Dose-volume Histogram Analysis Research Articles

Dose prediction for cervical cancer in radiotherapy based on the beam channel generative adversarial network

BackgroundExisting deep learning methods, such as generative adversarial network (GAN) technology, face challenges when dealing with mixed datasets, which involve a combination of Intensity Modulated Radiotherapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT). This issue significantly complicates the application of dose prediction in the field of radiotherapy. In this study, we propose a novel approach called beam channel GAN (Bc-GAN) to address the task of radiation dose prediction for mixed datasets. Bc-GAN introduces a dose prediction calculation method that requires less precision. By defining an approximate range for dose prediction, Bc-GAN limits the physical range of GAN prediction, resulting in more reasonable dose distribution predictions. MethodsWe adopt a beam angle weighting method to determine the beam angle in the dose calculation. The dose of the beam with the highest weight is calculated using medical images and is then inputted into the artificial intelligence dose prediction model as the input channel. Additionally, we collect data from a total of 346 patients with Cervical Cancer (CC) for dataset. After cleaning the data, we exclude 51 cases with incomplete organ delineation, leaving us with 295 cases (IMRT: VMAT = 137:158) randomly divided into three sets: the training set, the validation set, and the test set, with proportions of 205:60:30, respectively. The assessment of model predictions was conducted via an analysis of dose distributions on the tomographic plane, dose volume histogram (DVH), and dosimetric parameters within the target zones and organs at risk (OAR). ResultsAfter DVH analysis, minimal discrepancy was found between predicted and actual dose distributions in PTV and OAR. The predicted distribution aligned with clinical standards. Dosimetric parameters for PTV were generally lower in the predicted model, except for homogeneity index (HI) (0.238 ± 0.024, P = 0.017) and Dmax (53.599 ± 0.710 Gy, P = 1.8e-05). The prediction model varied in estimating doses for six organs. Specifically, small intestine showed higher V20 (67.92 ± 51.64 %, P = 0.019) and V30 (57.171 ± 1.213 %, P = 0.024) than manual planning. A similar trend was seen in colon's V30 (37.13 ± 61.14 %, P = 0.016). However, predicted bladder V30 (87.51 ± 41.44 %, P = 2.03e-16) was lower, indicating significant dosimetric differences. ConclusionOverall, this study presents an innovative prediction method for CC in radiotherapy using the Bc-GAN model, addressing the challenges posed by different radiotherapy techniques. The proposed approach allows IMRT and VMAT in radiotherapy to be used as training sets, enabling the potential for large-scale engineering and commercialization applications of artificial intelligence (AI). The Bc-GAN-based prediction method for CC in radiotherapy not only reduces the amount of data needed for the training set but also expedites the model generation process. This approach can be applied to guide the development of clinical radiation therapy plans. Furthermore, future studies should consider extending the dose prediction method to encompass other types of tumors.

Clinical impact of DVH uncertainties

Dose-volume histograms (DVH), along with dose and volume metrics, are central to radiotherapy planning. As such, errors have the potential to significantly impact the selection of appropriate treatment plans. Dose distributions that pass tests in one TPS may fail the same tests when transferred to another, even if using identical structures and dose grid information. This work shows the design and implementation of methods for assessing the accuracy of dose and volume computations performed by treatment planning systems (TPS), and other analytical tools. We demonstrate examples where differences in calculations between systems can change the assessment of a plan’s clinical acceptability. Our work also provides a more detailed DVH analysis of single targets than earlier published studies. This is relevant for SRS plans and small structure dose assessments. Very small structures are a particular problem because of their coarse digital representation, and the impact of this is thoroughly examined.Reference DVH curves were derived mathematically, based on Gaussian dose distributions centered on spherical structures. The structures and dose distributions were generated synthetically, and imported into RayStation, MasterPlan, and ProKnow. Corresponding DVHs were analytically derived and taken as ground truth references, for comparison with the commercial DVH calculations. Two commonly used dose metrics PCI and MGI were used to determine the limit of calculation accuracy for small structures. In addition, to measure the DVH differences between a larger range of commercial DVH calculators, the D95 metric from a set of real clinical plans was compared across both the 3 DVH calculators under test, and across a further six TPSs from other hospitals.We show that even slight deviations between the results of DVH calculators can lead to plan check failures, and we illustrate this with the commonly used D95 planning metric. We present clinical data across eight planning systems that highlight instances where plan checks would pass in one software and fail in another due to DVH calculation differences. For the smallest volumes tested, errors of up to 20% were observed in the DVHs. RayStation was tested down to a 3 mm radius sphere (≈0.1 cc) and this showed close to 10% error, reducing to 1% for 10 mm radius (≈4.0 cc) and 0.1% for 20 mm radius (≈33 cc). In clinical plans, the variation in D95 was up to 9% for the smallest volumes, and typically around 2% in the range 0.5 cc-20 cc, and 1% in 20 cc-70 cc, falling to <0.1% for large volumes. Paddick Conformity Index (PCI) and Modified Gradient Index (MGI) are commonly used plan quality indicators for very small volumes. For volumes ≈0.1 cc we observed errors of up to 40% in PCI, and up to 75% in MGI.Our study extends the range of tested DVH calculators in published work, and shows their performance over a wider range of volume sizes. We provide quantitative evidence of the critical need to test the accuracy of DVH calculators in the TPS before clinical use. This work is particularly relevant for both stereotactic plan evaluation and for assessment of small volume doses in published dose constraint recommendations. We demonstrate that significant errors can occur in DVHs for volumes less than 1 cc, even if the volumes themselves are calculated accurately. Even for large structures, deviations between the outputs of DVH calculators can lead to indicated or reported plan check failures if they do not include appropriate tolerances. We urge caution in the use of DVH metrics for these very small volumes and recommend that appropriate DVH uncertainty tolerances are set in organ dose constraints when using them to evaluate clinical plans.

