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Nasopharyngeal Ca OAR contouring


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Organs at risk contouring guidelines for Nasopharyngeal cancer

Published in: Healthcare

Nasopharyngeal Ca OAR contouring

  1. 1. Radiotherapy and Oncology; Volume 110 (2014); 390-397
  2. 2. Reference :
  4. 4.  Radiation Therapy is the preferred therapeutic treatment modality for Non- Metastatic Nasopharyngeal Carcinoma (NPC)  Intensity Modulated Radiation Therapy (IMRT) is the preferred modality in view of dose escalation to the primary with sparing of the organs at risk (OAR)  Accurate delineation and precise dosage of the target volume and the organs at risk are keys to a successful radiotherapy
  5. 5.  The normal tissues close to the nasopharynx which need to be spared for proper functioning are the organs at risk (OARs)  Temporal lobe  Brainstem  Spinal cord  Optic Nerve  Optic chiasm  Parotid gland  Submandibular gland  Pituitary
  6. 6.  Accurate and consistent OAR delineation is important in NPC treatment planning for adequate target volume coverage and reduction of dose to the OARs  However, large variations are observed while contouring the OARs  Also different contouring methods are available in the literature which further increase the inhomogeneity in contouring the OARs and thus leads to dose inhomogeneity  The diversity in OAR delineation leads to unmatched Dosimetric analyses and prevents side effect correlation studies
  7. 7.  The variation in OAR delineation mainly depends on :  Diversity of Subjective interpretations  Variations in actual contouring  This study focused mainly on the diversities in subjective interpretation
  8. 8.  Different OAR contouring methods were identified  Applied on 41 patients with non- metastatic NPC for treatment with IMRT (March 2011 – September 2011)  Retrospective analysis of 21 patients with NPC treated with IMRT (November 2004 – November 2006) and developing unilateral temporal lobe necrosis (TLN) was done  The area under Receiver Operating Characteristic (ROC) for these 21 patients with 2 temporal lobe contouring methods were compared and a more reasonable contouring method for temporal lobe was obtained
  9. 9.  Literature search of OAR delineation in head and neck cancers showed 2-4 contouring methods for middle ear, inner ear, temporal lobe, parotid gland and spinal cord  Search done on PubMed  Papers published till end of November 2012
  10. 10.  Total 553 papers were identified and out of these 5, 30, 13, 7, and 7 papers were found to be relevant for temporal lobe, parotid gland, spinal cord, inner ear and middle ear respectively  For other OARs, different contouring methods were referred based on human anatomy and CT and MRI based sectional anatomical references
  11. 11.  Temporal lobe contouring – 2 methods were used  Method 1 :  Brain tissue outside the sylvian fissure and basal ganglia, excluding the parahippocampus gyrus and hippocampus  Method 2 :  Temporal lobe including the parahippocampal gyrus and hippocampus, excluding the basal ganglia and insula
  12. 12.  Middle ear contouring – 3 methods  Contouring the combination of tympanum and Eustachian tube (ET)  Contouring the tympanum and bony part of the ET respectively  Contouring the ET, tympanic cavity and mastoid process, respectively  Inner ear contouring – 4 methods  Spinal cord contouring – 2 methods  Contouring the true spinal cord  Contouring the bony limits of spinal canal
  13. 13.  Gross Tumor Volume (GTV)  Clinical Target Volume (CTV) In accordance with ICRU 50, 62 and 83  Atlas based auto segmentation for primary OAR delineation (ABAS Version 2.01, ELEKTA)  The contouring was modified manually  3mm margin for planning Target Volume (PTV) and Planning at Risk volume (PRV)
  14. 14.  Dose to PTV : 70 Gy at 2.12 Gy per fraction (5 fractions per week)  For comparison of various contouring methods  Volume of all organs  Mean dose (Dmean) for the parotid gland, middle and inner ear  D1 of PRV (Dx/xcc, the minimum dose received by the ‘‘hottest’’ x% or x ml of the structure) for the spinal cord and temporal lobe
  15. 15.  Retrospective analysis of dosimetric parameters in 21 NPC patients with unilateral TLN who underwent IMRT between November 2004 and November 2006  Median follow-up time was 45 months (range: 38–63 months)  Latency of TLN was 35 months (range: 25–57 months) after completion of radiotherapy  MRI findings were independently reviewed by two radiologists
  16. 16.  A diagnosis of TLN was made if the MRI presented following signs :  White matter lesions (WMLs) - homogeneous lesions in the white matter  Solid, enhanced nodules with or without a necrotic centre and finger signs  Cysts of round or oval lesions  Tumor recurrence or metastasis of tumor was excluded.
