Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology
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To investigate patient set-up, tumor movement and shrinkage during 3D conformal radiotherapy for non-small cell lung cancer. ⋯ The application of the correction protocol resulted in a significant improvement in the set-up accuracy. There was wide variation in the observed tumor motion with more movement of lower lobe lesions. Tumor shrinkage was observed. The position of the tumor on the planning CT scan did not always coincide with the average position as measured during treatment.
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Comparative Study
Comparative analysis of intensity modulation inverse planning modules of three commercial treatment planning systems applied to head and neck tumour model.
Three commercial treatment planning modules for intensity modulated radiation therapy (IMRT) Inverse Planning, MDS-Nordion Helax-TMS, Varian Cadplan-Helios, and CMS Focus, were compared in an attempt to determine potential application limits or dosimetric differences among various optimisation algorithms. ⋯ Results obtained for the three IMRT TPS show in first instance that the optimisation algorithms analysed, as well as the conversion from computed fluences to multileaf sequences implemented in the planning systems can produce substantially equivalent dose plans (for target coverage and organs at risk sparing) if planning is performed with common strategies and once a strong understanding of each system feature is achieved. Secondly, a limited number of dose levels (about eight) is adequate at planning level.
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The relationship between the radiation dose and the risk of the osteoradionecrosis is well known. However, the dose to the mandible is not routinely assessed in the radiotherapy for head and neck cancer. The aim of our study was to analyze the mandibular dose distribution in the patients administered curative radiotherapy for squamous cell carcinoma of the oropharynx. Moreover, the clinical results have been analyzed. ⋯ Radiotherapy for oropharyngeal cancer is associated with high doses to the retromolar mandibular regions (the dose can be higher than prescribed in the ICRU reference point), ascending ramus and molar regions. Lower doses are absorbed at the condyles and mental symphysis. The single dose point (for example, the ICRU reference point) could be not used as a representative for the mandibular dose. In our small series of patients treated with hyperfractionated irradiation, these dose heterogeneities were not correlated to the patient- and treatment-related factors and are not related to the increased risk of late bone complications. The clinical relevance of mandibular dose distribution remains to be established in larger series of patients treated with conventionally and unconventionally fractionated irradiation.
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Appropriate planning target volume (PTV) definition is critical for local disease eradication in the treatment of non-small cell lung cancer (NSCLC). When margins are added to the gross tumour volume (GTV) in the standard way, the PTV formed may be too large to facilitate dose escalation due to normal tissue tolerance. To increase the feasibility of dose escalation with 3-dimensional conformal radiotherapy (3DCRT), this study examines an alternative method for the formation of the PTV in NSCLC. This strategy is based on the reduced probability of tumour cells from the GTV outwards and on the associated lower dose requirements to eradicate such subclinical disease. ⋯ Using this strategy with standard 3DCRT, all PTVs were irradiated to the required dose with this approach, but none of the corresponding Rind volumes had an acceptable dose distribution. The addition of dual volume planning or the use of intensity modulated radiation therapy may achieve an appropriate dose distribution in the Rind volume while not increasing the dose to the organs at risk and may thereby facilitate dose escalation.