Intensity-modulated Radiation Therapy Dose Research Articles

Development and Standardization of an Osteoradionecrosis Classification System in Head and Neck Cancer: Implementation of a Risk-Based Model.

Osteoradionecrosis of the jaw (ORN) can manifest in varying severity. The aim of this study is to identify ORN risk factors and develop a novel classification to depict the severity of ORN. Consecutive patients with head and neck cancer (HNC) treated with curative-intent intensity-modulated radiation therapy (IMRT) (≥45 Gy) from 2011 to 2017 were included. Occurrence of ORN was identified from in-house prospective dental and clinical databases and charts. Multivariable logistic regression model was used to identify risk factors and stratify patients into high-risk and low-risk groups. A novel ORN classification system was developed to depict ORN severity by modifying existing systems and incorporating expert opinion. The performance of the novel system was compared with 15 existing systems for their ability to identify and predict serious ORN event (jaw fracture or requiring jaw resection). ORN was identified in 219 of 2,732 (8%) consecutive patients with HNC. Factors associated with high risk of ORN were oral cavity or oropharyngeal primaries, received IMRT dose ≥60 Gy, current/ex-smokers, and/or stage III to IV periodontal condition. The ORN rate for high-risk versus low-risk patients was 12.7% versus 3.1% (P < .001) with an AUC of 0.71. Existing ORN systems overclassified serious ORN events and failed to recognize maxillary ORN. A novel ORN classification system, ClinRad, was proposed on the basis of vertical extent of bone necrosis and presence/absence of exposed bone/fistula. This system detected serious ORN events in 5.7% of patients and statistically outperformed existing systems. We identified risk factors for ORN and proposed a novel ORN classification system on the basis of vertical extent of bone necrosis and presence/absence of exposed bone/fistula. It outperformed existing systems in depicting the seriousness of ORN and may facilitate clinical care and clinical trials.

Prognostic Factors of Mandibular Osteoradionecrosis Including Accurate Colocalization of Avulsions and Dosimetric Dental Mapping Software, a Case-control Study

IntroductionOsteoradionecrosis of the mandible (ORN) remains a significant complication in the intensity modulated radiotherapy (IMRT) era. Dental dose cannot be predicted from heterogeneous IMRT dose distributions; mandibular dose metrics cannot guide dentist avulsion decisions in high risk ORN situations. Using a mapping tool to report dental root dose, avulsions and ORN sites, we reexamined ORN risk factors in a case-control study. MethodsFrom 2008 to 2019, 897 consecutive patients with oral cavity/oropharynx (OC/OR) or unknown primary cancer (CUP) and undergoing IMRT were analyzed to identify ORN cases. These were matched (1 ORN/2 controls) retrospectively for tumor, surgery, tobacco in a monocentric case-control study. Univariate and multivariate analyses integrated ORN factors and accurate dental dose data (grouped into 4 mandibular sectors). Generalizability was investigated in a simulated population database. Results171 patients were included. Median follow-up was 5.2 and 4.5 years in the ORN and control groups, respectively. Median time to ORN was 12 months. In univariate analysis, post-IMRT avulsions at the ORN site (Hazard ratio (HR) = 3.6; 95% confidence interval (CI) = 1.5-8.9; p=0.005), tumor laterality (HR =4.4; 95% CI = 1.4-14, p = 0.01), mean mandibular dose (HR = 1.1; 95% CI = 1.01-1.1; p = 0.018) and mean dose to the ORN site (HR = 1.1; 95% CI = 1.1-1.2; p < 0.001) correlated with higher ORN risk. In multivariate analysis, mean dose to the ORN site (HR = 1.1; 95% CI = 1.1-1.2; p < 0.001) and post-IMRT avulsions at the ORN site (HR = 4.6; 95% CI = 1.5-14.7; p = 0.009) were associated with ORN. For each increase in Gray in dental dose, the ORN risk increased by 12%. Simulations confirmed study observations. ConclusionDental dose and avulsions are associated with ORN with a 12% increase in risk with each additional Gray. Accurate dose information can help dentists in their decisions after IMRT.

