Spacer stability and prostate position variability during radiotherapy for prostate cancer applying a hydrogel to protect the rectal wall. Radiother Oncol. 2013;106:220-224. [PMID: 23333015 DOI: 10.1016/j.radonc.2012.11.010]

Unexpected change in hydrogel spacer volume during external-beam radiation therapy

PURPOSE

To reduce the rectal radiation dose during local radiation therapy of prostate cancer, a hydrogel spacer is typically implanted between the prostate and rectum. However, the spacer volume can change during external beam radiation therapy (EBRT). Therefore, we used magnetic resonance imaging (MRI) to determine changes in the spacer volume during EBRT and analyzed the data to identify patient factors influencing this change.

MATERIALS AND METHODS

A hydrogel spacer was implanted in each enrolled patient diagnosed with prostate cancer (n = 22, age = 69-86 years) for EBRT with a total dose of 70 Gy over 35 fractions. T2-weighted MRI images were acquired before (median = 8 days) and during EBRT, when the radiation dose of 48 Gy (median) was given at 55 days (median) after implantation. MRI images were used to determine the spacer volume as well as the maximum and minimum distances between the prostate and anterior wall of the rectum at the middle height of the prostate. Scatterplots were created to determine whether correlations existed between changes in the spacer volume and these two distances, while uni- and multivariate analyses were conducted to determine if the spacer volume change was influenced by the following patient factors: age, body mass index, estimated glomerular filtration rate, and visceral fat areas at the umbilical and femoral head positions.

RESULTS

The spacer volume increased in all 22 patients, with the smaller spacer volume before EBRT increasing by a larger amount during EBRT. This increase in the spacer volume was unaffected by other patient factors. However, it correlated with the change in the maximum distance between the prostate and anterior wall of the rectum.

CONCLUSION

To avoid adverse changes in the rectal radiation dose during EBRT, hydrogel spacer volume should be monitored, especially if the pre-EBRT volume is small.

Photothermal therapy: a novel potential treatment for prostate cancer

Prostate cancer (PCa) is a leading cause of cancer-related death in men, and most PCa patients treated with androgen deprivation therapy will progress to metastatic castration-resistant prostate cancer (mCRPC) due to the lack of efficient treatment. Recently, lots of research indicated that photothermal therapy (PTT) was a promising alternative that provided an accurate and efficient prostate cancer therapy. A photothermic agent (PTA) is a basic component of PPT and is divided into organic and inorganic PTAs. Besides, the combination of PTT and other therapies, such as photodynamic therapy (PDT), immunotherapy (IT), chemotherapy (CT), etc., provides an more efficient strategy for PCa therapy. Here, we introduce basic information about PTT and summarize the PTT treatment strategies for prostate cancer. Based on recent works, we think the combination of PPT and other therapies provides a novel possibility for PCa, especially CRPC clinical treatment.

Dose Distribution of High Dose-Rate and Low Dose-Rate Prostate Brachytherapy at Different Intervals-Impact of a Hydrogel Spacer and Prostate Volume

The study aimed to compare the dose distribution in permanent low-dose-rate brachytherapy (LDR-BT) and high-dose-rate brachytherapy (HDR-BT), specifically focusing on the impact of a spacer and prostate volume. The relative dose distribution of 102 LDR-BT patients (prescription dose 145 Gy) at different intervals was compared with the dose distribution of 105 HDR-BT patients (232 HDR-BT fractions with prescription doses of 9 Gy, n = 151, or 11.5 Gy, n = 81). A hydrogel spacer (10 mL) was only injected before HDR-BT. For the analysis of dose coverage outside the prostate, a 5 mm margin was added to the prostate volume (PV+). Prostate V100 and D90 of HDR-BT and LDR-BT at different intervals were comparable. HDR-BT was characterized by a considerably more homogenous dose distribution and lower doses to the urethra. The minimum dose in 90% of PV+ was higher for larger prostates. As a consequence of the hydrogel spacer in HDR-BT patients, the intraoperative dose at the rectum was considerably lower, especially in smaller prostates. However, prostate volume dose coverage was not improved. The dosimetric results well explain clinical differences between these techniques reported in the literature review, specifically comparable tumor control, higher acute urinary toxicity rates in LDR-BT in comparison to HDR-BT, decreased rectal toxicity after spacer placement, and improved tumor control after HDR-BT in larger prostate volumes.

Hyaluronic acid spacer in prostate cancer radiotherapy: dosimetric effects, spacer stability and long-term toxicity and PRO in a phase II study

BACKGROUND

Perirectal spacers may be beneficial to reduce rectal side effects from radiotherapy (RT). Here, we present the impact of a hyaluronic acid (HA) perirectal spacer on rectal dose as well as spacer stability, long-term gastrointestinal (GI) and genitourinary (GU) toxicity and patient-reported outcome (PRO).

METHODS

In this phase II study 81 patients with low- and intermediate-risk prostate cancer received transrectal injections with HA before external beam RT (78 Gy in 39 fractions). The HA spacer was evaluated with MRI four times; before (MR0) and after HA-injection (MR1), at the middle (MR2) and at the end (MR3) of RT. GI and GU toxicity was assessed by physician for up to five years according to the RTOG scale. PROs were collected using the Swedish National Prostate Cancer Registry and Prostate cancer symptom scale questionnaires.

RESULTS

There was a significant reduction in rectal V70% (54.6 Gy) and V90% (70.2 Gy) between MR0 and MR1, as well as between MR0 to MR2 and MR3. From MR1 to MR2/MR3, HA thickness decreased with 28%/32% and CTV-rectum space with 19%/17% in the middle level. The cumulative late grade ≥ 2 GI toxicity at 5 years was 5% and the proportion of PRO moderate or severe overall bowel problems at 5 years follow-up was 12%. Cumulative late grade ≥ 2 GU toxicity at 5 years was 12% and moderate or severe overall urinary problems at 5 years were 10%.

CONCLUSION

We show that the HA spacer reduced rectal dose and long-term toxicity.

Dosimetric Effects of the Supine and Prone Positions in Proton Therapy for Prostate Cancer

Purpose

To quantitatively evaluate how much the doses to organs at risk are affected in the prone position compared to the supine position in the proton therapy (PT) for prostate cancer.

Materials and Methods

Fifteen consecutive patients with clinically localized prostate cancer underwent treatment planning computed tomography scans in both the supine and prone positions. The clinical target volume (CTV) consisted of the prostate gland plus the seminal vesicles. The PT plans were designed using the standard lateral opposed fields with passively scattered proton beams for both treatment positions. The prescribed dose for each plan was set to 78 Gy (Relative biological effectiveness)/39 fractions to 50% of the planning target volume. Dose-volume metrics of the rectum and bladder in the two treatment positions were analyzed.

Results

It was confirmed that all the parameters of D05, D10, D20, D30, Dmean, and V90 examined in the rectum were significantly reduced in the prone position. There was no significant difference between the two positions in the bladder dose except for Dmean. The distance between the CTV and the rectum tended to increase with the patient in the prone position; at the prostate level, however, the maximum change was approximately 5 mm, and there was significant variation between cases.

Conclusions

We confirmed that the rectal doses were significantly lower in the prone compared with the supine position in PT. Although uncertain, the prone position could be an effective method to reduce the rectal dose in PT.

Four-year quality-of-life outcomes in low- to intermediate-risk prostate cancer patients following definitive stereotactic body radiotherapy versus management with active surveillance

OBJECTIVE

To review quality-of-life (QoL) metrics between patients who underwent definitive stereotactic body radiotherapy (SBRT) versus active surveillance (AS) for management of low- to intermediate-risk prostate cancer (PCa).

