The dosimetric impact of leaf interdigitation and leaf width on VMAT treatment planning in Pinnacle: comparing Pareto fronts.

To evaluate in an objective way the effect of leaf interdigitation and leaf width on volumetric modulated arc therapy plans in Pinnacle. Three multileaf collimators (MLCs) were modeled: two 10 mm leaf width MLCs, with and without interdigitating leafs, and a 5 mm leaf width MLC with interdigitating leafs. Three rectum patients and three prostate patients were used for the planning study. In order to compare treatment techniques in an objective way, a Pareto front comparison was carried out. 200 plans were generated in an automated way, per patient per MLC model, resulting in a total of 3600 plans. From these plans, Pareto-optimal plans were selected which were evaluated for various dosimetric variables. The capability of leaf interdigitation showed little dosimetric impact on the treatment plans, when comparing the 10 mm leaf width MLC with and without leaf interdigitation. When comparing the 10 mm leaf width MLC with the 5 mm leaf width MLC, both with interdigitating leafs, improvement in plan quality was observed. For both patient groups, the integral dose was reduced by 0.6 J for the thin MLC. For the prostate patients, the mean dose to the anal sphincter was reduced by 1.8 Gy and the conformity of the V(95%) was reduced by 0.02 using the thin MLC. The V(65%) of the rectum was reduced by 0.1% and the dose homogeneity with 1.5%. For rectum patients, the mean dose to the bowel was reduced by 1.4 Gy and the mean dose to the bladder with 0.8 Gy for the thin MLC. The conformity of the V(95%) was equivalent for the 10 and 5 mm leaf width MLCs for the rectum patients. We have objectively compared three types of MLCs in a planning study for prostate and rectum patients by analyzing Pareto-optimal plans which were generated in an automated way. Interdigitation of MLC leafs does not generate better plans using the SmartArc algorithm in Pinnacle. Changing the MLC leaf width from 10 to 5 mm generates better treatment plans although the clinical relevance remains to be proven.

Microdosimetry model for boron neutron capture therapy: I. Determination of microscopic quantities of heavy particles on a cellular scale.

Due to the limitations of existing microdosimetry models, a new model called MICOR has been developed to analyze the spatial distribution of microscopic energy deposition for boron neutron capture therapy (BNCT). As in most existing models, the reactions independent of the incident neutron energy such as the boron and the nitrogen capture reactions can be considered. While other models do not include reactions that are dependent on the neutron energy such as the proton recoil reaction, the present model is designed so that the energy deposition resulting from these reactions is included. The model MICOR has been extended to enable the determination of the biological effects of BNCT, which cannot be done with the existing models. The present paper describes the determination of several microscopic quantities such as the number of hits, the energy deposition in the cell nucleus, and the distribution of lineal and specific energy deposition. The companion paper (Radiat. Res. 155, 000-000 2001) deals with the conversion of these microscopic quantities into biological effects. The model is used to analyze the results of a radiobiological experiment performed at the HB11 facility in the HFR in Petten. This analysis shows the value of the model in determining the dose depositions on a cellular scale and the importance of the extension to the energy deposition of the proton recoil.

Microdosimetry model for boron neutron capture therapy: II. Theoretical estimation of the effectiveness function and surviving fractions.

A model has been developed to obtain a better understanding of the effects of boron neutron capture therapy (BNCT) on a cellular scale. This model, the microdosimetry model MICOR, has been developed to include all reactions important for BNCT. To make the model more powerful in the translation from energy deposition to biological effect, it has been designed to be capable of calculating the effectiveness function. Based on this function, the model can calculate surviving fractions, RBE values and boron concentration distributions. MICOR has been used to analyze an extensive set of biological experiments performed at the HB11 beam in Petten. For V79 Chinese hamster cells, the effectiveness function is determined and used to generate surviving fractions. These fractions are compared with measured surviving fractions, which results in a good agreement between the measured and calculated surviving fractions (within the uncertainties of the measurements).