A novel dose rate optimization method to maximize ultrahigh-dose-rate coverage of critical organs at risk without compromising dosimetry metrics in proton pencil beam scanning FLASH radiation therapy Journal Article
| Authors: | Zhao, X.; Huang, S.; Lin, H.; Choi, J. I.; Zhu, K.; Simone, C. B. 2nd; Yan, X.; Kang, M. |
| Article Title: | A novel dose rate optimization method to maximize ultrahigh-dose-rate coverage of critical organs at risk without compromising dosimetry metrics in proton pencil beam scanning FLASH radiation therapy |
| Abstract: | Purpose: This study aimed to investigate a dose rate optimization framework based on the spot-scanning patterns to improve ultrahigh-dose-rate coverage of critical organs at risk (OARs) for proton pencil beam scanning (PBS) FLASH radiation therapy (ultrahigh dose-rate (often referred to as >40 Gy per second) delivery) and present implementation of a genetic algorithm (GA) method for spot sequence optimization to achieve PBS FLASH dose rate optimization under relatively low nozzle beam currents. Methods and Materials: First, a multifield FLASH plan was developed to meet all the dosimetric goals and optimal FLASH dose rate coverage by considering the deliverable minimum monitor unit constraint. Then, a GA method was implemented into the in-house treatment platform to maximize the dose rate by exploring the best spot delivery sequence. A phantom study was performed to evaluate the effectiveness of the dose rate optimization. Then, 10 consecutive plans for patients with lung cancer previously treated using PBS intensity-modulated proton therapy were optimized using 45 GyRBE in 3 fractions for both transmission and Bragg peak FLASH radiation therapy for further validation. The spot delivery sequence of each treatment field was optimized using this GA. The ultrahigh-dose-rate–volume histogram and dose rate coverage V40GyRBE/s were investigated to assess the efficacy of dose rate optimization quantitatively. Results: Using a relatively low monitor unit/spot of 150, corresponding to a nozzle beam current of 65 nA, the FLASH dose rate ratio V40GyRBE/s of the OAR contour of the core was increased from 0% to ∼60% in the phantom study. In the patients with lung cancer, the ultrahigh-dose-rate coverage V40GyRBE/s was improved from 15.2%, 15.5%, 17.6%, and 16.0% before the delivery sequence optimization to 31.8%, 43.5%, 47.6%, and 30.5% after delivery sequence optimization in the lungs-GTV (gross tumor volume), spinal cord, esophagus, and heart (for all, P < .001). When the beam current increased to 130 nA, V40GyRBE/s was improved from 45.1%, 47.1%, 51.2%, and 51.4% to 65.3%, 83.5%, 88.1%, and 69.4% (P < .05). The averaged V40GyRBE/s for the target and OARs increased from 12.9% to 41.6% and 46.3% to 77.5% for 65 and 130 nA, respectively, showing significant improvements based on a clinical proton system. After optimizing the dose rate for the Bragg peak FLASH technique with a beam current of 340 nA, the V40GyRBE/s values for the lung GTV, spinal cord, esophagus, and heart were increased by 8.9%, 15.8%, 22%, and 20.8%, respectively. Conclusions: An optimal plan quality can be maintained as the spot delivery sequence optimization is a separate independent process after the plan optimization. Both the phantom and patient results demonstrated that novel spot delivery sequence optimization can effectively improve the ultrahigh-dose-rate coverage for critical OARs, which can potentially be applied in clinical practice for better OARs-sparing efficacy. © 2024 Elsevier Inc. |
| Keywords: | intensity modulated radiation therapy; treatment planning; lung neoplasms; radiotherapy dosage; radiotherapy; lung cancer; algorithms; radiation response; lung tumor; algorithm; radiotherapy, intensity-modulated; dosimetry; spinal cord; lung; radiotherapy planning, computer-assisted; phantoms, imaging; radiation dose distribution; biological organs; heart; esophagus; diseases; genetic algorithm; gross tumor volume; clinical target volume; phantoms; dose rate; organs at risks; proton therapy; procedures; critical organs; organs at risk; genetic algorithms; imaging phantom; humans; human; article; radiotherapy planning system; proton beams; proton beam therapy; flash radiotherapy; pencil beam; nozzles; beam-scanning; beam currents; algorithm methods; nozzle beams; rate optimizations; sequence optimization |
| Journal Title: | International Journal of Radiation Oncology, Biology, Physics |
| Volume: | 120 |
| Issue: | 4 |
| ISSN: | 0360-3016 |
| Publisher: | Elsevier Inc. |
| Date Published: | 2024-11-15 |
| Start Page: | 1181 |
| End Page: | 1191 |
| Language: | English |
| DOI: | 10.1016/j.ijrobp.2024.06.002 |
| PUBMED: | 38879087 |
| PROVIDER: | scopus |
| DOI/URL: | |
| Notes: | Article -- Source: Scopus |
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