Modulated Arc Radiotherapy Research Articles

Impact of the Use of Homogeneous and Heterogeneous Phantoms in Pretreatment Verification for Volumetric Modulated Arc Radiotherapy

The purpose of this study was to investigate the impact of quality assurance (QA) phantoms designed with different material to verify the accuracy of dose distribution for volumetric modulated arc radiotherapy (VMAT). Homogeneous and heterogeneous QA phantoms are developed to compare the pretreatment verification according to the different materials made in the phantom for routine VMAT of lung cancer. These phantoms have a quadrature rectangular shape with horizontal and vertical lengths of 300 mm and 315 mm, respectively, and with inserts of various slabs. The homogeneous QA phantom was constructed using only polymethyl methacrylate (ρ = 1.19 g/cm3). The heterogeneous QA phantom was constructed using a ceramic fiber board with a density of 0.3 g/cm3, which is similar to that of the lung in human thorax. Overall, the average gamma agreement values for the homogeneous and the heterogeneous QA phantoms were observed to be higher than 94.9% and 95.4% for two energies and the usual criteria. In addition, this study showed that the gamma agreement values obtained for both the homogeneous and the heterogeneous QA phantom agreed to within 2% for both the 2%/2 mm and the 3%/3 mm criteria. Furthermore, no statistically significant difference was observed in the gamma agreement values obtained using the homogeneous and the heterogeneous QA phantoms for both energies and the usual criteria (p > 0.05). Consequentially, this study found that patient specific QA results were not affected by phantoms made of the different materials.

Monitoring of platelet function parameters and microRNA expression levels in patients with prostate cancer treated with volumetric modulated arc radiotherapy.

Radiotherapy (RT) may result in platelet activation and thrombosis development. To the best of our knowledge, the potential effect of volumetric-modulated arc therapy (VMAT), a novel radiotherapy technique, on platelet function and microRNA (miRNA/miR) expression has not been previously investigated. The present study aimed to determine the effect of VMAT on the alterations in platelet function parameters and miRNA expression levels. A total of 25 patients with prostate cancer and 25 healthy subjects were included in the present study. Blood samples were collected from the patient group on the day prior to RT (pre-RT), the day RT was completed (post-RT day 0), and 40 days following the end of therapy (post-RT day 40). Platelet count, mean platelet volume (MPV) value, platelet aggregation, plasma P-selectin, thrombospondin-1, platelet factor 4, plasma miR-223 and miR-126 expression levels were measured. A significant decrease in platelet count in the post-RT day 0 group was measured in comparison with the pre-RT and the post-RT day 40 groups. Pre-RT MPV values were higher than those of the post-RT day 0 and the post-RT day 40 groups. No significant differences were observed in the levels of platelet activation markers or miR-223 and miR-126 expression levels between the RT groups. Although RT may result in a reduction in platelet and MPV counts, the results of the present study indicate that platelet activation markers are not affected by VMAT. Therefore, it is possible that no platelet activation occurs during VMAT, owing to the conformal dose distributions, improved target volume coverage and the sparing of normal tissues from undesired radiation.

What Is the Optimal Radiation Technique for Esophageal Cancer? A Dosimetric Comparison of Four Techniques.

