Clinical Outcomes of Spatially Fractionated GRID Radiotherapy in the Treatment of Bulky Tumors of the Head and Neck

Tuning spatially fractionated radiotherapy dose profiles using the moiré effect

Spatially Fractionated Radiotherapy (SFRT) has demonstrated promising potential in cancer treatment, combining the advantages of reduced post-radiation effects and enhanced local control rates. Within this paradigm, proton minibeam radiotherapy (pMBRT) was suggested as a new treatment modality, possibly producing superior normal tissue sparing to conventional proton therapy, leading to improvements in patient outcomes. However, an effective and convenient beam generation method for pMBRT, capable of implementing various optimum dose profiles, is essential for its real-world application. Our study investigates the potential of utilizing the moiré effect in a dual collimator system (DCS) to generate pMBRT dose profiles with the flexibility to modify the center-to-center distance (CTC) of the dose distribution in a technically simple way.We employ the Geant4 Monte Carlo simulations tool to demonstrate that the angle between the two collimators of a DCS can significantly impact the dose profile. Varying the DCS angle from 10∘ to 50∘ we could cover CTC ranging from 11.8 mm to 2.4 mm, respectively. Further investigations reveal the substantial influence of the multi-slit collimator's (MSC) physical parameters on the spatially fractionated dose profile, such as period (CTC), throughput, and spacing between MSCs. These findings highlight opportunities for precision dose profile adjustments tailored to specific clinical scenarios.The DCS capacity for rapid angle adjustments during the energy transition stages of a spot scanning system can facilitate dynamic alterations in the irradiation profile, enhancing dose contrast in normal tissues. Furthermore, its unique attribute of spatially fractionated doses in both lateral directions could potentially improve normal tissue sparing by minimizing irradiated volume. Beyond the realm of pMBRT, the dual MSC system exhibits remarkable versatility, showing compatibility with different types of beams (X-rays and electrons) and applicability across various SFRT modalities.Our study illuminates the dual MSC system's potential as an efficient and adaptable tool in the refinement of pMBRT techniques. By enabling meticulous control over irradiation profiles, this system may expedite advancements in clinical and experimental applications, thereby contributing to the evolution of SFRT strategies.

Practice Patterns of Spatially Fractionated Radiation Therapy: A Clinical Practice Survey

Purpose

Spatially fractionated radiation therapy (SFRT) is increasingly used for bulky advanced tumors, but specifics of clinical SFRT practice remain elusive. This study aimed to determine practice patterns of GRID and Lattice radiation therapy (LRT)-based SFRT.

Methods and Materials

A survey was designed to identify radiation oncologists' practice patterns of patient selection for SFRT, dosing/planning, dosimetric parameter use, SFRT platforms/techniques, combinations of SFRT with conventional external beam radiation therapy (cERT) and multimodality therapies, and physicists' technical implementation, delivery, and quality procedures. Data were summarized using descriptive statistics. Group comparisons were analyzed with permutation tests.

Results

The majority of practicing radiation oncologists (United States, 100%; global, 72.7%) considered SFRT an accepted standard-of-care radiation therapy option for bulky/advanced tumors. Treatment of metastases/recurrences and nonmetastatic primary tumors, predominantly head and neck, lung cancer and sarcoma, was commonly practiced. In palliative SFRT, regimens of 15 to 18 Gy/1 fraction predominated (51.3%), and in curative-intent treatment of nonmetastatic tumors, 15 Gy/1 fraction (28.0%) and fractionated SFRT (24.0%) were most common. SFRT was combined with cERT commonly but not always in palliative (78.6%) and curative-intent (85.7%) treatment. SFRT-cERT time sequencing and cERT dose adjustments were variable. In curative-intent treatment, concurrent chemotherapy and immunotherapy were found acceptable by 54.5% and 28.6%, respectively. Use of SFRT dosimetric parameters was highly variable and differed between GRID and LRT. SFRT heterogeneity dosimetric parameters were more commonly used (P = .008) and more commonly thought to influence local control (peak dose, P = .008) in LRT than in GRID therapy.

Conclusions

SFRT has already evolved as a clinical practice pattern for advanced/bulky tumors. Major treatment approaches are consistent and follow the literature, but SFRT-cERT combination/sequencing and clinical utilization of dosimetric parameters are variable. These areas may benefit from targeted education and standardization, and knowledge gaps may be filled by incorporating identified inconsistencies into future clinical research.

