Correlation between monitor units and pass rate of plan dose verification in VMAT plan for different cancers / 中华放射肿瘤学杂志

Objective:To analyze the correlation between the monitor units and pass rate of plan dose verification in the volumetric intensity modulated arc therapy (VMAT) plan.Methods:VMAT plans for 20 patients with nasopharyngeal carcinoma (NPC) and 30 patients with cervical cancer who underwent radiotherapy at Liuzhou Workers' Hospital from January to October 2020 were retrospectively chosen. The Detector 1500 array and Octavius 4D phantom from German PTW company were used for dose measurement. The pass rates of dose verification of relevant plans were analyzed under the conditions of 3%/2 mm and 2%/2 mm. The correlation between the monitor units and pass rate of plan dose verification in VMAT plans was assessed by Pearson's bivariate correlation analysis.Results:Under the condition of 3%/2 mm, the correlation coefficients between the monitor units and gamma pass rate were -0.873 ( P<0.001), -0.800 ( P<0.001), -0.781 ( P<0.001), -0.493 ( P=0.006) for NPC_1Arc, NPC_2Arc, NPC_1Arc+NPC_2Arc and Cervix_2Arc, respectively. Under the condition of 2%/2 mm, the correlation coefficients between the monitor units and gamma pass rate were -0.842 ( P<0.001), -0.770 ( P<0.001), -0.748 ( P<0.001) and -0.531 ( P=0.003) for NPC_1Arc, NPC_2Arc, NPC_1Arc+NPC_2Arc and Cervix_2Arc, respectively. Conclusion:Significant negative correlation can be observed between the monitor units and plan dose verification pass rate in VMAT plan.

A radiobiological and dosimetrical comparison between simultaneous integrated and sequential boost intensity-modulated arc treatment of locally advanced head-and-neck cancer

Purpose: The study aimed to compare the radiobiological and dosimetric parameters between sequential boost (SEQB) and simultaneous integrated boost (SIB) treatment regimen using intensity-modulated arc therapy technique in locally advanced head-and-neck cancer (LAHNC) patients. Materials and Methods: A total of 24 previously untreated LAHNC patients were randomized into SIB (n= 11) and SEQB (n = 13) arms. The planning computed tomography data set was transferred to the treatment planning system. All the target volumes and organ at risk volumes were delineated. Single plan for SIB group and three plans (three phases) were generated for SEQB group of patients. Radiobiological and dosimetric parameters were compared. Results: The BED10(planned) value for high-risk (HR) planning target volume (PTV) was same in both groups, whereas for intermediate-risk (IR) PTV and low-risk (LR) PTV, the values were higher in SEQB arm than SIB arm. The V95 values were 100% for all the target volumes in both arms of patients. The average D100 value for gross target volume, HR PTV, and IR PTV was higher in SEQB arm than that in the SIB arm. The average D100 value for LR PTV was higher in the SIB arm compared to that of the SEQB arm. The BED10(achieved) was calculated using D100 values of target volumes. The difference of BED10(achieved) values between SEQB arm and SIB arm further increased than the BED10(planned) values for all target volumes. The maximum doses for spinal cord, spinal cord planning risk volume, and brain stem were within the tolerance dose in both groups of patients. The left and right parotid glands sparing was comparable in both groups of patients. Average integral dose was higher in the SIB group than SEQB group. The average total monitor unit per fraction was higher in the SEQB arm than that in the SIB arm. Conclusion: SIB regimen may be considered as more logical and efficient over SEQB regimen in the treatment of LAHNC with comparable radiobiological and dosimetric parameters

Efficacy of volumetric intensity modulated arc therapy (VMAT) combined with chemotherapy in anal squamous cell carcinoma / 中华放射医学与防护杂志