BackgroundEsophageal cancer treatment requires large radiation fields due to the deep location of the esophagus in the mediastinum and the high incidence of radial spread. There is no optimal radiation technique to ensure appropriate target coverage and minimal dose to all normal structures.MethodsFifteen consecutive cases of locally advanced esophageal cancer treated with radical chemoradiation (CRT) were analyzed. The total prescribed dose was 50.4 Gy in 28 fractions. A total of 60 plans were generated for analysis, including four different methods for each case. Method 1 consisted of a four-field conformal technique; method 2 was a two-plan technique (antero-posterior (AP), postero-anterior (PA), two posterior oblique fields (RPO and LPO)); method 3 was a three-field conformal technique (AP, LPO, RPO); and method 4 was a volumetric modulated arc radiotherapy (VMAT) technique. Dose ratios were calculated using the minimum, maximum, mean, and median doses of methods 2-4 over the dose of method 1. Ratios for the planning target volume (PTV) and to surrounding organs were analyzed.ResultsThe mean PTV dose ratio ranged from 0.994 to 1.048 (SD = 0.01) representing an adequate target coverage for all techniques based on an analysis of variance (ANOVA). For the lungs, method 2 had the lowest lung V20 with a ratio of 0.861 (SD = 0.12), whereas method 3 had the highest with 1.644 (SD = 0.14). For the heart, method 3 had the lowest heart V40 with a mean dose ratio of 0.807 (SD = 0.09), whereas method 2 had the highest with 1.160 (SD = 0.11). For the liver, method 2 had the lowest V30 with a mean ratio of 0.857 (SD = 0.1) whereas method 4 had the highest with 1.672 (SD = 0.48). For the spinal cord, method 3 had the lowest mean dose ratio of 0.559 (SD = 0.09) whereas method 2 had the highest with 1.094 (SD = 0.04).ConclusionThe four radiation techniques for esophageal cancer treatment were appropriate for target coverage. Method 2 had the most organ-sparing effect for the lungs and liver, and method 3 for the heart and spinal cord. VMAT did not add any significant sparing. A case-by-case decision should be made based on the patient’s comorbidities.

High dose hypofractionated frameless volumetric modulated arc radiotherapy is a feasible method for treating canine trigeminal nerve sheath tumors.

The aim of this prospective pilot study was to evaluate the feasibility and effectiveness of curative intent high dose hypofractionated frameless volumetric modulated arc radiotherapy for treatment of canine trigeminal peripheral nerve sheath tumors. Client-owned dogs with a presumptive imaging-based diagnosis of trigeminal peripheral nerve sheath tumor were recruited for the study during the period of February 2010 to December 2013. Seven dogs were enrolled and treated with high dose hypofractionated volumetric modulated arc radiotherapy delivered by a 6 MV linear accelerator equipped with a micro-multileaf beam collimator. The plans were computed using a Monte Carlo algorithm with a prescription dose of 37 Gy delivered in five fractions on alternate days. Overall survival was estimated using a Kaplan-Meier curve analysis. Magnetic resonance imaging (MRI) follow-up examinations revealed complete response in one dog, partial response in four dogs, and stable disease in two dogs. Median overall survival was 952 days with a 95% confidence interval of 543-1361 days. Volumetric modulated arc radiotherapy was demonstrated to be feasible and effective for trigeminal peripheral nerve sheath tumor treatment in this sample of dogs. The technique required few sedations and spared organs at risk. Even though larger studies are required, these preliminary results supported the use of high dose hypofractionated volumetric modulated arc radiotherapy as an alternative to other treatment modalities.

Has New Technology Reduced or Increased the Variances of Volumetric Modulated Arc Radiation Therapy (VMAT) Compared to Non-VMAT Treatment Techniques?

Has New Technology Reduced or Increased the Variances of Volumetric Modulated Arc Radiation Therapy (VMAT) Compared to Non-VMAT Treatment Techniques?

Outcomes of salvage radiotherapy for recurrent prostate cancer after radical prostatectomy.

Salvage radiotherapy (SRT) provides effective biochemical control for patients with prostate cancer who have prostate specific antigen (PSA) failure after radical prostatectomy. However, the effect of SRT on long-term clinical outcomes remains unknown. Therefore, we report the natural history of patients treated with SRT. We identified 84 Chinese patients with prostate cancer treated with SRT to the prostatic fossa alone during 2006-2017 at Tuen Mun Hospital, Hong Kong. Survival was calculated using Kaplan-Meier method. Log-rank test and Cox regression were used to determine significance of clinical parameters with outcomes. Median SRT dose given was 70 Gy (range, 64-76 Gy). Median pre-SRT PSA level was 0.4 ng/mL (0.2-7.4 ng/mL). After SRT, 47 (56%) patients had undetectable (<0.1 ng/mL) PSA levels. After median follow-up of 48 months (2 months to 10 years), 25 (30%) patients had further biochemical progression. Subsequently, 12 patients received androgen deprivation therapy and nine (11%) developed distant metastasis. The 5-year biochemical progression-free survival, androgen deprivation therapy-free survival and metastasis-free survival were 62.7%, 83.5% and 86.7%, respectively. Early PSA failure after radical prostatectomy (hazard ratio 7.4), negative surgical margin (hazard ratio 2.7), positive extracapsular extension (hazard ratio 4.6), and detectable PSA levels after SRT (hazard ratio 17.3) were associated with lower biochemical progression-free survival after SRT. High-dose SRT with intensity-modulated radiotherapy/volumetric modulated arc radiotherapy is an effective local treatment that can prevent distant metastasis and avoid the need for androgen deprivation therapy in Chinese patients who have PSA failure after radical prostatectomy.

