Case solution and plan evaluation in intensity modulation radiotherapy for simple and complex volumes
Muşat, E.
Revista Medico-Chirurgicala a Societatii de Medici Si Naturalisti Din Iasi 111(1): 98-105
2007
ISSN/ISBN: 0048-7848 PMID: 17595852 Document Number: 606855
The objective of the study was to evaluate the feasibility of the high dose IMRT pacification in small and medium volumes, simple and complexes. The European Society of Therapeutic Radiation Oncology yearly organizes the course of IMRT. We detail the clinical case solution plans realised for two cases proposed in 2003: locally relapsed lung cancer (first case) and ethmoidal cancer (second case). The prescribed doses were 80 Gy in the lung cancer and 70 Gy in the ethmoid cancer. To the choice of the number and beam direction is added the low tolerance of surrounding normal tissue, the respiratory movement in the lung case and the high tissue heterogeneity, which modify the dose distribution in these regions. For the plans evaluation we used the dose homogeneity (U) in treated volume (PTV), the cover factor (FC), the normal tissue spare factor (FP) and the conformity index (CI). 1 is considered optimal value for FC, FP and CI. In the first case, the plan with five beams symmetric displayed improved the homogeneity in the PTV (of 0.3%) and the FP (of 24%) and thus, slightly improved CI (0.7 vs. 0.6) when compared with the "beam eye view technique". The last plan decreased the dose at the oesophagus, lung and cardiac volume but the general tissue spare (FP) significantly decreased. In the second case we used five symmetric displayed beams as standard plan. Adding a no-coplanar field oblique anterior and using a smaller PTV contribute to slightly improve the conformity index with the same factor (0.70, 0.71 vs. 0,67 respectively). Reduced PTV, symmetric displayed coplanar beams and a limited number of non-coplanar beams can contribute to improve the IMRT plan quality in small to medium PTV's simple or complex.