Development and evaluation of a clinical model for lung cancer patients using stereotactic body radiotherapy (SBRT) within a knowledge-based algorithm for treatment planning

The purpose of this study was to describe the development of a clinical model for lung cancer patients treated with stereotactic body radiotherapy (SBRT) within a knowledge-based algorithm for treatment planning, and to evaluate the model performance and applicability to different planning techniques, tumor locations, and beam arrangements. 105 SBRT plans for lung cancer patients previously treated at our institution were included in the development of the knowledge-based model (KBM). The KBM was trained with a combination of IMRT, VMAT, and 3D CRT techniques. Model performance was validated with 25 cases, for both IMRT and VMAT. The full KBM encompassed lesions located centrally vs. peripherally (43:62), upper vs. lower (62:43), and anterior vs. posterior (60:45). Four separate sub-KBMs were created based on tumor location. Results were compared with the full KBM to evaluate its robustness. Beam templates were used in conjunction with the optimizer to evaluate the model\u27s ability to handle suboptimal beam placements. Dose differences to organs-at-risk (OAR) were evaluated between the plans gener-ated by each KBM. Knowledge-based plans (KBPs) were comparable to clinical plans with respect to target conformity and OAR doses. The KBPs resulted in a lower maximum spinal cord dose by 1.0 ± 1.6 Gy compared to clinical plans, p = 0.007. Sub-KBMs split according to tumor location did not produce significantly better DVH estimates compared to the full KBM. For central lesions, compared to the full KBM, the peripheral sub-KBM resulted in lower dose to 0.035 cc and 5 cc of the esophagus, both by 0.4Gy ± 0.8Gy, p = 0.025. For all lesions, compared to the full KBM, the posterior sub-KBM resulted in higher dose to 0.035 cc, 0.35 cc, and 1.2 cc of the spinal cord by 0.2 ± 0.4Gy, p = 0.01. Plans using template beam arrangements met target and OAR criteria, with an increase noted in maximum heart dose (1.2 ± 2.2Gy, p = 0.01) and GI (0.2 ± 0.4, p = 0.01) for the nine-field plans relative to KBPs planned with custom beam angles. A knowledge-based model for lung SBRT consisting of multiple treatment modalities and lesion loca-tions produced comparable plan quality to clinical plans. With proper training and validation, a robust KBM can be created that encompasses both IMRT and VMAT techniques, as well as different lesion locations

RT for Patients with Compressed Air Tissue Expanders: Treatment Planning Solutions and Limitations

Purpose/Objective(s): Compressed air tissue expanders (CATEs) consist of a silicon shell containing a metallic CO2 reservoir, surgically placed in the chest wall post-mastectomy. CATEs pose significant challenges for RT: The high density reservoir causes artifacts on the planning CT, which encumber structure definition and cause misrepresentation of density information, in turn affecting dose calculation. This study describes a method to model the CATE in a commercial treatment planning system (TPS), and discusses the limitations of different dose calculation algorithms (DCAs) in and around the device. An understanding of DCA accuracy near the CATE is critical for assessing individual plan quality, appropriateness of DCA and planning technique, and even the decision to use a CATE in an RT setting. Materials/Methods: A CATE model was created in a commercial TPS. The CATE was imaged using optimal CT geometry and technique. Individual components were contoured and dimensions were verified against manufacturer specifications. The model was available for registration with a patient CT in the TPS. Assigned densities of the model were optimized by comparing measured and calculated transmission through the CATE. Transmission was measured with radiochromic film in various geometries. Dose was calculated using two commercially available DCAs: a convolution-based algorithm (CBA) and an explicit linear Boltzman transport equation solver algorithm (LBTEA). Doses were compared using profile and gamma analyses. Clinical impact was evaluated using CT data from 3 patients with CATEs. The CATE model was registered to each patient CT, and 3DRT plans were calculated using both DCAs. Clinically significant DVHs were analyzed. Results: For direct transmission through the CATE, both DCAs achieved greater than 99% gamma pass rate. However, for the region 0-1 cm adjacent to the CATE, gamma pass rate was greater than 98% for the LBTEA, but near 0% for the CBA. Compared to the LBTEA, the CBA overestimated mean dose in the CO2 reservoir and the air cavity by 5-7% and 10-13%, respectively. The CBA underestimated mean dose in the reservoir’s dose shadow and the adjacent chest wall by 0.5-5%. Changes in max dose were more variable and patient-specific. Conclusion: Approaching a CATE in an RT setting, clinicians must first obtain accurate patient density information. The CATE model described here is one practical method. Second, clinicians must understand the accuracy of their DCA near the CATE to evaluate plan quality. This work suggests that both the CBA and LBTEA accurately predicted beam transmission through the CATE, but the CBA overestimates dose within 1 cm lateral of the CATE. Finally, clinicians must decide if and how an acceptable plan can be delivered with the CATE in place. The decrease in target coverage due to attenuation by the CATE may require optimization techniques (such as field-in-field). These techniques should be used with careful consideration of the DCA’s uncertainty

