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Authors Institution
ISMAIL ZERGOUG Radiotherapy Department
EHSO EMIR ABDELKADER ORAN
ALGERIA
Theme
Radiation Oncology
The evaluation of AAA and MGS dose calculation algorithms in the treatment of nasopharyngeal cancer
Background

The ultimte goal of radiotherapy is to deliver a prescribed dose to the tumor while minimizing dose to critical structures. A good calculation algorithm that take into account accurately all the physical process involved in the beam particle media interaction. It should be also fast enough to be used in clinic.    

 

 

 

 

 

 

 

The aim of this study is to investigate and compare the accuracy of AAA and MGS dose calculation algorithms in the case of 3DCRT of nasopharyngal cancer.

Summary of Work

The accuracy of an inhomogeneity correction for AAA and MGS algorithms was evaluated by comparing with MC calculation. 30 patients were planned in 3DCRT with AAA (Eclipse v11) and MGS (XiO v4.4) algorithms. The treatment was delivered on SIEMENS Primus Linac 82 leafs with 1cm width and SIEMENS Somatom Sensation as a CT simulator. Identical image/structure sets were transferred from XiO to Eclipse TPS to ensure consistency.

Treatment planning:
– Five fields with single isocenter at hyoid bone: 2Laterals, 2 Posteriors obliques, 1 Posterior
– 50Gy 2Gy/fraction for PTV 50 =CTV t +CTV n +3mm
– 2 Lateral fields for the boost (PTV 66 =CTV t +3mm) to reach 66Gy 2Gy/fraction

Dosimetric analysis:
Plans were compared by noting the dosimetric parameters for the two algorithms :
Conformity index (CI), homogeneity index (HI), uniformity index (UI), maximum and mean dose to OARs.

Summary of Results

 

 

 

 

 

 

 

 

 

 

The dose in air region decreases in order of: MC<MGS<AAA.

MGS plans show better coverage than AAA plans; Much steeper PTV DVH for MGS than AAA that indicate greater dose homogeneity inside the PTV.

 

 

 

 

 

 

 

 

Higher HI and UI values for MGS than AAA. It's also represented by a lower standard deviation.

  UI HI CI
MGS 1.19±0.04 0.28±0.05 0.8± 0.08
AAA 1.23±0.07 0.33±0.09 0.82±0.07
p-value 0.01 0.05 0.007

A lower dose are received by OARs with MGS algorithm.

OARs average values Mean/Max Dose (cGy) Mean/Max Dose (cGy)
PTV66 MGS AAA
BrainStem 5125 5310
SpinalCord 4032 4080
Right lens 268 479
Left lens 237 380
Left optical nerf 850 2785
Right optical nerf 1582 1827
Left eye 262 (mean) 412 (mean)
Right eye 374 (mean) 525 (mean)
Chiasma 796 2086
Pituitary 2351 3518


 

Conclusion

– MGS was relatively more accurate than AAA in the treatment of nasopharyngal cancer.
– It demonstarted relatively lower dose deviation and a better coverage of PTV than that of AAA.
– The OARs have a little better avoidance with a general lower DVH with MGS than AAA algorithm .
– It will be interessted to make a comparaison in term of biological parameters; EUD, TCP/NTCP.

References

1- Asghar et al. IJMP, Vol. 12, No. 3, Summer 2015, 167-177

2- Doaa et al. JMEST, Vol. 2 Issue 4, April - 2015, 678-682

3- Lu L. Int J Cancer Ther Oncol, 1(2):01025, 2013

4- Vincent W.C et al. Medical Dosimetry 38 (2013) 209–214

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Background
Summary of Work
Summary of Results
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References
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