PMID- 19806336
OWN - NLM
STAT- MEDLINE
DCOM- 20091013
LR  - 20211020
IS  - 1439-099X (Electronic)
IS  - 0179-7158 (Linking)
VI  - 185
IP  - 10
DP  - 2009 Oct
TI  - The influence of different IMRT techniques on the peripheral dose: a comparison 
      between sMLM-IMRT and helical tomotherapy.
PG  - 696-702
LID - 10.1007/s00066-009-2005-9 [doi]
AB  - PURPOSE: To investigate how segmented multileaf modulation-(sMLM-)based 
      intensity-modulated radiotherapy (IMRT) and dynamic helical tomotherapy (ToTh) 
      affect the peripheral dose (PD) outside the treated region. MATERIAL AND METHODS: 
      A cuboid Perspex phantom was scanned in a computed tomograph. Different 
      artificial cases were contoured consisting of OARs surrounded by cylindrically 
      shaped planning target volumes (PTVs) with different dimensions. Radiotherapy 
      plans were generated with the sMLM system Konrad (Siemens) and with the ToTh 
      planning system. The plans were optimized in such a way that the dose-volume 
      histograms showed comparable results. The sMLM plans were applied with a linac 
      Primus (Siemens OCS), the ToTh plans with the HiArt system (TomoTherapy); both 
      with 6 MV. Measurements of PDs were performed along the longitudinal axis of the 
      phantom outside the primary beam at different distances from the edge of the PTV 
      (horizontal PD) and also at different depths at a fixed distance from the 
      isocenter (vertical PD). Additional experiments to separate the scatter dose 
      caused by the phantom were performed. This was realized by removing the part of 
      the phantom lying in the primary beam, then applying the same plans like before. 
      RESULTS: All PD values were normalized to the median dose of the PTV. The PD 
      values for the different PTVs decrease with decreasing PTV size. They also 
      decrease with increasing distance from the isocenter. The horizontal values are 
      in a range of 7% for the largest PTV (diameter = 15 cm) near the primary dose 
      region to 0.2% for the smallest PTV (diameter = 5 cm) far from the primary dose 
      region. The ToTh values are higher than the sMLM values by a maximal factor of 2 
      near the primary dose region. They become more similar with increasing distance 
      from the edge of the PTV in longitudinal direction. The PD values are nearly 
      equal at a distance of 25 cm from the edge of the PTV. The vertical PDs are 
      higher for the ToTh at depths of > 1 cm but higher for sMLM close to the surface. 
      By removing the scatter cube, the horizontal PD values at middle distances are 
      reduced to one third of the PD values with scatter cube for ToTh (0.5%) and to 
      one half for sMLM (0.8%). This means that without scatter cube the PD for ToTh is 
      lower than that for sMLM. The measured PD values without scatter cube are in the 
      same dimension as published data. CONCLUSION: The increasing PDs and their trend 
      with increasing PTV size can be explained by Compton scattering of photons from 
      the irradiated volume toward the off-axis measuring points. The further increase 
      of the PD in case of ToTh relative to sMLM is not easy to explain. Different 
      presumptions are possible. The larger field length (in longitudinal direction) of 
      the ToTh plans (consisting of the "real" field length and the overlap) relative 
      to the sMLM plans could be one reason for the higher PD values. The softer energy 
      spectrum of the HiArt machine with more sideward Compton scattering contributions 
      could be another reason.
FAU - Wiezorek, Tilo
AU  - Wiezorek T
AD  - Department of Radiotherapy, University Hospital Jena, Jena, Germany. 
      tilo.wiezorek@med.uni-jena.de
FAU - Schwahofer, Andrea
AU  - Schwahofer A
FAU - Schubert, Kai
AU  - Schubert K
LA  - eng
PT  - Comparative Study
PT  - Journal Article
DEP - 20091006
PL  - Germany
TA  - Strahlenther Onkol
JT  - Strahlentherapie und Onkologie : Organ der Deutschen Rontgengesellschaft ... [et 
      al]
JID - 8603469
SB  - IM
MH  - *Body Burden
MH  - *Phantoms, Imaging
MH  - Radiometry/*methods
MH  - Radiotherapy Dosage
MH  - Radiotherapy Planning, Computer-Assisted/*methods
MH  - Radiotherapy, Computer-Assisted/*methods
MH  - Radiotherapy, Intensity-Modulated/*methods
MH  - Scattering, Radiation
MH  - *Tomography, Spiral Computed
EDAT- 2009/10/07 06:00
MHDA- 2009/10/14 06:00
CRDT- 2009/10/07 06:00
PHST- 2009/02/26 00:00 [received]
PHST- 2009/07/24 00:00 [accepted]
PHST- 2009/10/07 06:00 [entrez]
PHST- 2009/10/07 06:00 [pubmed]
PHST- 2009/10/14 06:00 [medline]
AID - 10.1007/s00066-009-2005-9 [doi]
PST - ppublish
SO  - Strahlenther Onkol. 2009 Oct;185(10):696-702. doi: 10.1007/s00066-009-2005-9. 
      Epub 2009 Oct 6.