Changes in pharyngeal constrictor volumes during head and neck radiation therapy: Implications for dose delivery

OBJECTIVE: The objective of this study was to evaluate the anatomical changes and associated dosimetric consequences to pharyngeal constrictor muscles (PCMs) that occur during head and neck (H and N) radiotherapy (RT). MATERIALS AND METHODS: A cohort of 13 oropharyngeal cancer patients with daily cone beam computed tomography (CBCT) was retrospectively studied. On every 5th CBCT image, PCM was manually delineated by a radiation oncologist. The anterior-posterior PCM thickness was measured at the midline level of C3 vertebral body. Delivered dose to PCM was estimated by calculating dose on daily images and performing dose accumulation on corresponding planning CT images using a parameter-optimized B-spline-based deformable image registration algorithm. The mean and maximum delivered dose (Dmean, Dmax) to PCM were determined and compared with the corresponding planned quantities. RESULTS: The average (±standard deviation) volume increase (ΔV) and thickness increase (Δt) over the course of 35 total fractions were 54 ± 33% (11.9 ± 7.6 cc) and 63 ± 39% (2.9 ± 1.9 mm), respectively. The resultant cumulative mean dose increase from planned dose to PCM (ΔDmean) was 1.4 ± 1.3% (0.9 ± 0.8 Gy), while the maximum dose increase (ΔDmax) was 0.0 ± 1.6% (0.0 ± 1.1 Gy). Patients who underwent adaptive replanning (n = 6) showed a smaller mean dose increase than those without (n = 7); 0.5 ± 0.2% (0.3 ± 0.1 Gy) versus 2.2 ± 1.4% (1.4 ± 0.9 Gy). There were statistically significant (P = 0.001) strong correlations between ΔDmean and Δt (Pearson coefficient r = 0.78), as well as between ΔDmean and ΔV (r = 0.52). CONCLUSION: The patients underwent considerable anatomical changes to PCM during H and N RT. However, the resultant increase in dose to PCM was minor to moderate. PCM thickness measured at C3 level is a good predictor for the mean dose increase to PCM

Modeling Aeroform Tissue Expander for Postmastectomy Radiation Therapy

The AeroForm chest wall tissue expander (TE) is a silicon shell containing a metallic CO2 reservoir, placed surgically after mastectomy. The patient uses a remote control to release compressed CO2 from the reservoir to inflate the expander. AeroForm poses challenges in a radiation therapy setting: The high density of the metallic reservoir causes imaging artifacts on the planning CT, which encumber structure definition and cause misrepresentation of density information, in turn affecting dose calculation. Additionally, convolution-based dose calculation algorithms may not be well-suited to calculate dose in and around high-density materials. In this study, a model of the AeroForm TE was created in Eclipse treatment planning system (TPS). The TPS model was validated by comparing measured to calculated transmission through the AeroForm. Transmission was measured with various geometries using radiochromic film. Dose was calculated with both Varian\u27s Anisotropic Analytical Algorithm (AAA) and Acuros External Beam (AXB) algorithms. AAA and AXB were compared using dose profile and gamma analyses. While both algorithms modeled direct transmission well, AXB better modeled lateral scatter from the AeroForm TE. Clinical significance was evaluated using clinical data from four patients with AeroForm TEs. The AeroForm TPS model was applied, and RT plans were optimized using AAA, then re-calculated with AXB. Structures of clinical significance were defined and dose volume histogram analysis was performed. Compared to AXB, AAA overestimates dose in the AeroForm device. Changes in clinically significant regions were patient- and plan-specific. This study proposes a clinical procedure for modeling the AeroForm in a commercial TPS, and discusses the limitations of dose calculation in and around the device. An understanding of dose calculation accuracy in the vicinity of the AeroForm is critical for assessing individual plan quality, appropriateness of different planning techniques and dose calculation algorithms, and even the decision to use the AeroForm in a postmastectomy radiation therapy setting

Knowledge-Based Quality Assurance and Model Maintenance in Lung Cancer Radiation Therapy in a Statewide Quality Consortium of Academic and Community Practice Centers

