Dosimetric Parameters Research Articles

Dosimetric predictors of radiation pneumonitis in patients with prior immunotherapy exposure: A multi-institutional analysis

Background and purposeCombining immune checkpoint inhibitors (ICIs) and thoracic radiotherapy (TRT) may magnify the radiation pneumonitis (RP) risk. Dosimetric parameters can predict RP, but dosimetric data in context of immunotherapy are very scarce. To address this knowledge gap, we performed a large multicenter investigation to identify dosimetric predictors of RP in this under-studied population. Materials and methodsAll lung cancer patients from five institutions who underwent conventionally-fractionated thoracic intensity-modulated radiotherapy with prior ICI receipt were retrospectively compiled. RP was defined per CTCAE v5.0. Statistics utilized logistic regression modeling and receiver operating characteristic (ROC) analysis. ResultsThe vast majority of the 192 patients (median follow-up 14.7 months) had non-small cell lung cancer, received PD-1 inhibitors, and did not receive concurrent systemic therapy with TRT. Grades 1–5 RP occurred in 21.9%, 25.0%, 8.3%, 1.6%, and 1.0%, respectively. The mean MLD for patients with grades 1–5 RP was 10.7, 11.6, 12.6, 14.7, and 12.8 Gy, respectively. On multivariable analysis, tumor location and mean lung dose (MLD) significantly predicted for any-grade and grade ≥ 2 pneumonitis. Only MLD significantly predicted for grade ≥ 3 RP. ROC analysis was able to pictorially model RP risk probabilities for a variety of MLD thresholds, which can be an assistive tool during TRT treatment planning. ConclusionThis study, by far the largest to date of dosimetric predictors of RP in the immunotherapy era, illustrates that MLD is the most critical dose-volume parameter influencing RP risk. These data may provide a basis for revising lung dose constraints in efforts to better prevent RP in this rapidly expanding ICI/TRT population.

Management of tumor volume changes during preoperative radiotherapy for extremity soft tissue sarcoma: a new strategy of adaptive radiotherapy.

Using adaptive radiotherapy (ART), to determine objective clinical criteria that identify extremity soft tissue sarcoma (ESTS) patients requiring adaptation of their preoperative radiotherapy (RT) plan. We included 17 patients with a lower extremity ESTS treated between 2019 and 2021 with preoperative RT, using helicoidal intensity-modulated RT (IMRT) tomotherapy, before surgical resection. We collected clinical, tumor parameters and treatment data. Repositioning was ascertained by daily Megavoltage computed tomography (MVCT) imaging. Using the PreciseART technology we retrospectively manually delineated at least one MVCT for each patient per week and recorded volume and dosimetric parameters. A greater than 5% change between target volume and planned target volume (PTV) dosimetric coverage from the initial planning CT scan to at least one MVCT was defined as clinically significant. All 17 patients experienced significant tumor volume changes during treatment; 7 tumors grew (41%) and 10 shrank (59%). Three patients (18%), all undifferentiated pleomorphic sarcomas (UPS) with increased volume changes, experienced significant reductions in tumor dose coverage. Seven patients required a plan adaptation, as determined by practical criteria applied in our departmental practice. Among these patients, only one ultimately experienced a significant change in PTV coverage. Three patients had a PTV decrease of coverage. Among them, 2 did not receive plan adaptation according our criteria. None of the patients with decreased tumor volumes had reduced target volume coverage. Monitoring volume variations by estimating gross tumor volume (GTV) on MVCT, in addition to axial and sagittal linear tumor dimensions, appeared to be most effective for detecting reductions in PTV coverage throughout treatment. Variations in ESTS volume are evident during preoperative RT, but significant dosimetric variations are rare. Specific attention should be paid to grade 2-3 UPSs during the first 2 weeks of treatment. In the absence of dedicated software in routine clinical practice, monitoring of tumor volume changes by estimating GTV may represent a useful strategy for identifying patients whose treatment needs to be replanned.

The Role of Thoracic Vertebral Body Dosimetry in Minimizing Acute Hematologic Toxicities of Patients With Non-Small Cell Lung Cancer Receiving Lung Radiation Therapy and Immunotherapy

