Characterization of an Iodinated Rectal Spacer for Prostate Photon and Proton Radiation Therapy

Kamran, Sophia C.; McClatchy, David M.; Pursley, J.; Trofimov, Alexei V.; Remillard, Kyla; Saraf, Anurag; Ghosh, Anushka; Thabet, Ashraf; Sutphin, Patrick D.; Miyamoto, David T.; Efstathiou, Jason A.

doi:10.1016/j.prro.2021.09.009

Cited by 7 publications

(15 citation statements)

References 17 publications

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“…In agreement with our findings, the previous study has also shown that HU override is necessary for iodinated spacer. 34 In their study, they suggest HU override as a possible solution to increase the accuracy of the proton dose calculation. However, TPSs like RayStation and Pinnacle (Philips Radiation Oncology Systems, Milpitas, CA) do not have an HU override option, but rather, they provide a material density override option.…”

Section: Discussionmentioning

confidence: 99%

“…The mean HU of 120 is based on our measurement using solid water phantom and patient data from our institution and reported values in previous studies. 32 , 34 3D smoothing was applied to reduce the pixelation effect and simulate the realistic texture of hydrogel. All analyses were done using our MATLAB‐based in‐house image processing toolbox.…”

Section: Methodsmentioning

confidence: 99%

“…The SpaceOAR Vue material density was defined as 1.03 g/cm 3 and effective z = 14.47, which is consistent with the previous study. 34 However, in clinical practice, the stopping power ratio (SPR) is measured using a multilayer ion chamber to detect the shift of integral depth dose (IDD) due to the presence of the spacer. To confirm the material density of the spacer, we measured the SPR of the spacer under proton energies of 198.3 MeV.…”

Section: Methodsmentioning

confidence: 99%

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Systematic study of the iodinated rectal hydrogel spacer material discrepancy on accuracy of proton dosimetry

Hooshangnejad

Han

Feng

et al. 2022

J Applied Clin Med Phys

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Purpose Iodination of rectal hydrogel spacer increases the computed tomography (CT) visibility. The effect of iodinated hydrogel spacer material on the accuracy of proton dosimetry has not been fully studied yet. We presented a systematic study to determine the effect of iodination on proton dosimetry accuracy during proton therapy (PT). Methods PT plans were designed for 20 prostate cancer patients with rectal hydrogel spacer. Three variations of hydrogel density were considered. First, as the ground truth, the true elemental composition of hydrogel true material (TM), verified by our measurement of spacer stopping power ratio, was used for plan optimization and Monte Carlo dose calculation. The dose distribution was recalculated with (1) no material (NM) override based on the CT intensity of the iodinated spacer, and (2) the water material (WM) override, where spacer material was replaced by water. The plans were compared with the ground truth using the metrics of gamma index (GI) and dosimetric indices. Results The iodination of hydrogel spacer affected the proton dose distribution with the NM scenario showing the most deviation from the ground truth. The iodination of spacer resulted in a notable increase in CT intensity and led to the treatment planning systems mistreating the iodinated spacer as a high‐density material. Among the structures adjacent to the target, neurovascular bundles showed the largest dose difference, up to 350 cGy or about 5% of the prescribed dose with NM. Compared to the WM scenario, dose distribution similarity and GI passing ratios were lower in the NM scenario. Conclusion The inaccurate CT intensity‐based material for iodinated spacer resulted in errors in PT dose calculation. We found that the error was negligible if the iodinated spacer was replaced with water. Water density can be used as a clinically accessible and convenient alternative material override to true spacer material.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Systematic study of the iodinated rectal hydrogel spacer material discrepancy on accuracy of proton dosimetry

Hooshangnejad

Han

Feng

et al. 2022

J Applied Clin Med Phys

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“…Consequently, these rectal spacers are difficult to visualize on CT scans, which can make the contouring accuracy of the prostate and rectum challenging. This can potentially lead to higher inadvertent radiation to the surrounding structures during the planning phase if CT is the only modality available [ 20 ]. Due to the intrafractional and interfractional motions of the prostate, the treatment plan can be altered between the planning phase and in-treatment images based on changes in patient anatomy with a kV cone beam CT (CBCT) [ 20 ].…”

Section: Spacersmentioning

confidence: 99%

Application of Hydrogel Spacer SpaceOAR Vue for Prostate Radiotherapy

Hadigal

Gupta

2022

Tomography

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Damage in the surrounding structures, including the rectum, due to unintended exposure to radiation is a large burden to bear for patients who undergo radiation therapy for prostate cancer. The use of injectable rectal spacers to distance the anterior rectum from the prostate is a potential strategy to reduce the dose of unintended radiation to the rectum. Hydrogel spacers are gaining increasing popularity in the treatment regimen for prostate cancer. After FDA approval of SpaceOAR, specialists are receiving an increasing number of referrals for hydrogel placements. In this paper, we review hydrogel spacers, the supporting clinical data, the best practices for hydrogel placement, and the risk of adverse events.

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“…The primary function of the SpaceOAR Vue™, namely, stable and consistent peri-rectal spacing, has recently been objectively compared to that of its non-iodinated predecessor. In a rigorous longitudinal comparison analysis, it was found that, despite a moderately overall smaller average delineated volume, SpaceOAR Vue™ provided comparable relative prostate–rectal separation, appropriate positioning, stability over a course of EBRT, and dosimetric consistency without significant changes in plan quality or robustness relative to SpaceOAR™ ( 17 ).…”

Section: Introductionmentioning

confidence: 99%

Case Report: Role of an Iodinated Rectal Hydrogel Spacer, SpaceOAR Vue™, in the Context of Low-Dose-Rate Prostate Brachytherapy, for Enhanced Post-Operative Contouring to Aid in Accurate Implant Evaluation and Dosimetry

et al. 2021

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We present a case series of 13 consecutive patients with prostate cancer treated with low-dose-rate (LDR) brachytherapy, utilizing SpaceOAR Vue™, the recent iodinated iteration of the SpaceOAR™ hydrogel rectal spacer. Low- and favorable intermediate-risk patients receiving monotherapy and unfavorable intermediate- and high-risk patients undergoing a brachytherapy boost were included. Permanent brachytherapy can result in subacute and late rectal toxicity, and precise contouring of the anterior rectal wall and posterior aspect of the prostate is essential for accurate dosimetry to confirm a safe implant. Clearly visible on non-contrast CT imaging, SpaceOAR Vue™ can substantially aid in post-implant contouring and analysis. Not previously described in the literature in the context of LDR brachytherapy, we demonstrate the added clinical benefit of placing a well-visualized rectal spacer.

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Characterization of an Iodinated Rectal Spacer for Prostate Photon and Proton Radiation Therapy

Cited by 7 publications

References 17 publications

Systematic study of the iodinated rectal hydrogel spacer material discrepancy on accuracy of proton dosimetry

Systematic study of the iodinated rectal hydrogel spacer material discrepancy on accuracy of proton dosimetry

Application of Hydrogel Spacer SpaceOAR Vue for Prostate Radiotherapy

Case Report: Role of an Iodinated Rectal Hydrogel Spacer, SpaceOAR Vue™, in the Context of Low-Dose-Rate Prostate Brachytherapy, for Enhanced Post-Operative Contouring to Aid in Accurate Implant Evaluation and Dosimetry

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