Evaluation of Dynamic Multi-Leaf Collimator (MLC) versus Fixed MLC for Intensity Modulated Radiotherapy (IMRT) Using the Agility 160-Leaf Collimator.

This study aimed to evaluate the efficacy of static or step-and-shoot intensity-modulated radiotherapy (ssIMRT) and dynamic intensity-modulated radiotherapy (dIMRT) delivery techniques for various treatment sites. The treatment planning system (TPS) was utilized to develop optimal treatment plans for twenty-seven patients selected for this comparative study, including nine with head and neck cancer, nine with prostate cancer, and nine with cervical cancer. The prescribed doses were 7000cGy/33fr, 7425cGy/33fr, and 5000cGy/25fr for the nasopharynx, prostate, and cervix cases, respectively, in both ssIMRT and dIMRT delivery techniques. Plans were generated using the Monaco treatment planning system with a 6MV photon beam and nine equidistant fields. Plan evaluation criteria included dose-volume histogram analysis, dose homogeneity index, conformity index, radiation delivery time, and monitor unit requirements. All plans were optimized to ensure that 98% of the planning target volume (PTV) received at least 95% of the prescribed dose, while meeting the planning objectives for organs at risk. dIMRT plans exhibited superior conformity (CI = 0.85 ± 0.05) compared to ssIMRT plans (CI = 0.79 ± 0.08), with statistically significant differences (P < 0.01). Inhomogeneity within the PTV was significantly higher in ssIMRT plans (HI = 0.10 ± 0.02) compared to dIMRT plans (HI = 0.09 ± 0.01), with a significant difference (P < 0.01). Delivery time per fraction was significantly lower in dIMRT compared to ssIMRT (P < 0.01). Furthermore, dIMRT plans required a higher mean monitor unit value (1335.4 ± 172.2) compared to ssIMRT plans (974.4 ± 133.6) with a significant difference (P < 0.001). The findings of this study indicate that dIMRT provides improved target coverage, homogeneity, and conformity while reducing treatment delivery time compared to ssIMRT.

A Deep Learning Approach for the Fast Generation of Synthetic Computed Tomography from Low-Dose Cone Beam Computed Tomography Images on a Linear Accelerator Equipped with Artificial Intelligence

Artificial Intelligence (AI) is revolutionising many aspects of radiotherapy (RT), opening scenarios that were unimaginable just a few years ago. The aim of this study is to propose a Deep Leaning (DL) approach able to quickly generate synthetic Computed Tomography (CT) images from low-dose Cone Beam CT (CBCT) acquired on a modern linear accelerator integrating AI. Methods: A total of 53 patients treated in the pelvic region were enrolled and split into training (30), validation (9), and testing (14). A Generative Adversarial Network (GAN) was trained for 200 epochs. The image accuracy was evaluated by calculating the mean and mean absolute error (ME and ME) between sCT and CT. RT treatment plans were calculated on CT and sCT images, and dose accuracy was evaluated considering Dose Volume Histogram (DVH) and gamma analysis. Results: A total of 4507 images were selected for training. The MAE and ME values in the test set were 36 ± 6 HU and 7 ± 6 HU, respectively. Mean gamma passing rates for 1%/1 mm, 2%/2 mm, and 3%/3 mm tolerance criteria were respectively 93.5 ± 3.4%, 98.0 ± 1.3%, and 99.2 ± 0.7%, with no difference between curative and palliative cases. All the DVH parameters analysed were within 1 Gy of the difference between sCT and CT. Conclusion: This study demonstrated that sCT generation using the DL approach is feasible on low-dose CBCT images. The proposed approach can represent a valid tool to speed up the online adaptive procedure and remove CT simulation from the RT workflow.

