Anorectal dose-effect relations for late gastrointestinal toxicity following external beam radiotherapy for prostate cancer in the FLAME trial

Photon vs proton hypofractionation in prostate cancer: A systematic review and meta-analysis

BACKGROUND

High-level evidence on hypofractionated proton therapy (PT) for localized and locally advanced prostate cancer (PCa) patients is currently missing. The aim of this study is to provide a systematic literature review to compare the toxicity and effectiveness of curative radiotherapy with photon therapy (XRT) or PT in PCa.

METHODS

PubMed, Embase, and the Cochrane Library databases were systematically searched up to April 2022. Men with a diagnosis of PCa who underwent curative hypofractionated RT treatment (PT or XRT) were included. Risk of grade (G) ≥ 2 acute and late genitourinary (GU) OR gastrointestinal (GI) toxicity were the primary outcomes of interest. Secondary outcomes were five-year biochemical relapse-free survival (b-RFS), clinical relapse-free, distant metastasis-free, and prostate cancer-specific survival. Heterogeneity between study-specific estimates was assessed using Chi-square statistics and measured with the I2 index (heterogeneity measure across studies).

RESULTS

A total of 230 studies matched inclusion criteria and, due to overlapped populations, 160 were included in the present analysis. Significant lower rates of G ≥ 2 acute GI incidence (2 % vs 7 %) and improved 5-year biochemical relapse-free survival (95 % vs 91 %) were observed in the PT arm compared to XRT. PT benefits in 5-year biochemical relapse-free survival were maintained for the moderate hypofractionated arm (p-value 0.0122) and among patients in intermediate and low-risk classes (p-values < 0.0001 and 0.0368, respectively). No statistically relevant differences were found for the other considered outcomes.

CONCLUSION

The present study supports that PT is safe and effective for localized PCa treatment, however, more data from RCTs are needed to draw solid evidence in this setting and further effort must be made to identify the patient subgroups that could benefit the most from PT.

Predictors of radiation-induced late rectal toxicity in prostate cancer treatment: a volumetric and dosimetric analysis

Introduction

Prostate cancer (PCa) is a prevalent malignancy in European men, often treated with radiotherapy (RT) for localized disease. While modern RT achieves high success rates, concerns about late gastrointestinal (GI) toxicities persist. This retrospective study aims to identify predictors for late GI toxicities following definitive conventionally fractionated external beam RT (EBRT) for PCa, specifically exploring the dose to the rectal wall.

Materials and methods

A cohort of 96 intermediate- to high-risk PCa patients underwent EBRT between 2008 and 2016. Rectum and rectum wall contours were delineated, and 3D dose matrices were extracted. Volumetric and dosimetric indices were computed, and statistical analyses were performed to identify predictors using the Mann-Whitney U-rank test, logistic regression, and recursive feature elimination.

Results

In our cohort, 15 out of 96 patients experienced grade II late proctitis. Our analysis reveals distinct optimal predictors for rectum and rectum wall (RW) structures varying with α/β values (3.0 and 2.3 Gy) across prescribed doses of 68 to 76 Gy. Despite variability, RW predictors demonstrate greater consistency, notably V68Gy[%] to V74Gy[%] for α/β 3.0 Gy, and V68Gy[%] to V70Gy[%] for α/β 2.3 Gy. The model with α/β 2.3 Gy, featuring RW volume receiving 70 Gy (V70Gy[%]), stands out with a BIC value of 62.92, indicating its superior predictive effectiveness. Finally, focusing solely on the rectum structure, the V74Gy[%] emerges the best predictor for α/β 3.0 Gy, with a BIC value of 66.73.

Conclusion

This investigation highlights the critical role of V70Gy[%] in the rectum wall as a robust predictor for grade II late gastrointestinal (GI) toxicity following external beam radiation therapy (EBRT) for prostate cancer (PCa). Furthermore, our findings suggest that focusing on the rectum wall specifically, rather than the entire rectum, may offer improved accuracy in assessing proctitis development. A V70Gy (in EQD2 with α/β 2.3 Gy) of ≤5% and if possible ≤1% for the rectal wall should be achieved to minimize the risk of late grade II proctitis.