Investigation of the effect of bolus on skin dose in breast cancer treatment with tomotherapy and LINAC radiotherapy devices

In postmastectomy radiation therapy (PMRT), it is important that the chest wall skin is included in the target volume and receives an adequate dose. This study aims to investigate the effect of bolus on skin dose in breast cancer treatment with Tomotherapy and LINAC radiotherapy devices and to examine the accuracy of the surface dose calculated by treatment planning system (TPS) with thermoluminescence dosimetry (TLD). Female Alderson Rando Phantom's chest wall is virtually divided into 9 regions. Computed tomography (CT) images of the phantom were obtained with a section thickness of 3 mm. Two plans, with and without bolus, were created for each of the helical tomotherapy (HT), intensity-modulated radiotherapy (IMRT) and field-in-field (FiF) techniques. A bolus thickness of 0.5 cm was used for all bolus plans. Doses calculated from TPSs were obtained for 88 predetermined points on the chest wall. After irradiation, doses measured with TLDs were obtained. The effect of bolus use on the chest wall surface was examined. The increase in surface dose due to bolus use was 50.35%, 55.35% and 68.56% for HT, IMRT and FiF techniques in TPS, respectively. This increase in TLD measurements was 58.18%, 30.90% and 46.31% for HT, IMRT and FiF techniques, respectively. The best agreement between TPS and TLD doses for bolus and non-bolus plans was found in the HT technique. The difference between TPS and TLD doses decreased within the three treatment techniques due to bolus use. Since the chest wall skin cannot receive the required dose in IMRT and FiF techniques, bolus use is recommended until acute skin reactions occur. There is no need to use a bolus for the HT technique.

Effect of Intensity Level on Dose in Intensity-modulated Radiotherapy for Nasopharyngeal Carcinoma

Effect of Intensity Level on Dose in Intensity-modulated Radiotherapy for Nasopharyngeal Carcinoma

Do higher radiation doses improve survival for cervical esophageal squamous cell cancer patients treated with definitive chemoradiotherapy using intensity-modulated radiotherapy? A propensity-score matched analysis.

This study was conducted to determine whether higher doses of intensity-modulated radiotherapy (IMRT) could improve the survival rate in patients of cervical esophageal squamous cell carcinoma (CESCC), and lead to more severe treatment-related toxicity. The clinical records of stage I-IVA CESCC patients treated with definitive chemoradiotherapy (CRT) using IMRT between January 2013 and June 2018 were retrospectively analyzed. The patients in the high-dose (HD) group received ≥60 Gy and those in the standard-dose group received <60 Gy. A propensity score matching (PSM) was applied to balance the confounding factors between both groups. The primary endpoint was over-survival (OS). progression-free survival (PFS), loco-regional control (LRC), and treatment-related toxicity were also evaluated. A total of 136 patients with CESCC were included. Patients with N1-3 nodal and stages III-IVA of the disease (P < 0.05) were included in the HD group. The differences in the OS, PFS, and LRC between the two groups were not statistically significant (P = 0.350, 0.063, and 0.099, respectively). After PSM, significantly longer PFS and LRC were observed in the HD group. The difference in OS between the two groups was not statistically significant. There was no significant difference in the incidence of treatment-related toxicity between the two groups. The results of this PSM analysis suggested that higher doses may improve PFS and LRC for CESCC patients receiving CRT using OMRT, but do not demonstrate any statistically significant advantage in improving OS.

Dosimetric Analysis of Limiting Pelvic Bone Dose in Intensity-modulated Radiotherapy for Cervical Cancer

Numerous studies have indicated the significant importance of pelvic dose in the radiotherapy process for cervical cancer patients. However, research on the actual pelvic bone dose in the treatment of cervical cancer patients using different techniques is currently relatively limited. In this study, we selected 50 postoperative cervical cancer patients. For each patient, three treatment plans with pelvic dose constraints were designed: sIMRT, VMAT, and HT. Statistical analysis was conducted on the target area and organ at risk parameters of the three groups of plans. The results indicate that all three treatment plans meet the clinical requirements. Regarding organs at risk, compared to the sIMRT and VMAT groups, the HT group showed a reduction of 11.85% and 11.07%, respectively, in V40 of bladder. Additionally, compared to the sIMRT and HT groups, the VMAT group exhibited a reduction of 14.94% and 9.53%, respectively, in V10 of pelvic bone. Furthermore, compared to the sIMRT and HT groups, the VMAT group showed a reduction of 10.76% and 6.75%, respectively, in V20 of pelvic bone, and these differences were also statistically significant (t = 21.630, t = –16.621, P &lt; 0.05). In summary, individualized treatment design can be conducted in clinical practice based on the specific conditions of patients.

