Intracranial Stereotactic Radiation Therapy With Charged Particle Beams: An Opportunity to Regain the Momentum

Proton therapy for intracranial meningioma: a single-institution retrospective analysis of efficacy, survival and toxicity outcomes

PURPOSE

To report the outcomes of a large series of intracranial meningiomas (IMs) submitted to proton therapy (PT) with curative intent.

METHODS

We conducted a retrospective analysis on all consecutive IM patients treated between 2014 and 2021. The median PT prescription dose was 55.8 Gy relative biological effectiveness (RBE) and 66 GyRBE for benign/radiologically diagnosed and atypical/anaplastic IMs, respectively. Local recurrence-free survival (LRFS), distant recurrence-free survival (DRFS), overall survival (OS), and radionecrosis-free survival (RNFS) were evaluated with the Kaplan-Meier method. Univariable analysis was performed to identify potential prognostic factors for clinical outcomes. Toxicity was reported according to the latest Common Terminology Criteria for Adverse Events (CTCAE) version 5.0.

RESULTS

Overall, 167 patients were included. With a median follow-up of 41 months (range, 6-99), twelve patients (7%) developed tumor local recurrence after a median time of 39 months. The 5-year LRFS was 88% for the entire cohort, with a significant difference between benign/radiologically diagnosed and atypical/anaplastic IMs (98% vs. 47%, p < 0.001); this significant difference was maintained also for the 5-year OS and the 5-year DRFS rates. Patients aged ≤ 56 years reported significantly better outcomes, whereas lower prescription doses and skull base location were associated with better RNFS rates. Two patients experienced G3 acute toxicities (1.2%), and three patients G3 late toxicities (1.8%). There were no G4-G5 adverse events.

CONCLUSION

PT proved to be effective with an acceptable toxicity profile. To the best of our knowledge this is one of the largest series including IM patients submitted to PT.

Enhancing Tissue Equivalence in 7Li Heavy Ion Therapy with MC Algorithm Optimized Polymer-Based Bioinks

The unique physical properties of heavy ion beams, particularly their distinctive depth-dose distribution and sharp lateral dose reduction profiles, have led to their widespread adoption in tumor therapy worldwide. However, the physical properties of heavy ion beams must be investigated to deliver a sufficient dose to tumors without damaging organs at risk. These studies should be performed on phantoms made of biomaterials that closely mimic human tissue. Polymers can serve as soft tissue substitutes and are suitable materials for building radiological phantoms due to their physical, mechanical, biological, and chemical properties. Extensive research, development, and applications of polymeric biomaterials have been encouraged due to these properties. In this study, we investigated the ionization, recoils, phonon release, collision events, and lateral straggle properties of polymeric biomaterials that closely resemble soft tissue using lithium-ion beams and Monte Carlo Transport of Ions in Matter simulation. The results indicated that the Bragg peak position closest to soft tissue was achieved with a 7.3% difference in polymethylmethacrylate, with an average recoils value of 10.5%. Additionally, average values of 33% were observed in collision events and 22.6% in lateral straggle. A significant contribution of this study to the existing literature lies in the exploration of secondary interactions alongside the assessment of linear energy transfer induced by the 7Li beam used for treatment. Furthermore, we analyzed the tissue-equivalent properties of polymer biomaterials using heavy ion beams, taking into account phonon release resulting from ionization, recoils, lateral straggle, and all other interactions. This approach allows for the evaluation of the most suitable polymeric biomaterials for heavy ion therapy while considering the full range of interactions involved.

