title: A dosimetric analysis of 6 MV versus 15 MV photon energy plans for intensity modulated radiation therapy (IMRT) of carcinoma of cervix.
abstract: BACKGROUND
  Intensity modulated radiotherapy (IMRT) is being used to treat carcinoma of cervix (Ca Cx). Integral dose to normal tissue and increased leakage are the concern about IMRT. 6 MV photon beam is a good choice of energy for Ca Cx IMRT treatment.
  
  
  OBJECTIVE
  The objective of this study was to compare intensity modulated radiotherapy (IMRT) plans generated by 6 MV and 15 MV photon energies for carcinoma of cervix (Ca Cx) with regards to dosimetric parameters of planning target volume (PTV) and organs at risk (OAR), homogeneity index (HI), conformity index at 98% level (CI 98%), integral dose to normal tissue (NTID) and total number of monitor units (MUs).
  
  
  METHODS
  A cohort of 16 patients was selected for this study. All patients were to receive a dose of 50 Gy in 25 fractions. IMRT plans were generated for both energies using same dose-volume constraints.
  
  
  RESULTS
  Our results show a comparable coverage of planning target volume (PTV) for both energies. Volume of PTV receiving a prescription dose is 97.8 ± 0.5% and 98.8 ± 0.4% for the 6 MV and the 15 MV plans. Volume of PTV receiving a dose of 107% is 4.4 ± 7.8% and 16.1 ± 22.2%. Bladder and rectum mean doses for the 6 MV and the 15 MV photon plans were 39.8 ± 3.0 Gy and 40.0 ± 3.2 Gy, and 35.8 ± 3.1 Gy and 36.0 ± 3.1 Gy, respectively. Homogeneity index (HI) for both energies was 1.04. The conformity indices at 98% isodose (CI 98%) were 1.3 ± 0.1 and 1.4 ± 0.1 for 6 MV and 15 MV photon plans, respectively.
  
  
  CONCLUSIONS
  We conclude that a 6 MV photon is a good choice for Ca Cx IMRT as it produces a highly conformal, homogeneous plan with superior target coverage and better OAR sparing.
authors.affiliation: Department of Radiation Oncology, BLK Memorial Hospital, New Delhi, India ; Department of Physics, MMH College, Ghaziabad, UP, India.
authors.forename: Atul
authors.initials: A
authors.lastname: Tyagi
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: Department of Radiation Oncology, BLK Memorial Hospital, New Delhi, India.
authors.lastname: Sandeep
authors.affiliation: Department of Physics, MMH College, Ghaziabad, UP, India.
authors.forename: Man P
authors.initials: MP
authors.lastname: Singh
keywords: Carcinoma cervix; Conformity index; IMRT; Integral dose; Photon energy