Dosimetry Comparison between Volumetric Modulated Arc Therapy with RapidArc and Fixed Field Dynamic IMRT for Local-Regionally Advanced Nasopharyngeal Carcinoma

Objective: A dosimetric study was performed to evaluate the performance of volumetric modulated arc radiotherapy with RapidArc on locally advanced nasopharyngeal carcinoma (NPC). Methods: The CT scan data sets of 20 patients of locally advanced NPC were selected randomly. The plans were managed using volumetric modulated arc with RapidArc and fixed nine-field coplanar dynamic intensity-modulated radiotherapy (IMRT) for these patients. The dosimetry of the planning target volumes (PTV), the organs at risk (OARs) and the healthy tissue were evaluated. The dose prescription was set to 70 Gy to the primary tumor and 60 Gy to the clinical target volumes (CTV) in 33 fractions. Each fraction applied daily, five fractions per week. The monitor unit (MU) values and the delivery time were scored to evaluate the expected treatment efficiency. Results: Both techniques had reached clinical treatment’s requirement. The mean dose (Dmean), maximum dose (Dmax) and minimum dose (Dmin) in RapidArc and fixed field IMRT for PTV were 68.4±0.6 Gy, 74.8±0.9 Gy and 56.8±1.1 Gy; and 67.6±0.6 Gy, 73.8±0.4 Gy and 57.5±0.6 Gy (P<0.05), respectively. Homogeneity index was 78.85±1.29 in RapidArc and 80.34±0.54 (P<0.05) in IMRT. The conformity index (CI: 95%) was 0.78±0.01 for both techniques (P>0.05). Compared to IMRT, RapidArc allowed a reduction of Dmean to the brain stem, mandible and optic nerves of 14.1% (P<0.05), 5.6% (P<0.05) and 12.2% (P<0.05), respectively. For the healthy tissue and the whole absorbed dose, Dmean of RapidArc was reduced by 3.6% (P<0.05), and 3.7% (P<0.05), respectively. The Dmean to the parotids, the spinal cord and the lens had no statistical difference among them. The mean MU values of RapidArc and IMRT were 550 and 1,379. The mean treatment time of RapidArc and IMRT was 165 s and 447 s. Compared to IMRT, the delivery time and the MU values of RapidArc were reduced by 63% and 60%, respectively. Conclusion: For locally advanced NPC, both RapidArc and IMRT reached the clinic requirement. The target volume coverage was similar for the different techniques. The RapidArc technique showed some improvements in OARs and other tissue sparing while using reduced MUs and delivery time.

Helical tomotherapy and volumetric modulated arc therapy:New therapeutic arms in the breast cancer radiotherapy

AIM To analyse clinical and dosimetric results of helical tomotherapy(HT) and volumetric modulated arc therapy(VMAT) in complex adjuvant breast and nodes irradiation.METHODS Seventy-three patients were included(31 HT and 42 VMAT). Dose were 63.8 Gy(HT) and 63.2 Gy(VMAT) in the tumour bed, 52.2 Gy in the breast, 50.4 Gy in supraclavicular nodes(SCN) and internal mammary chain(IMC) with HT and 52.2 Gy and 49.3 Gy in IMC and SCN with VMAT in 29 fractions. Margins to particle tracking velocimetry were greater in the VMAT cohort(7 mm vs 5 mm).RESULTS For the HT cohort, the coverage of clinical target volumes was as follows: Tumour bed: 99.4% ± 2.4%; breast: 98.4% ± 4.3%; SCN: 99.5% ± 1.2%; IMC:96.5% ± 13.9%. For the VMAT cohort, the coverage was as follows: Tumour bed: 99.7% ± 0.5%, breast: 99.3% ± 0.7%; SCN: 99.6% ± 1.4%; IMC: 99.3% ± 3%. For ipsilateral lung, Dmean and V20 were 13.6 ± 1.2 Gy, 21.1% ± 5%(HT) and 13.6 ± 1.4 Gy, 20.1% ± 3.2%(VMAT). Dmean and V30 of the heart were 7.4 ± 1.4 Gy, 1% ± 1%(HT) and 10.3 ± 4.2 Gy, 2.5% ± 3.9%(VMAT). For controlateral breast Dmean was 3.6 ± 0.2 Gy(HT) and 4.6 ± 0.9 Gy(VMAT). Acute skin toxicity grade 3 was 5% in the two cohorts.CONCLUSION HT and VMAT in complex adjuvant breast irradiation allow a good coverage of target volumes with an acceptable acute tolerance. A longer follow-up is needed to assess the impact of low doses to healthy tissues.

