Variations in dosimetric distribution and plan complexity with collimator angles in hypofractionated volumetric arc radiotherapy for treating prostate cancer

Abstract

PurposeHypofractionated radiotherapy can reduce treatment durations and produce effects identical to those of conventionally fractionated radiotherapy for treating prostate cancer. Volumetric arc radiotherapy (VMAT) can decrease the treatment machine monitor units (MUs). Previous studies have shown that VMAT with multileaf collimator (MLC) rotation exhibits better target dose distribution. Thus, VMAT with MLC rotation warrants further investigation.Methods and materialsTen patients with prostate cancer were included in this study. The prostate gland and seminal vesicle received 68.75 and 55 Gy, respectively, in 25 fractions. A dual‐arc VMAT plan with a collimator angle of 0° was generated and the same constraints were used to reoptimize VMAT plans with different collimator angles. The conformity index (CI), homogeneity index (HI), gradient index (GI), normalized dose contrast (NDC), MU, and modulation complexity score (MCSV) of the target were analyzed. The dose–volume histogram of the adjacent organs was analyzed. A Wilcoxon signed‐rank test was used to compare different collimator angles.ResultsOptimum values of CI, HI, and MCSV were obtained with a collimator angle of 45°. The optimum values of GI, and NDC were observed with a collimator angle of 0°. In the rectum, the highest values of maximum dose and volume receiving 60 Gy (V60 Gy) were obtained with a collimator angle of 0°, and the lowest value of mean dose (Dmean) was obtained with a collimator angle of 45°. In the bladder, high values of Dmean were obtained with collimator angles of 75° and 90°. In the rectum and bladder, the values of V60 Gy obtained with the other tested angles were not significantly higher than those obtained with an angle of 0°.ConclusionThis study found that MLC rotation affects VMAT plan complexity and dosimetric distribution. A collimator angle of 45° exhibited the optimal values of CI, HI, and MCSv among all the tested collimator angles. Late side effects of the rectum and bladder are associated with high‐dose volumes by previous studies. MLC rotation did not have statistically significantly higher values of V60 Gy in the rectum and bladder than did the 0° angle. We thought a collimator angle of 45° was an optimal angle for the prostate VMAT treatment plan. The findings can serve as a guide for collimator angle selection in prostate hypofractionated VMAT planning.

Technical Note: Improving VMAT delivery efficiency by optimizing the dynamic collimator trajectory

“…Our suggested method allows either an optimal static angle or a dynamic angle trajectory to be identified. The optimal static angle can be expected to provide a reduced delivery time compared to an ill‐suited angle for any tumor type that has a nonsymmetric shape in the beam’s‐eye‐view (BEV) . The use of a dynamic angle trajectory may provide additional time savings compared to the optimal static angle if the BEV projection of the target changes as a function of the gantry angle.…”

The Effect of Different Colimator Angles in Prostate Radiotherapy Plans with Volumetric Modulated Arc Therapy (VMAT) Technique

“…This study identified the optimum collimator angles for optimizing dosimetric distribution for planning target volume (PTV), sparing of organs at risk (OARs), and plan complexity. The findings of this study could help planners to select appropriate collimator angles to obtain optimum results [8,9].…”

Optimization of collimator angles in dual-arc volumetric modulated arc therapy planning for whole-brain radiotherapy with hippocampus and inner ear sparing

“…Previous studies on the effect of collimator angle on VMAT plan quality proposed various optimal settings depending on the tumor site and shape 12 , 17 , 41 . For vertebrae metastases, Mancosu et al suggested a collimator angle of around 90° to align the MLC leaf motion with the spinal cord 41 .…”

“…For vertebrae metastases, Mancosu et al suggested a collimator angle of around 90° to align the MLC leaf motion with the spinal cord 41 . For prostate cancer, Li et al suggested an angle of 45° for the optimal dose distribution plan complexity 17 . For nasopharynx cancer, Otto found that 45° was preferable in most cases 12 .…”