Dosimetric Parameters Research Articles

3D-printed brachytherapy in patients with cervical cancer: improving efficacy and safety outcomes

ObjectiveThis study aims to evaluate the efficacy and safety of 3D printing technology in brachytherapy for cervical cancer, comparing its outcomes with conventional free hand implantation brachytherapy.MethodsA total of 50 cervical cancer patients treated at the First Affiliated Hospital of Gannan Medical College from January 2019 to July 2023 were included in this study. Patients were divided into two groups: 25 patients received intensity-modulated radiotherapy (IMRT) combined with 3D-printed brachytherapy, and 25 patients underwent IMRT combined with free hand brachytherapy implantation. Key indicators analyzed included short-term therapeutic effects, survival outcomes, operation times, the number of CT scans, the number of needles inserted, dosimetric parameters, and complications.ResultsThe use of 3D-printed brachytherapy significantly improved the safety of radiation therapy operations, especially for large tumors (≥ 30 mm), by providing more precise dose distribution and reducing the radiation doses received by critical organs such as the bladder and rectum. Compared to the artificial implant group (88% prevalence), the 3D-printed brachytherapy group showed a significantly lower incidence of radiation enteritis (29.2% prevalence, p < 0.001). There were no significant differences in other complications between the two groups. For instance, the incidence of radiation cystitis was relatively high in the 3D-printed brachytherapy group (79.2% prevalence) compared to the artificial implant group (64% prevalence, p = 0.240). The median follow-up period in this study was 22.5 months [IQR 18–29]. Among the 49 patients included, 43 had cervical squamous carcinoma and 6 had cervical adenocarcinoma. Short-term therapeutic response rates were comparable, with no significant difference in overall survival observed between the two groups.Conclusion3D-printed brachytherapy offers a more effective and safer therapeutic option for patients with cervical cancer, particularly for those with large tumors or complex anatomical structures.

Effect of breathing phase number on the 4D robust optimization for pancreatic cancer intensity modulated proton therapy

PurposeRespiratory movement, as one of the main challenges in proton therapy for pancreatic cancer patients, could not only lead to harm to normal tissues but also lead to failure of the tumor control, resulting in irreversible consequences. Including respiratory movements into the plan optimization, i.e. 4D robust optimization, may mitigate the interplay effect. However, 4D robust optimization considering images of all breathing phases is time-consuming and less efficient. This work aims to investigate the effect of the breathing phase number on the 4D robust optimization for pancreatic cancer intensity modulated proton therapy (IMPT) by examining plan quality and computational efficiency.MethodsA total of 15 pancreatic cancer patients were retrospectively analyzed. In this study, both anterior-fields and posterior-fields plans were created for each patient. For each plan, six four-dimensional (4D) robust treatment planning strategies with different numbers of respiratory phases and one three-dimensional (3D) treatment plan were created. Optimization of the plans were performed on all ten phases (10phase plan), two extreme phases (2phase plan), two extreme phases plus an intermediate state (3phase plan), two extreme phases plus the 3D CT (3Aphase plan), six phases during the exhalation stage (6Exphase plan), six phases during the inhalation stage (6Inphase plan) and 3D Computed Tomography (CT) scan image (3D plan), respectively. 4D dynamic dose (4DDD) was then calculated to access the interplay effect by considering respiratory motion and dynamic beam delivery. Plan quality and dosimetric parameters for the target and organs at risk (OARs) were then analyzed.ResultsCompared to the 4D plans, 3D plan performed terribly in terms of target coverage and organs at risk. Target dose in anterior-fields plan varied slightly among all six 4D treatment planning strategies. Both the 6Exphase and 6Inphase plans demonstrated performance that was comparable to the 10phase plan in target coverage, outperforming the other five plans for anterior-fields plan. It’s basically the same for the posterior-fields plan. The six strategies showed similar OARs sparing effect for both anterior-fields and posterior-fields plan. Compared with the 10phase plan, the average decline rates of the optimization time of the six plans of 2phase, 3phase, 3Aphase, 6Exphase, 6Inphase, and 3D were 73.26 ± 6.54% vs. 74.48 ± 6.63%, 65.80 ± 7.89% vs. 65.81 ± 9.58%, 54.67 ± 11.52% vs. 65.75 ± 9.58%, 42.14 ± 13.57% vs. 39.63 ± 16.93%, 37.72 ± 11.70% vs. 40.79 ± 13.62% and 75.52 ± 8.21% vs. 80.67 ± 5.62%, respectively (anterior vs. posterior). With the decrease of the number of phases selected for optimization, the decline rates increased, while the other dosimetry parameters generally showed a deterioration trend.ConclusionIn this study, a comprehensive evaluation of six 4D robust treatment planning strategies and one 3D treatment planning strategy for pancreatic cancer patients receiving IMPT was performed. The results showed that six 4D robust optimization strategies were comparable in common posterior field therapy. 2phase and 3phase (including 3Aphase) treatment planning strategies could replace the 10phase treatment planning strategy. It should be noted that patients with large motion amplitudes should receive special attention. The dosimetric performance of the 6Exphase and 6Inphase plans closely aligned with that of the 10phase plan in anterior fields. These plans offered a feasible alternative to 10phase treatment planning strategy by reducing optimization time while maintaining dose coverage of the target and protection of OARs. This research provides guidelines to reduce optimization time and improve clinical efficiency for pancreatic cancer IMPT.