Radiotherapy of non-tumoral refractory neurological pathologies

Intracranial radiotherapy has been improved, primarily because of the development of stereotactic approaches. While intracranial stereotactic body radiotherapy is mainly indicated for treatment of benign or malignant tumors, this procedure is also effective in the management of other neurological pathologies; it is delivered using GammaKnife® and linear accelerators. Thus, brain arteriovenous malformations in patients who are likely to experience permanent neurological sequelae can be managed by single session intracranial stereotactic body radiotherapy, or radiosurgery, in specific situations, with an advantageous benefit/risk ratio. Radiosurgery can be recommended for patients with disabling symptoms, which are poorly controlled by medication, such as trigeminal neuralgia, and tremors, whether they are essential or secondary to Parkinson's disease. This literature review aims at defining the place of intracranial stereotactic body radiotherapy in the management of patients suffering from non-tumoral refractory neurological pathologies. It is clear that the multidisciplinary collaboration of experienced teams from Neurosurgery, Neurology, Neuroradiology, Radiation Oncology and Medical Physics is needed for the procedures using high precision radiotherapy techniques, which deliver high doses to locations near functional brain areas.

Lower doses to hippocampi and other brain structures for skull-base meningiomas with intensity modulated proton therapy compared to photon therapy

BACKGROUND AND PURPOSE

Radiotherapy of skull-base meningiomas is challenging due to the close proximity of multiple sensitive organs at risk (OARs). This study systematically compared intensity modulated proton therapy (IMPT), non-coplanar volumetric modulated arc therapy (VMAT) and intensity modulated radiotherapy (IMRT) based on automated treatment planning. Differences in OARs sparing, with specific focus on the hippocampi, and low-dose delivery were quantified.

MATERIALS AND METHODS

Twenty patients, target diameter >3 cm, were included. Automated plan generation was used to calculate a VMAT plan with three non-coplanar arcs, an IMRT plan with nine non-coplanar beams with optimized gantry and couch angles, and an IMPT plan with three patient-specific selected non-coplanar beams. A prescription dose of 50.4 GyRBE in 28 fractions was used. The same set of constraints and prioritized objectives was used. All plans were rescaled to the same target coverage. Repeated measures ANOVA was used to assess the statistical significance of differences in OAR dose parameters between planning techniques.

RESULTS

Compared to VMAT and IMRT, IMPT significantly improved dose conformity to the target volume. Consequently, large dose reductions in OARs were observed. With respect to VMAT, the mean dose and D_40% in the bilateral hippocampus were on average reduced by 48% and 74%, respectively (p ≤ 0.005). With IMPT, the mean dose in the normal brain and volumes receiving 20-30 Gy were up to 47% lower (p ≤ 0.01). When comparing IMPT and IMRT, even larger dose differences in those OARs were observed.

CONCLUSION

For skull-base meningiomas IMPT allows for a considerable dose reduction in the hippocampi, normal brain and other OARs compared to both non-coplanar VMAT and IMRT, which may lead to a clinically relevant reduction of late neurocognitive side effects.

Dosimetry and characterization of a 25-MeV proton beam line for preclinical radiobiology research

PURPOSE

With the increase in proton therapy centers, there is a growing need to make progress in preclinical proton radiation biology to give accessible data to medical physicists and practicing radiation oncologists.

METHODS

A cyclotron usually producing radioisotopes with a proton beam at an energy of about 25 MeV after acceleration, was used for radiobiology studies. Depleted silicon surface barrier detectors were used for the beam energy measurement. A complementary metal oxide semiconductor (CMOS) sensor and a plastic scintillator detector were used for fluence measurement, and compared to Geant4 and an in-house analytical dose modeling developed for this purpose. Also, from the energy measurement of each attenuated beam, the dose-averaged linear energy transfer (LET_d ) was calculated with Geant4.

RESULTS

The measured proton beam energy was 24.85 ± 0.14 MeV with an energy straggling of 127 ± 22 keV before scattering and extraction in air. The measured flatness was within ± 2.1% over 9 mm in diameter. A wide range of LET_d is achievable: constant between the entrance and the exit of the cancer cell sample ranging from 2.2 to 8 keV/μm, beyond 20 keV/μm, and an average of 2-5 keV/μm in a scattering spread-out Bragg peak calculated for an example of a 6-mm-thick xenograft tumor.

CONCLUSION

The dosimetry and the characterization of a 25-MeV proton beam line for preclinical radiobiology research was performed by measurements and modeling, demonstrating the feasibility of delivering a proton beam for preclinical in vivo and in vitro studies with LET_d of clinical interest.