Intensity-modulated Radiation Therapy Methods Research Articles

Aspects of hypofractionation in modern radiation oncology

Background. In the modern world, the incidence of cancer diseases is rapidly increasing and is the second most common cause of death. This is preconditioned by the quantitative growth of the senior and elderly population, as well as the growth of the main risk factors for cancer, which is related to the socio-economic development of society. About half of cancer cases require radiation therapy (RT) as a component of multimodal treatment, therefore its improvement, namely the introduction of hypofractionated radiation regimens, is considered today as one of the most effective ways to increase availability of oncological care and optimize the use of health care system resources.
 Purpose. To find out clinical and medico-social advantages of the hypofractionated approach in radiation oncology in order to optimize the functioning of the health care system by increasing availability of treatment for cancer patients. To highlight the importance of hypofractionated RT in terms of evidence-based medicine for the most common oncological pathology and in neuro-oncology. To demonstrate the influence of the COVID-19 pandemic on the implementation of hypofractionated RT. To present our own experience of using hypofractionated radiation regimens in patients with glioblastoma (GB).
 Materials and methods. MEDLINE (Pubmed), EMBASE (Ovid), Web of Science (Web of Knowledge) databases were used to search for literature. The search was performed in the English-language sources with the following keywords: «Radiation», «Hypofractionation radiotherapy», «Hypofractionated radiotherapy», «Hypofractionated irradiation»; «Breast cancer»; «Prostate cancer»; «Lung cancer»; «Glioblastoma», COVID-19. Systematic reviews, meta-analyses, randomized controlled trials and retrospective clinical trials were reviewed in full. The primary sources were backreferenced to identify additional relevant studies related to hypofractionated radiation treatment regimens. The last date of the search is 05.25.2023. The authors’ own experience of the hypofractionated approach in the adjuvant radiation treatment of patients with GB is presented briefly, as a reflection of the relevance of the authors’ practical experience to the provisions of the narrative review, based on the results of a retrospective single-center non-randomized study conducted at the State Institution «Romodanov Neurosurgery Institute National Academy of Medical Sciences of Ukraine» in 2014–2020. The oncological results of 110 (69.2%) patients of the hypofractionated RT group (15 fractions, single fraction dose (SFD) 3.5 Gy, total fraction dose (TFD) 52.5 Gy) and 49 (30.8%) patients of the standard RT group (30 fractions, RVD 2.0 Gy, SVD 60.0 Gy) were compared. RT was performed with Trilogy linear accelerator (USA) (6 MeV) using the intensity-modulated radiotherapy method (IMRT). Overall survival (OS) and recurrence-free survival (RFS) in the groups were analyzed.
 Results and discussion. Hypofractionated approaches, which allow to significantly decrease the duration of radiation treatment, have clinical, medical and social advantages, including: increased comfort for a patient; reduction of the workload on staff and technological equipment of medical facilities; reduction of the cost of treatment. The introduction of hypofractionated RT allows to increase access to cancer care at the global level, reducing disparity in the results of treatment of cancer patients between low- and middle-income countries and the countries with high income level. Hypofractionated radiation regimens are included in the clinical guidelines of professional associations, as for the most common forms of cancer and for malignant brain tumors, and represent the standard of treatment for particular clinical cases. Our experience of using the hypofractionated radiation regimen is based on the adjuvant radiation treatment of 110 patients with GB and in terms of clinical results is a relevant concept presented in a narrative review. The analysis showed no statistical difference between the groups of standard fractionation and hypofractionated RT in OS (Logrank test p = 0.06757) and RFS (Logrank test p = 0.43374). In the hypofractionation group, with an observation time median of 22.3 months, the OS median was 16.5 (95% CI 14.1–18.8) months; median RFS was 9.0 (95% CI 8.0–10.0) months. In the standard radiation regimen group, with a median of observation time of 24.4 months, the median OS was 15.0 (95% CI 14.1–17.1) months; median RFS is 9.0 (95% CI 9.0–10.0) months.
 Conclusion. Development and implementation of the measures designed to optimize the use of resources of medical facilities of Ukraine is a necessary condition for maintaining high-quality care for cancer patients in the conditions of full-scale military aggression, which has been ongoing since February 24, 2022. Increased application of hypofractionated approaches in radiation oncology can be considered as a potential tool for optimization of the use of resources of the healthcare system of Ukraine and enhancing public health.

Assessment of Treatment Plan Quality between Flattening Filter and Flattening Filter Free Photon Beam for Carcinoma of the Esophagus with IMRT Technique.

