PMID- 10760444
OWN - NLM
STAT- MEDLINE
DCOM- 20000731
LR  - 20190708
IS  - 0360-3016 (Print)
IS  - 0360-3016 (Linking)
VI  - 44
IP  - 2
DP  - 1999 May 1
TI  - Inhomogeneous target-dose distributions: a dimension more for optimization?
PG  - 461-8
AB  - PURPOSE: To evaluate if the use of inhomogeneous target-dose distributions, 
      obtained by 3D conformal radiotherapy plans with or without beam intensity 
      modulation, offers the possibility to decrease indices of toxicity to normal 
      tissues and/or increase indices of tumor control stage III non-small cell lung 
      cancer (NSCLC). METHODS AND MATERIALS: Ten patients with stage III NSCLC were 
      planned using a conventional 3D technique and a technique involving noncoplanar 
      beam intensity modulation (BIM). Two planning target volumes (PTVs) were defined: 
      PTV1 included macroscopic tumor volume and PTV2 included macroscopic and 
      microscopic tumor volume. Virtual simulation defined the beam shapes and 
      incidences as well as the wedge orientations (3D) and segment outlines (BIM). 
      Weights of wedged beams, unwedged beams, and segments were determined by 
      optimization using an objective function with a biological and a physical 
      component. The biological component included tumor control probability (TCP) for 
      PTV1 (TCP1), PTV2 (TCP2), and normal tissue complication probability (NTCP) for 
      lung, spinal cord, and heart. The physical component included the maximum and 
      minimum dose as well as the standard deviation of the dose at PTV1. The most 
      inhomogeneous target-dose distributions were obtained by using only the 
      biological component of the objective function (biological optimization). By 
      enabling the physical component in addition to the biological component, PTV1 
      inhomogeneity was reduced (biophysical optimization). As indices for toxicity to 
      normal tissues, NTCP-values as well as maximum doses or dose levels to relevant 
      fractions of the organ's volume were used. As indices for tumor control, 
      TCP-values as well as minimum doses to the PTVs were used. RESULTS: When 
      optimization was performed with the biophysical as compared to the biological 
      objective function, the PTV1 inhomogeneity decreased from 13 (8-23)% to 4 (2-9)% 
      for the 3D-(p = 0.00009) and from 44 (33-56)% to 20 (9-34)% for the BIM plans (p 
      < 0. 00001). Minimum PTV1 doses (expressed as the lowest voxel-dose) were similar 
      for both objective functions. The mean and maximum target doses were 
      significantly higher with biological optimization for 3D as well as for BIM (all 
      p values < 0.001). Tumor control probability (estimated by TCP1 x TCP2) was 4.7% 
      (3D) and 6.2% (BIM) higher for biological optimization (p = 0.01 and p = 0.00002 
      respectively). NTCP(lung) as well as the percentage of lung volume exceeding 20 
      Gy was higher with the use of the biophysical objective function. NTCP(heart) was 
      also higher with the use of the biophysical objective function. The percentage of 
      heart volume exceeding 40 Gy tended to be higher but the difference was not 
      significant. For spinal cord, the maximum dose as well as NTCP(cord) were similar 
      for 3D plans (D(max): p = 0.04; NTCP: p = 0.2) but were significantly lower for 
      BIM (D(max): p = 0.002; NTCP: p = 0.008) if the biophysical objective function 
      was used. CONCLUSIONS: When using conventional 3D techniques, inhomogeneous dose 
      distributions offer the potential to further increase the probability of 
      uncomplicated local control. When using techniques as BIM that would lead to 
      large escalation of the median and maximum target doses, it seems indicated to 
      limit target-dose inhomogeneity to avoid dose levels that are so high that the 
      safety becomes questionable.
FAU - De Gersem, W R
AU  - De Gersem WR
AD  - Department of Radiotherapy and Nuclear Medicine, University Hospital Gent, 
      Belgium.
FAU - Derycke, S
AU  - Derycke S
FAU - Colle, C O
AU  - Colle CO
FAU - De Wagter, C
AU  - De Wagter C
FAU - De Neve, W J
AU  - De Neve WJ
LA  - eng
PT  - Journal Article
PL  - United States
TA  - Int J Radiat Oncol Biol Phys
JT  - International journal of radiation oncology, biology, physics
JID - 7603616
SB  - IM
CIN - Int J Radiat Oncol Biol Phys. 2001 Apr 1;49(5):1518-20. PMID: 11293435
MH  - Carcinoma, Non-Small-Cell Lung/pathology/*radiotherapy
MH  - *Computer Simulation
MH  - Esophagus
MH  - Heart
MH  - Humans
MH  - Lung
MH  - Lung Neoplasms/pathology/*radiotherapy
MH  - Physical Phenomena
MH  - Physics
MH  - *Radiation Protection
MH  - *Radiotherapy Planning, Computer-Assisted
MH  - Radiotherapy, Conformal/*methods
MH  - Spinal Cord
EDAT- 2000/04/13 09:00
MHDA- 2000/08/06 11:00
CRDT- 2000/04/13 09:00
PHST- 2000/04/13 09:00 [pubmed]
PHST- 2000/08/06 11:00 [medline]
PHST- 2000/04/13 09:00 [entrez]
AID - S0360-3016(98)00464-7 [pii]
AID - 10.1016/s0360-3016(98)00464-7 [doi]
PST - ppublish
SO  - Int J Radiat Oncol Biol Phys. 1999 May 1;44(2):461-8. doi: 
      10.1016/s0360-3016(98)00464-7.