Understanding the Benefit of Magnetic Resonance-guided Adaptive Radiotherapy in Rectal Cancer Patients: a Single-centre Study

AIMS

Neoadjuvant chemoradiotherapy followed by surgery is the mainstay of treatment for patients with rectal cancer. Standard clinical target volume (CTV) to planning target volume (PTV) margins of 10 mm are used to accommodate inter- and intrafraction motion of target. Treating on magnetic resonance-integrated linear accelerators (MR-linacs) allows for online manual recontouring and adaptation (MRgART) enabling the reduction of PTV margins. The aim of this study was to investigate motion of the primary CTV (CTVA; gross tumour volume and macroscopic nodes with 10 mm expansion to cover microscopic disease) in order to develop a simultaneous integrated boost protocol for use on MR-linacs.

MATERIALS AND METHODS

Patients suitable for neoadjuvant chemoradiotherapy were recruited for treatment on MR-linac using a two-phase technique; only the five phase 1 fractions on MR-linac were used for analysis. Intrafraction motion of CTVA was measured between pre-treatment and post-treatment MRI scans. In MRgART, isotropically expanded pre-treatment PTV margins from 1 to 10 mm were rigidly propagated to post-treatment MRI to determine overlap with 95% of CTVA. The PTV margin was considered acceptable if overlap was >95% in 90% of fractions. To understand the benefit of MRgART, the same methodology was repeated using a reference computed tomography planning scan for pre-treatment imaging.

RESULTS

In total, nine patients were recruited between January 2018 and December 2020 with T3a-T4, N0-N2, M0 disease. Forty-five fractions were analysed in total. The median motion across all planes was 0 mm, demonstrating minimal intrafraction motion. A PTV margin of 3 and 5mm was found to be acceptable in 96 and 98% of fractions, respectively. When comparing to the computed tomography reference scan, the analysis found that PTV margins to 5 and 10 mm only acceptably covered 51 and 76% of fractions, respectively.

CONCLUSION

PTV margins can be reduced to 3-5 mm in MRgART for rectal cancer treatment on MR-linac within an simultaneous integrated boost protocol.

Circulating tumour DNA is a potential biomarker for disease progression and response to targeted therapy in advanced thyroid cancer

BACKGROUND

Conventional biomarkers in thyroid cancer are not disease specific and fluctuate in advanced disease, making interpretation difficult. Circulating tumour DNA (ctDNA) has been shown to be a useful biomarker in other solid tumours. This is a multimutational study of ctDNA over multiple timepoints, designed to test the hypothesis that ctDNA is a potential biomarker in patients with advanced thyroid cancer.

METHODS

Mutational analysis of archival tumour tissue was performed using NGS with a targeted gene panel. Custom TaqMan assays were designed for plasma ctDNA testing using digital droplet polymerase chain reaction. Concentrations of detected ctDNA were correlated with the conventional biomarker concentration and axial imaging status defined by the Response Evaluation Criteria in Solid Tumours criteria.

RESULTS

Tumour tissue from 51 patients was obtained, with the following histologies: 32 differentiated (differentiated thyroid cancer [DTC]), 15 medullary (medullary thyroid cancer [MTC]), three poorly differentiated and one anaplastic. NGS analysis detected variants in 42 (82%) of cases. Plasma was assayed for these patients in 190 samples, and ctDNA was detected in 67% of patients. Earlier detection of disease progression was noted in three patients with MTC. In two cases (PTC and ATC), where conventional biomarkers were not detectable, ctDNA was detected before disease progression. Changes in ctDNA concentration occurred earlier than conventional markers in response to disease progression in multiple patients with DTC receiving targeted therapies.

CONCLUSION

The majority of patients with advanced thyroid cancer had detectable ctDNA. ctDNA measurement may offer superiority over conventional markers in several scenarios: earlier detection of progression in MTC; as an alternative biomarker when conventional markers are not available; more rapid assessment of the disease status in response to targeted therapies, thereby potentially allowing prompter discontinuation of futile therapies. These early results support the hypothesis that ctDNA may be a clinically useful biomarker in thyroid cancer.