Optimizing the prescription isodose level in stereotactic volumetric-modulated arc radiotherapy of lung lesions as a potential for dose de-escalation

BackgroundTo derive and exploit the optimal prescription isodose level (PIL) in inverse optimization of volumetric modulated arc radiotherapy (VMAT) as a potential approach to dose de–escalation in stereotactic body radiotherapy for non–small cell lung carcinomas (NSCLC).MethodsFor ten patients, inverse Monte Carlo dose optimization was performed to cover 95% PTV by varying prescription isodose lines (PIL) at 60 to 80% and reference 85%. Subsequently, these were re–normalized to the median gross tumor volume dose (GTV–based prescription) to assess the impacts of PTV and normal tissue dose reduction.ResultsWith PTV–based prescription, GTV mean dose was much higher with the optimized PIL at 60% with significant reduction of normal lung receiving 30 to 10 Gy (V30–10Gy), and observable but insignificant dose reduction to spinal cord, esophagus, ribs, and others compared with 85% PIL. Mean doses to the normal lung between PTV and GTV was higher with 60–70% PIL than 85%. The dose gradient index was 5.0 ± 1.1 and 6.1 ± 1.4 for 60 and 85% PIL (p < 0.05), respectively. Compared with the reference 85% PIL plan using PTV–base prescription, significant decreases of all normal tissue doses were observed with 60% and 70% PIL by GTV–based prescription. Yet, the resulting biological effective (BED) mean doses of PTV remain sufficiently high, ranging 104.2 to 116.9 Gy α/β = 10.ConclusionsOptimizing the PIL with VMAT has notable advantage of improving the dosimetric quality of lung SBRT and offers the potential of dose de–escalation for surrounding tissues while increasing the GTV dose simultaneously. The clinical implication of re–normalizing plans from PTV–prescription at 60–70% to the GTV median dose requires further investigations.

Use of volumetric modulated arc radiotherapy in patients with early stage glottic cancer.

We compared conformal, intensity-modulated radiotherapy (IMRT) and intensity-modulated arc therapy (IMAT) in early stage glottic cancer in terms of dosimetric features as target coverage, dose to the organs at risk and total treatment time. Five consecutive T1 glottic squamous cell carcinoma patients were selected for the study. Three-dimensional conformal radiotherapy (3D-CRT), 3-field or 5-field intensity-modulated radiotherapy (3F-IMRT and 5F-IMRT), or IMAT, which was in 2 different forms--a regular IMAT (R-IMAT) and an alternative IMAT (A-IMAT) with an unirradiated section, was planned for each patient. The prescribed dose was 63 Gy in 28 fractions. The minimum dose for 95% of the clinical target volume (D95), maximum dose point at clinical target volume (Dmax), total monitor units, left and right carotid artery doses (V35 and V50 - percentage of volume receiving 35 Gy and 50 Gy), and total treatment time were calculated for each plan. Median D95 values in the 5 plans studied with each technique ranged between 63 and 63.3 Gy (P = NS). Median Dmax values for each technique ranged between 65.4 and 70.8 Gy. The number of hot spots with IMRT and IMAT was significantly higher than with 3D-CRT plans. Conformal radiotherapy plans median V35 (93.6%) and V50 (76.6-83.3%) values for carotid arteries were significantly higher than with IMRT and IMAT (2.9%-11.4% and 0.0%). Average treatment times for 3D-CRT, 3F-IMRT, 5F-IMRT, R-IMAT and A-IMAT techniques were calculated as 64, 119, 147, 39 and 32 seconds, respectively. IMAT has significantly decreased the treatment time compared to IMRT and 3D-CRT with acceptable homogeneous clinical target volume coverage and low carotid dose.

Stereotactic Volume Modulated Arc Radiotherapy in Canine Meningiomas: Imaging-Based and Clinical Neurological Posttreatment Evaluation.

