Technology insight: Proton beam radiotherapy for treatment in pediatric brain tumors

Insights into Targeted and Stimulus-Responsive Nanocarriers for Brain Cancer Treatment

Brain cancers, especially glioblastoma multiforme, are associated with poor prognosis due to the limited efficacy of current therapies. Nanomedicine has emerged as a versatile technology to treat various diseases, including cancers, and has played an indispensable role in combatting the COVID-19 pandemic as evidenced by the role that lipid nanocarrier-based vaccines have played. The tunability of nanocarrier physicochemical properties -including size, shape, surface chemistry, and drug release kinetics- has resulted in the development of a wide range of nanocarriers for brain cancer treatment. These nanocarriers can improve the pharmacokinetics of drugs, increase blood-brain barrier transfer efficiency, and specifically target brain cancer cells. These unique features would potentially allow for more efficient treatment of brain cancer with fewer side effects and better therapeutic outcomes. This review provides an overview of brain cancers, current therapeutic options, and challenges to efficient brain cancer treatment. The latest advances in nanomedicine strategies are investigated with an emphasis on targeted and stimulus-responsive nanocarriers and their potential for clinical translation.

Extending deterministic transport capabilities for very-high and ultra-high energy electron beams

Focused Very-High Energy Electron (VHEE, 50-300 MeV) and Ultra-High Energy Electron (UHEE, > 300 MeV) beams can accurately target both large and deeply seated human tumors with high sparing properties, while avoiding the spatial requirements and cost of proton and heavy ion facilities. Advanced testing phases are underway at the CLEAR facilities at CERN (Switzerland), NLCTA at Stanford (USA), and SPARC at INFN (Italy), aiming to accelerate the transition to clinical application. Currently, Monte Carlo (MC) transport is the sole paradigm supporting preclinical trials and imminent clinical deployment. In this paper, we propose an alternative: the first extension of the nuclear-reactor deterministic chain NJOY-DRAGON for VHEE and UHEE applications. We have extended the Boltzmann-Fokker-Planck (BFP) multigroup formalism and validated it using standard radio-oncology benchmarks, complex assemblies with a wide range of atomic numbers, and comprehensive irradiation of the entire periodic table. We report that [Formula: see text] of water voxels exhibit a BFP-MC deviation below [Formula: see text] for electron energies under [Formula: see text]. Additionally, we demonstrate that at least [Formula: see text] of voxels of bone, lung, adipose tissue, muscle, soft tissue, tumor, steel, and aluminum meet the same criterion between [Formula: see text] and [Formula: see text]. For water, the thorax, and the breast intra-operative benchmark, typical average BFP-MC deviations of [Formula: see text] and [Formula: see text] were observed at [Formula: see text] and [Formula: see text], respectively. By irradiating the entire periodic table, we observed similar performance between lithium ([Formula: see text]) and cerium ([Formula: see text]). Deficiencies observed between praseodymium ([Formula: see text]) and einsteinium ([Formula: see text]) have been reported, analyzed, and quantified, offering critical insights for the ongoing development of the Evaluated Nuclear Data File mode in NJOY.

A systematic review of pediatric neuropsychological outcomes with proton versus photon radiation therapy: A call for equity in access to treatment

OBJECTIVE

There is increasing interest in the utilization of proton beam radiation therapy (PRT) to treat pediatric brain tumors based upon presumed advantages over traditional photon radiation therapy (XRT). PRT provides more conformal radiation to the tumor with reduced dose to healthy brain parenchyma. Less radiation exposure to brain tissue beyond the tumor is thought to reduce neuropsychological sequelae. This systematic review aimed to provide an overview of published studies comparing neuropsychological outcomes between PRT and XRT.

METHOD

PubMed, PsychINFO, Embase, Web of Science, Scopus, and Cochrane were systematically searched for peer-reviewed published studies that compared neuropsychological outcomes between PRT and XRT in pediatric brain tumor patients.

RESULTS

Eight studies were included. Six of the studies utilized retrospective neuropsychological data; the majority were longitudinal studies (n = 5). XRT was found to result in lower neuropsychological functioning across time. PRT was associated with generally stable neuropsychological functioning across time, with the exception of working memory and processing speed, which showed variable outcomes across studies. However, studies inconsistently included or considered medical and sociodemographic differences between treatment groups, which may have impacted neuropsychological outcomes.

CONCLUSIONS

Despite methodological limitations, including limited baseline neuropsychological evaluations, temporal variability between radiation treatment and first evaluation or initial and follow-up evaluations, and heterogenous samples, there is emerging evidence of sociodemographic inequities in access to PRT. With more institutions dedicating funding towards PRT, there may be the opportunity to objectively evaluate the neuropsychological benefits of patients matched on medical and sociodemographic variables.

Recent Updates on Radiation Therapy for Pediatric Optic Pathway Glioma

Optic pathway glioma (OPG) is a rare tumor located in optic nerve, optic tract, or optic chiasm. Treatment options for OPG include surgery, radiation therapy (RT), and chemotherapy. Although RT may provide favorable long-term outcomes in manner of either adjuvant or salvage aim, chemotherapy-first approach is increasingly performed due to possible late effects of RT. Proton beam RT may allow normal tissue sparing of radiation exposure compared to conventional X-ray treatment. Therefore, proton beam RT is expected to reduce complications from RT. This review discusses the recent updates on oncologic outcomes of OPG, late toxicities following RT, and compares the outcomes between X-ray treatment and proton beam RT.

Cross-translational models of late-onset cognitive sequelae and their treatment in pediatric brain tumor survivors

Pediatric brain tumor treatments have a high success rate, but survivors are at risk of cognitive sequelae that impact long-term quality of life. We summarize recent clinical and animal model research addressing pathogenesis or evaluating candidate interventions for treatment-induced cognitive sequelae. Assayed interventions encompass a broad range of approaches, including modifications to radiotherapy, modulation of immune response, prevention of treatment-induced cell loss or promotion of cell renewal, manipulation of neuronal signaling, and lifestyle/environmental adjustments. We further emphasize the potential of neuroimaging as a key component of cross-translation to contextualize laboratory research within broader clinical findings. This cross-translational approach has the potential to accelerate discovery to improve pediatric cancer survivors' long-term quality of life.

