Dosimetric performance of the new high‐definition multileaf collimator for intracranial stereotactic radiosurgery

• Type of Material: Article
• Authors: Anees Dhabbaan, Emory University; Eric Elder, Emory University; Eduard Schreibmann, Emory University; Ian Crocker, Emory University; Walter J Curran, Emory University; Nelson M Oyesiku, Emory University; Hui-Kuo Shu, Emory University; Timothy Fox, Emory University
• Language: English
• Date: 2010-01-01
• Publisher: American Association of Physicists in Medicine
• Publication Version: Final Published Version
• Copyright Statement: © 2010 The Authors.
• License: Creative Commons Attribution 3.0 Unported
• Final Published Version (URL): http://dx.doi.org/10.1120/jacmp.v11i3.3040
• Title of Journal or Parent Work: Journal of Applied Clinical Medical Physics
• ISSN: 1526-9914
• Volume: 11
• Issue: 3
• Start Page: 197
• End Page: 211
• Keywords: TUMORS; Life Sciences & Biomedicine; Conformity Index; RADIOTHERAPY; PHYSICAL DOSE DISTRIBUTIONS; normal tissue sparing; LEAF-WIDTH; DYNAMIC CONFORMAL ARCS; radiosurgery; Radiology, Nuclear Medicine & Medical Imaging; Novalis TX; IMPACT; INDEX; RADIATION-THERAPY; Science & Technology; BRAIN METASTASES; TREATMENT PLANS; high-definition MLC
• Research Categories: Health Sciences, Radiology; Health Sciences, Oncology

Abstract

The objective was to evaluate the performance of a high-definition multileaf collimator (MLC) of 2.5 mm leaf width (MLC 2.5 ) and compare to standard 5 mm leaf width MLC (MLC 5 ) for the treatment of intracranial lesions using dynamic conformal arcs (DCA) technique with a dedicated radiosurgery linear accelerator. Simulated cases of spherical targets were created to study solely the effect of target volume size on the performance of the two MLC systems independent of target shape complexity. In addition, 43 patients previously treated for intracranial lesions in our institution were retrospectively planned using DCA technique with MLC 2.5 and MLC 5 systems. The gross tumor volume ranged from 0.07 to 40.57 cm 3 with an average volume of 5.9 cm 3 . All treatment parameters were kept the same for both MLC-based plans. The plan evaluation was performed using figures of merits (FOM) for a rapid and objective assessment on the quality of the two treatment plans for MLC 2.5 and MLC 5 . The prescription isodose surface was selected as the greatest isodose surface covering ≥ 95% of the target volume and delivering 95% of the prescription dose to 99% of target volume. A Conformity Index (CI) and conformity distance index (CDI) were used to quantifying the dose conformity to a target volume. To assess normal tissue sparing, a normal tissue difference (NTD) was defined as the difference between the volume of normal tissue receiving a certain dose utilizing MLC 5 and the volume receiving the same dose using MLC 2.5 . The CI and normal tissue sparing for the simulated spherical targets were better with the MLC 2.5 as compared to MLC 5 . For the clinical patients, the CI and CDI results indicated that the MLC 2.5 provides better treatment conformity than MLC 5 even at large target volumes. The CI's range was 1.15 to 2.44 with a median of 1.59 for MLC 2.5 compared to 1.60-2.85 with a median of 1.71 for MLC 5 . Improved normal tissue sparing was also observed for MLC 2.5 over MLC 5 , with the NTD always positive, indicating improvement, and ranging from 0.1 to 8.3 for normal tissue receiving 50% (NTV 50 ), 70% (NTV 70 ) and 90% (NTV 90 ) of the prescription dose. The MLC 2.5 has a dosimetric advantage over the MLC 5 in Linac-based radiosurgery using DCA method for intracranial lesions, both in treatment conformity and normal tissue sparing when target shape complexity increases.