A dosimetric evaluation of flattening filter-free volumetric modulated arc therapy for postoperative treatment of cervical cancer

Objective The aim of the study was to compare flattening filter-free(FFF) beams and conventional flattening filter(FF) beams in volumetric modulated arc therapy(VMAT) for cervical cancer after surgery, through a retrospective planning study.Methods VMAT plans of FFF beams and normal FF beams were designed for a cohort of 15 patients. The prescribed dose was 45 Gy to 1.8 Gy per fraction, and at least 95% of the planning target volume received this dose. Doses were computed with a commercially available treatment planning system using a Monte Carlo(MC) algorithm. Plans were compared according to dose-volume histogram analysis in terms of planning target volume homogeneity and conformity indices(HI and CI), as well as organs at risk(OAR) dose and volume parameters. Results FFF-VMAT was similar to FF-VMAT in terms of CI, but inferior to FF-VMAT considering HI. No statistically differences were observed between FFF-VMAT and FF-VMAT in following organ at risks including pelvic bone marrow, small bowel, bladder, rectum, and normal tissue(NT)..Conclusion For patients with cervical cancer after hysterectomy, the FFF beam achieved target and OAR dose distribution similar to that of the FF beam. Reduction of beam-on time in cervical cancer is beneficial.

Dosimetric comparison of different multileaf collimators in volumetric modulated arc therapy for malignant pleural mesothelioma

Objective The aiom of the study was to compare the impacts of two types of multileaf collimators （MLC） [standard MLC with a width of 10 mm （sMLC） and micro-MLC with a width of 5 mm （mMLC）] on volumetric modulated arc therapy （VMAT） planning for malignant pleural mesothelioma. Methods VMAT for ten patients with inoperable malignant pleural mesotheliomas was retrospectively planned with the sMLC and mMLC. Histogram-based dose-volume parameters of the planning target vol- ume （PTV） [conformity index （CI） and homogeneous index （HI）] and organs-at-risk were compared for VMAT plans with sMLC （sMLC-VMAT） and mMLC （mMLC-VMAT）. Results The mMLC-VMAT plans were more efficient （average delivery time： 2.67±1.49 min） than the sMLC-VMAT plans （average delivery time： 4.21 ± 2.03 min; P 〈 0.05）. Moreover, compared to the sMLC plans, the mMLC plans demonstrated advantages in the dose coverage of the PTV （CI 0.75 ± 0.08 vs 0.73± 0.09; HI 1.09 ±0.02 vs 1.10± 0.02）, although the difference was not statistically significant （P 〉 0.05）. In addition, significant dose sparing in the fraction of the ipsilateral lung volume receiving 〉 20 Gy （V20; 54.72± 27.08 vs 58.52 ± 29.30） and 〉 30 Gy （V30; 42.74 ± 27.86 vs 46.86± 31.49） radiation, respectively, was observed for the mMLC plans （P 〈 0.05）. Conclusion Comparing sMLC-VMAT and mMLC-VMAT not only demonstrated the higher efficiency and better optimal target coverage of mMLC-VMAT, but also considerably improved the dose sparing of the ipsilateral lung in the VMAT plans for mali qnant pleural mesothelioma.