Ionizing Radiation-Induced GDF15 Promotes Angiogenesis in Human Glioblastoma Models by Promoting VEGFA Expression Through p-MAPK1/SP1 Signaling

Glioblastoma multiforme (GBM), the most aggressive cancer type that has a poor prognosis, is characterized by enhanced and aberrant angiogenesis. In addition to surgical resection and chemotherapy, radiotherapy is commonly used to treat GBM. However, radiation-induced angiogenesis in GBM remains unexplored. This study examined the role of radiation-induced growth/differentiation factor-15 (GDF15) in regulating tumor angiogenesis by promoting intercellular cross-talk between brain endothelial cells (ECs) and glioblastoma cells. Radiation promoted GDF15 secretion from human brain microvascular endothelial cells (HBMVECs). Subsequently, GDF15 activated the transcriptional promoter VEGFA in the human glioblastoma cell line U373 through p-MAPK1/SP1 signaling. Upregulation of vascular endothelial growth factor (VEGF) expression in U373 cells resulted in the activation of angiogenic activity in HBMVECs via KDR phosphorylation. Wound healing, tube formation, and invasion assay results revealed that the conditioned medium of recombinant human GDF15 (rhGDF15)-stimulated U373 cell cultures promoted the angiogenic activity of HBMVECs. In the HBMVEC-U373 cell co-culture, GDF15 knockdown mitigated radiation-induced VEGFA upregulation in U373 cells and enhanced angiogenic activity of HBMVECs. Moreover, injecting rhGDF15-stimulated U373 cells into orthotopic brain tumors in mice promoted angiogenesis in the tumors. Thus, radiation-induced GDF15 is essential for the cross-talk between ECs and GBM cells and promotes angiogenesis. These findings indicate that GDF15 is a putative therapeutic target for patients with GBM undergoing radio-chemotherapy.

Radiation Induced Cavernomas in the Treatment of Pediatric Medulloblastoma: Comparative Study Between Proton and Photon Radiation Therapy

Radiation induced cavernomas among children with medulloblastoma are common following external beam radiation (XRT) treatment with either photon or proton beams. However, with the increased utilization of proton beam therapy over the last decade we sought to determine if there was any difference in the development or natural history of these cavernous malformations (CM) or CM-like lesions. We performed a retrospective analysis of 79 patients from 2003 to 2019 who had undergone resection of medulloblastoma and subsequent XRT (30 photon or 49 proton beam therapy). The average age of patients at radiation treatment was 8.7 years old. Average follow up for patients who received photon beam therapy was 105 months compared to 56.8 months for proton beam therapy. A total of 68 patients (86.1%) developed post-radiation CMs, including 26 photon and 42 proton patients (86.7% and 85.7% respectively). The time to cavernoma development was significantly different, with a mean of 40.2 months for photon patients and 18.2 months for proton patients (p = 1.98 x 10^-4). Three patients, one who received photon and two who received proton beam radiation, required surgical resection of a cavernoma. Although CM or CM-like lesions are detected significantly earlier in patients after receiving proton beam therapy, there appears to be no significant difference between the two radiation therapy modalities in the development of significant CM requiring surgical resection or intervention other than continued follow up and surveillance.

A Multi-institutional Comparative Analysis of Proton and Photon Therapy-Induced Hematologic Toxicity in Patients With Medulloblastoma

PURPOSE

This multi-institutional retrospective study sought to examine the hematologic effects of craniospinal irradiation (CSI) in pediatric patients with medulloblastoma using proton or photon therapy.

METHODS AND MATERIALS

Clinical and treatment characteristics were recorded for 97 pediatric patients with medulloblastoma who received CSI without concurrent chemotherapy or with concurrent single-agent vincristine from 2000 to 2017. Groups of 60 and 37 patients underwent treatment with proton-based and photon-based therapy, respectively. Overall survival was determined by Kaplan-Meier curves with log-rank test. Comparisons of blood counts at each timepoint were conducted using multiple t tests with Bonferroni corrections. Univariate and multivariate analyses of time to grade ≥3 hematologic toxicity were performed with Cox regression analyses.

RESULTS

Median age of patients receiving proton and photon CSI was 7.5 years (range, 3.5-22.7 years) and 9.9 years (range, 3.6-19.5 years), respectively. Most patients had a diagnosis of standard risk medulloblastoma, with 86.7% and 89.2% for the proton and photon cohorts, respectively. Median total dose to involved field or whole posterior fossa was 54.0 Gy/Gy relative biological effectiveness (RBE) and median CSI dose was 23.4 Gy/Gy(RBE) (range, 18-36 Gy/Gy[RBE]) for both cohorts. Counts were significantly higher in the proton cohort compared with the photon cohort in weeks 3 to 6 of radiation therapy (RT). Although white blood cell counts did not differ between the 2 cohorts, patients receiving proton RT had significantly higher lymphocyte counts throughout the RT course. Similar results were observed when excluding patients who received vertebral body sparing proton RT or limiting to those receiving 23.4 Gy. Only photon therapy was associated with decreased time to grade ≥3 hematologic toxicity on univariate and multivariable analyses. No difference in overall survival was observed, and lymphopenia did not predict survival.

CONCLUSIONS

Patients who receive CSI using proton therapy experience significantly decreased hematologic toxicity compared with those receiving photon therapy.

Addressing the Biochemical Foundations of a Glucose-Based "Trojan Horse"-Strategy to Boron Neutron Capture Therapy: From Chemical Synthesis to In Vitro Assessment

Boron neutron capture therapy (BNCT) for cancer is on the rise worldwide due to recent developments of in-hospital neutron accelerators which are expected to revolutionize patient treatments. There is an urgent need for improved boron delivery agents, and herein we have focused on studying the biochemical foundations upon which a successful GLUT1-targeting strategy to BNCT could be based. By combining synthesis and molecular modeling with affinity and cytotoxicity studies, we unravel the mechanisms behind the considerable potential of appropriately designed glucoconjugates as boron delivery agents for BNCT. In addition to addressing the biochemical premises of the approach in detail, we report on a hit glucoconjugate which displays good cytocompatibility, aqueous solubility, high transporter affinity, and, crucially, an exceptional boron delivery capacity in the in vitro assessment thereby pointing toward the significant potential embedded in this approach.

