High brachytherapy doses can counteract hypoxia in cervical cancer—a modelling study

Radiobiological and dosimetric comparison of 60Co versus 192Ir high-dose-rate intracavitary-interstitial brachytherapy for cervical cancer

BACKGROUND

High-dose-rate (HDR) intracavitary-interstitial brachytherapy (IC-ISBT) is an effective treatment for bulky, middle, and advanced cervical cancer. In this study, we compared the differences between 60Co and 192Ir HDR IC-ISBT plans in terms of radiobiological and dosimetric parameters, providing a reference for clinical workers in brachytherapy.

METHODS

A total of 30 patients with cervical cancer receiving HDR IC-ISBT were included in this study, and IC-ISBT plans for each individual were designed with both 60Co and 192Ir at a prescribed dose of CTV D90 = 6 Gy while keeping the dose to OARs as low as possible. Physical dose and dose-volume parameters of CTV and OARs were extracted from TPS. The EQD2, EUBED, EUD, TCP, and NTCP were calculated using corresponding formulas. The differences between the 60Co and 192Ir IC-ISBT plans were compared using the paired t-test.

RESULTS

In each patient's 60Co and 192Ir IC-ISBT plan, the average physical dose and EQD2 of 60Co were lower than those of 192Ir, and there were statistically significant differences in D2cc and D1cc for the OARs (p < 0.05); there were statistically significant differences in D0.1 cc for the bladder (p < 0.05) and no significant differences in D0.1 cc for the rectum or intestines (p > 0.05). The EUBED ratio (60Co/192Ir) at the CTV was mostly close to 1 when neither 60Co or 192Ir passed their half-lives or when both passed two half-lives, and the difference between them was not significant; at the OARs, the mean value of 60Co was lower than that of 192Ir. There was no statistical difference between 60Co and 192Ir in the EUD (93.93 versus 93.92 Gy, p > 0.05) and TCP (97.07% versus 97.08%, p > 0.05) of the tumors. The mean NTCP value of 60Co was lower than that of 192Ir.

CONCLUSIONS

Considering the CTV and OARs, the dosimetric parameters of 60Co and 192Ir are comparable. Compared with 192Ir, the use of 60Co for HDR IC-ISBT can ensure a similar tumor control probability while providing better protection to the OARs. In addition, 60Co has obvious economic advantages and can be promoted as a good alternative to 192Ir.

Hypoxic gene expression is a prognostic factor for disease free survival in a cohort of locally advanced squamous cell cancer of the uterine cervix

INTRODUCTION

Tumour hypoxia in locally advanced squamous cervical cancer (LACC) has been shown to be of substantial prognostic importance. The aims of the present study were therefore to investigate if hypoxia could be identified by a newly validated hypoxic gene expression classifier and used as a prognostic factor for disease free survival (DFS).

MATERIAL AND METHODS

Paraffin embedded biopsies were obtained from 190 patients with LACC with squamous cell carcinoma treated 2005-2016 with chemo-radiation and image guided adaptive brachytherapy. Analysis of hypoxia was successful in 183 patients (96%). Hypoxic classification of tumours into 'more' or 'less' hypoxic was based on 15 genes using the same method as in a prospective head and neck cancer trial (NCT02661152). HPV was genotyped using INNO-LiPA. Local tumour invasion was evaluated by the T-score. Primary endpoint was DFS analysed by Kaplan-Meier and Cox regression. Events were death of any cause, persistent disease, or recurrence.

RESULTS

The FIGO₂₀₀₉ stage distribution was IB-IIA 9%, IIB 64%, and III-IVA 27%, and mean T-score was 7.2. Pathological nodes were present in 53%. Median observation time was 5.2 years. Local control rate at 5 years was 96%, and pelvic (loco-regional) control 91%. Overall, 36% of the tumours were classified as 'more' hypoxic. The frequency of 'more' hypoxic tumours increased with local tumour intrusion (30% for T-score 0-9 vs. 55% for T-score ≥10, p = 0.004). Hypoxia was associated with decreased DFS in univariate, HR 1.71 (1.04-2.82), and multivariate analysis, HR 1.75 (1.04-2.92), and the effect was particularly observed among tumours with a T-score ≥10. HPV 16/18 was not associated with improved DFS in neither in univariate nor in multivariate analysis.

CONCLUSION

Hypoxic gene expression is a prominent prognostic factor for DFS in LACC with SCC histology and should be considered for treatment stratification in clinical trials.

