Radiotherapy planning in a prostate cancer phantom model with intraprostatic dominant lesions using stereotactic body radiotherapy with volumetric modulated arcs and a simultaneous integrated boost

Aim

In the treatment of prostate cancer with radiation therapy, the addition of a simultaneous integrated boost (SIB) to the dominant intraprostatic lesions (DIL) may improve local control. In this study, we aimed to determine the optimal radiation strategy in a phantom model of prostate cancer using volumetric modulated arc therapy for stereotactic body radiotherapy (SBRT-VMAT) with a SIB of 1-4 DILs.

Methods

We designed and printed a three-dimensional anthropomorphic phantom pelvis to simulate individual patient structures, including the prostate gland. A total of 36.25 Gy (SBRT) was delivered to the whole prostate. The DILs were irradiated with four different doses (40, 45, 47.5, and 50 Gy) to assess the influence of different SIB doses on dose distribution. The doses were calculated, verified, and measured using both transit and non-transit dosimetry for patient-specific quality assurance using a phantom model.

Results

The dose coverage met protocol requirements for all targets. However, the dose was close to violating risk constraints to the rectum when four DILs were treated simultaneously or when the DILs were located in the posterior segments of the prostate. All verification plans passed the assumed tolerance criteria.

Conclusions

Moderate dose escalation up to 45 Gy seems appropriate in cases with DILs located in posterior prostate segments or if there are three or more DILs located in other segments.

Accuracy of the doses computed by the Eclipse treatment planning system near and inside metal elements

Metal artefacts degrade clinical image quality which decreases the confidence of using computed tomography (CT) for the delineation of key structures for treatment planning and leads to dose errors in affected areas. In this work, we investigated accuracy of doses computed by the Eclipse treatment planning system near and inside metallic elements for two different computation algorithms. An impact of CT metal artefact reduction methods on the resulting calculated doses has also been assessed. A water phantom including Gafchromic film and metal inserts was irradiated (max dose 5 Gy) using a 6 MV photon beam. Three materials were tested: titanium, alloy 600, and tungsten. The phantom CT images were obtained with the pseudo-monoenergetic reconstruction (PMR) and the iterative metal artefact reduction (iMAR). Image sets were used for dose calculation using an Eclipse treatment planning station (TPS). Monte Carlo (MC) simulations were used to predict the true dose distribution in the phantom allowing for comparison with doses measured by film and calculated by TPS. Measured and simulated percentage depth doses (PDDs) were not statistically different (p > 0.618). Regional differences were observed at edges of metallic objects (max 8% difference). However, PDDs simulated with and without film were statistically different (p < 0.002). PDDs calculated by the Acuros XB algorithm based on the dose-to-medium approach best matched the MC reference regardless of the CT reconstruction methods and inserts used (p > 0.078). PDDs obtained using other algorithms significantly differ from the MC values (p < 0.011). The Acuros XB algorithm with a dose-to-medium approach provides reliable dose calculation in all metal regions when using the Varian system. The inability of the AAA algorithm to model backscatter dose significantly limits its clinical application in the presence of metal. No significant impact on the dose calculation was found for a range of metal artefact reduction strategies.

Currently used in clinical practice beam rate changes have no significant effect on the reduction of clonogenic capacity of PNT1A cells in vitro

Background

Due to the lack of selectivity of ionizing radiation between normal and cancer cells, it is important to improve the existing radiation patterns. Lowering the risk of cancer recurrence and comfort during treatment are priorities in radiotherapy.

Materials and methods

In the experiment we used dose verification to determine the irradiation time calculated by a treatment planning system for 6XFFF and 10XFFF beams. Cells cultured under standard conditions were irradiated with a dose of 2 Gy at different beam rates 400 MU/min, 600 MU/min, 800 MU/min, 1000 MU/min, 1400 MU/min, 1600 MU/min and 2400 MU/min using 6XFFF, 10XFFF and 6XFF beams.

Results

The experiment was aimed at comparing the biological response of normal prostate cells after clinically applied radiation patterns. No statistically significant differences in the cellular response were observed. The wide range of beam rates as well as the beam profiles did not significantly affect cell proliferation.

Conclusions

High beam rates, without significantly affecting the clonogenic capacity of cells, have an impact on the quality of patient’s treatment. With the increasing beam rate the irradiation time is shortened, which has an important impact on patients’ health. This experiment can have a practical significance.

Prevalence of cardiac amyloidosis in patients with unexplained left ventricle hypertrophy

Background

Amyloid cardiomyopathy (CA) it is more frequently diagnosed due to rapidly developing imaging modalities. Misfolding of transthyretin (TTR) is the source of two distinct forms of amyloidosis (ATTR): acquired wild-type (ATTRwt) and hereditary (ATTRm). Types of TTR gene variants display genetic and ethnic variability. The aim of this prospective study was to assess the prevalence and types of pathogenic genetic variants associated with ATTRm amyloidosis in patients with unexplained left ventricle (LV) hypertrophy.

Methods

We evaluated prospectively 101 consecutive patients (37 (37%) females, age: 69.7±13.6 y.o.) in years 2016–2021. Analysis included clinical data, free light chain blood immunoglobulins and urine immunofixation, transthoracic echocardiography (TTE), single-photon emission computed tomography (SPECT) with 3,3-disphono-1,2-propanodicarboxylic acid (DPD), and in selected cases cardiac or soft tissue biopsy. Patients with DPD cardiac uptake in SPECT or positive histopathology or family history of ATTR were subjected to genetic testing by an amplicon-based next-generation TTR sequencing approach.