On the acceptance, commissioning, and quality assurance of electron FLASH units.

FLASH or ultra-high dose rate (UHDR) radiation therapy (RT) has gained attention in recent years for its ability to spare normal tissues relative to conventional dose rate (CDR) RT in various preclinical trials. However, clinical implementation of this promising treatment option has been limited because of the lack of availability of accelerators capable of delivering UHDR RT. Commercial options are finally reaching the market that produce electron beams with average dose rates of up to 1000Gy/s. We established a framework for the acceptance, commissioning, and periodic quality assurance (QA) of electron FLASH units and present an example of commissioning. A protocol for acceptance, commissioning, and QA of UHDR linear accelerators was established by combining and adapting standards and professional recommendations for standard linear accelerators based on the experience with UHDR at four clinical centers that use different UHDR devices. Non-standard dosimetric beam parameters considered included pulse width, pulse repetition frequency, dose per pulse, and instantaneous dose rate, together with recommendations on how to acquire these measurements. The 6- and 9-MeV beams of an UHDR electron device were commissioned by using this developed protocol. Measurements were acquired with a combination of ion chambers, beam current transformers (BCTs), and dose-rate-independent passive dosimeters. The unit was calibrated according to the concept of redundant dosimetry using a reference setup. This study provides detailed recommendations for the acceptance testing, commissioning, and routine QA of low-energy electron UHDR linear accelerators. The proposed framework is not limited to any specific unit, making it applicable to all existing eFLASH units in the market. Through practical insights and theoretical discourse, this document establishes a benchmark for the commissioning of UHDR devices for clinical use.

E-Brachy: New dosimetry package for electronic brachytherapy sources.

Large reported variability in the material composition and geometrical components of the Xoft electronic high-dose-rate brachytherapy Causes inter-source discrepancy in the source output. This variability is due to the manual manufacturing and assembly of thesources. This study aimed to develop a dosimetry software tool called E-Brachy to characterize the Xoft source and quantify the discrepancies in its photon spectrum and dosimetricproperties. E-Brachy is based on the Geant4 Monte Carlo toolkit and consists of two parts. In part one, the geometry and material composition for the source received in the computer-aided design format from the vendor were converted to the geometry description markup language format using the GUIMesh Python tool and integrated into the E-Brachy software. There was a large variation in material composition and thickness for some of the tube components. The simulation started from electrons and resulted in x-ray generations in the anode region. Multithreading, a track length estimation, and the uniform bremsstrahlung splitting variance reduction techniques were used to decrease the simulation time and increase the x-ray production. The photon energy, position, and momentum were saved into a phase space file as the photon exited the source, but before interacting with the external environment. The obtained x-ray energy spectrum was compared with measurements from the National Institute of Standards and Technology (NIST). In part two, by sampling from the generated photons, the dose rates and dosimetric parameters according to the TG-43 protocol were calculated for model S7500 and compared to the ones previously calculated for model S700 source, which were deemed identical by themanufacturer. The material composition that resulted in the most similar spectrum as the measured NIST spectrum with Pearson's correlation coefficient of 0.99 and a calculated Euclidean difference of keV was chosen for further dosimetric analysis of the model S7500 source. Characteristic peaks showed the presence of tungsten, yttrium, and silver in the source components. Differences in dose rates between the two source models surpassed 20% for polar angles , reaching a peak at cm and . The differences in the radial dose function values were within 5%. The relative difference in percentage between the anisotropy function values of the two models was closer to 0 for smaller values, but at higher polar angles, they increased to 300%. A software package called E-Brachy was successfully developed for the characterization and dosimetry of Xoft electronic brachytherapy sources. E-Brachy can be combined with spectral measurements to investigate the inter- and intra-source variability. The software package was tested by comparing the simulated spectra from the S7500 Xoft source model with NIST measurements and its TG-43 parameters with the S700 model. The TG-43 parameters between the two sources significantly exceed the recommendations ofTG-56.

