title: Influence of segment width on plan quality for volumetric modulated arc based stereotactic body radiotherapy.
abstract: OBJECTIVE
  To study the influence of segment width on plan quality for volumetric modulated arc based stereotactic body radiotherapy.
  
  
  BACKGROUND
  The redundancy of modulation for regularly shaped small volume tumors results in creation of many small segments and an increase of monitor units, with a consequent prolongation of treatment and uncertainty in treatment delivery.
  
  
  METHODS
  Six cases each in lung, abdomen and liver were taken for the study. For each case, three VMAT SBRT plans were generated with different penalties on minimum segment width of 0.5, 1.0 and 1.5 cm. A comparison was made on the metrics of dose volume histogram, dosimetric indices, monitor units (MUs) and delivery accuracy.
  
  
  RESULTS
  The mean reduction of total MUs when compared with 0.5 cm plan was observed as 12.7 ± 6.0% and 17.5 ± 7.2% for 1.0 cm and 1.5 cm of minimum segment width, respectively. The p value showed a significant degradation in dosimetric indices for 1.5 cm plans when compared with 0.5 cm and 1.0 cm plans. The average deviation of measured dose with TPS calculated was 3.0 ± 1.1%, 2.1 ± 0.84% and 1.8 ± 0.9% for 0.5, 1.0 and 1.5 cm, respectively. The calculated gamma index with pass criteria of 2% dose difference and 2 mm distance to agreement was 95.9 ± 2.8%, 96.5 ± 2.6% and 97.8 ± 1.6% as calculated for 0.5, 1.0 and 1.5 cm of penalties, respectively. In view of the trade off between delivery efficiency and plan quality, 1 cm minimum segment width plans showed an improvement.
  
  
  CONCLUSIONS
  VMAT SBRT plans with increased optimal value of minimum segment width showed better plan quality and delivery efficiency for stereotactic body radiotherapy.
authors.affiliation: Division of Radiation Oncology, Medanta - The Medicity, Gurgaon, Haryana, India ; Research and Development, Bharathiar University, Coimbatore, Tamilnadu, India.
authors.forename: Karthikeyan
authors.initials: K
authors.lastname: Nithiyanantham
authors.affiliation: Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bangalore, Karnataka, India ; Research and Development, Bharathiar University, Coimbatore, Tamilnadu, India.
authors.forename: Ganesh
authors.initials: G
authors.lastname: Kadirampatti Mani
authors.affiliation: Division of Radiation Oncology, Medanta - The Medicity, Gurgaon, Haryana, India ; Research and Development, Bharathiar University, Coimbatore, Tamilnadu, India.
authors.forename: Vikraman
authors.initials: V
authors.lastname: Subramani
authors.affiliation: Division of Radiation Oncology, Medanta - The Medicity, Gurgaon, Haryana, India ; Research and Development, Bharathiar University, Coimbatore, Tamilnadu, India.
authors.forename: Karrthick
authors.initials: K
authors.lastname: Karukkupalayam Palaniappan
authors.affiliation: Division of Radiation Oncology, Medanta - The Medicity, Gurgaon, Haryana, India.
authors.forename: Mohanraj
authors.initials: M
authors.lastname: Uthiran
authors.affiliation: Division of Radiation Oncology, Medanta - The Medicity, Gurgaon, Haryana, India.
authors.forename: Sennniandavar
authors.initials: S
authors.lastname: Vellengiri
authors.affiliation: Division of Radiation Oncology, Medanta - The Medicity, Gurgaon, Haryana, India.
authors.forename: Sambasivaselli
authors.initials: S
authors.lastname: Raju
authors.affiliation: Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bangalore, Karnataka, India.
authors.forename: Sanjay S
authors.initials: SS
authors.lastname: Supe
authors.affiliation: Division of Radiation Oncology, Medanta - The Medicity, Gurgaon, Haryana, India.
authors.forename: Tejinder
authors.initials: T
authors.lastname: Kataria
keywords: Minimum segment width; Optimization; Small field measurements; VMAT SBRT