Related Experiment Video
Updated: Jan 17, 2026
Stereotactic Radiosurgery for Gynecologic Cancer
Published on: April 17, 2012
Dosimetric Comparison of Stereotactic Radiosurgery and Stereotactic Radiotherapy Planning Techniques with Apex 2.5mm
Rechal Nisha Dsouza1, Krishna Sharan2, Suresh Sukumar3
1Medical Radiation Physics Programme, Department of Radiation Oncology, Manipal College of Health Professions, Manipal, Manipal Academy of Higher Education, Manipal, Karnataka, India.
Objective:
Apex 2.5mm micro-Multileaf Collimator(mMLC) provides conformal dose distribution to the tumor in stereotactic radiosurgery (SRS)/stereotactic radiotherapy(SRT) treatments. Since it is an add-on device to the linear accelerator(LINAC), it requires extra commissioning for quality assurance(QA) and treatment. Agility is an in-built MLC having a 5mm multileaf collimator(MLC) width that is capable of providing better outcomes for SRS/SRT. Hence, this study compares the apex-based dynamic conformal arc therapy(DCAT) and agility-based volumetric-modulated arc therapy(VMAT) treatment plans using 6MV flattening filter-free(FFF) radiation beams.
Methods:
The population included thirty patients with brain metastasis(BM) with median age of 58 years(35y-75y) treated between 2021 and 2024. The selected patients were grouped into five categories based on the dose to be delivered, with six patients in every group. The dose delivered in groups I, II, III, IV, and V were 16Gy/1fraction(Fr), 18Gy/1Fr, 20Gy/1Fr, 24Gy/1Fr, and 25Gy/5Fr respectively. Two treatment plans were generated for every patient using the apex-based DCAT and agility-based VMAT technique with 6 MV-FFF photon beam energy using Monaco(5.11.03) treatment planning system(TPS).
Result:
The planning target volume(PTV) and gross tumor volume(GTV) coverage were excellent in both planning techniques. Conformity index(CI), gradient index(GI), selectivity index(SI), and coverage ratios were similar in both plans. The homogeneity index(HI) was superior with apex-based plans. Total monitor units(MUs) were higher in agility-based plans, resulting in high beam-on time.
Conclusion:
As the apex is an add-on device to the collimator of the LINAC machine, it requires additional time for commissioning and QA before the treatment. Agility, with in built 5mm MLC, does not require extra commissioning. Dosimetrically, the treatment plans achieved with agility were comparable with apex-based plans except for total MUs. If this is kept aside, 5mm MLC agility-based VMAT FFF plans are capable of giving good outcomes for SRS/SRT treatments.
