A new variable for SRS plan quality evaluation based on normal tissue sparing: the effect of prescription isodose levels

Zhang, Q; Zheng, Dandan; Yu, Long-Chuan; Morgan, Bruno; Driewer, J; Zhang, M; Li, S; Zhou, Shun; Zhen, Weining; Thompson, Robert B.; Wahl, Andrew O.; Lin, Chi; Enke, Charles Arthur

doi:10.1259/bjr.20140362

Cited by 16 publications

(15 citation statements)

References 22 publications

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“…The results of the optimal IDL for VMAT plans in our study are consistent with the conclusion of the study concerning linac‐based dynamic conformal arc plans, which also indicates that lower IDL plans have lower GI and steeper dose falloff comparing with high IDL plans . Moreover, it is further proposed in our study that a too low IDL (<60%) should be avoided as it may increase the risk of radiation necrosis and also for safety concern.…”

Section: Discussionsupporting

confidence: 90%

“…For CK‐based SRS, Qianyi Xu et al concluded that lower IDL plans (49.6 ± 2.1%) outperform high IDL plans (88.6 ± 1.3%) with lower dose of normal brain tissue and better CI . A new index named dose‐dropping speed was proposed by Q. Zhang et al to evaluate the impact of IDL in linac‐based SRS using non‐coplanar dynamic conformal arcs as well . It is found that the dose‐dropping speed increases with decreasing IDL and reach a plateau around 60–70% IDL.…”

Section: Introductionmentioning

confidence: 99%

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Selection of prescription isodose line for brain metastases treated with volumetric modulated arc radiotherapy

et al. 2019

J Applied Clin Med Phys

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PurposeTo exploit the optimal prescription isodose line (IDL) for brain metastases treated with volumetric modulated arc radiotherapy (VMAT) as there is no consensus on the selection of IDL with VMAT.Methods and materialsEighteen patients with 20 brain tumors, who were treated with VMAT, were enrolled in this study. For each tumor of every patient, five plans were designed with IDL ranging from 50% to 90% in 10% increments. Different IDLs were obtained through adjusting the constraint parameters during planning optimization. Prescription dose (10 × 5 Gy) were identical for all plans, and the plans were compared in terms of gradient index (GI), conformity Index (CI), V26 Gy/VPTV, and V32 Gy/VPTV in normal brain tissue, which correlate to radiation necrosis.ResultsIDL with lowest GI has a median value of 60.0% (ranging from 50% to 80%). Except for one tumor with volume larger than 10 cc, the IDL with lowest GI varies from 50% to 70%, which depends on the shape of PTV, location, and whether the target volume is adjacent to crucial OAR. Moreover, there is no significant difference for CI with varying IDL plans. The average V26 Gy/VPTV and V32 Gy/VPTV in normal brain tissue 60% IDL plans are 27.3%, 31.7% lower than 90% IDL plans separately (P < 0.05). However, by further decreasing IDL from 60% to 50%, the average V26 Gy/VPTV and V32 Gy/VPTV may increase comparing with 60% IDL plans (P > 0.05). Furthermore, a lower IDL is found to result in higher mean dose to the target volume (P < 0.05).ConclusionsPlans using VMAT with PTV smaller than 10 cc tend to be optimal with IDL around 60–70% for lower GI, smaller V26 Gy/VPTV, V32 Gy/VPTV in normal brain tissue, and higher mean dose in tumor comparing with high IDL plans which have potential benefit in reducing risk of radiation necrosis and increasing the local control. However, IDL lower than 60% is not recommended for the disadvantage of increasing V26 Gy/VPTV and V32 Gy/VPTV in normal brain tissue.

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Section: Discussionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Selection of prescription isodose line for brain metastases treated with volumetric modulated arc radiotherapy

et al. 2019

J Applied Clin Med Phys

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“…A recent SRS study on brain lesions had proposed the dose dropping speed concept by fitting the mean dose in multiple rind structures around PTV with a double exponential function of the distance from the PTV surface. 17 An observation made in their study which matched with ours is that a significantly steep dose falloff and better normal tissue sparing was observed in prescribing to 60% -70% isodose lines than in 90% isodose line especially for smaller tumors. While exploring the wider range of 50% -90%, the dose dropping speed was found to increase with decreasing prescription isodose line and plateaus at 60% -70% isodose line.…”

Section: Figure 5 Andsupporting

confidence: 81%

CBCT-based dosimetric verification and alternate planning techniques to reduce the normal tissue dose in SBRT of lung patients

