Assessment of biological dosimetric margin for stereotactic body radiation therapy

Journal of Radiation Research

Saito

Nagata

2023

Self Cite

This study aimed to expand the biological conversion factor (BCF) model, which converts the physical dosimetric margin (PDM) to the biological dosimetric margin (BDM) for point prescription with 3-dimensional conformal radiation therapy (3DCRT) and the marginal prescription method with volumetric-modulated arc radiotherapy (VMAT). The VMAT of the marginal prescription and the 3DCRT of the point prescription with lung stereotactic body radiation therapy (SBRT) by using RayStation were planned. The biological equivalent dose (BED) for a dose per fraction (DPF) of 3–20 Gy was calculated from these plans. The dose was perturbed with the calculation using a 1-mm step isocenter shift. The dose covering 95% of the target was greater than or equal to 90% of the prescribed physical dose, and the BED were defined as the PDM and BDM, respectively. The BCF was created as a function of the DPF. The PDM and BDM for all DPFs were larger with the point prescription method than with the marginal prescription method. The marginal prescription method with a 60% isodose line had a larger PDM and BDM. The BCF with the point prescription was smaller than that with the marginal prescription in the left–right (LR), anterior–posterior (AP) and cranio–caudal (CC) directions. In the marginal prescription method, the 60% isodose line had a higher BCF. In conclusion, the improved BCF method could be converted to BDM for point prescription with 3DCRT and marginal prescription method with VMAT, which is required for stereotactic radiation therapy in radiobiology-based treatment planning.

“…The process for calculating the PDM and BDM was proposed in our previous study, as shown in Fig. 2 [ 4 ]. The treatment planning system used was RayStation (RaySearch, Sweden).…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Physical and biological dosimetric margin according to prescription method for stereotactic body radiation therapy

Journal of Radiation Research

Saito

Nagata

2023

Self Cite

“…These scenarios include a no setup error scenario, endpoint setup error scenario, and intermediate setup error scenario in the right‐left, inferior‐superior, and posterior‐anterior directions. The setup error, which was assumed to occur within the PTV margin, was determined to be the scenario 20 . Namely, the CTV dose with the setup error in the PTV‐based plan, which was used for the prescribed dose for the robust plan, was evaluated.…”

Section: Methodsmentioning

confidence: 99%

“…The setup error, which was assumed to occur within the PTV margin, was determined to be the scenario. 20 Namely, the CTV dose with the setup error in the PTV-based plan, which was used for the prescribed dose for the robust plan, was evaluated. The dose distribution in the moving coordinates of the PTVbased plan determined the dose constraint in the robust plan.…”

Section: Robust Planmentioning

confidence: 99%

Robust optimization of VMAT for prostate cancer accounting for geometric uncertainty

Wada

J Applied Clin Med Phys

Murakami

et al. 2022

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The aim of this study was to propose optimal robust planning by comparing the robustness with setup error with the robustness of a conventional planning target volume (PTV)-based plan and to compare the robust plan to the PTV-based plan for the target and organ at risk (OAR). Data from 13 patients with intermediate-to-high-risk localized prostate cancer who did not have T3b disease were analyzed. The dose distribution under multiple setup error scenarios was assessed using a conventional PTV-based plan. The clinical target volume (CTV) and OAR dose in moving coordinates were used for the dose constraint with the robust plan. The hybrid robust plan added the dose constraint of the PTV-rectum to the static coordinate system. When the isocenter was shifted by 10 mm in the superior-inferior direction and 8 mm in the right-left and anterior directions, the doses to the CTV, bladder, and rectum of the PTVbased plan, robust plan, and hybrid robust plan were compared. For the CTV D 99% in the PTV-based plan and hybrid robust plan, over 95% of the prescribed dose was secured in all directions, except in the inferior direction. There was no significant difference between the PTV-based plan and the hybrid robust plan for rectum V 70Gy , V 60Gy , and V 40Gy . This study proposed an optimization method for patients with prostate cancer. When the setup error occurred within the PTV margin, the dose robustness of the CTV for the hybrid robust plan was higher than that of the PTV-based plan, while maintaining the equivalent OAR dose.

Improved biological dosimetric margin model for different PTV margins with stereotactic body radiation therapy in homogeneous and nonhomogeneous tumor regions

Rep Pract Oncol Radiother.

Saito²,

Nagata³

2022

through different fractionation schemes or dose per fraction [1][2][3]. Fowler showed that BED modeling is useful for understanding normal tissue and tumor responses across different fractionation schemes and treatment methods [4].The relative biological effectiveness depends on the dose level, which is the dose per fraction (DPF) and the number of dose fractions. Our previous AbstrAct background: The purpose of this study was to improve the biological dosimetric margin (BDM) corresponding to different planning target volume (pTV) margins in homogeneous and nonhomogeneous tumor regions using an improved biological conversion factor (BCF) model for stereotactic body radiation therapy (sBrT). Materials and methods:The pTV margin was 5-20 mm from the clinical target volume. The biologically equivalent dose (BeD) was calculated using the linear-quadratic model. The biological parameters were α/β = 10 Gy, and the dose per fraction (DpF) was d = 3-20 Gy/fr. The isocenter was offset at intervals of 1 mm; 95% of the clinical target volume covered more than 90% of the prescribed physical dose, and BeD was defined as biological and physical DMs. The BCF formula was defined as a function of the DpF. results:The difference in the BCF caused by the DpF was within 0.05 for the homogeneous and nonhomogeneous phantoms. In the virtual nonhomogeneous phantom, the data with a pTV margin of 10-20 mm were not significantly different; thus, these were combined to fit the BCF. In the virtual homogeneous phantom, the BCF was fitted to each pTV margin. conclusions:The current study improved a scheme to estimate the BDM considering the size of the pTV margin and homogeneous and nonhomogeneous regions. This technique is expected to enable BeD-based treatment planning using treatment systems based on physical doses for sBrT.