PURPOSE: Locally advanced lung cancer (LALC) treatment planning is often complex due to challenging tradeoffs related to large targets near organs at risk, making the judgment of plan quality difficult. The purpose of this work was to update and maintain a multi-institutional knowledge-based planning (KBP) model developed by a statewide consortium of academic and community practices for use as a plan quality assurance (QA) tool. METHODS AND MATERIALS: Sixty LALC volumetric-modulated arc therapy plans from 2021 were collected from 24 institutions. Plan quality was scored, with high-quality clinical (HQC) plans selected to update a KBP model originally developed in 2017. The model was validated via automated KBP planning, with 20 cases excluded from the model. Differences in dose-volume histogram metrics in the clinical plans, 2017 KBP model plans, and 2022 KBP model plans were compared. Twenty recent clinical cases not meeting consortium quality metrics were replanned with the 2022 model to investigate potential plan quality improvements. RESULTS: Forty-seven plans were included in the final KBP model. Compared with the clinical plans, the 2022 model validation plans improved 60%, 65%, and 65% of the lung V20Gy, mean heart dose, and spinal canal D0.03cc metrics, respectively. The 2022 model showed improvements from the 2017 model in hot spot management at the cost of greater lung doses. Of the 20 recent cases not meeting quality metrics, 40% of the KBP model-replanned cases resulted in acceptable plans, suggesting potential clinical plan improvements. CONCLUSIONS: A multi-institutional KBP model was updated using plans from a statewide consortium. Multidisciplinary plan review resulted in HQC model training plans and model validation resulted in acceptable quality plans. The model proved to be effective at identifying potential plan quality improvements. Work is ongoing to develop web-based training plan review tools and vendor-agnostic platforms to provide the model as a QA tool statewide

Time trends and predictors of heart dose from breast radiation therapy in a large consortium of community and academic practices

Observational studies suggest that the risk of cardiac toxicity increases with increasing radiation dose to the heart, without a threshold for this effect. Although a recent systematic review summarized heart doses in the published literature, less is known about the range of heart doses delivered in routine practice in the United States today. The goal of this study was to assess the current state of cardiac sparing in a large prospective observational cohort, and to determine how cardiac dose varies by practice setting, technique, and patient characteristics

Contemporary practice patterns for palliative radiotherapy of bone metastases: Impact of a quality improvement project on extended fractionation

PURPOSE/OBJECTIVES: Radiotherapy (RT) effectively palliates bone metastases, though variability exists in practice patterns. National recommendations advocate against using extended fractionation (EF) with courses greater than ten fractions. We previously reported EF utilization of 14.8%. We analyzed practice patterns within a statewide quality consortium to assess EF use in a larger patient population following implementation of a quality measure focused on reducing EF. MATERIALS/METHODS: Patients treated for bone metastases within a statewide radiation oncology quality consortium were prospectively enrolled from March 2018 through October 2020. The EF quality metric was implemented March 1, 2018. Data on patient, physician and facility characteristics, fractionation schedules, and treatment planning and delivery techniques were collected. Multivariable binary logistic regression was used to assess EF. RESULTS: 1,445 consecutive patients treated with 1,934 plans were enrolled by 28 facilities. The median number of treatment plans per facility was 52 (range, 7-307). 60 different fractionation schedules were utilized. EF was delivered in 3.4% of plans. Initially, EF use was lower than expected and remained low over time. Significant predictors for EF use included complicated metastasis (OR 2.04, 95% CI: 1.04-4.02, p=0.04), lack of associated CNS or visceral disease (OR 2.27, 95% CI: 1.2-4.2, p=0.01), non-teaching versus teaching facilities (OR 8.97, 95% CI: 2.1-38.5, p\u3c0.01), and treating physicians with more years in practice (OR 12.82, 95% CI: 3.9-42.4, p\u3c0.01). CONCLUSIONS: Within a large, prospective population-based dataset, fractionation schedules for palliative RT of bone metastases remain highly variable. Resource-intensive treatments including EF persist, though EF use was low following implementation of a quality measure. Complicated metastases, lack of CNS or visceral disease, treatment at non-teaching facilities or by physicians with more years in practice significantly predict use of EF. These results support ongoing efforts to more clearly understand and address barriers to high value radiation approaches in the palliative setting

Contemporary Practice Patterns for Radiotherapy of Bone Metastases: Preliminary Analysis of Prospective Data from a Statewide Consortium Focusing on Extended Fractionation