As compared to the flattened photon beam, removing the flattening filter (FF) from the head of a gantry decreases the average energy of the photon beam and increases the dose rate, leading to an impact on the quality of treatment plans. This study aimed to compare the quality of intensity-modulated radiation therapy (IMRT) treatment plans for esophageal cancer with and without a flattened filter photon beam. In this analytical study, 12 patients, who had already been treated with a 6X FF photon beam, were treated based on new IMRT methods using a 6X the flattening filter-free (FFF) photon beam. Both 6X FF IMRT and 6X FFF IMRT plans used identical beam parameters and planning objectives. All plans were evaluated with planning indices and doses for organs at risk (OARs). Insignificant dose variation was for HI, CI, D98%, and V95% between FF and FFF photon beam IMRT plans. FF-based IMRT plan delivered a 15.51 % and 11.27% higher mean dose to both lungs and heart than the FFF plan, respectively. The integral dose (ID) for the heart and lungs was 11.21% and 15.51%, respectively, less in the IMRT plan with an FFF photon beam. In contrast to the FF photon beam, a filtered photon beam-oriented IMRT plan provides significant OAR sparing without losing the quality of the treatment plan. High monitor units (MUs), low ID, and Beam on Time (BOT) are major highlights of the IMRT plan with FFF beam.

Dosimetric evaluation of irregular surface compensator and intensity-modulated radiotherapy in breast radiotherapy.

BackgroundThis dosimetric study aims to evaluate the dosimetric advantage of the irregular surface compensator (ISC) compared with the intensity-modulated radiotherapy (IMRT).Materials and methodsTen patients with whole breast irradiation were planned with the ISC and IMRT techniques. Six different beam directions were selected for IMRT and ISC plans. The treatment plans were evaluated with respect to planning target coverage, dose homogeneity index (DHI) and organs at risk (OARs) sparing. Monitor units (MUs) and the delivery time were analysed for treatment efficiency.ResultsThe ISC technique provides a better coverage of the PTV and statistically significantly better homogeneity of the dose distribution. For the ipsilateral lung and heart, ISC and IMRT techniques deliver almost the same dose in all plans. However, MU counts and delivery time were significantly lower with the IMRT technique (p < 0.05).ConclusionFor breast radiotherapy, when the ISC method was compared to the IMRT method, ISC provided better dose distribution for the target.

Dosimetric comparison of different radiotherapy techniques to determine the absorbed fetal dose in pregnant patients with left-sided breast cancer

In our study, we aimed to measure the dose exposed by the fetus during three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) treatment techniques in pregnant patients who had to undergo radiotherapy due to breast cancer with thermoluminescence dosimetry (TLD) and compare these measurements with treatment planning system (TPS). 2.5 mm- thick computed tomography (CT) images of Alderson Rando phantom device were taken for measurements. In order to compare the TPS and TLD readings in PTV, 60 TLDs were placed in the target volume in the Rando phantom. Twenty-four TLDs were placed in the 30th and 31st sections of the phantom, which is likely to be in the volumetric size of the first trimester of pregnancy which is also located 25.84 cm from the lower limit of the PTV. Six MV were used in seven different treatment techniques and the measurements were repeated 5 times for each technique and averaged. Fetal doses for all treatment techniques in TPS were found as 0.00 cGy. However, TLD measurements were measured between 3.36 ± 0.19 cGy and 16.10 ± 2.04. In 3D-CRT treatment technique the fetus received the lowest dose. In addition, for plans made using the IMRT method, it is seen that the MSS-IMRT technique provides better fetal protection compared to the SW-IMRT technique. The 3D-CRT should be the first priority for a pregnant patient who has to undergo left breast RT, but if the desired dose-volume histogram (DVH) cannot be obtained with 3D-CRT, 5 MSS-IMRT technique may be preferred.

Dosimetric comparison of level II lymph nodes between mono-isocentric and dual-isocentric approaches in 3D-CRT and IMRT techniques in breast radiotherapy of mastectomy patients