Prospective, longitudinal comparison of neurocognitive change in pediatric brain tumor patients treated with proton radiotherapy versus surgery only

BACKGROUND

Proton radiotherapy (PRT) reduces the volume of normal tissue receiving radiation dose, which may lead to better neurocognitive outcomes. We examined change in neurocognitive scores over time in pediatric brain tumor patients treated with proton craniospinal irradiation (CSI), proton focal RT, or surgery only.

METHODS

Patients received annual neurocognitive evaluations for up to 6 years. We examined Full Scale IQ (FSIQ), Verbal Comprehension Index (VCI), Perceptual Reasoning Index (PRI), Working Memory Index (WMI), and Processing Speed Index (PSI) scores. General linear mixed models examined change in scores over time by treatment group, adjusting for significant covariates.

RESULTS

Scores from 93 patients treated between 2012 and 2017 (22 proton CSI, 31 proton focal, and 40 surgery only) were examined. Treatment groups were similar on gender (51.6% male), age at treatment (median = 9.7 y), and length of follow-up (median = 2.9 y). The surgery only group had proportionately more gliomas (P < 0.001), and the proton CSI group had more infratentorial tumors (P = 0.001) and higher total RT dose (P = 0.004). The proton focal and surgery only groups exhibited stable neurocognitive scores over time across all indexes (all P > 0.05). In the proton CSI group, WMI, PSI, and FSIQ scores declined significantly (P = 0.036, 0.004, and 0.017, respectively), while VCI and PRI scores were stable (all P > 0.05).

CONCLUSIONS

Focal PRT was associated with stable neurocognitive functioning into survivorship. Outcomes were similar whether patients received focal PRT or no radiotherapy, even in neurocognitive domains known to be particularly radiosensitive. Proton CSI emerged as a neurocognitive risk factor, consistent with photon outcomes research.

Bragg Peak Localization with Piezoelectric Sensors for Proton Therapy Treatment

A full chain simulation of the acoustic hadrontherapy monitoring for brain tumours is presented in this work. For the study, a proton beam of 100 MeV is considered. In the first stage, Geant4 is used to simulate the energy deposition and to study the behaviour of the Bragg peak. The energy deposition in the medium produces local heating that can be considered instantaneous with respect to the hydrodynamic time scale producing a sound pressure wave. The resulting thermoacoustic signal has been subsequently obtained by solving the thermoacoustic equation. The acoustic propagation has been simulated by FEM methods in the brain and the skull, where a set of piezoelectric sensors are placed. Last, the final received signals in the sensors have been processed in order to reconstruct the position of the thermal source and, thus, to determine the feasibility and accuracy of acoustic beam monitoring in hadrontherapy.

The role of proton therapy in pediatric malignancies: Recent advances and future directions

Proton radiotherapy has promised an advantage in safely treating pediatric malignancies with an increased capability to spare normal tissues, reducing the risk of both acute and late toxicity. The past decade has seen the proliferation of more than 30 proton facilities in the United States, with increased capacity to provide access to approximately 3,000 children per year who will require radiotherapy for their disease. We provide a review of the initial efforts to describe outcomes after proton therapy across the common pediatric disease sites. We discuss the main attempts to assess comparative efficacy between proton and photon radiotherapy concerning toxicity. We also discuss recent efforts of multi-institutional registries aimed at accelerating research to better define the optimal treatment paradigm for children requiring radiotherapy for cure.

Superior Intellectual Outcomes After Proton Radiotherapy Compared With Photon Radiotherapy for Pediatric Medulloblastoma

PURPOSE

Proton radiotherapy (PRT) may lessen the neuropsychological risk traditionally associated with cranial radiotherapy for the treatment of pediatric brain tumors by reducing the dose to normal tissue compared with that of photon radiotherapy (XRT). We examined the change in intellectual scores over time in patients with pediatric medulloblastoma treated with craniospinal PRT versus XRT.

METHODS

Intelligence test scores were obtained for a sample of pediatric patients treated between 2007 and 2018 on the same medulloblastoma protocols that differed only in radiotherapy modality (PRT v XRT). Growth curve analyses compared change in scores over time since diagnosis between groups.

RESULTS

Longitudinal intelligence data from 79 patients (37 PRT, 42 XRT) were examined. Groups were similar on most demographic/clinical variables, including sex (67.1% male), age at diagnosis (mean, 8.6 years), craniospinal irradiation dose (median, 23.4 Gy), length of follow-up (mean, 4.3 years), and parental education (mean, 14.3 years). Boost dose (P < .001) and boost margin (P = .001) differed between groups. Adjusting for covariates, the PRT group exhibited superior long-term outcomes in global intelligence quotient (IQ), perceptual reasoning, and working memory compared with the XRT group (all P < .05). The XRT group exhibited a significant decline in global IQ, working memory, and processing speed (all P < .05). The PRT group exhibited stable scores over time in all domains with the exception of processing speed (P = .003).

CONCLUSION

To our knowledge, this is the first study to compare intellectual trajectories between pediatric patients treated for medulloblastoma with PRT versus those treated with XRT on comparable, contemporary protocols. PRT was associated with more favorable intellectual outcomes in most domains compared with XRT, although processing speed emerged as a vulnerable domain for both groups. This study provides the strongest evidence to date of an intellectual sparing advantage with PRT in the treatment of pediatric medulloblastoma.

