Enhancing Precision in Radiotherapy Delivery: Validating Monte Carlo Simulation Models for 6 MV Elekta Synergy Agility LINAC Photon Beam Using Two Models of the GAMOS Code

The most crucial requirement in radiation therapy treatment planning is a fast and accurate treatment planning system that minimizes damage to healthy tissues surrounding cancer cells. The use of Monte Carlo toolkits has become indispensable for research aimed at precisely determining the dose in radiotherapy. Among the numerous algorithms developed in recent years, the GAMOS code, which utilizes the Geant4 toolkit for Monte Carlo simula-tions, incorporates various electromagnetic physics models and multiple scattering models for simulating particle interactions with matter. This makes it a valuable tool for dose calculations in medical applications and throughout the patient’s volume. The aim of this present work aims to vali-date the GAMOS code for the simulation of a 6 MV photon-beam output from the Elekta Synergy Agility linear accelerator. The simulation involves mod-eling the major components of the accelerator head and the interactions of the radiation beam with a homogeneous water phantom and particle information was collected following the modeling of the phase space. This space was po-sitioned under the X and Y jaws, utilizing three electromagnetic physics mod-els of the GAMOS code: Standard, Penelope, and Low-Energy, along with three multiple scattering models: Goudsmit-Saunderson, Urban, and Wentzel-VI. The obtained phase space file was used as a particle source to simulate dose distributions (depth-dose and dose profile) for field sizes of 5 × 5 cm2 and 10 × 10 cm2 at depths of 10 cm and 20 cm in a water phantom, with a source-surface distance (SSD) of 90 cm from the target. We compared the three electromagnetic physics models and the three multiple scattering mod-els of the GAMOS code to experimental results. Validation of our results was performed using the gamma index, with an acceptability criterion of 3% for the dose difference (DD) and 3 mm for the distance-to-agreement (DTA). We achieved agreements of 94% and 96%, respectively, between simulation and experimentation for the three electromagnetic physics models and three mul-tiple scattering models, for field sizes of 5 × 5 cm2 and 10 × 10 cm2 for depth-dose curves. For dose profile curves, a good agreement of 100% was found between simulation and experimentation for the three electromagnetic physics models, as well as for the three multiple scattering models for a field size of 5 × 5 cm2 at 10 cm and 20 cm depths. For a field size of 10 × 10 cm2, the Penelope model dominated with 98% for 10 cm, along with the three multiple scattering models. The Penelope model and the Standard model, along with the three multiple scattering models, dominated with 100% for 20 cm. Our study, which compared these different GAMOS code models, can be crucial for enhancing the accuracy and quality of radiotherapy, contributing to more effective patient treatment. Our research compares various electro-magnetic physics models and multiple scattering models with experimental measurements, enabling us to choose the models that produce the most reli-able results, thereby directly impacting the quality of simulations. This en-hances confidence in using these models for treatment planning. Our re-search consistently contributes to the progress of Monte Carlo simulation techniques in radiation therapy, enriching the scientific literature.

Prognostic factors and failure patterns in non-metastatic nasopharyngeal carcinoma after intensity-modulated radiotherapy

Background: The prognostic values of staging parameters require continual re?assessment amid changes in diag?nostic and therapeutic methods. This study aimed to identify the prognostic factors and failure patterns of non?meta?static nasopharyngeal carcinoma(NPC) in the intensity?modulated radiotherapy(IMRT) era.Methods: We reviewed the data from 749 patients with newly diagnosed, biopsy?proven, non?metastatic NPC in our cancer center(South China, an NPC endemic area) between January 2003 and December 2007. All patients under?went magnetic resonance imaging(MRI) before receiving IMRT. The actuarial survival rates were estimated using the Kaplan–Meier method, and survival curves were compared using the log?rank test. Multivariate analyses with the Cox proportional hazards model were used to test for the independent prognostic factors by backward eliminating insigniicant explanatory variables.Results: The 5?year occurrence rates of local failure, regional failure, locoregional failure, and distant failure were 5.4, 3.0, 7.4, and 17.4%, respectively. The 5?year survival rates were as follows: local relapse?free survival, 94.6%; nodal relapse?free survival, 97.0%; distant metastasis?free survival, 82.6%; disease?free survival, 75.1%; and overall survival, 82.0%. Multivariate Cox regression analysis revealed that orbit involvement was the only signiicant prognostic fac?tor for local failure(P = 0.011). Parapharyngeal tumor extension, retropharyngeal lymph node involvement, and the laterality, longest diameter, and Ho's location of the cervical lymph nodes were signiicant prognostic factors for both distant failure and disease failure(all P < 0.05). Intracranial extension had signiicant prognostic value for distant failure(P = 0.040).Conclusions: The key failure pattern for NPC was distant metastasis in the IMRT era. With changes in diagnostic and therapeutic technologies as well as treatment modalities, the signiicant prognostic parameters for local control have also been altered substantially.