AbstractAim:To evaluate the dosimetric parameters of level II lymph nodes in chest wall three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) of mastectomy patients using dual-isocentric (DIT) and mono-isocentric techniques (MIT).Materials and methods:Computed tomography (CT) images of 20 mastectomy patients undergoing chest wall external radiotherapy were used as the input data for the abovementioned techniques. Selected dosimetric parameters were calculated for the axillary level I–III lymph nodes, chest wall, heart and lung. Paired t-test statistical analysis was used for comparing the results of MIT and DIT in both 3D-CRT and IMRT methods.Results:There were significant differences in Dmin (minimum dose), Dmax (maximum dose) and maximum–minimum dose between MIT and DIT techniques (13, −8·6, −52·2% differences for Dmin, Dmax and maximum–minimum, respectively) in IMRT. There were also significant differences for Dmean (mean dose), Dmax and maximum–minimum dose (7·8, −11·4, −44·6% differences in Dmean, Dmax and maximum–minimum, respectively) in 3D-CRT (p &lt; 0·05). In addition, there were not any differences in the dosimetric parameters for heart, lung and level I and III lymph nodes.Conclusion:In both 3D-CRT and IMRT methods, level II lymph node dose distribution in MIT was closer to the prescribed dose compared with DIT due to the position of these nodes in the field junction area. To achieve a better dose homogeneity, it could be recommended to use MIT instead of DIT in 3D-CRT and IMRT for mastectomy patients.

Estimation of radiation-induced second cancer risk associated with the institutional field matching craniospinal irradiation technique: A comparative treatment planning study

To estimate and compare the lifetime attributable risk (LAR) of radiation-induced second cancer (SC) in pediatric medulloblastoma patients planned with institutional 3D conformal field matching method, gap junction method and Intensity Modulated Radiotherapy (IMRT). The epidemiological studies on childhood cancer survivors reported that long-term cancer survivors who received radiotherapy are at a significantly increased risk for the development of SC. Hence, the increased concern to predict the SC risk for long-term survivors. In addition to institutional field matching planning method, IMRT and gap junction methods were created for ten pediatric medulloblastoma patients. The risk estimates were made based on the site-specific cancer risk coefficient provided by the BEIR VII committee according to the organ equivalent dose for various critical organs. Also, plans were compared for target volume dose distribution and dose received by critical organs. When compared to the gap junction method, the IMRT and institutional field matching method were superior in normal tissue sparing and dose conformity. However, highly significant volume of low dose associated with IMRT was the main concern for the SC risk. The accumulated LAR for all the critical organs with 3D conformal gap junction and IMRT method was 23-25% while for the 3D conformal field matching method it was 21%. The LAR associated with the institutional field matching technique was substantially lower. As this method is highly robust and easy to set up, it can be a better choice of a craniospinal irradiation technique where 3DCRT is the only choice of treatment.

Fluence profiles and energy spectral distributions of 100, 110, and 125 kVp photon beams: results of Monte Carlo simulations for a Varian OBI 1.4 CBCT

Cone Beam Computed Tomography (CBCT) imaging for daily patient localization has gained enormous popularity as one of Image Guided Radiation Therapy (IGRT) methods in recent years. This is largerly due to the need of higher precision and accuracy in conformal beam delivery technique which is known as Intensity Modulated Radiation Therapy (IMRT). The success of this IMRT method is mainly determined by the treatment planning systems. The aim of this research is to provide detailed characteristics of incident photon beams for different beam energies from a Varian OBI 1.4 CBCT. The detailed characteristics consists of energy spectral distributions and fluence profiles. This information is critical to the future development of accurate treatment planning systems. BEAMnrc as one of EGSnrc Monte Carlo user code, has been used to simulate 100, 110, and 125 kVp photon beams from x-ray tube of a Varian OBI 1.4 CBCT. The details of each particle’s complete history including where it has been and where it has interacted is stored in a phase space (phsp) data file. The phsp files are analyzed to obtain fluence profiles and energy spectral distributions.

Assessment and Comparison of Homogeneity and Conformity Indexes in Step-and-Shoot, Compensator-Based Intensity Modulated Radiation Therapy (IMRT) and Three-Dimensional Conformal Radiation Therapy (3D CRT) in Prostate Cancer

Introduction: Intensity modulated radiation therapy (IMRT) and three-dimensional conformal radiation therapy (3D CRT) are two treatment modalities in prostate cancer, which provide acceptable dose distribution in tumor region with sparing the surrounding normal tissues. IMRT is based on inverse planning optimization; in which, intensity of beams is modified by using multileaf collimators and also compensators with optimum shapes in step and shoot (SAS) and compensator-based method, respectively. Materials and Methods: Prescribed dose was 80 Gy for both IMRT procedures and 70 Gy for 3D CRT. Treatment plans of 15 prostate cancer candidates were compared to target the minimum dose, maximum dose, V 76 Gy (for IMRT plans) V 66.5 Gy (for 3D CRT), mean dose, conformity index (CI), and homogeneity index (HI). Results: Dose conformity in compensators-based IMRT was better than SAS and 3D CRT. The same outcome was also achieved for homogeneity index. The target coverage was achieved 95% of prescribed dose to 95% of planning target volume (PTV) in 3D CRT and 95% of prescribed dose to 98% of PTV in IMRT methods. IMRT increases maximum dose of tumor region, improves CI and HI of target volume, and also reduces dose of organs at risks. Conclusion: Results of this study showed that both IMRT methods provide better target coverage in comparison of 3D CRT. In SAS technique, maximum dose reduced compared with compensator-based IMRT while, in the later method, CI and HI improved; it must be mentioned that 3D CRT also had the acceptable HI and CI results. IMRT approaches represented better homogeneity and conformity over 3D CRT and in comparison of two IMRT methods, all acceptable results can be achieved in compensator IMRT.