Improving dosimetric outcome for hippocampus and cochlea sparing whole brain radiotherapy using spot-scanning proton arc therapy

This feasibility study shows that Spot-scanning Proton Arc therapy (SPArc) is able to significantly reduce the dose to the hippocampus and cochlea compared to both Volumetric Modulated Arc Photon Therapy (VMAT) and the robust optimized Intensity Modulated Proton Therapy (ro-IMPT) plans in whole brain radiotherapy. Furthermore, SPArc not only improves plan robustness but could potentially deliver a treatment as efficient as ro-IMPT when proton system's energy layer switch time is less than 1 s.

Neurocognitive Outcomes and Interventions in Long-Term Survivors of Childhood Cancer

Recent research has demonstrated that survivors of childhood cancer are at risk for a myriad of late effects that affect physical and mental quality of life. We discuss the patterns and prevalence of neurocognitive problems commonly experienced by survivors of CNS tumors and acute lymphoblastic leukemia, the two most commonly researched cancer diagnoses. Research documenting the direct effects of tumor location and treatment type and intensity is presented, and patient characteristics that moderate outcomes (eg, age at diagnosis and sex) are discussed. Potential biologic mechanisms of neurotoxic treatment exposures, such as cranial irradiation and intrathecal and high-dose antimetabolite chemotherapy, are reviewed. Genetic, brain imaging, and neurochemical biomarkers of neurocognitive impairment are discussed. Long-term survivors of childhood cancer are also at risk for physical morbidity (eg, cardiac, pulmonary, endocrine) and problems with health behaviors (eg, sleep); research is reviewed that demonstrates these health problems contribute to neurocognitive impairment in survivors with or without exposure to neurotoxic therapies. We conclude this review with a discussion of literature supporting specific interventions that may be beneficial in the treatment of survivors who already experience neurocognitive impairment, as well as in the prevention of impairment manifestation.

The role of proton beam therapy in central neurocytoma: A single-institution experience

PURPOSE

Central neurocytomas (CNs) are rare World Health Organization grade II tumors managed with surgery and radiation therapy. We report our experience in managing CN with proton beam therapy (PBT) when radiation therapy was used.

METHODS AND MATERIALS

We identified 61 patients with pathologically diagnosed CN treated at our institution between 1996 and 2016, of which 24 met inclusion criteria. Patient, tumor, and treatment characteristics are reported in context of progression-free survival and treatment-related adverse events.

RESULTS

Of 24 patients identified, median age at diagnosis was 21 years (range, 14-60). Median maximal tumor diameter was 4.5 cm (range, 1.4-6.8). Eighteen (75%) patients underwent upfront surgery alone. Sixteen (67%) patients received adjuvant or salvage PBT at a median dose of 54 Gy (relative biological effectiveness). Median follow-up was 56 months. Median progression-free survival (PFS) was 61 months. Eleven patients had disease progression with median time to progression of 22 months. Of the 5 patients with gross total resection, 4 experienced local recurrence and had MIB-1 >4% (range, 4.5-30). There was improved PFS with addition of PBT to definitive surgery (log-rank, P = .06); there was no disease progression to date. In patients who experienced disease recurrence/progression, MIB-1 <4% was associated with improved PFS (log-rank, P = .007). All patients tolerated PBT well with toxicities typical for cranial irradiation and with no grade 3+ toxicities.

CONCLUSION

In our cohort, CN with elevated MIB-1 index were at increased risk for disease progression. However, adjuvant radiation therapy appears to effectively prevent failure. PBT toxicities appear to be comparable to if not less than published photon experiences.

Factors influencing risk-based care of the childhood cancer survivor in the 21st century

The population of adult survivors of childhood cancer continues to grow as survival rates improve. Although it is well established that these survivors experience various complications and comorbidities related to their malignancy and treatment, this risk is modified by many factors that are not directly linked to their cancer history. Research evaluating the influence of patient-specific demographic and genetic factors, premorbid and comorbid conditions, health behaviors, and aging has identified additional risk factors that influence cancer treatment-related toxicity and possible targets for intervention in this population. Furthermore, although current long-term follow-up guidelines comprehensively address specific therapy-related risks and provide screening recommendations, the risk profile of the population continues to evolve with ongoing modification of treatment strategies and the emergence of novel therapeutics. To address the multifactorial modifiers of cancer treatment-related health risk and evolving treatment approaches, a patient-centered and risk-adapted approach to care that often requires a multidisciplinary team approach, including medical and behavioral providers, is necessary for this population. CA Cancer J Clin 2018;68:133-152. © 2018 American Cancer Society.

Executive functioning, academic skills, and quality of life in pediatric patients with brain tumors post-proton radiation therapy

Radiation therapy (RT) is integral in the treatment of pediatric brain tumors; however, photon RT (XRT) often results in intellectual decline, executive functioning (EF) deficits, academic underachievement/failure, and lower health-related quality of life (HRQoL). Proton RT (PRT) provides more targeted therapy, minimizing damage to the developing brain, yet few studies have examined its neuropsychological effects. This study investigated the role of EF in academic skills and HRQoL in a sample of children treated with PRT. A mediation model was proposed in which academic skills mediated relations between aspects of EF and school-based HRQoL (sHRQoL). Sixty-five children (x̅_age = 12.4; 43.9% male) treated with PRT completed follow-up neuropsychological testing as part of routine care. Measures included assessment of intellectual functioning, EF, attention, and academic skills (reading, math, spelling). Parents reported on children's EF and attention problems. sHRQoL was assessed via child self-report. Children who underwent PRT demonstrated relatively intact intelligence, academics, attention, EF, and sHRQoL, but were at risk for reduced processing speed. Poorer working memory and processing speed were related to lower sHRQoL. Better EF and faster processing speed were associated with better academic skills, which were linked to higher sHRQoL. Better working memory was associated with better math performance, which was linked to higher sHRQoL; this relationship did not hold for reading or spelling. Results highlight the importance of EF skills in academic performance and sHRQoL, and the need for routine screening of EF deficits and proactive supports. Supports may include cognitive rehabilitation and in-class accommodations. Overall, results compare favorably to XRT outcomes reported in the literature.

Effects of vertebral-body-sparing proton craniospinal irradiation on the spine of young pediatric patients with medulloblastoma

Purpose

To investigate the long-term effects of vertebral-body-sparing proton craniospinal irradiation (CSI) on the spine of young patients with medulloblastoma.