Combined Radiotherapy Using a Method for Biologically Informed IMRT Planning

Radiotherapy (RT) regimens routinely employ multiple courses that vary by delivery modality and/or fractionation schedule as part of initial or follow up treatment. The combination of RTs ideally should consider the biological effect of the total composite dose distribution. Biological effect can be quantified by biological effective dose (BED) which is a function of the RT modality, dose fractionation, and tissue radiosensitivity. This work describes a method of optimizing a follow up intensity modulated RT (IMRT) plan that considers BED from prior RT. Required inputs for this method are the desired composite BED objectives (BEDref) for target volume(s) and organs at risk (OARs). First, the physical dose in each CT voxel from prior RT (Dprior) is converted to BED (BEDprior). The difference between BEDref and BEDprior gives the optimal BED distribution for the follow up IMRT plan (BEDIMRT). Next, the optimal physical dose (DIMRT) corresponding to BEDIMRT is calculated for each voxel as a function of the number of IMRT fractions (nIMRT). Commercial IMRT treatment planning systems require optimization objectives to be specified for contoured structures, not individual voxels, so a workaround is proposed: 1) for each structure, BEDref is converted to physical dose (Dopti) as a function of nIMRT, and 2) for each voxel, the difference of Dopti and DIMRT is calculated. The result is a "base dose distribution" (Dbase) that is used with standard inverse optimization tools to optimize an IMRT plan so that the sum of Dbase and the IMRT dose approaches Dopti for each voxel. This method was implemented using a custom software workflow to calculate Dbase as a function of Dprior and input BEDref values. Validation was performed by comparing the workflow output with hand calculated Dbase values at randomly selected points within clinically significant regions. Satisfactory agreement was considered to be within 5%. Feasibility of the method was demonstrated using an RT trial protocol for glioblastoma multiforme that combines permanent low dose rate brachytherapy (BT) using collagen tiles embedded with 131Cs seeds and follow-up IMRT (20 fractions). The Dbase distribution was obtained from the software as a function of the BT dose and BEDref for one patient model. Comparison of Dbase values from the software and hand calculated values resulted in agreement within 5% for 22/25 points and within 10% for 3/25 points. Discrepancies >5% (max 9.4%) were attributed to data precision resolution effects inherent in the DICOM standard. The resulting IMRT plan was deemed clinically acceptable and the composite dose distribution achieved dosimetric objectives for all target and OARs. A method for optimizing a follow up IMRT plan that considers dose from prior RT to produce a desired composite BED distribution was derived and proof of concept was successfully demonstrated. Further validation of this method with additional patients and multimodality RT protocols will be performed.

Evaluation of the effect of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc radiotherapy (VMAT) techniques on survival response in cell lines with a new radiobiological modeling.

The optimal radiobiological model, which assesses the biological effects of novel radiotherapy techniques that concurrently modify multiple physical factors, has not yet been defined. This study aimed to investigate the impact of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) on cellular response in head and neck cancer and melanoma models. Clonogenic analysis, DNA double-strand break analysis, apoptosis, and cell cycle analysis were performed on cancer stem cell models, cancer models, and normal tissue cell models to assess radiation sensitivity. The segmented radiation approach used in IMRT applications enhanced radiosensitivity and cytotoxicity in the cancer models, while changes in dose rate had varying effects on cytotoxicity depending on the tumor cell type. VMAT increased cellular resistance, favoring treatment outcomes. The biological processes were influenced differently by dose rate, IMRT, and VMAT depending on the tumor cell type. The selection of the most appropriate technique is crucial in representing new radiotherapy approaches. The obtained data can serve as a model to address clinical questions in daily practice. The integration of non-standard outcomes with standard applications should be considered in clinical settings.

Accounting for fractionation and heterogeneous dose distributions in the modelling of osteoradionecrosis in oropharyngeal carcinoma treatment

Background and purposeOsteoradionecrosis (ORN) of the mandible is a severe complication following radiotherapy (RT). With a renewed interest in hypofractionation for head and neck radiotherapy, more information concerning ORN development after high fraction doses is important. The aim of this explorative study was to develop a model for ORN risk prediction applicable across different fractionation schemes using Equivalent Uniform Doses (EUD). Material and methodsWe performed a retrospective cohort study in 334 oropharyngeal squamous cell carcinoma (OPSCC) patients treated with either a hypofractionated Stereotactic Body Radiation Therapy (HF-SBRT) boost or conventional Intensity Modulated Radiation Therapy (IMRT). ORN was scored with the CTCAE v5.0. HF-SBRT and IMRT dose distributions were converted into equivalent dose in 2 Gy fractions (α/β = 0.85 Gy) and analyzed using EUD. The parameter a that led to an EUD that best discriminated patients with and without grade ≥ 2 ORN was selected. Patient and treatment-related risk factors of ORN were analyzed with uni- and multivariable regression analysis. ResultsA total of 32 patients (9.6%) developed ORN grade ≥ 2. An EUD(a = 8) best discriminated between ORN and non-ORN (AUC = 0.71). In multivariable regression, pre-RT extractions (SHR = 2.34; p = 0.012), mandibular volume (SHR = 1.04; p = 0.003), and the EUD(a = 8) (SHR = 1.14; p < 0.001) were significantly associated with ORN. ConclusionRisk models for ORN based on conventional DVH parameters cannot be directly applied to HF-SBRT fractionation schemes and dose distributions. However, after correcting for fractionation and non-uniform dose distributions using EUD, a single model can distinguish between ORN and non-ORN after conventionally fractionated radiotherapy and hypofractionated boost treatments.