PO0223: How Hot is Too Hot? Assessing the Role of the V200 and Other Dosimetric Parameters in the Evolution of Complications Following HDR Cervical Brachytherapy

PO0223: How Hot is Too Hot? Assessing the Role of the V200 and Other Dosimetric Parameters in the Evolution of Complications Following HDR Cervical Brachytherapy

Subclinical cardiac damage monitoring in breast cancer patients treated with an anthracycline-based chemotherapy receiving left-sided breast radiation therapy: subgroup analysis from a phase 3 trial.

This study, derived from the phase 3 SAFE trial (ClinicalTrials.gov identifier: NCT2236806), explores subclinical cardiac damage in breast cancer patients receiving anthracycline-based chemotherapy and left-sided breast radiation therapy (RT). Eligible patients were randomized to a cardioprotective pharmacological therapy (bisoprolol, ramipril, or both) or placebo, with cardiac surveillance at multiple time-point using standard and 3-dimensional echocardiography. Dosimetric parameters were analysed, including mean heart dose (MHD) and various metrics for heart substructures, employing advanced contouring techniques and auto-contouring software. In the analysis of left-sided breast RT patients, the study encompassed 39 out of 46 irradiated individuals, focusing on GLS and 3D-LVEF outcomes with ≥ 10% worsening, defined as subclinical heart damage. Distinct RT schedules were used, with placebo exhibiting the highest ≥ 10% worsening (36.4%). In terms of treatment arms, bisoprolol exhibited 11.1% worsening, while ramipril 16.7% and bisoprolol + ramipril 25%. For patients with no subclinical damage, the mean MHD was 1.5Gy; for patients with subclinical heart damage, the mean MHD was 1.6Gy (p = 0.94). Dosimetric parameters related to heart and heart substructures (left anterior descending artery, right and left atrium, right and left ventricle) showed no statistically significant differences between patients with and without subclinical damage. Our results emphasize the crucial role of cardioprotective measures in mitigating adverse effects, highlighting RT as having negligible influence on cardiac performance. An extended follow-up assessment of the whole series is warranted to determine whether a subclinical effect could significantly influence clinical outcomes and cardiac events.

Estimation of weighted computed tomography dose index (CTDIw) in megavoltage computed tomography (MVCT)

Abstract Introduction Advanced technologies in radiation treatment deliveries require high accuracy and precision in setup before treatment to get accurate dose delivery for planned target volumes. During imaging procedures, patients are getting extra doses from kilovoltage computed tomography (KVCT) and megavoltage computed tomography (MVCT). Computed tomography dose index is an important dosimetric parameter to know the degree of radiation-induced side effects. Aim The main aim of this study is to quantify the dose received by patients during MVCT imaging procedures, weighted computed tomography dose index (CTDIw), volume computed tomography dose index (CTDIvol) and dose length product (DLP). Methods and materials This study has been performed on Radixact X9 LINAC machine with 6MV flattening filter-free (FFF) photon beam for treatment and imaging with 3.5 MeV average photon energy. CTDIw and dose length product (DLP) have been calculated for different scanning lengths 18 cm, 10 cm and 0.7 cm with fine, normal and coarse modes with standard imaging A1SL1 ion chamber, cheese phantom and tomoelectrometer. Results CTDIw, CTDIvol, and DLP have been calculated with cheese phantom using A1SL1 ion chamber. CTDIw for 0.7 cm is 2.16 cGy, 1.14 cGy and 0.77 cGy for fine normal and coarse modes, respectively. Conclusion CTDIw is a dosimetric index to know the dose levels at center and periphery of patient according to scan length. It gives an idea about how much additional dose is received by the patient during the imaging procedures. High pitch gives the lesser absorbed dose. DLP gives the knowledge about stochastic effects from radiation to patients after MVCT.

Dosimetric benefit and clinical feasibility of deep inspiration breath-hold and volumetric modulated arc therapy-based postmastectomy radiotherapy for left-sided breast cancer

