Dosimetric and volumetric effects in clinical target volume and organs at risk during postprostatectomy radiotherapy

Evaluating the geometric and dosimetric impact of applying anisotropic CTV to PTV margins in image-guided post-prostatectomy radiation therapy

INTRODUCTION

Guidelines for clinical target volume (CTV) to planning target volume (PTV) margins in post-prostatectomy radiation therapy (PPRT) are varied and often not clearly defined. Assessment of appropriateness of margins is commonly measured on prevalence of geographic miss.

METHODS

Cone-beam CT (CBCT) images (n = 92) for 10 PPRT patients were incorporated to provide on-treatment information on the appropriateness of six different CTV expansion margins in terms of geographic miss and change in dose-volume statistics for CTV, rectum and bladder. Uniform margins included 10 mm, 5 mm, 10 mm + 5 mm posteriorly and 5 mm + 3 mm posteriorly. In addition, two anisotropic margins were evaluated by separating the superior and inferior portions of the CTV before expansion. Treatment plans were created for each PTV retrospectively.

RESULTS

The frequency of geographic miss was the smallest for the large uniform expansions but resulted in the highest organ-at-risk (OAR) doses. Geographic miss in the smaller uniform and anisotropic PTVs was more prevalent but commonly to a small volume < 1% of CTV. When averaged over all CBCT fractions, V95% dose for all CTV margins remained > 99%. The anisotropic expansions generated smaller irradiated target volumes and consequently saw up to 7.3% reduction in bladder dose when compared with similar uniform expansion margins.

CONCLUSION

Supplementing the incidence of geographic miss with dosimetric information on target coverage and OAR doses provides more informed assessment of the appropriateness of different CTV expansion margins. Our study extends the evaluation of anisotropic margins for PPRT.

Risk Factors of Acute Radiation-Induced Lung Injury Induced by Radiotherapy for Esophageal Cancer

Objective

To investigate the risk factors of acute radiation-induced lung injury (acute RILI) induced by radiotherapy for esophageal cancer.

Methods

A total of 206 patients with esophageal cancer who received radiotherapy in our hospital from January 2017 to March 2020 were selected. The general data such as gender, age, and comorbidities of the patients were collected, as well as the levels of cytokines (TNF-α, TNF-β, and IL-6) in peripheral blood before radiotherapy; radiotherapy dose-related parameters were recorded during radiotherapy. Follow-up was 12 months after radiotherapy. The patients with induced acute RILI after radiotherapy were set as the observation group (n = 75). Patients without acute RILI after radiotherapy were set as the control group (n = 131). Univariate and multivariate logistic regression analysis was performed on the risk factors of acute RILI induced by radiotherapy for esophageal cancer.

Results

Univariate analysis and multivariate logistic regression analysis showed that the combined diabetes, total radiation dose, combined lung disease, physical factors (V30, Dmean), and preradiotherapy cytokine (TNF-α, TNF-β, and IL-6) elevated level was an independent risk factor for radiotherapy-induced acute RILI in esophageal cancer (P < 0.05).

Conclusion

Concomitant diabetes, total radiation dose, lung disease, physical factors (V30, Dmean), and levels of cytokines (TNF-α, TNF-β, and IL-6) before radiation therapy are risk factors for acute RILI induced by radiation therapy in esophageal cancer. The possibility of acute RILI should be comprehensively assessed according to the patient's condition, and the radiotherapy regimen should be adjusted to reduce and avoid the induction of acute radiation-induced lung injury.

Evaluating the impact of possible interobserver variability in CBCT-based soft-tissue matching using TCP/NTCP models for prostate cancer radiotherapy

Background

Prostate alignment is subject to interobserver variability in cone-beam CT (CBCT)-based soft-tissue matching. This study aims to analyze the impact of possible interobserver variability in CBCT-based soft-tissue matching for prostate cancer radiotherapy.

Methods

Retrospective data, consisting of 156 CBCT images from twelve prostate cancer patients with elective nodal irradiation were analyzed in this study. To simulate possible interobserver variability, couch shifts of 2 mm relative to the resulting patient position of prostate alignment were assumed as potential patient positions (27 possibilities). For each CBCT, the doses of the potential patient positions were re-calculated using deformable image registration-based synthetic CT. The impact of the simulated interobserver variability was evaluated using tumor control probabilities (TCPs) and normal tissue complication probabilities (NTCPs).

Results

No significant differences in TCPs were found between prostate alignment and potential patient positions (0.944 ± 0.003 vs 0.945 ± 0.003, P = 0.117). The average NTCPs of the rectum ranged from 5.16 to 7.29 (%) among the potential patient positions and were highly influenced by the couch shift in the anterior–posterior direction. In contrast, the average NTCPs of the bladder ranged from 0.75 to 1.12 (%) among the potential patient positions and were relatively negligible.

Conclusions

The NTCPs of the rectum, rather than the TCPs of the target, were highly influenced by the interobserver variability in CBCT-based soft-tissue matching. This study provides a theoretical explanation for daily CBCT-based image guidance and the prostate-rectum interface matching procedure.

Trial registration: Not applicable.

Analysis of the Influence of Peripheral Anatomical Changes for CBCT-Guided Prostate Cancer Radiotherapy

Purpose:

To analyze the influence of the bladder and rectum filling and the body contour changes on the prostate target dose.