Prognostic value and predictive threshold of tumor volume for patients with locally advanced nasopharyngeal carcinoma receiving intensity-modulated radiotherapy

Background: Gross target volume of primary tumor(GTV?P) is very important for the prognosis prediction of patients with nasopharyngeal carcinoma(NPC), but it is unknown whether the same is true for locally advanced NPC patients treated with intensity?modulated radiotherapy(IMRT). This study aimed to clarify the prognostic value of tumor volume for patient with locally advanced NPC receiving IMRT and to ind a suitable cut?of value of GTV?P for prognosis prediction.Methods: Clinical data of 358 patients with locally advanced NPC who received IMRT were reviewed. Receiver oper?ating characteristic(ROC) curves were used to identify the cut?of values of GTV?P for the prediction of diferent end?points [overall survival(OS), local relapse?free survival(LRFS), distant metastasis?free survival(DMFS), and disease?free survival(DFS)] and to test the prognostic value of GTV?P when compared with that of the American Joint Committee on Cancer T staging system.Results: The 358 patients with locally advanced NPC were divided into two groups by the cut?of value of GTV?P as determined using ROC curves: 219(61.2%) patients with GTV?P ≤46.4 mL and 139(38.8%) with GTV?P >46.4 mL. The 3?year OS, LRFS, DMFS, and DFS rates were all higher in patients with GTV?P ≤46.4 mL than in those with GTV?P > 46.4 mL(all P < 0.05). Multivariate analysis indicated that GTV?P >46.4 mL was an independent unfavorable prognostic factor for patient survival. The ROC curve veriied that the predictive ability of GTV?P was superior to that of T category(P < 0.001). The cut?of values of GTV?P for the prediction of OS, LRFS, DMFS, and DFS were 46.4, 57.9, 75.4 and 46.4 mL, respectively.Conclusion: In patients with locally advanced NPC, GTV?P >46.4 mL is an independent unfavorable prognostic indi?cator for survival after IMRT, with a prognostic value superior to that of T category.

Significant value of 18F-FDG-PET/CT in diagnosing small cervical lymph node metastases in patients with nasopharyngeal carcinoma treated with intensity-modulated radiotherapy

