Transitioning from conventional photon therapy to proton therapy for primary brain tumors

INTRODUCTION

Proton radiation therapy (PT) has become a treatment option alongside photon therapy (XRT) for lower-grade gliomas (LGG). In this single-institution retrospective study, we investigate the patient characteristics and treatment outcomes, including pseudo-progression (PsP), for LGG patients selected for PT.

METHOD

Adult patients with grade 2-3 glioma consecutively treated with radiotherapy (RT) from May 2012 to December 2019 were retrospectively included in this cohort study. Tumor characteristics and treatment data were collected. The groups treated with PT and XRT were compared regarding treatment characteristics, side effects, occurrence of PsP, and survival outcomes. PsP was defined as new or growing lesions followed by either decrease or stabilization during a 12 month-period with no treatment.

RESULTS

Out of 143 patients meeting the inclusion criteria, 44 were treated with PT, 98 with XRT and one with mixed PT + XRT. The patients receiving PT were younger, had a lower tumor grade, more oligodendrogliomas and received a lower mean brain and brainstem dose. PsP was observed in 21 out of 126 patients, with no difference between XRT and PT (p = .38). The rate of fatigue in immediate connection to RT (zero to three months after) was higher for XRT than for PT (p = .016). The PT patients had a significantly better PFS and OS than the XRT patients (p = .025 and .035), but in multivariate analysis radiation modality was non-significant. Higher average dose to both brain and brainstem was associated with inferior PFS and OS (p < .001). Median follow-up time were 69 months and 26 months for XRT and PT patients, respectively.

CONCLUSION

Contrary to previous studies, there was no difference in risk of PsP for XRT and PT. PT was associated with lower rates of fatigue <3 months after RT. The superior survival outcomes for PT indicates that the patients with the best prognosis were referred to PT.

Factors Associated With Travel Distance in the Receipt of Proton Breast Radiation Therapy

Introduction

Proton radiation therapy (PBT) may reduce cardiac doses in breast cancer treatment. Limited availability of proton facilities could require significant travel distances. This study assessed factors associated with travel distances for breast PBT.

Materials and Methods

Patients receiving breast PBT at the University of Pennsylvania from 2010 to 2021 were identified. Demographic, cancer, and treatment characteristics were summarized. Straight-line travel distances from the department to patients' addresses were calculated using BatchGeo. Median and mean travel distances were reported. Given non-normality of distribution of travel distances, Wilcoxon rank sum or Kruskal-Wallis test was used to determine whether travel distances differed by race, clinical trial participation, disease laterality, recurrence, and prior radiation.

Results

Of 1 male and 284 female patients, 67.8% were White and 21.7% Black. Median travel distance was 13.5 miles with interquartile range of 6.1 to 24.8 miles, and mean travel distance was 13.5 miles with standard deviation of 261.4 miles. 81.1% of patients traveled less than 30 and 6.0% more than 100 miles. Black patients' travel distances were significantly shorter than White patients' and non-Black or non-White patients' travel distances (median = 4.5, 16.5, and 11.3 miles, respectively; P < .0001). Patients not on clinical trials traveled more those on clinical trials (median = 14.7 and 10.2 miles, respectively; P = .032). There was no difference found between travel distances of patients with left-sided versus right-sided versus bilateral disease (P = .175), with versus without recurrent disease (P = .057), or with versus without prior radiation (P = .23).

Conclusion

This study described travel distances and demographic and clinicopathologic characteristics of patients receiving breast PBT at the University of Pennsylvania. Black patients traveled less than White and non-Black or non-White patients and comprised a small portion of the cohort, suggesting barriers to travel and PBT. Patients did not travel further to receive PBT for left-sided or recurrent disease.

Predicting neurocognitive function in pediatric brain tumor early survivorship: The neurological predictor scale and the incremental validity of tumor size

BACKGROUND

The Neurological Predictor Scale (NPS) quantifies cumulative exposure to conventional treatment-related neurological risks but does not capture potential risks posed by tumors themselves. This study evaluated the predictive validity of the NPS, and the incremental value of tumor location and size, for neurocognitive outcomes in early survivorship following contemporary therapies for pediatric brain tumors.

PROCEDURE

Survivors (N = 69) diagnosed from 2010 to 2016 were administered age-appropriate versions of the Wechsler Intelligence Scales. Hierarchical multiple regressions examined the predictive and incremental validity of NPS score, tumor location, and tumor size.