METHODS

A prospectively maintained PCa database was reviewed containing results of patient-reported QoL surveys. Patients with localized disease who chose AS or SBRT and completed at least one survey within four years of treatment were included. Patients who received salvage therapy were excluded. Survey results were compared across time using mixed-effects repeated measures analysis of covariance models that adjusted for factors significant in univariate analysis. A group x time interaction effect was examined to compare rate of change over time between AS and SBRT. P < 0.05 was significant.

RESULTS

148 AS and 161 SBRT patients were included. Significantly more SBRT patients had intermediate-risk disease (p < 0.0001). AS had significantly worse sexual function compared to SBRT across time. While not significant, bowel function scores were lower for SBRT patients across time points. SBRT patients had significantly lower anxiety than AS patients at 24 months (p < 0.011) and 36 months (p < 0.010). Urinary function though worse in SBRT patients at 12 months in EPIC, was not significantly different in both groups across time points.

CONCLUSION

SBRT patients have excellent QoL compared to AS with regard to anxiety post treatment. Though SBRT patients initially have worse urinary and bowel function than AS, scores were eventually similar in both cohorts by 48 months. SBRT patients have significantly worse sexual function post treatment. This study may help facilitate counseling in patients choosing PCa treatment.

The Feasibility of Haar Feature-Based Endoscopic Ultrasound Probe Tracking for Implanting Hydrogel Spacer in Radiation Therapy for Pancreatic Cancer

Purpose

We proposed a Haar feature-based method for tracking endoscopic ultrasound (EUS) probe in diagnostic computed tomography (CT) and Magnetic Resonance Imaging (MRI) scans for guiding hydrogel injection without external tracking hardware. This study aimed to assess the feasibility of implementing our method with phantom and patient images.

Materials and Methods

Our methods included the pre-simulation section and Haar features extraction steps. Firstly, the simulated EUS set was generated based on anatomic information of interpolated CT/MRI images. Secondly, the efficient Haar features were extracted from simulated EUS images to create a Haar feature dictionary. The relative EUS probe position was estimated by searching the best matched Haar feature vector of the dictionary with Haar feature vector of target EUS images. The utilization of this method was validated using EUS phantom and patient CT/MRI images.

Results

In the phantom experiment, we showed that our Haar feature-based EUS probe tracking method can find the best matched simulated EUS image from a simulated EUS dictionary which includes 123 simulated images. The errors of all four target points between the real EUS image and the best matched EUS images were within 1 mm. In the patient CT/MRI scans, the best matched simulated EUS image was selected by our method accurately, thereby confirming the probe location. However, when applying our method in MRI images, our method is not always robust due to the low image resolution.

Conclusions

Our Haar feature-based method is capable to find the best matched simulated EUS image from the dictionary. We demonstrated the feasibility of our method for tracking EUS probe without external tracking hardware, thereby guiding the hydrogel injection between the head of the pancreas and duodenum.

Separation effect and development of implantation technique of hydrogel spacer for prostate cancers

PURPOSE

The purpose was to improve the placement of a hydrogel spacer in prostate cancer patients receiving radiotherapy.

METHODS AND MATERIALS

One hundred and sixty patients with prostate cancer were classified into 3 groups as follows: group 1, no spacer (n = 30); group 2, spacer placed using conventional technique (n = 100); and group 3, spacer placed using new technique (n = 30). When placing the spacer, the tip of the needle was placed at the middle of the prostate gland (group 2) or at a level corresponding to a cranial:caudal ratio of 6:4 and as close to the prostate gland as possible (group 3). The separation effect was then examined and compared among the groups.

RESULTS

The separation in group 2 was larger than that in group 1 from the base to the apex (4 mm) level of the prostate, while the separation in group 3 was larger than that in group 2 from the middle to the apex (4 mm) level of the prostate. The separation values for the middle to the apex, the spacer thickness from the apex (10 mm) level to the apex, the rectal exclusion from the middle to the apex, and the laterality were correlated with the 50 and 60 Gray relative biological effectiveness (Gy(RBE)) rectal dose (p = 4.1 × 10^-9 - 0.046). The separation vales were strongly correlated with the spacer thickness at the apex (10 mm) and apex (4 mm) (p = 1.1 × 10^-18 - 1.8 × 10^-17). The rectal volumes at 10-60 Gy(RBE) differed among the groups (p = 5.1 × 10^-19 - 5.4 × 10^-3). The rectal volumes in group 2 were smaller than those in group 1 at all dose levels, while those in group 3 were smaller than those in group 2 at dose levels of 30-50 Gy(RBE).

CONCLUSIONS

The separation, spacer thickness and rectal exclusion from the middle to the apex of the prostate and the laterality of the hydrogel spacer affected the reduction in the rectal dose. The rectal dose can be further reduced by implanting a spacer on the caudal and the prostate side.

EUS-guided hydrogel microparticle injection in a cadaveric model

BACKGROUND AND AIMS

A potential method to reduce gastrointestinal toxicity during radiation therapy in pancreatic head cancer is to create a physical space between the head of the pancreas (HOP) and the duodenum. To date, there have been early reports on the feasibility of endoscopic ultrasound (EUS)-guided hydrogel injection into the interface between the HOP and the duodenum to increase the peri-pancreatic space for radiotherapy. We aimed to evaluate the technical feasibility of EUS-guided hydrogel injection for the creation of space at the peri-pancreatic interface in a cadaveric model.

METHODS

Baseline abdominal computerized tomography (CT) was performed on three unfixed cadaveric specimens. The hydrogel was injected transduodenally into the interface between the HOP and duodenum using linear-array EUS and a 19G needle for fine needle aspiration (FNA). This procedure was repeated along the length of the HOP. CT imaging and gross dissection were performed after the procedure to confirm the localization of the hydrogel and to measure the distance between the HOP and the duodenum.

RESULTS

All cadavers underwent successful EUS-guided injection of the hydrogel. Cadavers 1, 2, and 3 were injected with 9.5, 27, and 10 cc of hydrogel, respectively; along the HOP, the formation of the peri-pancreatic space was a maximum size of 11.77, 13.20, and 12.89 mm, respectively. The hydrogel injections were clearly visualized as hyperechoic bullae during EUS and on post-procedure CT images without any artifacts in all cases.

CONCLUSIONS

We demonstrated that EUS-guided delivery of hydrogel is feasible, and that it increases the peri-pancreatic space in a cadaveric model. The polyethylene glycol (PEG) hydrogel was clearly visible on EUS and CT, without significant artifacts. This may lead to new treatment approaches for pancreatic carcinomas.

Preliminary analysis of prostate positional displacement using hydrogel spacer during the course of proton therapy for prostate cancer

In recent years, a novel technique has been employed to maintain a distance between the prostate and the rectum by transperineally injecting a hydrogel spacer (HS). However, the effect of HS on the prostate positional displacement is poorly understood, despite its stability with HS in place. In this study, we investigated the effect of HS insertion on the interfraction prostate motion during the course of proton therapy (PT) for Japanese prostate cancer patients. The study population consisted of 22 cases of intermediate-risk prostate cancer with 11 cases with HS insertion and 11 cases without HS insertion. The irradiation position and preparation were similar for both groups. To test for reproducibility, regular confirmation computed tomography (RCCT) was done four times during the treatment period, and five times overall [including treatment planning CT (TPCT)] in each patient. Considering the prostate position of the TPCT as the reference, the change in the center of gravity of the prostate relative to the bony anatomy in the RCCTs of each patient was determined in the left-right (LR), superior-inferior (SI) and anterior-posterior (AP) directions. As a result, no significant difference was observed across the groups in the LR and SI directions. Conversely, a significant difference was observed in the AP direction (P < 0.05). The proportion of the 3D vector length ≤5 mm was 95% in the inserted group, but 55% in the non-inserted group. Therefore, HS is not only effective in reducing rectal dose, but may also contribute to the positional reproducibility of the prostate.

