PMID- 27908151
OWN - NLM
STAT- MEDLINE
DCOM- 20170320
LR  - 20170320
IS  - 2473-4209 (Electronic)
IS  - 0094-2405 (Linking)
VI  - 43
IP  - 12
DP  - 2016 Dec
TI  - Technical Note: A direct ray-tracing method to compute integral depth dose in 
      pencil beam proton radiography with a multilayer ionization chamber.
PG  - 6405
AB  - PURPOSE: To introduce a fast ray-tracing algorithm in pencil proton radiography 
      (PR) with a multilayer ionization chamber (MLIC) for in vivo range error mapping. 
      METHODS: Pencil beam PR was obtained by delivering spots uniformly positioned in 
      a square (45 x 45 mm(2) field-of-view) of 9 x 9 spots capable of crossing the 
      phantoms (210 MeV). The exit beam was collected by a MLIC to sample the integral 
      depth dose (IDD(MLIC)). PRs of an electron-density and of a head phantom were 
      acquired by moving the couch to obtain multiple 45 x 45 mm(2) frames. To map the 
      corresponding range errors, the two-dimensional set of IDD(MLIC) was compared 
      with (i) the integral depth dose computed by the treatment planning system (TPS) 
      by both analytic (IDD(TPS)) and Monte Carlo (IDD(MC)) algorithms in a volume of 
      water simulating the MLIC at the CT, and (ii) the integral depth dose directly 
      computed by a simple ray-tracing algorithm (IDD(direct)) through the same CT 
      data. The exact spatial position of the spot pattern was numerically adjusted 
      testing different in-plane positions and selecting the one that minimized the 
      range differences between IDD(direct) and IDD(MLIC). RESULTS: Range error mapping 
      was feasible by both the TPS and the ray-tracing methods, but very sensitive to 
      even small misalignments. In homogeneous regions, the range errors computed by 
      the direct ray-tracing algorithm matched the results obtained by both the 
      analytic and the Monte Carlo algorithms. In both phantoms, lateral 
      heterogeneities were better modeled by the ray-tracing and the Monte Carlo 
      algorithms than by the analytic TPS computation. Accordingly, when the pencil 
      beam crossed lateral heterogeneities, the range errors mapped by the direct 
      algorithm matched better the Monte Carlo maps than those obtained by the analytic 
      algorithm. Finally, the simplicity of the ray-tracing algorithm allowed to 
      implement a prototype procedure for automated spatial alignment. CONCLUSIONS: The 
      ray-tracing algorithm can reliably replace the TPS method in MLIC PR for in vivo 
      range verification and it can be a key component to develop software tools for 
      spatial alignment and correction of CT calibration.
FAU - Farace, Paolo
AU  - Farace P
AD  - Proton Therapy Unit, Hospital of Trento, Trento 38100, Italy.
FAU - Righetto, Roberto
AU  - Righetto R
AD  - Proton Therapy Unit, Hospital of Trento, Trento 38100, Italy.
FAU - Deffet, Sylvain
AU  - Deffet S
AD  - Institute of Information and Communication Technologies, Universite Catholique de 
      Louvain (UCL), Louvain-La-Neuve, 1348, Belgium.
FAU - Meijers, Arturs
AU  - Meijers A
AD  - Ion Beam Applications (IBA), Louvain-la-Neuve, 1348, Belgium.
FAU - Vander Stappen, Francois
AU  - Vander Stappen F
AD  - Ion Beam Applications (IBA), Louvain-la-Neuve, 1348, Belgium.
LA  - eng
PT  - Journal Article
PL  - United States
TA  - Med Phys
JT  - Medical physics
JID - 0425746
RN  - 0 (Protons)
SB  - IM
MH  - Phantoms, Imaging
MH  - *Protons
MH  - *Radiation Dosage
MH  - *Radiography
MH  - Radiometry/*instrumentation
EDAT- 2016/12/03 06:00
MHDA- 2017/03/21 06:00
CRDT- 2016/12/03 06:00
PHST- 2016/12/03 06:00 [entrez]
PHST- 2016/12/03 06:00 [pubmed]
PHST- 2017/03/21 06:00 [medline]
AID - 10.1118/1.4966703 [doi]
PST - ppublish
SO  - Med Phys. 2016 Dec;43(12):6405. doi: 10.1118/1.4966703.