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Underdosage of the upper-airway mucosa for small fields as used in intensity-modulated radiation therapy: A comparison between radiochromic film measurements, Monte Carlo simulations, and collapsed cone convolution calculations

Martens, C; Reynaert, N; De Wagter, C; Nilsson, Per LU ; Coghe, M; Palmans, H; Theirens, H and De Neve, W (2002) In Medical Physics 29(7). p.1528-1535
Abstract
Head-and-neck tumors are often situated at an air-tissue interface what may result in an underdosage of part of the tumor in radiotherapy treatments using megavoltage photons. especially for small fields. In addition to effects of transient electronic disequilibrium, for these small fields, an increased lateral electron range in air will result in an important extra reduction of the central axis (lose beyond the cavity. Therefore dose calculation algorithms need to model electron transport accurately. We simulated the trachea by a 2 cm diameter cylindrical air cavity with the rin) situated 2 cm beneath the phantom surface. A 6 MV photon beam from an Elekta SLi plus linear accelerator, equipped with the standard multileaf collimator (MLC),... (More)
Head-and-neck tumors are often situated at an air-tissue interface what may result in an underdosage of part of the tumor in radiotherapy treatments using megavoltage photons. especially for small fields. In addition to effects of transient electronic disequilibrium, for these small fields, an increased lateral electron range in air will result in an important extra reduction of the central axis (lose beyond the cavity. Therefore dose calculation algorithms need to model electron transport accurately. We simulated the trachea by a 2 cm diameter cylindrical air cavity with the rin) situated 2 cm beneath the phantom surface. A 6 MV photon beam from an Elekta SLi plus linear accelerator, equipped with the standard multileaf collimator (MLC), was assessed. A 10 x 2 cm(2) and a 10 K 1 cm(2) field, both widthwise collimated by the MLC, were applied with their long side parallel to the cylinder axis. Central axis dose rebuild-up was studied. Radiochromic film measurements were performed in an in-house manufactured polystyrene phantom with the films oriented either along or perpendicular to the beam axis. Monte Carlo simulations were performed with BEAM and EGSnrc. Calculations were also performed using the pencil beam (PB) algorithm and the collapsed cone convolution (CCC) algorithm of Helax-TMS (MDS Nordion, Kanata. Canada) version 6.0.2 and using the CCC algorithm of Pinnacle (ADAC Laboratories, Milpitas. CA, USA) version 4.2. A very good agreement between the film measurements and the Monte Carlo simulations was found. The CCC algorithms were not able to predict the interface dose accurately when lateral electronic disequilibrium occurs, but were shown to be a considerable improvement compared to the PB algorithm. The CCC algorithms overestimate the dose in the rebuild-up region. The interface dose was overestimated by a maximum of 31% or 54%, depending on the implementation of the CCC algorithm. At a depth of I rum, the maximum dose overestimation was 14% or 24%. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
collapsed, Monte Carlo, radiochromic film, air cavity, small fields, cone convolution calculations
in
Medical Physics
volume
29
issue
7
pages
1528 - 1535
publisher
American Association of Physicists in Medicine
external identifiers
  • wos:000176930900018
  • pmid:12148735
  • scopus:0035996450
ISSN
0094-2405
DOI
10.1118/1.1487421
language
English
LU publication?
yes
id
4c18ef91-780d-43b4-9136-05a2c9b53078 (old id 333239)
date added to LUP
2007-11-16 13:29:07
date last changed
2017-01-01 06:56:13
@article{4c18ef91-780d-43b4-9136-05a2c9b53078,
  abstract     = {Head-and-neck tumors are often situated at an air-tissue interface what may result in an underdosage of part of the tumor in radiotherapy treatments using megavoltage photons. especially for small fields. In addition to effects of transient electronic disequilibrium, for these small fields, an increased lateral electron range in air will result in an important extra reduction of the central axis (lose beyond the cavity. Therefore dose calculation algorithms need to model electron transport accurately. We simulated the trachea by a 2 cm diameter cylindrical air cavity with the rin) situated 2 cm beneath the phantom surface. A 6 MV photon beam from an Elekta SLi plus linear accelerator, equipped with the standard multileaf collimator (MLC), was assessed. A 10 x 2 cm(2) and a 10 K 1 cm(2) field, both widthwise collimated by the MLC, were applied with their long side parallel to the cylinder axis. Central axis dose rebuild-up was studied. Radiochromic film measurements were performed in an in-house manufactured polystyrene phantom with the films oriented either along or perpendicular to the beam axis. Monte Carlo simulations were performed with BEAM and EGSnrc. Calculations were also performed using the pencil beam (PB) algorithm and the collapsed cone convolution (CCC) algorithm of Helax-TMS (MDS Nordion, Kanata. Canada) version 6.0.2 and using the CCC algorithm of Pinnacle (ADAC Laboratories, Milpitas. CA, USA) version 4.2. A very good agreement between the film measurements and the Monte Carlo simulations was found. The CCC algorithms were not able to predict the interface dose accurately when lateral electronic disequilibrium occurs, but were shown to be a considerable improvement compared to the PB algorithm. The CCC algorithms overestimate the dose in the rebuild-up region. The interface dose was overestimated by a maximum of 31% or 54%, depending on the implementation of the CCC algorithm. At a depth of I rum, the maximum dose overestimation was 14% or 24%.},
  author       = {Martens, C and Reynaert, N and De Wagter, C and Nilsson, Per and Coghe, M and Palmans, H and Theirens, H and De Neve, W},
  issn         = {0094-2405},
  keyword      = {collapsed,Monte Carlo,radiochromic film,air cavity,small fields,cone convolution calculations},
  language     = {eng},
  number       = {7},
  pages        = {1528--1535},
  publisher    = {American Association of Physicists in Medicine},
  series       = {Medical Physics},
  title        = {Underdosage of the upper-airway mucosa for small fields as used in intensity-modulated radiation therapy: A comparison between radiochromic film measurements, Monte Carlo simulations, and collapsed cone convolution calculations},
  url          = {http://dx.doi.org/10.1118/1.1487421},
  volume       = {29},
  year         = {2002},
}