Methods and materials

Six children between the ages of 3 and 5 years with medulloblastoma were treated with vertebral-body-sparing proton CSI after maximal safe resection. Radiation therapy was delivered in the supine position with posterior beams targeting the craniospinal axis, and the proton beam was stopped anterior to the thecal sac. Patients were treated with a dose of either 23.4 Gy or 36 Gy to the craniospinal axis followed by a boost to the posterior fossa and any metastatic lesions. Chemotherapy varied by protocol. Radiographic effects on the spine were evaluated with serial imaging, either with magnetic resonance imaging scans or plain film using Cobb angle calculations, the presence of thoracic lordosis, lumbar vertebral body-to-disc height ratios, and anterior-posterior height ratios. Clinical outcomes were evaluated by patient/family interview and medical chart review.

Results

Overall survival and disease free survival were 83% (5/6) at follow-up. Median clinical and radiographic follow-up were 13.6 years and 12.3 years, respectively. Two patients were clinically diagnosed with scoliosis and treated conservatively. At the time of follow-up, no patients had experienced chronic back pain or required spine surgery. No patients were identified to have thoracic lordosis. Diminished growth of the posterior portions of vertebral bodies was identified in all patients, with an average posterior to anterior ratio of 0.88, which was accompanied by compensatory hypertrophy of the posterior intervertebral discs.

Conclusion

Vertebral-body-sparing CSI with proton beam did not appear to cause increased severe spinal abnormalities in patients treated at our institution. This approach could be considered in future clinical trials in an effort to reduce toxicity and the risk of secondary malignancy and to improve adult height.

Simulation of positron emitters for monitoring of dose distribution in proton therapy

AIM

The purpose of this work was to estimate the dependency between the produced positron emitters and the proton dose distribution as well as the dependency between points of annihilation and the proton dose distribution.

BACKGROUND

One important feature of proton therapy is that, through the non-elastic nuclear interaction of protons with the target nuclei such as ¹²C, ¹⁴N and ¹⁶O, it produces a small number of positron-emitting radioisotopes along the beam-path. These radioisotopes allow imaging the Bragg peak position which is related to the proton dose distribution by using positron emission tomography.

METHODS

In this study, the GEANT4 toolkit was applied to simulate a soft and bone tissue phantom in proton therapy to evaluate the positron emitter productions and the actual annihilation points of β⁺. Simulation was done by delivering pencil and spread-out Bragg peak (SOBP) proton beams.

RESULTS

The findings showed that (¹⁵O, ¹¹C, ¹³N) and (¹¹C, ¹⁵O, ³⁸K, ³⁰P, ³⁹Ca, ¹³N) are the most suitable positron emitters in the soft and bone tissue respectively. By increasing the proton energy, the distance between the peak of annihilation profile and Bragg peak is almost constant, but the distance between the Bragg peak position and positron annihilation point peak in bone tissue is smaller than that in the soft tissue. The peak of β⁺ activity distribution becomes sharper at higher proton energies.

CONCLUSIONS

There is a good relationship between the positions of positron annihilation profile and positron emitters radioactive decay. Also, GEANT4 is a powerful and suitable tool for simulation of nuclear interactions and positron emitters in tissues.

Comparing Intelligence Quotient Change After Treatment With Proton Versus Photon Radiation Therapy for Pediatric Brain Tumors

PURPOSE

Compared with photon radiation (XRT), proton beam radiation therapy (PBRT) reduces dose to normal tissues, which may lead to better neurocognitive outcomes. We compared change in intelligence quotient (IQ) over time in pediatric patients with brain tumors treated with PBRT versus XRT.

PATIENTS AND METHODS

IQ scores were available for 150 patients (60 had received XRT, 90 had received PBRT). Linear mixed models examined change in IQ over time since radiation therapy (RT) by RT group, controlling for demographic/clinical characteristics. Craniospinal and focal RT subgroups were also examined.

RESULTS

In the PBRT group, no change in IQ over time was identified (P = .130), whereas in the XRT group, IQ declined by 1.1 points per year (P = .004). IQ slopes did not differ between groups (P = .509). IQ was lower in the XRT group (by 8.7 points) versus the PBRT group (P = .011). In the craniospinal subgroup, IQ remained stable in both the PBRT (P = .203) and XRT groups (P = .060), and IQ slopes did not differ (P = .890). IQ was lower in the XRT group (by 12.5 points) versus the PBRT group (P = .004). In the focal subgroup, IQ scores remained stable in the PBRT group (P = .401) but declined significantly in the XRT group by 1.57 points per year (P = .026). IQ slopes did not differ between groups (P = .342).

CONCLUSION

PBRT was not associated with IQ decline or impairment, yet IQ slopes did not differ between the PBRT and XRT groups. It remains unclear if PBRT results in clinically meaningful cognitive sparing that significantly exceeds that of modern XRT protocols. Additional long-term data are needed to fully understand the neurocognitive impact of PBRT in survivors of pediatric brain tumors.

Impact of Spot Size and Beam-Shaping Devices on the Treatment Plan Quality for Pencil Beam Scanning Proton Therapy

PURPOSE

This study aimed to assess the clinical impact of spot size and the addition of apertures and range compensators on the treatment quality of pencil beam scanning (PBS) proton therapy and to define when PBS could improve on passive scattering proton therapy (PSPT).

METHODS AND MATERIALS

The patient cohort included 14 pediatric patients treated with PSPT. Six PBS plans were created and optimized for each patient using 3 spot sizes (∼12-, 5.4-, and 2.5-mm median sigma at isocenter for 90- to 230-MeV range) and adding apertures and compensators to plans with the 2 larger spots. Conformity and homogeneity indices, dose-volume histogram parameters, equivalent uniform dose (EUD), normal tissue complication probability (NTCP), and integral dose were quantified and compared with the respective PSPT plans.