Dysphagia-optimised Intensity-modulated Radiotherapy Techniques in Pharyngeal Cancers: Is Anyone Going to Swallow it?

Dysphagia after primary chemoradiotherapy or radiation alone in pharyngeal cancers can have a devastating impact on a patient's physical, social and emotional state. Establishing and validating efficient dysphagia-optimised radiotherapy techniques is, therefore, of paramount importance in an era where health-related quality of life measures are increasingly influential determinants of curative management strategies, particularly as the incidence of good prognosis, human papillomavirus-driven pharyngeal cancer in younger patients continues to rise. The preferential sparing achievable with intensity-modulated radiotherapy (IMRT) of key swallowing structures implicated in post-radiation dysfunction, such as the pharyngeal constrictor muscles (PCM), has generated significant research into toxicity-mitigating strategies. The lack of randomised evidence, however, means that there remains uncertainty about the true clinical benefits of the dosimetric gains offered by technological advances in radiotherapy. As a result, we feel that IMRT techniques that spare PCM cannot be incorporated into routine practice. In this review, we discuss the swallowing structures responsible for functional impairment, analyse the studies that have explored the dose-response relationship between these critical structures and late dysphagia, and consider the merits of reported dysphagia-optimised IMRT (Do-IMRT) approaches, thus far. Finally, we discuss the dysphagia/aspiration-related structures (DARS) study (ISRCTN 25458988), which is the first phase III randomised controlled trial designed to investigate the impact of swallow-sparing strategies on improving long-term function. To maximise patient benefits, improvements in radiation delivery will need to integrate with novel treatment paradigms and comprehensive rehabilitation strategies to eventually provide a patient-centric, personalised treatment plan.

Evaluation of a multi-atlas CT synthesis approach for MRI-only radiotherapy treatment planning

BACKGROUND AND PURPOSE

Computed tomography (CT) imaging is the current gold standard for radiotherapy treatment planning (RTP). The establishment of a magnetic resonance imaging (MRI) only RTP workflow requires the generation of a synthetic CT (sCT) for dose calculation. This study evaluates the feasibility of using a multi-atlas sCT synthesis approach (sCTa) for head and neck and prostate patients.

MATERIAL AND METHODS

The multi-atlas method was based on pairs of non-rigidly aligned MR and CT images. The sCTa was obtained by registering the MRI atlases to the patient's MRI and by fusing the mapped atlases according to morphological similarity to the patient. For comparison, a bulk density assignment approach (sCTbda) was also evaluated. The sCTbda was obtained by assigning density values to MRI tissue classes (air, bone and soft-tissue). After evaluating the synthesis accuracy of the sCTs (mean absolute error), sCT-based delineations were geometrically compared to the CT-based delineations. Clinical plans were re-calculated on both sCTs and a dose-volume histogram and a gamma analysis was performed using the CT dose as ground truth.

RESULTS

Results showed that both sCTs were suitable to perform clinical dose calculations with mean dose differences less than 1% for both the planning target volume and the organs at risk. However, only the sCTa provided an accurate and automatic delineation of bone.

CONCLUSIONS

Combining MR delineations with our multi-atlas CT synthesis method could enable MRI-only treatment planning and thus improve the dosimetric and geometric accuracy of the treatment, and reduce the number of imaging procedures.