IntroductionHematologic toxicities (HTs) are among the most common toxicities of combined immunotherapy and radiotherapy (RT). It remains essential to prevent RT-induced HTs because they can cause treatment discontinuation (influencing antitumoral effects), and because lymphopenia might dampen the effects of immunotherapy. To date, there are no studies examining the impact of thoracic vertebral body (TVB) RT dose on HTs in non-small cell lung cancer (NSCLC) patients receiving combined lung RT and PD(L)-1 immunotherapy. MethodsFor standardization, all doses were reported as 2-Gy equivalents (EQD2). Mirroring publications prior to the immunotherapy era, TVB volumes referred to T1-T10 and specific dosimetric parameters (DmeanEQD2, V5EQD2‒V60EQD2) were analyzed. Logistic regression estimated associations between grade ≥3 HTs (HT3+) and dosimetric/clinical parameters. Normal tissue complication probability (NTCP) models were constructed by logistic regression analysis modeling for HT3+. Receiver operating characteristic (ROC) analysis delineated TVB dosimetric thresholds, stratification of which was able to evaluate post-RT absolute lymphocyte count (ALC) and immunotherapy responses. Areas under the curve (AUCs) for NTCP models were corroborated by bootstrapping (optimism-corrected) methodology. ResultsIn 132 patients, there were 26 (19.7%) instances of HT3+. On multivariate analysis, DmeanEQD2 and V5EQD2‒V20EQD2 associated with HT3+ (P<0.05 for all). The NTCP models illustrated a 50% probability of HT3+ at a DmeanEQD2=39.8 Gy, V5EQD2=87.4%, V10EQD2=77.0%, and V20EQD2=68.4%. ROC analysis delineated optimal thresholds of HT3+ with DmeanEQD2 ±30.2 Gy, V5EQD2 ±69.1%, V10EQD2 ±64.6%, and V20EQD2 ±53.5%. Patients treated with values above those cutoffs had over double the risk of HT3+, with significant differences in post-RT ALC and immunotherapy responses (P<0.05 for all). AUCs for each individual parameter ranged from 0.743 to 0.798, and combining all four aforementioned cutoffs into a ROC curve resulted in a qualitatively higher AUC (0.836). ConclusionsThis hypothesis-generating work suggests that TVB dosimetry may equate with HT3+ in NSCLC patients undergoing combined lung RT/immunotherapy. Applying TVB dose constraints in this population could reduce HT3+ and avoid dampening of immunotherapy responses, but prospective validation is required.

A deep learning-based dose prediction method for evaluation of radiotherapy treatment planning

[Purpose]To address the issue of low accuracy in dose distribution prediction in radiotherapy, we propose a deep learning-based model for predicting three-dimensional dose distribution in tumor radiation therapy. The model utilizes quantitative evaluation methods to assess the treatment plans. [Methods]We selected a dataset of 130 cervical cancer patients, including CT images and target region files. A deep learning U-Net model based on convolutional neural networks and residual blocks was employed to automatically extract multi-scale and multi-level feature maps of CT images, target regions, and anatomical structures of critical organs for intensity-modulated radiation therapy (IMRT) treatment plans and perform three-dimensional dose distribution prediction. Quantitative analysis methods, including error measures such as maximum dose (Dmax), mean dose (Dmean), V20, and D95, were used. [Results]For cervical cancer cases, DVH (dose-volume histogram) graphs were generated based on the evaluation results, directly reflecting the differences between the actual and predicted doses. The actual errors met the basic requirements, and a quantitative evaluation approach was used to optimize the dosimetric parameters. The specific quantification results are: DSC: 86.52 ± 9.31, 95% HD: 3.74 ± 1.49, JD: 0.112 ± 0.026, MSD: 0.067 ± 0.031. [Conclusion]Through training the deep learning model, we have successfully captured the complex nonlinear relationship between IMRT plan feature map parameters and three-dimensional dose distribution. In practical clinical applications, this trained model can accurately predict personalized three-dimensional dose distribution for new patients and effectively assess treatment plans in a quantitative manner. The source code is available at: https://github.com/xiebw9509/Radiotherapy_dose_prediction.

Dosimetric Parameters After VMAT Adaptive Radiotherapy in Patients With Locally Advanced NSCLC Undergoing 4DCT.

To investigate dosimetric differences in organs at risk (OARs) and cardiac substructures in patients with locally advanced non-small cell lung cancer (NSCLC) between the adaptive radiotherapy (ART) and non-ART groups. Thirty patients were treated with definitive radiotherapy +/- chemotherapy. Cardiac substructures including the left anterior descending coronary artery (LAD) and large vessels, were contoured. Eight patients experienced tumor shrinkage and were replanned (ART). Cumulative plans after ART were compared to the original plans (not considering volume reduction) in terms of dosimetric parameters. The cumulative plans of the ART group (n=8) and non-ART group (n=22) were compared in terms of the same dosimetric parameters. Within the ART group, the following parameters were found to be significantly improved after re-planning: mean lung dose (MLD) (13.79 Gy vs. 15.6 Gy), V20Gy both lungs (17.88% vs. 27.38%), ipsilateral MLD (20.87 Gy vs. 24.44 Gy), and esophagus mean dose (20.79 Gy vs. 24.2 Gy). No dosimetric differences were observed in heart substructures. Dosimetric parameters, particularly LAD, were significantly worse in the ART group than in the non-ART group. This is probably because this OAR was not considered in the plan optimization after re-planning, because it was not routinely contoured as an OAR. Our analysis showed an improvement in dosimetric parameters in the lungs and esophagus in the ART group. This approach may lead to a possible reduction in toxicity. Contouring of cardiac substructures could lead to a plan optimization of their parameters and eventually reduce the risk of cardiac toxicities in these patients.

