PMID- 20668338
OWN - NLM
STAT- MEDLINE
DCOM- 20101116
LR  - 20100803
IS  - 1361-6560 (Electronic)
IS  - 0031-9155 (Linking)
VI  - 55
IP  - 16
DP  - 2010 Aug 21
TI  - Monte Carlo evaluation of RapidArc oropharynx treatment planning strategies for 
      sparing of midline structures.
PG  - 4465-79
LID - 10.1088/0031-9155/55/16/S03 [doi]
AB  - The aim of the study was to perform the Monte Carlo (MC) evaluation of RapidArc 
      (Varian Medical Systems, Palo Alto, CA) dose calculations for four oropharynx 
      midline sparing planning strategies. Six patients with squamous cell cancer of 
      the oropharynx were each planned with four RapidArc head and neck treatment 
      strategies consisting of single and double photon arcs. In each case, RTOG0522 
      protocol objectives were used during planning optimization. Dose calculations 
      performed with the analytical anisotropic algorithm (AAA) are compared against 
      BEAMnrc/DOSXYZnrc dose calculations for the 24-plan dataset. Mean dose and 
      dose-to-98%-of-structure-volume (D(98%)) were used as metrics in the evaluation 
      of dose to planning target volumes (PTVs). Mean dose and 
      dose-to-2%-of-structure-volume (D(2%)) were used to evaluate dose differences 
      within organs at risk (OAR). Differences in the conformity index (CI) and the 
      homogeneity index (HI) as well as 3D dose distributions were also observed. AAA 
      calculated PTV mean dose, D(98%), and HIs showed very good agreement with MC dose 
      calculations within the 0.8% MC (statistical) calculation uncertainty. Regional 
      node volume (PTV-80%) mean dose and D(98%) were found to be overestimated (1.3%, 
      sigma = 0.8% and 2.3%, sigma = 0.8%, respectively) by the AAA with respect to MC 
      calculations. Mean dose and D(2%) to OAR were also observed to be consistently 
      overestimated by the AAA. Increasing dose calculation differences were found in 
      planning strategies exhibiting a higher overall fluence modulation. From the plan 
      dataset, the largest local dose differences were observed in heavily shielded 
      regions and within the esophageal and sinus cavities. AAA dose calculations as 
      implemented in RapidArc demonstrate excellent agreement with MC calculations in 
      unshielded regions containing moderate inhomogeneities. Acceptable agreement is 
      achieved in regions of increased MLC shielding. Differences in dose are 
      attributed to inaccuracies in the AAA-modulated fluence modeling, modeling of 
      material inhomogeneities and dose deposition within low-density materials. The 
      use of MC dose calculations leads to the same general conclusion as using AAA 
      that a two arc delivery with limited collimator opening can provide the greatest 
      amount of midline sparing compared to the other techniques investigated.
FAU - Bush, K
AU  - Bush K
AD  - Department of Medical Physics, BC Cancer Agency-Vancouver Island Center, 2410 Lee 
      Avenue, Victoria, British Columbia, Canada.
FAU - Zavgorodni, S
AU  - Zavgorodni S
FAU - Gagne, I
AU  - Gagne I
FAU - Townson, R
AU  - Townson R
FAU - Ansbacher, W
AU  - Ansbacher W
FAU - Beckham, W
AU  - Beckham W
LA  - eng
PT  - Journal Article
DEP - 20100729
PL  - England
TA  - Phys Med Biol
JT  - Physics in medicine and biology
JID - 0401220
SB  - IM
MH  - Algorithms
MH  - Anisotropy
MH  - Humans
MH  - Monte Carlo Method
MH  - Oropharyngeal Neoplasms/*radiotherapy
MH  - Phantoms, Imaging
MH  - Photons
MH  - Radiotherapy/*methods
MH  - Radiotherapy Dosage
MH  - Radiotherapy Planning, Computer-Assisted/*methods
MH  - Radiotherapy, Intensity-Modulated/*methods
MH  - Reproducibility of Results
EDAT- 2010/07/30 06:00
MHDA- 2010/11/17 06:00
CRDT- 2010/07/30 06:00
PHST- 2010/07/30 06:00 [entrez]
PHST- 2010/07/30 06:00 [pubmed]
PHST- 2010/11/17 06:00 [medline]
AID - S0031-9155(10)49801-2 [pii]
AID - 10.1088/0031-9155/55/16/S03 [doi]
PST - ppublish
SO  - Phys Med Biol. 2010 Aug 21;55(16):4465-79. doi: 10.1088/0031-9155/55/16/S03. Epub 
      2010 Jul 29.