Background: Little is known about the nature of metaistasis to small cervical lymph nodes(SCLNS) in the patients with nasopharyngeal carcinoma(NPC)examined by using 18-fluoro-2-deoxy-glucose(^(18)F-FDG) positron emission tomography/computed tomography(PET/CT).The present study aimed to evaluate the diagnostic values of PET/CT in identifying metastasis in SCLNs in NPC patients.Methods: Magnetic resonance images(MRI) and PET/CT scans for 470 patients with newly diagnosed, non-distant metastatic NPC were analyzed. Metastatic rates of SCLNs were defined by the positive number of SCLNs on PET/CT scans and total number of SCLNs on MRI scans. Receiver operating characteristic curve was applied to compare PET/CT-determined stage with MRI-determined stage.Results: In total, 2082 SCLNs were identified, with 808(38.8%) ≥ 5 and < 6 mm in diameter(group A), 526(25.3%)≥ 6 and < 7 mm in diameter(group B),374(18.0%)≥ 7 and < 8 mm in diameter(group C), 237(11.4%) ≥8 and<9 mm in diameter(group D),and 137(6.5%) ≥ 9 and <10 mm in diameter(group E).The overall metastatic rates examined by using PET/CT for groups A, B,C,D, and E were 3.5%, 8.0%, 31.3%, 60.0%, and 83.9%, respectively(P< 0.001). In level IV/Vb, the metastatic rate for nodes ≥ 8 mm was 84.6%. PET/CT examination resulted in modification of N category and overall stage for 135(28.7%) and 46(9.8%) patients, respectively. The areas under curve of MRIdetermined and PET/CT-determined overall stage were 0.659 and 0.704 for predicting overall survival, 0.661 and 0.711 for predicting distant metastasis-free survival, and 0.636 and 0.663 for predicting disease-free survival.Conclusions: PET/CT was more effective than MRI in identifying metastatic SCLNs, and the radiologic diagnostic criteria for metastatic lymph nodes in level IV/Vb should be re-defined.

A model to predict the risk of lethal nasopharyngeal necrosis after re-irradiation with intensity-modulated radiotherapy in nasopharyngeal carcinoma patients

Background:For patients with nasopharyngeal carcinoma(NPC) who undergo re-irradiation with intensity-modulated radiotherapy(IMRT),lethal nasopharyngeal necrosis(LNN) is a severe late adverse event.The purpose of this study was to identify risk factors for LNN and develop a model to predict LNN after radical re-irradiation with IMRT in patients with recurrent NPC.Methods:Patients who underwent radical re-irradiation with IMRT for locally recurrent NPC between March 2001 and December 2011 and who had no evidence of distant metastasis were included in this study.Clinical characteristics,including recurrent carcinoma conditions and dosimetric features,were evaluated as candidate risk factors for LNN.Logistic regression analysis was used to identify independent risk factors and construct the predictive scoring model.Results:Among 228 patients enrolled in this study,204 were at risk of developing LNN based on risk analysis.Of the 204 patients treated,31(15.2%) developed LNN.Logistic regression analysis showed that female sex(P = 0.008),necrosis before re-irradiation(P = 0.008),accumulated total prescription dose to the gross tumor volume(GTV) ≥ 145.5 Gy(P = 0.043),and recurrent tumor volume >25.38 cm3(P = 0.009) were independent risk factors for LNN.A model to predict LNN was then constructed that included these four independent risk factors.Conclusions:A model that includes sex,necrosis before re-irradiation,accumulated total prescription dose to GTV,and recurrent tumor volume can effectively predict the risk of developing LNN in NPC patients who undergo radical re-irradiation with IMRT.

Clinical treatment considerationsin the intensity-modulated radiotherapy era for patients with NO-category nasopharyngeal carcinoma and enlarged neck lymph nodes

Background:Nasopharyngeal carcinoma(NPC) shows a high proportion of lymph node metastasis,and treatment guidelines have been developed for positive nodes.However,no irradiation guidelines have been proposed for patients with enlarged neck lymph nodes(ENLNs) that do not meet the radiological criteria of 10 mm in diameter for positive lymph nodes.This study aimed to determine the prognostic value and radiation dose for ENLNs in NO-category NPC patients treated with intensity-modulated radiotherapy(IMRT).Methods:We reviewed the medical data of 251 patients with non-metastatic,NO-category NPC treated with IMRT.Receiver operating characteristic curves were used to calculate the cut-off value of the ENLN diameter for the prediction of disease failure.The biological equivalent dose(BED) for ENLNs was calculated.Patient survival was compared between the small and large ENLN groups.Independent prognostic factors were identified using the Cox proportional hazards model.Results:The estimated 4-year regional relapse-free survival rate was higher in patients with ENLNs ≥5.5 mm than in those with ENLNs <5.5 mm(100%vs.98.8%,P=0.049),whereas disease-free,overall,and distant metastasis-free survival rates were similar between the two groups.After adjusting for various factors,ENLN diameter was not identified as an independent prognostic factor(P > 0.05 for all survival rates).In the subgroup analysis,patients receiving BED ≥72 Gy had a similar prognosis as patients receiving BED <72 Gy in both the small and large ENLN groups.The multivariate analysis also confirmed that BED≥72 Gy was not associated with significantly improved prognosis in patients with NO-category NPC.Conclusions:A BED of 72 Gy to ENLNs is considerably sufficient to provide a clinical benefit to patients with NO-category NPC.Prospective studies are warranted to validate the findings in the present study.