To evaluate the dosimetric benefits and clinical feasibility of deep inspiratory breath-hold (DIBH) combined with volumetric modulated arc therapy (VMAT) in left-sided postmastectomy radiotherapy (PMRT). Eligible patients with left-sided breast cancer undergoing DIBH-based PMRT were prospectively included. Chest wall, supra/infraclavicular fossa, and/or internal mammary node irradiation (IMNI) were planned with a prescription dose of 43.5 Gy in 15 fractions. VMAT plans were designed on free breathing (FB)—and DIBH-CT to compare dosimetric parameters in heart, left anterior descending artery (LAD) and lung. Cone-beam computed tomography (CBCT) was performed before and after treatment to evaluate inter- and intra-fractional setup errors. Heart position and dose variations during treatment were estimated by fusing CBCT with DIBH-CT scans.Twenty patients were included with 10 receiving IMNI. In total, 193 pre-treatment and 39 pairs pre- and post-treatment CBCT scans were analyzed. The Dmean, Dmax, and V5−40 of the heart, LAD, and left lung were significantly lower in DIBH than FB (p < 0.05 for all), except for V5 of LAD (p = 0.167). The cardiopulmonary dosimetric benefits were maintained regardless of IMNI. The inter- and intra-fractional setup errors were < 0.3 cm; and the overall estimated PTV margins were < 1.0 cm. During treatment, the mean dice similarity coefficient of heart position and the mean ratio of heart Dmean between CBCT and DIBH-CT plans was 0.95 (0.88–1.00) and 100% (70.6–119.5%), respectively. DIBH-VMAT could effectively reduce the cardiopulmonary doses with acceptable reproducibility and stability in left-sided PMRT regardless of IMNI.

Dosimetry model for photobiomodulation based on anthropometric and hemodynamic variables in patients with orofacial pain post-Covid-19: Study protocol for randomized clinical trial.

Orofacial pain and tension headache are symptoms that affect a large portion of the population, compromising productivity, social ability, and functional development. The treatment for reducing painful sensation should be chosen carefully, as pharmacological treatment may bring side effects and overload the organism of patients in pain. Low-level laser therapy has been used with local and systemic [vascular] applications for pain control. However, there is still uncertainty in the literature about the ideal dosimetric parameters for photobiomodulation treatment according to patient characteristics. The objective of this project is to validate a dosimetry model based on the relationship between the effects of photobiomodulation with anthropometric and hemodynamic variables, both in local application and systemic application in patients with symptoms of orofacial pain and tension headache. For this purpose, 180 participants with orofacial pain post-covid eligible participants will be randomly assigned to Group 1-Local Photobiomodulation, Group 2-Vascular Photobiomodulation, Group 3-Placebo Local Photobiomodulation, or Group 4-Placebo Vascular Photobiomodulation [Therapy EC-DMC device, São Carlos, Brazil,- 660 nm, 100mW] using stratified block randomization. Before the application, sociodemographic information such as age, skin phototype [classified by the Fitzpatrick scale], weight, height, body mass index [BMI], oxygen saturation [SaO2], blood pressure [BP], heart rate [HR], and thickness of skin, fat, and facial muscles will be collected. During the application, we will collect local temperature, SaO2, BP, and HR. Before and after laser application, blood levels of lactate and hemoglobin, BP, and HR will be measured in the first and last session. In addition to demographic, anthropometric, and hemodynamic variables, the penetrated energy will be quantified using a power meter, and information from orofacial pain and headache symptom questionnaires will be analyzed. The Monte Carlo simulation technique will be used to systematically study the relationship between the light penetration profile into the target tissues and the most relevant variables, namely BMI, tissue layer thicknesses, and skin phototype. Light transmittance, measured in vivo and simulated, will be compared to validate a personalized dosimetry model. The results of this study contribute to validating a Monte Carlo Simulation model to calculate the appropriate dosimetry for photobiomodulation therapies in the control of patients with Post-Covid-19 orofacial pain. Trial registration number: NCT06065969.

Impact of contrast-enhanced CT in the dosimetry of SBRT for liver metastases treated with MR-Linac

BackgroundTo investigate the impact of using contrast-enhanced computed tomography (CHCT) in the dosimetry of stereotactic body radiation therapy (SBRT) for liver metastases treated with MR-Linac.MethodsA retrospective study was conducted on 21 liver cancer patients treated with SBRT (50 Gy in 5 fractions) using a 1.5 Tesla Unity MR-Linac. The clinical treatment plans optimised on plain computed tomography (pCT) were used as reference. The electronic density (ED) of regions of interest (ROIs) including the liver, duodenum, esophagus, spinal cord, heart, ribs, and lungs, from pCT and CHCT, was analysed. The average ED of each ROI from CHCT was used to generate synthetic CT (sCT) images by assigning the average ED value from the CHCT to the pCT. Clinical plans were recalculated on sCT images. Dosimetric comparisons between the original treatment plan (TPpCT) and the sCT plan (TPsCT) were performed using dose-volume histogram (DVH) parameters, and gamma analysis.ResultsSignificant ED differences (p < 0.05) were observed in the liver, great vessels, heart, lungs, and spinal cord between CHCT and pCT, with the lungs showing the largest differences (average deviation of 11.73% and 12.15% for the left and right lung, respectively). The target volume covered by the prescribed dose (VDpre), and the dose received by 2% and 98% of the volume (D2%, and D98%, respectively) showed statistical differences (p < 0.05), while the gradient index (GI) and the conformity index (CI) did not. Average deviations in target volume dosimetric parameters were below 1.02%, with a maximum deviation of 5.57% for. For the organs at risk (OARs), significant differences (p < 0.05) were observed for D0.35cc and D1.2cc of the spinal cord, D10cc for the stomach, D0.5cc for the heart, and D30% for the liver-GTV, with mean deviations lower than 1.83% for all the above OARs. Gamma analysis using 2%-2 mm criteria yielded a median value of 95.64% (range 82.22–99.65%) for the target volume and 99.40% (range 58–100%) for the OARs.ConclusionThe findings suggest that the use of CHCT in the SBRT workflow for liver metastases may result in minor target volume overdosage, indicating its potential for adoption in clinical settings. However, its use should be further explored in a broader context and tied to personalized treatment approaches.