Narayanasamy

Feddock

Gleason

et al. 2015

Int J Cancer Ther Oncol

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Original ArticleAbstract Purpose: Confirmation of treatment delivery accuracy in stereotactic body radiotherapy (SBRT) of lung tumors suggests the possibility of treatment margin, or aperture reduction. In this investigation, the dose delivery to lung tumors using SBRT techniques was verified, and the feasibility of normal tissue sparing via aperture reduction or altered prescription isodose line was assessed. Methods: Planned and delivered doses to the gross tumor volume (GTV) and planning target volume (PTV) were compared for 10 patients using planning CT and conebeam CT image. Potential for reduction in normal tissue dose were assessed using 2 alternate treatment plans -reduced PTVs and alternate prescription techniques. Plans were assessed using conformity index, homogeneity index and the ratio of 50% / 100% isodose volumes (R50%). Results: The planned and delivered mean doses were consistent to within 4%. However, the mean dose delivered to the GTV exceeded the prescription dose (Rx) by 19% and is consistent with our planning technique of prescribing to the 80% isodose line. When reducing treatment margins and retaining a constant dose-volume constraint, block margins had to be increased which produced a constant effective field aperture outside of the GTV. Prescription to a lower isodose line using stereotactic-like planning techniques yielded the only method by which the volume of the prescription isodose could be affected, although this yielded increases in normal tissue dose due to the increased monitor units required. Conversely, conventional prescription techniques using wider field apertures were effective in reducing absolute values of normal tissue dose. Although dose conformity was similar across different prescription isodose lines, homogeneity index and R50% values were significantly different in the 60%-70% prescription isodose line plans than the 80%, 90% prescription plans. Conclusion: Traditional margin reduction techniques did not affect a reduction in the volume of normal tissue irradiated to the prescribed dose. Prescribing to low isodose lines yields reduced volumes of the prescribed dose, but at the expense of normal tissue dose.

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“…Since the dose decreases exponentially (15–17) with the out‐of‐field distance, the basis of our model is an exponential function. In regard to the conclusion of Zang et al, (18) a simple exponential decay function has been selected rather than a double exponential function, shown in Eq. (1).…”

Section: Methodsmentioning

confidence: 99%

Estimating and reducing dose received by cardiac devices for patients undergoing radiotherapy

Bourgouin

Varfalvy

Archambault

2015

J Applied Clin Med Phys

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The objectives of this project are to quantify the dose reduction effect provided by a lead shield for patients with cardiac implantable electronic devices (CIED) during a clinically realistic radiation treatment on phantom and to provide a simple model of dose estimation to predict dose received by CIED in a wide range of situations. The shield used in this project is composed of a lead sheet wrapped in thermoplastic. Dose measurements were made with a plastic scintillation detector (PSD). The phantom was treated with ten different plans. Three of these cases were treated with intensity‐modulated radiation therapy (IMRT) and the others received standard 3D conformal radiation therapy (3D CRT). Lateral dose measurement for photon fields was made to establish a dose prediction model. On average, the use of the lead shield reduced the dose to CIEDs by 19%±13%. Dose reduction was most important for breast cases, with a mean reduction of 31%±15%. In three cases, the total dose reduction was more than 25 cGy over the complete treatment. For the three IMRT cases, the mean dose reduction was 11%±9%. On average, the difference between the TPS prediction and the measurement was 71%, while it was only 14% for the dose prediction model. It was demonstrated that a lead shield can be efficiently used for reducing doses to CIED with a wide range of clinical plans. In patients treated with IMRT modality treatment, the shielding should be used only for those with more than two anterior fields over seven fields. In the case of 3D CRT patients, the shielding should be used for those with a dose on the CIED higher than 50 cGy and with a reduction of dose higher than 10 cGy. The dose prediction model developed in this study can be an easy way to have a better estimation of the out‐of‐field dose than the TPS.PACS number(s): 87.55.N, 87.55.km

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A new variable for SRS plan quality evaluation based on normal tissue sparing: the effect of prescription isodose levels

Abstract: A new variable was proposed based on which normal tissue sparing was quantitatively evaluated, comparing different prescription IDLs in SRS.

Cited by 16 publications

References 22 publications

Selection of prescription isodose line for brain metastases treated with volumetric modulated arc radiotherapy

Selection of prescription isodose line for brain metastases treated with volumetric modulated arc radiotherapy

CBCT-based dosimetric verification and alternate planning techniques to reduce the normal tissue dose in SBRT of lung patients

Estimating and reducing dose received by cardiac devices for patients undergoing radiotherapy

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