Simultaneous integrated boost with stereotactic radiotherapy for dominant intraprostatic lesion of localized prostate cancer: a dosimetric planning study

Dominant intraprostatic lesion (DIL) has been known as the most common local recurrence site of prostate cancer. We evaluated the feasibility of simultaneous integrated boost (SIB) to DIL with CyberKnife stereotactic body radiotherapy (CK-SBRT). We selected 15 patients with prostate cancer and visible DIL and compared 3 plans for each patient: 1) No boost plan of 35 Gy to prostate, 2) DIL_40 plan of SIB 40 Gy to DIL and 35 Gy to prostate, and 3) DIL_45 plan with 45 Gy to DIL and 35 Gy to the prostate in 5 fractions. All targets satisfied with the prescription coverage per protocol. However, some patients failed to meet the D_max of the rectum in DIL_40 plans (n = 4), and DIL_45 plans (n = 6). Violations of bladder constraints occurred in four DIL_45 plans. Consequently, the DIL boost with SBRT was possible in 73% of patients with DIL_40 plans, and 60% of patients with DIL_45 plans without any violation of normal organ constraints. All patients who experienced constraint violations had DILs in posterior segments. DIL boost using CK-SBRT could be an option for localized prostate cancer patients. For patients who had DIL in posterior segments, a moderate dose escalation of 40 Gy seemed appropriate.

Effect of a hydrogel spacer on the intrafractional prostate motion during CyberKnife treatment for prostate cancer

The purpose of this study was to evaluate the effect of a hydrogel spacer on intrafractional prostate motion during CyberKnife treatment. The retrospective study enrolled 24 patients (with the hydrogel spacer = 12, without the hydrogel spacer = 12) with two fiducial markers. Regarding intrafractional prostate motion, the offset values (mm) of three axes (X-axis; superior [+] to inferior [-], Y-axis; right [+] to left [-], Z-axis; posterior [+] to anterior [-]) obtained from fiducial markers position between a digitally reconstructed radiographs images and live images in the Target Locating System were used, and extracted from generated log files. The mean values of the offset and each standard deviation were calculated for each patient, and both the groups were compared. For all the patients, a total of 2204 offset values and timestamps (without the hydrogel spacer group: 1065, with the hydrogel spacer group: 1139) were recorded for the X-, Y-, and Z-axes, respectively. The offset values (mean ± standard deviation) for the X-, Y-, and Z-axes were -0.04 ± 0.92 mm, -0.03 ± 0.97 mm (P = 0.66), 0.02 ± 0.51, -0.02 ± 0.49 mm (P = 0.50), and 0.56 ± 0.97 mm, 0.34 ± 1.07 mm (P = 0.14), in patients inserted without or with the hydrogel spacer, respectively. There was no effect of a hydrogel spacer on the intrafractional prostate motion in the three axes during CyberKnife treatment for prostate cancer.

Impact of hydrogel peri-rectal spacer insertion on prostate gland intra-fraction motion during 1.5 T MR-guided stereotactic body radiotherapy

Background

The assessment of organ motion is a crucial feature for prostate stereotactic body radiotherapy (SBRT). Rectal spacer may represent a helpful device in order to outdistance rectal wall from clinical target, but its impact on organ motion is still a matter of debate. MRI-Linac is a new frontier in radiation oncology as it allows a superior visualization of the real-time anatomy of the patient and the current highest level of adaptive radiotherapy.

Methods

We present data regarding a total of 100 fractions in 20 patients who underwent MRI-guided prostate SBRT for low-to-intermediate risk prostate cancer with or without spacer. Translational and rotational shifts were computed on the pre- and post-treatment MRI acquisitions referring to the delivery position for antero-posterior, latero-lateral and cranio-caudal direction, and assessed using the Mann-Whitney U-Test.

Results

All patients were treated with a five sessions schedule (35 Gy/5fx) using MRI-Linac for a median fraction treatment time of 50 min (range, 46–65). In the entire study sample, median rotational displacement was 0.1° in cranio-caudal, − 0.002° in latero-lateral and 0.01° in antero-posterior direction; median translational shift was 0.11 mm in cranio-caudal, − 0.24 mm in latero-lateral and − 0.22 mm in antero-posterior. A significant difference between spacer and no-spacer patients in terms of rotational shifts in the antero-posterior direction (p = 0.033) was observed; also for translational shifts a positive trend was detected in antero-posterior direction (p = 0.07), although with no statistical significance. We observed statistically significant differences in the pre-treatment planning phase in favor of the spacer cohort for several rectum dose constraints: rectum V32Gy < 5% (p = 0.001), V28 Gy < 10% (p = 0.001) and V18Gy < 35% (p = 0.039). Also for bladder V35 Gy < 1 cc, the use of spacer provided a dosimetric advantage compared to the no-spacer subpopulation (p = 0.04). Furthermore, PTV V33.2Gy > 95% was higher in the spacer cohort compared to the no-spacer one (p = 0.036).

Conclusion

In our experience, the application of rectal hydrogel spacer for prostate SBRT resulted in a significant impact on rotational antero-posterior shifts contributing to limit prostate intra-fraction motion. Further studies with larger sample size and longer follow-up are required to confirm this ideally favorable effect and to assess any potential impact on clinical outcomes.

Association of the Placement of a Perirectal Hydrogel Spacer With the Clinical Outcomes of Men Receiving Radiotherapy for Prostate Cancer: A Systematic Review and Meta-analysis

Importance

Perirectal spacers are intended to lower the risk of rectal toxic effects associated with prostate radiotherapy. A quantitative synthesis of typical clinical results with specific perirectal spacers is limited.

Objective

To evaluate the association between perirectal hydrogel spacer placement and clinical outcomes of men receiving radiotherapy for prostate cancer.

Data Sources

A systematic search was performed of the Cochrane Central Register of Controlled Trials, MEDLINE, and Embase for articles published through September 2019.

Study Selection

Studies comparing men who received a hydrogel spacer vs men who did not receive a spacer (controls) prior to prostate radiotherapy.

Data Extraction and Synthesis

Via random-effects meta-analysis, group comparisons were reported using the weighted mean difference for continuous measures and the risk ratio for binary measures.

Main Outcomes and Measures

Procedural results, the percentage volume of rectum receiving at least 70 Gy radiation (v70), early (≤3 months) and late (>3 months) rectal toxic effects, and early and late changes in bowel-related quality of life on the Expanded Prostate Cancer Index Composite (minimal clinically important difference, 4 points).

Results

The review included 7 studies (1 randomized clinical trial and 6 cohort studies) involving 1011 men (486 who received a hydrogel spacer and 525 controls), with a median duration of patient follow-up of 26 months (range, 3-63 months). The success rate of hydrogel spacer placement was 97.0% (95% CI, 94.4%-98.8% [5 studies]), and the weighted mean perirectal separation distance was 11.2 mm (95% CI, 10.1-12.3 mm [5 studies]). Procedural complications were mild and transient, occurring in 0% to 10% of patients within the studies. The hydrogel spacer group received 66% less v70 rectal irradiation compared with controls (3.5% vs 10.4%; mean difference, -6.5%; 95% CI, -10.5% to -2.5%; P = .001 [6 studies]). The risk of grade 2 or higher rectal toxic effects was comparable between groups in early follow-up (4.5% in hydrogel spacer group vs 4.1% in control group; risk ratio, 0.82; 95% CI, 0.52-1.28; P = .38 [6 studies]) but was 77% lower in the hydrogel spacer group in late follow-up (1.5% vs 5.7%; risk ratio, 0.23; 95% CI, 0.06-0.99; P = .05 [4 studies]). Changes in bowel-related quality of life were comparable between groups in early follow-up (mean difference, 0.2; 95% CI, -3.1 to 3.4; P = .92 [2 studies]) but were greater in the hydrogel spacer group in late follow-up (mean difference, 5.4; 95% CI, 2.8-8.0; P < .001 [2 studies]).

