Authors | Institution | |
ISMAIL ZERGOUG | Radiotherapy Department EHSO EMIR ABDELKADER ORAN ALGERIA |
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The evaluation of AAA and MGS dose calculation algorithms in the treatment of nasopharyngeal cancer |
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.
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.
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 |
– 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.
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