Accuracy of relocation, evaluation of geometric uncertainties and clinical target volume (CTV) to planning target volume (PTV) margin in fractionated stereotactic radiotherapy for intracranial tumors using relocatable Gill‐Thomas‐Cosman (GTC) frame

• Published in: Journal of applied clinical medical physics 2011, Vol.12 (2), p.29-38
• Main Authors: Das, Saikat, Isiah, Rajesh, Rajesh, B., Ravindran, B. Paul, Singh, Rabi Raja, Backianathan, Selvamani, Subhashini, J.
• Format: Article
• Language: English
• Subjects: Accuracy; Adolescent; Adult; Brain cancer; Brain Neoplasms - radiotherapy; Child; depth helmet; Dose Fractionation, Radiation; Equipment Design; Female; Gill‐Thomas‐Cosman frame; Humans; Male; Medical imaging; Meningioma - radiotherapy; Middle Aged; Models, Theoretical; Optic Nerve Glioma - radiotherapy; Patients; Pituitary Neoplasms - radiotherapy; quality assurance; Quality Control; Radiation Oncology - instrumentation; Radiation Oncology Physics; Radiation therapy; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; random error; Reproducibility of Results; stereotactic radiotherapy; Stereotaxic Techniques - instrumentation; systematic error; Tumors
• ISSN: 1526-9914; 1526-9914
• DOI: 10.1120/jacmp.v12i2.3260

The present study is aimed at determination of accuracy of relocation of Gill‐Thomas‐Cosman frame during fractionated stereotactic radiotherapy. The study aims to quantitatively determine the magnitudes of error in anteroposterior, mediolateral and craniocaudal directions, and determine the margin between clinical target volume to planning target volume based on systematic and random errors. Daily relocation error was measured using depth helmet and measuring probe. Based on the measurements, translational displacements in anteroposterior (z), mediolateral (x), and craniocaudal (y) directions were calculated. Based on the displacements in x, y and z directions, systematic and random error were calculated and three‐dimensional radial displacement vector was determined. Systematic and random errors were used to derive CTV to PTV margin. The errors were within ± 2 mm in 99.2% cases in anteroposterior direction (AP), in 99.6% cases in mediolateral direction (ML), and in 97.6% cases in craniocaudal direction (CC). In AP, ML and CC directions, systematic errors were 0.56, 0.38, 0.42 mm and random errors were 1.86, 1.36 and 0.73 mm, respectively. Mean radial displacement was 1.03 mm ± 0.34. CTV to PTV margins calculated by ICRU formula were 1.86, 1.45 and 0.93 mm; by Stroom's formula they were 2.42, 1.74 and 1.35 mm; by van Herk's formula they were 2.7, 1.93 and 1.56 mm (AP, ML and CC directions). Depth helmet with measuring probe provides a clinically viable way for assessing the relocation accuracy of GTC frame. The errors were within ± 2 mm in all directions. Systematic and random errors were more along the anteroposterior axes. According to the ICRU formula, a margin of 2 mm around the tumor seems to be adequate. PACS number: 87.55.‐x