Pre-therapy PET-based voxel-wise dosimetry prediction by characterizing intra-organ heterogeneity in PSMA-directed radiopharmaceutical theranostics

Background and objectiveTreatment planning through the diagnostic dimension of theranostics provides insights into predicting the absorbed dose of RPT, with the potential to individualize radiation doses for enhancing treatment efficacy. However, existing studies focusing on dose prediction from diagnostic data often rely on organ-level estimations, overlooking intra-organ variations. This study aims to characterize the intra-organ theranostic heterogeneity and utilize artificial intelligence techniques to localize them, i.e. to predict voxel-wise absorbed dose map based on pre-therapy PET.Methods23 patients with metastatic castration-resistant prostate cancer treated with [177Lu]Lu-PSMA I&T RPT were retrospectively included. 48 treatment cycles with pre-treatment PET imaging and at least 3 post-therapeutic SPECT/CT imaging were selected. The distribution of PET tracer and RPT dose was compared for kidney, liver and spleen, characterizing intra-organ heterogeneity differences. Pharmacokinetic simulations were performed to enhance the understanding of the correlation. Two strategies were explored for pre-therapy voxel-wise dosimetry prediction: (1) organ-dose guided direct projection; (2) deep learning (DL)-based distribution prediction. Physical metrics, dose volume histogram (DVH) analysis, and identity plots were applied to investigate the predicted absorbed dose map.ResultsInconsistent intra-organ patterns emerged between PET imaging and dose map, with moderate correlations existing in the kidney (r = 0.77), liver (r = 0.5), and spleen (r = 0.58) (P < 0.025). Simulation results indicated the intra-organ pharmacokinetic heterogeneity might explain this inconsistency. The DL-based method achieved a lower average voxel-wise normalized root mean squared error of 0.79 ± 0.27%, regarding to ground-truth dose map, outperforming the organ-dose guided projection (1.11 ± 0.57%) (P < 0.05). DVH analysis demonstrated good prediction accuracy (R2 = 0.92 for kidney). The DL model improved the mean slope of fitting lines in identity plots (199% for liver), when compared to the theoretical optimal results of the organ-dose approach.ConclusionOur results demonstrated the intra-organ heterogeneity of pharmacokinetics may complicate pre-therapy dosimetry prediction. DL has the potential to bridge this gap for pre-therapy prediction of voxel-wise heterogeneous dose map.

Assessing Heterogeneity Effects on Points A, B, and Organs at Risk Doses in High-dose-Rate Brachytherapy for Cervical Cancer - A Comparison of 192Ir and 60Co Sources Using Monte Carlo N-Particle 5.

The present article deals with investigating the effects of tissue heterogeneity consideration on the dose distribution of 192Ir and 60Co sources in high-dose-rate brachytherapy (HDR-BT). A Monte Carlo N-Particle 5 (MCNP5) code was developed for the simulation of the dose distribution in homogeneous and heterogeneous phantoms for cervical cancer patients. The phantoms represented water-equivalent and human body-equivalent tissues. Treatment data for a patient undergoing HDR-BT with a 192Ir source were used as a reference for validation, and for 60Co, AAPM Task Group 43 methodology was also applied. The dose values were calculated for both source types in the phantoms. The results showed a good agreement between the calculated dose in the homogeneous phantom and the real patient's treatment data, with a relative difference of less than 5% for both sources. However, when comparing the absorbed doses at critical points such as Point A right, Point A left, Point B right, Point B left, bladder International Commission on Radiation Units and Measurement (ICRU) point, and recto-vaginal ICRU point, the study revealed significant percentage differences (approximately 5.85% to 12.02%) between the homogeneous and heterogeneous setups for both 192Ir and 60Co sources. The analysis of dose-volume histograms (DVH) indicated that organs at risk, notably the rectum and bladder, still received doses within recommended limits. The study concludes that 60Co and 192Ir sources can be effectively used in HDR-BT, provided that careful consideration is given to tissue heterogeneity effects during treatment planning to ensure optimal therapeutic outcomes.

Cone-beam computed tomography-guided online adaptive radiotherapy for pharyngeal cancer with whole neck irradiation: dose-volume histogram analysis between adapted and scheduled plans.

The present study aimed to evaluate whether an adapted plan with Ethos™ could be used for pharyngeal cancer. Ten patients with pharyngeal cancer who underwent chemoradiotherapy with available daily cone-beam computed tomography (CBCT) data were included. Simulated treatments were generated on the Ethos™ treatment emulator using CBCTs every four to five fractions for two plans: adapted and scheduled. The simulated treatments were divided into three groups: early (first-second week), middle (third-fourth week), and late (fifth-seventh week) periods. Dose-volume histogram parameters were compared for each period between the adapted and scheduled plans in terms of the planning target volume (PTV) (D98%, D95%, D50% and D2%), spinal cord (Dmax and D1cc), brainstem (Dmax) and ipsilateral and contralateral parotid glands (Dmedian and Dmean). The PTV D98%, D95% and D2% of the adapted plan were significantly higher than those of the scheduled plans in all periods, except for D98% in the late period. The adapted plan significantly reduced the spinal cord Dmax and D1cc compared with the scheduled plan in all periods. Ipsilateral and contralateral parotid glands Dmean of the adapted plan were lower than those of scheduled plan in the late period. In conclusion, the present study revealed that the adapted plans could maintain PTV coverage while reducing the doses to organs at risk in each period compared with scheduled plans.