RESULTS

Participants (51% female) aged 6-20 years (M = 13.22, SD = 4.09) completed neurocognitive evaluations 5.16 years (SD = 1.29) postdiagnosis. The NPS significantly predicted Full-Scale Intelligence Quotient (FSIQ; ΔR2  = .079), Verbal Comprehension Index (VCI; ΔR2  = 0.051), Perceptual Reasoning Index (PRI; ΔR2  = 0.065), and Processing Speed Index (PSI; ΔR2  = 0.049) performance after controlling for sex, age at diagnosis, and maternal education. Tumor size alone accounted for a significant amount of unique variance in FSIQ (ΔR2  = 0.065), PRI (ΔR2  = 0.076), and PSI (ΔR2  = 0.080), beyond that captured by the NPS and relevant covariates. Within the full model, the NPS remained a significant independent predictor of FSIQ (β = -0.249, P = 0.016), VCI (β = -0.223, P = 0.048), and PRI (β = -0.229, P = 0.037).

CONCLUSIONS

Tumor size emerged as an independent predictor of neurocognitive functioning and added incrementally to the predictive utility of the NPS. Pretreatment disease burden may provide one of the earliest markers of neurocognitive risk following contemporary treatments. With perpetual treatment advances, measures quantifying treatment-related risk may need to be updated and revalidated to maintain their clinical utility.

Treatment planning of total marrow irradiation with intensity-modulated spot-scanning proton therapy

Purpose

The goal of this study is to investigate treatment planning of total marrow irradiation (TMI) using intensity-modulated spot-scanning proton therapy (IMPT). The dosimetric parameters of the intensity-modulated proton plans were evaluated and compared with the corresponding TMI plans generated with volumetric modulated arc therapy (VMAT) using photon beams.

Methods

Intensity-modulated proton plans for TMI were created using the Monte Carlo dose-calculation algorithm in the Raystation 11A treatment planning system with spot-scanning proton beams from the MEVION S250i Hyperscan system. Treatment plans were generated with four isocenters placed along the longitudinal direction, each with a set of five beams for a total of 20 beams. VMAT-TMI plans were generated with the Eclipse-V15 analytical anisotropic algorithm (AAA) using a Varian Trilogy machine. Three planning target volumes (PTVs) for the bones, ribs, and spleen were covered by 12 Gy. The dose conformity index, D80, D50, and D10, for PTVs and organs at risk (OARs) for the IMPT plans were quantified and compared with the corresponding VMAT plans.

Results

The mean dose for most of the OARs was reduced substantially (5% and more) in the IMPT plans for TMI in comparison with VMAT plans except for the esophagus and thyroid, which experienced an increase in dose. This dose reduction is due to the fast dose falloff of the distal Bragg peak in the proton plans. The conformity index was found to be similar (0.78 vs 0.75) for the photon and proton plans. IMPT plans provided superior superficial dose coverage for the skull and ribs in comparison with VMAT because of increased entrance dose deposition by the proton beams.

Conclusion

Treatment plans for TMI generated with IMPT were superior to VMAT plans mainly due to a large reduction in the OAR dose. Although the current IMPT-TMI technique is not clinically practical due to the long overall treatment time, this study presents an enticing alternative to conventional TMI with photons by providing superior dose coverage of the targets, increased sparing of the OARs, and enhanced radiobiological effects associated with proton therapy.

Intensity Modulated Proton Therapy Better Spares Non-Adjacent Organs and Reduces the Risk of Secondary Malignant Neoplasms in the Treatment of Sinonasal Cancers

This study compare dosimetric parameters and secondary malignancy risk (SMN) using intensity modulated proton therapy (IMPT) and volumetric modulated arc therapy (VMAT) plans for the treatment of sinonasal cancer (SC). After IRB-approval, 10 patients previously treated with IMPT for cancers of the ethmoid, sphenoid, maxillary, or frontal sinuses were identified. Dosimetrists blinded to the IMPT plans generated VMAT plans for comparison. Volume coverage and dose to organs at risk (OAR) were recorded and compared. Organ equivalent dose (OED) of tissues outside of the treatment volume was used to define the excess absolute and relative risk of SMNs. In all cases, both VMAT and IMPT provided acceptable target volume coverage and were able to meet OAR constraints. IMPT was superior for brain V10, V30, and mean, brainstem D0.01 ipsilateral cochlea V30, contralateral cochlea mean, contralateral lacrimal gland mean, contralateral parotid mean, spinal cord D0.01 and body outside of the CTV V10, V20, and V30. VMAT was superior for ipsilateral eye mean, ipsilateral lens mean, CTV V100 and maximum hotspot. The relative risk of SMNs with VMAT compared to IMPT is 3.35 (95% CI, 1.92-5.89). For the treatment of SC, IMPT spares OARs that are not immediately adjacent to the treatment volume and reduces the risk of SMNs when compared to VMAT. VMAT spares OARs abutting the target volume better than IMPT and has more homogenous target coverage. Tumors of the ethmoid sinus, benefit more from IMPT, while tumors located elsewhere require application of our findings on a case by case basis.