  17. 17.  SPSS 16.0  Friedman test to compare middle/inner ear Dmean  Paired-t test to compare parotid gland volume and Dmean  Paired-t test to compare spinal cord volume and D1 of PRV  Wilcoxon-test to compare temporal lobe volume, and D1 of PRV
  18. 18.  For the 21 patients with unilateral TLN, 3 steps were adopted Paired-t test Multivariate analysis using the binary logistic regression model Areas under the ROC curves Used to compare all the dosimetric parameters between the temporal lobes with and without radiation-induced damage for every method : D1–D60, D1–D40 cc, V10 to V75, D1–D60 of PRV, and V20–V75 of the PRV at five units intervals Used to identify the most relevant parameters associated with TLN Of the most relevant parameters from the two contouring methods were compared to select a more reasonable contouring method
  19. 19. D1 of PRV was identified as the most relevant parameter for TLN for both methods Method 2 had a slightly larger area under the ROC curve than method 1 (0.86 vs. 0.85) 64 Gy was the critical point for the D1 of PRV There was no significant difference between the areas under the ROC curves of the two contouring methods (p = 0.27)
  20. 20.  Significant differences in the volume and selected parameters of all organs were observed using different contouring methods (p < 0.05)  Significant differences between the ipsilateral and contralateral temporal lobe were observed for all dosimetric parameters (p < 0.05)
  21. 21.  Based on the anatomic definition and pathogenesis of radiation induced injury, a contouring method was recommended for :  Temporal lobe  Middle ear  Inner ear  Parotid gland  Spinal cord  For other organs whose contouring is rarely described, it was recommended to outline the whole organ according to their anatomic definition
  22. 22.  The middle ear, inner ear and Temporomandibular joint (TMJ) should be delineated on the bone window  The temporal lobe and brainstem on the brain window  However, the lateral boundary of the temporal lobe and other organs should be delineated on the soft tissue window
  23. 23.  Temporal lobe : Should include the hippocampus, parahippocampal gyrus and uncus  The basal ganglia and insula are located anteriorly and superiorly to the hippocampus and parahippocampal gyrus and should be excluded  Spinal cord : Visible true spinal cord should be contoured from the foramen magnum (the level of the odontoid process of the axis) to 2 cm below the inferior edge of the head of the collarbone  Parotid gland : Whole gland should be outlined including the CTV, but not the GTV
  24. 24. 1: Cerebellum 2: Raphe dorsalis 3: Parahippocampal gyrus 4: Temporal pole 5: Inferior temporal gyrus 6: Occipital gyrus 7: Hippocampus 8: Amygdala 9: Middle temporal gyrus 10: Superior temporal gyrus 11: Insula 12: Orbitofrontal gyrus 13: Inferior parietal lobule 14: Thalamus 15: Superior parietal lobule 16: Post‐ and precentral operculum 17: Anterior cingulate gyrus 18: Posterior cingulate gyrus 19: Inferior, middle and superior frontal gyri
  25. 25.  Middle ear : The tympanic cavity and bony part of the Eustachian Tube (ET) should be contoured individually  The tympanic cavity is delineated  Laterally by the tympanic membrane, defined by the ligature between the two bony structures with an increased density along the anterior and posterior walls of the most medial aspect of the outer air canal  the sharp narrow region connected anteriorly to the ET, and the interface between the temporal bone and air at all other walls  Inner ear : Delineation of the cochlea and Internal Auditory Canal (IAC) should be done individually  The cochlea is located anteriorly to the IAC
  26. 26. 1: Cochlea (basal turn) 2: Tensor tympani muscle 3: Manubrium of malleus 4: Facial nerve canal 5: Stapedius muscle 6: Round window