Benefits and Limitations of Volumetric Modulated Arc Therapy in Treating Bilateral Breast Cancer with Regional Lymph Nodes

Purpose: The study was performed comparing dosimetric characteristics of volumetric modulated arc therapy (VMAT) and field-in-field (FiF) techniques on a patient with synchronous bilateral breast carcinoma. Methods: The patients with bilateral breast cancer treatment were included in this study. A total dose of 40.05 Gy in 15 fractions was prescribed to the Planning Target Volume (PTV) of the whole bilateral breast cancer with the supraclavicular and infraclavicular nodes, with a complementary boost of 10 Gy in 4 fractions to the surgical bed (PTVboost). For both radiotherapy techniques, several VxGy parameters were analyzed for the PTVs, together with the Conformity index (CI), the Homogeneity index (HI) and the critical organs at risk (OARs), lungs and heart. Results: The patient was treated by the VMAT technique and the daily treatment time was less than 20 minutes with daily CBCT imaging. In the VMAT plan, the PTV 95% dose covered 38.89 ± 0.81 Gy, compared to 37.26 ± 1.02 Gy in the FiF technique. The VMAT plan improved the dose homogeneity index and lower dose in lung towards high dose region. Conclusion: The study demonstrates the viability of the VMAT technique in the treatment of bilateral breast cancer. The introduced single isocentric VMAT technique is fast to deliver and it increases the dose homogeneity of the target volume with some limitations. The treatment was well tolerated, without interruption of the treatment courses caused by treatment-related toxicities.

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.

A Systematic Approach to Patient-Specific Quality Assurance for Volumetric Modulated Arc Therapy

We developed the first non-commercial treatment planning system for volumetric modulated arc therapy(VMAT) in the United States. Because VMAT involves multi-parameter modulations, it is imperative to develop a comprehensive, rigorous and yet, practical procedure for routine patient-specific quality assurance(QA). In this paper, we presented our own approach as being currently implemented in our institution.Our patient-specific QA procedure involves multi-levels: pre-treatment QA,on-treatment QA, and posttreatment QA. The pre-treatment QA focuses on dosimetry verification, which is done with the commercial Map CHECK in Map PHAN mounted on an isocentric mounting fixture(IMF). This method is also referred to the fixed-gantry technique,i.e., the beams always remain perpendicular to the detector plane. The on-treatment QA involves in vivo optically stimulated luminescent dosimetry(OSLD).Prior to the treatment, two nano Dot TM OSLD dosimeters are placed on the patient abdomen under 1 cm bolus at the isocenter location. The irradiated dosimeters are then read by a nano Dot TM reader and the average reading of the two is calculated. The post-treatment QA involves the analysis of the Dyna Log and DLog files. The Dyna Log is a treatment log file that contains the planned and actual leaf positions at a given gantry angle. The DLog is a treatment log file that contains the planned segmented treatment table(STT) and the corresponding segment boundary samples, i.e., the actual delivered MU and gantry angle increment at each control point.

Long-term follow-up of volumetric modulated arc therapy in definitive radiotherapy for cervical cancer: A single-center retrospective experience

Objective:To evaluate the treatment outcomes and toxicity of volumetric modulated arc therapy(VMAT)in definitive radiotherapy for patients with cervical cancer.Methods:Medical records of 440 patients with cervical cancer treated with VMAT in definitive radiotherapy with or without concurrent chemotherapy between January 2010 and June 2015 in our institution were retrospectively reviewed.A dose of 45 Gy was prescribed to the planning target volume with VMAT in 25 fractions,followed by high-dose rate intracavitary brachytherapy with 28–36 Gy in 4–6 fractions.Survival time was estimated using Kaplan-Meier method.Risk factors for treatment failure were identified using Cox proportional hazards regression model.Results:The median follow-up periods were 58.3 months(range:2.7–112.9 months).The 3-and 5-year survival rates were overall survival(OS)79.4%and 74.4%,cancer-specific survival(CSS)81.4%and 77.1%,progressionfree survival(PFS)73.3%and 71.1%,locoregional control(LC)83.3%and 82%and distant metastasis-free survival(DMFS)80.8%and 77.7%,respectively.The 5-year OS for patients with different stages was IB191.6%,IB2100%,IIA 82.5%,IIB 74.4%,IIIA 57.1%,IIIB 61.7%and IVB 17.6%,respectively.Of the 124 patients with recurrence,93 patients(75.0%)experienced distant failure.Multivariate analysis showed that non-squamous cell carcinoma of the cervix(P<0.001),more advanced stage(P=0.004),pelvic lymph node metastasis(P<0.001)and para-aortic lymph node metastasis(P=0.019)were all independent risk factors of PFS.The incidence of grades 3–4 late bowel toxicities was 2.7%.No grades 3–4 bladder toxicity was observed.Conclusion:This study demonstrated that the use of VMAT in definitive radiotherapy resulted in satisfactory outcomes with acceptable toxicities for patients with cervical cancer.Distant metastasis predominated as the pattern of disease relapse.Further studies are needed to investigate the intensified systemic therapies.