Methods:

A total of 190 cone-beam CT (CBCT) image data sets from 16 patients with prostate cancer were used in this study. Dose reconstruction was performed on the virtual CT generated by the deformable planning CT. Then, the effects of the bladder filling, rectal filling, and the patient’s body contour changes of the PCTV1 (the prostate area, B1) and PCTV2 (the seminal vesicle area, B2) on the target dose were analyzed. Correlation analysis was performed for the ratio of bladder and rectal volume variation and the variation of the bladder and rectal dose.

Results:

The mean Dice coefficients of B1, B2, bladder, and rectum were 0.979, 0.975, 0.888 and 0.827, respectively, and the mean Hausdorff distances were 0.633, 1.505, 2.075, and 1.533, respectively. With the maximum volume variations of 142.04 ml for the bladder and 40.50 ml for the rectum, the changes of V₁₀₀, V₉₅, D₂, and D₉₈ were 1.739 ± 1.762 (%), 0.066 ± 0.169 (%), 0.562 ± 0.442 (%), and 0.496 ± 0.479 (%) in PCTV1 and 1.686 ± 1.051 (%), 0.240 ± 0.215 (%), 1.123 ± 0.925 (%), and 0.924 ± 0.662 (%) in PCTV2, respectively. With a 10% increase in the volume of the bladder and rectum, the V₇₅, V₇₀, and V₆₅ of rectum increased at 0.73 (%), 0.71 (%), and 1.18 (%), and the V₇₅, V₇₀, and V₆₅ of bladder changed at −0.21 (%), −0.32 (%), and −0.39 (%), respectively.

Conclusion:

Significant correlations were observed between the volume variation and the dose variation of the bladder and rectum. However, when a bladder and rectal filling protocol was adopted, the target dose coverage can be effectively ensured based on CBCT guidance to correct the prostate target position.

Salvage radiation therapy in prostate cancer: relationship between rectal dose and long-term, self-reported rectal bleeding

Purpose

To quantify the relationship between the rectal dose distribution and the prevalence of self-reported rectal bleeding among men treated with salvage radiotherapy (ST) delivered by three-dimensional conformal radiotherapy (3DCRT) for prostate cancer. To use this relationship to estimate the risk of rectal bleeding for a contemporary cohort of patients treated with volumetric modulated arc therapy (VMAT) ST.

Methods and patients

Rectal bleeding of any grade was reported by 56 (22%) of 255 men in a PROM-survey at a median follow-up of 6.7 years after 3DCRT ST. Treatment plan data were extracted and dose–response relationships for the rectal volumes receiving at least 35 Gy (V_35Gy) or 63 Gy (V_63Gy) were calculated with logistic regression. These relationships were used to estimate the risk of rectal bleeding for a cohort of 253 patients treated with VMAT ST.

Results

In the dose–response analysis of patients in the 3DCRT ST cohort, both rectal V_35Gy and V_63Gy were statistically significant parameters in univariable analysis (p = 0.005 and 0.003, respectively). For the dose–response models using either rectal V_35Gy or V_63Gy, the average calculated risk of rectal bleeding was 14% among men treated with VMAT ST compared to a reported prevalence of 22% for men treated with 3DCRT ST.

Conclusions

We identified dose–response relationships between the rectal dose distribution and the risk of self-reported rectal bleeding of any grade in a long-term perspective for men treated with 3DCRT ST. Furthermore, VMAT ST may have the potential to decrease the prevalence of late rectal bleeding.

Moderately HRT vs. CRT for localized prostate cancer using image-guided VMAT with SIB: evaluation of acute and late toxicities

Purpose

This retrospective study aims at investigating the effects of moderately hypofractionated radiation therapy (HRT) on acute and late toxicities as well as on early biochemical control and therapeutic efficiency compared to conventional radiation therapy (CRT) in prostate cancer.

Patients and methods

We analyzed 55 HRT patients irradiated with the total dose of 60 Gy in 20 fractions delivered over 4 weeks. These patients were compared to a control group of 55 patients who received CRT with a total of <78 Gy in 37–39 fractions delivered over circa 8 weeks. External beam radiation therapy (EBRT) was conducted using daily image-guided (cone beam CT) volumetric modulated arc therapy (VMAT) and a simultaneously integrated boost (SIB) for both groups to protect the rectum. Acute toxicities were evaluated according to Common Terminology Criteria for Adverse Events (CTCAE) v5, whereas chronic toxicities were assessed in accordance with LENT-SOMA. Patient traits were compared by implementing t‑tests and Wilcoxon–Whitney tests for continuous variables, whereas discrete characteristics were evaluated by applying two-tailed Fisher’s exact tests. In addition, we calculated average treatment effects (ATE). Thereby, propensity score matching (PSM) based on nearest-neighbor matching considering age, comorbidities, and risk stratification as covariates was applied. The statistical analysis was conducted using Stata 14.2 (StataCorp LLC, TX, USA).

Results

As confirmed by the descriptive tests, the ATE revealed that the intensity and occurrence of urinary frequency (p = 0.034) and proctitis (p = 0.027) significantly decreased for the HRT group, whereas all other acute toxicities did not differ significantly between the HRT and CRT groups. For late toxicities, neither statistical tests nor ATE estimation showed significant differences. Also, no significant difference was found regarding the decrease in prostate specific antigen (PSA) after a median follow-up of 13 months (range 2–28 months), which indicates biochemical freedom from progression.

Conclusion

HRT offers several medical and economic advantages and should therefore be considered as a useful alternative to CRT.