# Nuclear Science and Techniques

《核技术》(英文版) ISSN 1001-8042 CN 31-1559/TL     2018 Impact factor 0.961

Nuclear Science and Techniques ›› 2019, Vol. 30 ›› Issue (11): 168

• NUCLEAR CHEMISTRY,RADIOCHEMISTRY,RADIOPHARMACEUTICALS AND NUCLEAR MEDICINE •

### Quantifying lateral penumbra advantages of collimated spot-scanning beam for intensity-modulated proton therapy

Chun-Bo Liu1 • Yun-Tao Song1,2 • Hong-Dong Liu1 • Hai-Zhou Xue3 • Han-Sheng Feng2

1. 1 University of Science and Technology of China, Hefei 230026, China
2 Institute of Plasma Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China
3 Hefei CAS Ion Medical and Technical Devices Co., Ltd, Hefei 230088, China
• Contact: Han-Sheng Feng E-mail:hsfeng@ipp.ac.cn
• Supported by:
This work was supported by the Key Program of the 13th Five-Year Plan, the Hefei Institutes of Physical Science of the Chinese Academy of Sciences (No. KP-2017-24).
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Chun-Bo Liu, Yun-Tao Song, Hong-Dong Liu, Hai-Zhou Xue, Han-Sheng Feng. Quantifying lateral penumbra advantages of collimated spot-scanning beam for intensity-modulated proton therapy.Nuclear Science and Techniques, 2019, 30(11): 168

Abstract: Intensity-modulated proton therapy (IMPT) is becoming essential for proton therapy and is under rapid development. However, for IMPT, the lateral penumbra of the spot-scanning proton beam is still an urgent issue to be solved. Patient-specific block collimators (PSBCs), which can block unnecessary doses, play a crucial role in passive scattering delivery technology but are rarely used in spot scanning. One objective of this study is to investigate the lateral penumbra variations of intensity-modulated spot scanning with and without a PSBC. For fields with varying degrees of sharpness and at varying depths in a water phantom, the lateral penumbral widths were calculated using a Monte Carlo-based dose engine from RayStation 6. The results suggest that the lateral penumbral widths can be reduced by more than 30% for uniform target volumes, regardless of whether a range-shifter is used, and that the maximum dose beyond the field edges can be reduced significantly. The results of patient cases show that the doses in organs-at-risk near the edge of the target volume decrease if a PSBC is implemented. This study demonstrates that intensity-modulated spot scanning with a PSBC can effectively reduce the lateral penumbra and block unnecessary doses and is therefore promising for clinical applications in spot-scanning proton therapy.