Multicentric development and evaluation of [18F]FDG PET/CT and CT radiomic models to predict regional and/or distant recurrence in early-stage non-small cell lung cancer treated by stereotactic body radiation therapy.

To develop machine learning models to predict regional and/or distant recurrence in patients with early-stage non-small cell lung cancer (ES-NSCLC) after stereotactic body radiation therapy (SBRT) using [18F]FDG PET/CT and CT radiomics combined with clinical and dosimetric parameters. We retrospectively collected 464 patients (60% for training and 40% for testing) from University Hospital of Liège and 63 patients from University Hospital of Brest (external testing set) with ES-NSCLC treated with SBRT between 2010 and 2020 and who had undergone pretreatment [18F]FDG PET/CT and planning CT. Radiomic features were extracted using the PyRadiomics toolbox®. The ComBat harmonization method was applied to reduce the batch effect between centers. Clinical, radiomic, and combined models were trained and tested using a neural network approach to predict regional and/or distant recurrence. In the training (n = 273) and testing sets (n = 191 and n = 63), the clinical model achieved moderate performances to predict regional and/or distant recurrence with C-statistics from 0.53 to 0.59 (95% CI, 0.41, 0.67). The radiomic (original_firstorder_Entropy, original_gldm_LowGrayLevelEmphasis and original_glcm_DifferenceAverage) model achieved higher predictive ability in the training set and kept the same performance in the testing sets, with C-statistics from 0.70 to 0.78 (95% CI, 0.63, 0.88) while the combined model performs moderately well with C-statistics from 0.50 to 0.62 (95% CI, 0.37, 0.69). Radiomic features extracted from pre-SBRT analog and digital [18F]FDG PET/CT outperform clinical parameters in the prediction of regional and/or distant recurrence and to discuss an adjuvant systemic treatment in ES-NSCLC. Prospective validation of our models should now be carried out.

Patient Selection and Outcomes for Hypofractionated Accelerated Radiation and Concurrent Chemotherapy for Non–Small-Cell Lung Cancer

Purpose/ObjectivesAdoption of hypofractionated accelerated radiation therapy (HART) with concurrent chemotherapy has been limited by toxicity concerns. We aimed to describe outcomes of patients treated with HART and concurrent chemotherapy and to evaluate dosimetry to organs at risk to guide patient selection. Materials/MethodsWe evaluated a retrospective cohort of NSCLC patients treated with concurrent chemotherapy with HART (>2.2 Gy per fraction) or standard fractionated radiation therapy (SFRT; 2-2.2 Gy fractions). Dosimetric parameters to key organs at risk were compared, and toxicity, patterns of recurrence and survival were calculated for the cohorts. ResultsFifty-three patients treated with HART were compared with 100 patients treated with SFRT. Median dose per fraction for the HART cohort was 2.75 Gy (range 2.4-3 Gy). HART patients had significantly lower doses to the lung, heart, and esophagus due to patient selection. The HART group and had rates of grade 2+ pneumonitis (9.4 vs. 19%, P = .16) and grade 2+ esophagitis (20.8 vs. 45%, P < .01) that compared favorably to SFRT. Cumulative incidence of in-field recurrence trended lower in the HART cohort (7.6% vs. 23.1%, P = .058). Among the HART group, 88.7% (47/53) met the newly proposed lung constraints based on the degree of hypofractionation ConclusionIn select patients with favorable dosimetry to organs at risk, definitive HART with concurrent chemotherapy achieved excellent local control with low toxicity. These results are being used to inform a prospective study on the safety and efficacy of HART with concurrent chemotherapy for select NSCLC patients.

Cardiac radiation dose is associated with inferior survival but not cardiac events in patients with locally advanced non-small cell lung cancer in the era of immune checkpoint inhibitor consolidation

PurposeWe assessed the association of cardiac radiation dose with cardiac events and survival post-chemoradiation therapy (CRT) in patients with locally advanced non-small cell lung cancer (LA-NSCLC) after adoption of modern radiation therapy (RT) techniques, stricter cardiac dose constraints, and immune checkpoint inhibitor (ICI) consolidation. Methods and MaterialsThis single-institution, multi-site retrospective study included 335 patients with LA-NSCLC treated with definitive, concurrent CRT between October 2017 and December 2021. All patients were evaluated for ICI consolidation. Planning dose constraints included heart mean dose < 20 Gy (<10 Gy if feasible) and heart volume receiving ≥ 50 Gy (V50Gy) < 25 %. Twenty-one dosimetric parameters for three different cardiac structures (heart, left anterior descending coronary artery [LAD], and left ventricle) were extracted. Primary endpoint was any major adverse cardiac event (MACE) post-CRT, defined as acute coronary syndrome, heart failure, coronary revascularization, or cardiac-related death. Secondary endpoints were: grade ≥ 3 cardiac events (per CTCAE v5.0), overall survival (OS), lung cancer-specific mortality (LCSM), and other-cause mortality (OCM). ResultsMedian age was 68 years, 139 (41 %) had baseline coronary heart disease, and 225 (67 %) received ICI consolidation. Proton therapy was used in 117 (35 %) and intensity-modulated RT in 199 (59 %). Median LAD V15Gy was 1.4 % (IQR 0–22) and median heart mean dose was 8.7 Gy (IQR 4.6–14.4). Median follow-up was 3.3 years. Two-year cumulative incidence of MACE was 9.5 % for all patients and 14.3 % for those with baseline coronary heart disease. Two-year cumulative incidence of grade ≥ 3 cardiac events was 20.4 %. No cardiac dosimetric parameter was associated with an increased risk of MACE or grade ≥ 3 cardiac events. On multivariable analysis, cardiac dose (LAD V15Gy and heart mean dose) was associated with worse OS, driven by an association with LCSM but not OCM. ConclusionsWith modern RT techniques, stricter cardiac dose constraints, and ICI consolidation, cardiac dose was associated with LCSM but not OCM or cardiac events in patients with LA-NSCLC.