A Case Report on Initial Experience of Lattice Radiation Therapy for Managing Massive Non-small Cell Lung Cancer and Renal Pelvic Cancer

Lattice radiation therapy (LRT) is an advanced treatment approach specifically designed for massive tumors. It aims to deliver high-dose regions within tumors while ensuring the safety of the surrounding dose-limiting organs at risk (OAR). This case report introduces two unique clinical cases: a 63-year-old male diagnosed with a massive non-small cell lung cancer (NSCLC) tumor and a 61-year-old male with an inoperable recurrent left-sided adrenal mass intricately surrounded by dose-limiting bowel structures. Both patients underwent LRT to enhance tumor control and maintain less toxicity. Notably, both patients displayed a significant tumor volume reduction accompanied by minimal adverse effects during the 12-month follow-up period. While these initial results suggest that LRT may be effective and safe for treating large tumors, further investigation through exhaustive research and multicenter trials is necessary to fully understand and determine the specifics of lattice radiation therapy techniques.

Monte Carlo optimization of a GRID collimator for preclinical megavoltage ultra-high dose rate spatially-fractionated radiation therapy

Objective. A 2-dimensional pre-clinical SFRT (GRID) collimator was designed for use on the ultra-high dose rate (UHDR) 10 MV ARIEL beamline at TRIUMF. TOPAS Monte Carlo simulations were used to determine optimal collimator geometry with respect to various dosimetric quantities. Approach. The GRID-averaged peak-to-valley dose ratio (PVDR) and mean dose rate of the peaks were investigated with the intent of maximizing both values in a given design. The effects of collimator thickness, focus position, septal width, and hole width on these metrics were found by testing a range of values for each parameter on a cylindrical GRID collimator. For each tested collimator geometry, photon beams with energies of 10, 5, and 1 MV were transported through the collimator and dose rates were calculated at various depths in a water phantom located 1.0 cm from the collimator exit. Main results. In our optimization, hole width proved to be the only collimator parameter which increased both PVDR and peak dose rates. From the optimization results, it was determined that our optimized design would be one which achieves the maximum dose rate for a PVDR ≥ 5 at 10 MV. Ultimately, this was achieved using a collimator with a thickness of 75 mm, 0.8 mm septal and hole widths, and a focus position matched to the beam divergence. This optimized collimator maintained the PVDR of 5 in the phantom between water depths of 0–10 cm at 10 MV and had a mean peak dose rate of 3.06 ± 0.02 Gy s − 1 at 0–1 cm depth. Significance. We have investigated the impact of various GRID-collimator design parameters on the dose rate and spatial fractionation of 10, 5, and 1 MV photon beams. The optimized collimator design for the 10 MV ultra-high dose rate photon beam could become a useful tool for radiobiology studies synergizing the effects of ultra-high dose rate (FLASH) delivery and spatial fractionation.

An International Consensus on the Design of Prospective Clinical–Translational Trials in Spatially Fractionated Radiation Therapy for Advanced Gynecologic Cancer

Simple Summary

Spatially fractionated radiation therapy (SFRT) delivers intentionally heterogenous dose to tumors. This is a major departure from current radiation therapy, which strives for uniform dose. Early pilot experience suggests promising treatment outcomes with SFRT in patients with challenging bulky tumors, including gynecologic cancer. Well-conducted prospective multi-institutional clinical trials are now needed to further test SFRT as a treatment modality. However, clinical trial development is hampered by the variabilities in SFRT approach and the overall unfamiliarity with heterogeneous dosing. A broad consensus among SFRT experts, potential investigators, and the wider radiation oncology community is needed so that clinical trials in SFRT can be successfully designed and carried out. We developed an international consensus guideline for the design parameters of clinical/translational trials in SFRT for gynecologic cancer. High-to-moderate consensus was achieved, and harmonized fundamental design parameters for SFRT trials in advanced gynecologic cancer were defined.

