Adequacy of inhale-exhale breathhold CT based ITV margins and image-guided registration for free-breathing pancreas and liver SBRTReport as inadecuate

Adequacy of inhale-exhale breathhold CT based ITV margins and image-guided registration for free-breathing pancreas and liver SBRT - Download this document for free, or read online. Document in PDF available to download.

Radiation Oncology

, 9:11

Cancer imaging and new preclinical diagnostics in radiation oncologyClinical Radiation Oncology


PurposeTo evaluate use of breath-hold CTs and implanted fiducials for definition of the internal target volume ITV margin for upper abdominal stereotactic body radiation therapy SBRT. To study the statistics of inter- and intra-fractional motion information.

Methods and materials11 patients treated with SBRT for locally advanced pancreatic cancer LAPC or liver cancer were included in the study. Patients underwent fiducial implantation, free-breathing CT and breath-hold CTs at end inhalation-exhalation. All patients were planned and treated with SBRT using volumetric modulated arc therapy VMAT. Two margin strategies were studied: Strategy I uses PTV = ITV + 3 mm; Strategy II uses PTV = GTV + 1.5 cm. Both CBCT and kV orthogonal images were taken and analyzed for setup before patient treatments. Tumor motion statistics based on skeletal registration and on fiducial registration were analyzed by fitting to Gaussian functions.

ResultsAll 11 patients met SBRT planning dose constraints using strategy I. Average ITV margins for the 11 patients were 2 mm RL, 6 mm AP, and 6 mm SI. Skeletal registration resulted in high probability RL = 69%, AP = 4.6%, SI = 39% that part of the tumor will be outside the ITV. With the 3 mm ITV expansion Strategy 1, the probability reduced to RL 32%, AP 0.3%, SI 20% for skeletal registration; and RL 1.2%, AP 0%, SI 7% for fiducial registration. All 7 pancreatic patients and 2 liver patients failed to meet SBRT dose constraints using strategy II. The liver dose was increased by 36% for the other 2 liver patients that met the SBRT dose constraints with strategy II.

ConclusionsImage guidance matching to skeletal anatomy is inadequate for SBRT positioning in the upper abdomen and usage of fiducials is highly recommended. Even with fiducial implantation and definition of an ITV, a minimal 3 mm planning margin around the ITV is needed to accommodate intra-fractional uncertainties.

KeywordsSBRT Pancreas Liver Fiducial Radiotherapy Stereotactic body radiation therapy Electronic supplementary materialThe online version of this article doi:10.1186-1748-717X-9-11 contains supplementary material, which is available to authorized users.

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Author: Wensha Yang - Benedick A Fraass - Robert Reznik - Nicholas Nissen - Simon Lo - Laith H Jamil - Kapil Gupta - Howard Sand


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