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Open Access Research

IGRT versus non-IGRT for postoperative head-and-neck IMRT patients: dosimetric consequences arising from a PTV margin reduction

Michael Schwarz1, Kristina Giske1, Armin Stoll1, Simeon Nill1, Peter E Huber23, Jürgen Debus3, Rolf Bendl14 and Eva M Stoiber13*

Author Affiliations

1 Department of Medical Physics in Radiation Oncology, DKFZ INF 280, Heidelberg, Germany

2 Department of Radiation Oncology, DKFZ INF 280, Heidelberg, Germany

3 Department of Radiation Oncology, INF 400, University Hospital Heidelberg, Heidelberg, Germany

4 Heilbronn University, Medical Informatics, Max-Planck-Str. 39, Heilbronn, Germany

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Radiation Oncology 2012, 7:133  doi:10.1186/1748-717X-7-133

Published: 8 August 2012

Abstract

Background

To evaluate the impact of image-guided radiation therapy (IGRT) versus non-image-guided radiation therapy (non-IGRT) on the dose to the clinical target volume (CTV) and the cervical spinal cord during fractionated intensity-modulated radiation therapy (IMRT) for head-and-neck cancer (HNC) patients.

Material and Methods

For detailed investigation, 4 exemplary patients with daily control-CT scans (total 118 CT scans) were analyzed. For the IGRT approach a target point correction (TPC) derived from a rigid registration focused to the high-dose region was used. In the non-IGRT setting, instead of a TPC, an additional cohort-based safety margin was applied. The dose distributions of the CTV and spinal cord were calculated on each control-CT and the resulting dose volume histograms (DVHs) were compared with the planned ones fraction by fraction. The D50 and D98 values for the CTV and the D5 values of the spinal cord were additionally reported.

Results

In general, the D50 and D98 histograms show no remarkable difference between both strategies. Yet, our detailed analysis also reveals differences in individual dose coverage worth inspection. Using IGRT, the D5 histograms show that the spinal cord less frequently receives a higher dose than planned compared to the non-IGRT setting. This effect is even more pronounced when looking at the curve progressions of the respective DVHs.

Conclusions

Both approaches are equally effective in maintaining CTV coverage. However, IGRT is beneficial in spinal cord sparing. The use of an additional margin in the non-IGRT approach frequently results in a higher dose to the spinal cord than originally planned. This implies that a margin reduction combined with an IGRT correction helps to maintain spinal cord dose sparing best as possible. Yet, a detailed analysis of the dosimetric consequences dependent on the used strategy is required, to detect single fractions with unacceptable dosimetric deviations.

Keywords:
Head-and-neck cancer; Adaptive radiotherapy; Image-guided radiation therapy; Correction strategies; Dose re-calculation