Performance assessment of variant UNet-based deep-learning dose engines for MR-Linac-based prostate IMRT plans

Objective. UNet-based deep-learning (DL) architectures are promising dose engines for traditional linear accelerator (Linac) models. Current UNet-based engines, however, were designed differently with various strategies, making it challenging to fairly compare the results from different studies. The objective of this study is to thoroughly evaluate the performance of UNet-based models on magnetic-resonance (MR)-Linac-based intensity-modulated radiation therapy (IMRT) dose calculations. Approach. The UNet-based models, including the standard-UNet, cascaded-UNet, dense-dilated-UNet, residual-UNet, HD-UNet, and attention-aware-UNet, were implemented. The model input is patient CT and IMRT field dose in water, and the output is patient dose calculated by DL model. The reference dose was calculated by the Monaco Monte Carlo module. Twenty training and ten test cases of prostate patients were included. The accuracy of the DL-calculated doses was measured using gamma analysis, and the calculation efficiency was evaluated by inference time. Results. All the studied models effectively corrected low-accuracy doses in water to high-accuracy patient doses in a magnetic field. The gamma passing rates between reference and DL-calculated doses were over 86% (1%/1 mm), 98% (2%/2 mm), and 99% (3%/3 mm) for all the models. The inference times ranged from 0.03 (graphics processing unit) to 7.5 (central processing unit) seconds. Each model demonstrated different strengths in calculation accuracy and efficiency; Res-UNet achieved the highest accuracy, HD-UNet offered high accuracy with the fewest parameters but the longest inference, dense-dilated-UNet was consistently accurate regardless of model levels, standard-UNet had the shortest inference but relatively lower accuracy, and the others showed average performance. Therefore, the best-performing model would depend on the specific clinical needs and available computational resources. Significance. The feasibility of using common UNet-based models for MR-Linac-based dose calculations has been explored in this study. By using the same model input type, patient training data, and computing environment, a fair assessment of the models’ performance was present.

Learning curve of lung dose optimization in intensity-modulated radiotherapy for locally advanced non-small cell lung cancer.

Intensity-modulated radiotherapy (IMRT) has been increasingly used for patients with locally advanced non-small cell lung cancer (LA-NSCLC). However, there are some barriers to implementing IMRT for LA-NSCLC, including the complexity of treatment plan optimization. This study aimed to evaluate the learning curve of lung dose optimization in IMRT for LA-NSCLC and identify the factors that affect the degree of achievement of lung dose optimization. We retrospectively evaluated 40 consecutive patients with LA-NSCLC who received concurrent chemoradiotherapy at our institution. These 40 patients were divided into two groups: 20 initially treated patients (earlier group) and 20 subsequently treated patients (later group). Patient and tumor characteristics were compared between the two groups. The dose-volume parameter ratio between the actually delivered IMRT plan and the simulated three-dimensional conformal radiotherapy plan was also compared between the two groups to determine the learning curve of lung dose optimization. The dose-volume parameter ratio for lung volume to receive more than 5 Gy (lung V5) and mean lung dose (MLD) significantly decreased in later groups. The spread of the beam path and insufficient optimization of dose coverage of planning target volume (PTV) might cause poor control of lung V5, MLD. A learning curve for lung dose optimization was observed with the accumulation of experience. Appropriate techniques, such as restricting the beam path and ensuring dose coverage of PTV during the optimization process, are essential to control lung dose in IMRT for LA-NSCLC.

A Prospective Study of Intensity-modulated Radiation Therapy Using a Standard Radiation Dose for High-grade Glioma.