The Relationship between the Different Prostate Intensity Modulated Radiation Therapy Techniques and Patient’s Anatomical Parameters

Introduction: Intensity Modulated Radiotherapy (IMRT) is a common method for treating prostate cancers. Different IMRT methods can apply for irradiating the prostate, but there is not clear that which of these methods can provide better dose distribution for each patient individually. Therefore, the aim of this study was to evaluate the relationship between the different prostate IMRT techniques and Patients anatomical parameters for determining the appropriate IMRT method for each patient regarding to his anatomical parameters. Materials and Methods: 50 patients with low to high risk prostate cancer were considered for hypo fractionated IMRT (70.2Gy in 26 fractions). CT and MRI (T2 weighted) scans were obtained and imported to the treatment planning system (Eclipse version 11, Varian corporation, USA). Planning tumor volume (PTV) and organs at risk (OARs) were contoured on these images. 4 different IMRT plans including 9 fields, 7 fields, 5 fields and beam angle optimization were created for each patient. Furthermore, the dose distributions of these techniques were evaluated using cost function value that determined the differences between the ideal dose distribution and calculated one. anatomical parameters including OARs volume, joint volumes between OAR and PTV, prostate volume, PTV volume, width and height in the central slice of prostate and femur distance was measured. The relationship between the cost function values with the anatomical parameters were assessed in this study. Results: 9 and 7 fields IMRT had lower cost function values compared to other techniques with increasing the prostate volume, PTV volume and joint volumes between the PTV and OARs. Increasing the OAR volumes, patient’s width and height in the central slice of prostate and femur distance had not any effect in creating differences between the above 4 mentioned IMRT techniques. Conclusion: Prostate IMRT with 9 and 7 fields can be used interchangeably because of their close value of cost function in all patients, especially they can provide better dose distribution in patients with large PTVs (more than 350cc) and large joint volumes between the OARs and PTV (25 cc for rectum and 50 cc for bladder) compared to 5 fields and beam angle optimization IMRT. All of the mentioned IMRT techniques provided relatively the same dose distributions in patients with small PTV and joint volumes and all range of the other mentioned anatomical parameters.

Radiation- induced cognitive impairments

Introduction: Ionizing radiation is non-surgical treatment of brain tumors and metastases. Preclinical studies have showed main insights into harmful effects of radiation on the nervous system in vivo and in vitro. Cognitive impairment such as progressive memory, executive and attention performance deficits indicates a significant risk for patients experiencing conventional radiotherapy. Changes in hippocampus-dependent cognition often state radiation-induced cognitive destruction. Radiation-induced brain injury can impair neuronal, glial and vascular parts of the brain and may cause to molecular, cellular and functional alterations. Materials and Method: In order to investigate this topic, the articles were searched for in the following bibliographic database: PubMed, Scopus, Science Direct and Google scholar and among the words used when searching were: cranial irradiation, cognitive impairment. Results and Conclusion: To avoid of the hippocampus impairment in cranial irradiating, whereas allowing for same dose sending to the remainder of the brain, poses severe challenges given the central position and unique anatomic shape of the hippocampus. Recently, previous studies showed that the ability of modern intensity-modulated radiotherapy methods, like LINAC-based intensity-modulated radiotherapy and helical tomotherapy, to permit for the delivery of extremely conformal dose distributions.

Optimization of Clarkson's Method for Calculating Absorbed Dose under Compensator Filters used in Intensity-modulated Radiation Therapy.

