An algorithm for thoracic re-irradiation using biologically effective dose: a common language on how to treat in a "no-treat zone"

Biological adaptive radiotherapy for short-time dose compensation in lung SBRT patients

BACKGROUND

Conventional adaptive radiation therapy (ART) primarily focuses on adapting to anatomical changes during radiation therapy but does not account for biological effects such as changes in radiosensitivity and tumor response, particularly during treatment interruptions. These interruptions may allow sublethal damage repair in tumor cells, reducing the effectiveness of stereotactic body radiation therapy (SBRT).

PURPOSE

The aim of this study was to develop and evaluate a novel biological adaptive radiotherapy (BART) framework to compensate for the biological effects of radiation interruptions during SBRT for lung cancer.

METHODS

This study involved lung SBRT patients using volumetric modulated arc therapy. We evaluated the biological dose loss using a microdosimetric kinetic model during four interruption durations (30, 60, 90, and 120 min). The reduction in the biological dose due to interruptions was calculated. The physical dose was calculated from the decreased biological dose in the in-house software, which was incorporated into the TPS. The optimization process was conducted for dose compensation in the TPS. To quantitatively assess the impact of BART on dose distribution, we evaluated the differences in target dose coverage and organ-at-risk (OAR) exposure between the original plan (without interruption), the plan with interruption, the BART plan, and the plan summing the dose before the interruption and the physical dose after compensation (compensated PD plan). The compensated PD plan assumed no biological dose reduction before the interruption.

RESULTS

Without BART compensation, interruptions of 30, 60, 90, and 120 min resulted in biological dose reductions, ranging from 12.1% to 19.0% for D50% of the gross tumor volume (GTV) and from 16.4% to 24.9% for D98% of the PTV. After applying BART, the differences were minimized to -1.5% to -0.6% for D50% of the GTV and -0.1% to 0.9% for D98% of the PTV. In contrast, the compensated PD plan exhibited larger residual deviations, with dose differences ranging from -9.9% to -14.0% for D50% of the GTV and -12.3% to -7.3% for D98% of the PTV. The volume differences between the BART plan and the plan without interruption remained within -0.8% to -0.4% for V5Gy and -0.2% to 0.0% for V20Gy, while differences between the BART and compensated PD plans were similarly small. The maximum dose to the spinal cord (D0.1cc) also remained within -0.2 to 0.1 Gy for the BART plan relative to the plan without interruption and -0.1 to -0.5 Gy compared to the compensated PD plan. These results confirm that the OAR doses remained within clinically acceptable constraints across all evaluated plans.

CONCLUSION

This study demonstrated that the BART framework effectively compensates for the biological dose reduction caused by interruptions during lung cancer SBRT. BART successfully maintained target dose coverage and minimized biological dose loss for the target, while keeping OAR doses within safe limits, including for the lungs and spinal cord. The introduction of BART marks a significant advancement in adaptive radiotherapy, offering a comprehensive approach to managing interruptions and improving clinical outcomes.

American Radium Society Appropriate Use Criteria Systematic Review and Guidelines on Reirradiation for Non-Small Cell Lung Cancer Executive Summary

Definitive thoracic reirradiation can improve outcomes for select patients with non-small cell lung cancer (NSCLC) with locoregional recurrences. To date, there is a lack of systematic reviews on safety or efficacy of NSCLC reirradiation and dedicated guidelines. This American Radium Society Appropriate Use Criteria Systematic Review and Guidelines provide practical guidance on thoracic reirradiation safety and efficacy and recommends consensus of strategy, techniques, and composite dose constraints to minimize risks of high-grade/fatal toxicities. Preferred Reporting Items for Systematic Reviews and Meta-Analyses systematic review assessed all studies published through May 2020 evaluating toxicities, local control and/or survival for NSCLC thoracic reirradiation. Of 251 articles, 52 remained after exclusions (3 prospective) and formed the basis for recommendations on the role of concurrent chemotherapy, factors associated with toxicities, and optimal reirradiation modalities and dose-fractionation schemas. Stereotactic body radiation therapy improves conformality/dose escalation and is optimal for primary-alone failures, but caution is needed for central lesions. Concurrent chemotherapy with definitive reirradiation improves outcomes in nodal recurrences but adds toxicity and should be individualized. Hyperfractionated reirradiation may reduce long-term toxicities, although data are limited. Intensity modulated reirradiation is recommended over 3D conformal reirradiation. Particle therapy may further reduce toxicities and enable safer dose escalation. Acute esophagitis/pneumonitis and late pulmonary/cardiac/esophageal/brachial plexus toxicities are dose limiting for reirradiation. Recommended reirradiation composite dose constraints (2 Gy equivalents): esophagus V60 <40%, maximum point dose (Dmax) < 100 Gy; lung V20 <40%; heart V40 <50%; aorta/great vessels Dmax < 120 Gy; trachea/proximal bronchial tree Dmax < 110 Gy; spinal cord Dmax < 57 Gy; brachial plexus Dmax < 85 Gy. Personalized thoracic reirradiation approaches and consensus dose constraints for thoracic reirradiation are recommended and serve as the basis for ongoing Reirradiation Collaborative Group and NRG Oncology initiatives. As very few prospective and small retrospective studies formed the basis for generating the dose constraint recommended in this report, further prospective studies are needed to strengthen and improve these guidelines.