We evaluated the treatment outcomes of intensity-modulated radiation therapy (IMRT) using a standard radiation dose in patients with high-grade glioma (HGG). We conducted a prospective, single-institutional, single-arm trial. Patients aged 20-75 years with histologically proven HGG were enrolled. Surgical procedures and chemotherapy regimens were not regulated. The prescribed dose of postoperative IMRT was 60 Gy in 30 fractions over six weeks. The primary endpoint was overall survival (OS). Secondary endpoints were progression-free survival (PFS), completion rate of IMRT, and Grade 3 or higher non-hematological toxicity. Between 2016 and 2019, 20 patients were enrolled. According to the World Health Organization 2016 Classification, glioblastoma, anaplastic astrocytoma, and anaplastic oligodendroglioma were present in nine, six, and five of the recruited patients, respectively. Gross total resection, partial resection, and biopsy were performed in four, nine, and seven patients, respectively. All patients received concurrent and adjuvant chemotherapy using temozolomide with or without bevacizumab. The completion rate of IMRT was 100%. The median follow-up period was 29 months (range=6-68 months). Median OS and PFS were 30 and 14 months, respectively. No patients experienced Grade 3 or higher non-hematological toxicity. The 2-year OS rates were 100%, 57%, and 33% in Radiation Therapy Oncology Group-Recursive Partitioning Analysis (RTOG-RPA) classes I/II, IV, and V, respectively (p=0.002; log-rank test). IMRT using the standard radiation dose in patients with HGG can be carried out safely. RTOG-RPA class appears to be useful to estimate patient prognoses.

Commissioning and dosimetric validation of a novel compensator-based Co-60 IMRT system for evaluating suitability to automated treatment planning.

A novel compensator-based system has been proposed which delivers intensity-modulated radiation therapy (IMRT) with cobalt-60 beams. This could improve access to advanced radiotherapy in low- and middle-income countries. For this system to be clinically viable and to be adapted into the Radiation Planning Assistant (RPA), being developed to offer automated planning services in low- and middle-income countries, it is necessary to commission and validate it in a commercial treatment planning system (TPS). The novel treatment device considered here employs a cobalt-60 source and nine compensators. Each compensator is produced by 3-D printing a thin plastic mold which is then filled on-demand within the machine with reusable 2-mm-diameter spherical tungsten balls. This system was commissioned in the Eclipse TPS and validation tests were conducted with Monte Carlo using Geant4 Application for Tomographic Emission for percentage depth dose, in-plane profiles, penumbra, and IMRT dose validation. And the American Association of Physicists in Medicine Task Group 119 benchmarking testing was performed. Additionally, compensator-based cobalt-60 IMRT plans were created for 46 head-and-neck cancer cases and compared to the linac-based volumetric modulated arc therapy (VMAT) plans used clinically, then dosimetric parameters were evaluated. Beam-on time for each field was calculated. In addition, the measurement was also performed in a limited environment and compared with the Monte Carlo simulations. The differences in percent depth doses and in-plane profiles between the Eclipse and Monte Carlo simulations were 0.65%±0.41% and 1.02%±0.99%, respectively, and the 80%-20% penumbra agreed within 0.46±0.27mm. For the Task Group 119 validation plans, all treatment planning goals were met and gamma passing rates were>95% (3%/3mm criteria). In 46 clinical head-and-neck cases, the cobalt-60 compensator-based IMRT plans had planning target volume (PTV) coverages similar to linac-based VMAT plans: all dosimetric values for PTV were within 1.5%. The organs at risk dose parameters were somewhat higher in cobalt-60 compensator-based IMRT plans versus linac-based VMAT plans. The mean dose differences for the spinal cord, brain, and brainstem were 4.43±1.92, 3.39±4.67, and 2.40±3.71Gy, while those for the rest of the organs were<1Gy. The average beam-on time per field was 0.42±0.10min for the 6 MV multi-leaf-collimator plans while those for the cobalt-60 compensator plans were 0.17±0.01 and 0.31±0.01min at the dose rates of 350 and 175 cGy/min. There was a good agreement between in-plane profiles from measurements and Monte Carlo simulations, which differences are 1.34±1.90% and 0.13±2.16% for two different fields. A novel compensator-based IMRT system using cobalt-60 beams was commissioned and validated in a commercial TPS. Plan quality with this system was comparable to that of linac-based plans in all test cases with shorter estimated beam-on times. This system enables reliable, high-quality plans with reduced cost and complexity and may have benefits for underserved regions of the world. This system is being integrated into the RPA, a web-based platform for auto-contouring and auto-planning.