Background: Intensity Modulated Radiation Therapy (IMRT) is extensively used in the treatment of malignancies. Clarkson’s method is one of the leading methods for dose calculation at open points present in irregular fields.Objective: The aim of this study is to generalize the Clarkson’s method for dose calculation at points under compensator filters in IMRT method and its application in IMRT quality control as well.Material and Methods: In this experimental study, compensator filters were designed in two forms: flat filter and block piled-up compensator. The measurements for the compensator filters and open fields in 5 and10 cm depths at energy levels (6, 10 and 18 MV) and in fields with different dimensions were performed using “Mapcheck2” dosimeter. The aim of performing calculations is to derive the theoretical dose by the generalized Clarkson’s equation and comparing it with data resulted from the measurement for confirming the Clarkson’s equation presented. Results: These results demonstrate the data derived from the generalized Clarkson’s method are in good agreement with the data resulted from measurement; the highest error of the proposed equation was 3% for flat filter, and less than 5% for block-piled-up filter. Higher error in the block-piled-up filter compared with the flat filter was due to the presence of leakage between these blocks.Conclusion: The results of this study demonstrated that the presented equation is reliable and valid, and the proposed equation can be applied for dose calculation at all points under the compensator filter or the shielded areas.

Late rectal bleeding after volumetric-modulated arc therapy for localised prostatic cancer

AbstractAimLate adverse effects following radiation therapy for prostate cancer involve the urinary and lower gastrointestinal tracts, with continuous rectal bleeding being the most serious issue. We focused on late adverse effects, particularly rectal bleeding after volumetric-modulated arc therapy (VMAT), for patients with locally advanced prostate cancer.Materials and MethodsSeventy-three patients with localized prostate cancer were treated with radiation therapy using VMAT with an image-guided radiation therapy system. Patient age at the start of irradiation ranged from 54 to 81 years (median, 71 years). The follow-up period ranged from 23 to 87 months (median, 57 months). The prescribed total irradiation dose was 76 Gy in 38 fractions.ResultsLate rectal bleeding was observed in 14 (19%) patients, with nine (12.3%), four (5.5%), and one (1.4%) being classified as grades 1, 2, and 3, respectively. One grade 3 patient with rectal bleeding had severe diabetes and was administered intravenous warfarin for cardiomyopathy.FindingsVMAT may provide better accuracy and involve fewer time constraints for patients compared with other intensity-modulated radiation therapy (IMRT) methods. The incidence of late rectal bleeding in VMAT is almost equivalent to that of other IMRT methods.

A Phase II Study of Two-Step Intensity Modulated Radiation Therapy (IMRT) with Chemotherapy for Loco-Regionally Advanced Nasopharyngeal Cancer (NPC) (JCOG1015)

A phase II study of adaptive two-step IMRT with chemotherapy (Cx) for NPC (JCOG1015, UMIN-CTR: UMIN000005448) was conducted to evaluate the efficacy and safety. Acute toxicities and treatment compliance had been reported, and this is the final report on efficacy. Patients (pts) aged 20-75 years with stages II-IVB NPC with performance status of 0-1 were enrolled. As adaptive two-step IMRT, computed tomography planning was done twice before the start of IMRT for initial plan of 46 Gy/23 fractions (fr) and at the third or fourth week of treatment for boost plan of 24 Gy/12 fr with a total radiation dose of 70 Gy/ 35 fr. Individual case review was performed. Cx (cisplatin 80 mg/ m2 /3-weeks × 3 cycles) was given concurrently with IMRT, followed by adjuvant Cx (cisplatin 70 mg/ m2 with 5-FU 700 mg/m2 for 5 days/4-weeks × 3 cycles). The primary endpoint was 3-year overall survival (OS). The sample size was set as 75 pts by precision-base so that the 95% confidence interval (CI) for the estimated 3-year OS would be ±10% around the expected value of 74% based on the predicted proportion of stage (UICC 7th) II:III:IV = 20%:40%:40%. If upper limit of the 95% CI of estimated 3-year OS based on the actual proportion of stage was not lower than the expected value of target population by the conventional treatment, we conclude that adaptive two-step IMRT method was to be considered as a standard treatment. As a secondary endpoint, xerostomia score was evaluated. The expected incidences of Grade 2 or more xerostomia at 1, 2, and 3 years after IMRT were 30%, 25%, and 20%. From April 2011 to October 2014, 75 pts were enrolled from 12 institutions. The pts consisted of 60 men and 15 women with the median age of 55 years (range, 28-75). At least 2 cycles of concurrent Cx with a total dose of 70 Gy was completed in 74 pts (99%). However, the full protocol treatment including 3 cycles of adjuvant Cx was completed for 39 pts (52%). The 3-year OS for the 75 pts was 88% [95% CI; 78%-94%]. The upper and lower limit of the 95% CI of the 3-year OS (94%) was higher than the target population’s expected 3-year OS of 75% adjusted by the stage with actual proportion of stage II:III:IV = 21%:44%:35%; thus the primary endpoint was met. The 3-year progression-free survival (PFS) and loco-regional PFS were 71% [59%-80%] and 77% [66%-85%]. Loco-regional recurrences were noted in 13 pts (17%). In terms of late toxicities, 15 pts (20%) showed grade 3 toxicities including hearing impaired, aspiration, and dysphagia. No grade 4-5 toxicities were noted. Grade 2 or more xerostomia was noted in 26% (18/70), 12% (8/69), and 9% (6/65) at 1, 2, and 3 years after start of IMRT. Adaptive two-step IMRT for NPC showed an excellent 3-year OS with acceptable toxicities, and the incidence of xerostomia was satisfactorily low. This method would be a new standard treatment for locally advanced NPC.

