Image guidance in clinical practice - Influence of positioning inaccuracy on the dose distribution for prostate cancer.

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. 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: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). 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. 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.

Bell K ，Dzierma Y ，Morlo M ，Nüsken F ，Licht N ，Rübe C ... -  《-》

Image guidance and positioning accuracy in clinical practice: influence of positioning errors and imaging dose on the real dose distribution for head and neck cancer treatment.

Bell K ，Licht N ，Rübe C ，Dzierma Y ... -  《Radiation Oncology》

Influence of daily imaging on plan quality and normal tissue toxicity for prostate cancer radiotherapy.

Bell K ，Heitfeld M ，Licht N ，Rübe C ，Dzierma Y ... -  《Radiation Oncology》

Dosimetric and radiobiological consequences of computed tomography-guided adaptive strategies for intensity modulated radiation therapy of the prostate.

To examine a range of scenarios for image-guided adaptive radiation therapy of prostate cancer, including different schedules for megavoltage CT imaging, patient repositioning, and dose replanning. We simulated multifraction dose distributions with deformable registration using 35 sets of megavoltage CT scans of 13 patients. We computed cumulative dose-volume histograms, from which tumor control probabilities and normal tissue complication probabilities (NTCPs) for rectum were calculated. Five-field intensity modulated radiation therapy (IMRT) with 18-MV x-rays was planned to achieve an isocentric dose of 76 Gy to the clinical target volume (CTV). The differences between D95, tumor control probability, V70Gy, and NTCP for rectum, for accumulated versus planned dose distributions, were compared for different target volume sizes, margins, and adaptive strategies. The CTV D95 for IMRT treatment plans, averaged over 13 patients, was 75.2 Gy. Using the largest CTV margins (10/7 mm), the D95 values accumulated over 35 fractions were within 2% of the planned value, regardless of the adaptive strategy used. For tighter margins (5 mm), the average D95 values dropped to approximately 73.0 Gy even with frequent repositioning, and daily replanning was necessary to correct this deficit. When personalized margins were applied to an adaptive CTV derived from the first 6 treatment fractions using the STAPLE (Simultaneous Truth and Performance Level Estimation) algorithm, target coverage could be maintained using a single replan 1 week into therapy. For all approaches, normal tissue parameters (rectum V(70Gy) and NTCP) remained within acceptable limits. The frequency of adaptive interventions depends on the size of the CTV combined with target margins used during IMRT optimization. The application of adaptive target margins (<5 mm) to an adaptive CTV determined 1 week into therapy minimizes the need for subsequent dose replanning.

Battista JJ ，Johnson C ，Turnbull D ，Kempe J ，Bzdusek K ，Van Dyk J ，Bauman G ... -  《-》

Image-guided IMRT for localized prostate cancer with daily repositioning: inferring the difference between planned dose and delivered dose distribution.

To investigate the dosimetric impact of daily on-line repositioning during a full course of IMRT for prostate cancer. Twenty patients were treated with image-guided IMRT. Each pre-treatment plan (Plan A) was compared with a post-treatment plan sum (Plan B) based on couch shifts measured. The delivered dose to the prostate without a daily repositioning was inferred by considering each daily couch shift during the whole course of image-guided IMRT (i.e., plan B). Dose metrics were compared for prostate CTV (P-CTV) and PTV (P-PTV) and for organs at risk. Ten patients were treated with a 5 mm margin and 10 patients with a 10 mm margin. For plan A vs. plan B: the average D95, D98, D50, D mean and EUD were: 76.4 Gy vs. 73.9 Gy (p = 0.0007), 75.4 Gy vs. 72.3 Gy (p = 0.001), 78.9 Gy vs. 78.4 Gy (p = 0.014), 78.7 Gy vs. 77.8 Gy (p = 0.003) and 78.1 Gy vs. 75.9 Gy (p = 0.002), respectively for P-CTV, and 73.2 Gy vs. 69.3 Gy (p = 0.0006), 70.7 Gy vs. 66.0 Gy (p = 0.0008), 78.3 Gy vs. 77.5 Gy (p = 0.001), 77.8 Gy vs. 76.4 Gy (p = 0.0002) and 74.4 Gy vs. 69.2 Gy (p = 0.003), respectively for P-PTV. Margin comparison showed no differences in dose metrics between the two plans except for D98 of the rectum in plan B which was significantly higher with a 10 mm margin. The absence of daily image-guided IMRT resulted in a significantly less uniform and less homogeneous dose distribution to the prostate. A reduction in PTV margin showed neither a lower target coverage nor a better spare of OAR with and without daily image-guided IMRT.

Arnaud A ，Maingon P ，Gauthier M ，Naudy S ，Dumas JL ，Martin E ，Peignaux-Casasnovas K ，Truc G ，Bonnetain F ，Crehange G ... -  《-》