Plan evaluation tool for spatially fractionated radiation therapy for unresectable large tumors via spatial biological effective dose modeling in combination therapy

We present the utility of a plan evaluation tool for a multi-course radiation treatment consisting of a highly heterogeneous SFRT plan followed by a course of curative radiation therapy for large and bulky unresectable tumors. For a more accurate plan assessment, this novel method calculates the voxelized biological effective dose (BED) spatially from each course and combines them into a single spatial BED distribution (s-BED). Ten previously treated head and neck (H&N) cancer patients with MLC-based 3D-conformal SFRT (15 Gy in 1 fraction) followed by a curative course of VMAT for 66-70 Gy in 33-35 fractions were retrospectively analyzed using this new s-BED method. The s-BED calculations were based on the standard linear-quadratic (LQ) model. Evaluations of mean BED using this s-BED method were compared to other methodologies that use each course's DVH, mean dose, and prescription dose. From this, tumor control probability (TCP) was calculated using these different methodologies. Lastly, doses to nearby organs at risk (OARs) were evaluated using the s-BED method and compared to each course's physical dose distribution. The OARs evaluated were the spinal cord, brainstem, optic pathway, cochlea, parotid glands, larynx, esophagus, and mandible. From the physical dose distributions, a s-BED distribution and a spatial EQD2 (s-EQD2) distribution were able to be calculated and visualized. The various methods of calculating mean BED using each course's dose prescription, mean dose, DVH, and from the s-BED resulted in varying mean BED: 121.8 Gy, 99.7 Gy, 88.3 Gy, and 100.6 Gy, respectively. In turn, this also gave varying predictions in tumor response: 100.0%, 98.2%, 92.3%, and 91.1%, respectively. Of the 8 H&N patients who received follow-up imaging, 7 (87.5%) had local tumor control. Reported toxicities of this cohort saw 2 cases of grade 3 toxicities (skin desquamation), 3 grade 1 toxicities (oral mucositis and odynophagia), and 1 grade 4 toxicity (necrotizing fasciitis). The composite s-BED distributions provided a means of better understanding the effective biological dose being delivered to both the target and nearby OARs spatially. Future utilization of this method during the treatment planning process may allow for more personalized treatment prescriptions for the SFRT course and the follow-up combination therapy, potentially enhancing therapeutic benefits in managing large and bulky unresectable tumors.

Biological dose-based fractional dose optimization of Bragg peak FLASH-RT for lung cancer treatment

BACKGROUND

The FLASH effect is dose-dependent, and fractional dose optimization may enhance it, improving normal tissue sparing.

PURPOSE

This study investigates the performance of fractional dose optimization in enhancing normal tissue sparing for Bragg peak FLASH radiotherapy (FLASH-RT).

METHODS

15 lung cancer patients, including eight with peripherally located tumors and seven with centrally located tumors, were retrospectively analyzed. A uniform fractionation prescription of 50 Gy in five fractions was utilized, corresponding to a biological equivalent dose (BED) of 100 Gy, calculated using an α/β value of 10 Gy. For each patient, uniform (UFD) and nonuniform fractional dose (non-UFD) plans were designed. In UFD FLASH plans, five multi-energy Bragg peak beams were optimized using single-field optimization, each delivering 10 Gy to the target. In non-UFD FLASH plans, fractional doses were optimized to enhance sparing effects while ensuring the target received a BED comparable to UFD plans. A dose-dependent FLASH enhancement ratio (FER) was integrated with the BED to form the FER-BED metric to compare the UFD and non-UFD plans. An α/β value of 3 Gy was applied for normal tissues in the calculations.