Dosimetric evaluation of VMAT radiation therapy technique for breast cancer after conservative surgery based on three different types of multileaf collimators

Objective Radiotherapy combined with conservative surgery plays an important role in the treatment of early-stage breast cancer. Volumetric modulated arc therapy(VMAT) has been introduced into clinical practice. The purpose of this study was to investigate the dosimetric effects of different multileaf collimators(MLC) on VMAT radiotherapy plans for treating breast cancer.Methods Fifteen breast cancer patients who were treated using a conventional technique in our department were selected to participate in this retrospective analysis. VMAT plans based on three types of Elekta MLCs [Beam Modulator(BM) with 4-mm leaf width, Agility with 5-mm leaf width and MLCi2 with 10-mm leaf width] were independently generated for each patient. Plan comparisons were performed based on dose-volume histogram(DVH) analysis including dosimetric parameters such as the homogeneity index(HI), conformity index(CI), Dmax, Dmin, and Dmean for the planning treatment volume(PTV), in addition to dose-volume parameters for the organs at risk(OARs). The delivery efficiency of the three types of MLCs was compared in terms of the beam delivery time and the monitor units(MUs) per fraction for each plan. Results Both target uniformity and conformity were improved in plans for Agility and BM MLC compared with the plan using MLCi2. The mean HI decreased from 1.14 for MLCi2 to 1.13 for BM and 1.10 for Agility, while the mean CI increased from 0.68 for MLCi2 to 0.73 for BM and 0.75 for Agility. Furthermore, at both low and high dose levels, smaller volumes of ipsilateral lung, heart, contralateral lung, and breast were irradiated with Agility MLC than with the other two types of MLCs. The delivery time with Agility MLC was reduced by 10.8% and 32.1%, respectively, compared with that for MLCi2 and BM.Conclusion Our results indicate that the Agility MLC exhibits a dosimetric advantage and a significant improvement in delivery efficiency for the treatment of breast cancer using VMAT.

Neoadjuvant radiotherapy dose escalation for locally advanced rectal cancers in the new era of radiotherapy:A review of literature