Comparative Study of Eclipse and RayStation Multi-Criteria Optimization-Based Prostate Radiotherapy Treatment Planning Quality

Multi-criteria optimization (MCO) function has been available on commercial radiotherapy (RT) treatment planning systems to improve plan quality; however, no study has compared Eclipse and RayStation MCO functions for prostate RT planning. The purpose of this study was to compare prostate RT MCO plan qualities in terms of discrepancies between Pareto optimal and final deliverable plans, and dosimetric impact of final deliverable plans. In total, 25 computed tomography datasets of prostate cancer patients were used for Eclipse (version 16.1) and RayStation (version 12A) MCO-based plannings with doses received by 98% of planning target volume having 76 Gy prescription (PTV76D98%) and 50% of rectum (rectum D50%) selected as trade-off criteria. Pareto optimal and final deliverable plan discrepancies were determined based on PTV76D98% and rectum D50% percentage differences. Their final deliverable plans were compared in terms of doses received by PTV76 and other structures including rectum, and PTV76 homogeneity index (HI) and conformity index (CI), using a t-test. Both systems showed discrepancies between Pareto optimal and final deliverable plans (Eclipse: -0.89% (PTV76D98%) and -2.49% (Rectum D50%); RayStation: 3.56% (PTV76D98%) and -1.96% (Rectum D50%)). Statistically significantly different average values of PTV76D98%,HI and CI, and mean dose received by rectum (Eclipse: 76.07 Gy, 0.06, 1.05 and 39.36 Gy; RayStation: 70.43 Gy, 0.11, 0.87 and 51.65 Gy) are noted, respectively (p < 0.001). Eclipse MCO-based prostate RT plan quality appears better than that of RayStation.

Application of a Radiopaque Viscous Hydrogel Spacer for Prostate Cancer Radiation Therapy: A Prospective Phase 2 Study

PURPOSE

The aim of this study was to evaluate the application of a radiopaque viscous spacer (RVS) for prostate cancer radiation therapy (RT), including injection procedure, toxicity, treatment planning, image guidance, and imaging results up to 12 months after RT.

METHODS AND MATERIALS

RVS (median, 10 mL) was injected between prostate and rectal wall in 30 patients. Cone beam computed tomography (CT) was performed during the course of RT, a magnetic resonance imaging 3 and 12 months after RT. Injection and treatment tolerability were analyzed. The resulting distribution was compared with a control group of 30 patients with an initially fluid spacer.

RESULTS

Procedure- or device-related adverse events were not observed. Signs of hydrogel migration were not found in any case. The volume decreased by 25% at 3 months after RT, and small residues were detected at 12 months after RT in 3 cases (10%). The median rectal volume percentage within the 90% isodose was 3.0% (interquartile range, 1.5%-4.5%). Acute and late gastrointestinal toxicities were found in 17% and 3%, respectively (all grade 1). The median distance between prostate and rectum at the base/midplane/apex was greater for RVS in comparison to initially fluid spacer (14/12/11 mm vs 12/10/10 mm, respectively), the gel symmetry (right vs left from midline) was comparable. The application was assessed to be easier to control by the users, and visibility in cone beam CT as good.

CONCLUSIONS

The injection of a radiopaque viscous hydrogel spacer resulted in a prostate-rectum distance of >10 mm in most cases. The resulting rectum volume within the high-dose region and RT toxicity were very low. Advantages in comparison to the conventional hydrogel spacer are predominantly an improved placement control during the injection process and good visibility on CT.

Risk Modeling for Individualization of the FLAME Focal Boost Approach in External Beam Radiation Therapy for Patients With Localized Prostate Cancer

PURPOSE

The FLAME trial (NCT01168479) showed that isotoxic focal boosting to the intraprostatic lesion(s) in patients with intermediate- and high-risk prostate cancer improves 5-year disease-free survival (DFS). Although the near-minimum dose to the gross tumor volume (D98%) was associated with improved outcomes, a closer look suggested that this might not be the same for all patients. Therefore, we investigated whether risk factors that are associated with a benefit of focal boosting can be identified.