Two-step Intensity-modulated Radiation Therapy for Oropharyngeal Cancer: Initial Clinical Experience and Validation of Clinical Staging.

To evaluate the clinical results of two-step intensity-modulated radiation therapy (IMRT) for oropharyngeal cancer. Eighty patients were treated with two-step IMRT between 2002 and 2014. Whole-neck radiotherapy (44.0-50.0 Gy/22-25 fractions) was delivered by IMRT, followed by boost IMRT to the high-risk clinical target volume (total dose of 70.0 Gy/35 fractions). Forty-seven patients received concurrent chemotherapy. Immunohistochemistry for human papillomavirus type 16 (HPV/p16) was performed for 64 patients. The 5-year overall survival and locoregional control rates for stage I, II, III, and IVA-B disease were 80.0%, 75.0%, 78.0%, and 64.0% and 100.0%, 75.0%, 92.0%, and 82.0%, respectively. Overall survival was significantly higher in HPV/p16-positive patients than in HPV/p16-negative patients (p=0.01). Xerostomia of grade 2 or more was noted in 10 patients. Favourable overall survival and locoregional control rates with excellent salivary preservation were obtained using the two-step IMRT method for oropharyngeal cancer.

Normal lung sparing Tomotherapy technique in stage III lung cancer

PurposeRadiation pneumonitis (RP) has been a challenging obstacle in treating stage III lung cancer patients. Beam angle optimization (BAO) technique for Tomotherapy was developed to reduce the normal lung dose for stage III non-small cell lung cancer (NSCLC). Comparative analyses on plan quality by 3 different Intensity-modulated radiation therapy (IMRT) methods with BAO were done.Materials and methodsTen consecutive stage IIIB NSCLC patients receiving linac-based static IMRT (L-IMRT) with total 66 Gy in 33 fractions to the PTV were selected. Two additional Tomotherapy-based IMRT plans (helical beam (TH-IMRT) and static beam (TD-IMRT)) were generated on each patient. To reduce the normal lung dose, Beam angles were optimized by using complete and directional block functions in Tomotherapy based on knowledge based statistical analysis. Plan quality was compared with target coverage, normal organ sparing capability, and normal tissue complication probability (NTCP). Actual beam delivery times and risk of RP related with planning target volume (PTV) were also evaluated.ResultsThe best PTV coverage measured by conformity index and homogeneity index was achievable by TH-IMRT (0.82 and 1.06), followed by TD-IMRT (0.81 and 1.07) and L-IMRT (0.75 and 1.08). Mean lung dose was the lowest in TH-IMRT plan followed by TD-IMRT and L-IMRT, all of which were ≤20 Gy. TH-IMRT plan could significantly lower the lung volumes receiving low to medium dose levels: V5~30 when compared to L-IMRT plan; and V5~20 when compared to TD-IMRT plan, respectively. TD-IMRT plan was significantly better than L-IMRT with respects to V20 and V30 and there was no significant difference with respect to V40 among three plans. The NTCP of the lung was the lowest in TH-IMRT plan, followed by TD-IMRT and L-IMRT (6.42% vs. 6.53% vs. 8.11%). Beam delivery time was the shortest in TD-IMRT plan followed by L-IMRT. As PTV length increased, NTCP and Mean lung dose proportionally increased significantly in all three plans.ConclusionAdvantageous profiles by TH-IMRT could be achieved by BAO by complete and directional block functions. Current observation could help radiation oncologists to make wise selection of IMRT method for stage IIIB NSCLC.