BACKGROUND The standard treatment of locally advanced rectal cancers(LARC)consists on neoadjuvant chemoradiotherapy followed by total mesorectal excision.Different data in literature showed a benefit on tumor downstaging and pathological complete response(pCR)rate using radiotherapy dose escalation,however there is shortage of studies regarding dose escalation using the innovative techniques for LARC(T3-4 or N1-2).AIM To analyze the role of neoadjuvant radiotherapy dose escalation for LARC using innovative radiotherapy techniques.METHODS In December 2020,we conducted a comprehensive literature search of the following electronic databases:PubMed,Web of Science,Scopus and Cochrane library.The limit period of research included articles published from January 2009 to December 2020.Screening by title and abstract was carried out to identify only studies using radiation doses equivalent dose 2 Gy fraction(EQD2)≥54 Gy and Volumetric Modulated Arc Therapy(VMAT),intensity-modulated radiotherapy or image-guided radiotherapy(IGRT)techniques.The authors’searches generated a total of 2287 results and,according to PRISMA Group(2009)screening process,21 publications fulfil selection criteria and were included for the review.RESULTS The main radiotherapy technique used consisted in VMAT and IGRT modality.The mainly dose prescription was 55 Gy to high risk volume and 45 Gy as prophylactic volume in 25 fractions given with simultaneous integrated boosts technique(42.85%).The mean pCR was 28.2%with no correlation between dose prescribed and response rates(P value≥0.5).The R0 margins and sphincter preservation rates were 98.88%and 76.03%,respectively.After a mean follow-up of 35 months local control was 92.29%.G3 or higher toxicity was 11.06%with no correlation between dose prescription and toxicities.Patients receiving EQD2 dose>58.9 Gy and BED>70.7 Gy had higher surgical complications rates compared to other group(P value=0.047).CONCLUSION Dose escalation neoadjuvant radiotherapy using innovative techniques is safe for LARC achieving higher rates of pCR.EQD2 doses>58.9 Gy is associated with higher rate of surgical complications.

Complex Target Volume Delineation and Treatment Planning in Radiotherapy for Malignant Pleural Mesothelioma (MPM)

Introduction: Radiotherapy alone or combined with surgery and/or chemotherapy is being investigated in the treatment of malignant pleural mesothelioma (MPM). This study aimed to simulate a Volumetric Modulated Arc Therapy (VMAT) treatment of a patient with MPM. Materials and Methods: CT images from a patient with intact lungs were imported via DICOM into the Pinnacle3 treatment planning (TP) system (TPS) and used as a model for MPM to delineate organs at risk (OAR) and both clinical and planning target volumes (CTV and PTV) with a margin of 5 mm. Elekta Synergy with 6 MV photons and 80 leafs MLCi2 was employed. VMAT plans were generated using two coplanar arcs with gantry rotation angles of 178° - 182°, the collimator angles of each arc were set to 90°, Octavius® 4D 729 was employed for quality assurance while the calculated and measured doses were compared using VeriSoft. Results: A TP was achieved. The Gamma volume analysis with criteria of 3 mm distance to agreement and 3% dose difference yielded the gamma passing rate = 99.9%. The reference isodose was 42.75 Gy with the coverage constraints for the PTV D95 and V95 = 95.0% of 45 Gy. The remaining dosimetric parameters met the recommendations from the clinically acceptable guidelines for the radiotherapy of MPM. Conclusion: Using well-defined TV and VMAT, a consistent TP compared to similar ones from publications was achieved. We obtained a high agreement between the 3D dose reconstructed and the dose calculated.

Training and evaluation of a knowledge-based model for automated treatment planning of multiple brain metastases

Aim: Volumetric modulated arc therapy (VMAT) has been utilized to plan and treat multiple cranial metastases using a single isocenter due to its ability to provide steep dose gradients around targets as well as low doses to critical structures. VMAT treatment is delivered in a much shorter time compared to using a single isocenter for the treatment of each lesion. However, there is a need to develop methods to reduce the treatment planning time for these cases while also standardizing the plan quality. In this work we demonstrate the use of RapidPlan, which is knowledge-based treatment (KBP) planning software to plan multiple cranial SRS cases. Methods: The 66 patient plans with 125 lesions (range 1-4, median 1) were used to train a model. In addition, the model was validated using 10 cases that were previously treated and chosen randomly. The clinical plans were compared to plans generated by RapidPlan for target coverage and critical organ dose. Results: Coverage to the target volume, gradient index, conformity index and minimum dose to the target showed no significant difference between the original clinical plan vs. the plan generated by KBP. A comparison of doses to the critical organs namely the brainstem, brain, chiasm, eyes, optic nerves and lenses showed no significant difference. Target dose homogeneity was slightly better with the clinical plan, however this difference was also statistically insignificant. ;Conclusion: This work demonstrates that KBP can be trained and efficiently utilized to help not only speed up the planning process but also help standardize the treatment plan quality.