Conclusions and Relevance

For men receiving prostate radiotherapy, injection of a hydrogel spacer was safe, provided prostate-rectum separation sufficient to reduce v70 rectal irradiation, and was associated with fewer rectal toxic effects and higher bowel-related quality of life in late follow-up.

Hydrogel Spacer Reduces Rectal Dose during Proton Therapy for Prostate Cancer: A Dosimetric Analysis

Purpose

Proton therapy for prostate cancer may reduce bowel dose and risk of bowel symptoms relative to photon-based methods. Here, we determined the effect of using a biodegradable, injectable hydrogel spacer on rectal dose on plans for treating prostate cancer with intensity-modulated proton therapy (IMPT) or passive scattering proton therapy (PSPT).

Materials and Methods

Pairs of IMPT and PSPT plans for 9 patients were created from fused computed tomography/magnetic resonance imaging scans obtained before and after spacer injection. Calculated values of rectal V40, V60, V70, V80, and maximum dose (Dmax) were compared with Wilcoxon signed rank tests. Displacements at the base (BP), midgland (MP), and apex (AP) of the prostate relative to the anterior rectal wall with the spacer in place were averaged for each patient and correlated with V70 by using linear regression models.

Results

The presence of a spacer reduced all dosimetric parameters for both PSPT and IMPT, with the greatest difference in V70, which was 81.1% lower for PSPT-with-spacer than for IMPT-without-spacer. Median displacements at BP, MP, and AP were 12 mm (range 7-19), 2 mm (range 0-4), and 1 mm (range 0-5) without the spacer and 19 mm (range 12-23), 10 mm (range 8-16), and 7 mm (range 2-12) with the spacer. Modest linear trends were noted between rectal V70 and displacement for IMPT-with-spacer and PSPT-with-spacer. When displacement was ≥8 mm, V70 was ≤5.1% for IMPT-with-spacer and PSPT-with-spacer.

Conclusion

Use of biodegradable hydrogel spacers for prostate cancer treatment provides a significant reduction of radiation dose to the rectum with proton therapy. Significant reductions in rectal dose occurred in both PSPT and IMPT plans, with the greatest reduction for IMPT-with-spacer relative to PSPT alone. Prospective studies are ongoing to assess the clinical impact of reducing rectal dose with hydrogel spacers.

A novel and innovative device to retract rectum during radiation therapy of pelvic tumors

An effective radiotherapy treatment entails maximizing radiation dose to the tumor while sparing the surrounding and normal tissues. With the advent of SBRT with extreme hypo-fractionation in treating tumors including prostate where ablative dose is delivered in smaller number of fractions, rectum remains a dose-limiting organ and at the risk of rectal toxicity or secondary cancer. The same limitation of rectal toxicity exists for high-dose rate (HDR) treatments of cervical, endometrial, or prostate cancer when creating even a short distance between the anterior rectal wall and field of radiation is ideal in delivering ablative dose to the target. An effective solution to such problem is to physically displace rectum as the organ at risk. This research presents an organ retractor device that is designed to displace the rectum away from the path of radiation beam employing a Nitinol shape memory alloy that is designed for displacing the rectum upon actuation. A control system regulates the motion in a reproducible and safe manner by creating the desirable shape in moving the anterior rectal wall. The study finds the novel organ retractor device to be a promising tool that can be applied in a clinical setting for minimizing dose to the rectum during treatment of pelvic tumors, and creating the potential to deliver an ablative dose to tumor volume or to escalate the dose when needed.

MRI findings of absorbable hydrogel spacer for prostate cancer therapy: a pictorial review

Prior studies have shown that dose-escalated radiation therapy for prostate cancer improves clinical outcomes. However, this is associated with increased rectal toxicity. Hydrogel spacer for prostate cancer therapy is an effective way of decreasing rectal toxicity in the late post-therapeutic stages. In some occasions, the gel spacer may not be placed symmetrically between the rectum and prostate. There are several forms of a malpositioned spacer, including lateral displacement, rectal wall infiltration, and prostate capsule infiltration. This manuscript is aimed at evaluating appropriately positioned and malpositioned gel spacers, primarily via magnetic resonance imaging. There are limited educational imaging guides that address what radiologists should evaluate on post-spacer placement imaging. This pictorial review will specifically evaluate post-injection pitfalls such as asymmetry, rectal wall infiltration, and subcapsular injection.

Dose Prediction Model for Duodenum Sparing With a Biodegradable Hydrogel Spacer for Pancreatic Cancer Radiation Therapy

PURPOSE

We previously have shown the feasibility of duodenum sparing using a biodegradable hydrogel spacer in pancreatic cancer radiation therapy. In this study, we propose an overlap volume histogram (OVH) prediction model to select patients who might benefit from hydrogel placement and to predict the hydrogel spacing required to achieve clinical constraints.

METHODS AND MATERIALS

OVH metrics for the duodenum were collected from the stereotactic body radiation therapy plans of 232 patients with unresectable pancreatic cancer (33 Gy in 5 fractions). OVH metrics L_9cc and L_3cc were defined as the tumor volume expansion distance at which 9 cm³ and 3 cm³ volumes of the duodenum overlap with tumor. D_9cc and D_3cc of the duodenum were defined as the dose-volume histogram dose to 9 cm³ and 3 cm³, respectively, of the duodenum. Prediction models were established by linear regression between L_x and D_x, where x = 3 cm³ and 9 cm³. OVH thresholds were obtained for predicting the target spacer thickness. The accuracy of the prediction model was then evaluated using treatment plans on pre-and post-hydrogel injection computed tomography scans from 2 cadaver specimens and 6 patients with previously treated locally advanced pancreatic cancer with simulated spacer.

RESULTS

Linear regression analysis showed a significant correlation between L_x and D_x (r² = 0.51 and 0.51 for L_3cc-D_3cc and L_9cc-D_9cc, respectively; both P < .01). The OVH thresholds were Lˆ_3cc = 7 mm and Lˆ_9cc = 13 mm. The observed planning doses D_3cc and D_9cc of duodenum from pre-and post-hydrogel injection computed tomography scans of cadaver specimens and clinical patients with simulated spacer using predicted target spacer thickness were within the OVH model prediction range.

CONCLUSION

Our model may predict which patients require placement of a hydrogel spacer before stereotactic body radiation therapy to meet predefined dose constraints. Furthermore, by predicting the required target hydrogel thickness, the spacer injection can be better guided to improve efficacy.

The role of radioprotective spacers in clinical practice: a review

The delivery of high dose radiotherapy to tumors is often limited by the proximity of the surrounding radiosensitive normal tissues, even using modern techniques such as intensity modulated radiation therapy (IMRT). Previous studies have reported that placement of a spacer can effectively displace normal tissues. So that they are some distance away from the lesion, thus allowing for the safe delivery of high-dose radiation. The application of radioprotective spacers was first reported 30 years ago regarding radiotherapy of tongue and abdominal cancers; more recently, they are increasingly being used in prostate cancer. This review focuses on the published data concerning the features of different types of spacers and their application in various tumor sites. Placement-related complications and the cost-effectiveness of the spacers are also discussed. With the increasing use of high-precision radiotherapy in clinical practice, especially the paradigm-changing stereotactic body radiotherapy (SBRT), more robust studies are warranted to further establish the role of radioprotective spacers through materials development and novel placement techniques.