Quantitative estimates of the effects of concomitant chemotherapy on acute dysphagia in patients receiving radical treatment for head and neck cancer

e22134

Purpose: To generate quantitative parameters describing the effect of concomitant chemotherapy on incidence of grade 3 dysphagia (CTCAE v3.0, assisted feeding) using dose response curves in patients receiving radical treatment for head and neck cancer. Methods: Patients treated at a single centre in prospective phase I and II trials of concomitant chemo-IMRT (CRT) (n=85) and the phase III trial of IMRT vs. conventional radiotherapy (PARSPORT) (n=82) formed the basis of this non-randomized comparison. Patients in the PARSPORT trial received radiation alone (RT). Radiation dose for all patients was radiobiologically equivalent to at least 70Gy in 35 fractions. Concomitant chemotherapy was cisplatin (100 mg/m2) on days 1 and 29. G3 dysphagia was recorded prospectively. Dose volume histograms (DVH) were generated for the pharyngeal mucosa. The mean dose (converted to equivalent dose in 2Gy/fraction, MD2) was used as a univariate descriptor of the DVH, for the generation of the dose response curves. A logistic function of the form p=1/[1+(MD50/D)k] was fitted where, p is the probability of the incidence of toxicity, D is the mean dose, MD50 is the mean dose at which 50% of patients experience toxicity and k describes the increase in incidence with increasing dose. The dose response curves were fitted using non-linear logistic regression. Results: The mean MD2 to the pharyngeal mucosa were 56Gy and 55.8Gy respectively, in the CRT and RT groups. There was a statistically significant difference of 25% (95% CI: 10–38, p=0.002) in the incidence of G3 dysphagia between the CRT (68%) and RT (43%) groups. Fitting dose response curves to the clinical data yielded parameter values (95% CIs) of MD50=46 Gy (42–49), k=4.8 (2.3–7.2) for the CRT group and MD50= 58 Gy (55–61), k=3 (1.6-.45) for RT group. Dose response gradients for CRT and RT showed approximately 1.95% and 1.3% increase (respectively) in probability of G3 dysphagia resulting from an increase in mean dose of 1Gy between doses of 30Gy to 70Gy. Conclusions: Addition of concomitant chemotherapy increases the incidence of G3 dysphagia by 0.65% for every 1 Gy increase in radiation dose. The observed MD50 for G3 dysphagia is lower for RT alone (46 Gy vs. 58 Gy).

No significant financial relationships to disclose.

Pneumococcal hemolytic uremic syndrome

We report Hemolytic Uremic Syndrome (HUS) induced by Streptococcus pneumoniae in a 20 month-old girl. She responded well to hemodialysis.

Plasmapheresis: an adjunct therapy in severe progressive neuropsychiatric lupus

OBJECTIVE

We report our experience with use of plasmapheresis (PP) as an adjunct therapy in severe progressive neuropsychiatric systemic lupus erythematosus (NPSLE).

METHOD

Three patients of NPSLE (including 2 with status epilepticus) who were progressively worsening on steroids or combination of pulse cyclophosphamide (CPM) and steroids were treated with PP followed by synchronized CPM. Pre and post treatment SLE Disease Activity Index (SLEDAI) and laboratory tests were carried out.

RESULTS

Significant clinical improvement with decrease in SLEDAI occurred immediately following PP. Mean SLEDAI before and after PP were 33 and 11. Mean erythrocyte sedimentation rate decreased from 121 to 31. Rebound flare of disease activity noted in two patients between 7th-10th day requiring additional immunosuppressants or steroids.

CONCLUSIONS

PP used as an adjunct therapy in severe, progressive NPSLE is well tolerated and can turn the patient around. PP should be followed by synchronized pulse CPM to prevent disease flare.

Labeling of MR brain images using Boolean neural network

Presents a knowledge-based approach for labeling two-dimensional (2-D) magnetic resonance (MR) brain images using the Boolean neural network (BNN), which has binary inputs and outputs, integer weights, fast learning and classification, and guaranteed convergence. The approach consists of two components: a BNN clustering algorithm and a constraint satisfying Boolean neural network (CSBNN) labeling procedure. The BNN clustering algorithm is developed to initially segment an image into a number of regions. Then the segmented regions are labeled with the CSBNN, which is a modified version of BNN. The CSBNN uses a knowledge base that contains information on image-feature space and tissue models as constraints. The method is tested using sets of MR brain images. The regions of the different brain tissues are satisfactorily segmented and labeled. A comparison with the Hopfield neural network and the traditional simulated annealing method for image labeling is provided. The comparison results show that the CSBNN approach offers a fast, feasible, and reliable alternative to the existing techniques for medical image labeling.

