Treatment planning consideration for very high-energy electron FLASH radiotherapy. (March 2023)

• Record Type: Journal Article
• Authors: Zhang, Guoliang; Zhang, Zhengzhao; Gao, Wenchao; Quan, Hong
• Is Part Of: Physica medica. Volume 107(2023)
• Publication Date: 2023-03
• Subjects: VHEE -- FLASH -- Dose rate -- Irradiation time -- Treatment plan quality; Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2023.102539
• Languages: English
• ISSNs: 1120-1797

Abstract

Highlights: VHEE beams have the potential of taking a place in novel FLASH radiation therapy. The PBS delivery mode has been widely used in proton therapy and has the potential to be applied in electron. Treatment plan consideration for VHEE FLASH radiation therapy. A quantitative comparison for FLASH-related parameters between different energies was performed. Abstract: Purpose: Very high-energy electron (VHEE) can make up the insufficient treatment depth of the low-energy electron while offering an intermediate dosimetric advantage between photon and proton. Combining FLASH with VHEE, a quantitative comparison between different energies was made, with regard to plan quality, dose rate distribution (both in PTV and OAR), and total duration of treatment (beam-on time). Methods: In two patient cases (head and lung), we created the treatment plans utilizing the scanning pencil beam via the Monte Carlo simulation and a PTV-based optimization algorithm. Geant4 was used to simulate VHEE pencil beams and sizes of 0.3–5 mm defined by the full width at half maximum (FWHM). Monoenergetic beams with Gaussian distribution in x and y directions (ISOURC = 19) were used as the source of electrons. A large-scale non-linear solver (IPOPT) was used to calculate the optimal spot weights. After optimization, a quantitative comparison between different energies was made regarding treatment plan quality, dose rate distribution (both in PTV and OAR), and total beam duration. Results: For head (80 MeV, 100 MeV, and 120 MeV) and lung cases (100 MeV, 120 MeV, and 140 MeV), the minimum beam intensity needs to be ∼2.5 × 10 11 electrons/s and ∼9.375 × 10 11 electrons/s to allow > 90 % volume of PTV reaching the average dose rate (DADR) higher than 40 Gy/s. At this beam intensity (fraction dose: 10 Gy), the overall irradiation time for the head case is 5258.75 ms (80 MeV), 5149.75 ms (100 MeV), and 4976.75 ms (120 MeV), including scanning time 872.75 ms. For lung cases, this number is 1034.25 ms (100 MeV), 981.55 ms (120 MeV), and 928.15 ms (140 MeV), including scanning time 298.75 ms. The plan of higher energy always performs with a higher dose rate (both in PTV and OAR) and thereby costs less delivery time (beam-on time). Conclusion: The study systematically investigated the currently known FLASH parameters for VHEE radiotherapy and successfully established a benchmark reference for its FLASH dose rate performance.