induced side-effects are common as these procedures are dose-dependent to eliminate the tumor in toto. Therefore, the ultra-fast delivery of Flash-RT has been shown promise in reducing radiation-induced side effects in healthy tissues without compromising the anti-cancer effects of treatment.
Animal experiments have revealed a “protective effect” of Flash-RT, where the damage to normal tissue was less than that observed with conventional radiotherapy. In an experimental group, 84% progression-free survival rate was observed over a 16-month period. In 2019, Flash-RT of 15Gy given for just 90 milliseconds was tried on the first human patient with T-cell cutaneous (3.5cm) lymphoma at the Lausanne University Hospital, Switzerland by Bourhis et al. They used the Oriatron eRT 6 5.6-MeV Linac, a prototype specifically designed to accelerate electrons in FLASH mode. Three weeks after the procedure, the patient had minimal (grade 1 epithelitis and edema) reaction in the soft tissues surrounding the tumor. At 5-month follow-up, the tumor response was complete. It was concluded that Flash-RT could be a potential feasible option as a safe procedure with a favorable outcome.
The exact mechanism of Flash-RT is not yet fully understood, though several hypotheses have been proposed to explain the potential benefits: the oxygen effect of inducing instant oxygen depletion, reactive oxygen species (ROS)-mediated cell damage, and a modified immune and inflammatory response.
It is now speculated that since Flash-RT delivers the radiation dose much more quickly, treatment times could potentially be significantly reduced. This would greatly enhance the patient comfort and convenience, as well as increase cancer treatment capacity. The current challenges in its implementation as a therapeutic radiotherapy option are being explored. The radiation produced by Flash-RT must be able to penetrate deep-seated tumors, which may not be possible with electron beam. This may be overcome with use of photon or proton-beam-based Flash-RT or very high energy electrons. Therefore, major technological advances are needed to enable such sources that will allow the required dose and depth to reach the more commonly occurring tumors.
Flash-RT could be utilized for the treatment of radioresistant tumors and when conventional radiotherapy would cause side effects by the high doses needed for local tumor control. This could benefit many patients who are not considered candidates for radiotherapy.
To conclude, radiobiology and clinical practice aspects of Flash-RT need to be explored further. So far it appears that if safety and efficacy can be confirmed in clinical trials, Flash-RT could transform radiation oncology and might even replace conventional radiotherapy in the future, for certain cancers.