Objective To investigate the efficacy of concurrent chemoradiotherapy for anal squamous cell carcinoma (ASCC) in the era of intensity-modulated radiotherapy.Methods A total of 19 patients with ASCC who underwent definitive radiotherapy in our hospital since 2011 were collected.The survival curves were depicted with K-M method.Risk factors of disease progression were analyzed using case-control study.Results The median follow-up time was 31 months.The 3 year-LFS and 3 year-OS were 88.1％ and 91.7％,respectively.Grade 3 acute toxicities during the chemoradiotherapy were mainly white blood cell reduction (15.8％),platelet reduction (10.5％),diarrhea (15.8％),and skin reaction (31.6％).Compared with historical data,volumetric intensity modulated arc therapy was superior to conventional radiotherapy in the treatment outcome and normal tissue protection in ASCC.Univariate analysis showed that concurrent chemotherapy with capecitabine was a favorable factor in disease progression (P＜ 0.05).Conclusions Volumetric intensity modulated arc therapy for ASCC may have advantages in terms of efficacy and normal tissue protection.Concurrent chemotherapy with a double-drug regimen containing capecitabine may be a beneficial factor in disease progression.

Dosimetric comparison on heart and lung among three modalities in treatment of thoracic esophageal cancer / 中华放射医学与防护杂志

Objective To compare the dosimetric differences in heart and lung among three radiotherapy techniques in the treatment of thoracic esophageal cancer. Methods A total of 15 thoracic esophageal cancer patients treated in Zhejiang Cancer Hospital during the period of January 2015 to February 2016 were enrolled in this retrospective dosimetric study. Three radiotherapy treatment plans, including intensity-modulated radiotherapy ( IMRT) , volumetric intensity modulated arc therapy ( VMAT) with Raystation 4. 0v TPS, and tomotherapy (TOMO) plans with TomoTTM v2. 0. 5 TPS were generated for each patient with a prescribed dose of 60 Gy at 2 Gy per fraction. Dosimetric differences in planning target volume ( PTV) , heart, cardiac subunits and lung were compared. Results The mean volumes of PTV, heart and lung were (399 ±355), (671 ±274) and (3907 ±1717)cm3, respectively. Compared with VMAT and IMRT, TOMO reduced the maximum dose of PTV, heart, left atrium and lung ( H=10. 889, 7. 433, 12. 080, 11. 401, P <0. 05). No difference was observed in conformity or homogeneity among these three plans. Conclusions TOMO reduced the maximum dose to PTV, heart, left atrium and lung compared with VMAT and IMRT, However, no difference in conformity and homogeneity was observed. The impact of dosimetric advantage of TOMO needs further verification due to the interaction between heart and lung for thoracic esophageal cancer patients.

Analysis of VMAT dosimetric verifications with different techniques / 中华放射肿瘤学杂志

Objective To investigate the gamma (γ) passing rates for volumetric-modulated arc therapy (VMAT) dosimetric verification with different techniques.Methods A total of 12 VMAT plans for the treatment of different anatomical sites in cancer patients were chosen.The Octavius 4D system was used to measure the dose distributions in two different settings:the gantry was rotating (three-dimensional (3D) and 2D γ-analysis) and the gantry was fixed at 0°(2D γ-analysis).The γ passing rates were analyzed with 3%/3 mm and 2%/2 mm criteria, using the paired t test or Wilcoxon signed-rank test.The 2D γ passing rates for different irradiation methods were calculated.Results For the 3D and 2D dose distributions obtained at a rotating gantry angle as well as the 2D dose distribution obtained at zero gantry angle, the average γ passing rates were 96.03%, 96.98%, and 98.90% for 3%/3 mm (P=0.227, P=0.000, P=0.003);82.08%, 84.04%, and 90.90% for 2%/2 mm (P=0.379, P=0.000, P=0.000).For the 2D dose distributions obtained with different irradiation methods, the average γ passing rate was 98.99% for 3%/3 mm and 93.68% for 2%/2 mm.Conclusions The VMAT dosimetric verification based on a 3D volumetric dosimeter at a rotating gantry position can be clinically useful for delivery quality assurance (QA), and can achieve the most reliable dose calculation for VMAT, which has more referential values.