Intensified intensity-modulated radiotherapy in anal cancer with prevalent HPV p16 positivity

AIM: To investigate the toxicity and response of intensity-modulated radiotherapy schedule intensified with a simultaneous integrated boost in anal canal cancer.METHODS: From March 2009 to March 2014, we retrospectively analyzed 41 consecutive patients treated with intensity-modulated radiotherapy(IMRT) and concurrent chemotherapy for anal canal squamous cell carcinoma at our center. Radiotherapy was delivered via simultaneous integrated boost(SIB) technique by helical tomotherapy, and doses were adapted to two clinical target volumes according to the tumor-nodemetastasis(TNM) stage: 50.6 Gy and 41.4 Gy in 23 fractions in T1N0, 52.8 Gy and 43.2 Gy in 24 fractionsin T2N0, and 55 Gy and 45 Gy in 25 fractions in all patients with N positive and/or ≥ T3, respectively, to planning target volumes 1 and 2. The most common chemotherapy regimen was 5-fluorouracil and mitomycin-based. Human papilloma virus(HPV) p16 expression was performed by immunohistochemistry and evaluated in the majority of patients. Acute and late toxicity was scored according to CTCAe v 3.0 and RTOG scales.RESULTS: The median follow-up was 30 mo(range:12-71). Median age was 63 years(range 32-84). The stage of disease was: stage Ⅰ in 2 patients, stage Ⅱin 13 patients, stage ⅢA in 12 patients, and stage ⅢB in 14 patients, respectively. Two patients were known to be HIV positive(4.9%). HPV p16 expression status was positive in 29/34(85.3%) patients. The 4-year progression-free survival and overall survival in HPVpositive patients were 78% and 92%, respectively.Acute grade 3 skin and gastrointestinal toxicities were reported in 5% and 7.3% of patients, respectively;patients' compliance to the treatment was good due to a low occurrence of severe acute toxicity, although treatment interruptions due to toxicity were required in 7.3% of patients. At 6 mo from end of treatment,36/40(90%) patients obtained complete response;during follow-up, 5(13.8%) patients presented with disease progression(local or systemic).CONCLUSION: In our experience, intensified SIBIMRT with chemotherapy is very feasible in clinical practice, with excellent results in terms of overall survival and local control.

Dosimetric Comparative Analysis of Volumetric Modulated Arc Therapy and Intensity-Modulated Radiation Therapy in Cervical Cancer

Objective:To carry out dosimetric comparison between volumetric modulated arc therapy(VMAT)and intensity-modulated radiation therapy(IMRT)in cervical cancer.Methods:50 postoperative cervical cancer patients were included in this study.The patients were admitted for treatment from January 2021 to January 2022.VMAT and IMRT plans were designed for each patient to analyze the dose distribution in the target area of the two treatment techniques.Results:Comparing the monitor unit for single treatment(638.21±116.21 MU)and time of single treatment(143.21±23.14 s)in the observation group and the monitor unit for single treatment(932.14±74.11 MU)and time of single treatment(223.14±17.26 s)in the control group,there was significant difference(P<0.05);there was also significant difference(P<0.05)between the normal tissue(bladder and rectum)of the observation group and that(bladder and rectum)of the control group.Conclusion:VMAT is more effective in cervical cancer,and it has a certain protective effect on normal tissues in patients and can reduce the radiation dose.