A retrospective comparison of induction chemoimmunotherapy versus chemotherapy followed by concurrent chemoradiotherapy and consolidation immunotherapy in stage III non-small cell lung cancer.

Patients with locally advanced non-small cell lung cancer (LA-NSCLC) usually bear high tumor burden and are not tolerated well to concurrent chemoradiation therapy (CRT) followed by consolidation immunotherapy. We investigated the feasibility of chemoimmunotherapy as induction therapy before CRT for LA-NSCLC. We retrospectively analyzed data from 91 patients with unresectable stage III NSCLC treated with either induction chemoimmunotherapy or chemotherapy before CRT. Tumor responses, survival statistics, and toxic effects were compared. The dosimetric parameters of the RT protocol were evaluated. The primary endpoint was progression-free survival (PFS). The overall response (ORR), the depth of response (DpR) were accessed at the end of CRT (ORRinduc+CRT, DpRinduc+CRT) and induction therapy (ORRinduc, DpRinduc). The median PFS (mPFS) were significantly longer in the chemoimmunotherapy induction group (13.5 months vs. 11.2 months; HR, 0.56; 95% CI, 0.32-0.97; p=0.036). The ORRinduc+CRT, median DpRinduc+CRT (mDpRinduc+CRT) and mDpRinduc were significantly higher in the chemoimmunotherapy induction group (ORRinduc+CRT, 84.0% vs. 65.9%, p=0.044; mDpRinduc+CRT, 49.5% vs. 39.0%, p = 0.012; mDpRinduc, 38.5% vs. 28.0%, p=0.044). Incidence of treatment-related adverse events (AE) was similar between groups, with myelosuppression being the most common grade ≥ 3 AE. Regarding radiotherapy, adopting a mapping strategy with a 5-8 mm margin for clinical tumor volume resulted in decreased radiation doses to critical organs in the chemoimmunotherapy induction group. Chemoimmunotherapy induction therapy before CRT improves efficacy with comparable incidence of AEs compared to chemotherapy induction in LA-NSCLC patients. Further studies are warranted to validate these findings.

Dosimetric Comparison and Selection Criteria of Intensity-Modulated Proton Therapy and Intensity-Modulated Radiation Therapy for Adaptive Re-Plan in T3-4 Nasopharynx Cancer Patients.

Proton therapy requires caution when treating patients with targets near neural structures. Intuitive and quantitative guidelines are needed to support decision-making concerning the treatment modality. This study compared dosimetric profiles of intensity-modulated proton therapy (IMPT) and intensity-modulated radiation therapy (IMRT) using helical tomotherapy (HT) for adaptive re-planning in cT3-4 nasopharyngeal cancer (NPCa) patients, aiming to establish criteria for selecting appropriate treatment modalities. HT and IMPT plans were generated for 28 cT3-4 NPCa patients undergoing definitive radiotherapy. Dosimetric comparisons were performed for target coverage and high-priority organs at risk (OARs). The correlation between dosimetric parameters and RT modality selection was analyzed with the target OAR distances. Target coverages were similar, while IMPT achieved better dose spillage. HT was more favorable for brainstem D1, optic chiasm Dmax, optic nerves Dmax, and p-cord D1. IMPT showed advantages for oral cavity Dmean. Actually, 14 IMPT and 14 HT plans were selected as adaptive plans, with IMPT allocated to most cT3 patients (92.9% vs. 42.9%, p = 0.013). The shortest distances from the target to neural structures were negatively correlated with OAR doses. Receiver operating characteristic curve analyses were carried out to discover the optimal cut-off values of the shortest distances between the target and the OARs (temporal lobes and brainstem), which were 0.75 cm (AUC = 0.908, specificity = 1.00) and 0.85 cm (AUC = 0.857, specificity = 0.929), respectively. NPCa patients with cT4 tumor or with the shortest distance between the target and critical neural structures < 0.8 cm were suboptimal candidates for IMPT adaptive re-planning. These criteria may improve resource utilization and clinical outcomes.