Radiation therapy margin reduction for patients with localized prostate cancer: A prospective study of the dosimetric impact and quality of life.

To investigate the impact of reducing Clinical Target Volume (CTV) to Planning Target Volume (PTV) margins on delivered radiation therapy (RT) dose and patient reported quality-of-life (QOL) for patients with localized prostate cancer. Twenty patients were included in a single institution IRB-approved prospective study. Nine were planned with reduced margins (4mm at prostate/rectum interface, 5mm elsewhere), and 11 with standard margins (6/10mm). Cumulative delivered dose was calculated using deformable dose accumulation. Each daily CBCT dataset was deformed to the planning CT (pCT), dose was computed, and accumulated on the resampled pCT using a parameter-optimized, B-spline algorithm (Elastix, ITK/VTK). EPIC-26 patient reported QOL was prospectively collected pre-treatment, post-treatment, and at 2-, 6-, 12-, 18-, 24-, 36-, 48-, and 60-month follow-ups. Post -RT QOL scores were baseline corrected and standardized to a [0-100] scale using EPIC-26 methodology. Correlations between QOL scores and dosimetric parameters were investigated, and the overall QOL differences between the two groups (QOLMargin-reduced -QOLcontrol ) were calculated. The median QOL follow-up length for the 20 patients was 48months. Difference between delivered dose and planned dose did not reach statistical significance (p>0.1) for both targets and organs at risk between the two groups. At 4years post-RT, standardized mean QOLMargin-reduced -QOLcontrol were improved for Urinary Incontinence, Urinary Irritative/Obstructive, Bowel, and Sexual EPIC domains by 3.5, 14.8, 10.2, and 16.1, respectively (higher values better). The control group showed larger PTV/rectum and PTV/bladder intersection volumes (7.2±5.8, 18.2±8.1cc) than the margin-reduced group (2.6±1.8, 12.5±8.3cc), though the dose to these intersection volumes did not reach statistical significance (p>0.1) between the groups. PTV/rectum intersection volume showed a moderate correlation (r=-0.56, p<0.05) to Bowel EPIC domain. Results of this prospective study showed that margin-reduced group exhibited clinically meaningful improvement of QOL without compromising the target dose coverage.

RADT-13. A BIOLOGIC EQUIVALENT DOSE COMPARISON BETWEEN RADIOSURGERY AND COLLAGEN TILE BRACHYTHERAPY FOR POST-OPERATIVE TREATMENT OF A BRAIN METASTASIS RESECTION CAVITY

Abstract INTRODUCTION Recurrence of a previously irradiated brain metastasis represents a challenging clinical scenario. Repeat radiosurgery results in sub-optimal local control (LC). Two independently published prospective cohort studies demonstrated durable LC in this setting with collagen tile brachytherapy (CTBT), a novel Cesium-131 carrier. Here we compare biologically equivalent dosimetric parameters of CTBT to radiosurgery to understand dose metrics that may underlie durable LC from CTBT. METHODS A patient was selected from the multi-institutional prospective CTBT registry (NCT04427384) with a brain metastasis resection cavity near brainstem. Planning was performed for radiosurgery (30Gy in 5 fractions, BED of 48Gy) and CTBT (Cs-131, activity of 3.5U). To directly compare dosimetric parameters between radiosurgery and CTBT, biologic equivalent doses (BED) were calculated for brainstem(α/β of 3, BED3) and oncologically at-risk tissue(α/β of 10, BED10). TG101 brainstem dose-constraints were referenced, and respective BED were calculated. RESULTS The resection cavity was 4mm away from brainstem and contained 7 CTBT tiles (28 Cs131 seeds). Gradient index (GI) (24Gy BED10 volume/48Gy BED10 volume) was 3.8 for radiosurgery and 2.2 for CTBT. Conformality index (CI) (48Gy BED10 volume/CTV volume) was 1.2 for radiosurgery and 2.6 for CTBT. BED10 to 90% of the cavity wall (2mm rim around the resection cavity) was 49.6Gy for radiosurgery and 92.6Gy for CTBT. BED3 dose limit goals (max dose 31Gy in 5 fractions, BED3 95.1Gy and threshold dose 23Gy in 5 fractions, BED3 of 58.3Gy to 0.5cc) were met for both radiosurgery and CTBT. CONCLUSION BED comparisons demonstrate that CTBT leads to higher CI, lower GI, and higher dose to the cavity wall than radiosurgery while meeting BED3 dose limit goals to an adjacent organ at risk. These dose characteristics might underlie durable LC seen in the recurrent brain metastasis setting, though larger scale analyses are being performed with with clinical outcomes on NCT04427384.

