Wu Wei, Zhang Weijie, Li Jiaxin, Wang Wei, Lin Yuting, Li Qiang, Gao Hao
Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, China.
University of Chinese Academy of Sciences, Beijing, China.
Med Phys. 2025 Jun;52(6):3625-3634. doi: 10.1002/mp.17869. Epub 2025 May 7.
Minibeam radiation therapy (MBRT) employs a highly modulated spatial dose distribution characterized by the peak-to-valley dose ratio (PVDR). Carbon minibeam radiation therapy (cMBRT) offers higher PVDR and relative biological effectiveness (RBE) compared to proton MBRT. However, achieving uniform target dose (UTD) coverage while maintaining a high PVDR in organs at risk (OAR) remains challenging.
To address this challenge and optimize the balance between PVDR in OAR and target dose homogeneity, we introduce the scissor-beam (SB) approach for cMBRT.
The SB method introduces scissor beam (SB) splitting, where each original beam is divided into a primary beam and a complementary beam. The primary beam maintains the same angle as the original beam, while the complementary beam is rotated by a small degree. This rotation angle is determined based on the center-to-center distance and the relative positions of the OAR and the target. Monte Carlo simulation using GATE/GEANT4 were performed for dose calculations. The effectiveness of SB was evaluated in comparison to conventional cMBRT method (MB) and crossfire (CF) method in terms of target dose uniformity, OAR sparing, and PVDR in OAR across three clinical cases: lung, pancreas, and head-and-neck (HN) cancers.
Compared to MB (2 mm center to center distance(d)), SB increased OAR PVDR by 150% and matched the PVDR of MB (4 mm d) with ≤5% difference across lung, pancreas, and head and neck (HN) cases. SB improved target conformity (CI) by 118%-167% over MB (4 mm d), reducing lung D by 12%-27%, liver D by 18%, and brainstem/spinal cord D by 42%-54%. Relative to CF, SB maintained similar PVDR (≤4% difference) while enhancing OAR sparing: 33% lower left lung D, 71% reduced kidney D, and complete spinal cord sparing (pancreas) and HN cases saw 37% lower brainstem D with SB. These results highlight the effectiveness of the SB method in achieving better target dose uniformity and OAR sparing while maintaining comparable PVDR values.
We have proposed a novel SB method for cMBRT. SB provides a better balance between UTD and PVDR in OAR compared to MB. Additionally, SB demonstrates superior OAR protection compared to CF. This innovative approach holds significant potential to enhance the therapeutic ratio of cMBRT, offering improved treatment outcomes and reduced risks for patients.
微束放射治疗（MBRT）采用具有峰谷剂量比（PVDR）特征的高度调制空间剂量分布。与质子MBRT相比，碳微束放射治疗（cMBRT）具有更高的PVDR和相对生物效应（RBE）。然而，在危及器官（OAR）中保持高PVDR的同时实现均匀靶区剂量（UTD）覆盖仍然具有挑战性。
为应对这一挑战并优化OAR中PVDR与靶区剂量均匀性之间的平衡，我们引入了用于cMBRT的剪刀束（SB）方法。
SB方法引入了剪刀束（SB）分割，即将每个原始束分为一个主束和一个互补束。主束与原始束保持相同角度，而互补束旋转一个小角度。该旋转角度根据中心距以及OAR与靶区的相对位置确定。使用GATE/GEANT4进行蒙特卡罗模拟以进行剂量计算。在三个临床病例（肺癌、胰腺癌和头颈癌）中，就靶区剂量均匀性、OAR保护以及OAR中的PVDR而言，将SB的有效性与传统cMBRT方法（MB）和交叉照射（CF）方法进行了比较。
与MB（中心距2毫米（d））相比，SB使OAR的PVDR提高了150%，并且在肺癌、胰腺癌和头颈癌病例中，SB的PVDR与MB（4毫米d）的PVDR相差≤5%。与MB（4毫米d）相比，SB使靶区适形性（CI）提高了118% - 167%，使肺剂量降低了12% - 27%，肝脏剂量降低了18%，脑干/脊髓剂量降低了42% - 54%。相对于CF，SB保持了相似的PVDR（相差≤4%），同时增强了对OAR的保护：左肺剂量降低33%，肾脏剂量降低71%，在胰腺癌和头颈癌病例中，SB完全保护脊髓，脑干剂量降低37%。这些结果突出了SB方法在实现更好的靶区剂量均匀性和OAR保护的同时保持可比PVDR值方面的有效性。
我们为cMBRT提出了一种新颖的SB方法。与MB相比，SB在OAR的UTD和PVDR之间实现了更好的平衡。此外，与CF相比，SB显示出对OAR的卓越保护。这种创新方法具有显著潜力来提高cMBRT的治疗比，为患者提供更好的治疗效果并降低风险。