Intensity-modulated vaginal brachytherapy applicator and single- and multi-channel applicators in vaginal cuff brachytherapy.

To compare the dosimetric performance of vaginal intensity-modulated brachytherapy (IM-BRT) applicator and single- (SC-BRT) and multi-channel brachytherapy (MC-BRT) applicators for vaginal cuff brachytherapy (VC-BRT). Fifteen patients with uterine-confined endometrium cancer who received adjuvant VC-BRT were included in this study. IM-BRT, SC-BRT, and MC-BRT treatment plans were created for two different clinical target volume (CTV) definitions: 1. Standard CTV, called CTVs; and 2. Virtually defined CTV, called CTVv, with asymmetrical tumor extension > 5 mm in thickness. Plan comparison was performed using dose-volume histogram (DVH) and treatment planning parameters. According to DVH analysis, D98 for CTVv and D2 for both CTVs and CTVv showed statistically significant differences between IM-BRT and SC-BRT plans, but there was no significant difference between IM-BRT and MC-BRT plans in terms of D98 and D2 for both CTVs and CTVv. Additionally, for CTVv plans, IM-BRT was found to be significantly superior to SC-BRT for the rectum (D2cc, V5Gy, and V7Gy), bladder (D2cc and V7Gy), and small bowel (D2cc, V5Gy, and V7Gy). On the other hand, DVH parameters of the sigmoid showed large difference between IM-BRT and SC-BRT plans, but it was not statistically significant. Similarly, the use of IM-BRT applicator demonstrated a noticeable dose reduction in all defined OARs when compared with MC-BRT applicator, but statistically significant for the rectum V7Gy (p = 0.03) only. While the IM-BRT applicator is still in pre-clinical phase, our investigation demonstrated the proof-of-concept in real patient treatment plans with promising dosimetric results compared with SC-BRT and MC-BRT plans in selected patient group.

Dosimetric impact of CT metal artifact reduction for spinal implants in stereotactic body radiotherapy planning.

Metal artifacts due to spinal implants may affect the accuracy of dose calculation for radiotherapy. However, the dosimetric impact of metal artifact reduction (MAR) for spinal implants in stereotactic body radiotherapy (SBRT) plans has not been well studied. The objective of this study was to evaluate the dosimetric impact of MAR in spinal SBRT planning with three clinically common dose calculation algorithms. Gammex phantom and 10 patients' computed tomography (CT) images were studied to investigate the effects of titanium implants. A commercial orthopedic MAR algorithm was employed to reduce artifacts. Dose calculations for SBRT were conducted on both artifact-corrected and uncorrected images using three commercial algorithms [analytical anisotropic algorithm (AAA), Acuros XB (AXB), and Monte Carlo (MC)]. Dose discrepancies between artifact-corrected and uncorrected cases were appraised using a dose-volume histogram (DVH) and 3-dimensional (3D) gamma analysis with different distance to agreement (DTA) and dose difference criteria. The gamma agreement index (GAI) was denoted as G(∆D, DTA). Statistical analysis of t-test was utilized to evaluate the dose differences of different algorithms. The phantom study demonstrated that titanium metal artifacts can be effectively reduced. The patient cases study showed that dose differences between the artifact-corrected and uncorrected datasets were small evaluated by gamma index and DVH. Gamma analysis found that even the strict criterion local G(1,1) had average values ≥93.9% for the three algorithms. For all DVH metrics, average differences did not exceed 0.7% in planning target volume (PTV) and 2.1% in planning risk volume of spinal cord (PRV-SC). Statistical analysis showed that the observed dose differences of MC method were significantly larger than those of AAA (P<0.01 for D98% of PTV and P<0.001 for D0.1cc of spinal cord) and AXB methods (P<0.001 for D98% and P<0.0001 for D0.1cc). Dosimetric impact of artifacts caused by titanium implants is not significant in spinal SBRT planning, which indicates that dose calculation algorithms might not be very sensitive to CT number variation caused by titanium inserts.

