The heterogeneous CTV-PTV margins should be given for different parts of tumors during tomotherapy.

Ying Tong,Tonghai Liu,Yong Yin,Guanzhong Gong,Pinjing Cheng,Jie Lu,Jinhu Chen

doi:10.18632/oncotarget.21631

Abstract

ObjectiveThe purpose of this study was to evaluate CTV-PTV margins of tumors for tomotherapy.MethodsSetup errors were analyzed for 151 patients receiving helical tomotherapy treatment. 53 patients had head and neck tumors, 45 had thoracic tumors, 20 had abdominal tumors, and 33 had pelvic tumors. The setup errors were calculated in six directions, i.e. +X (left), -X (right), +Y (head), -Y (foot), +Z (ventral), and -Z (dorsal), after Megavoltage CT (MVCT) images were registered to simulation CT images. And then the CTV-PTV margins were calculated.ResultsThe setup errors along the +Z direction were significantly higher than that along the –Z direction (p<0.05). The CTV-PTV margins on +X, -X, +Y, -Y, +Z, and -Z directions were asymmetric for all tumors, and the heterogeneity were more remarkable on the +Z and –Z directions. The CTV-PTV margins on +Z and –Z were 4.1 mm, 4.6 mm, 5.2 mm, and 8.4 mm; and 3.9 mm, 7.7 mm, 3.3 mm, and 7.7 mm for head and neck tumors, thoracic tumors, abdominal tumors, and pelvic tumors, respectively.ConclusionsThe CTV-PTV margins for patients with different types of tumors were heterogeneous during tomotherapy. The individual margins of six directions should be given for those patients who accept tomotherapy.

Highlights

The clinical target volume (CTV)-planning target volume (PTV) margins on +X, -X, +Y, -Y, +Z, and -Z directions were asymmetric for all tumors, and the heterogeneity were more remarkable on the +Z and –Z directions
The CTV-PTV margins for patients with different types of tumors were heterogeneous during tomotherapy
Tomotherapy is a common practice for optimal dose distribution in precise radiotherapy of tumors, which has the functionalities of intensity modulated radiation therapy (IMRT), image guide radiation therapy (IGRT), and adaptive radiation therapy (ART) [1]

Summary

Introduction

Tomotherapy is a common practice for optimal dose distribution in precise radiotherapy of tumors, which has the functionalities of intensity modulated radiation therapy (IMRT), image guide radiation therapy (IGRT), and adaptive radiation therapy (ART) [1]. Since tomotherapy has a preferable intensity modulation ability compared to traditional IMRT techniques, the dose gradients can be sharper between tumors and adjacent normal tissue. Tomotherapy with its high-dose gradients has advantages in treating complex-shaped tumors [3]. A previous study showed that helical tomotherapy can reduce the dose to the rectum during prostatic tumors treatment [4]. Another study indicated that the helical tomotherapy treatment could achieve a lower dose to the adjacent tissues compared with IMRT in breast cancers, and the V95 could increase by 21% [5]. Tomotherapy had become the preferred radiation therapy approach for craniospinal irradiation (CSI), as previous studies have demonstrated that tomotherapy can achieve high conformity, excellent dose homogeneity, and healthy tissues paring in CSI [6, 7]

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Conclusion