Non-classic radiation-induced liver disease after intensity-modulated radiotherapy for Child–Pugh grade B patients with locally advanced hepatocellular carcinoma

BackgroundThe incidence of classic radiation-induced liver disease (cRILD) has been significantly reduced. However, non-classic radiation-induced liver disease (ncRILD) remains a major concern following radiotherapy in patients with hepatocellular carcinoma (HCC). This study evaluated the incidence of ncRILD following intensity-modulated radiotherapy (IMRT) for Child–Pugh grade B (CP-B) patients with locally advanced HCC and established a nomogram for predicting ncRILD probability.MethodsSeventy-five CP-B patients with locally advanced HCC treated with IMRT between September 2014 and July 2021 were included. The max tumor size was 8.39 cm ± 5.06, and the median prescribed dose was 53.24 Gy ± 7.26. Treatment-related hepatotoxicity was evaluated within three months of completing IMRT. A nomogram model was formulated to predict the probability of ncRILD, using univariate and multivariate analysis.ResultsAmong CP-B patients with locally advanced HCC, ncRILD occurred in 17 (22.7%) patients. Two patients (2.7%) exhibited a transaminase elevation of ≥ G3, fourteen (18.7%) exhibited a Child–Pugh score increase of ≥ 2, and one (1.3%) demonstrated both a transaminase elevation of ≥ G3 and a Child–Pugh score increase of ≥ 2. No cRILD cases were observed. A mean dose to the normal liver of ≥ 15.1 Gy was used as the cutoff for ncRILD. Multivariate analysis revealed that the prothrombin time before IMRT, tumour number, and mean dose to the normal liver were independent risk factors for ncRILD. The nomogram established on the basis of these risk factors displayed exceptional predictive performance (AUC = 0.800, 95% CI 0.674–0.926).ConclusionsThe incidence of ncRILD following IMRT for CP-B patients with locally advanced HCC was acceptable. A nomogram based on prothrombin time before IMRT, tumour number, and mean dose to the normal liver accurately predicted the probability of ncRILD in these patients.

Dosimetric analysis of Rapid Arc (VMAT) treatment planning in head and neck cancer for quality assurance treatment

The current investigation aimed to compare the treatment plans of simultaneous integrated boost (SIB) fixed intensity modulated radiation therapy (IMRT) and SIB RapidArc (RA) using a number of dosimetric indices. In this study, 29 patients of nasopharyngeal carcinoma (NPC) were considered for treatment plan evaluation of SIB RA and SIB IMRT. The plans were evaluated using conformity index (CI), target coverage (TC), gradient index (GI), external volume Index (EI), homogeneity index (HI), dose heterogeneity index (DHI), standard deviation (SD), and unified dosimetric index (UDI). The dose of each planned target volume (PTV) and organs at risk (OARs) was determined using their respective mean and median doses. In accordance with the results, there is no noticeable difference in the values of CI, TC, GI, EI, and UDI for SIB RA and SIB IMRT. DHI of PTV 54 is better for SIB IMRT as compared to SIB RA and DHI of PTV 60, PTV 70 is same for both techniques. HI, SD and sparing of OARs results in better values for SIB RA as compared to SIB IMRT. However, PTV 54 and PTV 60′s doses indicate over dosage. The dose of PTV 70 is found to be within the limits of prescribed dose for both SIB RA and SIB IMRT. SIB RA homogeneity, sparing of OAR, and SD are observed to be superior to SIB IMRT. In the case of RA, less time and a monitor unit are used. In conclusion, SIB RA is thought to be better than SIB IMRT for the treatment of NPC.

Treatment planning with a 2.5MV photon beam for radiation therapy.

The shallow depth of maximum dose and higher dose fall-off gradient of a 2.5MV beam along the central axis that is available for imaging on linear accelerators is investigated for treatment of shallow tumors and sparing the organs at risk (OARs) beyond it. In addition, the 2.5MV beam has an energy bridging the gap between kilo-voltage (kV) and mega-voltage (MV) beams for applications of dose enhancement with high atomic number (Z) nanoparticles. We have commissioned and utilized a MATLAB-based, open-source treatment planning software (TPS), matRad, for intensity-modulated radiation therapy (IMRT) dose calculations. Treatment plans for prostate, liver, and head and neck (H&N), nasal cavity, two orbit cases, and glioblastoma multiforme (GBM) were performed and compared to a conventional 6MV beam. Additional Monte Carlo calculations were also used for benchmarking the central axis dose. Both beams had similar planning target volume (PTV) dose coverage for all cases. However, the 2.5MV beam deposited 6%-19% less integral doses to the nasal cavity, orbit, and GBM cases than 6MV photons. The mean dose to the heart in the liver plan was 10.5% lower for 2.5MV beam. The difference between the doses to OARs of H&N for two beams was under 3%. Brain mean dose, brainstem, and optic chiasm max doses were, respectively, 7.5%-14.9%, 2.2%-8.1%, and 2.5%-19.0% lower for the 2.5MV beam in the nasal cavity, orbit, and GBM plans. This study demonstrates that the 2.5MV beam can produce clinically relevant treatment plans, motivating future efforts for design of single-energy LINACs. Such a machine will be capable of producing beams at this energy beneficial for low- and middle-income countries, and investigations on dose enhancement from high-Z nanoparticles.

