Proton beam re-irradiation for gastrointestinal malignancies: a systematic review

FLASH proton reirradiation, with or without hypofractionation, mitigates chronic toxicity in the normal murine intestine, skin, and bone

Background and purpose

The normal tissue sparing afforded by FLASH radiotherapy (RT) is being intensely investigated for potential clinical translation. Here, we studied the effects of FLASH proton RT (F-PRT) in the reirradiation setting, with or without hypofractionation. Chronic toxicities in three murine models of normal tissue toxicity including the intestine, skin, and bone were investigated.

Materials and methods

In studies of the intestine, single-dose irradiation was performed with 12 Gy of Standard proton RT (S-PRT), followed by a second dose of 12 Gy of F-PRT or S-PRT. Additionally, a hypofractionation scheme was applied in the reirradiation setting (3 x 6.4 Gy of F-PRT or S-PRT, given every 48 hrs). In studies of skin/bone of the murine leg, 15 Gy of S-PRT was followed by hypofractionated reirradiation with F-PRT or S-PRT (3 x 11 Gy).

Results

Compared to reirradiation with S-PRT, F-PRT reduced intestinal fibrosis and collagen deposition in the reirradiation setting and significantly increased survival rate, demonstrating its protective effects on intestinal tissues. In previously irradiated leg tissues, reirradiation with hypofractionated F-PRT created transient dermatitis that fully resolved in contrast to reirradiation with hypofractionated S-PRT. Lymphedema was also alleviated after a second course of radiation with F-PRT, along with significant reductions in the accumulation of fibrous connective tissue in the skin compared to mice reirradiated with S-PRT. The delivery of a second course of fractionated S-PRT induced tibial fractures in 83.3% of the mice, whereas only 20% of mice reirradiated with F-PRT presented with fractures.

Conclusion

These studies provide the first evidence of the sparing effects of F-PRT, in the setting of hypofractionated reirradiation. The results support FLASH as highly relevant to the reirradiation regimen where it exhibits significant potential to minimize chronic complications for patients undergoing RT.

Factors Associated With and Characteristics of Patients Receiving Proton Therapy at the End of Life

Purpose

To identify the characteristics, indications, and toxicities among patients receiving proton beam therapy (PBT) in the final year of life at an academic medical center.

Materials and Methods

A retrospective review of patients who received PBT within the final 12 months of life was performed. Electronic medical records were reviewed for patient and treatment details from 2010 to 2019. Patients were followed from the start of PBT until death or last follow-up. Acute (3 months) toxicities were graded using the Common Terminology Criteria for Adverse Events v5.0. Imaging response was assessed using the Response Evaluation Criteria in Solid Tumors v1.1. The χ2 test was used to evaluate factors associated with palliative treatment. Simple logistic regression was used to evaluate factors associated with toxicity.

Results

Bet299 patients were treated at the end of life (EOL) out of 5802 total patients treated with PBT (5.2%). Median age was 68 years (19-94 years), 58% male. The most common cancer was nonsmall cell lung cancer (27%). Patients were treated for symptom palliation alone (11%), durable control (57%), curative intent (16%), local recurrence (14%), or oligometastatic disease (2%). Forty-five percent received reirradiation. Median treatment time was 32 days (1-189 days). Acute toxicity was noted in 85% of the patients (31% G1, 53% G2, 15% G3). Thirteen patients (4%) experienced chronic toxicity. Breast and hematologic malignancy were associated with palliative intent χ2 (1, N = 14) = 17, P = .013; (χ2 (1, N = 14) = 18, P = .009).

Conclusion

The number of patients treated with PBT at the EOL was low compared to all comers. Many of these patients received treatment with definitive doses and concurrent systemic therapy. Some patients spent a large portion of their remaining days on treatment. A prognostic indicator may better optimize patient selection for PBT at the EOL.

Association of Race With Receipt of Proton Beam Therapy for Patients With Newly Diagnosed Cancer in the US, 2004-2018

IMPORTANCE

Black patients are less likely than White patients to receive guideline-concordant cancer care in the US. Proton beam therapy (PBT) is a potentially superior technology to photon radiotherapy for tumors with complex anatomy, tumors surrounded by sensitive tissues, and childhood cancers.

OBJECTIVE

To evaluate whether there are racial disparities in the receipt of PBT among Black and White individuals diagnosed with all PBT-eligible cancers in the US.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study evaluated Black and White individuals diagnosed with PBT-eligible cancers between January 1, 2004, and December 31, 2018, in the National Cancer Database, a nationwide hospital-based cancer registry that collects data on radiation treatment, even when it is received outside the reporting facility. American Society of Radiation Oncology model policies were used to classify patients into those for whom PBT is the recommended radiation therapy modality (group 1) and those for whom evidence of PBT efficacy is still under investigation (group 2). Propensity score matching was used to ensure comparability of Black and White patients' clinical characteristics and regional availability of PBT according to the National Academy of Medicine's definition of disparities. Data analysis was performed from October 4, 2021, to February 22, 2022.

EXPOSURE

Patients' self-identified race was ascertained from medical records.

MAIN OUTCOMES AND MEASURES

The main outcome was receipt of PBT, with disparities in this therapy's use evaluated with logistic regression analysis.

RESULTS

Of the 5 225 929 patients who were eligible to receive PBT and included in the study, 13.6% were Black, 86.4% were White, and 54.3% were female. The mean (SD) age at diagnosis was 63.2 (12.4) years. Black patients were less likely to be treated with PBT than their White counterparts (0.3% vs 0.5%; odds ratio [OR], 0.67; 95% CI, 0.64-0.71). Racial disparities were greater for group 1 cancers (0.4% vs 0.8%; OR, 0.49; 95% CI, 0.44-0.55) than group 2 cancers (0.3% vs 0.4%; OR, 0.75; 95% CI, 0.70-0.80). Racial disparities in PBT receipt among group 1 cancers increased over time (annual percent change = 0.09, P < .001) and were greatest in 2018, the most recent year of available data.

CONCLUSIONS AND RELEVANCE

In this cross-sectional study, Black patients were less likely to receive PBT than their White counterparts, and disparities were greatest for cancers for which PBT was the recommended radiation therapy modality. These findings suggest that efforts other than increasing the number of facilities that provide PBT will be needed to eliminate disparities.

Dose-Escalated Magnetic Resonance Image–Guided Abdominopelvic Reirradiation With Continuous Intrafraction Visualization, Soft Tissue Tracking, and Automatic Beam Gating

Purpose

Methods and Materials

Results

Conclusions

Executive Summary of Clinical and Technical Guidelines for Esophageal Cancer Proton Beam Therapy From the Particle Therapy Co-Operative Group Thoracic and Gastrointestinal Subcommittees

Radiation therapy (RT) is an integral component of potentially curative management of esophageal cancer (EC). However, RT can cause significant acute and late morbidity due to excess radiation exposure to nearby critical organs, especially the heart and lungs. Sparing these organs from both low and high radiation dose has been demonstrated to achieve clinically meaningful reductions in toxicity and may improve long-term survival. Accruing dosimetry and clinical evidence support the consideration of proton beam therapy (PBT) for the management of EC. There are critical treatment planning and delivery uncertainties that should be considered when treating EC with PBT, especially as there may be substantial motion-related interplay effects. The Particle Therapy Co-operative Group Thoracic and Gastrointestinal Subcommittees jointly developed guidelines regarding patient selection, treatment planning, clinical trials, and future directions of PBT for EC.