Hydrogel spacers in prostate radiotherapy: a promising approach to decrease rectal toxicity

High-dose radiation is a well-established method of treatment for prostate cancer. The main limiting structure for dose escalation is the rectum. The risk of rectal toxicity is related to dose received by the rectum. Several strategies for reducing dose to rectum have been explored; these include endorectal balloons as well as injection of rectal spacers like hydrogels. They create greater distance between rectal wall and prostate to confer a dosimetric advantage to the rectum. Early clinical studies with hydrogels have shown favorable outcomes. A low incidence of major procedural adverse effects with hydrogel use has been reported and it is well tolerated by patients. Hydrogel holds promise in establishing itself as an adjunct to standard of care in prostate radiation.

A Novel Absorbable Radiopaque Hydrogel Spacer to Separate the Head of the Pancreas and Duodenum in Radiation Therapy for Pancreatic Cancer

PURPOSE

We assessed the feasibility and theoretical dosimetric advantages of an injectable hydrogel to increase the space between the head of the pancreas (HOP) and duodenum in a human cadaveric model.

METHODS AND MATERIALS

Using 3 human cadaveric specimens, an absorbable radiopaque hydrogel was injected between the HOP and duodenum by way of open laparotomy in 1 case and endoscopic ultrasound (EUS) guidance in 2 cases. The cadavers were subsequently imaged using computed tomography and dissected for histologic confirmation of hydrogel placement. The duodenal dose reduction and planning target volume (PTV) coverage were characterized using pre- and postspacer injection stereotactic body radiation therapy (SBRT) plans for the 2 cadavers with EUS-guided placement, the delivery method that appeared the most clinically desirable. Modeling studies were performed using 60 SBRT plans consisting of 10 previously treated patients with unresectable pancreatic cancer, each with 6 different HOP-duodenum separation distances. The duodenal volume receiving 15 Gy (V15), 20 Gy (V20), and 33 Gy (V33) was assessed for each iteration.

RESULTS

In the 3 cadaveric studies, an average of 0.9 cm, 1.1 cm, and 0.9 cm HOP-duodenum separation was achieved. In the 2 EUS cases, the V20 decreased from 3.86 cm³ to 0.36 cm³ and 3.75 cm³ to 1.08 cm³ (treatment constraint <3 cm³), and the V15 decreased from 7.07 cm³ to 2.02 cm³ and 9.12 cm³ to 3.91 cm³ (treatment constraint <9 cm³). The PTV coverage improved or was comparable between the pre- and postinjection studies. Modeling studies demonstrated that a separation of 8 mm was sufficient to consistently reduce the V15, V20, and V33 to acceptable clinical constraints.

CONCLUSIONS

Currently, dose escalation has been limited owing to radiosensitive structures adjacent to the pancreas. We demonstrated the feasibility of hydrogel separation of the HOP and duodenum. Future studies will evaluate the safety and efficacy of this technique with the potential for more effective dose escalation using SBRT or intensity-modulated radiation therapy to improve the outcomes in patients with unresectable pancreatic cancer.

Quality of Life After Radiation Therapy for Prostate Cancer With a Hydrogel Spacer: 5-Year Results

PURPOSE

To evaluate quality of life changes up to 5 years after prostate cancer radiation therapy (RT) with a hydrogel spacer.

METHODS AND MATERIALS

In the years 2010 to 2011, 114 patients received external beam radiation therapy to the prostate; 54 patients were selected for a hydrogel injection before the beginning of RT. Treatment was performed applying fractions of 2 Gy up to a total dose of 76 Gy (n=96) or 78 Gy (n=18, all with hydrogel). Patients were surveyed before RT; at the last day of RT; and a median time of 2 months, 17 months, and 63 months after RT using a validated questionnaire (Expanded Prostate Cancer Index Composite). A mean score change of >5 points was defined as clinically relevant.

RESULTS

For patients treated with a hydrogel spacer, mean bowel function and bother score changes of >5 points in comparison with baseline levels were found only at the end of RT (10-15 points; P<.01). No spacer patient reported moderate or big problems with his bowel habits overall. Mean bother score changes of 21 points at the end of RT, 8 points at 2 months, 7 points at 17 months, and 6 points at 63 months after RT were found for patients treated without a spacer. A bowel bother score change >10 points was found in 6% versus 32% (P<.01) at 17 months and in 5% versus 14% (P=.2) at 63 months with versus without a spacer.

CONCLUSIONS

The first 5-year quality of life results in a group of prostate cancer patients treated with a hydrogel spacer demonstrate excellent treatment tolerability, in particular regarding bowel problems. Further studies with dose-escalated or re-irradiation concepts can be encouraged.

Hydrogel rectum-prostate spacers mitigate the uncertainties in proton relative biological effectiveness associated with anterior-oblique beams

AIM

Anterior-oblique (AO) proton beams can form an attractive option for prostate patients receiving external beam radiotherapy (EBRT) as they avoid the femoral heads. For a cohort with hydrogel prostate-rectum spacers, we asked whether it was possible to generate AO proton plans robust to end-of-range elevations in linear energy transfer (LET) and modeled relative biological effectiveness (RBE). Additionally we considered how rectal spacers influenced planned dose distributions for AO and standard bilateral (SB) proton beams versus intensity-modulated radiotherapy (IMRT).

MATERIAL AND METHODS

We studied three treatment strategies for 10 patients with rectal spacers: (A) AO proton beams, (B) SB proton beams and (C) IMRT. For strategy (A) dose and LET distributions were simulated (using the TOPAS Monte Carlo platform) and the McNamara model was used to calculate proton RBE as a function of LET, dose per fraction, and photon α/β. All calculations were performed on pretreatment scans: inter- and intra-fractional changes in anatomy/set-up were not considered.

RESULTS

For 9/10 patients, rectal spacers enabled generation of AO proton plans robust to modeled RBE elevations: rectal dose constraints were fulfilled even when the variable RBE model was applied with a conservative α/β = 2 Gy. Amongst a subset of patients the proton rectal doses for the planning target volume plans were remarkably low: for 2/10 SB plans and 4/10 AO plans, ≤10% of the rectum received ≥20 Gy. AO proton plans delivered integral doses a factor of approximately three lower than IMRT and spared the femoral heads almost entirely.

CONCLUSION

Typically, rectal spacers enabled the generation of anterior beam proton plans that appeared robust to modeled variation in RBE. However, further analysis of day-to-day robustness would be required prior to a clinical implementation of AO proton beams. Such beams offer almost complete femoral head sparing, but their broader value relative to IMRT and SB protons remains unclear.

Post-Prostatectomy Image-Guided Radiotherapy: The Invisible Target Concept

In the era of intensity-modulated radiation therapy, image-guided radiotherapy (IGRT) appears crucial to control dose delivery and to promote dose escalation while allowing healthy tissue sparing. The place of IGRT following radical prostatectomy is poorly described in the literature. This review aims to highlight some key points on the different IGRT techniques applicable to prostatic bed radiotherapy. Furthermore, methods used to evaluate target motion and to reduce planning target volume margins will also be explored.