RADT-36. A SINGLE-CENTRE EXPERIENCE WITH HYPERARC FRACTIONATED STEREOTACTIC RADIOSURGERY [FSRS] FOR BENIGN BRAIN TUMOURS

Abstract BACKGROUND Treating benign brain tumours with fSRS may have radiobiologic and clinical advantages, such as lower rates of symptomatic oedema and radionecrosis[1]. HyperArc (HA, Varian Medical System) is an isocentric VMAT technique developed for non-coplanar, MLC-based stereotactic radiotherapy with automated optimizations and delivery. Here we report our initial clinical experience of HyperArc fSRS in treating benign brain tumours. MATERIALS AND METHODS We retrospectively reviewed 21 cases of benign brain tumours treated at the Bon Secours Radiotherapy Cork between May 2020-May 2023. Clinical and dosimetric parameters are reported. RESULTS A total of 21 patients were treated in a total of 105 SRS fractions, all using a 5-fraction regimen (5x5Gy, N = 20). The commonest tumour was meningioma (N = 9), followed by vestibular schwannoma (N = 7) and pituitary adenoma (N = 5). Median patient age was 59 years (range 26-86). Median PTV was 4.65 cc (IQR 1.9-14.6), median number of arcs was 4 (range 3-4), median PTV coverage was 99.6 % (IQR 98.0-99.9). Median prescription isodose was 79%. Median Paddick conformity index and gradient index was 0.86 (IQR 0.83-0.98) and 3.0 (IQR 2.9-3.2) respectively. Median follow-up was 7 months. No patient suffered from toxicity ≥ grade 2 (Common Toxicity Criteria, Version 5). Only 2/21 patients required steroid therapy during fSRS. No patient had a seizure. CONCLUSION HyperArc fSRS is a feasible option for benign brain tumours. Initial clinical experience in terms of plan quality and acute toxicity is encouraging. fSRS for benign brain tumours should be prospectively studied. REFERENCES: 1. Lehrer EJ et al IJROBP 2019 Mar1;103(3):610-630

Noninvasive cardiac radioablation for ventricular tachycardia: dosimetric comparison between linear accelerator- and robotic CyberKnife-based radiosurgery systems

BackgroundFew dosimetric comparisons have been published between linear accelerator (LA)-based systems and CyberKnife (CK)-based robotic radiosurgery systems for cardiac radio-ablation in ventricular tachycardia. This study aimed to compare the dosimetry of noninvasive cardiac radio-ablation deliverable on LA with that on CK.MethodsThirteen patients who underwent noninvasive cardiac radio-ablation by LA were included. The prescribed dose was 25 Gy in 1 fraction, and the average planning target volume was 49.8 ± 31.0 cm3 (range, 14.4–93.7 cm3). CK plans were generated for comparison.ResultsBoth the CK and LA plans accomplished appropriate dose coverage and normal tissue sparing. Compared with the LA plans, the CK plans achieved significantly lower gradient indices (3.12 ± 0.71 vs. 3.48 ± 0.55, p = 0.031) and gradient measures (1.00 ± 0.29 cm vs. 1.17 ± 0.29 cm, p < 0.001). They had similar equivalent conformity indices (CK vs. LA: 0.84 ± 0.08 vs. 0.87 ± 0.07, p = 0.093) and maximum doses 2 cm from the planning target volume (PTV) in any direction (CK vs. LA: 50.8 ± 9.9% vs. 53.1 ± 5.3%, p = 0.423). The dosimetric advantages of CK were more prominent in patients with a PTV of ≤ 50 cm3 or a spherical PTV. In patients with a PTV of > 50 cm3 or a non-spherical PTV, the LA and CK plans were similar regarding dosimetric parameters. CK plans involved more beams (232.2 ± 110.8 beams vs. 10.0 ± 1.7 arcs) and longer treatment times (119.2 ± 43.3 min vs. 22.4 ± 1.6 min, p = 0.007).ConclusionsBoth CK and LA are ideal modalities for noninvasive cardiac radio-ablation. Upfront treatment should be considered based on clinical intent.