METHODS AND MATERIALS

We described the distribution of clinical characteristics and the number of high-risk factors with respect to the D98% in 526 FLAME trial patients. We used penalized Cox regression to develop a prediction model. To investigate a potential benefit in patient subgroups, we compared the model-based predictions of 5-year DFS assuming standard whole-gland radiation therapy of 77 Gy to the predictions assuming an additional focal boost with D98% of 95 Gy.

RESULTS

Patients with high-risk factors were well represented in the group of 120 patients that received D98% > 85 Gy and showed fewer recurrences compared with the group that received 77 Gy. Applying the model simulating a standard dose of 77 Gy, we predicted a high DFS for grade group (GG) 1 patients, whereas patients with high-risk characteristics appeared to show a low DFS. All risk groups showed a high level of DFS when simulating D98% of 95 Gy.

CONCLUSIONS

Our results suggest that GG 1 patients already show a low level of failure at a standard dose of 77 Gy, limiting the additional benefit of focal boosting. In contrast, patients with high-risk characteristics, especially GG 4 or 5, show a low 5-year DFS, while focal boosting might improve this substantially. This suggests that reaching a high focal boost dose may be particularly beneficial for these patients.

Long-term findings of rectal endoscopy and rectal bleeding after moderately hypofractionated, intensity-modulated radiotherapy for prostate cancer

To present rectal endoscopic findings and toxicity after definitive moderately hypofractionated, intensity-modulated radiotherapy (IMRT) for prostate cancer. We retrospectively reviewed patients who underwent IMRT for prostate cancer and underwent post-radiotherapy endoscopies between 2008 and 2018. Endoscopic findings were reviewed and graded using Vienna Rectoscopy Score (VRS). We have analyzed the association between endoscopic findings and rectal bleeding, and investigated risk factors for rectal bleeding. Total 162 patients met the inclusion criteria of this study. There was a trend of VRS worsening during the initial 3 years after radiotherapy followed by recovery. Rectal bleeding was highest at 1 year after radiotherapy and improved thereafter. The 5-year cumulative incidence of grade ≥ 2 rectal bleeding was 14.8%. In the multivariable Cox regression analysis, cardiovascular disease (hazard ratio [HR] 2.732, P = 0.037), rectal wall V65 (HR 1.158, P = 0.027), and VRS ≥ 3 in first post-radiotherapy endoscopy (HR 2.573, P = 0.031) were significant risk factors for rectal bleeding. After IMRT for prostate cancer, VRS and rectal bleeding worsened over 1-3 years after radiotherapy and recovered. Cardiovascular disease, rectal wall V65, and VRS ≥ 3 in first post-radiotherapy endoscopy were significant risk factors for rectal bleeding.

Microbiome and metabolome dynamics during radiotherapy for prostate cancer

BACKGROUND

Prostate cancer patients treated with radiotherapy are susceptible to acute gastrointestinal (GI) toxicity due to substantial overlap of the intestines with the radiation volume. Due to their intimate relationship with GI toxicity, faecal microbiome and metabolome dynamics during radiotherapy were investigated.

MATERIAL & METHODS

This prospective study included 50 prostate cancer patients treated with prostate (bed) only radiotherapy (PBRT) (n = 28) or whole pelvis radiotherapy (WPRT) (n = 22) (NCT04638049). Longitudinal sampling was performed prior to radiotherapy, after 10 fractions, near the end of radiotherapy and at follow-up. Patient symptoms were dichotomized into a single toxicity score. Microbiome and metabolome fingerprints were analyzed by 16S rRNA gene sequencing and ultra-high-performance liquid chromatography hybrid high-resolution mass spectrometry, respectively.

RESULTS

The individual α-diversity did not significantly change over time. Microbiota composition (β-diversity) changed significantly over treatment (PERMANOVA p-value = 0.03), but there was no significant difference in stability when comparing PBRT versus WPRT. Levels of various metabolites were significantly altered during radiotherapy. Baseline α-diversity was not associated with any toxicity outcome. Based on the metabolic fingerprint, no natural clustering according to toxicity profile could be achieved.