Intensity-modulated Radiotherapy for Sinonasal Teratocarcinosarcoma

Surgical excision and postoperative radiotherapy are widely accepted therapeutic modalities for sinonasal teratocarcinosarcoma （SNTCS）. Previous studies have shown that intensity-modulated radiation therapy （IMRT） is safe and effective for the treatment of some sinonasal malignancies. We hypothesize that use of IMRT for SNTCS may result in clinical benefits. We report here two cases of SNTCS that were treated by IMRT. One patient was given extensive IMRT involving elective neck irradiation. Follow-up examinations revealed no recurrence and metastasis 3.5 years after IMRT. Another patient simultaneously suffered from multiple systematical diseases and was administered involved-field radiotherapy. He was found to have a marginal recurrence during the follow up and eventually died 8 months after disease diagnosis. It was suggested in this study that appropriate use of IMRT for the treatment of SNTCS may achieve excellent local control.

Effect of intensity-modulated radiotherapy combined with local hyperthermia on Mortalin expression in advanced liver cancer lesions and its relationship with cell proliferation and EMT

Objective:To investigate the effect of intensity-modulated radiotherapy combined with local hyperthermia on Mortalin expression in advanced liver cancer lesions and its relationship with cell proliferation and EMT.Methods: A total of 82 patients with advanced liver cancer who were treated in this hospital between February 2016 and September 2017 were chosen as the research subjects, and the therapeutic regimens were reviewed and used to divide these patients into the control group (n=43) who received intensity-modulated radiotherapy and the combined treatment group (n=39) who received intensity-modulated radiotherapy combined with local hyperthermia. Abdominal puncture was done after treatment to obtain liver cancer tissue samples, and the differences in Mortalin gene, cell proliferation gene and EMT gene expression in tissues were compared.Results: After treatment, Mortalin mRNA expression in liver cancer tissues of combined treatment group was lower than that of control group;Fbxw7 mRNA expression in liver cancer tissues was higher than that of control group whereas NCX1, PRMT5 and XBP1S mRNA expression were lower than those of control group;Twist, ZEB-1, ZEB-2, Snail and HOXB7 mRNA expression in liver cancer tissues were lower than those of control group. Pearson test showed that the Mortalin gene expression in liver cancer tissues was directly correlated with cell proliferation genes and EMT genes.Conclusion:Intensity-modulated radiotherapy combined with local hyperthermia can effectively reduce Mortalin gene expression, and further optimize patients'condition by inhibiting hepatic cell proliferation, EMT activity and other pathways.

The Dosimetric Characteristics and Potential Limitation in Clinical Application of a Low Energy Photon Intra-Operative Radiotherapy System

Purpose: To investigate the dosimetric characteristics of a low energy photon intra-operative radiotherapy (IORT) system and explore its potential limitation in clinical application. Methods: A special water phantom, a parallel-plate ionization chamber and an electrometer were used to measure the depth dose rate, isotropy of dose distribution in X/Y plane, dosimetry reproducibility of bare probe and spherical applicators of different size which were used in comparison with the system data. Results: The difference in depth dose rate between the measurement and system data for bare probe is -2.16% ± 1.36%, the range of the relative deviation for isotropy in the X/Y plane is between -1.9% and 2.1%. The difference in depth dose rate, transfer coefficient, isotropy in X/Y plane between the measurement and system data for the whole set of spherical applicators is -10.0% - 2.3%, -8.9% - 4.2% and -1.6% - 2.6%, respectively. Higher surface dose rate and steeper gradient depth dose are observed in smaller spherical applicators. The depth dose rate and isotropy for bare probe and spherical applicators have been shown good reproducibility. The uncertainty of measurement is associated with the positioning accuracy, energy response, noise current and correction function f’(R). Conclusions: Thorough commissioning of the low energy photon IORT system helps us better understand the dosimetry characteristics, verify the system data, obtain adequate data for clinical application and routine quality assurance. The steep gradient depth dose and limited treatment range may restrain its potential in clinical application.