Online Adaptive Radiotherapy for Pharyngeal Cancer: Dose-Volume Histogram Analysis between Adapted and Scheduled Plan

The present study aimed to evaluate whether online adapted plan with artificial intelligence (AI) driven work flow could be used in clinical settings with variable changes of the targets and organs at risk (OARs) for pharyngeal cancer. Ten patients with pharyngeal cancer who underwent chemoradiotherapy at our institution between January and July 2020 were included for the analysis. All patients had been previously aligned daily with cone-beam computed tomography (CBCT) and treated by O-ring Linac. A simulated treatment was performed on the treatment emulator. Weekly fractions, once in every 4-5 fractions, were simulated in the treatment emulator for each patient using their previous on-treatment CBCTs. The dataset was divided into three groups according to the treatment period (1st-2nd week, 20 CBCTs), middle (3rd-4th week, 20 CBCTs), and late (5th-7th week, 30 CBCTs) period. In the present study, all of reference plan generation in treatment emulator were created on the initial plans of two-step method using 12 equidistant field IMRT. The prescribed dose was 70 Gy in 35 fractions and normalized to the dose of 68.6 Gy (98% dose) to 95% of the planning target volume (PTV). The adaptation process on treatment emulator includes auto-segmentation of daily anatomy, calculation of the dose in scheduled plans using the same monitor units and optimization and calculation of the dose in adapted plan. Dose-volume histogram (DVH) parameters between adapted and scheduled plans in terms of PTV (D98%, D95%, D50% and D2%), spinal cord (Dmax and D1cc), brain stem (Dmax), ipsilateral and contralateral parotid glands (Dmedian and Dmean) were evaluated in each period. D98% of PTV of adapted plan was significantly higher than that of scheduled plan in early and middle period (p = 0.02 and <0.01, respectively). D95% of PTV of adapted plan was significantly higher than that of scheduled plan in all periods (p<0.01). D2% of PTV of adapted plan was significantly lower than that of scheduled plan in all periods (p = 0.04, 0.04 and 0.02 in each period, respectively). There was not significant difference in D50% of PTV between adapted and scheduled plan in all periods. In terms of OARs, Dmax of spinal cord of adapted plan was significantly lower than that of scheduled plan in all periods (p<0.01). Similarly, D1cc of spinal cord of adapted plan was lower than that of scheduled plan. Dmean of ipsilateral and contralateral parotid glands of adapted plan were lower than those of scheduled plan in the late period (p<0.01 and 0.03, respectively). The present study revealed that adapted plan with AI driven work flow could create dosimetrically better plans for pharyngeal cancer compared to scheduled plan. It was suggested that online adaptive radiotherapy could be necessary to maintain PTV coverage while reducing the dose to OARs in all periods for pharyngeal cancer.

Retrospective Analysis of the Areas Responsible for Light Flash and Odor During Proton Beam Therapy and Photon Therapy.

Background Abnormal sensations were frequently experienced by patients who received irradiation of the brain or head and neck region. We have previously suggested correlations with irradiation of the nasal cavity and retina. Purpose We performed a retrospective dose-volume histogram analysis focused on the brain and head and neck tumor to examine the relationship between these abnormal sensations and the details of irradiation. Methods Multivariate logistic regression models were applied for the presence or absence of light flash and odor. Gender, age, radiotherapy method (proton beam therapy vs. photon radiotherapy), dose of retina, optic nerve, chiasmatic gland, pituitary, nasal cavity, oral cavity, frontal lobe, parietal lobe, occipital lobe, temporal lobe, amygdala, and hippocampus were set as candidates of explanatory variables. Results Light flash and odor during radiotherapy have been suggested to be associated with younger age and retina and nasal cavity irradiation. Multivariate analyses including dose-volume histograms indicated that light flash was related to age, chiasmatic gland irradiation, and pituitary dose, and odor was related to age and nasal cavity irradiation. Conclusion Our results indicate that light flash during radiotherapy is caused by irradiation of the visual pathway and that odor is caused by irradiation of the nasal cavity or olfactory bulb.

Dosimetric Comparison Study Between Free Breathing and Breath Hold Techniques in Patients Treated by Liver-Directed Stereotactic Body Radiation Therapy.

Background Breathing motion management is the key to delivering stereotactic body radiation therapy (SBRT) for liver lesions. This study aimed to compare the dosimetric parameters of liver SBRT using two different techniques: free breathing and breath hold. Method The study included 11 patients with liver metastases or hepatocellular carcinoma who underwent liver-directed SBRT. A dosimetric comparison was performed using dose-volume histogram analysis, evaluating parameters such as the maximum dose to 5 cc of bowel volume, mean liver dose (MLD), and liver V20and V30. Statistical analyses were performed to compare results. Results The findings revealed that the breath hold technique resulted in significantly lower doses to the bowel and smaller volumes of normal liver tissue receiving 20 Gy (V20) and 30 Gy (V30) than the free breathing. Although there was no statistically significant difference in the MLD between the two techniques, the breath hold technique resulted in a lower MLD. Conclusion This dosimetric comparison study suggests that the breath hold technique is associated with lower radiation exposure to the bowel and normal liver tissues. Although this may not be feasible for all patients, it may be an appropriate procedure for selected individuals. Further research is needed to validate these findings in different patient populations and explore their impact on clinical outcomes and patient-reported quality of life.

