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. 2023 Aug 31;28(1):309.
doi: 10.1186/s40001-023-01278-1.

Study on the transferability of the knowledge-based VMAT model to predict IMRT plans in prostate cancer radiotherapy

Suyan Bi #  1 , Xingru Sun #  2 , Wan Fatihah Binti Wan Sohaimi  3 , Ahmad Lutfi Bin Yusoff  4
Affiliations

Study on the transferability of the knowledge-based VMAT model to predict IMRT plans in prostate cancer radiotherapy

Suyan Bi et al. Eur J Med Res. .

Abstract

Objective: The aim of this study was to investigate the feasibility of VMAT library-derived model transfer in the prediction of IMRT plans by dosimetry comparison among with three groups of IMRT plans: two groups of automatic IMRT plans generated by the knowledge-based the volumetric modulated arc therapy (VMAT) model and intensity-modulated radiation therapy (IMRT) model and one group of manual IMRT plans.

Methods: 52 prostate cancer patients who had completed radiotherapy were selected and randomly divided into 2 groups with 40 and 12 separately. Then both VMAT and IMRT plans were manually designed for all patients. The total plans in the group with 40 cases as training datasets were added to the knowledge-based planning (KBP) models for learning and finally obtained VMAT and IMRT training models. Another 12 cases were selected as the validation group to be used to generated auto IMRT plans by KBP VMAT and IMRT models. At last, the radiotherapy plans from three groups were obtained: the automated IMRT plan (V-IMRT) predicted by the VMAT model, the automated IMRT plan (I-IMRT) predicted by the IMRT model and the manual IMRT plan (M-IMRT) designed before. The dosimetric parameters of planning target volume (PTV) and organ at risks (OARs) as well as the time parameters (monitor unit, MU) were statistically analyzed.

Results: The dose limit of all plans in the training datasets met the clinical requirements. Compared with the training plans added to VMAT model, the dosimetry parameters have no statistical differences in PTV (P > 0.05); the dose of X% volume (Dx%) with D25% and D35% in rectal and the maximum dose (Dmax) in the right femoral head were lower (P = 0.04, P = 0.01, P = 0.00) while D50% in rectal was higher (< 0.05) in the IMRT model plans. In the 12 validation cases, both automated plans showed better dose distribution compared with the M-IMRT plan: the Dmax of PTV in the I-IMRT plans and the dose in volume of interesting (VOI) of bladder and bilateral femoral heads were lower with a statistically significant difference (P < 0.05). Compared with the I-IMRT plans, dosimetric parameters in PTV and VOI of all OARs had no statistically significant differences (P > 0.05), but the Dmax in left femoral heard and D15% in the right femoral head were lower and have significant differences (P < 0.05). Furthermore, the low-dose regions, which was defined as all volumes outside of the PTV (RV) with the statistical parameters of mean dose (Dmean), the volume of covering more than 5 Gy dose (V5Gy), and also the time parameter (MU) required to perform the plan were considered. The results showed that Dmean in V-IMRT was smaller than that in the I-IMRT plan (P = 0.02) and there was no significant difference in V5Gy and MU (P > 0.05).

Conclusion: Compared with the manual plan, the IMRT plans generated by the KBP models had a significant advantage in dose control of both OARs and PTV. Compared to the I-IMRT plans, the V-IMRT plans was not only without significant disadvantages, but it also achieved slightly better control of the low-dose region, which meet the clinical requirements and can used in the clinical treatment. This study demonstrates that it is feasible to transfer the KBP VMAT model in the prediction of IMRT plans.

Keywords: IMRT planning; Knowledge-based planning; Model transfer; Prostate radiotherapy; VMAT automated planning model.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Flowchart of the research protocol
Fig. 2
Fig. 2
Changes in R2 values before and after the cleaning of the model
Fig. 3
Fig. 3
Residual plots between the actual results and the predicted results of DVH principal component analysis of OARs. In the IMRT model, the rectum, bladder, left femoral head, and right femoral head are, respectively, (a) through (d), and in the VMAT model group, they are, respectively, (e) through (h). The first primary component score (PCS1) of the predicted DVH for each plan’s structure is represented by the horizontal coordinate, and the PCS1 of the corresponding actual DVH of the structures is represented by the vertical coordinate. The figure’s dashed line denotes the error range, while the solid line shows that the predicted and actual numbers are equivalent
Fig. 4
Fig. 4
Comparison of DVH of PTV (a) and OAR[rectum (b), bladder (c), Lt femur (d) and Rt femur (e)] of IMRT plan generated by two models with manual IMRT plan
See this image and copyright information in PMC

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