Dosimetric comparison of gamma knife and linear accelerator (VMAT and IMRT) plans of SBRT of Lung tumours

This study evaluates dosimetric differences in Stereotactic Body Radiation Therapy (SBRT) for lung tumors using plans of Gamma Knife, and Volumetric Modulated Arc Therapy (VMAT), Intensity-Modulated Radiation Therapy (IMRT) plans based on Linear Accelerator, aiming to inform the reader of appropriate treatment strategy selection. Ten patients with 23 lung tumor lesions treated with SBRT at Zhongshan Hospital of Dalian University were analyzed. Plans of Gamma Knife, and VMAT, IMRT plans based on Linear Accelerator were created for each lesion, totaling 18 plans per type. Lesions were treated with 30–50 Gy in 5–10 fractions. Dosimetric parameters, including gradient index (GI), heterogeneity index (HI), conformity index (CI), and doses to the plan target volumes (PTVs), the gross tumor volumes (GTVs) and organs at risk (OARs) were compared. Plans of Gamma Knife showed superior HI and GI, higher PTV and GTV doses, and reduced doses to the ipsilateral and contralateral lungs, esophagus, spinal cord, and heart compared to VMAT and IMRT plans (p < 0.05). However, Plans of Gamma Knife required longer delivery times. When comparing VMAT and IMRT plans, VMAT plans had shorter delivery times than IMRT plans, but required more monitor units (MUs). Additionally, IMRT plans delivered a lower mean dose to the ipsilateral lung compared to VMAT plans. Gamma Knife SBRT plans achieves steeper dose falloff and minimizes radiation to normal lung tissue compared to VMAT and IMRT plans, but with longer delivery times. VMAT and IMRT plans displayed similar dose distributions for lung SBRT.

Dose-Volume Constraints Parameters for Lung Tissue in Thoracic Radiotherapy Following Immune Checkpoint Inhibitor Treatment.

This study aims to identify risk factors associated with symptomatic radiation pneumonitis (RP, Grade ≥ 2) following immunotherapy preceding thoracic radiotherapy (ICI-TRT) and establish safe dose constraints. This retrospective study enrolled patients diagnosed with non-small-cell lung cancer (NSCLC) who underwent thoracic radiotherapy (TRT) following immune checkpoint inhibitors (ICIs) treatment. The primary endpoint was the occurrence of symptomatic RP (Grade ≥ 2), as defined by the Common Terminology Criteria for Adverse Events version 5.0. Clinical and lung dosimetric parameters were analyzed to determine their associations with symptomatic RP. Dosimetric parameters included mean lung dose (MLD) and the percentage of lung volume receiving ≥10 Gy (V10), ≥20 Gy (V20), ≥30 Gy (V30), and ≥40 Gy (V40). Receiver operating characteristic curves were used to predict the risk of developing symptomatic RP to establish optimal threshold values for each dosimetric predictor. Among the 118 patients included, the incidence of symptomatic RP was 25.4%. Tumor locations, intervals between immunotherapy and radiotherapy, and MLD, V10, V20, V30, and V40 were identified as independent risk factors for symptomatic RP. The area under the curve (AUC) values for MLD, V10, V20, V30, and V40 were 0.788 (95% confidence interval [CI] 0.704-0.873), 0.789 (95% CI 0.705-0.874), 0.791 (95% CI 0.706-0.876), 0.784 (95% CI 0.697-0.871), and 0.749 (95% CI 0.656-0.842), respectively. The optimal threshold values for MLD, V10, V20, V30, and V40 were 9.7 Gy, 26.3%, 15.9%, 13.3%, and 8.6%, respectively. These thresholds are lower than current guideline recommendations, and maintaining dosimetric parameters below these values resulted in a cumulative symptomatic RP incidence of <12%. The recommended dose thresholds for MLD, V10, V20, V30, and V40 are lower than the current guidelines, underscoring the importance of radiotherapy planning to minimize symptomatic RP occurrence in patients receiving ICI-TRT.

