FLASH radiotherapy (FLASH-RT) is a novel radiotherapy approach based on the use of ultra-high dose radiation to treat malignant cells. Although tumours can be reduced or eradicated using radiotherapy, toxicities induced by radiation can compromise healthy tissues. The FLASH effect is the observation that treatment delivered at an ultra-high dose rate is able to reduce adverse toxicities present at conventional dose rates. While this novel technique may provide a turning point for clinical practice, the exact mechanisms underlying the causes or influences of the FLASH effect are not fully understood. The study presented here uses data collected from 41 experimental investigations (published before March 2024) of the FLASH effect. Searchable databases were constructed to contain the outcomes of the various experiments in addition to values of beam parameters that may have a bearing on the FLASH effect. An in-depth review of the impact of the key beam parameters on the results of the experiments was carried out. Correlations between parameter values and experimental outcomes were studied. Pulse Dose Rate had positive correlations with almost all end points, suggesting viability of FLASH-RT as a new modality of radiotherapy. The collective results of this systematic review study suggest that beam parameter qualities from both FLASH and conventional radiotherapy can be valuable for tissue sparing and effective tumour treatment.

OBJECTIVE:   Evaluate the dosimetric impact of selective/elective nodal treatment with dose-escalated radiotherapy for regionally advanced non-small-cell lung cancer (NSCLC) using proton therapy (PT) or intensity-modulated radiotherapy (IMRT).
METHODS:   Five consecutive patients with regionally advanced NSCLC underwent treatment planning for high-dose involved-field (IF) treatment (positron emission tomography-positive gross disease) with or without selective/elective nodal irradiation, defined as the extended field (EF). Four treatment plans were developed for each patient: i) IMRT to treat IF to 74 Gy (IFrT); ii) IMRT to treat high-risk nodes to 44 Gy and IF to 74 Gy (EFrT); iii) PT to treat IF to 74CGE (IFpT); and iv) PT to treat high-risk nodes to 44CGE and IF to 74CGE (EFpT). High-risk nodes were defined as mediastinal, hilar, and supraclavicular lymph node stations adjacent to foci of PET-positive gross disease. The IMRT and PT plans were isoeffective. Dose to organs at risk (OARs), including the lung, esophagus, heart and spinal cord, were evaluated.
RESULTS:   The average IF clinical target volume (CTV) was 397 cc (344-428), while the average EF CTV was 642 cc (530-753 cc). Comparing IMRT with PT, mean lung dose reduced 3.4 Gy/CGE and 3.7 Gy/CGE; lung V20 reduced 4% and 5% for EF and IF, respectively.
CONCLUSIONS:   Selective/elective nodal irradiation with protons reduces normal-lung exposure compared to selective/elective nodal irradiation with IMRT.