Absorbed dose calculation for a realistic CT-derived mouse phantom irradiated with a standard Cs-137 cell irradiator using a Monte Carlo method.

Computed tomography (CT) derived Monte Carlo (MC) phantoms allow dose determination within small animal models that is not feasible with in-vivo dosimetry. The aim of this study was to develop a CT-derived MC phantom generated from a mouse with a xenograft tumour that could then be used to calculate both the dose heterogeneity in the tumour volume and out of field scattered dose for pre-clinical small animal irradiation experiments. A BEAMnrc Monte-Carlo model has been built of our irradiation system that comprises a lead collimator with a 1 cm diameter aperture fitted to a Cs-137 gamma irradiator. The MC model of the irradiation system was validated by comparing the calculated dose results with dosimetric film measurement in a polymethyl methacrylate (PMMA) phantom using a 1D gamma-index analysis. Dose distributions in the MC mouse phantom were calculated and visualized on the CT-image data. Dose volume histograms (DVHs) were generated for the tumour and organs at risk (OARs). The effect of the xenographic tumour volume on the scattered out of field dose was also investigated. The defined gamma index analysis criteria were met, indicating that our MC simulation is a valid model for MC mouse phantom dose calculations. MC dose calculations showed a maximum out of field dose to the mouse of 7% of Dmax. Absorbed dose to the tumour varies in the range 60%-100% of Dmax. DVH analysis demonstrated that tumour received an inhomogeneous dose of 12 Gy-20 Gy (for 20 Gy prescribed dose) while out of field doses to all OARs were minimized (1.29 Gy-1.38 Gy). Variation of the xenographic tumour volume exhibited no significant effect on the out of field scattered dose to OARs. The CT derived MC mouse model presented here is a useful tool for tumour dose verifications as well as investigating the doses to normal tissue (in out of field) for preclinical radiobiological research.

Comparison of intensity-modulated radiation therapy (IMRT), 3D conformal proton therapy and intensity-modulated proton therapy (IMPT) for the treatment of metastatic brain cancer.

The purpose of this study has been to compare photon intensity modulated radiation therapy (IMRT) against both conformal and intensity modulated proton therapy (IMPT) plans for metastatic brain cancer. Ten IMRT patients with brain cancer were chosen retrospectively, with prescription doses in the range of 20 to 40 Gy, delivered in 3 to 5 fractions using Varian TrueBeam STx machine. Three proton plans with proton double scattering, single collimation static-IMPT, and energy layer by layer collimation dynamic-IMPT were then generated for the same patients using the Mevion S250 system for conformal plans and the S250i system for IMPT plans. Each plan had respective treatment planning systems that include Brainlab iPlan for IMRT, Varian Eclipse for proton double scattering, and RaySearch Raystation for IMPT. Dosimetric and radiobiologic comparisons were made through dose-volume histogram (DVH) analysis of the target and the organs at risk (OAR); and with parameters of equivalent uniform dose (EUD), tumor control probability (TCP), and normal tissue complication probability (NTCP), respectively. A set of variables α/β ratio, survival fraction, and clonogenic cell density were selected and varied to observe their effect on the abovementioned parameters. Doses were observed to be more homogeneous for patients with brain malignancies with photon IMRT treatments, while dose conformity is improved with proton PBS treatments. Normal tissue is, on average, spared more through both proton treatment options. The minimum doses, closely approximated by dose to 98% of the target volume, are similar across treatment modalities with slight variations.

Effects of reconstruction methods on dose distribution for lung stereotactic body radiotherapy treatment plans.

The aim of the present study was to investigate the effect of tumour motion on various imaging strategies as well as on treatment plan accuracy for lung stereotactic body radiotherapy treatment (SBRT) cases. The ExacTrac gating phantom and paraffin were used to investigate respiratory motion and represent a lung tumour, respectively. Four-dimensional computed tomography (4DCT) imaging was performed, while the phantom was moving sinusoidally with 4s cycling time with three different amplitudes of 8, 16, and 24mm. Reconstructions were done with maximum (MIP) and average intensity projection (AIP) methods. Comparisons of target density and volume were performed using two reconstruction techniques and references values. Volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) were planned based on reconstructed computed tomography (CT) sets, and it was examined how density variations affect the dose-volume histogram (DVH) parameters. 4D cone beam computed tomography (CBCT) was performed with the Elekta Versa HD linac imaging system before irradiation and compared with 3D CBCT. Thus, various combinations of 4DCT reconstruction methods and treatment alignment methods have been investigated. Point measurements as well as 2 and 3D dose measurements were done by optically stimulated luminescence (OSL), gafchromic films, and electronic portal imaging devices (EPIDs), respectively. The mean volume reduction was 7.8% for the AIP and 2.6% for the MIP method. The obtained Hounsfield Unit (HU) values were lower for AIP and higher for MIP when compared with the reference volume density. In DVH analysis, there were no statistical differences for D95%, D98%, and Dmean (p > 0.05). However, D2% was significantly affected by HU changes (p < 0.01). A positional variation was obtained up to 2mm in moving direction when 4D CBCT was applied after 3D CBCT. Dosimetric measurements showed that the main part of the observed dose deviation was due to movement. In lung SBRT treatment plans, D2% doses differ significantly according to the reconstruction method. Additionally, it has been observed that setups based on 3D imaging can cause a positional error of up to 2mm compared to setups based on 4D imaging. It is concluded that MIP has advantages over AIP in defining internal target volume (ITV) in lung SBRT applications. In addition, 4D CBCT and 3D EPID dosimetry are recommended for lung SBRT treatments.