Abstract

Despite the unexpectedly high tumor responses and limited treatment-related toxicities observed with SFRT, prospective multi-institutional clinical trials of SFRT are still lacking. High variability of SFRT technologies and methods, unfamiliar complex dose and prescription concepts for heterogeneous dose and uncertainty regarding systemic therapies present major obstacles towards clinical trial development. To address these challenges, the consensus guideline reported here aimed at facilitating trial development and feasibility through a priori harmonization of treatment approach and the full range of clinical trial design parameters for SFRT trials in gynecologic cancer. Gynecologic cancers were evaluated for the status of SFRT pilot experience. A multi-disciplinary SFRT expert panel for gynecologic cancer was established to develop the consensus through formal panel review/discussions, appropriateness rank voting and public comment solicitation/review. The trial design parameters included eligibility/exclusions, endpoints, SFRT technology/technique, dose/dosimetric parameters, systemic therapies, patient evaluations, and embedded translational science. Cervical cancer was determined as the most suitable gynecologic tumor for an SFRT trial. Consensus emphasized standardization of SFRT dosimetry/physics parameters, biologic dose modeling, and specimen collection for translational/biological endpoints, which may be uniquely feasible in cervical cancer. Incorporation of brachytherapy into the SFRT regimen requires additional pre-trial pilot investigations. Specific consensus recommendations are presented and discussed.

Should Peak Dose Be Used to Prescribe Spatially Fractionated Radiation Therapy?-A Review of Preclinical Studies

Spatially fractionated radiotherapy (SFRT) is characterized by the coexistence of multiple hot and cold dose subregions throughout the treatment volume. In preclinical studies using single-fraction treatment, SFRT can achieve a significantly higher therapeutic index than conventional radiotherapy (RT). Published clinical studies of SFRT followed by RT have reported promising results for bulky tumors. Several clinical trials are currently underway to further explore the clinical benefits of SFRT. However, we lack the important understanding of the correlation between dosimetric parameters and treatment response that we have in RT. In this work, we reviewed and analyzed this important correlation from previous preclinical SFRT studies. We reviewed studies prior to 2022 that treated animal-bearing tumors with minibeam radiotherapy (MBRT) or microbeam radiotherapy (MRT). Eighteen studies met our selection criteria. Increased lifespan (ILS) relative to control was used as the treatment response. The preclinical SFRT dosimetric parameters analyzed were peak dose, valley dose, average dose, beam width, and beam spacing. We found that valley dose was the dosimetric parameter with the strongest correlation with ILS (p-value < 0.01). For studies using MRT, average dose and peak dose were also significantly correlated with ILS (p-value < 0.05). This first comprehensive review of preclinical SFRT studies shows that the valley dose (rather than the peak dose) correlates best with treatment outcome (ILS).

Radiobiological and Treatment-Related Aspects of Spatially Fractionated Radiotherapy

The continuously evolving field of radiotherapy aims to devise and implement techniques that allow for greater tumour control and better sparing of critical organs. Investigations into the complexity of tumour radiobiology confirmed the high heterogeneity of tumours as being responsible for the often poor treatment outcome. Hypoxic subvolumes, a subpopulation of cancer stem cells, as well as the inherent or acquired radioresistance define tumour aggressiveness and metastatic potential, which remain a therapeutic challenge. Non-conventional irradiation techniques, such as spatially fractionated radiotherapy, have been developed to tackle some of these challenges and to offer a high therapeutic index when treating radioresistant tumours. The goal of this article was to highlight the current knowledge on the molecular and radiobiological mechanisms behind spatially fractionated radiotherapy and to present the up-to-date preclinical and clinical evidence towards the therapeutic potential of this technique involving both photon and proton beams.

Minibeam radiation therapy enhanced tumor delivery of PEGylated liposomal doxorubicin in a triple-negative breast cancer mouse model

Background:

Minibeam radiation therapy is an experimental radiation therapy utilizing an array of parallel submillimeter planar X-ray beams. In preclinical studies, minibeam radiation therapy has been shown to eradicate tumors and cause significantly less damage to normal tissue compared to equivalent radiation doses delivered by conventional broadbeam radiation therapy, where radiation dose is uniformly distributed.

Methods:

Expanding on prior studies that suggested minibeam radiation therapy increased perfusion in tumors, we compared a single fraction of minibeam radiation therapy (peak dose:valley dose of 28 Gy:2.1 Gy and 100 Gy:7.5 Gy) and broadbeam radiation therapy (7 Gy) in their ability to enhance tumor delivery of PEGylated liposomal doxorubicin and alter the tumor microenvironment in a murine tumor model. Plasma and tumor pharmacokinetic studies of PEGylated liposomal doxorubicin and tumor microenvironment profiling were performed in a genetically engineered mouse model of claudin-low triple-negative breast cancer (T11).

