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Effect of Multi-Leaf Collimator Angle Optimization on the Planning Parameters in Intensity-Modulated Radiotherapy for
Chun-Yan Deng1, Jia-Huan Cai1, Ji-Yong Zhang1
1Department of Radiation Oncology, Cancer Hospital of Shantou University Medical College, Shantou, China.
Abstract:
IntroductionTo investigate the effect of multi-leaf collimator (MLC) angle optimization on the planning parameters in intensity-modulated radiotherapy (IMRT) for thoracic tumors.MethodsForty-two patients (21 esophageal cancer, 21 lung cancer) were retrospectively enrolled. For each patient, two IMRT plans were designed in Eclipse treatment planning system: one with the MLC angle set to 0°, which triggered automatic field splitting due to excessive X-jaw aperture; the other with the MLC angle adjusted to keep the X-jaw aperture below 13.8 cm, thereby avoiding field splitting. The homogeneity index (HI) and conformity index (CI) of target volume, doses of organs at risk (OARs), monitor units (MUs) and treatment time were compared. Dose verification was performed.ResultsFor both esophageal and lung cancer patients, the two groups of plans met the clinical requirements and the dose distribution of target volume was similar. Compared with the plan of the MLC at 0°, the number of MUs and the treatment time were significantly reduced by adjusting the MLC angle to avoid automatic field splitting by the planning system. The average number of MUs in esophageal cancer and lung cancer patients was reduced from 1015.7 ± 162.8 and 1122.0 ± 315.3 to 853.3 ± 113.0 and 886.5 ± 264.8, respectively, and the average treatment time was shortened from 1.6 ± 0.3 min and 1.8 ± 0.6 min to 1.4 ± 0.2 min and 1.5 ± 0.5 min, respectively. The Dmean, V5Gy and V10Gy of the lung in patients with esophageal cancer and the Dmean, V10Gy and V20Gy of the lung in patients with lung cancer were significantly reduced (P < 0.05). Dose verification showed no significant difference between the two methods.ConclusionsFor thoracic tumors with a large transverse range, the method of adjusting the MLC angle to prevent automatic field splitting may effectively reduce MUs and treatment time while maintaining target coverage and OAR safety.
