What is an acceptably smoothed fluence? Dosimetric and delivery considerations for dynamic sliding window IMRT

<p>Abstract</p> <p>Background</p> <p>The study summarised in this report aimed to investigate the interplay between fluence complexity, dose calculation algorithms, dose calculation spatial resolution and delivery characteristics (monitor units, effective field width and dose delivery against dose prediction agreement) was investigated. A sample set of complex planning cases was selected and tested using a commercial treatment planning system capable of inverse optimisation and equipped with tools to tune fluence smoothness.</p> <p>Methods</p> <p>A set of increasingly smoothed fluence patterns was correlated to a generalised expression of the Modulation Index (MI) concept, in nature independent from the specific planning system used that could therefore be recommended as a predictor to score fluence "quality" at a very early stage of the IMRT QA process. Fluence complexity was also correlated to delivery accuracy and characteristics in terms of number of MU, dynamic window width and agreement between calculation and measurement (expressed as percentage of field area with a <it>γ </it>> 1 (%FA)) when comparing calculated vs. delivered modulated dose maps. Different resolutions of the calculation grid and different photon dose algorithms (pencil beam and anisotropic analytical algorithm) were used for the investigations.</p> <p>Results and Conclusion</p> <p>i) MI can be used as a reliable parameter to test different approaches/algorithms to smooth fluences implemented in a TPS, and to identify the preferable default values for the smoothing parameters if appropriate tools are implemented; ii) a MI threshold set at MI < 19 could ensure that the planned beams are safely and accurately delivered within stringent quality criteria; iii) a reduction in fluence complexity is strictly correlated to a corresponding reduction in MUs, as well as to a decrease of the average sliding window width (for dynamic IMRT delivery); iv) a smoother fluence results in a reduction of dose in the healthy tissue with a potentially relevant clinical benefit; v) increasing the smoothing parameter s, MI decreases with %FA: fluence complexity has a significant impact on the accuracy of delivery and the agreement between calculation and measurements improves with the advanced algorithms.</p

GPU-accelerated automatic identification of robust beam setups for proton and carbon-ion radiotherapy

Abstract. We demonstrate acceleration on graphic processing units (GPU) of automatic identification of robust particle therapy beam setups, minimizing negative dosimetric effects of Bragg peak displacement caused by treatment-time patient positioning errors. Our particle therapy research toolkit, RobuR, was extended with OpenCL support and used to implement calculation on GPU of the Port Homogeneity Index, a metric scoring irradiation port robustness through analysis of tissue density patterns prior to dose optimization and computation. Results were benchmarked against an independent native CPU implementation. Numerical results were in agreement between the GPU implementation and native CPU implementation. For 10 skull base cases, the GPU-accelerated implementation was employed to select beam setups for proton and carbon ion treatment plans, which proved to be dosimetrically robust, when recomputed in presence of various simulated positioning errors. From the point of view of performance, average running time on the GPU decreased by at least one order of magnitude compared to the CPU, rendering the GPU-accelerated analysis a feasible step in a clinical treatment planning interactive session. In conclusion, selection of robust particle therapy beam setups can be effectively accelerated on a GPU and become an unintrusive part of the particle therapy treatment planning workflow. Additionally, the speed gain opens new usage scenarios, like interactive analysis manipulation (e.g. constraining of some setup) and re-execution. Finally, through OpenCL portable parallelism, the new implementation is suitable also for CPU-only use, taking advantage of multiple cores, and can potentially exploit types of accelerators other than GPUs

Examples of isodose distributions (Head and Neck case) for the two extreme smoothing conditions s25 (left) and s80 (right)

<p><b>Copyright information:</b></p><p>Taken from "What is an acceptably smoothed fluence? Dosimetric and delivery considerations for dynamic sliding window IMRT"</p><p>http://www.ro-journal.com/content/2/1/42</p><p>Radiation Oncology (London, England) 2007;2():42-42.</p><p>Published online 23 Nov 2007</p><p>PMCID:PMC2234418.</p><p></p> Isodose lines are normalised to the dose prescribed to the smaller volume receiving the higher prescribed dose. The 73% isodose refers to the 90% of the dose prescribed to the large volume

DVHs of targets and organs at risk (Head and Neck case) for the two extreme smoothing conditions s25 and s80