RESULTS

The results clearly indicated that PBS with the largest spots does not necessarily offer a dosimetric or clinical advantage over PSPT. With comparable target coverage, the mean dose (Dmean) to healthy organs was on average 6.3% larger than PSPT when using this spot size. However, adding apertures to plans with large spots improved the treatment quality by decreasing the average Dmean and EUD by up to 8.6% and 3.2% of the prescribed dose, respectively. Decreasing the spot size further improved all plans, lowering the average Dmean and EUD by up to 11.6% and 10.9% compared with PSPT, respectively, and eliminated the need for beam-shaping devices. The NTCP decreased with spot size and addition of apertures, with maximum reduction of 5.4% relative to PSPT.

CONCLUSIONS

The added benefit of using PBS strongly depends on the delivery configurations. Facilities limited to large spot sizes (>∼8 mm median sigma at isocenter) are recommended to use apertures to reduce treatment-related toxicities, at least for complex and/or small tumors.

Spontaneous Resolution of Radiotherapy-induced Craniopharyngioma Cyst

Craniopharyngioma cyst enlargement after surgery and radiation therapy is often presumed to represent a treatment failure, instigating further management strategies. We present an eight-year-old girl with a small intrasellar residuum post-resection who then developed cystic enlargement post-radiotherapy. With close surveillance, the cyst spontaneously resolved.

Proton Beam Therapy for Non-Small Cell Lung Cancer: Current Clinical Evidence and Future Directions

Lung cancer is the leading cancer cause of death in the United States. Radiotherapy is an essential component of the definitive treatment of early-stage and locally-advanced lung cancer, and the palliative treatment of metastatic lung cancer. Proton beam therapy (PBT), through its characteristic Bragg peak, has the potential to decrease the toxicity of radiotherapy, and, subsequently improve the therapeutic ratio. Herein, we provide a primer on the physics of proton beam therapy for lung cancer, present the existing data in early-stage and locally-advanced non-small cell lung cancer (NSCLC), as well as in special situations such as re-irradiation and post-operative radiation therapy. We then present the technical challenges, such as anatomic changes and motion management, and future directions for PBT in lung cancer, including pencil beam scanning.

Dosimetric feasibility of real-time MRI-guided proton therapy

PURPOSE

Magnetic resonance imaging (MRI) is a prime candidate for image-guided radiotherapy. This study was designed to assess the feasibility of real-time MRI-guided proton therapy by quantifying the dosimetric effects induced by the magnetic field in patients' plans and identifying the associated clinical consequences.

METHODS

Monte Carlo dose calculation was performed for nine patients of various treatment sites (lung, liver, prostate, brain, skull-base, and spine) and tissue homogeneities, in the presence of 0.5 and 1.5 T magnetic fields. Dose volume histogram (DVH) parameters such as D95, D5, and V20 as well as equivalent uniform dose were compared for the target and organs at risk, before and after applying the magnetic field. The authors further assessed whether the plans affected by clinically relevant dose distortions could be corrected independent of the planning system.

RESULTS

By comparing the resulting dose distributions and analyzing the respective DVHs, it was determined that despite the observed lateral beam deflection, for magnetic fields of up to 0.5 T, neither was the target coverage jeopardized nor was the dose to the nearby organs increased in all cases except for prostate. However, for a 1.5 T magnetic field, the dose distortions were more pronounced and of clinical concern in all cases except for spine. In such circumstances, the target was severely underdosed, as indicated by a decrease in D95 of up to 41% of the prescribed dose compared to the nominal situation (no magnetic field). Sites such as liver and spine were less affected due to higher tissue homogeneity, typically smaller beam range, and the choice of beam directions. Simulations revealed that small modifications to certain plan parameters such as beam isocenter (up to 19 mm) and gantry angle (up to 10°) are sufficient to compensate for the magnetic field-induced dose disturbances. The authors' observations indicate that the degree of required corrections strongly depends on the beam range and direction relative to the magnetic field. This method was also applicable to more heterogeneous scenarios such as skull-base tumors.

CONCLUSIONS

This study confirmed the dosimetric feasibility of real-time MRI-guided proton therapy and delivering a clinically acceptable dose to patients with various tumor locations within magnetic fields of up to 1.5 T. This work could serve as a guide and encouragement for further efforts toward clinical implementation of hybrid MRI-proton gantry systems.

Antiproton induced DNA damage: proton like in flight, carbon-ion like near rest

Biological validation of new radiotherapy modalities is essential to understand their therapeutic potential. Antiprotons have been proposed for cancer therapy due to enhanced dose deposition provided by antiproton-nucleon annihilation. We assessed cellular DNA damage and relative biological effectiveness (RBE) of a clinically relevant antiproton beam. Despite a modest LET (~19 keV/μm), antiproton spread out Bragg peak (SOBP) irradiation caused significant residual γ-H2AX foci compared to X-ray, proton and antiproton plateau irradiation. RBE of ~1.48 in the SOBP and ~1 in the plateau were measured and used for a qualitative effective dose curve comparison with proton and carbon-ions. Foci in the antiproton SOBP were larger and more structured compared to X-rays, protons and carbon-ions. This is likely due to overlapping particle tracks near the annihilation vertex, creating spatially correlated DNA lesions. No biological effects were observed at 28–42 mm away from the primary beam suggesting minimal risk from long-range secondary particles.

A dosimetric comparison of intensity-modulated proton therapy optimization techniques for pediatric craniopharyngiomas: a clinical case study

BACKGROUND

To evaluate the dosimetric characteristics of intensity-modulated proton therapy (IMPT) optimization techniques and pencil-beam scanning (PBS) nozzle designs on pediatric craniopharyngiomas.

PROCEDURE

We compared a double-scatter (DS) plan with IMPT plans using single-field uniform dose (SFUD) optimization or multi-field optimization (MFO) and different PBS nozzles. The clinical impacts of SFUD versus MFO, range shifters, and two different PBS nozzles were compared. For target coverage assessment, the conformity index and inhomogeneity coefficient were evaluated.

