title: Dosimetric impact of point A definition on high-dose-rate brachytherapy for cervical cancer: evaluations on conventional point A and MRI-guided, conformal plans.
abstract: OBJECTIVE
  To investigate the dosimetric impact of point A definitions on both conventional point A plans and MRI-guided conformal high-dose-rate (HDR) brachytherapy plans.
  
  
  METHODS
  Fifty-five HDR plans of 36 patients with FIGO stage I to IV cervical cancer were retrospectively studied; these included 30 conventional treatments and 25 conformal plans. Two different point A definitions were explored: the revised Manchester point A and the new point A as recommended by the American Brachytherapy Society. Conventional plans were produced by varying only the point A definition and the normalized isodose lines. Conformal plans were retrospectively generated per GEC-ESTRO recommendations based upon 3.0 Tesla MRI data.
  
  
  RESULTS
  SMALL YET SIGNIFICANT VARIATIONS WERE FOUND IN POINT A LOCATIONS (MEAN: 0.5 cm, maximum: 2.1 cm, p < 0.001). The use of a new point A caused minimal dose variation for both conventional and conformal plans. Conventional plans normalized to the new point A generated up to 12% (avg. 1-3%) higher overall dose in terms of higher total reference air kerma than plans normalized to other points. Dosimetric changes due to point A definitions were up to 11-12% (avg. less than 2%) on target volumes or organs-at-risk.
  
  
  CONCLUSIONS
  For both conventional and conformal plans, the new point A definition leads to smaller variations caused during implant and/or differences in patient anatomy. Using the new point A is expected to produce more consistent brachytherapy plans and improve outcome analysis.
authors: Radiation Oncology Department, University of Iowa, USA.
authors: James
authors: J
authors: Anderson
authors: Yunfei
authors: Y
authors: Huang
authors: Yusung
authors: Y
authors: Kim
keywords: MRI-guided; brachytherapy; cervical cancer; high-dose-rate brachytherapy; point A
references: Radiother Oncol. 2006 Jan;78(1):67-77
references: 16403584
references: Br J Radiol. 1953 May;26(305):252-7
references: 13042092
references: Brachytherapy. 2012 Jan-Feb;11(1):33-46
references: 22265436
references: Radiother Oncol. 2005 Mar;74(3):235-45
references: 15763303
references: Int J Radiat Oncol Biol Phys. 2005 Jul 1;62(3):901-11
references: 15936576
references: Int J Radiat Oncol Biol Phys. 2010 Jan 1;76(1):104-9
references: 19619956
references: Int J Radiat Oncol Biol Phys. 2011 Jul 1;80(3):947-55
references: 20934275
references: Int J Radiat Oncol Biol Phys. 2000 Aug 1;48(1):201-11
references: 10924990
references: Int J Radiat Oncol Biol Phys. 2009 Nov 1;75(3):803-9
references: 19286328
references: Int J Radiat Oncol Biol Phys. 2007 Jun 1;68(2):491-8
references: 17331668