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Background: GTV delineation is the first crucial step in radiotherapy and requires high accuracy, especially with the growing use of highly conformal and adaptive radiotherapy techniques. If GTV delineations of observers concord, they are considered to be of high accuracy. The aim of the study is to determine the interobserver agreement for GTV delineations of supraglottic laryngeal carcinoma on CT and on CT combined with MR-images and to determine the effect of adding MR images to CT-based delineation on the delineated volume and the interobserver agreement. Methods: Twenty patients with biopsy proven T1-T4 supraglottic laryngeal cancer, treated with curative intent were included. For all patients a contrast enhanced planning CT and a 1.5-T MRI with gadolinium were acquired in the same head-and-shoulder mask for fixation as used during treatment. For MRI, a two element surface coil was used as a receiver coil. Three dedicated observers independently delineated the GTV on CT. After an interval of 2 weeks, a set of co-registered CT and MR-images was provided to delineate the GTV on CT. Common volumes (C) and encompassing volumes (E) were calculated and C/E ratios were determined for each pair of observers. The conformity index general (CIgen) was used to quantify the interobserver agreement. Results: In general, a large variation in interobserver agreement was found for CT (range: 0.29-0.77) as well as for CT-MR delineations (range: 0.17-0.80). The mean CIgen for CT (0.61) was larger compared to CT-MR (0.57) (p = 0.032). Mean GTV volume delineated on CT-MR (6.6 cm³) was larger compared to CT (5.6 cm³) (p = 0.002). Conclusion: Delineation on CT with co-registered MR-images resulted in a larger mean GTV volume and in a decrease in interobserver agreement compared to CT only delineation for supraglottic laryngeal carcinoma. [ABSTRACT FROM AUTHOR]

Background and purpose: Since lymph nodes volumes are generally four times the volume of the primary PTV, the advantage of using tight margins around the primary PTV is not clear. Therefore treatment margins of T2-T4 laryngeal carcinoma for IMRT are generally chosen in such a way that the PTV is comparable to that in conventional radiotherapy. The aim of this study is to quantify the effect of volume reduction of the primary PTV of T2-T4 laryngeal carcinoma with regard to late toxicity despite elective irradiation of lymph node levels II to IV. Methods: Two treatment plans based on conservative (GTV-PTV = 15 mm and 20 mm cranial), and on evidence-based tight margins (GTV-PTV = 8 mm) were calculated for 16 patients. Toxicity effects were estimated based on the dose distributions. Results: Compared to conservative margins, using tight margins resulted in: 1) significant reduction of the normal tissue complication probability (NTCP) for swallowing muscles and submandibular glands, 2) significant reduction of the mean dose in all organs at risk (OAR), 3) a mean dose smaller than 60 Gy for all OARs except for the laryngeal cartilages. When the lymph node levels II to IV were prescribed with an elective dose, an NTCP reduction of 53% for the swallowing muscles and of 23% for the submandibular glands was found by using tight instead of conservative margins. When positive nodes were present, NTCP reduction amounted to 29% and 15%, respectively. Conclusions: There is a potential benefit in realizing evidence-based tight margins for laryngeal cancer patients despite elective irradiation of lymph node levels II to IV. [ABSTRACT FROM AUTHOR]

Purpose: To determine the variation in target delineation of nasopharyngeal carcinoma and the impact of measures to minimize this variation. Materials and methods: For ten nasopharyngeal cancer patients, ten observers each delineated the Clinical Target Volume (CTV) and the CTV elective. After 3D analysis of the delineated volumes, a second delineation was performed. This implied improved delineation instructions, a combined delineation on CT and co-registered MRI, forced use of sagittal reconstructions, and an on-line anatomical atlas. Results: Both for the CTV and the CTV elective delineations, the 3D SD decreased from Phase 1 to Phase 2, from 4.4 to 3.3 mm for the CTV and from 5.9 to 4.9 mm for the elective. There was an increase agreement, where the observers intended to delineate the same structure, from 36 to 64 surface % (p = 0.003) for the CTV and from 17 to 59% (p = 0.004) for the elective. The largest variations were at the caudal border of the delineations but these were smaller when an observer utilized the sagittal window. Hence, the use of sagittal side windows was enforced in the second phase and resulted in a decreased standard deviation for this area from 7.7 to 3.3 mm (p = 0.001) for the CTV and 7.9 to 5.6 mm (p = 0.03) for the CTV elective. Discussion: Attempts to decrease the variation need to be tailored to the specific causes of the variation. Use of delineation instructions multimodality imaging, the use of sagittal windows and an on-line atlas result in a higher agreement on the intended target. [ABSTRACT FROM AUTHOR]