Impact of the type of imaging modality on target volumes delineation and dose distribution in pharyngo-laryngeal squamous cell carcinoma: comparison between pre- and per-treatment studies

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• 作者：Xavier Geets ; Jean-Francois Daisne ; Milan Tomsej ; Thierry Duprez ; Max Lonneux and Vincent Gré ; goire
• 刊名：Radiotherapy and Oncology
• 出版年：2006
• 出版时间：March 2006
• 年：2006
• 卷：78
• 期：3
• 页码：291-297
• 全文大小：130 K

文摘

Background and purpose

It has been shown that the use of pre-treatment FDG-PET impacted on the GTV delineation of pharyngo-laryngeal tumors. The goals of this study were to evaluate (1) the impact of FDG-PET GTV on dose distribution, and (2) the impact of per-treatment re-imaging on target volume delineation and dose distribution.

Materials and methods

Eighteen patients with squamous cell carcinoma of the oropharynx or larynx/hypopharynx were treated with curative intent by forward planning IMRT. Prior to treatment and on average after a dose of 46 Gy, all patients underwent contrast-enhanced CT, MRI and FDG-PET. After coregistration, GTVs were delineated manually on CT and MRI and automatically on FDG-PET. From these volumes, CTVs and PTVs were derived using consistent guidelines. Planning was performed using conformal radiotherapy.

Results

GTVs, CTVs and PTVs based on pre-treatment FDG-PET were significantly smaller than those based on pre-treatment CT. Such difference in target volumes (TV) translated into a significant reduction in the irradiated volumes (reduction of 13 and 18 % of the V₅₀ and V₉₅, respectively), D_mean to ipsilateral parotids (30.7 and 38.6 % for FDG-PET and CT based plans, respectively) and to controlateral parotids (11.2 and 14.4 % for FDG-PET and CT based plans, respectively). TVs based on per-treatment CT or MRI were also significantly smaller compared to those delineated from pre-treatment CT. Volumes delineated with MRI were significantly smaller than those delineated with CT. Due to radiotherapy-induced peri-tumoral inflammation, automatic delineation of FDG-PET GTV could not be performed. Such reductions in TVs translated into a reduction of the irradiated volumes compared to pre-treatment CT planning (reduction for V₅₀ of 19 and 32 % , and for V₉₅ of 22 and 40 % , for CT and MRI, respectively); D_mean to the ipsilateral parotids were also reduced (ipsilateral parotid D_mean of 20.4 % for CT and of 20.1 % for MRI compared to 24.7 % for pre-treatment CT).

Conclusions

: The use of pre-treatment FDG-PET and per-treatment CT or MRI significantly impacts on the delineation of TVs in pharyngo-laryngeal SCC, translating into more normal tissue sparing after conformal radiotherapy planning.