Abstract
BackgroundModern radiotherapy offers various possibilities for image guided verification of patient positioning. Different clinically relevant IGRT (image guided radiotherapy) scenarios were considered with regard to their influence on dosimetric plan quality and normal tissue complication probability (NTCP).MethodsThis study is based on treatment plans of 50 prostate patients. We evaluate the clinically performed IGRT and simulate the influence of different daily IGRT scenarios on plan quality. Imaging doses of planar and cone-beam-CT (CBCT) images for three different energies (6 MV, 1 MV and 121 kV) were added to the treatment plans. The plan quality of the different scenarios was assessed by a visual inspection of the dose distribution and dose-volume-histogram (DVH) and a statistical analysis of DVH criteria. In addition, an assessment of the normal tissue complication probability was performed.ResultsDaily 1MV-CBCTs result in undesirable high dose regions in the target volume. The DVH shows that the scenarios with actual imaging performed, daily kV-CBCT and daily 6MV imaging (1x CBCT, 4x planar images per week) do not differ exceedingly from the original plan; especially imaging with daily kV-CBCT has little influence to the sparing of organs at risk. In contrast, daily 1MV- CBCT entails an additional dose of up to two fraction doses. Due to the additional dose amount some DVH constraints for plan acceptability could no longer be satisfied, especially for the daily 1MV-CBCT scenario. This scenario also shows increased NTCP for the rectum.ConclusionDaily kV-CBCT has negligible influence on plan quality and is commendable for the clinical routine. If no kV-modality is available, a daily IGRT scenario with one CBCT per week and planar axial images on the other days should be preferred over daily MV-CBCT.
Highlights
Modern radiotherapy offers various possibilities for image guided verification of patient positioning
The aim of this study is to assess in how far the plan quality and the modelled normal tissue complication probability (NTCP) endpoints considered in treatment planning are affected by daily image-guidance for one of the most frequent IGRT indications, prostate cancer
For the kV modality the findings fit well with the literature mentioned above
Summary
Modern radiotherapy offers various possibilities for image guided verification of patient positioning. Different clinically relevant IGRT (image guided radiotherapy) scenarios were considered with regard to their influence on dosimetric plan quality and normal tissue complication probability (NTCP). Modern radiotherapy achieves highly conformal dose distributions even for complex-shaped target volumes, combining tumour coverage and sparing of organs at risk (OAR). Imageguidance (IGRT) is a prerequisite, and it has been advocated that daily imaging should be performed. The aim of this study is to assess in how far the plan quality and the modelled NTCP endpoints considered in treatment planning are affected by daily image-guidance for one of the most frequent IGRT indications, prostate cancer. Prostate radiotherapy is one of the main candidates for daily imaging due to inter-and intra-fraction mobility of the prostate and different filling levels of the surrounding organs (bladder and rectum). The vicinity of these organs to the target volume
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