European astronaut radiation related cancer risk assessment using dosimetric calculations of organ dose equivalents

An illustrative sample mission of a Mars swing-by mission lasting one calendar year was chosen to highlight the application of European risk assessment software to cancer (all solid cancer plus leukaemia) risks from radiation exposures in space quantified with organ dose equivalent rates from model calculations based on the quantity Radiation Attributed Decrease of Survival (RADS). The relevant dose equivalent to the colon for radiation exposures from this Mars swing-by mission were found to vary between 198 and 482 mSv. These doses depend on sex and the two other factors investigated here of: solar activity phase (maximum or minimum); and the choice of space radiation quality factor used in the calculations of dose equivalent. Such doses received at typical astronaut ages around 40 years old will result in: the probability of surviving until retirement age (65 years) being reduced by a range from 0.38% (95%CI: 0.29; 0.49) to 1.29% (95%CI: 1.06; 1.56); and the probability of surviving cancer free until retirement age being reduced by a range from 0.78% (95%CI: 0.59; 0.99) to 2.63% (95%CI: 2.16; 3.18). As expected from the features of the models applied to quantify the general dosimetric and radiation epidemiology parameters, the cancer incidence risks in terms of surviving cancer free, are higher than the cancer mortality risks in terms of surviving, the risks for females are higher than for males, and the risks at solar minimum are higher than at solar maximum.

Dosimetric Comparison of Commonly Used Volumetric Modulated Arc Therapy Field Arrangements Based on Flattening Filter-Free Beams for Synchronous Bilateral Breast Carcinoma Radiation Therapy

Dosimetric Comparison of Commonly Used Volumetric Modulated Arc Therapy Field Arrangements Based on Flattening Filter-Free Beams for Synchronous Bilateral Breast Carcinoma Radiation Therapy

Can we skip the simulation step for radiation treatment planning in patients with symptomatic bone metastases?

255 Background: Patients with bone metastases may require urgent radiation treatment (RT) due to severe pain, neurologic or other symptoms. Conventional approaches typically involve a 3-step process: initial consultation, followed several days later by a planning CT (pCT) simulation and dosimetric planning, and finally RT delivery. The time frame from consultation to RT can be up to 2 weeks, overly lengthy for severely symptomatic patients. We explored the viability of using diagnostic CT (dCT) imaging, usually available to radiation oncologists at the time of consultation, for RT planning - with the ultimate goal of removing the simulation step to reduce the interval from consultation to RT. In this initial phase of the project, we set out to compare differences in key dosimetric parameters from dCT- and pCT- generated RT plans. Methods: We retrospectively reviewed patients (n=28) treated for bone metastases at a single academic institution from 2020-2023. We utilized rigid image registration to transfer physician contours from pCT images to dCT images to account for changes in patient positioning. Beam arrangements, energies, and administered monitor units were also transferred from the pCT to the dCT for accurate dose calculation. We calculated RT dose coverage of each target metastasis using “V100”, or the percentage of the target lesion receiving 100% of the RT prescription dose. Correspondingly, the “V95” and the maximum point dose (“hotspot”) in patients were also calculated. Results: Out of 28 patients, 24 were treated to single and 4 to multiple (2-4) bone metastases. We excluded patients who had no dCT (n=7) or whose body positioning on the dCT (e.g. arms) created obstructions for beam arrangements (n=2). Eventually, 24 clinical plans made from 19 patients’ pCTs were migrated to their dCTs to generate comparable dosimetric plans. For all 24 dCT-based plans (12 spines and 12 extremities), the mean full dose coverage V100 decreased by 7.14% ± 15.89%. Overall, the plans had 91.14% ± 18.6% for V95 to PTV. Hotspots rose by 2.75% ± 3.61%. Two cases were observed to have full-dose-coverage drop over 40%: one was caused by patient’s outline change induced by different couches used for diagnosis and simulation, and the other one had an initial coverage of 57.6% for V100 in the original clinical plan. The remaining plans had a drop of 3.14% ± 8.37% on V100, and 96.1% ± 8.2% for V95. Conclusions: It was feasible to generate radiation treatment plans for bone metastases with good tumor coverage using dCT imaging. Patient selection plays a crucial role in dCT-based treatment planning, as the dose distribution is highly sensitive to anatomical variations resulting from patient positioning. This treatment planning approach circumvents the simulation step and would reduce patients' wait time for RT, thereby enabling more rapid access to RT for patients suffering with symptoms from bone metastases.