Non-Classic Radiation-Induced Liver Disease after Intensity-Modulated Radiotherapy for Hepatocellular Carcinoma with Child–Pugh Grade B

<h3>Purpose/Objective(s)</h3> While the incidence of classic radiation-induced liver disease (cRILD) has been significantly reduced, non-classic radiation-induced liver disease (ncRILD) is still considered as the major limitation that affects the efficacy of radiotherapy (RT) for hepatocellular carcinoma (HCC) patients at present. The purpose of this study was to evaluate the incidence of ncRILD following intensity-modulated radiotherapy (IMRT) in HCC patients with Child–Pugh grade B and establish the nomogram for ncRILD predication. <h3>Materials/Methods</h3> Between September 2014 and July 2021, a total of 75 HCC patients with Child–Pugh grade B treated by IMRT were included. Treatment-related hepatotoxicity was evaluated within 3-month post to the completing RT. In this study, nomogram model was formulated to predict probability of ncRILD in univariate and multivariate analysis. <h3>Results</h3> ncRILD occurred in 17 patients (22.7%). Two of the patients (2.7%) had ≥ G3 transaminase elevation, 14 (18.7%) had a Child–Pugh score increase ≥ 2, and the remaining patient (1.3%) had ≥ G3 transaminase elevation and simultaneous Child–Pugh score increase ≥ 2. No cases of cRILD were observed. A mean dose ≥ 15.1 Gy to the normal liver for ncRILD was the cut-off. Multivariate analysis revealed that prothrombin time before IMRT, tumor number, and mean dose to the normal liver were independent risk factors for ncRILD. The nomogram based on these risk factors displayed exceptional prediction performance (AUC = 0.800, 95% CI, 0.674-0.926). <h3>Conclusion</h3> The incidence of ncRILD following IMRT for HCC patients with Child–Pugh grade B was acceptable. The nomogram based on prothrombin time before RT, tumor number and mean dose to the normal liver showed accurate prediction for the probability of ncRILD in these patients.

Osteoradionecrosis in head and neck cancer patients: Risk factors and comparison of grading systems.

e18057 Background: We aimed to identify the incidence and risk factors for osteoradionecrosis (ORN) in head and neck cancer (HNC) patients. We also compared frequency of severity scores across different ORN grading systems. Methods: Retrospective review was conducted for HNC patients who were managed at our institution (2011-2018) with curative-intent definitive, pre- or post-operative intensity-modulated radiation therapy (IMRT) with 45Gy, and underwent pre-IMRT dental evaluation. Jaw ORN was defined based on: 1) clinical signs (exposed bone, bone spicules, sequestra, infection and fistula), 2) radiological finding (abnormal bone pattern, radiographic sequestra and pathological fracture), and 3) treatment required and response to therapy, either conservative (chlorhexidine rinse, antibiotics, PENTOCLO, and hyperbaric oxygen) or surgical (sequestrectomy, debridement, and jaw resection). ORN events were retrospectively graded using 6 different grading systems. Pre-IMRT periodontal condition (PC) was classified by universal multi-dimensional staging system based on number of teeth and bone loss (stages 0 to IV). Multivariable analysis (MVA) using logistic regression was applied to identify risk factors of ORN. Results: A total of 2735 HNC patients were included; median age 61 years, 30% (n = 807) current/ex-smokers, 72% (n = 1914) had moderate to severe PC (stage II-IV), 53% (n = 1459) oral cavity/oropharynx (OC/OP) primary tumor. The median IMRT dose was 70Gy/35 fractions, 43% (n = 1170) received concurrent chemotherapy, and 37% (n = 1006) underwent surgery. A total of 227 patients (8.3%) developed ORN. There was discrepancy in different grading system for capturing and reporting the degree of severity (i.e. grade) of ORN (table). On MVA, risk factors for ORN were: current/ex-smoker (OR 1.5, 95% CI: 1.12-2, p&lt; 0.01), stage II-IV PC (OR 1.7, 95% CI: 1.17-2.36, p&lt; 0.01), primary OC/OP tumor (OR 4.4, 95% CI: 3.08-6.29, p&lt; 0.001], and IMRT dose prescription ≥60Gy (OR 3.5, 95%CI: 1.11-11.33, p&lt; 0.01). Conclusions: ORN is relatively uncommon in HNC patients, however it can be under-reported by different grading systems. Risk factors for ORN were: smoking history, pre-IMRT poor PC condition, OC/OP primary tumor, and higher dose (≥60Gy) IMRT.[Table: see text]

Does CyberKnife improve dose distribution versus IMRT and VMAT on a linear accelerator in low-risk prostate cancer?