Clinical outcomes and relevance of composite V12 Gy in patients with four or more brain metastases treated with single fraction stereotactic radiosurgery

ObjectiveTissue V12Gy (total brain volume receiving 12Gy including target) can predict for late toxicity in single target benign disease treated with stereotactic radiosurgery(SRS). The value of this metric remains uncertain for multiple brain metastases. This retrospective cohort study reports the outcomes and to evaluate predictors of toxicity in patients with four or more brain metastases treated with single fraction SRS. Methods226 patients with 2160 metastases treated from 2014-21 were retrospectively studied. Symptomatic late toxicity (new/progressive neurological symptoms ≥ 3 months post SRS) with MRI changes suggestive of treatment-effect were analysed. Kaplan-Meier and competing risk analysis was used to assess survival and toxicity respectively. ResultsMedian number of metastases/patient was 6 (range 4-41) and median composite tissue V12Gy (inclusive of PTV) was 11.3cc (IQR 6.1cc - 17.1cc). 16/226 patients developed symptomatic late R-AE and cumulative incidence was 4.9% at 1 year and 6.9% at 2 years. Total target volume was significantly predictive of the risk of late R-AE. Volume of the largest lesion, V12Gy and V15Gy did not predict for late R-AE, but plotted graphs showed suggestions of linear relationships between dosimetric parameters and late R-AE. ConclusionWithin the limitations of this study, the cumulative incidence of symptomatic toxicity remains acceptable despite routinely accepting a composite tissue V12Gy in excess of 10cc to treat multiple brain metastases. Advances in KnowledgeV12Gy has limitations as a plan-quality metric in multiple brain metastases treated with SRS. There is insufficient evidence to have a defined target limit as <10cc.

The influence of pelvic bone dose-volume parameters on bone marrow suppression during radiotherapy in stage I-III rectal cancer patients based on real world data

BackgroundThe aim of this study was to evaluate the impact of pelvic bone dose-volume parameters on bone marrow suppression during radiotherapy (RT) in rectal cancer patients with stage I-III disease receiving either neoadjuvant radiotherapy (neo-RT) or curative-intent radiotherapy (cur-RT). Materials and methodsThis was a retrospective study with data mined from an electronic medical record review at a single institution. Between January 2016 and September 2022, rectal cancer patients who consecutively received neo-RT or cur-RT in our department were included. The data collected included complete baseline peripheral blood counts and hematological toxicity (HT) data collected during RT. The radiation dose-volume parameters of three pelvic bone marrow (PBM) subsites [iliac bone marrow (IBM), lumbosacral bone marrow (LSBM), and lower pelvis bone marrow (LPBM)] were collected. The primary endpoint was grade ≥ 2 HT (HT2+), including leukopenia, neutropenia, anemia, thrombocytopenia and total HTs. Logistic regression was employed to analyze the associations of HT2+ with dosimetric parameters and clinicopathologic characteristics. Receiver operating characteristic (ROC) curves and the area under the curve (AUC) were generated to verify the prediction efficacy of the pelvic bone dose-volume parameters combined with clinicopathologic indices. ResultsA total of 130 patients with stage I-III rectal cancer with complete clinical data were included. During neo-RT and cur-RT, 57 (43.8%) of these patients experienced HT2+. Multivariate analysis revealed that gender, the IBM-Dmean, the IBM-V15 and the IBM-V40 were significantly associated with Grade 2+ leukopenia (P < 0.05), and the AUC of gender combined with the IBM-Dmean, the IBM-V15 and the IBM-V40 in predicting Grade 2+ leukopenia was 0.834. The optimal cutoff values were an IBM-Dmean = 2692.75 cGy, an IBM-V15 = 86.65%, and an IBM-V40 = 20.75%. Patients who received oxaliplatin-containing concurrent chemotherapy (ChT) regimens were more likely to experience Grade 2+ thrombocytopenia (P=0.054). The AUC of concurrent ChT regimens in predicting Grade 2+ thrombocytopenia was 0.678. Female gender was significantly associated with Grade 2+ anemia and total HT2+ status. ConclusionAmong rectal cancer patients with stage I-III disease who received neo-RT or cur-RT, female patients with higher IBM-Dmean, IBM-V15 and IBM-V40 were more likely to experience Grade 2+ leukopenia, and oxaliplatin-containing concurrent ChT regimens were identified as a potential factor for increasing the incidence of Grade 2+ thrombocytopenia.

Verification of mean dose in a tumor using 3D-printed tumor-model scintillators in anthropomorphic phantoms and a spherical phantom

To enhance treatment outcomes of radiotherapy, accurate verification of dosimetric parameters such as the mean, minimum, and maximum doses is essential. This study aimed to measure the mean absorbed dose in a tumor-shaped target and compare the results with the calculated value of the treatment planning system. Tumor model scintillators (TMSs) mimicking brain tumors were fabricated with a commercial 3D printer based on stereolithography files of tumors. The TMSs were irradiated following treatment plans made with the Leksell Gamma Plan® (Elekta AB, Stockholm, Sweden), and the mean dose in each TMS was measured three times and compared with the calculated value. Eleven TMSs were set at the center of a spherical solid water phantom. Two additional TMSs were fabricated according to images of vestibular schwannomas and were set at the tumor location in head model phantoms following each patient's head shape. The mean relative differences between the measured and calculated mean doses were less than one percent. This method provides an independent parameter for evaluating the accuracy of the treatment planning system.

