In search of the ideal dosimetric system for FLASH dose rates
A short commentary to a just published article discussing the advancements of a diamond detector dedicated for FLASH-RT applications.
FLASH radiation therapy is being extensively studied by many research groups and institutions as a promising technique to treat tumours.
Improving treatments is a common goal shared by both clinicians and the industry with a double challenge: on one hand, to overcome the resistance of certain tumours which are unresponsive to treatment and, on the other hand, to avoid long-term side effects that limit its use. Because of the risk of side effects, it is sometimes difficult to increase the doses for radiotherapy to be more effective. Researchers have gone a long way toward the understanding of biological mechanism of radiotherapy and new approaches are being developed to ensure a greater number of patients to benefit from radiotherapy. ElectronFlash from SIT is at the forefront in such field and represents the most advanced pre-clinical research system.
Researchers are now tackling another challenge, consisting in defining a reliable dosimetric system that can be used in conjunction with FLASH-RT in a clinical setting.
Extreme irradiation conditions are challenging in terms of dosimetry. Passive dosimetric systems have been successfully used at present. Unfortunately, a delay of hours or even days can be needed in order to get the response from the passive detector irradiation.
Due to such drawbacks of passive dosimetry, active real-time dosimetric systems – Ionization chambers, aluminium calorimeters, solid states detectors – would be highly preferred.
However, all the commercially available active dosimeters have been shown to suffer from serious issues at UH-DPP values, such as dose rate dependence, saturation effect, and strong nonlinearity of their response.
It is a complex job that requires the engagement of the best minds and the most appropriate structures. Tor Vergata University of Rome has developed a new detector, the ‘Flash diamond’, which can appropriately measure electron beam up to 26 cGy/p!
The results of what has been done and achieved so far is the subject of the article that we present to you today and that we invite you to read in full [https://aapm.onlinelibrary.wiley.com/doi/pdf/10.1002/mp.15473 ].
In the study, a systematic investigation of the main physical properties affecting the diamond response in UH-DPP conditions was carried out, with the intention of developing a diamond detector, namely a FLASH diamond (fD), specifically designed for FLASH-RT applications. A comprehensive dosimetric and metrological characterization of such a detector is currently ongoing. The study was based on the assumption that a fine tuning of the physical properties of the produced prototypes would allow to meet the challenging requirements of FLASH-RT dosimetry. Several diamond detectors were thus realized by systematically varying their active area (and thus sensitivity) as well as boron concentration in the p-type layer (and thus series resistance). They were tested under ElectronFlash linac irradiation in different setup conditions, by using EBT-XD Gafchromic films as reference dosimeters. Based on the obtained results, two prototypes were finally realized and independently characterized in two different facilities – using two different ElectronFlash linac machines, at SIT factory in Aprilia and at Institut Curie.
Given the level of complexity of the topic, we refer to the original article for detailed results. Nonetheless we can affirm that researchers have demonstrated the feasibility of a diamond detector for FLASH-RT applications. Work is in progress to perform a comprehensive dosimetric characterization of the proposed fD detectors.
Stay tuned for some more ground-breaking development to come soon!