Assessment and Comparison of Homogeneity and Conformity Indexes in Step-and-Shoot and Compensator-Based Intensity Modulated Radiation Therapy (IMRT) and Three-Dimensional Conformal Radiation Therapy (3D CRT) in Prostate Cancer

Intensity modulated radiation therapy (IMRT) and three-dimensional conformal radiation therapy (3D CRT) are two treatment modalities in prostate cancer, which provide acceptable dose distribution in tumor region with sparing the surrounding normal tissues. IMRT is based on inverse planning optimization; in which, intensity of beams is modified by using multileaf collimators and also compensators with optimum shapes in step and shoot (SAS) and compensator-based method, respectively. In the recent study, some important parameters were compared in two IMRT and 3D CRT methods. Prescribed dose was 80 Gy for both IMRT procedures and 70 Gy for 3D CRT. Treatment plans of 15 prostate cancer candidates were compared to target the minimum dose, maximum dose, V 76 Gy (for IMRT plans) V 66.5 Gy (for 3D CRT), mean dose, conformity index (CI), and homogeneity index (HI). Dose conformity in compensators-based IMRT was better than SAS and 3D CRT. The same outcome was also achieved for homogeneity index. The target coverage was achieved 95% of prescribed dose to 95% of planning target volume (PTV) in 3D CRT and 95% of prescribed dose to 98% of PTV in IMRT methods. IMRT increases maximum dose of tumor region, improves CI and HI of target volume, and also reduces dose of organs at risks.

Dosimetric Analysis on the Effect of Target Motion in the Delivery of Conventional IMRT, RapidArc and Tomotherapy

One of the methods to consider the effect of respiratory motion of a tumor target in radiotherapy is to establish a treatment plan with the internal target volume (ITV) created based on an accurate analysis of the target motion displacement. When this method is applied to intensity modulated radiotherapy (IMRT), it is expected to yield a different treatment dose distribution under the motion condition according to the IMRT method. In this study, we prepared ITV-based IMRT plans with conventional IMRT using fixed gantry angle beams, RapidArc using volumetric modulated arc therapy, and tomotherapy using helical therapy. Then, the variation in dose distribution caused by the target motion was analyzed by the dose measurement in the actual motion condition. A delivery quality assurance plan was prepared for the established IMRT plan and the dose distribution in the actual motion condition was measured and analyzed using a two-dimensional diode detector placed on a moving phantom capable of simulating breathing movements. The dose measurement was performed considering only a uniform target shape and motion in the superior-inferior (SI) direction. In this condition, it was confirmed that the error of the dose distribution due to the target motion is minimum in tomotherapy. This is thought to be due to the characteristic of tomotherapy that treats the target sequentially by dividing it into several slices. When the target shape is uniform and the main target motion direction is SI, it is considered that tomotherapy for the ITV-based IMRT method has a characteristic which can reduce the dose difference compared with the plan dose under the target motion condition.

Measurement-based Monte Carlo simulation of high definition dose evaluation for nasopharyngeal cancer patients treated by using intensity modulated radiation therapy

Measurement-based Monte Carlo (MBMC) simulation using a high definition (HD) phantom was used to evaluate the dose distribution in nasopharyngeal cancer (NPC) patients treated with intensity modulated radiation therapy (IMRT). Around nasopharyngeal cavity, there exists many small volume organs-at-risk (OARs) such as the optic nerves, auditory nerves, cochlea, and semicircular canal which necessitate the use of a high definition phantom for accurate and correct dose evaluation. The aim of this research was to study the advantages of using an HD phantom for MBMC simulation in NPC patients treated with IMRT. The MBMC simulation in this study was based on the IMRT treatment plan of three NPC patients generated by the anisotropic analytical algorithm (AAA) of the Eclipse treatment planning system (Varian Medical Systems, Palo Alto, CA, USA) using a calculation grid of 2 mm2. The NPC tumor was treated to a cumulative dose of 7000 cGy in 35 fractions using the shrinking-field sequential IMRT (SIMRT) method. The BEAMnrc MC Code was used to simulate a Varian EX21 linear accelerator treatment head. The HD phantom contained 0.5 × 0.5 × 1 mm3 voxels for the nasopharyngeal area and 0.5 × 0.5 × 3 mm3 for the rest of the head area. An efficiency map was obtained for the amorphous silicon aS1000 electronic portal imaging device (EPID) to adjust the weighting of each particle in the phase-space file for each IMRT beam. Our analysis revealed that small volume organs such as the eighth cranial nerve, semicircular canal, cochlea and external auditory canal showed an absolute dose difference of ≥200 cGy, while the dose difference for larger organs such as the parotid glands and tumor was negligible for the MBMC simulation using the HD phantom. The HD phantom was found to be suitable for Monte Carlo dose volume analysis of small volume organs.

