PMID- 20527544
OWN - NLM
STAT- MEDLINE
DCOM- 20100628
LR  - 20170214
IS  - 0094-2405 (Print)
IS  - 0094-2405 (Linking)
VI  - 37
IP  - 5
DP  - 2010 May
TI  - Automated beam model optimization.
PG  - 2110-20
AB  - PURPOSE: The beam model in a three dimensional treatment planning system (TPS) 
      defines virtually the mechanical and dosimetric characteristics of a treatment 
      unit. The manual optimization of a beam model during commissioning can be a time 
      consuming task due to its iterative nature. Furthermore, the quality of the beam 
      model commissioning depends on the user's ability to manage multiple parameters 
      and assess their impact on the agreement between measured and calculated dose. 
      The objective of this work is to develop and validate the performance of an 
      automated beam model optimization system (ABMOS) based on intensity modulated 
      radiotherapy (IMRT) beam measurements to improve beam model accuracy while 
      streamlining the commissioning process. METHODS: The ABMOS was developed to 
      adjust selected TPS beam model parameters iteratively to maximize the agreement 
      between measured and calculated 2D dose maps obtained for an IMRT beam pattern. A 
      2D diode array with high spatial resolution detectors was used to sample the 
      entire IMRT beam pattern in a single dose measurement. The use of an IMRT beam 
      pattern with large number of monitor units was selected to highlight the 
      difference between planned and delivered dose and improve the signal to noise 
      ratio in the low dose regions. ABMOS was applied to the optimization of a beam 
      model for an Elekta Synergy S treatment unit. The optimized beam model was 
      validated for two anatomical sites (25 paraspinal and 25 prostate cases) using 
      two independent patient-specific IMRT quality control (QC) methods based on ion 
      chamber and 2D diode array measurements, respectively. The conventional approach 
      of comparing calculated and measured beam profiles and percent-depth dose curves 
      was also used to assess improvement in beam model after ABMOS optimization. 
      Elements of statistical process control were applied to the process of 
      patient-specific QC performed with the ion chamber and the 2D array to complement 
      the model comparison. RESULTS: After beam model optimization with ABMOS, 
      improvement in planned to delivered dose agreement was demonstrated with both 
      patient-specific IMRT QC methods and the calculated to measured profile 
      comparison. In terms of ion chamber measurements, the largest improvement was 
      observed for the paraspinal cases with the mean measured to calculated dose 
      difference at the low dose points decreasing from - 13.8% to 2.0% with the 
      optimized beam model. The 2D diode array patient-specific QC also demonstrated 
      clearly the improvement in beam model for both paraspinal and prostate cases 
      with, on average, more than 96% of the diodes satisfying tolerances of 3% of dose 
      difference or 2 mm of distance to agreement after ABMOS optimization. The 
      capability index (C(pk)) for both patient-specific QC methods also increased with 
      the optimized beam model. CONCLUSIONS: In this work, ABMOS was developed to use 
      2D diode array measurements of an IMRT beam pattern for the automated 
      multivariable optimization of a TPS beam model. Based on the observed 
      improvements in patient-specific QC results for 25 paraspinal and 25 prostate 
      plans, optimization of the remaining clinical beam models using ABMOS is now 
      ongoing in the institution.
FAU - Letourneau, Daniel
AU  - Letourneau D
AD  - Radiation Medicine Program, Princess Margaret Hospital, Toronto, Ontario, Canada. 
      daniel.letourneau@rmp.uh.on.ca
FAU - Sharpe, Michael B
AU  - Sharpe MB
FAU - Owrangi, Amir
AU  - Owrangi A
FAU - Jaffray, David A
AU  - Jaffray DA
LA  - eng
PT  - Journal Article
PL  - United States
TA  - Med Phys
JT  - Medical physics
JID - 0425746
SB  - IM
MH  - Automation
MH  - Humans
MH  - Radiometry
MH  - Radiotherapy Planning, Computer-Assisted/*methods
MH  - Radiotherapy, Intensity-Modulated
EDAT- 2010/06/10 06:00
MHDA- 2010/06/29 06:00
CRDT- 2010/06/10 06:00
PHST- 2010/06/10 06:00 [entrez]
PHST- 2010/06/10 06:00 [pubmed]
PHST- 2010/06/29 06:00 [medline]
AID - 10.1118/1.3373519 [doi]
PST - ppublish
SO  - Med Phys. 2010 May;37(5):2110-20. doi: 10.1118/1.3373519.