Comparison study of intensity modulated arc therapy using single or multiple arcs to intensity modulated radiation therapy for high-risk prostate cancer

PURPOSE: Intensity modulated arc therapy (IMAT) is a form of intensity modulated radiation therapy (IMRT) that delivers dose in single or multiple arcs. We compared IMRT plans versus single-arc field (1ARC) and multi-arc fields (3ARC) IMAT plans in high-risk prostate cancer. MATERIALS AND METHODS: Sixteen patients were studied. Prostate (PTVP), right pelvic (PTVRtLN) and left pelvic lymph nodes (PTVLtLN), and organs at risk were contoured. PTVP, PTVRtLN, and PTVLtLN received 50.40 Gy followed by a boost to PTVB of 28.80 Gy. Three plans were per patient generated: IMRT, 1ARC, and 3ARC. We recorded the dose to the PTV, the mean dose (DMEAN) to the organs at risk, and volume covered by the 50% isodose. Efficiency was evaluated by monitor units (MU) and beam on time (BOT). Conformity index (CI), Paddick gradient index, and homogeneity index (HI) were also calculated. RESULTS: Average Radiation Therapy Oncology Group CI was 1.17, 1.20, and 1.15 for IMRT, 1ARC, and 3ARC, respectively. The plans' HI were within 1% of each other. The DMEAN of bladder was within 2% of each other. The rectum DMEAN in IMRT plans was 10% lower dose than the arc plans (p < 0.0001). The GI of the 3ARC was superior to IMRT by 27.4% (p = 0.006). The average MU was highest in the IMRT plans (1686) versus 1ARC (575) versus 3ARC (1079). The average BOT was 6 minutes for IMRT compared to 1.3 and 2.9 for 1ARC and 3ARC IMAT (p < 0.05). CONCLUSION: For high-risk prostate cancer, IMAT may offer a favorable dose gradient profile, conformity, MU and BOT compared to IMRT.

The study of two-dimensional dosimetric verifications of volumetric intensity-modulated arc therapy based on electronic portal imaging devices / 中华放射肿瘤学杂志

Objective To develop an accurate 2D dose reconstruction model using electronic portal imaging device (EPID).2D dosimetric verifications of volumetric intensity-modulated arc therapy (VIMAT)were done using the model.And the results were compared to other dosimeters.Methods The EPID-based dose reconstruction model was using convolve,deconvolve and correction function.The dose profiles which were obtained by the ion chamber were used to determine the model parameters.A total of 12 VIMAT plans for the treatment of anatomical sites of various complexities were chosen.The results obtained from EPID were compared to other dosimeters and treatment planning system (TPS).The ion chamber was used to measure the central point absolute doses.Other dosimeters were used to measure the plane dose distributions.All dosimeters measured the dose at 10 cm depth.The results were analyzed using γevaluation method.Results Regarding absolute central point doses,the ion chamber results were within 1.5％ of the EPID results.For the comparison to Seven29 and Matrixx,the average γ pass rates with 2％and 2 mm criteria were 98.9％ and 99.8％ respectively.For the dose distributions measured by EPID and calculated by TPS,the γ pass rates with 3％ and 3 mm criteria were 99.9％.Conclusions The presented results which were obtained from the comparison of measured and calculated doses show the reliability of our EPID-based dose reconstruction model.With the model,EPID can be a reliable and fast tool for IMRT plan dosimetric verification.The model expanded to the 3D dosimetric verification in the uniform phantom will be considered as the next work.

Dosimetric Characteristics of Multileaf Collimator-based Intensity-modulated Arc Therapy for Stereotactic Radiosurgery / 의학물리

This study was designed to evaluate radiosurgery technique using multiple noncoplanar arc therapy with intensity modulated fine MLC shaped photon beam. The stereotactic radiosurgery was performed with 6-MV X-ray beams from a Clinac 21EX LINAC (Varian, Palo Alto, CA, USA) with a MLC-120, which features a full 40 x 40 cm field and is the first MLC for general use that offers 0.5 cm resolution for high precision treatment of small and irregular fields. We used a single isocenter and five gantry-couch combinations with a set of intensity modulated arc therapy. We investigated dosimetric characteristics of 2 cm sized spherical target volume with film (X-OMAT V2 film, Kodak Inc, Rochester NY, USA) dosimetry within 25 x 25 cm acrylic phantom. A simulated single isocentric treatment using inversely planned 3D radiotherapy planning system demonstrated the ability to conform the dose distribution to an spherical target volume. The 80% dose level was adequate to encompass the target volume in frontal, sagittal, and transverse planes, and the region between the 40% and 80% isodose lines was 4.0~4.5 mm and comparable to the dose distribution of the Boston Arcs. We expect that our radiosurgery technique could be a treatment option for irregular-shaped large intracranial target.