Weak carcinogenic effect of masheri, a pyrolysed tobacco product, in mouse skin tumor models

Two commonly used varieties of masheri, pyrolysed tobacco products, were tested for their skin carcinogenicity in Swiss mice and the more sensitive strain of Swiss bare mice. In Swiss mice, painting of brown and black varieties of masheri extract did not show any tumorgenic effect; however, a marginal synergistic effect of 7,12-dimethylbenz[a]anthracene (DMBA) and black masheri extract was observed when DMBA was used as an initiator. In Swiss bare mice, black masheri extract induced tumors in 20%-35% animals at both the doses tested. In an initiation/promotion protocol with DMBA as an initiator, induction of tumors in 50%-52% Swiss bare mice and a slight synergistic effect of black masheri extract were observed with a low dose of DMBA, suggesting a synergistic effect.

Formation and persistence of isoniazid-DNA adducts in mouse tissues

Further confirmation is provided to support the identity of the product formed by the in vitro reaction of isoniazid (INH) with cytosine as 4-deamino-4-isoniazidocytosine (INH-cytosine). Use of INH-treated mice, in which the tissue DNA is prelabelled by the neonatal administration of [3H]-deoxycytidine, has revealed the presence of two other DNA products in addition to INH-cytosine. Tissue differences in the persistence of these three DNA products suggest the presence of repair reactions for certain adducts. These processes and the effects of hepatotoxicity lead to a selective retention of adducts in the DNA of lung which is the target tissue for INH-carcinogenicity in mice. INH-modified DNA templates are weakly promutagenic during in vitro DNA synthesis. The implications of these observations for the role of INH as an initiating agent and for the species differences in its carcinogenicity are discussed.

Antitumor activity of new nitrosoureas on Yoshida sarcoma ascites cells implanted into the colon wall of rats

The chemotherapeutic activity of 12 newly synthesized nitrosoureas was compared in tests using Yoshida sarcoma ascites cells implanted into the wall of the descending colon in Sprague-Dawley rats. Cyclophosphamide and the nitrosoureas BCNU, MeCCNU, and chlorozotocin served as positive controls. Among the nitrosoureas tested, 1-(2-hydroxyethyl)-3-(2-chloroethyl)-3-nitrosourea (hydroxyethyl-CNU), chlorozotocin, 1-(2-chloroethyl)-1-nitroso-3-(4-morpholino) urea, 1-(2-chloroethyl)-1-nitroso-3-(1-piperidino) urea, 4-[1-(2-chloroethyl)-1-nitroso-3-[4-(2,6-dimethylmorpholino)] urea, and 1-(2-chloroethyl)-1-nitroso-3-(3,4-methylenedioxybenzyl) urea were found to be the most active compounds in this tumor model. Based on the present results, morpholino-CNU is considered the most promising compound among these newly synthesized BCNU analogues.

Antitumor activity of 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU) and 1-(2-chloroethyl)-3-(4-methyl-cyclohexyl)-1-nitrosourea (MeCCNU) on Yoshida sarcoma ascites cells implanted into the colon wall of rats

Three thousand Yoshida sarcoma cells were inoculated into the wall of the descending colon of each of 120 male Sprague-Dawley rats. On day 8 after the tumor implantation, the animals were at random divided into four groups of 30 rats each. The effect of cyclophosphamide (70 mg/kg), BCNU (25 mg/kg), and methyl-CCNU (45 mg/kg) after single i.p. application was investigated. The Yoshida sarcoma transplanted into the colon is sensitive to all three chemotherapeutic drugs. At the doses given cyclophosphamide showed the best results. The two nitrosoureas had a comparable antitumor activity but methyl-CCNU showed a more distinct toxic effect. The introduction of this model for testing new cytostatics in animal experiments is discussed.