Browsing by Author "Ahn, Yong Chan"

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International guideline for the delineation of the clinical target volumes (CTV) for nasopharyngeal carcinoma
(ELSEVIER IRELAND LTD, 2018-01-01) Lee, Anne W.; Ng, Wai Tong; Pan, Jian Ji; Poh, Sharon S.; Ahn, Yong Chan; AlHussain, Hussain; Corry, June; Grau, Cai; Gregoire, Vincent; Harrington, Kevin J.; Hu, Chao Su; Kwong, Dora L.; Langendijk, Johannes A.; Le, Quynh Thu; Lee, Nancy Y.; Lin, Jin Ching; Lu, Tai Xiang; Mendenhall, William M.; O'Sullivan, Brian; Ozyar, Enis; Peters, Lester J.; Rosenthal, David I.; Soong, Yoke Lim; Tao, Yungan; Yom, Sue S.; Wee, Joseph T.
Purpose: Target delineation in nasopharyngeal carcinoma (NPC) often proves challenging because of the notoriously narrow therapeutic margin. High doses are needed to achieve optimal levels of tumour control, and dosimetric inadequacy remains one of the most important independent factors affecting treatment outcome. Method: A review of the available literature addressing the natural behaviour of NPC and correlation between clinical and pathological aspects of the disease was conducted. Existing international guidelines as well as published protocols specified by clinical trials on contouring of clinical target volumes (CTV) were compared. This information was then summarized into a preliminary draft guideline which was then circulated to international experts in the field for exchange of opinions and subsequent voting on areas with the greatest controversies. Results: Common areas of uncertainty and variation in practices among experts experienced in radiation therapy for NPC were elucidated. Iterative revisions were made based on extensive discussion and final voting on controversial areas by the expert panel, to formulate the recommendations on contouring of CTV based on optimal geometric expansion and anatomical editing for those structures with substantial risk of microscopic infiltration. Conclusion: Through this comprehensive review of available evidence and best practices at major institutions, as well as interactive exchange of vast experience by international experts, this set of consensus guidelines has been developed to provide a practical reference for appropriate contouring to ensure optimal target coverage. However, the final decision on the treatment volumes should be based on full consideration of individual patients' factors and facilities of an individual centre (including the quality of imaging methods and the precision of treatment delivery). (C) 2017 Elsevier B.V. All rights reserved.
International Guideline on Dose Prioritization and Acceptance Criteria in Radiation Therapy Planning for Nasopharyngeal Carcinoma
(ELSEVIER SCIENCE INC, 2019-01-01) Lee, Anne W.; Ng, Wai Tong; Pan, Jian Ji; Chiang, Chi-Leung; Poh, Sharon S.; Choi, Horace C.; Ahn, Yong Chan; AlHussain, Hussain; Corry, June; Grau, Cai; Gregoire, Vincent; Harrington, Kevin J.; Hu, Chao Su; Kwong, Dora L.; Langendijk, Johannes A.; Le, Quynh Thu; Lee, Nancy Y.; Lin, Jin Ching; Lu, Tai Xiang; Mendenhall, William M.; O'Sullivan, Brian; Ozyar, Enis; Peters, Lester J.; Rosenthal, David I.; Sanguineti, Giuseppe; Soong, Yoke Lim; Tao, Yungan; Yom, Sue S.; Wee, Joseph T.
Purpose: The treatment of nasopharyngeal carcinoma requires high radiation doses. The balance of the risks of local recurrence owing to inadequate tumor coverage versus the potential damage to the adjacent organs at risk (OARs) is of critical importance. With advancements in technology, high target conformality is possible. Nonetheless, to achieve the best possible dose distribution, optimal setting of dose targets and dose prioritization for tumor volumes and various OARs is fundamental. Radiation doses should always be guided by the As Low As Reasonably Practicable principle. There are marked variations in practice. This study aimed to develop a guideline to serve as a global practical reference. Methods and Materials: A literature search on dose tolerances and normal-tissue complications after treatment for nasopharyngeal carcinoma was conducted. In addition, published guidelines and protocols on dose prioritization and constraints were reviewed. A text document and preliminary set of variants was circulated to a panel of international experts with publications or extensive experience in the field. An anonymized voting process was conducted to rank the proposed variants. A summary of the initial voting and different opinions expressed by members were then recirculated to the whole panel for review and reconsideration. Based on the comments of the panel, a refined second proposal was recirculated to the same panel. The current guideline was based on majority voting after repeated iteration for final agreement. Results: Variation in opinion among international experts was repeatedly iterated to develop a guideline describing appropriate dose prioritization and constraints. The percentage of final agreement on the recommended parameters and alternative views is shown. The rationale for the recommendations and the limitations of current evidence are discussed. Conclusions: Through this comprehensive review of available evidence and interactive exchange of vast experience by international experts, a guideline was developed to provide a practical reference for setting dose prioritization and acceptance criteria for tumor volumes and OARs. The final decision on the treatment prescription should be based on the individual clinical situation and the patient's acceptance of optimal balance of risk. (C) 2019 Elsevier Inc. All rights reserved.
International Recommendations on Reirradiation by Intensity Modulated Radiation Therapy for Locally Recurrent Nasopharyngeal Carcinoma
(ELSEVIER SCIENCE INC, 2021-01-01) Ng, Wai Tong; Soong, Yoke Lim; Ahn, Yong Chan; AlHussain, Hussain; Choi, Horace C. W.; Corry, June; Gregoire, Vincent; Harrington, Kevin J.; Hu, Chao Su; Jensen, Kenneth; Kwong, Dora L.; Langendijk, Johannes A.; Le, Quynh Thu; Lee, Nancy Y.; Lin, Jin Ching; Lu, Tai Xiang; Mendenhall, William M.; O'Sullivan, Brian; Ozyar, Enis; Pan, Jian Ji; Peters, Lester J.; Poh, Sharon S.; Rosenthal, David I.; Sanguineti, Giuseppe; Tao, Yungan; Wee, Joseph T.; Yom, Sue S.; Chua, Melvin L. K.; Lee, Anne W. M.
Purpose: Reirradiation for locally recurrent nasopharyngeal carcinoma (NPC) is challenging because prior radiation dose delivered in the first course is often close to the tolerance limit of surrounding normal structures. A delicate balance between achieving local salvage and minimizing treatment toxicities is needed. However, high-level evidence is lacking because available reports are mostly retrospective studies on small series of patients. Pragmatic consensus guidelines, based on an extensive literature search and the pooling of opinions by leading specialists, will provide a useful reference to assist decision-making for these difficult decisions. Methods and Materials: A thorough review of available literature on recurrent NPC was conducted. A set of questions and preliminary draft guideline was circulated to a panel of international specialists with extensive experience in this field for voting on controversial areas and comments. A refined second proposal, based on a summary of the initial voting and different opinions expressed, was recirculated to the whole panel for review and reconsideration. The current guideline was based on majority voting after repeated iteration for final agreement. Results: The initial round of questions showed variations in clinical practice even among the specialists, reflecting the lack of high-quality supporting data and the difficulties in formulating clinical decisions. Through exchange of comments and iterative revisions, recommendations with high-to-moderate agreement were formulated on general treatment strategies and details of reirradiation (including patient selection, targets contouring, dose prescription, and constraints). Conclusion: This paper provides useful reference on radical salvage treatment strategies for recurrent NPC and optimization of reirradiation through review of published evidence and consensus building. However, the final decision by the attending clinician must include full consideration of an individual patient's condition, understanding of the delicate balance between risk and benefits, and acceptance of risk of complications. (C) 2021 Elsevier Inc. All rights reserved.