Dosimetric analysis of LAD dose in left-sided breast cancer radiotherapy with deep inspiratory breath hold

Objectives To analyze the dose to the left anterior descending artery (LAD) in patients who have received radiotherapy for left breast cancer with Deep Inspiratory Breath Hold (DIBH) technique and compare it with other cardiac dosimetric parameters, as well as the accepted dose constraints. Materials and Methods 20 patients (10 prospective and 10 retrospective) were selected for this study. All patients underwent 2 non-contrast radiation planning CT scans of 2.5 mm thickness - one with DIBH and one with free breathing. Contouring was done using the Radiation Therapy Oncology Group (RTOG) guidelines. LAD was delineated and given a PRV of 3 mm and 5 mm. Dose-volume histograms (DVH) were used to obtain the data from the approved plans. Results The lung volume receiving 17 Gy in percentage, Dmean of the heart, LAD Dmean and Dmax, and the Dmean and Dmax received by 3 mm and 5 mm PRVs were both very well achieved when compared to the dose constraints given by the DBCG HYPO trial. The study found a higher correlation between the mean heart dose and the 5 mm PRV dose (R2 = 0.81 and 0.71 respectively for the mean and max dose) than the 3 mm PRV, and a positive correlation between the heart dose and LAD making it a useful structure for predicting acute cardiac events. Conclusion The study of 20 patients found that DIBH is effective to minimize cardiac dose and potentially cardiac toxicity, with heart and LAD doses being comparable or lower compared to other studies. The LAD doses recorded were significantly less than those in non-DIBH studies, demonstrating the feasibility of routine contouring and recording LAD dose in left-sided breast radiation patients. Further research is needed to determine the dosimetry and clinical consequences of the Dmean and Dmax of the 5mm PRV to the LAD.

Inverse versus convolution treatment planning algorithms for gamma knife radiosurgery.

To compare the convolution and inverse algorithm plans. The cross-sectional study was conducted from January to May 2022 at the Icon Gamma Knife Centre, Al- Taj Hospital, Baghdad, Iraq, and comprised patients with malignant and benign brain tumours who underwent gamma knife therapy. Each patient's brain was imaged using computed tomography and magnetic resonance imaging. The neurosurgeon prescribed the dose depending on the tumour volume and type, while the medical physicist generated the two plans based on inverse and convolution algorithms. The prescribed dose was delivered to 50% of the isodose line of the tumour. Each plan was evaluated with respect to tumour conformity index, coverage, gradient index, number of shots, and time of treatment. Of the 30 patients, 17(56.7%) were males and 13(43.3%) were females. The overall mean age was 46.29±15.20 years (range: 10-71 years). The mean dose delivered was 15.86±3.86Gy, and the mean number of gamma radiation shots was 12.56±6.95. There was significant difference between the two algorithm plans for all dosimetric parameters, with the inverse plan providing higher coverage and selectivity than convolution plan, but taking longer time(p<0.05), while plan was inverse plan better than convolution plan in terms of gradient and conformity (p<0.05). With more extended treatment, the inverse plan was found to have superior selectivity, coverage, gradient index and Paddick conformity index values compared to the convolution plan.

On the significance of the different geometrical and dosimetric parameters in microbeam and minibeam radiation therapy a retrospective evaluation.

Spatially Fractionated Radiation Therapy (SFRT) is an unconventional therapeutic approach with the potential to disrupt the classical paradigms of conventional radiation therapy. The high spatial dose modulation in SFRT is believed to activate distinct radiobiological mechanisms which lead to remarkable increases in normal tissue tolerance. To make optimal use of SFRT and its benefits, a deeper understanding of the biological response and its relationship with the complex dosimetric and geometric components of SFRT is essential. A retrospective evaluation of preclinical studies was conducted to gain insight into the dosimetric and geometric parameters that are most correlated with normal tissue response. Current literature evaluates the response of tissue to MBRT and MRT according to various end points, e.g. the level of desquamation, degree of necrosis, or the amount of malcalcification. A set of metrics was developed to allow a quantitative comparison of these results. The strongest correlations were observed with the doses in both the peaks and valleys as well as the ratio of the area covered by the peak over the total area. This emphasises the geometry of the beam. MBRT challenged previous uniform dose-distribution paradigms by highlighting the critical role of Peak Dose alongside Valley Dose in tissue sparing whereas MRT underscores the significant influence of geometric beam parameters on tissue preservation. The data exhibits variability in the results obtained using different animal models and endpoints and additional research is warranted to explore the trends observed in this study under controlled conditions.