Craniospinal Irradiation: A Dosimetric Comparison Between O-Ring Linac and Conventional C-arm Linac

PurposeThe aim of this study was to perform a dosimetric evaluation between craniospinal irradiation volumetric modulated arc therapy plans designed for an O-Ring and a conventional C-arm Linac. Methods and MaterialsTwo adult patients were selected for this study. Two plans were designed one for a TrueBeam Edge and one for Halcyon O-ring Linac for each patient. The evaluation of the plans was conducted in terms of dose volume histogram analysis of the target volume and organs at risk (OARs) along with total plan monitor units and beam-on time. Paired sample t test was performed to compare Dmax and Dmean of OARs for each plan's comparison. The delivery of volumetric modulated arc therapy plans was evaluated using Octavius 4D phantom. ResultsAll plans demonstrated dose distributions with sufficient planned target volume conformity and homogeneity. The Homogeneity Index and Conformity Index for all plans were found comparable. The paired sample t test did not demonstrate significant difference in terms of Dmax and Dmean of OARs between plans for both patients. All plans met the threshold of 90%, with Halcyon plans having higher gamma passing rates. ConclusionsCraniospinal irradiation plans generated for Halcyon and Edge are equivalent in terms of plan quality and dose sparing at OARs. The small variations may have originated from the differences in beam profile or mean energy, the degree of the modulation for each plan and characteristics of multi leaf collimators for each treatment unit. Halcyon is able to deliver a distinctly faster treatment, but Edge provides an automatic rotational correction for patient positioning.

Detailed analysis of failure patterns using deformable image registration in hypopharyngeal cancer patients treated with sequential boost intensity-modulated radiotherapy.

Sequential boost intensity-modulated radiotherapy (SQB-IMRT) uses two different planning CTs (pCTs) and treatment plans. SQB-IMRT is a form of adaptive radiotherapy that allows for responses to changes in the shape of the tumour and organs at risk (OAR). On the other hand, dose accumulation with the two plans can be difficult to evaluate. The purpose of this study was to analyse patterns of loco-regional failure using deformable image registration (DIR) in hypopharyngeal cancer patients treated with SQB-IMRT. Between 2013 and 2019, 102 patients with hypopharyngeal cancer were treated with definitive SQB-IMRT at our institution. Dose accumulation with the 1st and 2nd plans was performed, and the dose to the loco-regional recurrent tumour volume was calculated using the DIR workflow. Failure was classified as follows: (i) in-field (≥95% of the recurrent tumour volume received 95% of the prescribed dose); (ii) marginal (20-95%); or (iii) out-of-field (<20%). After a median follow-up period of 25months, loco-regional failure occurred in 34 patients. Dose-volume histogram analysis showed that all loco-regional failures occurred in the field within 95% of the prescribed dose, with no marginal or out-of-field recurrences observed. The dosimetric analysis using DIR showed that all loco-regional failures were within the high-dose region. More aggressive treatment may be required for gross tumours.

Near-Maximum Rib Dose is the Most Relevant Risk Factor for Ipsilateral Spontaneous Rib Fracture: A Dosimetric Analysis of Breast Cancer Patients after Radiotherapy

<h3>Purpose/Objective(s)</h3> Spontaneous rib fracture (SRF) is a common late complication in treated breast cancer patients. This study evaluated the incidence and risk factors of ipsilateral SRF after radiotherapy (RT) in breast cancer patients. In addition, we identified dosimetric parameters that were significantly associated with ipsilateral SRF. <h3>Materials/Methods</h3> We retrospectively reviewed 2,204 patients with breast cancer who underwent RT between 2014 and 2016, and were followed up with bone scans. We evaluated clinical risk factors for ipsilateral SRF. Dose-volume histogram analysis was also performed for patients (n = 538) whose dosimetric data were available. All ipsilateral ribs were manually delineated, and dosimetric parameters of the ribs were converted into the equivalent dose in 2 Gy fractions (EQD2). <h3>Results</h3> Ipsilateral SRF occurred in 14.5% of patients 3 years after RT. The median time to develop ipsilateral SRF was 15 months. In multivariate analysis of all patients, a hypofractionated dose scheme and abnormally low bone density were significant clinical risk factors for ipsilateral SRF. In dosimetric analysis, near-maximum rib dose (D2cc) best predicted ipsilateral SRF. The cutoff value of D2cc was EQD2 52 Gy, as determined by receiver operating characteristic analysis. In multivariate analysis including dosimetric variables, D2cc EQD2 ≥ 52 Gy was the only significant risk factor for ipsilateral SRF. <h3>Conclusion</h3> Our data demonstrated that near-maximum rib dose was the best dosimetric parameter to predict ipsilateral SRF in RT-treated breast cancer patients. Additionally, we suggest that the dose for the rib be constrained to D2cc EQD2 < 52 Gy to minimize the risk of ipsilateral SRF.