Selective partial salivary glands sparing during intensity-modulated radiation therapy for nasopharyngeal carcinoma

Objective This study evaluated the dosimetric consequences of selective partial salivary gland sparing during intensity-modulated radiotherapy(IMRT) for patients with nasopharyngeal carcinoma(NPC).Methods Ten patients with NPC were enrolled in the study.Two IMRT plans were produced for each patient:conventional(control) and partial salivary glands-sparing(treatment),with dose constraints to the entire parotid glands or partial salivary glands(including the parotid and submandibular glands,delineated with the adjacent distance of at least 0.5 cm between the glands and PTV,the planning target volume) in planning,respectively.Dosimetric parameters were compared between the two plans,including the V_(110%),V_(100%),V_(95%)(the volume covered by more than 110%,100%,or 95% of the prescribed dose),Dmin(the minimum dose) of PTV,homogeneity index(HI),conformity index(CI),and the mean dose and percentage of the volume receiving 30 Gy or more(V_(30)) for the parotid glands and submandibular glands.Results Treatment plans had significantly lower mean doses and V_(30) to both the entire parotid glands and partial parotid glands than those in control plans.The mean doses to the partial submandibular glands were also significantly lower in treatment plans than in control plans.The PTV coverage was comparable between the two plans,as indicated by V_(100%),V_(95%),Dmin,CI,and HI.The doses to critical structures,including brainstem and spinal cord,were slightly but not significantly higher in treatment plans than in control plans.Conclusion A selective partial salivary gland-sparing approach reduces the doses to parotid and submandibular glands during IMRT,which may decrease the risk of post-radiation xerostomia while not compromising target dose coverage in patients with NPC.

Establishment of a prediction model for severe acute radiation enteritis associated with cervical cancer radiotherapy

BACKGROUND Cervical cancer is one of the most common gynecological malignant tumors.Radiation enteritis(RE)leads to radiotherapy intolerance or termination of radiotherapy,which negatively impacts the therapeutic effect and seriously affects the quality of life of patients.If the incidence of RE in patients can be predicted in advance,and targeted clinical preventive treatment can be carried out,the side effects of radiotherapy in cervical cancer patients can be significantly reduced.Furthermore,accurate prediction of RE is essential for the selection of individualized radiation dose and the optimization of the radiotherapy plan.AIM To analyze the relationships between severe acute RE(SARE)of cervical cancer radiotherapy and clinical factors and dose-volume parameters retrospectively.METHODS We included 50 cervical cancer patients who received volumetric modulated arc therapy(VMAT)from September 2017 to June 2018 in the Department of Radiotherapy at The First Affiliated Hospital Soochow University.Clinical and dose-volume histogram factors of patients were collected.Logistic regression analysis was used to evaluate the predictive value of each factor for SARE.A nomogram to predict SARE was developed(SARE scoring system≥3 points)based on the multiple regression coefficients;validity was verified by an internal verification method.RESULTS Gastrointestinal and hematological toxicity of cervical cancer VMAT gradually increased with radiotherapy and reached the peak at the end of radiotherapy.The main adverse reactions were diarrhea,abdominal pain,colitis,anal swelling,and blood in the stool.There was no significant difference in the incidence of gastrointestinal toxicity between the radical and postoperative adjuvant radiotherapy groups(P>0.05).There were significant differences in the small intestine V_(20),V_(30),V_(40),and rectal V40 between adjuvant radiotherapy and radical radiotherapy after surgery(P<0.05).Univariate and multivariate analyses revealed anal bulge rating(OR:14.779,95%CI:1.281-170.547,P=0.031)and disease activity index(DAI)score(OR:53.928,95%CI:3.822-760.948,P=0.003)as independent predictors of SARE.CONCLUSION Anal bulge rating(>0.500 grade)and DAI score(>2.165 points)can predict SARE.The nomogram shows potential value in clinical practice.