Radiobiological comparison between Cobalt-60 and Iridium-192 high-dose-rate brachytherapy sources: Part I-cervical cancer

PURPOSE

This study aimed to compare the biological effective doses (BEDs) to clinical target volume (CTV) and organs at risk (OARs) for cervical cancer patients treated with high-dose-rate (HDR) Iridium-192 (¹⁹² Ir) or Cobalt-60 (⁶⁰ Co) brachytherapy (BT) boost and to determine if the radiobiological differences between the two isotopes are clinically relevant.

METHODS

Considering all radiosensitivity parameters and their reported variations, the BEDs to CTV and OARs during HDR ⁶⁰ Co/¹⁹² Ir BT boost were evaluated at the voxel level. The anatomical differences between individuals were also taken into account by retrospectively considering 25 cervical cancer patients. The intrafraction repair, proliferation, hypoxia-induced radiosensitivity heterogeneity, relative biological effectiveness (RBE), and source aging dose-rate variation were also taken into account. The comparisons in CTV were performed based on equivalent uniform BED (EUBED).

RESULTS

Considering nominal parameters with no RBE correction, the CTV EUBEDs were almost similar with a median ratio of ∼1.00 (p < 0.00001), whereas RBE correction resulted in 3.9%-5.5% (p = 0.005, median = 4.8%) decrease for ⁶⁰ Co with respect to ¹⁹² Ir. For OARs, the median values of D_2cc (in EQD2₃ ) for ⁶⁰ Co were lower than that of ¹⁹² Ir up to 9.2% and 11.3% (p < 0.00001) for nominal parameters and fast repair conditions, respectively. In addition, for a nominal value (reported range) of radiosensitive parameters, the CTV EUBED differences of up to 6% (5%-10%) were assessed for HDR-BT component.

CONCLUSION

The RBE values are the most important cause of discrepancies between the two sources. By comparing BED/EUBEDs to CTV and OARs between ⁶⁰ Co and ¹⁹² Ir sources, this numerical study suggests that a dose escalation to ∼4% is feasible and safe while sparing well the surrounding normal tissues. This 4% dose escalation should be benchmarked with clinical evidences (such as the results of clinical trials) before it can be used in clinical practice.

Stochastic multicellular modeling of x-ray irradiation, DNA damage induction, DNA free-end misrejoining and cell death

The repair or misrepair of DNA double-strand breaks (DSBs) largely determines whether a cell will survive radiation insult or die. A new computational model of multicellular, track structure-based and pO₂-dependent radiation-induced cell death was developed and used to investigate the contribution to cell killing by the mechanism of DNA free-end misrejoining for low-LET radiation. A simulated tumor of 1224 squamous cells was irradiated with 6 MV x-rays using the Monte Carlo toolkit Geant4 with low-energy Geant4-DNA physics and chemistry modules up to a uniform dose of 1 Gy. DNA damage including DSBs were simulated from ionizations, excitations and hydroxyl radical interactions along track segments through cell nuclei, with a higher cellular pO₂ enhancing the conversion of DNA radicals to strand breaks. DNA free-ends produced by complex DSBs (cDSBs) were able to misrejoin and produce exchange-type chromosome aberrations, some of which were asymmetric and lethal. A sensitivity analysis was performed and conditions of full oxia and anoxia were simulated. The linear component of cell killing from misrejoining was consistently small compared to values in the literature for the linear component of cell killing for head and neck squamous cell carcinoma (HNSCC). This indicated that misrejoinings involving DSBs from the same x-ray (including all associated secondary electrons) were rare and that other mechanisms (e.g. unrejoined ends) may be important. Ignoring the contribution by the indirect effect toward DNA damage caused the DSB yield to drop to a third of its original value and the cDSB yield to drop to a tenth of its original value. Track structure-based cell killing was simulated in all 135306 viable cells of a 1 mm³ hypoxic HNSCC tumor for a uniform dose of 1 Gy.

Long-term effectiveness and safety of image-based, transperineal combined intracavitary and interstitial brachytherapy in treatment of locally advanced cervical cancer

PURPOSE

The aim of the study was to evaluate the impact of image-based combined intracavitary-interstitial brachytherapy (IC-ISBT) using a transperineal template in locally advanced cervical cancer treatment.

METHODS AND MATERIALS

A total of 94 patients of cervical cancer stage IIB-IVA underwent image-based transperineal interstitial brachytherapy without tandem (ISBT) or with tandem (IC-ISBT) between June 2008 and June 2018 at our institution. After pelvic chemoradiation, 42 patients underwent ISBT and 52 IC-ISBT. Dosimetric data, clinical response, and toxicity records of these patients were reviewed.