Results:

Minibeam radiation therapy (28 Gy) and broadbeam radiation therapy (7 Gy) increased PEGylated liposomal doxorubicin tumor delivery by 7.1-fold and 2.7-fold, respectively, compared to PEGylated liposomal doxorubicin alone, without altering the plasma disposition. The enhanced tumor delivery of PEGylated liposomal doxorubicin by minibeam radiation therapy is consistent after repeated dosing, is associated with changes in tumor macrophages but not collagen or angiogenesis, and nontoxic to local tissues. Our study indicated that the minibeam radiation therapy’s ability to enhance the drug delivery decreases from 28 to 100 Gy peak dose.

Discussion:

Our studies suggest that low-dose minibeam radiation therapy is a safe and effective method to significantly enhance the tumor delivery of nanoparticle agents.

The role of the spatially fractionated radiation therapy in the management of advanced bulky tumors

Spatially fractionated radiation therapy (SFRT) refers to the delivery of a single large dose of radiation within the target volume in a heterogeneous pattern using either a custom GRID block, multileaf collimators, and virtual methods such as helical tomotherapy or synchrotron-based microbeams. The potential impact of this technique on the regression of bulky deep-seated tumors that do not respond well to conventional radiotherapy has been remarkable. To date, a large number of patients have been treated using the SFRT techniques. However, there are yet many technical and medical challenges that have limited their routine use to a handful of clinics, most commonly for palliative intent. There is also a poor understanding of the biological mechanisms underlying the clinical efficacy of this approach. In this article, the methods of SFRT delivery together with its potential biological mechanisms are presented. Furthermore, technical challenges and clinical achievements along with the radiobiological models used to evaluate the efficacy and safety of SFRT are highlighted.

A novel external beam radiotherapy method for cervical cancer patients using virtual straight or bending boost areas; an in-silico feasibility study

Aim

To investigate the potential role of a novel spatially fractionated radiation therapy (SFRT) method where heterogeneous dose patterns are created in target areas with virtual rods, straight or curving, of variable position, diameter, separation and alignment personalised to a patient’s anatomy. The images chosen for this study were CT scans acquired for the external beam part of radiotherapy.

Methods

Ten patients with locally advanced cervical cancer were retrospectively investigated with SFRT. The dose prescription was 30 Gy in 5 fractions to 90% target volume coverage. Peak-and-valley (SFRT_1) and peak-only (SFRT_2) strategies were applied to generate the heterogeneous dose distributions. The planning objectives for the target (CTV) were D_90% ≥ 30 Gy, V_45Gy ≥ 50–55% and V_60Gy ≥ 30%. The planning objectives for the organs at risk (OAR) were: D_2cm3 ≤ 23.75 Gy, 17.0 Gy, 19.5 Gy, 17.0 Gy for the bladder, rectum, sigmoid and bowel, respectively. The plan comparison was performed employing the quantitative analysis of the dose-volume histograms.

Results

The D_2cm3 was 22.4 ± 2.0 (22.6 ± 2.1) and 13.9 ± 2.9 (13.2 ± 3.0) for the bladder and the rectum for SFRT_1 (SFRT_2). The results for the sigmoid and the bowel were 2.6 ± 3.1 (2.8 ± 3.0) and 9.1 ± 5.9 (9.7 ± 7.3), respectively. The hotspots in the target volume were V_45Gy = 43.1 ± 7.5% (56.6 ± 5.6%) and V_60Gy = 15.4 ± 5.6% (26.8 ± 6.6%) for SFRT_1 (SFRT_2). To account for potential uncertainties in the positioning, the dose prescription could be escalated to D_90% = 33–35 Gy to the CTV without compromising any constraints to the OARs

Conclusion

In this dosimetric study, the proposed novel planning technique for boosting the cervix uteri was associated with high-quality plans, respecting constraints for the organs at risk and approaching the level of dose heterogeneity achieved with routine brachytherapy. Based on a sample of 10 patients, the results are promising and might lead to a phase I clinical trial.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13014-021-01838-x.