COMBINATION OF PRONE POSITION AND INTENSITY-MODULATED RADIATION THERAPY (IMRT) REDUCES SMALL BOWEL DOSES IN RADIATION THERAPY FOR GYNECOLOGIC MALIGNANCIES

Objective： To evaluate if the combination of both prone position on a belly board and intensity-modulated radiotherapy （IMRT） further reduces the radiation dose to small bowel in pelvic RT for gynecologic malignancies. Methods： Conformal pelvic RT plans were computed in 13 patients with gynecologic malignancies who had pre-existing planning computed tomography （CT） scans in both the supine position and prone position on a belly board. There were 10 cervical cancer and 3 endometrial cancer patients. A limited arc technique （180° arc length） and an extended arc technique （340° arc length） were used in IMRT plans. Normal tissue regions of interest （ROI） included small bowel, large bowel and bladder. Dose and volume for normal tissue structures were traced and compared between supine and prone plans using the paired t-test. Results： For the limited arc technique, prone position using a belly board device improved small bowel sparing. Analysis of the results showed a 12~26 Gy reduction of volume of small bowel irradiation compared to the supine position. With the extended arc technique, there was no obvious radiation reduction in the prone position. Large bowel and bladder dose showed no significant differences between prone and supine position with either technique. Conclusion： Prone positioning on a belly board decreases the small bowel dose in gynecologic pelvic IMRT, and the magnitude of improvement depended on the limited arc IMRT technique used.

The Effect of the Size of Radiotherapy Photon Beams on the Absorbed Dose to an Al_2O_3 Dosimeter

The effect of the size of radiotherapy photon beams on the absorbed dose to an Al2O3 dosimeter was investigated using the Monte Carlo method. The EGSnrc/DOSRZnrc program code was used to simulate the absorbed dose to the Al2O3 dosimeter, as well as the absorbed dose to water at the corresponding position in the absence of the dosimeter. The incident beams were 60Co γ and 6 MV with a different beam radius ranging from 0.1 cm to 2 cm. Results revealed that the absorbed dose ratio factor depends on the size of the incident photon beam. When the radius of the incident beam is smaller than that of the dosimeter, the absorbed dose ratio factor decreases as the incident beam size increases. The absorbed dose ratio factor reaches its minimum when the radius of the incident beam is almost the same as that of the dosimeter. When the radius of the incident beam is larger than that of the dosimeter, the absorbed dose ratio factor increases as the incident beam size increases. The maximum difference among these absorbed dose ratio factors can be up to 14% in 60Co γ beams and 23% in 6 MV beams. However, when the size of the incident beam is much larger than that of the dosimeter, the effect of the incident beam size on the absorbed dose ratio factor becomes quite small. The maximum discrepancy between the absorbed dose ratio factors and the average value is not more than 1%.

Three-Dimensional Conformal and Intensity Modulated Dynamic Radiotherapy in Juvenile Nasopharyngeal Angiofibroma

Objective: Juvenile Nasopharyngeal Angiofibroma (JNA) is a benign neoplasm with a high vascularity component, greater craniofacial involvement in adolescent patients, and aggressive local behaviour. In unresectable patients, radiotherapy is a therapeutic option for local control. Our aim in this study was to analyze the clinical benefit and local control provided by two modalities of radiotherapy: the Three-Dimensional Conformal (3DC) technique and volumetric modulated arc therapy (VMAT), applied to pediatric patients with JNA considered unresectable and non-recurrent. Methods: In retrospective study, the information was recorded from pediatric patients with a diagnosis of non-recurrent and unresectable JNA treated with radiotherapy at the Oncology Hospital of the National Medical Center SXXI of Mexico City, from March 2010 to March 2021. Radiotherapy management and its association with clinical outcomes of tumour control, and symptoms were assessed. In addition, an evaluation of acute and chronic toxicity was performed. Results: It was found that the median age was 14 years. 9 patients (37.5%) underwent 3DC and 15 (62.5%) VMAT. In terms of local control, and progression-free survival, we did not find significant difference between radiotherapy modalities (p ≤ 0.57). Acute toxicity for both modalities presented statistical differences for radio epithelitis (p = 0.03). Only Grade I and II radiation-induced acute toxicity was observed. Regarding chronic toxicity, statistical significance was observed for craniofacial hypoplasia, in relation to its absence in the VMAT group (p = 0.001). Conclusion: The VMAT presents improvements in dosimetry parameters that improve patient toxicity. In both techniques adequate tumour control was observed, however, the rarity of the disease is a limitation to establish the most appropriate therapeutic technique.

