Image guidance in clinical practice – Influence of positioning inaccuracy on the dose distribution for prostate cancer. (February 2018)

• Record Type: Journal Article
• Authors: Bell, Katharina; Dzierma, Yvonne; Morlo, Melanie; Nüsken, Frank; Licht, Norbert; Rübe, Christian
• Is Part Of: Physica medica. Volume 46(2018)
• Page Start: 81
• Page End: 88
• Publication Date: 2018-02
• Subjects: Prostate -- IGRT -- Positioning accuracy -- NTCP modelling; Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2018.01.015
• Languages: English
• ISSNs: 1120-1797

Abstract

Highlights: PTV coverage suffers markedly by positioning inaccuracy. Especially individual patients show large deviations from the original plan. For this collective organs at risk generally remain well spared. Abstract: Background: In order to consider potential positioning errors there are different recipes for safety-margins for CTV-to-PTV expansion. The aim of this study is to simulate the effect of positioning inaccuracy with clinically realistic patient treatment plans. Methods: For a collective of 40 prostate patients, the isocenter was shifted back appropriately to the applied table shifts after positioning verification, simulating that no positioning correction had been performed and the treatment plans were recalculated. All the treatment fractions with the appropriate isocenter-shifts were added to yield a new plan considering two scenarios: 1) Extreme scenario: summation of only shifted plans. 2) Realistic scenario: consideration of the original treatment plan for the fractions with verification imaging. Afterwards all plans were analysed and compared with each other regarding target coverage, sparing of organs at risk (OAR) and normal tissue complication probability (NTCP). Results: Dose distributions and especially DVH show a deterioration of the target-coverage caused by the positioning inaccuracy. Deviations in dose at a single point can reach values of over 10 Gy. In single cases minimum plan agreement only achieved 66% pass within 3% local dose for the realistic case. Organs at risk and NTCP analysis result in a slightly better sparing of the rectum. Measures of quality like homogeneity and conformity differ just minimally regarding the different scenarios. Conclusion: PTV-coverage suffers markedly by the positioning uncertainties, the shifted plans are in large parts clinically not acceptable. Surprisingly sparing of the OAR is not negatively affected by potential positioning errors for this prostate collective.