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Published on: May 9, 2014
A novel uniform-spaced fast rescanning method for carbon-ion radiotherapy
Jun Zhang1,2,3,4,5, Xiaoyan An1,2,3,4, Ningning Chai1,2,3,4,6
1Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, China.
Background:
Phase-controlled Rescanning (PCR) technique has been used in clinical practice. The feature of the phase-controlled rescanning (PCR) method is that the beam intensity is adjusted by the accelerator actively. In this work, we developed a simplified fast rescanning method, called uniform-spaced rescanning (USR), which does not require the active adjustment of the beam intensity by the accelerator.
Purpose:
The motion compensation effectiveness of the USR was verified by comparing the four-dimensional dose distributions (4DDDs) between the USR and PCR methods. Furthermore, 4D treatment plans based on the range-adapted internal target volume (raITV) and four-dimensional robust optimization (4DRO) under the beam delivery of USR were also evaluated.
Methods:
4DCT datasets and respiratory curves from 25 lung tumor patients were used. The beam delivery simulations included the following scenario combinations: six prescription doses (2, 5, 10, 15, 20, 25 Gy (RBE)) under a single fraction, five beam intensities (1, 2, 3, 4, 5 × 108 particles per second (pps)), and three motion management techniques (no gating, gating with 30% duty cycle (DC), and gating with rescanning (2, 4, 6× USR/PCR)). Similarly, the 4DDDs of the two-field raITV and 4DRO plans were calculated with the same beam delivery parameters. Dose metrics such as the target dose coverage of D95 and homogeneity index (HI) were analyzed.
Results:
The D95 of the 4× USR was greater than 95% for all the beam intensity scenarios. The D95, HI and beam delivery time under the USR method were very similar to the PCR method with the increase of rescanning number. Under the 2, 4, 6× USR, the average CTV-D95 values of the raITV plans were higher than that of the 4DRO plans (94.9%/94.4%; 96.9%/96.4%; 97.7%/96.7%), and smaller HI values were observed for the raITV plans (11.7%/21.2%; 9.1%/17.7%; 7.9%/17.4%). For the organ at risks (OARs) sparing, the 4DRO plans could provide a better protection of the ipsilateral lung than the raITV plans.
Conclusion:
The USR method could achieve the similar motion compensation effects to the PCR method, but the complexity of beam control is simplified. The raITV plans could provide a better target dose coverage but lower OARs sparing effects than the 4DRO plans.