BackgroundHypofractionated stereotactic body radiation therapy (SBRT) for prostate cancer (PCa) can be delivered with the robot-assisted CyberKnife (CK) system or on a linear accelerator using dynamic intensity-modulated radiotherapy (IMRT) or volumetric arc radiotherapy (VMAT). This retrospective study was performed to determine whether CK offers better dose distribution than IMRT and/or VMAT.Materials and methodsTreatment plans for three techniques were prepared using the same treatment parameters (36.35 Gy, 7.25 Gy/fr). We evaluated target coverage, conformity index (CI), homogeneity index (HI), gamma index (GI), and organs at risk (OAR) constraints.ResultsThe mean planning target volume (PTV) dose for CK (39.58 Gy) was significantly greater than VMAT or IMRT (both 36.25 Gy). However, CK resulted in a wider dose range (31.48 to 45.89 Gy) vs. VMAT and IMRT (34.6–38.76 Gy). The mean dose to the rectum (V36Gy, mm3) was significantly lower (p < 0.001) in the CK plans (219.78 vs. 519.59 and 422.62, respectively). The mean bladder dose (V37Gy, mm3) was significantly greater for CK (3256 vs. 1090.75 for VMAT and 4.5 for IMRT (p < 0.001). CK yielded significantly better CI (1.07 vs. 1.17 and 1.25 for VMAT and IMRT, respectively; p < 0.01) and HI values (1.27 vs. 1.07 and 1.04; p < 0.01). GI values for the δd = 3mm, δ% = 3% criteria were 99.86 (VMAT), 99.07 (IMRT) and 99.99 (CK). For δd = 2mm, δ% = 2%, the corresponding values were 98.3, 93.35, and 97.12, respectively.ConclusionsFor most variables, CK was superior to both VMAT and IMRT. However, dynamic IMRT techniques, especially VMAT, do not differ significantly from CK plans and are therefore acceptable alternatives to CyberKnife.

Intensity-Modulated Radiotherapy with Regional Hyperthermia for High-Risk Localized Prostate Carcinoma.

Simple SummarySeveral randomized controlled trials have shown that concurrent use of deep regional hyperthermia and radiotherapy results in a significant increase in local control of cervical and rectal cancer. Intensity-modulated radiotherapy (IMRT) plus androgen deprivation therapy (ADT) has recently become standard treatment for high-risk localized prostate carcinoma; however, as there is room for improvement in outcomes, we have been using hyperthermia to improve the effect of IMRT. This retrospective analysis shows that addition of regional hyperthermia to IMRT plus ADT is a promising approach as it improves clinical outcomes with acceptable toxicity. Importantly, a higher thermal dose was significantly correlated with better biochemical disease-free survival. Further investigations, including prospective trials with detailed treatment protocols, are needed.Background: The purpose of this study was to evaluate the efficacy and toxicity of adding regional hyperthermia to intensity-modulated radiotherapy (IMRT) plus neoadjuvant androgen deprivation therapy (ADT) for high-risk localized prostate carcinoma. Methods: Data from 121 consecutive patients with high-risk prostate carcinoma who were treated with IMRT were retrospectively analyzed. The total planned dose of IMRT was 76 Gy in 38 fractions for all patients; hyperthermia was used in 70 of 121 patients. Intra-rectal temperatures at the prostate level were measured to evaluate thermal dose. Results: Median number of heating sessions was five and the median total thermal dose of CEM43T90 was 7.5 min. Median follow-up duration was 64 months. Addition of hyperthermia to IMRT predicted better clinical relapse-free survival. Higher thermal dose with CEM43T90 (>7 min) predicted improved biochemical disease-free survival. The occurrence of acute and delayed toxicity ≥Grade 2 was not significantly different between patients with or without hyperthermia. Conclusions: IMRT plus regional hyperthermia represents a promising approach with acceptable toxicity for high-risk localized prostate carcinoma. Further studies are needed to verify the efficacy of this combined treatment.