RESULTS

Although both proton therapy techniques achieved adequate target coverage, IMPT achieved a better conformity index of 0.78 versus 0.60 for DS. For the inhomogeneity coefficient, IMPT with MFO performed better than using SFUD or DS. MFO with the dedicated nozzle (MFO-DN) achieved the best result of 0.023, as compared to values of 0.03 or higher for the other plans. IMPT achieved lower doses to the normal tissues, as compared to DS; MFO-DN had the best results. The DN provided the best beam-spot characteristics and the sharpest lateral penumbra. MFO reduced the need for range shifters.

CONCLUSIONS

As compared to DS proton therapy for pediatric craniopharyngiomas, IMPT achieved significantly better target coverage and dose sparing of normal tissue. Nozzle designs that provided small beam spots and sharp lateral penumbra allowed for better target coverage and reduced dose to normal tissue. In the case of shallow targets, MFO, in contrast to SFUD, required minimal use of range shifters, which preserved the penumbra and the dosimetric advantage. MFO-DN proved to be the optimal technique for IMPT.

Definitive treatment of leptomeningeal spinal metastases in children

BACKGROUND

Uniquely in children, the existence of leptomeningeal spinal metastases does not confer a uniformly grave prognosis. Although the radiation tolerance of the spinal cord is of significant concern in these cases, the chemo- and radiosensitivity of these lesions argues for an aggressive approach where possible.

METHODS

The records of the Indiana University Health Proton Therapy Center were reviewed for patients undergoing proton beam therapy with curative intent for LSM between January 1, 2004 and July 7, 2012. Patients with microscopic disease only on LP were not included. Particulars of therapy, including dose, field sizes, toxicities, and outcomes were collated.

RESULTS

Twenty-two children received therapy as described, of median age 5 years (range 1.1-17.1). Patients had medulloblastoma (n = 9), ATRT (n = 4), ependymoma, and PNET (n = 3 each). Five lesions (23%) were chemo-recurrent, though no patient had prior radiation to the spine. Median follow-up was 14 months (range 4-33) for all living patients. Fifteen (68%) children continued to have local control at last follow-up visit. Median dose was 37.8 Gy (range 21.6-54 Gy). Eight patients with chemo-recurrent disease or diffuse cord seeding did poorly, with local control and overall survival achieved in four. The 12-month overall survival was 68% with grade 1 skin erythema as the most frequent toxicity.

CONCLUSIONS

We describe a cohort of LSM patients treated with RT with definitive intent, and the only available data from the proton environment. Durable response is possible for these children in over two-thirds of cases. Significant toxicity was infrequent using proton radiotherapy and these fractionation schemes.

Evaluating the effect of therapeutic stem cells on TRAIL resistant and sensitive medulloblastomas

Mesenchymal stem cells (MSC) are emerging as novel cell-based delivery agents; however, a thorough investigation addressing their therapeutic potential in medulloblastomas (MB) has not been explored to date. In this study, we engineered human MSC to express a potent and secretable variant of a tumor specific agent, tumor necrosis factor-apoptosis-inducing ligand (S-TRAIL) and assessed the ability of MSC-S-TRAIL mediated MB killing alone or in combination with a small molecule inhibitor of histone-deacetylase, MS-275, in TRAIL-sensitive and -resistant MB in vitro and in vivo. We show that TRAIL sensitivity/resistance correlates with the expression of its cognate death receptor (DR)5 and MSC-S-TRAIL induces caspase-3 mediated apoptosis in TRAIL-sensitive MB lines. In TRAIL-resistant MB, we show upregulation of DR4/5 levels when pre-treated with MS-275 and a subsequent sensitization to MSC-S-TRAIL mediated apoptosis. Using intracranially implanted MB and MSC lines engineered with different combinations of fluorescent and bioluminescent proteins, we show that MSC-S-TRAIL has significant anti-tumor effects in mice bearing TRAIL-sensitive and MS-275 pre-treated TRAIL-resistant MBs. To our knowledge, this is the first study that explores the use of human MSC as MB-targeting therapeutic-vehicles in vivo in TRAIL-sensitive and resistant tumors, and has implications for developing effective therapies for patients with medulloblastomas.

Risk of second cancers after photon and proton radiotherapy: a review of the data

Control rates for pediatric and adult malignancies are now approximately 80 and 60%, respectively, due to dramatic improvements in surgery, chemotherapy, and radiotherapy. However, radiotherapy is responsible for many of the adverse late effects of treatment, which is now well documented in the literature. The most serious and life threatening side effect of radiotherapy that affects both children and adults is radiation-induced second primary cancers.

Imaging changes in very young children with brain tumors treated with proton therapy and chemotherapy

SUMMARY

PT promises to reduce side effects in children with brain tumors by sparing normal tissue compared with 3D conformal or intensity-modulated radiation therapy. Information is lacking about the combined effects of PT and chemotherapy in young children. We describe imaging changes in 8 very young children with localized brain tumors who received PT after chemotherapy. Mostly transient signal abnormalities and enhancement in brain parenchyma were observed by serial MR imaging, which were consistent with radiation-induced effects on normal-appearing tissue. Correlation with PT planning data revealed that the areas of imaging abnormality were located within or adjacent to the volume that received the highest radiation dose. Radiologists should be aware of these findings in children who receive PT after chemotherapy. In this report, we describe the time course of these PT-related imaging findings and correlate them with treatment and clinical outcomes.

Pituitary hormone dysfunction after proton beam radiation therapy in children with brain tumors

OBJECTIVE

To characterize endocrine dysfunction in pediatric patients with brain tumors who received proton beam (PB) radiation therapy and to compare those treated with PB radiotherapy only versus combined conventional and PB irradiation.

METHODS

A retrospective review of medical records of patients ≤18 years of age who received PB radiation therapy for a brain tumor between 2000 and 2008 was performed. Variables analyzed included patient demographics, tumor type, therapeutic modalities, radiation doses, and types and timing of endocrine dysfunction.