Activity-Based Costing of Intensity-Modulated Proton versus Photon Therapy for Oropharyngeal Cancer

PURPOSE

In value-based health care delivery, radiation oncologists need to compare empiric costs of care delivery with advanced technologies, such as intensity-modulated proton therapy (IMPT) and intensity-modulated radiation therapy (IMRT). We used time-driven activity-based costing (TDABC) to compare the costs of delivering IMPT and IMRT in a case-matched pilot study of patients with newly diagnosed oropharyngeal (OPC) cancer.

MATERIALS AND METHODS

We used clinicopathologic factors to match 25 patients with OPC who received IMPT in 2011-12 with 25 patients with OPC treated with IMRT in 2000-09. Process maps were created for each multidisciplinary clinical activity (including chemotherapy and ancillary services) from initial consultation through 1 month of follow-up. Resource costs and times were determined for each activity. Each patient-specific activity was linked with a process map and TDABC over the full cycle of care. All calculated costs were normalized to the lowest-cost IMRT patient.

RESULTS

TDABC costs for IMRT were 1.00 to 3.33 times that of the lowest-cost IMRT patient (mean ± SD: 1.65 ± 0.56), while costs for IMPT were 1.88 to 4.32 times that of the lowest-cost IMRT patient (2.58 ± 0.39) (P < .05). Although single-fraction costs were 2.79 times higher for IMPT than for IMRT (owing to higher equipment costs), average full cycle cost of IMPT was 1.53 times higher than IMRT, suggesting that the initial cost increase is partly mitigated by reductions in costs for other, non-RT supportive health care services.

CONCLUSIONS

In this matched sample, although IMPT was on average more costly than IMRT primarily owing to higher equipment costs, a subset of IMRT patients had similar costs to IMPT patients, owing to greater use of supportive care resources. Multidimensional patient outcomes and TDABC provide vital methodology for defining the value of radiation therapy modalities.

Design and characterization of a prototype tertiary device for proton beam stereotactic radiosurgery

Though potentially beneficial, proton beam stereotactic radiosurgery has not been adopted widely secondary to the technical challenge of safely delivering multiple focused beams of proton radiation. In this study, we describe the design and characterization of a proton beam stereotactic radiosurgery system that can be adopted by existing passive scattering systems. This system utilizes a helmet-like device in which patient-specific brass apertures required for final beam collimation are positioned on a scaffold that is separate from the treatment gantry. The proton snout is then fitted with a generic aperture to focus the primary proton beam onto the patient specific apertures that are in the helmet-like device. The patient-specific apertures can all be placed at the start of the treatment, thus treatment with multiple beams can be accomplished without the delay of switching the apertures. In this report we describe a prototype design of this collimation system and dosimetric testing to verify efficacy. Subsequently, we describe a custom 3D printing of a prototype device and report on overall localization accuracy using Winston-Lutz tests. Our results show that it is possible to develop an add-on device for proton beam radiosurgery that is safe and efficient and capable of wide adoption on existing proton delivery systems.

The Biological Basis for Enhanced Effects of Proton Radiation Therapy Relative to Photon Radiation Therapy for Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinomas (HNSCCs) often present as local-regionally advanced disease at diagnosis, for which a current standard of care is x-ray-based radiation therapy, with or without chemotherapy. This approach provides effective local regional tumor control, but at the cost of acute and late toxicity that can worsen quality of life and contribute to mortality. For patients with human papillomavirus (HPV)-associated oropharyngeal squamous cell carcinoma (SCC) in particular, for whom the prognosis is generally favorable, de-escalation of the radiation dose to surrounding normal tissues without diminishing the radiation dose to tumors is desired to mitigate radiation-related toxic effects. Proton radiation therapy (PRT) may be an excellent de-escalation strategy because of its physical properties (that eliminate unnecessary radiation to surrounding tissues) and because of its biological properties (including tumor-specific variations in relative biological effectiveness [RBE] and linear energy transfer [LET]), in combination with concurrent systemic therapy. Early clinical evidence has shown that compared with x-ray-based radiation therapy, PRT offers comparable disease control with fewer and less severe treatment-related toxicities that can worsen the quality of life for patients with HNSCC. Herein, we review aspects of the biological basis of enhanced HNSCC cell response to proton versus x-ray irradiation in terms of radiation-induced gene and protein expression, DNA damage and repair, cell death, tumor immune responses, and radiosensitization of tumors.