RESULTS

Bragg peak FLASH plans showed high dose conformality for both peripheral and central tumors, with all plans achieving a conformality index (the ratio of the volume receiving the prescribed dose to the CTV volume) below 1.2. In non-UFD plans, fractional doses ranged from 5.0 Gy to 20.0 Gy. Compared to UFD plans, non-UFD plans achieved similar BED coverage (BED98%: 96.6 Gy vs. 97.1 Gy, p = 0.256), while offering improved organ-at-risk sparing. Specifically, the FER-BED15cc for the heart reduced by 10.5% (9.4 Gy vs. 10.5 Gy, p = 0.017) and the V6.7GyFER-BED for the ipsilateral lung decreased by 4.3% (29 .1% vs. 30.4%, p = 0.008). No significant difference was observed in FER-BED0.25cc of spinal cord (UFD: 7.1 Gy, non-UFD: 6.9 Gy, p = 0.626) and FER-BED5cc in esophagus (UFD: 0.4 Gy, non-UFD: 0.4 Gy, p = 0.831).

CONCLUSIONS

Bragg peak FLASH-RT achieved high dose conformality for both peripheral and central tumors. Fractional dose optimization, using a single beam per fraction delivery mode, enhanced normal tissue sparing by leveraging both fractionation and FLASH effects.

FCB-CHOPS: An Evolution of a Commonly Used Acronym for Evaluating Radiation Treatment Plans

Checklists have been used across many fields as a systematic framework to reduce human error and improve safety. In radiation oncology, the CB-CHOP acronym was previously developed as a tool to aid physicians in assessing the quality of radiation treatment plans for approval. This manuscript updates the acronym for the modern era with the addition of F and S to create FCB-CHOPS: fusion, contours, beams, coverage, heterogeneity, organs at risk, prescription, and dose summation. These 2 additions reflect the evolution and importance of image fusion to aid in the delineation of targets and organs at risk and dose summation to reflect the increased incidence of reirradiation and the need to consider prior treatment courses in the final plan evaluation. Utilization of this and similar checklists is critical in maintaining high-quality and safe radiation oncology treatments.

Tumor reirradiation: Issues, challenges and perspectives for radiobiology

The radiobiology of tumor reirradiation is poorly understood. It pertains to tumors and their sensitivity at the time of relapse, encompassing primary tumors, metastases, or secondary cancers developed in or proximal to previously irradiated tissues. The ability to control the pathology depends, in part, on understanding this sensitivity. To date, literature data remains limited regarding changes in the radiosensitivity of tissues after initial irradiation, and most proposals are based on conjecture. The response of healthy tissues at the site of irradiation raises concerns about radio-induced complications. Cumulative dose is likely a major factor in this risk, thus using equivalent dose calculations might help reduce the risk of complications. However, the correlation between mathematical equivalence formulas and clinical effects of radiobiological origin is weak, and the lack of knowledge of the alpha/beta (α/β) ratio of healthy tissues remains an obstacle to the extensive use of these formulas. However, tissues exposed to recovery dose may have a tolerance to irradiation much higher than assumed, thus further biological work remains to be developed. Also, the functionality of previously irradiated tissues could be useful in selecting the most suitable irradiation beams. Finally, research on the genomics of irradiated healthy tissues could improve the prediction of side effects and personalize radiotherapy.

Salvage percutaneous high-dose-rate brachyablation after stereotactic body radiation therapy for early-stage non-small cell lung cancer

Patients with primary tumor progression after stereotactic body radiation therapy (SBRT) for stage I non-small cell lung cancer (NSCLC) have a second chance at complete tumor eradication with salvage local therapies, including lung resection, repeat course of SBRT, and percutaneous ablative therapies. In this paper, we presented our institution's initial experience with percutaneous high-dose-rate (HDR) brachyablation for a relapsed stage I NSCLC that had been treated with SBRT 4.3 years earlier. Lung tumor measuring approximately 5 cm in maximum tumor dimension at the time of relapse was histopathologically confirmed to be persistent squamous cell carcinoma, and successfully treated with a single fraction of 24 Gy with HDR brachyablation. Treatment was delivered via two percutaneous catheters inserted under CT-guidance, and treated in less than 20 minutes. The patient was discharged home later the same day without the need for a chest tube, and has been monitored with serial surveillance scans every 3 to 6 months without evidence of further lung cancer progression or complications at 2.8 years post-HDR brachyablation procedure and 7.8 years after initial SBRT.

Review and recommendations on deformable image registration uncertainties for radiotherapy applications

Deformable image registration (DIR) is a versatile tool used in many applications in radiotherapy (RT). DIR algorithms have been implemented in many commercial treatment planning systems providing accessible and easy-to-use solutions. However, the geometric uncertainty of DIR can be large and difficult to quantify, resulting in barriers to clinical practice. Currently, there is no agreement in the RT community on how to quantify these uncertainties and determine thresholds that distinguish a good DIR result from a poor one. This review summarises the current literature on sources of DIR uncertainties and their impact on RT applications. Recommendations are provided on how to handle these uncertainties for patient-specific use, commissioning, and research. Recommendations are also provided for developers and vendors to help users to understand DIR uncertainties and make the application of DIR in RT safer and more reliable.