Validation of rectal sparing throughout the course of proton therapy treatment in prostate cancer patients treated with SpaceOAR®

The purpose of this study was to investigate the consistency of rectal sparing using multiple periodic quality assurance computerized tomography imaging scans (QACT) obtained during the course of proton therapy for patients with prostate cancer treated with a hydrogel spacer. Forty-one low- and intermediate-risk prostate cancer patients treated with image-guided proton therapy with rectal spacer hydrogel were analyzed. To assess the reproducibility of rectal sparing with the hydrogel spacer, three to four QACTs were performed for each patient on day 1 and during weeks 1, 3, and 5 of treatment. The treatment plan was calculated on the QACT and the rectum V90%, V75%, V65%, V50%, and V40% were evaluated. For the retrospective analysis, we evaluated each QACT and compared it to the corresponding treatment planning CT (TPCT), to determine the average change in rectum DVH points. We were also interested in how many patients exceeded an upper rectum V90% threshold on a QACT. Finally, we were interested in a correlation between rectum volume and V90%. On each QACT, if the rectum V90% exceeded the upper threshold of 6%, the attending physician was notified and the patient was typically prescribed additional stool softeners or laxatives and reminded of dietary compliance. In all cases of the rectum V90% exceeding the threshold, the patient had increased gas and/or stool, compared to the TPCT. On average, the rectum V90% calculated on the QACT was 0.81% higher than that calculated on the TPCT. The average increase in V75%, V65%, V50%, and V40% on the QACT was 1.38%, 1.59%, 1.87%, and 2.17%, respectively. The rectum V90% was within ± 1% of the treatment planning dose in 71.2% of the QACTs, and within ± 5% in 93.2% of the QACTs. The 6% threshold for rectum V90% was exceeded in 7 out of 144 QACTs (4.8%), identified in 5 of the 41 patients. We evaluated the average rectum V90% across all QACTs for each of these patients, and it was found that the rectum V90% never exceeded 6%. 53% of the QACTs had a rectum volume within 5 cm3 of the TPCT volume, 68% were within 10 cm3. We found that patients who exceeded the threshold on one or more QACTs had a lower TPCT rectal volume than the overall average. By extrapolating patient anatomy from three to four QACT scans, we have shown that the use of hydrogel in conjunction with our patient diet program and use of stool softeners is effective in achieving consistent rectal sparing in patients undergoing proton therapy.

Emerging Technologies and Techniques in Radiation Therapy

The past decade has brought an improved ability to precisely target and deliver radiation as well as other focal prostate-directed therapy. Stereotactic body radiotherapy (SBRT), proton beam radiation, high-dose-rate (HDR) brachytherapy, as well as nonradiotherapy treatments such as cryoablation and high-intensity focused ultrasound are several therapeutic modalities that have been investigated for the treatment of prostate cancer in an attempt to reduce toxicity while improving cancer control. However, high-risk prostate cancer requires a comprehensive treatment of the prostate as well as areas at risk for cancer spread. Therefore, most new radiation treatment (SBRT, HDR, and proton beam radiation) modalities have been largely investigated in combination with regional radiation therapy. Though the evidence is evolving, the use of SBRT, HDR, and proton beam radiation is promising. Nonradiation focal therapy has been proposed mainly for partial gland treatment in men with low-risk disease, and its use in high-risk prostate cancer patients remains experimental.

Interdisciplinary consensus statement on indication and application of a hydrogel spacer for prostate radiotherapy based on experience in more than 250 patients

Background

The aim of the study was to reach a consensus on indication and application of a hydrogel spacer based on multicentre experience and give new users important information to shorten the learning curve for this innovative technique.

Methods

The interdisciplinary meeting was attended by radiation oncologists and urologists, each with experience of 23 – 138 hydrogel injections (SpaceOAR®) in prostate cancer patients before dose-escalated radiotherapy. User experience was discussed and questions were defined to comprise practical information relevant for successful hydrogel injection and treatment. Answers to the defined key questions were generated. Hydrogel-associated side effects were collected to estimate the percentage, treatment and prognosis of potential risks.

Results

The main indication for hydrogel application was dose-escalated radiotherapy for histologically confirmed low or intermediate risk prostate cancer. It was not recommended in locally advanced prostate cancer. The injection or implantation was performed under transrectal ultrasound guidance via the transperineal approach after prior hydrodissection. The rate of injection-related G2-toxicity was 2% (n = 5) in a total of 258 hydrogel applications. The most frequent complication (n = 4) was rectal wall penetration, diagnosed at different intervals after hydrogel injection and treated conservatively.

Conclusions

A consensus was reached on the application of a hydrogel spacer. Current experience demonstrated feasibility, which could promote initiation of this method in more centres to reduce radiation-related gastrointestinal toxicity of dose-escalated IGRT. However, a very low rate of a potential serious adverse event could not be excluded. Therefore, the application should carefully be discussed with the patient and be balanced against potential benefits.

Impact of hydrogel spacer injections on interfraction prostate motion during prostate cancer radiotherapy

Background The dosimetric advantage of prostate-rectum spacers to displace the anterior rectal wall outside of the high-dose radiation regions has been clearly established in prostate cancer radiotherapy (RT). The aim of this study was to assess the impact of hydrogel spacer (HS) in the interfraction prostate motion in patients undergoing RT for prostate cancer. Material and methods Twenty prostate cancer patients implanted with three fiducial markers (FM) with (n = 10) or without (n = 10) HS were analyzed. Displacements between the prostate isocenter based on the FM's position and the bony anatomy were quantified in the left-right (LR), anterior-posterior (AP), superior-inferior (SI) axes by offline analyses of 122 cone beam computed tomography scans. Group systematic (M), systematic (Σ) and random (σ) setup errors were determined. Results In patients with or without HS, the overall mean interfraction prostate displacements were 0.4 versus -0.4 mm (p = 0.0001), 0.6 versus 0.6 mm (p = 0.85), and -0.6 mm versus -0.3 mm (p = 0.48) for the LR, AP, and SI axes, respectively. Prostate displacements >5 mm in the AP and SI directions were similar for both groups. No differences in M, Σ and σ setup errors were observed in the three axes between HS + or HS- patients. Conclusions HS implantation does not significantly influence the interfraction prostate motion in patients treated with RT for prostate cancer. The major expected benefit of HS is a reduction of the high-dose levels to the rectal wall without influence in prostate immobilization.

Current role of spacers for prostate cancer radiotherapy

Radiotherapy is an established curative treatment method for prostate cancer. Optimal tumor control rates can only be achieved with high local doses, associated with a considerable risk of rectal toxicity. Apart from already widely adapted technical advances, as intensity-modulated radiation therapy, the application of spacers placed between the prostate and rectum has been increasingly used in the last years. Biodegradable spacers, including hydrogel, hyaluronic acid, collagen or an implantable balloon, can be injected or inserted in a short procedure under transrectal ultrasound guidance via a transperineal approach. A distance of about 1.0-1.5 cm is usually achieved between the rectum and prostate, excluding the rectal wall from the high isodoses. Several studies have shown well tolerated injection procedures and treatments. Apart from considerable reduction of rectal irradiation, a prospective randomized trial demonstrated a reduction of rectal toxicity after hydrogel injection in men undergoing prostate image-guided intensity-modulated radiation therapy. The results are encouraging for continuing evaluation in dose escalation, hypofractionation, stereotactic radiotherapy or re-irradiation trials in the future.

Prostate motion during radiotherapy of prostate cancer patients with and without application of a hydrogel spacer: a comparative study

Background and purpose

The use of a tissue expander (hydrogel) for sparing of the rectum from increased irradiation during prostate radiotherapy is becoming popular. The goal of this study is to investigate the effect of a tissue expander (hydrogel) on the intrafraction prostate motion during radiotherapy.

