Dosimetric assessment of tumor control probability in intensity and volumetric modulated radiotherapy plans

Pretreatment patient-specific quality assurance prediction based on 1D complexity metrics and 3D planning dose: classification, gamma passing rates, and DVH metrics

PURPOSE

Highly modulated radiotherapy plans aim to achieve target conformality and spare organs at risk, but the high complexity of the plan may increase the uncertainty of treatment. Thus, patient-specific quality assurance (PSQA) plays a crucial role in ensuring treatment accuracy and providing clinical guidance. This study aims to propose a prediction model based on complexity metrics and patient planning dose for PSQA results.

MATERIALS AND METHODS

Planning dose, measurement-based reconstructed dose and plan complexity metrics of the 687 radiotherapy plans of patients treated in our institution were collected for model establishing. Global gamma passing rate (GPR, 3%/2mm,10% threshold) of 90% was used as QA criterion. Neural architecture models based on Swin-transformer were adapted to process 3D dose and incorporate 1D metrics to predict QA results. The dataset was divided into training (447), validation (90), and testing (150) sets. Evaluation of predictions was performed using mean absolute error (MAE) for GPR, planning target volume (PTV) HI and PTV CI, mean absolute percentage error (MAPE) for PTV D95, PTV D2 and PTV Dmean, and the area under the receiver operating characteristic (ROC) curve (AUC) for classification. Furthermore, we also compare the prediction results with other models based on either only 1D or 3D inputs.

RESULTS

In this dataset, 72.8% (500/687) plans passed the pretreatment QA under the criterion. On the testing set, our model achieves the highest performance, with the 1D model slightly surpassing the 3D model. The performance results are as follows (combine, 1D, and 3D transformer): The AUCs are 0.92, 0.88 and 0.86 for QA classification. The MAEs of prediction are 0.039, 0.046, and 0.040 for 3D GPR, 0.018, 0.021, and 0.019 for PTV HI, and 0.075, 0.078, and 0.084 for PTV CI. Specifically, for cases with 3D GPRs greater than 90%, the MAE could achieve 0.020 (combine). The MAPE of prediction is 1.23%, 1.52%, and 1.66% for PTV D95, 2.36%, 2.67%, and 2.45% for PTV D2, and 1.46%, 1.70%, and 1.71% for PTV Dmean.

CONCLUSION

The model based on 1D complexity metrics and 3D planning dose could predict pretreatment PSQA results with high accuracy and the complexity metrics play a leading role in the model. Furthermore, dose-volume metric deviations of PTV could be predicted and more clinically valuable information could be provided.

A Dosimetric and Radiobiological Comparison of Intensity Modulated Radiotherapy, Volumetric Modulated Arc Therapy and Helical Tomotherapy Planning Techniques in Synchronous Bilateral Breast Cancer

OBJECTIVE

The present investigation intends to identify the optimal radiotherapy treatment plan for synchronous bilateral breast cancer (SBBC) using dosimetric and radiobiological indexes for three techniques, namely, helical tomotherapy (HT), volumetric modulated arc therapy (VMAT), and intensity-modulated radiotherapy (IMRT).

METHODS

Twenty SBBC treated female patients treatment planning data (average age of 52.5 years) were used as the sample for the present study. Three different plans were created using 50 Gy in a 25 fraction dose regime. Poisson, Niemierko, and LKB models were applied for calculating normal tissue complication probability (NTCP) and tumour control probability (TCP).

RESULT

The target average dose comparison between IMRT with HT and VMAT with HT was highly substantial (P=0.001). The percentage of TCP for IMRT, VMAT, and HT in the Poisson model were 93.70±0.28, 94.68±0.30, and 94.34±0.57, respectively (p<0.05). The dose maximum was lower for the whole lung in the HT plan, with an average dose of 49.31Gy±3.9 (p<0.009). The NTCP values of both Niemierko and LKB models were lower for the heart, lungs, and liver for the IMRT plan.