RESULTS

Clinical stage distribution was as follows: IIB: 22.4% (21), IIIA: 10.6% (10), IIIB: 56.4% (53), and IVA: 10.6% (10). Mean high-risk clinical target volume was 75.72 cc, and mean cumulative equivalent of 2 Gy per fraction for high-risk clinical target volume was 81 Gy. The median followup was 35.5 months. Overall 3- and 5-year local control, disease-free survival (DFS), and overall survival (OS) were 84% and 84%, 69.1% and 62.9%, and 80.9% and 71.5%, respectively. Local control (90.4% vs. 76.2%; p = 0.048) and DFS (78.8% vs. 57.1%; p = 0.04) were significantly better in the patients of IC-ISBT arm. IC-ISBT (hazard ratio: 0.763; 95% confidence interval 0.217, 1.38; p = 0.046) and D90 dose >85 Gy (hazard ratio: 0.957; 95% confidence interval 0.927, 1.07; p = 0.037) were predictors of better DFS on univariate analysis. Overall survival was not affected significantly by any of the factors. Grade 3 and 4 late complications were recorded in 3.2% (3) of patients and were similar in both arms (p = 0.86). However, the mean rectum 2 cc dose was significantly lower in the IC-ISBT arm (p = 0.038).

CONCLUSIONS

Combined IC-ISBT is a safe and effective approach to treat ICBT unsuitable cases. It integrates the benefits of ICBT to the adaptability of ISBT around various targets and should be practiced whenever feasible to provide superior outcomes in locally advanced cervical cancer.

Approaches to combat hypoxia in cancer therapy and the potential for in silico models in their evaluation

AIM

The negative impact of tumour hypoxia on cancer treatment outcome has been long-known, yet there has been little success combating it. This paper investigates the potential role of in silico modelling to help test emerging hypoxia-targeting treatments in cancer therapy.

METHODS

A Medline search was undertaken on the current landscape of in silico models that simulate cancer therapy and evaluate their ability to test hypoxia-targeting treatments. Techniques and treatments to combat tumour hypoxia and their current challenges are also presented.

RESULTS

Hypoxia-targeting treatments include tumour reoxygenation, hypoxic cell radiosensitization with nitroimidazoles, hypoxia-activated prodrugs and molecular targeting. Their main challenges are toxicity and not achieving adequate delivery to hypoxic regions of the tumour. There is promising research toward combining two or more of these techniques. Different types of in silico therapy models have been developed ranging from temporal to spatial and from stochastic to deterministic models. Numerous models have compared the effectiveness of different radiotherapy fractionation schedules for controlling hypoxic tumours. Similarly, models could help identify and optimize new treatments for overcoming hypoxia that utilize novel hypoxia-targeting technology.

CONCLUSION

Current therapy models should attempt to incorporate more sophisticated modelling of tumour angiogenesis/vasculature and vessel perfusion in order to become more useful for testing hypoxia-targeting treatments, which typically rely upon the tumour vasculature for delivery of additional oxygen, (pro)drugs and nanoparticles.

Radiobiological dose calculation parameters for cervix cancer brachytherapy: A systematic review

The GEC-ESTRO recommendation in cervical cancer treatment planning, including external beam radiotherapy and brachytherapy boosts, is to use radiobiological dose calculations. Such calculations utilize the linear-quadratic model to estimate the effect of multiple cellular response factors and dose delivery parameters. The radiobiological parameters utilized in these calculations are literature values estimated based on clinical and experimental results. However, the impact of the uncertainties associated with these parameters is often not fully appreciated. This review includes a summary of the radiobiological dose calculation (for both high-dose-rate and pulsed-dose-rate brachytherapy boost treatments) for cervical cancer and a compilation of the reported values of the associated parameters. As discrepancies exist between conventionally recommended and published values, equivalencies between current brachytherapy boosts may be imprecise and could create underappreciated uncertainties in the radiobiological dose calculations. This review highlights these uncertainties by calculating the radiobiological dose delivered by the brachytherapy boost when assuming different radiobiological parameter values (within the range reported by previous research). Furthermore, conventional treatment planning does not consider the effects of proliferation of the tumor over the treatment time, which can significantly decrease its radiobiological dose and can introduce an additional variance of over 7 Gy₁₀. Further investigation of uncertainties in parameter values and modifications of current dose models could improve the accuracy of radiobiological dose calculation.

Localized prostate cancer with pelvic arteriovenous malformation treated with low-dose-rate brachytherapy after transcatheter embolization: Two case reports

Background

We describe two patients who underwent low‐dose‐rate prostate brachytherapy after embolization for pelvic arteriovenous malformation.