Volume and dosimetric changes and initial clinical experience of a two-step adaptive intensity modulated radiation therapy (IMRT) scheme for head and neck cancer

PurposeThe aim of this study was to show the benefit of a two-step intensity modulated radiotherapy (IMRT) method by examining geometric and dosimetric changes. Material and MethodsTwenty patients with pharyngeal cancers treated with two-step IMRT combined with chemotherapy were included. Treatment-planning CT was done twice before IMRT (CT-1) and at the third or fourth week of IMRT for boost IMRT (CT-2). Transferred plans recalculated initial plan on CT-2 were compared with the initial plans on CT-1. Dose parameters were calculated for a total dose of 70Gy for each plan. ResultsThe volumes of primary tumors and parotid glands on CT-2 regressed significantly. Parotid glands shifted medially an average of 4.2mm on CT-2. The mean doses of the parotid glands in the initial and transferred plans were 25.2Gy and 30.5Gy, respectively. D2 (dose to 2% of the volume) doses of the spinal cord were 37.1Gy and 39.2Gy per 70Gy, respectively. Of 15 patients in whom xerostomia scores could be evaluated 1–2years after IMRT, no patient complained of grade 2 or more xerostomia. ConclusionsThis two-step IMRT method as an adaptive RT scheme could adapt to changes in body contour, target volumes and risk organs during IMRT.

Second cancer incidence risk estimates using BEIR VII models for standard and complex external beam radiotherapy for early breast cancer.

To compare organ specific cancer incidence risks for standard and complex external beam radiotherapy (including cone beam CT verification) following breast conservation surgery for early breast cancer. Doses from breast radiotherapy and kilovoltage cone beam CT (CBCT) exposures were obtained from thermoluminescent dosimeter measurements in an anthropomorphic phantom in which the positions of radiosensitive organs were delineated. Five treatment deliveries were investigated: (i) conventional tangential field whole breast radiotherapy (WBRT), (ii) noncoplanar conformal delivery applicable to accelerated partial beast irradiation (APBI), (iii) two-volume simultaneous integrated boost (SIB) treatment, (iv) forward planned three-volume SIB, and (v) inverse-planned three volume SIB. Conformal and intensity modulated radiotherapy methods were used to plan the complex treatments. Techniques spanned the range from simple methods appropriate for patient cohorts with a low cancer recurrence risk to complex plans relevant to cohorts with high recurrence risk. Delineated organs at risk included brain, salivary glands, thyroid, contralateral breast, left and right lung, esophagus, stomach, liver, colon, and bladder. Biological Effects of Ionizing Radiation (BEIR) VII cancer incidence models were applied to the measured mean organ doses to determine lifetime attributable risk (LAR) for ages at exposure from 35 to 80 yr according to radiotherapy techniques, and included dose from the CBCT imaging. All LAR decreased with age at exposure and were lowest for brain, thyroid, liver, and bladder (<0.1%). There was little dependence of LAR on radiotherapy technique for these organs and for colon and stomach. LAR values for the lungs for the three SIB techniques were two to three times those from WBRT and APBI. Uncertainties in the LAR models outweigh any differences in lung LAR between the SIB methods. Constraints in the planning of the SIB methods ensured that contralateral breast doses and LAR were comparable to WBRT, despite their added complexity. The smaller irradiated volume of the ABPI plan contributed to a halving of LAR for contralateral breast compared with the other plan types. Daily image guided radiotherapy (IGRT) for a left breast protocol using kilovoltage CBCT contributed <10% to LAR for the majority of organs, and did not exceed 22% of total organ dose. Phantom measurements and calculations of LAR from the BEIR VII models predict that complex breast radiotherapy techniques do not increase the theoretical risk of second cancer incidence for organs distant from the treated breast, or the contralateral breast where appropriate plan constraints are applied. Complex SIB treatments are predicted to increase the risk of second cancer incidence in the lungs compared to standard whole breast radiotherapy; this is outweighed by the threefold reduction in 5 yr local recurrence risk for patients of high risk of recurrence, and young age, from the use of radiotherapy. APBI may have a favorable impact on risk of second cancer in the contralateral breast and lung for older patients at low risk of recurrence. Intensive use of IGRT increased the estimated values of LAR but these are dominated by the effect of the dose from the radiotherapy, and any increase in LAR from IGRT is much lower than the models' uncertainties.