CONCLUSION

The sparing of organs at risk was higher in the HT plan dosimetrically, and the TCP was higher in the three techniques. The comparison between the three techniques shows that the IMRT and HT techniques could be considered for treating SBBC.

Clinical Impact of the Bolus in Intensity-Modulated Radiotherapy and Volumetric-Modulated Arc Therapy for Stage I-II Nasal Natural Killer/T-Cell Lymphoma

INTRODUCTION

To estimate the clinical impact of bolus in intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) for stage I-II nasal natural killer/T-cell lymphoma (NNKTCL), including target quality, organs at risk (OARs) sparing, and tumor control probability (TCP).

METHODS

Two different treatment plans were designed in IMRT and VMAT for 10 stage I-II NNKTCL patients. The clinical plans added bolus perfectly contacting the nose skin, similar to common clinical planning design practices. The edited bolus plans resulted from dose recalculation with the edited bolus, which simulated the actual shape of a commercial flat bolus during treatment. All the plans were with no beam passing through the couch avoiding beam attenuation caused by the couch. Differences between both types of plans in target quality, OARs sparing, and TCP were evaluated.

RESULTS

Compared with clinical plans, the D98%, D2%, Dmean, and TCP of edited bolus plans with IMRT slightly decreased (p = 0.002, 0.015, 0.000, and 0.000), the homogeneity index increased 8.33% (p = 0.024), and the doses to a small number of OARs slightly changed. Similar results were obtained for VMAT.

CONCLUSION

The bolus deformation in practical clinical treatment resulted clinically in tiny changes with respect to the target coverage, OARs sparing, and TCP in both IMRT and VMAT for stage I-II NNKTCL. This implied that the clinical impact of the boluscan be negligible when utilizing it to increase the dose to irregularly shaped tumors in the nasal area.

Applying Non-Homogeneous Dose Optimization to Improve Conventionally Fractionated Radiation Plan Quality in Patients with Non-Small Cell Lung Cancer

PURPOSE

Nonhomogeneous dose optimization (NHDO) is exploited in stereotactic body radiation therapy (SBRT) to increase dose delivery to the tumor and allow rapid dose falloff to surrounding normal tissues. We investigate changes in plan quality when NHDO is applied to inverse-planned conventionally fractionated radiation therapy (CF-RT) plans in patients with non-small cell lung cancer.

METHODS AND MATERIALS

Patients with near-central non-small cell lung cancer treated with CF-RT in 2018 at a single institution were identified. CF-RT plans were replanned using NHDO techniques, including normalizing to a lower isodose line, while maintaining clinically acceptable normal tissue constraints and target coverage. Tumor control probabilities were calculated. We compared delivered CF-RT plans using homogenous dose optimization (HDO) versus NHDO using Wilcoxon signed-rank tests. Median values are reported.

RESULTS

Thirteen patients were replanned with NHDO techniques. Planning target volume coverage by the prescription dose was similar (NHDO = 96% vs HDO = 97%, P = .3). All normal-tissue dose constraints were met. NHDO plans were prescribed to a lower-prescription isodose line compared with HDO plans (85% vs 97%, P = .001). NHDO increased mean dose to the planning target volume (73 Gy vs 67 Gy), dose heterogeneity, and dose falloff gradient (P < .03). NHDO decreased mean dose to surrounding lungs, esophagus, and heart (relative reduction of 6%, 14%, and 15%, respectively; P < .05). Other normal tissue objectives improved with NHDO, including total lung V40 and V60, heart V30, and maximum esophageal dose (P < .05). Tumor control probabilities doubled from 31.6% to 65.4% with NHDO (P = .001).

CONCLUSIONS

In select patients, NHDO principles used in SBRT optimization can be applied to CF-RT. NHDO results in increased tumor dose, reduction in select organ-at-risk dose objectives, and better maintenance of target coverage and normal-tissue constraints compared with HDO. Our data demonstrate that principles of NHDO used in SBRT can also improve plan quality in CF-RT.