A systematic review and meta-analysis of radiotherapy planning studies comparing multi leaf collimator designs

Dosimetric comparison of O-ring versus conventional C-arm linear accelerator for volumetric modulated arc therapy (VMAT) of head and neck cancer and carcinoma cervix patients

The objective of this study is dosimetric comparison between the O-ring Halcyon and C-arm Clinac iX linac for volumetric modulated arc therapy (VMAT) plans for head & neck (H&N) cancer and carcinoma cervix patients. Total 60 patients of H&N cancer and carcinoma cervix were enrolled prospectively from March 2021 to March 2023. VMAT plans with 6 MV photons for Halcyon and Clinac iX were generated and compared for each patient by dose volume histogram for planning target volume coverage and organ at risk (OAR) sparing. There were no differences in between both the linacs for PTV D2% and D98%, homogeneity index, conformity index, Dmax (maximum dose) and Dmean (mean dose) of OAR. Halcyon had significantly shorter treatment time compared to Clinac iX. Halcyon delivered higher integral dose and monitor units. O-ring Halcyon produces VMAT plans comparable to other C-arm linacs for H&N and carcinoma cervix patients.

Improving the modelling of a multi-leaf collimator with tilted leaf sides used in radiotherapy

Background and purpose

Multi-leaf collimators (MLCs) with tilted leaf sides have a complex transmission behaviour that is not easily matched by radiotherapy treatment planning systems (TPSs). We sought to develop an MLC model that can accurately match test fields and clinically relevant plans at different centres.

Materials and methods

Two new MLC models were developed and evaluated within a research version of a commercial TPS. Prototype I used adjusted-constant transmissions and Prototype II used variable transmissions at the tongue-and-groove and leaf-tip regions. Three different centres evaluated these prototypes for a tilted MLC and compared them with their initial MLC model using test fields and patient-specific quality-assurance measurements of clinically relevant plans. For the latter, gamma passing rates (GPR) at 2 %/2mm were recorded.

Results

For the prototypes the same set of MLC parameters could be used at all centres, with only a slight adjustment of the offset parameter. For centres A and C, average GPR were >95 % and within 0.5 % GPR difference between the standard, and prototype models. In center B, prototypes I and II improved the agreement in clinically relevant plans, with an increase in GPR of 2.3 % ± 0.8 % and 3.0 ± 0.8 %, respectively.

Conclusions

The prototype MLC models were either similar or superior to the initial MLC model, and simpler to configure because fewer trade-offs were required. Prototype I performed comparably to the more sophisticated Prototype II and its configuration can be easily standardized, which can be useful to reduce variability and improve safety in clinical practice.

Effects of Multileaf Collimator Design and Function When Using an Optimized Dynamic Conformal Arc Approach for Stereotactic Radiosurgery Treatment of Multiple Brain Metastases With a Single Isocenter: A Planning Study

Background Stereotactic radiosurgery (SRS) or fractionated SRS (fSRS) are effective options for the treatment of brain metastases. When treating multiple metastases with a linear accelerator-based approach, a single isocenter allows for efficient treatment delivery. In this study, we present our findings comparing dosimetric parameters of Brainlab (Munich, Germany) Elements™ Multiple Brain Mets SRS (MME) software (version 1.5 versus version 2.0) for a variety of scenarios and patients. The impact of multileaf collimator design and function on plan quality within the software was also evaluated. Materials and methods Twenty previously treated patients with a total of 58 lesions (from one to seven lesions each) were replanned with an updated version of the multiple brain Mets software solution. For each plan, the mean conformity index (CI), mean gradient index (GI), the volume of normal brain receiving 12 Gy (V12), and mean brain dose were evaluated. Additionally, all v2.0 plans were further evaluated with jaw tracking for by Elekta (Stockholm, Sweden) and HD120™ multileaf collimator by Varian Medical Systems (Palo Alto, USA). Results The new software version demonstrated improvements for CI, GI and V12 (p <0.01). For the Elekta Agility™ multileaf collimator, jaw tracking improved all dosimetric parameters except for CI (p =0.178) and mean brain dose (p =0.93). For the Varian with HD120 multileaf collimator, all parameters improved. Conclusions The software enhancements in v2.0 of the software provided improvements in planning efficiency and dosimetric parameters. Differences in multileaf collimator design may provide an additional incremental benefit in a subset of clinical scenarios.