Case presentation

Case 1: A 76‐year‐old man was referred for definitive treatment of intermediate‐risk prostate cancer (prostate‐specific antigen 8.667 ng/mL, cT2aN0M0, Gleason score 3 + 4 = 7). We planned low‐dose‐rate brachytherapy. However, magnetic resonance imaging and computed tomography demonstrated a large pelvic arteriovenous malformation. We performed embolization of the arteriovenous malformation before initiating treatment to lower the risk of rupture of the arteriovenous malformation during low‐dose‐rate brachytherapy. Case 2: A 69‐year‐old man was referred for the definitive treatment of high‐risk prostate cancer (prostate‐specific antigen 5.81 ng/mL, cT2aN0M0, Gleason score 4 + 4 = 8) with a pelvic arteriovenous malformation. Similar to Case 1, we performed embolization of the arteriovenous malformation before initiating treatment. In both cases, low‐dose‐rate brachytherapy could be performed without complications.

Conclusions

Low‐dose‐rate brachytherapy after transcatheter embolization of pelvic arteriovenous malformations can safely and effectively treat localized prostate cancer with pelvic arteriovenous malformations.

Accounting for Two Forms of Hypoxia for Predicting Tumour Control Probability in Radiotherapy: An In Silico Study

The progress in functional imaging and dose delivery has opened the possibility of targeting tumour hypoxia with radiotherapy. Advanced approaches apply quantitative information on tumour oxygenation retrieved from imaging in dose prescription. These do not, however, take into account the potential difference in radiosensitivity of chronically and acutely hypoxic cells. It was the aim of this study to evaluate the implications of assuming the same or different sensitivities for the hypoxic cells. An in silico 3D-model of a hypoxic tumour with heterogeneous oxygenation was used to model the probabilities of tumour control with different radiotherapy regimens. The results show that by taking into account the potential lower radioresistance of chronically hypoxic cells deprived of oxygen and nutrients, the total dose required to achieve a certain level of control is substantially reduced for a given fractionation scheme in comparison to the case when chronically and acutely hypoxic cells are assumed to have similar features. The results also suggest that the presence of chronic hypoxia could explain the success of radiotherapy for some hypoxic tumours. Given the implications for clinical dose escalation trials, further exploration of the influence of the different forms of hypoxia on treatment outcome is therefore warranted.

Prognostic implication of simultaneous anemia and lymphopenia during concurrent chemoradiotherapy in cervical squamous cell carcinoma

Radioresistance often leads to poor survival in concurrent chemoradiotherapy-treated cervical squamous cell carcinoma, and reliable biomarkers can improve prognosis. We compared the prognostic potential of hemoglobin, absolute neutrophil count, and absolute lymphocyte count with that of squamous cell carcinoma antigen in concurrent chemoradiotherapy-treated squamous cell carcinoma. We analyzed 152 patients with concurrent chemoradiotherapy and high-dose-rate intracavitary brachytherapy-treated cervical squamous cell carcinoma. Hemoglobin, absolute neutrophil count, absolute lymphocyte count, and squamous cell carcinoma antigen were quantitated and correlated with survival, using Cox regression, receiver operating characteristic curve analysis, and Kaplan-Meier plots. Both hemoglobin and absolute lymphocyte count in the second week of concurrent chemoradiotherapy (Hb2 and ALC2) and squamous cell carcinoma antigen in the third week of concurrent chemoradiotherapy (mid-squamous cell carcinoma antigen) correlated significantly with disease-specific survival and progression-free survival. The ratio of high-dose-rate intracavitary brachytherapy dose to total dose (high-dose-rate intracavitary brachytherapy ratio) correlated significantly with progression-free survival. Patients with both low Hb2 (≤11 g/dL) and ALC2 (≤639 cells/µL) showed a lower 5-year disease-specific survival rate than those with high Hb2 and/or ALC2, regardless of mid-squamous cell carcinoma antigen (mid-squamous cell carcinoma antigen: ≤4.7 ng/mL; 5-year disease-specific survival rate: 85.5% vs 94.6%, p = 0.0096, and mid-squamous cell carcinoma antigen: >4.7 ng/mL; 5-year disease-specific survival rate: 43.8% vs 66.7%, p = 0.192). When both Hb2 and ALC2 were low, the low high-dose-rate intracavitary brachytherapy ratio (≤0.43) subgroup displayed significantly lower 5-year disease-specific survival rate compared to the subgroup high high-dose-rate intracavitary brachytherapy ratio (>0.43) (62.5% vs 88.2%, p = 0.0067). Patients with both anemia and lymphopenia during concurrent chemoradiotherapy showed poor survival, independent of mid-squamous cell carcinoma antigen, and escalating high-dose-rate intracavitary brachytherapy ratio might improve survival.