PTV margin definition in hypofractionated IGRT of localized prostate cancer using cone beam CT and orthogonal image pairs with fiducial markers

Radiation Oncology

Daniel R Zwahlen²  Gabriela Studer¹  Yousef Najafi¹  Christoph Glanzmann¹  Alessandra Tini¹  Stephan Kloeck¹  Christian Bolesch¹  Peter Dimmerling¹  Stephanie Lang¹  Christoph Oehler² 

[1] Department of Radiation Oncology, University Hospital Zurich, Zurich, Switzerland;Department of Radiation Oncology, Hospital Graubuenden, Chur, Switzerland

关键词: Hypofractionation;    PTV margin definition;    Cone beam CT;    VMAT;    IGRT;    Radiation therapy;    Prostate cancer;   

Others  :  1228544
DOI  :  10.1186/s13014-014-0229-z

 received in 2014-01-28, accepted in 2014-10-03,  发布年份 2014

【 摘 要 】

Purpose

To evaluate PTV margins for hypofractionated IGRT of prostate comparing kV/kV imaging or CBCT.

Patients and methods

Between 2009 and 2012, 20 patients with low- (LR), intermediate- (IR) and high-risk (HR) prostate cancer were treated with VMAT in supine position with fiducial markers (FM), endorectal balloon (ERB) and full bladder. CBCT¿s and kV/kV imaging were performed before and additional CBCT¿s after treatment assessing intra-fraction motion. CTV_P for 5 patients with LR and CTV_PSV for 5 patients with IR/HR prostate cancer were contoured independently by 3 radiation oncologists using MRI. The van Hark formula (PTV margin =2.5? +0.7?) was applied to calculate PTV margins of prostate/seminal vesicles (P/PSV) using CBCT or FM.

Results

172 and 52 CBCTs before and after RT and 507 kV/kV images before RT were analysed. Differences between FM in CBCT or in planar kV image pairs were below 1 mm. Accounting for both random and systematic uncertainties anisotropic PTV margins were 5-8 mm for P (LR) and 6-11 mm for PSV (IR/HR). Random uncertainties like intra-fraction and inter-fraction (setup) uncertainties were of similar magnitude (0.9-1.4 mm). Largest uncertainty was introduced by CTV delineation (LR: 1-2 mm, IR/HR: 1.6-3.5 mm). Patient positioning using bone matching or ERB-matching resulted in larger PTV margins.

Conclusions

For IGRT CBCT or kV/kV-image pairs with FM are interchangeable in respect of accuracy. Especially for hypofractionated RT, PTV margins can be kept in the range of 5 mm or below if stringent daily IGRT, ideally including prostate tracking, is applied. MR-based CTV delineation optimization is recommended.

【 授权许可】

   
2014 Oehler et al.; licensee BioMed Central Ltd.

【 图 表 】

Figure 1.

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