Methods and material

Real time prostate motion was analysed for 26 patients and 742 fractions; 12 patients with and 14 patients without hydrogel (SpaceOAR™). The intra-fraction motion was quantified and compared between the two groups.

Results

The average (±standard deviation) of the mean motion during the treatment for patients with and without hydrogel was 1.5 (±0.8 mm) and 1.1 (±0.9 mm) respectively (p < 0.05). The average time of motion >3 mm for patients with and without hydrogel was 7.7 % (±1.1 %) and 4.5 % (±0.9 %) respectively (p > 0.05). The hydrogel age, fraction number and treatment time were found to have no effect (R² < 0.05) on the prostate motion.

Conclusions

Differences in intrafraction motion in patients with hydrogel and without hydrogel were within measurement uncertainty (<1 mm). This result confirms that the addition of a spacer does not negate the need for intrafraction motion management if clinically indicated.

A radiopaque polymer hydrogel used as a fiducial marker in gynecologic-cancer patients receiving brachytherapy

PURPOSE

We assessed a novel Food and Drug Administration-approved hydrogel, synthesized as absorbable iodinated particles, in gynecologic-cancer patients undergoing computed tomography (CT) or magnetic resonance (MR) based brachytherapy after external beam radiation.

METHODS AND MATERIALS

Nineteen patients underwent CT-guided (n = 13) or MR-guided (n = 6) brachytherapy for gynecologic cancers. Seventy-seven hydrogel injections were placed. The hydrogel material was injected into gross residual disease and/or key anatomic landmarks in amounts ranging from 0.1 to 0.4 mL. The visibility of the tracer was scored on CT and on MR images using a 5-point scoring scale. A Cohen's kappa statistic was calculated to assess interobserver agreement. To assess the unadjusted effects of baseline parameters on hydrogel visibility, we modeled visibility using a linear mixed-effect model.

RESULTS

Injections were without complication. The kappa statistic was 0.77 (95% confidence interval [CI], 0.68-0.87). The volume of hydrogel injected was significantly associated with visibility on both CT (p = 0.032) and magnetic resonance imaging (p = 0.016). We analyzed visibility by location, controlling for amount. A 0.1-cc increase in volume injected was associated with increases of 0.54 (95% CI = 0.05-1.03) in the CT visibility score and 0.83 (95% CI = 0.17-1.49) in the MR visibility score. Injection of 0.4 cc or more was required for unequivocal visibility on CT or MR. No statistically significant correlation was found between tumor type, tumor location, or anatomical location of injection and visibility on either CT or magnetic resonance imaging.

CONCLUSIONS

In this first report of an injectable radiopaque hydrogel, targets were visualized to assist with three-dimensional-based brachytherapy in gynecologic malignancies. This marker has potential for several applications, is easy to inject and visualize, and caused no acute complications.

PEG spacer gel and adaptive planning vs single plan in external prostate radiotherapy--clinical dosimetry evaluation

OBJECTIVE

Spacer gel is used to reduce the rectal dose in prostate radiotherapy. It is injected to increase the distance between the prostate and rectum. During the course of external radiotherapy treatment, physiological changes in rectal volume exist. When using polyethylene glycol material, such as DuraSeal(®) (Covidien, Mansfield, MA), gel resorption also occurs. Together, these factors alter the original dose plan distribution.

METHODS

External dose planning and calculations were simulated using images acquired from 10 patients who were treated with brachytherapy and gel. The CT series was taken relative to gel injection: pre 1 day, post 1 day, post 1 month and post 2 months. Adaptive planning was compared with a single plan.

RESULTS

Adaptive planning shows better results compared with the single plan used in the total treatment course; however, the effect is minor.

CONCLUSION

Gel usage is clearly favourable to rectal DVH. Using adaptive planning with gel improves rectal DVH but is not necessary according to this study.

ADVANCES IN KNOWLEDGE

Spacer gel is used in prostate radiotherapy to increase distance between the prostate and the rectum, thus reducing the rectal doses. During the treatment course, gel resorption exists which affects the rectal doses. The usefulness of adaptive planning to compensate this resorption effect has not been studied before.

Clinical evaluation of an endorectal immobilization system for use in prostate hypofractionated Stereotactic Ablative Body Radiotherapy (SABR)

Background

The objective of this study was to evaluate a novel prostate endorectal immobilization system (EIS) for improving the delivery of hypofractionated Stereotactic Ablative Body Radiotherapy (SABR) for prostate cancer.

Methods

Twenty patients (n = 20) with low- or intermediate-risk prostate cancer (T1-T2b, Gleason Score < 7, PSA ≤ 20 ng/mL), were treated with an EIS in place using Volumetric Modulated Arc Therapy (VMAT), to a prescription dose of 26 Gy delivered in 2 fractions once per week; the intent of the institutional clinical trial was an attempt to replicate brachytherapy-like dosimetry using SABR. EBT3 radiochromic film embedded within the EIS was used as a quality assurance measure of the delivered dose; additionally, prostate intrafraction motion captured using pre- and post-treatment conebeam computed tomography (CBCT) scans was evaluated. Treatment plans were generated for patients with- and without the EIS to evaluate its effects on target and rectal dosimetry.

Results

None of the observed 3-dimensional prostate displacements were ≥ 3 mm over the elapsed treatment time. A Gamma passing rate of 95.64 ± 4.28 % was observed between planned and delivered dose profiles on EBT3 film analysis in the low-dose region. No statistically significant differences between treatment plans with- and without-EIS were observed for rectal, bladder, clinical target volume (CTV), and PTV contours (p = 0.477, 0.484, 0.487, and 0.487, respectively). A mean rectal V80% of 1.07 cc was achieved for plans using the EIS.

Conclusions

The EIS enables the safe delivery of brachytherapy-like SABR plans to the prostate while having minimal impact on treatment planning and rectal dosimetry. Consistent and reproducible immobilization of the prostate is possible throughout the duration of these treatments using such a device.

Ion therapy of prostate cancer: daily rectal dose reduction by application of spacer gel

Background

Ion beam therapy represents a promising approach to treat prostate cancer, mainly due to its high conformity and radiobiological effectiveness. However, the presence of prostate motion, patient positioning and range uncertainties may deteriorate target dose and increase exposure of organs at risk. Spacer gel injected between prostate and rectum may increase the safety of prostate cancer (PC) radiation therapy by separating the rectum from the target dose field. The dosimetric impact of the application of spacer gel for scanned carbon ion therapy of PC has been analyzed at Heidelberg Ion-Beam Therapy Center (HIT).

Materials and methods

The robustness of ion therapy treatment plans was investigated by comparison of two data sets of patients treated with and without spacer gel. A research treatment planning system for ion therapy was used for treatment plan optimization and calculation of daily dose distributions on 2 to 9 Computed Tomography (CT) studies available for each of the 19 patients. Planning and daily dose distributions were analyzed with respect to target coverage, maximal dose to the rectum (excluding 1 ml of the greatest dose; Dmax-1 ml) and the rectal volume receiving dose greater than 90% of prescribed target dose (V90_Rectum), respectively.

Results

The application of spacer gel did substantially diminish rectum dose. Dmax-1 ml on the treatment planning CT was on average reduced from 100.0 ± 1.0% to 90.2 ± 4.8%, when spacer gel was applied. The robustness analysis performed with daily CT studies demonstrated for all analyzed patient cases that application of spacer gel results in a decrease of the daily V90_Rectum index, which calculated over all patient cases and CT studies was 10.2 ± 10.4 [ml] and 1.1 ± 2.1 [ml] for patients without and with spacer gel, respectively.