RESULTS

Thirty-eight patients were identified, of whom 31 (19 boys and 12 girls; mean age, 11.9 ± 3.3 years) had undergone endocrine evaluation. Of these patients, 19 received PB radiotherapy only and 12 received conventional plus PB irradiation. Before irradiation, a cranial surgical procedure was performed in 28 study subjects, and 22 received chemotherapy. The mean duration of follow-up after radiation therapy was 1.8 ± 0.8 years. Nine patients (47%) in the PB only group and 4 (33%) in the conventional plus PB group developed endocrine dysfunction (no significant difference) after cranial irradiation. Children with endocrine sequelae treated with PB irradiation alone received fewer cobalt gray equivalents than those treated with conventional plus PB irradiation (5,384 ± 268 versus 5,775 ± 226, respectively; P<.02), and pituitary hormone deficiencies were detected later during follow-up in those who received PB radiotherapy only versus conventional plus PB irradiation (1.17 ± 0.4 years versus 0.33 ± 0.11 year, respectively; P<.01).

CONCLUSION

A high rate of endocrine sequelae was seen in our study. Children with brain tumors treated with conventional plus PB irradiation developed endocrine dysfunction faster and received a higher radiation dose than those receiving PB radiotherapy only. Prior surgical treatment and chemotherapy were additional risk factors. Large prospective studies are needed to evaluate further the incidence of endocrine sequelae after PB irradiation in children.

Atypical teratoid/rhabdoid tumors in adults: a case report and treatment-focused review

Atypical teratoid/rhabdoid tumor is predominantly a childhood tumor and has only been rarely reported in adults; therefore, treatment regimens are often extrapolated from the pediatric experience. Typically, children are treated with craniospinal radiation therapy which is often followed by systemic chemotherapy. Employing pediatric regimens to treat this tumor in adult patients poses a particular risk for myelosuppression, as the prescribed doses in pediatric protocols exceed those tolerated by adults, and conventional craniospinal radiation can be associated with prolonged myelotoxicity and a depletion of the bone marrow reserve in vertebrae of adults. Here we present a case of a woman with a pineal region atypical teratoid/rhabdoid tumor, an unusual adult cancer presenting in an atypical location. This is followed by a review of the disease in adult patients with an emphasis on treatment and suggestions to minimize myelotoxicity.

Assessing the risk of second malignancies after modern radiotherapy

Recent advances in radiotherapy have enabled the use of different types of particles, such as protons and heavy ions, as well as refinements to the treatment of tumours with standard sources (photons). However, the risk of second cancers arising in long-term survivors continues to be a problem. The long-term risks from treatments such as particle therapy have not yet been determined and are unlikely to become apparent for many years. Therefore, there is a need to develop risk assessments based on our current knowledge of radiation-induced carcinogenesis.

Auditory late effects of childhood cancer therapy: a report from the Children's Oncology Group

Children treated for malignancies may be at risk for early- or delayed-onset hearing loss that can affect learning, communication, school performance, social interaction, and overall quality of life. Survivors at particular risk include those treated with platinum compounds (cisplatin and/or carboplatin) for neuroblastoma, hepatoblastoma, osteosarcoma, or germ-cell tumors and/or those treated with radiation that affects the ear at doses of >30 Gy for pediatric head and neck tumors. The aims of the Auditory/Hearing Late Effects Task Force of the Children's Oncology Group in this report were to (1) review ototoxicity resulting from childhood cancer therapy including platinum compounds (cisplatin and carboplatin) and radiation, (2) describe briefly cochlear pathophysiology and genetics of cisplatin-related hearing loss, (3) explain the impact of hearing loss resulting from chemotherapy and radiation, and (4) offer recommendations regarding evaluation and management of pediatric patients who are at risk for treatment-related hearing loss. A questionnaire is included as a tool to assist pediatricians in assessment.

Comparing plaque brachytherapy and proton therapy for choroidal melanoma: a review of the literature

The aims of conservative treatment in patients with ocular melanoma are globe retention, good visual acuity (VA) and local control. Two well-established radiation conservative treatment options are proton beam radiotherapy and episcleral plaque brachytherapy (EPB). Patients who receive treatment with either of these options will experience some degree of radiation-related ocular complications and poor VA. The purpose of this review of the literature is to establish whether there is a significant clinical difference in normal tissue morbidity and local tumour control between proton therapy and EPB, and whether this difference can justify the purchase and implementation of additional proton therapy facilities. Based on this review, evidence suggested that both treatment options are comparable, and that neither proton therapy nor EPB is clinically superior than the other regarding normal tissue morbidity and local tumour control. This review highlighted the need for further research on a larger scale in order to bridge the gap that is apparent within the literature.

Charged particles in radiation oncology

Radiotherapy is one of the most common and effective therapies for cancer. Generally, patients are treated with X-rays produced by electron accelerators. Many years ago, researchers proposed that high-energy charged particles could be used for this purpose, owing to their physical and radiobiological advantages compared with X-rays. Particle therapy is an emerging technique in radiotherapy. Protons and carbon ions have been used for treating many different solid cancers, and several new centers with large accelerators are under construction. Debate continues on the cost:benefit ratio of this technique, that is, on whether the high costs of accelerators and beam delivery in particle therapy are justified by a clear clinical advantage. This Review considers the present clinical results in the field, and identifies and discusses the research questions that have resulted with this technique.

Number of patients potentially eligible for proton therapy

A group of Swedish radiation oncologists and hospital physicists have estimated the number of patients in Sweden suitable for proton beam therapy in a facility where one of the principal aims is to facilitate randomized and other studies in which the advantage of protons can be shown and the magnitude of the differences compared with optimally administered conventional radiation treatment, also including intensity-modulated radiation therapy (IMRT) and brachytherapy, can be shown. The estimations have been based on current statistics of tumour incidence in Sweden, number of patients potentially eligible for radiation treatment, scientific support from clinical trials and model dose planning studies and knowledge of the dose-response relations of different tumours together with information on normal tissue complication rates. In Sweden, it is assessed that between 2200 and 2500 patients annually are eligible for proton beam therapy, and that for these patients the potential therapeutic benefit is so great as to justify the additional expense of proton therapy. This constitutes between 14-15% of all irradiated patients annually.