Active Breathing Coordinator reduces radiation dose to the stomach in patients with left breast cancer

Background/Purpose Gastric dose parameters comparison for deep inspiration breath-hold (DIBH) or free breathing (FB) mode during radiotherapy (RT) for left-sided breast cancer patients (LSBCPs) has not been investigated before. This study aimed to analyze the impact of Active Breath Coordinator (ABC)-DIBH technique on the dose received by the stomach during RT for LSBCPs and to provide organ-specific dosimetric parameters. Materials and methods The study included 73 LSBCPs. The dosimetric parameters of the stomach were compared between FB and DIBH mode. The correlation between the stomach volume and dosimetric parameters was analyzed. Results Compared to FB mode, statistically significant reductions were observed in gastric dose parameters in ABC-DIBH mode, including Dmax (46.60 vs 17.25, p < 0.001), D1cc (38.42 vs 9.60, p < 0.001), Dmean (4.10 vs 0.80, p < 0.001), V40Gy (0.50 vs 0.00, p < 0.001), V30Gy (6.30 vs 0.00, p < 0.001), V20Gy (20.80 vs 0.00, p < 0.001), V10Gy (51.10 vs 0.77, p < 0.001), and V5Gy (93.20 vs 9.60, p < 0.001). ABC-DIBH increased the distance between the stomach and the breast PTV when compared to FB, from 1.3 cm to 2.8 cm (p < 0.001). Physiologic decrease in stomach volume was not found from FB to ABC-DIBH (415.54 cm3 vs 411.61 cm3, p = 0.260). The stomach volume showed a positive correlation with V40Gy (r2 = 0.289; p < 0.05), V30Gy (r2 = 0.287; p < 0.05), V20Gy (r2 = 0.343; p < 0.05), V10Gy (r2 = 0.039; p < 0.001), V5Gy (r2 = 0.439; p < 0.001), Dmax (r2 = 0.269; p < 0.05) and D1cc (r2 = 0.278; p < 0.05) in FB mode. While in ABC-DIBH mode, most stomach dosimetric parameters were not correlated with gastric volume. Conclusions The implementation of ABC-DIBH in LSBCPs radiotherapy resulted in lower irradiation of the stomach. Larger stomach volume was associated with statistically significantly higher dose irradiation in FB mode. To reduce radiotherapy related side effects in FB mode, patients should be fast for at least 2 hours before the CT simulation and treatment.

Robustness of hypofractionated breast radiotherapy after breast-conserving surgery with free breathing.

This study aimed to evaluate the robustness with respect to the positional variations of five planning strategies in free-breathing breast hypofractionated radiotherapy (HFRT) for patients after breast-conserving surgery. Twenty patients who received breast HFRT with 42.72 Gy in 16 fractions were retrospectively analyzed. Five treatment planning strategies were utilized for each patient, including 1) intensity-modulated radiation therapy (IMRT) planning (IMRTpure); 2) IMRT planning with skin flash tool extending and filling the fluence outside the skin by 2cm (IMRTflash); 3) IMRT planning with planning target volume (PTV) extended outside the skin by 2cm in the computed tomography dataset (IMRTePTV); 4) hybrid planning, i.e., 2 Gy/fraction three-dimensional conformal radiation therapy combined with 0.67 Gy/fraction IMRT (IMRThybrid); and 5) hybrid planning with skin flash (IMRThybrid-flash). All plans were normalized to 95% PTV receiving 100% of the prescription dose. Six additional plans were created with different isocenter shifts for each plan, which were 1mm, 2mm, 3mm, 5mm, 7mm, and 10mm distally in the X (left-right) and Y (anterior-posterior) directions, namely, (X,Y), to assess their robustness, and the corresponding doses were recalculated. Variation of dosimetric parameters with increasing isocenter shift was evaluated. All plans were clinically acceptable. In terms of robustness to isocenter shifts, the five planning strategies followed the pattern IMRTePTV, IMRThybrid-flash, IMRTflash, IMRThybrid, and IMRTpure in descending order. V 95% of IMRTePTV maintained at 99.6% ± 0.3% with a (5,5) shift, which further reduced to 98.2% ± 2.0% with a (10,10) shift. IMRThybrid-flash yielded the robustness second to IMRTePTV with less risk from dose hotspots, and the corresponding V 95% maintained >95% up until (5,5). Considering the dosimetric distribution and robustness in breast radiotherapy, IMRTePTV performed best at maintaining high target coverage with increasing isocenter shift, while IMRThybrid-flash would be adequate with positional uncertainty<5mm.

Fully automated volumetric modulated arc therapy technique for radiation therapy of locally advanced breast cancer