  27. 27.  Accurate and consistent OAR delineation is important for proper execution of an IMRT plan  Nelms et al* : The most variable contours in head and neck cancer are the brainstem, parotid gland and spinal cord - These had a consistency score of 70/100.  The contouring variations occur both due to subjective diversity in OAR interpretation and variations in actual anatomical contouring  This study focused on subjective OAR interpretation  This study showed that various contouring methods will lead to different dosimetric parameters * Benjamin E. Nelms, Wolfgang A. Tomé, Greg Robinson, James Wheeler, Variations in the Contouring of Organs at Risk: Test Case From a Patient With Oropharyngeal Cancer, International Journal of Radiation Oncology*Biology*Physics, Volume 82, Issue 1, 1 January 2012, Pages 368- 378, ISSN 0360-3016,
  28. 28.  Radiation-induced temporal lobe injury :  Characterized by TLN  Observed in around 1-5% patients of NPC after radiotherapy  D1 of PRV was the most relevant dosimetric parameter for TLN  64 Gy was the critical dose, similar to the 65 Gy limit recommended by RTOG 0225 protocol  The area under the ROC curves was not significantly different between the two contouring methods  This may be explained as follows:  The D1 of PRV is mainly impacted by the inferior and medial aspect of the temporal lobe, where TLN is mostly observed.  Both methods included the inferior and medial aspect
  29. 29.  Method 2 was recommended for contouring the temporal lobe for the following reasons :  The hippocampus and parahippocampal gyrus are located close to the target volume, in which the TLN usually occurred (13/21 in this study), while in the basal ganglia and insula rarely occurred (1/21 in this study)  The symptoms of TLN such as decreased memory, acalculia et al. are correlated with the damage to the hippocampus and parahippocampal gyrus
  30. 30.  Radiation-induced middle ear damage :  Characterized by otitis media with effusion (OME)  26–40% NPC patients within 5 years after radiotherapy  Two factors contributed to OME:  damage to the ET, tensor veli palatini muscle, cartilage or nerves  direct radiation damage leading to non-infectious inflammation  The injuries of ET and tympanic cavity (including the otosteon) are relevant to the development of OME and should be contoured and protected individually
  31. 31.  Sensorineural Hearing loss :  Due to inner ear radiation injury  Morbidity rates of 11-57%  Precise mechanism is obscure and contributed also by the concurrent chemotherapy  The recommendation to contour the cochlea and IAC individually is based on inner ear function
  32. 32.  Radiation-induced xerostomia :  Mainly seen due to radiation damage to the parotid gland  Contouring the whole salivary gland minus the GTV may be more suitable for getting the better dosimetric parameters that correspond with the change of salivary function after radiotherapy
  33. 33.  This atlas was based mainly on CT scan and referred to MRI  MRI has a better resolution for soft tissue, and is usually used to diagnose the soft tissue disease  Glands, muscles and other soft tissues should be contoured by referring to MRI  CT can more reliably indicate bone boundaries and joint structures  the TMJ, middle / inner ear and mandible, which are mainly defined by bone limit, could be contoured based on CT alone
  34. 34.  Different OARs contouring methods result in different Dosimetric parameters  A contouring guideline is necessary to facilitate the generation of uniform and comparable dosimetric parameters  The present atlas, based on anatomic definitions and the pathogenesis of radiation-induced injury, may help reach a consensus on subjective interpretation of the OARs delineation to reduce inter institutional differences in NPC patients