Dosimetric study between a single isocenter dynamic conformal arc therapy technique and Gamma Knife radiosurgery for multiple brain metastases treatment: impact of target volume geometrical characteristics

Abstract

Purpose To compare linac-based mono-isocentric radiosurgery with Brainlab Elements Multiple Brain Mets (MBM) SRS and the Gamma Knife using a specific statistical method and to analyze the dosimetric impact of the target volume geometric characteristics. A dose fall-off analysis allowed to evaluate the Gradient Index relevancy for the dose spillage characterization. Material and methods Treatments were planned on twenty patients with three to nine brain metastases with MBM 2.0 and GammaPlan 11.0. Ninety-five metastases ranging from 0.02 to 9.61 cc were included. Paddick Index (PI), Gradient Index (GI), dose fall-off, volume of healthy brain receiving more than 12 Gy (V12Gy) and DVH were used for the plan comparison according to target volume, major axis diameter and Sphericity Index (SI). The multivariate regression approach allowed to analyze the impact of each geometric characteristic keeping all the others unchanged. A parallel study was led to evaluate the impact of the isodose line (IDL) prescription on the MBM plan quality. Results For mono-isocentric linac-based radiosurgery, the IDL around 70–75% was the best compromise found. For both techniques, the GI and the dose fall-off decreased with the target volume. In comparison, PI was slightly improved with MBM for targets < 1 cc or SI > 0.78. GI was improved with GP for targets < 2.5 cc. The V12Gy was higher with MBM for lesions > 0.4 cc or SI < 0.84 and exceeded 10 cc for targets > 5 cc against 6.5 cc with GP. The presence of OAR close to the PTV had no impact on the dose fall off values. The dose fall-off was higher for volumes < 3.8 cc with GP which had the sharpest dose fall-off in the infero-superior direction up to 30%/mm. The mean beam-on time was 94 min with GP against 13 min with MBM. Conclusions The dose fall-off and the V12Gy were more relevant indicators than the GI for the low dose spillage assessment. Both evaluated techniques have comparable plan qualities with a slightly improved selectivity with MBM for smaller lesions but with a healthy tissues sparing slightly favorable to GP at the expense of a considerably longer irradiation time. However, a higher healthy tissue exposure must be considered for large volumes in MBM plans.

Plan quality assessment of modern radiosurgery technologies in the treatment of multiple brain metastases

“…The Gη 12Gy indices reported for CyberKnife and Gamma Knife plans in this study (figure 3 and table 6) were similar to the range of 44.0% to 51.2% observed by the authors who initially proposed the quality index (Dimitriadis and Paddick 2018). Chea et al (2021) did note the superiority of the dedicated SRS platforms could be due to quality index being more favourable to these systems as a consequence of the relatively higher mean dose of each target and lower V12Gy volumes exhibited by these platforms. Unfortunately, a lack of studies involving linac based SRS plans for multiple brain metastases utilising this plan quality index made it difficult to ascertain if the values recorded for the HyperArc plans are to be expected.…”

Whole Brain Irradiation or Stereotactic RadioSurgery for five or more brain metastases (WHOBI-STER): A prospective comparative study of neurocognitive outcomes, level of autonomy in daily activities and quality of life

“…Such an experience was based on the use of Gamma Knife radiosurgery whose excellent conformity index, Paddick index, dose fall-off and gradient index, especially in challenging situations (i.e. irradiation of adjacent or critically located targets [48] , [49] , [50] ), characterize a different dose distribution in healthy brain tissue with respect to the LINAC-based stereotactic technique, thus being able to produce different neurocognitive outcomes [51] . An evaluation of these is therefore useful and should be carried our for both techniques.…”

Radiotherapy in Current Neuro-Oncology: There Is Still Much to Reveal

“…In recent years, a LINAC-based RT technique-namely Volumetric Modulated Arc Therapy (VMAT), which was typically employed for limiting radiationrelated adverse events in extracranial sites [14,15]-has been enhanced with advanced Treatment Planning Systems (TPS) to plan a simultaneous radiation dose delivery to multiple brain metastases with maximal sparing of healthy tissue, similarly to what is achievable with GK [8]. Regarding the therapeutic index, these two stereotactic techniques constantly confront dosimetric challenges, and no clinical study has yet confirmed a clear benefit of the one over the other [16]. CK and GK are irreplaceably useful for RT treatments of extremely challenging targets wrapped around critical structures [17].…”