BackgroundThis study aimed to evaluate an a-priori multicriteria plan optimization algorithm (mCycle) for locally advanced breast cancer radiation therapy (RT) by comparing automatically generated VMAT (Volumetric Modulated Arc Therapy) plans (AP-VMAT) with manual clinical Helical Tomotherapy (HT) plans.MethodsThe study included 25 patients who received postoperative RT using HT. The patient cohort had diverse target selections, including both left and right breast/chest wall (CW) and III-IV node, with or without internal mammary node (IMN) and Simultaneous Integrated Boost (SIB). The Planning Target Volume (PTV) was obtained by applying a 5 mm isotropic expansion to the CTV (Clinical Target Volume), with a 5 mm clip from the skin. Comparisons of dosimetric parameters and delivery/planning times were conducted. Dosimetric verification of the AP-VMAT plans was performed.ResultsThe study showed statistically significant improvements in AP-VMAT plans compared to HT for OARs (Organs At Risk) mean dose, except for the heart and ipsilateral lung. No significant differences in V95% were observed for PTV breast/CW and PTV III-IV, while increased coverage (higher V95%) was seen for PTV IMN in AP-VMAT plans. HT plans exhibited smaller values of PTV V105% for breast/CW and III-IV, with no differences in PTV IMN and boost. HT had an average (± standard deviation) delivery time of (17 ± 8) minutes, while AP-VMAT took (3 ± 1) minutes. The average γ passing rate for AP-VMAT plans was 97%±1%. Planning times reduced from an average of 6 h for HT to about 2 min for AP-VMAT.ConclusionsComparing AP-VMAT plans with clinical HT plans showed similar or improved quality. The implementation of mCycle demonstrated successful automation of the planning process for VMAT treatment of locally advanced breast cancer, significantly reducing workload.

Image-guided Interstitial Brachytherapy in the Treatment of Primary and Recurrent Vulvovaginal Gynaecological Malignancies

AimsTo evaluate the use, outcomes and toxicities of high dose rate brachytherapy (HDRB) to the vulvovaginal region in previously irradiated and radiotherapy-naïve patients for primary or recurrent gynaecological malignancies. Materials and methodsFrom January 2010 to December 2020, 94 women with a median age of 64 years (range 31–88 years) were treated with interstitial HDRB for vulvovaginal disease. Treatment details, including cumulative radiotherapy doses, were recorded together with reported toxicity, using Common Terminology Criteria for Adverse Events (CTCAE) grading. Dosimetric parameters, including D90, V100 and V150 together with treatment response at 3 months, overall survival, relapse-free survival and long-term toxicity data, were collated from referring centres. ResultsThe median follow-up was 78 months (range 2–301). Primary sites of disease included vagina (37), endometrium (29), vulva (16), ovary (7) and cervix (5). Eighty-six (91.5%) patients were treated with curative intent, eight (8.5%) were palliative treatments. Fifty patients received HDRB for recurrent disease, 39 patients for primary disease and five as part of adjuvant treatment. The anatomical site of disease treated with HDRB ranged from vagina (76), vulva (14) and peri-urethral sites (four). The 2- and 5-year local relapse-free survival rates were 76% and 72%, respectively; 15 patients experienced local failure only, whereas six patients had local and nodal/distant failure. The median time to local recurrence was 8 months (range 2–88 months). The 2- and 5-year overall survival rates for all patients were 67% and 47%, respectively; the median overall survival was 59 months. Seventy-nine (84%) patients had a complete response measured with imaging at 3 months. Grade 3 toxicity was reported in 14 patients (14.8%). ConclusionThis retrospective series suggests the use of interstitial brachytherapy for vulvovaginal gynaecological malignancy to be an effective and safe treatment option. Good local control was achieved with a tolerable toxicity profile; it is a valuable treatment modality.

Dosimetric parameters and safety analysis of 3D-printing non-coplanar template-assisted interstitial brachytherapy for non-centrally recurrent cervical cancer

IntroductionThe prognosis of patients with non-central recurrent cervical cancer (NRCC) remains poor, and treatment options are limited. We aimed to explore the accuracy and safety of the 3D-printed non-coplanar template (3D-PNCT)-assisted 192Ir interstitial brachytherapy (ISBT) in the treatment of NRCC.Material and methodsA total of 36 patients with NRCC who received 3D-PNCT-guided 192Ir ISBT in the First Affiliated Hospital of Zhengzhou University from January 2021 to July 2022 were included in this study. There were 36 3D-PNCTs that were designed and printed. The prescribed dose was 30–36 Gy, divided into five to six times, once a week. To evaluate whether the actual parameters were consistent with the preoperative design, the dosimetric parameters of pre- and postoperative treatment plans were compared, including dose of 90% high-risk clinical target volume (HR-CTV D90), volume percentage of 100% and 150% prescribed dose V100% and V150%, homogeneity index (HI), conformal index (CI), external index (EI), and dose received by 2 cm3 (D2cm3) of the rectum, colon, bladder, and ileum. The safety parameters including occurrence of bleeding, infection, pain, radiation enteritis, and radiation cystitis within 3 months after operation were recorded.ResultsAll patients successfully completed the treatment and achieved the goals of the preoperative plan. There was no significant difference in the accuracy (HRCTVD90, V100%, EI, CI, and HI) and safety (D2cm3 of rectum, colon, bladder, and ileum) parameters of the postoperative plan compared with the preoperative plan (all p&amp;gt;0.05). Major side effects included bleeding at the puncture site (13.9%), postoperative pain (8.3%), acute radiation cystitis (13.9%), and radiation enteritis (19.4%). There were no serious perioperative complications and no grade 3–4 acute radiotherapy side effects.Conclusion3D-PNCT-assisted 192Ir ISBT can be accurately and safely applied in the treatment of patients with NRCC.