Proposed Hydrogel-Implant Quality Score and a Matched-Pair Study for Prostate Radiation Therapy

Relationship between hydrogel spacer distribution and dosimetric parameters in linear-accelerator-based stereotactic body radiotherapy for prostate cancer

PURPOSE

To explore the potential of quantitative parameters of the hydrogel spacer distribution as predictors for separating the rectum from the planning target volume (PTV) in linear-accelerator-based stereotactic body radiotherapy (SBRT) for prostate cancer.

METHODS

Fifty-five patients underwent insertion of a hydrogel spacer and were divided into groups 1 and 2 of the PTV separated from and overlapping with the rectum, respectively. Prescribed doses of 36.25-45 Gy in five fractions were delivered to the PTV. The spacer cover ratio (SCR) and hydrogel-implant quality score (HIQS) were calculated.

RESULTS

Dosimetric and quantitative parameters of the hydrogel spacer distribution were compared between the two groups. For PTV, D99% in group 1 (n = 29) was significantly higher than that in group 2 (n = 26), and Dmax, D0.03cc, D1cc, and D10% for the rectum were significantly lower in group 1 than in group 2. The SCR for prostate (89.5 ± 12.2%) in group 1 was significantly higher (p < 0.05) than that in group 2 (74.7 ± 10.3%). In contrast, the HIQS values did not show a significant difference between the groups. An area under the curve of 0.822 (95% confidence interval, 0.708-0.936) for the SCR was obtained with a cutoff of 93.6%, sensitivity of 62.1%, and specificity of 100%.

CONCLUSIONS

The SCR seems promising to predict the separation of the rectum from the PTV in linear-accelerator-based SBRT for prostate cancer.

Evaluating the Quality-of-Life Effect of Apical Spacing with Hyaluronic Acid Prior to Hypofractionated Prostate Radiation Therapy: A Secondary Analysis

PURPOSE

Recently, a randomized trial demonstrated that a hyaluronic acid (HA) spacer placed before prostate hypofractionated intensity modulated radiation therapy improved rectal dosimetry and reduced acute grade 2+ gastrointestinal toxicity. However, 26.5% of patients receiving the spacer experienced a minimal clinically important decline (MCID) in bowel quality-of-life (QOL). The purpose of this study is to evaluate whether certain characteristics of the rectal spacer, as determined on postimplant imaging, were associated with change in bowel QOL at 3-months.

METHODS AND MATERIALS

This is a secondary analysis of the 136 patients who received the HA spacer on the randomized trial. Postimplant spacer characteristics (ie, prostate-rectum spacing at superior/midgland/inferior/apex planes, symmetry, prostate volume, spacer volume) were systematically analyzed from structure sets using custom software code. Characteristics demonstrating significant associations with rectal V30 on multivariate linear regression were identified. Linear regression models were used to analyze the associations of such characteristics with change (baseline to 3 months) in both bowel and urinary QOL.

RESULTS

Apical spacing (mean 9.4 (standard deviation 4.0)) was significantly smaller than spacing measurements at more superior planes. 95.6% of patients had a symmetrical implant. Apical spacing (P < .001) and prostate volume (P = .01) were significantly associated with rectal V30 on multivariate analysis. However, only apical spacing (0.38/mm; P = .01) was associated with change in bowel QOL, even with adjustment of baseline bowel score (-0.33; P < .01). Percentages of patients with bowel MCID were 14.8% for >= 10 mm versus 36.6% for <10 mm apical spacing (P = .01). Apical spacing was not associated with change in urinary QOL (-0.09; P = .72), when adjusted for baseline urinary QOL (-0.52; P < .01).

CONCLUSIONS

Greater apical spacing was associated with improved rectal dosimetry and smaller decline in bowel QOL at 3-months. Further prospective data are needed to fully understand the ramifications of increased apical spacing.

SpaceOAR Hydrogel Spacer for Reducing Radiation Toxicity During Radiotherapy for Prostate Cancer. A Systematic Review

OBJECTIVE

To evaluate the association between SpaceOAR and radiation dosing, toxicity and quality-of-life vs no spacer across all radiotherapy modalities for prostate cancer.

METHODS

A systematic search of the Cochrane Central Register of Controlled Trials, MEDLINE, and Embase was performed from database inception through May 2020. Two reviewers independently screened titles/abstracts and full papers. Data extraction was performed, and quality assessed by 1 reviewer and checked by a second, using a third reviewer as required. The synthesis was narrative.

RESULTS

19 studies (3,622 patients) were included (only 1 randomized controlled trial, in image-guided intensity-modulated radiotherapy (IG-IMRT), 18 comparatives non-randomized controlled trials in external-beam radiotherapy (EBRT), brachytherapy, and combinations thereof). No hypofractionation studies were found. Regardless of radiotherapy type, SpaceOAR significantly reduced rectal radiation dose (eg, V40 average difference -6.1% in high dose-rate brachytherapy plus IG-IMRT to -9.1% in IG-IMRT) and reduced gastrointestinal and genitourinary toxicities (eg, late gastrointestinal toxicity 1% vs 6% (P = .01), late genitourinary toxicity of 15% vs 32% (P < .001) in stereotactic body radiotherapy). Improvements were observed in most Expanded Prostate Cancer Index Composite quality-of-life domains (eg, bowel function score decrease at 3 and 6 months: Average change of zero vs -6.25 and -3.57 respectively in low dose-rate brachytherapy plus EBRT).

CONCLUSION

The randomized controlled trial in IG-IMRT demonstrated that SpaceOAR reduces rectal radiation dose and late gastrointestinal and genitourinary toxicities, with urinary, bowel, and sexual quality-of-life improvement. These advantages were verified in observational studies in various radiotherapy types. Further research is required in hypofractionation.

Effect of the timing of hydrogel spacer placement on prostate and rectal dosimetry of low-dose-rate brachytherapy implants

Purpose

To verify the dose sparing effect of hydrogel spacer (SpaceOAR™) on rectal dosimetry for prostate brachytherapy, and to determine whether prostate and rectal dosimetry was affected by the time gap between hydrogel spacer injection and brachytherapy dosimetry.

Material and methods

The ¹⁰³Pd brachytherapy dosimetry of 174 consecutive intermediate- and high-risk patients injected with hydrogel was compared with a dosimetry of 174 contemporaneous patients without hydrogel injections. Of the SpaceOAR™ patients, 91 had hydrogel injected upon completion of brachytherapy implant, while the remaining 83 patients had hydrogel placed prior to external beam radiation therapy (EBRT), followed 2-10 weeks later by brachytherapy. Brachytherapy implants were either planned with the prostate undistorted by any hydrogel or planned with hydrogel in place. Dosimetry of the prostate and tissues at risk was determined from CT imaging on the day of brachytherapy implant.

Results

SpaceOAR™ significantly reduced mean and maximum rectal doses as well as rectal wall V₅₀, but there was a statistically significant reduction of planning target volume (PTV) D₉₀ to 121.1% of the prescribed dose in hydrogel patients compared to 123.3% in the non-hydrogel patients. Rectal dosimetry was similar between patients injected with hydrogel after brachytherapy and those with spacer injected prior to EBRT. However, patients who had hydrogel placed prior to EBRT had statistically significantly higher dosimetry indices of PTV and urethra relative to those with spacer placed at the completion of brachytherapy.

Conclusions

There was a significant rectal dose sparing in the cohort with hydrogel spacer compared to a reference group without spacer injection. The rectal dose sparing effect was similar in the sub-group of patients injected with hydrogel prior to EBRT and the sub-group injected with hydrogel at the conclusion of brachytherapy.