左侧乳腺癌保乳术后质子与光子放疗剂量学对比研究

目的比较在深吸气屏气呼吸模式(DIBH)下左侧乳腺癌保乳术后光子调强放疗(IMRT)、质子调强放疗(IMPT)剂量学差异。方法选取2020年11月至2022年5月中国科学技术大学附属第一医院离子医学中心(合肥离子医学中心)在DIBH模式下接受左侧乳腺癌保乳术后放疗的7例女性患者病历资料,计划靶区(PTV)处方剂量均为50 Gy(5周,25次),对于影像学(包括功能性影像)上高度怀疑有残留或复发病灶的区域局部加量至PTV_(boost):60 Gy。分别在瓦里安Eclipse 15.5计划系统上设计IMRT计划和Eclipse 16.1计划系统上设计IMPT计划。对2组计划靶区剂量分布、适形指数(CI)、均匀性指数(HI)、两侧肺、健侧乳腺(右乳)、心脏及左冠状动脉前降支(LAD)照射剂量进行统计分析。结果质子与光子放疗计划相比,PTV最大剂量(D_(max))(P=0.389)和平均剂量(D_(mean))(P=0.044)、PTV_(boost) D_(max)(P=0.226)和D_(mean)(P=0.018)、CI(P=0.035)和HI(P=0.419)、患侧肺部(左侧)D_(max)(P=0.153)、健侧肺(右肺)D_(max)(P=0.318)和D_(mean)(P=0.046)、心脏D_(max)(P=0.014)、LAD D_(max)(P=0.025)、健侧乳腺(右乳)D_(max)(P=0.097)均和光子计划无差异。但质子计划左侧肺D_(mean)(P<0.01)、V_(5)(P<0.001)、V_(20)(P<0.001)及心脏D_(mean)(P<0.001)、LAD D_(mean)(P<0.001)、健侧乳腺(右乳)D_(mean)(P=0.010)均明显低于光子计划。结论DIBH下左侧乳腺癌保乳术后质子和光子计划均满足临床要求。但采用质子放疗可显著降低对心脏及其亚单位、患侧肺和健侧乳腺的照射剂量。

Progress in image-guided radiotherapy for the treatment of non-small cell lung cancer

Lung cancer is one of the most common malignant tumors. It has the highest incidence and mortality rate of all cancers worldwide. Late diagnosis of nonsmall cell lung cancer(NSCLC) is very common in clinical practice, and most patients miss the chance for radical surgery. Thus, radiotherapy plays an indispensable role in the treatment of NSCLC. Radiotherapy technology has evolved from the classic two-dimensional approach to three-dimensional conformal and intensity-modulated radiotherapy. However, how to ensure delivery of an accurate dose to the tumor while minimizing the irradiation of normal tissues remains a huge challenge for radiation oncologists, especially due to the positioning error between fractions and the autonomous movement of organs. In recent years, image-guided radiotherapy(IGRT) has greatly increased the accuracy of tumor irradiation while reducing the irradiation dose delivered to healthy tissues and organs. This paper presents a brief review of the definition of IGRT and the various technologies and applications of IGRT. IGRT can help ensure accurate dosing of the target area and reduce radiation damage to the surrounding normal tissue. IGRT may increase the local control rate of tumors and reduce the incidence of radio-therapeutic complications.

Technological advances in radiotherapy for esophageal cancer

Radiotherapy with concurrent chemotherapy and surgery represent the main treatment modalities in esophageal cancer.The goal of modern radiotherapy approaches,based on recent technological advances,is to minimize post-treatment complications by improving the gross tumor volume definition (positron emission tomography-based planning),reducing interfraction motion (image-guided radiotherapy) and intrafraction motion (respiratory-gated radiotherapy),and by better dose delivery to the precisely defined planning target volume (intensity-modulated radiotherapy and proton therapy).Reduction of radiotherapy-related toxicity is fundamental to the improvement of clinical results in esophageal cancer,although the dose escalation concept is controversial.