<p><b>Copyright information:</b></p><p>Taken from "What is an acceptably smoothed fluence? Dosimetric and delivery considerations for dynamic sliding window IMRT"</p><p>http://www.ro-journal.com/content/2/1/42</p><p>Radiation Oncology (London, England) 2007;2():42-42.</p><p>Published online 23 Nov 2007</p><p>PMCID:PMC2234418.</p><p></p

Healthy tissue analysis: volumetric differences for the s50 (or s80) plans and the s25 plans, as a function of different dose levels

<p><b>Copyright information:</b></p><p>Taken from "What is an acceptably smoothed fluence? Dosimetric and delivery considerations for dynamic sliding window IMRT"</p><p>http://www.ro-journal.com/content/2/1/42</p><p>Radiation Oncology (London, England) 2007;2():42-42.</p><p>Published online 23 Nov 2007</p><p>PMCID:PMC2234418.</p><p></p

(a) Example of fluence, for a Head and Neck case, for the three smoothing conditions

<p><b>Copyright information:</b></p><p>Taken from "What is an acceptably smoothed fluence? Dosimetric and delivery considerations for dynamic sliding window IMRT"</p><p>http://www.ro-journal.com/content/2/1/42</p><p>Radiation Oncology (London, England) 2007;2():42-42.</p><p>Published online 23 Nov 2007</p><p>PMCID:PMC2234418.</p><p></p> The white overlays show the target volumes and the main organs at risk. (b) The three components (), (dashed lines) and (solid lines) of the total spectrum for the two extreme conditions s25 (red) and s80 (green). (c) Mean spectra, averaged over the 17 fluence maps for the three smoothing conditions. It is shown also the ratio between the spectra for s50 (s80) and s25 respectively. (d) Mean modulation index MI

Photons, protons or carbon ions for stage I non-small cell lung cancer - Results of the multicentric ROCOCO in silico study

Purpose: To compare dose to organs at risk (OARs) and dose-escalation possibility for 24 stage I non-small cell lung cancer (NSCLC) patients in a ROCOCO (Radiation Oncology Collaborative Comparison) trial.Methods: For each patient, 3 photon plans [Intensity-modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT) and CyberKnife], a double scattered proton (DSP) and an intensity-modulated carbon-ion (IMIT) therapy plan were created. Dose prescription was 60 Gy (equivalent) in 8 fractions.Results: The mean dose and dose to 2% of the clinical target volume (CTV) were lower for protons and ions compared with IMRT (p < 0.01). Doses to the lungs, heart, and mediastinal structures were lowest with IMIT (p < 0.01), doses to the spinal cord were lowest with DSP (p < 0.01). VMAT and CyberKnife allowed for reduced doses to most OARs compared with IMRT. Dose escalation was possible for 8 patients. Generally, the mediastinum was the primary dose-limiting organ.Conclusion: On average, the doses to the OARs were lowest using particles, with more homogenous CTV doses. Given the ability of VMAT and CyberKnife to limit doses to OARs compared with IMRT, the additional benefit of particles may only be clinically relevant in selected patients and thus should be carefully weighed for every individual patient. (C) 2018 Elsevier B.V. All rights reserved.Biological, physical and clinical aspects of cancer treatment with ionising radiatio

Benefit of particle therapy in re-irradiation of head and neck patients. Results of a multicentric in silico ROCOCO trial

AbstractBackground and PurposeIn this multicentric in silico trial we compared photon, proton, and carbon-ion radiotherapy plans for re-irradiation of patients with squamous cell carcinoma of the head and neck (HNSCC) regarding dose to tumour and doses to surrounding organs at risk (OARs).Material and MethodsTwenty-five HNSCC patients with a second new or recurrent cancer after previous irradiation (70Gy) were included. Intensity-modulated proton therapy (IMPT) and ion therapy (IMIT) re-irradiation plans to a second subsequent dose of 70Gy were compared to photon therapy delivered with volumetric modulated arc therapy (VMAT).ResultsWhen comparing IMIT and IMPT to VMAT, the mean dose to all investigated 22 OARs was significantly reduced for IMIT and to 15 out of 22 OARs (68%) using IMPT. The maximum dose to 2% volume (D2) of the brainstem and spinal cord were significantly reduced using IMPT and IMIT compared to VMAT. The data are available on www.cancerdata.org.ConclusionsIn this ROCOCO in silico trial, a reduction in mean dose to OARs was achieved using particle therapy compared to photons in the re-irradiation of HNSCC. There was a dosimetric benefit favouring carbon-ions above proton therapy. These dose reductions may potentially translate into lower severe complication rates related to the re-irradiation