PMID- 19673187
OWN - NLM
STAT- MEDLINE
DCOM- 20090910
LR  - 20170214
IS  - 0094-2405 (Print)
IS  - 0094-2405 (Linking)
VI  - 36
IP  - 7
DP  - 2009 Jul
TI  - Dosimetric effects of rotational output variation and x-ray target degradation on 
      helical tomotherapy plans.
PG  - 2881-8
AB  - In this study, two potential sources of IMRT delivery error have been identified 
      for helical tomotherapy delivery using the HiART system (TomoTherapy, Inc., 
      Madison, WI): Rotational output variation and target degradation. The HiArt 
      system is known to have output variation, typically about +/- 2%, due to the 
      absence of a dose servo system. On the HiArt system, x-ray target replacement is 
      required approximately every 10-12 months due to target degradation. Near the end 
      of target life, the target thins and causes a decrease in the beam energy and a 
      softening of the beam profile at the lateral edges of the beam. The purpose of 
      this study is to evaluate the dosimetric effects of rotational output variation 
      and target degradation by modeling their effects and incorporating them into 
      recalculated treatment plans for three clinical scenarios: Head and neck, partial 
      breast, and prostate. Models were created to emulate both potential sources of 
      error. For output variation, a model was created using a sine function to match 
      the amplitude (+/- 2%), frequency, and phase of the measured rotational output 
      variation data. A second model with a hypothetical variation of +/- 7% was also 
      created to represent the largest variation that could exist without violating the 
      allowable dose window in the delivery system. A measured beam profile near the 
      end of target life was used to create a modified beam profile model for the 
      target degradation. These models were then incorporated into the treatment plan 
      by modifying the leaf opening times in the delivery sinogram. A new beam model 
      was also created to mimic the change in beam energy seen near the end of target 
      life. The plans were then calculated using a research version of the PLANNED 
      ADAPTIVE treatment planning software from TomoTherapy, Inc. Three plans were 
      evaluated in this study: Head and neck, partial breast, and prostate. The D50 of 
      organs at risk, the D95 for planning target volumes (PTVs), and the local dose 
      difference were used to evaluate the changes in the modified treatment plans. 
      Dosimetric effects from rotational variation were found to be low (less than 1%) 
      for a typical variation of +/- 2%. Even using a variation of +/- 7%, DVH values 
      and dose distributions were altered by less than 2% for all scenarios. The 
      dosimetric effects of target degradation were found to be slightly more 
      significant. For a model using data taken just before target failure, dosimetric 
      differences of 2%-4% were observed in the recalculated plans when compared to the 
      original plans. The largest effects (up to 4.5%) were observed for PTVs that were 
      located at deeper depths as seen in the prostate plan. Overall, the recalculated 
      plans show that the dosimetric effects of rotational variation and target 
      degradation are on the order of 1%-4% for helical tomotherapy on the HiART system 
      and do not pose a risk for significant deviations from the original treatment 
      plan.
FAU - Staton, Robert J
AU  - Staton RJ
AD  - Department of Radiation Physics, M. D. Anderson Cancer Center Orlando, Orlando, 
      Florida 32806, USA. robert.staton@gmail.com
FAU - Langen, Katja M
AU  - Langen KM
FAU - Kupelian, Patrick A
AU  - Kupelian PA
FAU - Meeks, Sanford L
AU  - Meeks SL
LA  - eng
PT  - Journal Article
PL  - United States
TA  - Med Phys
JT  - Medical physics
JID - 0425746
RN  - 059QF0KO0R (Water)
SB  - IM
MH  - Breast Neoplasms/radiotherapy
MH  - Female
MH  - Head and Neck Neoplasms/radiotherapy
MH  - Humans
MH  - Male
MH  - Models, Theoretical
MH  - Phantoms, Imaging
MH  - Prostatic Neoplasms/radiotherapy
MH  - Radiotherapy Dosage
MH  - Radiotherapy, Intensity-Modulated/instrumentation/*methods
MH  - Rectum/radiation effects
MH  - Rotation
MH  - Time Factors
MH  - Urinary Bladder/radiation effects
MH  - Water/chemistry
MH  - X-Rays
EDAT- 2009/08/14 09:00
MHDA- 2009/09/11 06:00
CRDT- 2009/08/14 09:00
PHST- 2009/08/14 09:00 [entrez]
PHST- 2009/08/14 09:00 [pubmed]
PHST- 2009/09/11 06:00 [medline]
AID - 10.1118/1.3134262 [doi]
PST - ppublish
SO  - Med Phys. 2009 Jul;36(7):2881-8. doi: 10.1118/1.3134262.