Conclusions

The dosimetric benefit of increasing the distance between prostate and rectum using spacer gel for PC treatment with carbon ion beams has been quantified. Application of spacer gel substantially reduced rectal exposure to high treatment dose and, therefore, can reduce the hazard of rectal toxicity in ion beam therapy of PC. The results of this study enable modifications of the PC ion therapy protocol such as dose escalation or hypofractionation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13014-015-0348-1) contains supplementary material, which is available to authorized users.

A review of rectal toxicity following permanent low dose-rate prostate brachytherapy and the potential value of biodegradable rectal spacers

Permanent radioactive seed implantation provides highly effective treatment for prostate cancer that typically includes multidisciplinary collaboration between urologists and radiation oncologists. Low dose-rate (LDR) prostate brachytherapy offers excellent tumor control rates and has equivalent rates of rectal toxicity when compared with external beam radiotherapy. Owing to its proximity to the anterior rectal wall, a small portion of the rectum is often exposed to high doses of ionizing radiation from this procedure. Although rare, some patients develop transfusion-dependent rectal bleeding, ulcers or fistulas. These complications occasionally require permanent colostomy and thus can significantly impact a patient's quality of life. Aside from proper technique, a promising strategy has emerged that can help avoid these complications. By injecting biodegradable materials behind Denonviller's fascia, brachytherpists can increase the distance between the rectum and the radioactive sources to significantly decrease the rectal dose. This review summarizes the progress in this area and its applicability for use in combination with permanent LDR brachytherapy.

Spacer application for prostate cancer radiation therapy

Definitive radiotherapy is a well-recognized treatment option for localized prostate cancer. Rectum toxicity is the dose-limiting toxicity. Dose-volume correlations have been reported in many studies. The application of a spacer to increase the distance between the prostate and anterior rectal wall is an innovative technique, considerably reducing the dose to the rectum. Hyaluronic acid, human collagen, an inflatable balloon or hydrogel are potential materials to create the desired effect. The number of clinical studies is rapidly increasing. Well-tolerated injection or implantation techniques and low rectal treatment-related toxicity have been demonstrated in prospective studies. Long-term clinical results and the results of randomized studies are needed to better define the beneficial effect for the patient.

Rectal ulcer associated with SpaceOAR hydrogel insertion during prostate brachytherapy

We present a case of rectal ulceration associated with SpaceOAR hydrogel insertion during low-dose-rate (LDR) brachytherapy in a patient with prostate cancer.

Optimization of radiation therapy techniques for prostate cancer with prostate-rectum spacers: a systematic review

Dose-escalated radiation therapy for localized prostate cancer improves disease control but is also associated with worse rectal toxicity. A spacer placed between the prostate and rectum can be used to displace the anterior rectal wall outside of the high-dose radiation regions and potentially minimize radiation-induced rectal toxicity. This systematic review focuses on the published data regarding the different types of commercially available prostate-rectum spacers. Dosimetric results and preliminary clinical data using prostate-rectum spacers in patients with localized prostate cancer treated by curative radiation therapy are compared and discussed.

Rectal toxicity after intensity modulated radiotherapy for prostate cancer: which rectal dose volume constraints should we use?

BACKGROUND

To define rectal dose volume constraints (DVC) to prevent ⩾grade2 late rectal toxicity (LRT) after intensity modulated radiotherapy (IMRT) for prostate cancer (PC).

MATERIAL AND METHODS

Six hundred thirty-seven PC patients were treated with primary (prostate median dose: 78Gy) or postoperative (prostatic bed median dose: 74Gy (adjuvant)-76Gy (salvage)) IMRTwhile restricting the rectal dose to 76Gy, 72Gy and 74Gy respectively. The impact of patient characteristics and rectal volume parameters on ⩾grade2 LRT was determined. DVC were defined to estimate the 5% and 10% risk of developing ⩾grade2 LRT.

RESULTS

The 5-year probability of being free from ⩾grade2 LRT, non-rectal blood loss and persisting symptoms is 88.8% (95% CI: 85.8-91.1%), 93.4% (95% CI: 91.0-95.1%) and 94.3% (95% CI: 92.0-95.9%) respectively. There was no correlation with patient characteristics. All volume parameters, except rectal volume receiving ⩾70Gy (R70), were significantly correlated with ⩾grade2 LRT. To avoid 10% and 5% risk of ⩾grade2 LRT following DVC were derived: R40, R50, R60 and R65 <64-35%, 52-22%, 38-14% and 5% respectively.

CONCLUSION

Applying existing rectal volume constraints resulted in a 5-year estimated risk of developing late ⩾grade2 LRT of 11.2%. New rectal DVC for primary and postoperative IMRT planning of PC patients are proposed. A prospective evaluation is needed.

Application of a hydrogel spacer for postoperative salvage radiotherapy of prostate cancer

BACKGROUND

In contrast to primary radiotherapy, no reports are available for a hydrogel spacer application in postoperative salvage radiotherapy for prostate cancer.

CASE REPORT

A 77-year-old patient presented 20 years after radical prostatectomy with a digitally palpable local recurrence at the urethrovesical anastomosis (PSA 5.5 ng/ml). The hydrogel spacer (10 ml, SpaceOAR™) was injected between the local recurrence and rectal wall under transrectal ultrasound guidance. Treatment planning was performed with an intensity-modulated technique up to a total dose of 76 Gy in 2-Gy fractions. The same planning was performed based on computed tomography before spacer injection for comparison.

RESULTS

The local recurrence, initially directly on the rectal wall, could be displaced more than  1 cm from the rectal wall after hydrogel injection. With a mean total dose of 76 Gy to the planning target volume, rectal wall volumes included in the 70 Gy, 60 Gy, 50 Gy isodoses were 0 cm(3), 0 cm(3), and 0.4 cm(3) with a spacer and 2.9 cm(3), 4.5 cm(3), and 6.2 cm(3) without a spacer, respectively. The patient reported rectal urgency during radiotherapy, completely resolving after the end of treatment. The PSA level was 5.4 ng/ml a week before the end of radiotherapy and dropped to 0.9 ng/ml 5 months after radiotherapy.

CONCLUSION

A hydrogel spacer was successfully applied for dose-escalated radiotherapy in a patient with macroscopic local prostate cancer recurrence at the urethrovesical anastomosis to decrease the dose at the rectal wall. This option can be considered in specifically selected patients.

DuraSeal as a spacer to reduce rectal doses in low-dose rate brachytherapy for prostate cancer

The purpose of this study was to evaluate the utility of off-label use of DuraSeal polyethylene glycol (PEG) gel in low-dose rate (LDR) prostate brachytherapy seed implantation to reduce rectal doses. Diluted DuraSeal was easy to use and, in spite of a clearance effect, useful in decreasing D₂cc rectal doses.

[Prostate-rectum spacers: optimization of prostate cancer irradiation]

In the curative radiotherapy of localized prostate cancer, improvements in biochemical control observed with dose escalation have been counterbalanced by an increase in radiation-induced toxicity. The injection of biodegradable spacers between prostate and rectum represents a new frontier in the optimization of radiotherapy treatments for patients with localized disease. Transperineal injection of different types of spacers under transrectal ultrasound guidance allows creating a 7-to-20 mm additional space between the prostate and the anterior rectal wall lasting 3 to 12 months. Dosimetrically, a relative reduction in the rectal volume receiving at least 70 Gy (V70) in the order of 43% to 84% is observed with all types of spacers, regardless of the radiotherapy technique used. Preliminary clinical results show for all spacers a good tolerance and a possible reduction in the acute side effects rate. The aim of the present systematic review of the literature is to report on indications as well as dosimetric and clinical advantages of the different types of prostate-rectum spacers commercially available (hydrogel, hyaluronic acid, collagen, biodegradable balloon).