CONCLUSIONS

Radiation dose and treatment volume demonstrated limited effects on microbiome and metabolome fingerprints. In addition, no distinctive signature for toxicity status could be established. There is an ongoing need for toxicity risk stratification tools for diagnostic and therapeutic purposes, but the current evidence implies that the translation of metabolic and microbial biomarkers into routine clinical practice remains challenging.

Focal injection of a radiopaque viscous spacer before focal brachytherapy as re-irradiation for locally recurrent prostate cancer

PURPOSE

Close vicinity of the target volume and a sensitive organ may prevent an effective radiotherapy/brachytherapy. A liquid hydrogel spacer cannot be placed well focally in specific small areas or fatty tissue. The purpose of this study was to report the injection technique and results of a radiopaque viscous hydrogel spacer.

METHODS

The radiopaque viscous spacer was applied focally using transrectal ultrasound guidance before focal brachytherapy in re-irradiated areas in two patients. The technical feasibility of the injection between the recurrence and the rectum / bladder, the resulting distance, visibility in different imaging modalities, stability within several months, dose distribution, toxicity and tumor control up to 18 months after treatment was analyzed.

RESULTS

After hydrodissection, the needle was moved from the base towards the apex during injection of each syringe, respectively. The viscous spacer could be successfully injected focally and resulted in a planned distancing of the target volume (right lobe and seminal vesicle area) and the rectum of at least 1 cm and additional distancing to the bladder of at least 5 mm. Both brachytherapy treatments were performed without relevant toxicities. The PSA nadirs indicated a satisfactory short-term response to the treatment.

CONCLUSIONS

The viscous hydrogel spacer can be injected focally at a specific prostate lobe or seminal vesicles. A viscous spacer remains stable within fatty tissue in any areas that are accessible by an ultrasound guided needle injection to create a distance between the high brachytherapy dose within the target and the organ at risk.

Dose-volume analysis of planned versus accumulated dose as a predictor for late gastrointestinal toxicity in men receiving radiotherapy for high-risk prostate cancer

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Interfractional variations in organs at risk were observed in prostate radiotherapy.

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Rectal accumulated dose was significantly higher at the intermediate-high dose region.

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Rectal planned dose was significantly higher at the very high dose region.

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Dose>78.2 Gy to 0.03 cc of rectum was predictive of late Grade 2 toxicity.

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Patient age>72 years was predictive of late Grade 2 rectal toxicity.

Background and purpose

Significant dose deviations have been reported between planned (D_P) and accumulated (D_A) dose in prostate radiotherapy. This study aimed to develop multivariate analysis (MVA) models associating Grade 1 and 2 gastrointestinal (GI) toxicity with clinical and D_P or D_A dosimetric variables separately.

Materials and methods

Dose volume (DV) metrics were compared between D_A and D_P for 150 high-risk prostate cancer patients. MV models were generated from significant clinical and dosimetric variables (p < 0.05) at univariate level. Dose-based-region of interest (DB-ROI) metrics were included. Model performance was measured, and additional subgroup analysis were performed.

Results

Rectal D_A demonstrated a higher intermediate-high dose (V_{30-65 Gy} and DB-ROI at 15–50 mm) compared to D_P. Conversely, at the very high dose region, rectal D_A (V_{75 Gy} and DB-ROI at 5–10 mm) were significantly lower. In MVA, rectal DB-ROI at 10 mm was predictive for Grade ≥ 1 GI toxicity for D_A and D_P. Age, rectal D_A for D_{0.03 cc}, and rectal D_P for DB-ROI 10 mm were predictors for Grade 2 GI toxicity. Subgroup analysis revealed that patients ≥ 72 years old and a rectal D_A of ≥ 78.2 Gy were highly predictive of Grade 2 GI toxicity.

Conclusions

The dosimetric impact of a higher dose rectal dose in D_A due to volumetric changes was minimal and was not predictive of detrimental clinical toxicity apart from rectal D_{0.03 cc} ≥ 78.2 Gy for Grade 2 GI toxicity. The use of the DB-ROI method can provide equivalent predictive power as the DV method in toxicity prediction.