Carbon ion radiation therapy for sinonasal malignancies: Promising results from 2282 cases from the real world

The aim of this study is to compare the effectiveness of carbon ion radiation therapy (CIRT), proton radiation therapy (PRT), and photon‐based intensity‐modulated radiation therapy (IMRT) in the treatment of sinonasal malignancies. We identified studies through systematic review and divided them into three cohorts (CIRT group/PRT group/IMRT group). Primary outcomes of interest were overall survival (OS) and local control (LC). We pooled the outcomes with meta‐analysis and compared the survival difference among groups using Chi² (χ²) test. A representative sample of 2282 patients with sinonasal malignancies (911 in the CIRT group, 599 in the PRT group, and 772 in the IMRT group) from 44 observation studies (7 CIRT, 16 PRT, and 21 IMRT) was included. The pooled 3‐year OS, LC, distant metastasis–free survival, and progression‐free survival rates were 67.0%, 72.8%, 69.4%, and 52.8%, respectively. Through cross‐group analysis, the OS was significantly higher after CIRT (75.1%, 95% CI: 67.1%‐83.2%) than PRT (66.2%, 95% CI: 57.7%‐74.6%; χ² = 13.374, P < .0001) or IMRT (63.8%, 95% CI: 55.3%‐72.3%; χ² = 23.814, P < .0001). LC was significantly higher after CIRT (80.2%, 95% CI: 73.9%‐86.5%) than PRT (72.9%, 95% CI: 63.7%‐82.0%; χ² = 8.955, P = .003) or IMRT (67.8%, 95% CI: 59.4%‐76.2%; χ² = 30.955, P < .0001). However, no significant difference between PRT and IMRT for OS and LC was observed. CIRT appeared to provide better OS and LC for patients with malignancies of nasal cavity and paranasal sinuses. A prospective randomized clinical trial is needed to confirm the superiority of CIRT in the treatment of sinonasal tumors.

A Beam-Angle-Selection Method to Improve Inter-Fraction Motion Robustness for Lung Tumor Irradiation With Passive Proton Scattering

In terms of dose distribution, protons are more sensitive to range variations than photons due to their unique properties. The aim of this study was to develop a method to identify patient-specific robust proton beam angles for lung tumor irradiation by investigating the association between water equivalent thickness (WET) variation and inter-fraction motion-induced target dose degradation. Using 3-dimensional computed tomography (3D-CT) images, the impact of WET variations on the target dose coverage of a series of coplanar proton beams was evaluated for 4 patients with lung cancer. Using ray tracing, WET maps, or WET baseline, were estimated for the internal target volume (ITV) at every 5° gantry interval in the axial plane. After calculating the WET baseline, the planning CT was shifted 5 mm in each anterior-posterior (AP), superior-inferior (SI), and left-right (LR) direction, yielding a total of 6 shifted CTs, and differential WET maps between the planning CT and each shifted CT were calculated. Target dose differences were associated with the average WET change between the original planning CT and the shifted CTs for all 360° gantry rotation beams. Target and OAR dose metrics in the ΔWET-guided plans were compared with those of the clinical plans. The WET variation maps showed areas of both high and low WET variations, with overall similar patterns yet individual differences reflecting tumor position differences. For all 4 patients investigated in this study, the coplanar plans demonstrated a strong correlation between WET changes and ITV dose reductions. Target dose coverage was more stable with the ΔWET-guided plan while OAR doses were comparable to the clinical plan. The WET variation maps have been used in this pilot study to identify proton beam angles that are either sensitive or robust to WET changes in proton passive scattering. This work demonstrates the feasibility of using WET variation maps to assist the planner in inter-fraction motion-robust proton beam angle selection.

Clinical Course and Autopsy Findings of a Patient with Clival Chordoma Who Underwent Multiple Surgeries and Radiation during a 10-Year Period

The management of clival chordoma remains problematic. We present the case of a 48-year-old woman with clival chordoma who underwent multiple surgeries and radiation therapy, including gamma knife stereotactic radiosurgery (GK-SRS), during a 10-year clinical course. The tumor was initially removed by gross total resection via the trans-sphenoidal approach, followed by external linac radiation therapy. The tumor recurred at the clivus 5 years after the initial operation. After repeated trans-sphenoidal removal of recurrent tumors, she twice underwent GK-SRS for a tumor remnant adjacent to the brainstem. Although this part of the tumor was controlled by GK-SRS, there was further tumor extension toward the sphenoid and maxillary sinuses. Ultimately, lower cranial nerve dysfunction developed due to tumor extension into the lower part of the clivus and the patient died of respiratory failure. Autopsy revealed the tumor to extend from the lower clivus to the bilateral middle fossae. The lower part of the tumor extended to the nasal cavity and to the posterior wall of the pharynx, resulting in compression of the upper pharyngeal region. The tumor around the jugular foramen compressed the lower cranial nerves bilaterally. Tumor cells did not, however, invade the intradural space microscopically. Although chordoma is not biologically malignant, this tumor can show massive extension with destruction of bony structures and extracranial invasion of connective tissues. Therefore, the optimal treatment strategy is to remove the tumor mass as extensively as possible, including normal bony structures and connective tissues surrounding the tumor, using skull base surgical techniques.