Results

Enrolled patients presented with marked LV hypertrophy with maximum wall thickness of 18.9±4 mm. Based on performed tests 34 patients (33.7%) were diagnosed with amyloidosis, including 17 cases of light-chain amyloidosis (AL), 16 of ATTR, and 1 case of other type of amyloidosis. Overall, patients with CA presented with mean 2.6±0.9 NYHA class. In TTE there was LV maximum wall thickness of 19.5±4 mm and LV mass value index value of 182±48 g/m2, decreased global longitudinal strain value (GLS, −14.1±5%) and advanced diastolic dysfunction (EA 2.2±1.1, E/E' 22±9). Overall, there were 8 cases of ATTRwt and eight patients were diagnosed ATTRm. There were detected following types of TTR variants - c.302C&gt;T p.(Ala101Val) in a single male patient, c.325G&gt;A p.(Glu109Lys) in a single male patient and c.157T&gt;C p.(Phe53Leu) in six patients. Overall, 10 patients with ATTR presented with polyneuropathy, additionally six had diagnosed carpal tunnel syndrome. All patients with ATTRm had positive family history for CA.

Conclusions

In patients with unexpected LV hypertrophy evaluated in a cardiology referral center a high number of patients may suffer from underlying CA. Types of detected TTR gene variants associated with CA included most often Phe53Leu, and rare variants Ala101Val, Glu109Lys.

Funding Acknowledgement

Type of funding sources: None.

Scintigraphic and echocardiographic evaluation of patients with cardiac transthyretin amyloidosis and first-degree relatives

Funding Acknowledgements

Type of funding sources: Other. Main funding source(s): Pfizer Research Grant (ID#57165999)

Background

Misfolding of transthyretin (TTR) is the source of two distinct forms of amyloidosis (ATTR): acquired or wild-type (ATTRwt) and hereditary (ATTRm), which is transmitted in an autosomal dominant inheritance with a variable penetrance.  Types of transthyretin (TTR) gene mutations display genetic and ethnic variability.

Purpose

The aim of this prospective study was to assess the TTR gene variants, echocardiographic parameters and regional left ventricle 99mTc-DPD uptake among patients with ATTR and first-degree relatives.

Methods

We present data based on evaluation of first 25 patients (13 (52%) females), including 10 (40%) index patients with ATTR (age 66.4 ± 13 years) and 15 (60%) first-degree relatives who were studied between June 2020 and February 2021. Analysis included clinical data, free light chain blood immunoglobulins and urine immunofixation, transthoracic echocardiography (TTE) with global longitudinal strain (GLS) analysis, single-photon emission computed tomography (SPECT) with 3,3-disphono-1,2-propanodicarboxylic acid (DPD), genetic testing by an amplicon-based next-generation TTR sequencing approach, and in selected cases cardiac or soft tissue biopsy.

Results

Overall, 6 index patients were diagnosed with ATTRm and 4 with ATTRwt presenting mixed, cardiac or neuropathic phenotype. There were detected following types of TTR variants - Phe53Leu, Ala101Val, Glu112Lys, Glu109Lys. Nine out of 10 index patients were diagnosed with amyloid cardiomyopathy (CA) with grade 2-3 tracer uptake in SPECT and symptomatic heart failure (NYHA 2.2 ± 1.1; NT-proBNP value 2224 ± 2799 pg/ml). In both ATTRm and ATTRwt there were patients presenting with either focal or diffuse tracer pattern evaluated by SPECT technique. In TTE there was marked left ventricle (LV) hypertrophy with maximum wall thickness of 22 ± 5 mm and LV mass value index value of 382 ± 111 g/m2. All patients with CA had abnormal global longitudinal strain (GLS, -14.5 ± 5%) and diastolic dysfunction (EA 1.56 ± 0.76, E/E’ 16 ± 11). None of relatives expressed tracer uptake in scintigraphy. Overall, 5 first-degree relatives were diagnosed with Phe53Leu variant, among them two patients presented with decreased GLS value.

Conclusions

Patients with ATTR presented in TTE with LV hypertrophy, decreased GLS value, diastolic dysfunction and grade 2-3 in scintigraphy with either focal or diffuse tracer uptake in SPECT technique. None of first-degree relatives expressed increased tracer uptake in scintigraphy. However, some of relatives who were diagnosed with pathogenic TTR variant presented with decreased GLS value.

Comparison of three different phantoms used for Winston-Lutz test with Artiscan software

Background

One of the most important test in every quality assurances process of medical linear accelerators is the Winston-Lutz test, allowing an evaluation of the treatment isocentre in the light of uncertainty of the position of the collimator, the gantry and the couch.

Aim

The purpose of this work was analysis of the results of the Winston-Lutz test performed with three different phantoms for two different accelerators.

Materials and methods

Measurements were performed on two Varian machines: TrueBeam equipped with aS1200 EPID and TrueBeam equipped with aS1000 EPID. During the study three different phantoms dedicated for verification of the radiation isocentre were used: PTW Isoball, AQUILAB Isocentre Phantom and Varian Isocentre Cube. Analysis of the DICOM images was performed in Artiscan software.

Results

For TrueBeam with as1200 EPID, gantry MV isocentre was about 0.18 mm larger for Varian Isocentre Cube than for two other phantoms used in this study. The largest variability of this parameter was observed for the couch. The results differed to 1.16 mm. For TrueBeam with as1000 EPID, results for collimator isocentre with PTW Isoball phantom were about 0.10 mm larger than for two other phantoms. For the gantry, results obtained with Varian Isocentre Cube were 0.21 mm larger.

Conclusion

The obtained results for all three phantoms are within the accepted tolerance range. The largest differences were observed for treatment couch, which may be related to the phantom mobility during couch movement.