Image-guided radiation therapy using surgical clips for localization of colonic metastasis from thyroid cancer
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CASE REPORT
Open Access
Image-guided radiation therapy using surgical clips for localization of colonic metastasis from thyroid cancer Alvin Szeto1, Lee Chin1, Patrick Whelan2, Jennifer Wilson3 and Justin Lee1*
Abstract A 67-year old man with a history of papillary thyroid cancer (PTC) presented with metastatic disease to the left colon in the form of a 6.1x1.0 cm bleeding, ulcerated mass. Radiopaque surgical clips were used as fiducial markers to localize the gross tumor volume (GTV) as well as the corresponding clinical target volume (CTV) and planning target volume (PTV). Daily cone beam computed tomography (CBCT) image guidance was utilized to verify the tumor position. Inter- and intrafraction movement of the tumor mass was assessed. Gastrointestinal bleeding was controlled using palliative image-guided radiation therapy (IGRT). Keywords: Fiducial markers, Image-guided radiation therapy, Surgical clips, Thyroid cancer, Colonic metastasis, Lower gastrointestinal bleed
Background Papillary thyroid cancer (PTC) is the most common form of well differentiated thyroid cancer and is usually associated with good prognosis [1]. Recurrence rates are reported between 10-33% depending on stage and histological subtype [2]. Common sites for distant metastases of PTC include mediastinal lymph nodes, lung and bone [3]. Here, we discuss a patient with recurrent PTC with distant metastases to mediastinal lymph nodes, lung, spine, as well as colon. Gastrointestinal metastases of thyroid cancer account for 0.5-1% metastatic sites [3]. To date, there are only a small number of patient reports documenting metastatic disease from the thyroid to the colon [4-6]. Radiation treatment of tumors of the colon is not typically performed as it presents a challenge to visualize and consistently target mobile abdominal organs. Treatment planning without adequate visualization of the target area can result in wide treatment margins and excessive toxicity. Movement of the intra-abdominal organs can result in underdosing of the target or overdosing of the surrounding organs. Furthermore, conventional CBCT * Correspondence: [email protected] 1 Department of Radiation Oncology, Sunnybrook Odette Cancer Centre, University of Toronto, 2075 Bayview Avenue, Toronto, ON M4N 3M5, Canada Full list of author information is available at the end of the article
techniques rely on bony matching, which does not necessarily correlate with internal organ motion. Use of fiducial markers, such as surgical clips, can narrow the treatment volume and improve radiation targeting. Previous studies demonstrate that use of surgical clips for targeting prostate cancer, results in a reduction in total setup error, smaller planning target volume (PTV) margin and rectal sparing [7]. Despite these potential benefits, fiducial markers may also have a negative impact on clinical outcomes if the PTV margin is significantly reduced without careful consideration of intrafraction organ motion. [8]. Here, we present a unique case of multi-site metastasis of papillary th
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