Purpose/Objective(s): National guidelines recommend various effective dose and fractionation schemes for palliative radiotherapy (RT) of bone metastases, including noninferior outcomes with single fraction regimens. For Choosing Wisely, ASTRO advocated against use of extended fractionation schemes with greater than 10 fractions. We previously reported a retrospective assessment of heterogeneity in RT management of bone metastases. Herein, we sought to prospectively analyze current practice patterns of palliative RT in the treatment of bone metastases in diverse clinical settings. Specifically, we investigated possible predictors of extended treatment courses. Materials/Methods: Within a statewide radiation oncology quality consortium, patients were consecutively enrolled between March 2018 and February 2019 in both academic and non-academic facilities. Data on patient characteristics, provider and facility characteristics, dose and fractionation schedules, treatment planning and delivery techniques and image guidance were collected. Multivariable binary logistic regression was employed to assess use of extended fractionation (\u3e10 fractions) RT. Results: A total of 444 consecutive patients were enrolled by 24 treating facilities. The median case volume per center was 15 (range, 1-55), with a total of 608 plans from 411 patients available for analysis. The median number of plans per patient was 1 (range, 1-4). The most commonly employed dose and fractionation schedules were 3 Gy x 10 fractions (54%), 4 Gy x 5 fractions (14%), and 8 Gy x 1 fraction (11%). A minority of plans (5%) used extended fractionation. IMRT was utilized for 9% of plans, while cone beam CT image guidance was used in 14% of cases. A majority of plans (64%) were designed for uncomplicated osseous metastatic lesions. For uncomplicated lesions 13% of plans were prescribed 8 Gy x 1 fraction, while 5% were prescribed greater than 10 fractions. The only significant predictor of use of extended fractionation was type of treatment facility with academic centers significantly less likely to use more than 10 fractions per plan (OR=0.16, 95% CI: 0.04-0.72, p\u3c0.02). Conclusion: This is our initial analysis of contemporary practice patterns of palliative RT for bone metastases using prospective data recently collected from our statewide consortium. Within a large, consecutively enrolled patient cohort, we demonstrate that palliative RT for management of bone metastases remains diverse. Resource-intensive treatments including image guidance and extended fractionation exist, with type of treatment facility significantly predicting use of extended fractionation. Taken together, these preliminary results support our ongoing collection of the prospective data needed to more clearly understand the barriers to high value RT approaches in this setting

Changing Practice Patterns in the Radiation Treatment Delivery for Locally Advanced Lung Cancer: Results from a Statewide Consortium

Purpose/Objective(s): In 2014, the RTOG 0617 trial defined the standard radiation therapy (RT) dose as 60 Gy with concurrent chemotherapy in locally advanced non-small cell lung cancer (LA-NSCLC) patients. Further analyses of the study showed a decrease in grade 3 pneumonitis with static intensity modulated radiation therapy (sIMRT). Radiation treatment techniques used in routine clinical practice have evolved from 3D conformal radiation therapy (3DCRT) to sIMRT and more recently to rotational IMRT (rIMRT). However, the uptake of lower lung tumor RT dose recommendations and RT treatment techniques used in the “real world” setting is not known. The purpose of this study was to evaluate patterns of practice of both radiation dose and type of radiation technique used in a statewide radiation oncology consortium. Materials/Methods: From 2012 to 2018, 2741 patients with lung cancer treated with curative intent RT at 24 institutions participating in a statewide Radiation Oncology Quality Consortium were enrolled. Patients with small cell lung cancer, previous surgical resection, and patients who did not complete treatment were excluded. Furthermore, for RT dose analyses, outliers of RT doses (\u3c45 Gy and \u3e100 Gy) were excluded. Patients lacking DICOM information regarding treatment plans were excluded for the RT technique analyses. Changes in prescription doses and treatment techniques over time were evaluated. Trends over time in academic (n=4) vs. non-academic centers (n=20) were also analyzed. Academic centers were defined as those with a medical residency training program. Sample t-tests were used to compare means. Results: 1134 patients were analyzed for RT dose analysis, while 1087 patients were evaluated for the RT treatment technique. The mean prescription RT dose delivered to tumor decreased from 63 Gy to 60 Gy (p\u3c0.001) over the 6-year time period. In the earlier years of the data collection (2012-2013), \u3e50% of the cases were treated with 3DCRT and rIMRT was used in ≤5%. However, by 2018, the rate of rIMRT increased to 56.9% (p\u3c0.0001). See Table below. Similar practice patterns were seen in academic and non-academic centers for both RT dose and treatment technique analyses. Conclusion: In this large prospective “real world” study from a statewide consortium of practicing radiation oncologists, prescription mean RT dose used to treat LA-NSCLC has decreased to 60 Gy as per evidence-based guidelines. The primary treatment technique of delivering RT in LA-NSCLC has also changed in this interval. More than half of LA-NSCLC patients are now receiving rIMRT. The clinical implications of potential increases in low dose volumes (e.g., Lung and Heart V5) resulting from rIMRT will have to be evaluated going forward, especially in the changing systemic therapy paradigm that includes immunotherapy. [Figure presented