Feasibility of Proton Beam Therapy as a Rescue Therapy in Heavily Pre-Treated Retinoblastoma Eyes

Commissioning of a novel gantry-less proton therapy system

Purpose

The focus of this article is to describe the configuration, testing, and commissioning of a novel gantry-less synchrotron-based proton therapy (PT) facility.

Materials and methods

The described PT system delivers protons with a water equivalent range between 4 and 38 cm in 1800 energy layers. The fixed beam delivery permits a maximum field size of 28 × 30 cm2. The patient positioning and imaging system includes a six-degree-of-freedom robotic arm, a convertible patient chair, a vertical 4DCT, and an orthogonal 2D X-ray imaging system.

Results

The spot positioning reproducibility was consistent within ±1 mm. The width (σ) of the beam profile at the isocenter was energy dependent and ranged from 2.8 mm to 7.7 mm. Absolute dose reproducibility was measured and deviations were found to be <0.62% for all possible beam scenarios. The built-in dose monitoring system was successfully tested for its ability to generate interlocks under specific conditions (beam spot deviation ≥2 mm, individual spot dose ≥10% or ≥0.25 Gy, spot energy deviation ≥0.5 MeV). The robot positioning exhibited a consistent reproducibility within ±1 mm. All tested scenarios achieved laser-free initial 3D/3D image-guided positioning within ±5 mm. Subsequent 2D/3D positioning showed an accuracy of ±1 mm. A single 2D/3D image registration event corrected positions in all cases. Results of gamma analysis (3%, 3 mm) demonstrated pass rates greater than 95% for head and neck, thorax, abdomen treatment plans.

Conclusions

We report on the performance of a novel single-room gantry-less PT system comprised of a compact synchrotron and an adjustable (from nearly horizontal to almost vertical) patient positioning system. The commissioning results show high accuracy and reproducibility of the main proton beam parameters and the patient positioning system. The new PT facility started patient treatments in March 2023, which were the first in Israel and the Middle Eastern region.

Craniospinal irradiation and/or intraventricular radioimmunotherapy after high-dose chemotherapy and autologous stem cell rescue in patients with CNS retinoblastoma-Safety and outcomes

BACKGROUND

The prognosis for patients with central nervous system (CNS) retinoblastoma (RB) (trilateral or stage 4b metastatic RB) treated with high-dose chemotherapy and autologous stem cell transplant (HDC-ASCT) remains poor. The impact of irradiation when administered as part of upfront therapy post HDC-ASCT on treatment outcomes and survival is unknown.

METHODS

We performed a retrospective review of all patients with CNS RB (seven stage 4b, eight trilateral, one pineal lesion belonging to methylation group RB) who underwent induction chemotherapy with an intent to proceed to HDC-ASCT at two institutions.

RESULTS

Twelve of 16 patients (n = 75%) achieved an objective response to induction chemotherapy, while four patients had progressive/refractory disease; two patients responded to subsequent therapy and proceeded to ASCT, and two patients did not. Seven of 14 patients who underwent HDC-ASCT, received radiotherapy as part of upfront therapy post HDC-ASCT in the form of craniospinal irradiation (CSI) (n = 3), intraventricular radioimmunotherapy (n = 3), or both CSI and intraventricular radioimmunotherapy (n = 1). The Kaplan-Meier estimate of overall survival for these patients was 62.5% at 5 years; no patients developed second malignant neoplasms within the radiation fields. For the seven patients who did not receive radiotherapy, the overall survival was 28.6% at 5 years.

CONCLUSIONS

CSI (23.4 Gy) alone or in conjunction with intraventricular RIT may have clinical utility in eliminating persistent MRD post HDC-ASCT, contributing to improved disease-free survival in patients with CNS RB. This treatment strategy merits evaluation in a prospective, multicenter clinical trial for patients with CNS metastatic RB.

Current Molecular and Clinical Landscape of ATRT - The Link to Future Therapies

ATRT is a highly aggressive and rare pediatric CNS tumor of very young children. Its genetic hallmark is bi-allelic inactivation of SMARCB1 encoding INI1. Rarely SMARCA4 encoding BRG1 is affected. Up to 30% are associated with constitutional heterozygous pathogenic variants in one of the two genes, giving rise to the Rhabdoid-Tumor-Predisposition-Syndromes (RTPS) 1 and 2. Characteristic DNA methylation profiles distinguish ATRT from other SMARCB1-deficient entities. Three distinct subtypes ATRT-MYC, -TYR, and -SHH are on record. ATRT-SHH may be further divided into the subgroups ATRT-SHH1A, -SHH1B, and -SHH2. The cure of ATRT remains challenging, notwithstanding an increasing understanding of molecular pathomechanisms and genetic background. The implementation of multimodal institutional treatment protocols has improved prognosis. Regardless of treatment approaches, clinical risk factors such as age, metastases, and DNA methylation subtype affect survival probability. We provide a critical appraisal of current conventional multimodal regimens and emerging targeted treatment approaches investigated in clinical trials and entity-specific registries. Intense treatment approaches featuring radiotherapy (RT) and high-dose chemotherapy (HDCT) face the difficulty of balancing tumor control and treatment-related toxicity. Current approaches focus on minimizing radiation fields by proton beam therapy or to withhold RT in HDCT-only approaches. Still, a 40-75% relapse rate upon first-line treatment reveals the need for novel treatment strategies in primary and even more in recurrent/refractory (r/r) disease. Among targeted treatments, immune checkpoint inhibitors and epigenetically active agents appear most promising. Success remains limited in single agent approaches. We hypothesize that mechanism-informed combination therapy will enhance response, as the low mutational burden of ATRT may contribute to acquiring resistance to single targeted agents. As DNA methylation group-specific gene expression profiles appear to influence response to distinct agents, the future treatment of ATRT should respect clinical and biological heterogeneity in risk group adjusted treatment protocols.

Special Issue of Cancers: "Retinoblastoma: Current Challenges and Promising New Approaches"

Despite being a rare pediatric cancer arising in the developing retina from red/green cone precursors, retinoblastoma is the most common eye cancer worldwide and occupies an emblematic position in oncology and human genetics for the following reasons:-Historically, the discovery of RB1 and the recessive nature of its mutations led to the prototypic description of anti-oncogenes or tumor suppressor genes [...].

A case of retinoblastoma resulting in phthisis bulbi after proton beam radiation therapy

Purpose

Proton beam radiation therapy (PBRT) is a treatment option for advanced retinoblastoma (RB) resistant to chemotherapy and focal ophthalmic treatment. Here we report a case of RB with phthisis bulbi following PBRT.

Observations

A 16-day-old boy with a family history of RB was referred to our institution. Initial examination revealed an extensive white mass in the right eye and a small tumor near the optic disk of the left eye. The patient was diagnosed with bilateral RB and treated with chemotherapy and focal ophthalmic therapy. The right eye showed shrinkage in the treatment course. The tumor control was not achieved bilaterally, and, therefore, PBRT was performed to preserve the eyes. However, the right eye became significantly phthisical following PBRT and ultimately required enucleation.

Conclusions and importance

PBRT for RB may result in phthisis bulbi. Further investigations of its role and possible complications are warranted.