3D-CRT, IMRT and VMAT for flank irradiation due to pediatric Wilms tumor: A comparative planning study with XCAT phantoms

PurposeTo compare the dosimetric parameters and radiogenic risks from 3D-CRT, IMRT and VMAT for flank irradiation due to pediatric Wilms tumor. MethodsTwo computational XCAT phantoms simulating an average 5- and 10-year-old patient were used. Four different planning target volumes (PTVs) for right flank (RF) and left flank (LF) irradiation with or without paraaortic lymph nodes (LNs) and eight surrounding organs-at-risk (OARs) were contoured on the phantoms’ CT sections. Forty-eight 3D-CRT, IMRT and VMAT plans were created using 6 and 10-MV photons on the two phantoms. The target coverage index (TCI), homogeneity index (HI), conformity index (CI), conformation number (CN) and OAR exposure were determined through dose-volume histogram (DVH) analysis. Second cancer risks were estimated using a non-linear model and DVH data. ResultsThe IMRT and VMAT for LF + LN and RF + LN irradiation reduced the radiation dose to four to six out of the eight OARs compared to 3D-CRT. Conventional treatment provided a better organ sparing for RF and LF irradiation. The IMRT and VMAT led to superior planning parameters in respect to 3D-CRT for all PTVs and both patient’s ages (3D-CRT: TCI = 59.80 % - 82.26 %, CI = 0.55–0.81, CN = 0.40–0.64, HI = 1.11–1.15; IMRT: TCI = 96.04 % - 99.72 %, CI = 0.85–0.91, CN = 0.85–0.88, HI = 1.03–1.05; VMAT: TCI = 96.02 % - 99.69 %, CI = 0.86–0.91, CN = 0.85–0.89, HI = 1.03–1.06). The excess-absolute-risk for developing secondary small intestine, liver and stomach malignancies from 3D-CRT were (7.99–19.32) × 10-4, (0.29–3.83) × 10-4 and (0.37–4.50) × 10-4 persons-year, respectively. The corresponding risks from intensity modulated techniques reached to 22.26 × 10-4, 4.58 × 10-4 and 5.42 × 10-4 persons-year. ConclusionsThis dataset related to plan quality, radiation dose and risks to OARs allows the selection of the proper treatment technique for flank irradiation based on the patient’s age and target site.

A deep learning approach to generate synthetic CT in low field MR-guided radiotherapy for lung cases

IntroductionThis study aims to apply a conditional Generative Adversarial Network (cGAN) to generate synthetic Computed Tomography (sCT) from 0.35 Tesla Magnetic Resonance (MR) images of the thorax. MethodsSixty patients treated for lung lesions were enrolled and divided into training (32), validation (8), internal (10,TA) and external (10,TB) test set. Image accuracy of generated sCT was evaluated computing the mean absolute (MAE) and mean error (ME) with respect the original CT. Three treatment plans were calculated for each patient considering MRI as reference image: original CT, sCT (pure sCT) and sCT with GTV density override (hybrid sCT) were used as Electron Density (ED) map. Dose accuracy was evaluated comparing treatment plans in terms of gamma analysis and Dose Volume Histogram (DVH) parameters. ResultsNo significant difference was observed between the test sets for image and dose accuracy parameters. Considering the whole test cohort, a MAE of 54.9 ± 10.5 HU and a ME of 4.4 ± 7.4 HU was obtained.Mean gamma passing rates for 2%/2mm, and 3%/3mm tolerance criteria were 95.5 ± 5.9% and 98.2 ± 4.1% for pure sCT, 96.1 ± 5.1% and 98.5 ± 3.9% for hybrid sCT: the difference between the two approaches was significant (p = 0.01). As regards DVH analysis, differences in target parameters estimation were found to be within 5% using hybrid approach and 20% using pure sCT. ConclusionThe DL algorithm here presented can generate sCT images in the thorax with good image and dose accuracy, especially when the hybrid approach is used. The algorithm does not suffer from inter-scanner variability, making feasible the implementation of MR-only workflows for palliative treatments.