A prospective study to assess high-dose hypofractionated volume modulated arc radiotherapy feasibility and efficacy in canine meningiomas was conducted. Thirty-nine patients with encephalic and spinal meningiomas assumed from MRI findings were recruited and received high-dose hypofractionated volumetric modulated arc radiotherapy by a linear accelerator equipped with an external beam modulator micro-multileaf collimator and an XVI cone beam computed tomography system. The prescribed mean dose was 33 Gy in five fractions. The treatment feasibility was tested through planned and delivered dose agreement checks. Regular clinical examinations were performed during and after irradiation time, with regard to mentation, deambulation, cranial nerve dysfunction, and seizures. Serial MRI exams were done 60 days after irradiation and after 4, 6, 12, 18, and 24 mo. Volumetric disease reduction criteria implemented with clinical neurological systematic evaluation were adopted to assess the course and to categorize patients' responses. Complete and partial responses were observed on the whole in 65.5% of alive patients 24 mo after irradiation. Two-yr overall and disease-specific survival rates were 74.3% and 97.4%, respectively, and the putative radiotoxic effects were found to be few and slight.

Chest wall dose reduction using noncoplanar volumetric modulated arc radiation therapy for lung stereotactic ablative radiation therapy

PurposeStereotactic ablative radiation therapy (SABR) to lung tumors close to the chest wall can cause rib fractures or chest wall pain. We evaluated and propose a clinically practical solution of using noncoplanar volumetric modulated arc radiation therapy (VMAT) to reduce chest wall dose from lung SABR. Methods and materialsTwenty lung SABR VMAT plans in which the chest wall volume receiving 30 Gy or higher (V30) exceeded 30 mL were replanned by noncoplanar VMAT with opposite 15° couch kicks. Dosimetric parameters including chest wall V30 and V40; lung V5, V10, V20, and mean dose; Paddick high-dose conformity index; intermediate-dose conformity index; and monitor units (MU) for each plan were used to evaluate the plan quality. The treatment time was also estimated by delivering the entire treatment. Two-sided paired t test was used to evaluate the difference of the dosimetric parameters between coplanar 1 arc (cVMAT1), coplanar 2 arcs (cVMAT2), and noncoplanar two arcs (nVMAT2) plans; differences with P < .05 were considered statistically significant. ResultsV30 and V40 for chest wall were reduced on average by 20% ± 9% and 15% ± 11% (mean ± standard deviation) from cVMAT2 plans to nVMAT2 plans (P < .01 for both comparisons) and by 8% ± 7% and 16% ± 13% from cVMAT1 plans to cVMAT2 plans (P < .003 for both comparisons). The differences in lung mean dose were <0.2 Gy among cVMAT1, cVMAT2, and nVMAT2. There were no significant differences in lung V5, V10, and V20. On average, the number of MU increased 14% for nVMAT2 compared with cVMAT2. The Paddick high-dose conformity indexes were 0.88 ± 0.03, 0.89 ± 0.04, and 0.91 ± 0.03, and intermediate-dose conformity indexes were 3.88 ± 0.49, 3.80 ± 0.44 and 3.51 ± 0.38 for cVMAT1, cVMAT2, and nVMAT2, respectively. ConclusionsWe found that noncoplanar VMAT plans are feasible, clinically practical to deliver, and significantly reduce V30 and V40 of chest wall without increasing lung dose.

Effect of angle correction factors of MatriXX on VMAT dose verification

Objective To investigate the effect of the angle correction factors of ionization chamber array Matrixx on the dosimetric verification of volumetric modulated arc therapy plan. Methods The Matrixx (IBA) was put in the middle of the MultiCube Phantom. Computed tomography scan was performed and the results were sent to the Raystation treatment planning system (TPS). All data calculated from TPS and actually measured using MatriXX were gained under the following conditions: 6 MV, 100 MU, 28 cm×28 cm radiation field. And the directions of beam were from 0°to 180°with an interval of 5°(except an interval of 1° from 85° to 95°). The angle correction factors (CF)(θ) cor of MatriXX were calculated by the calculated dose values from TPS and the measured values using MatriXX and then mirrored to the opposite side. CF (θ) cor values were compared with CF (θ) def values that were given by manufacturer. The comparison was made by paired t-test. Results CF (θ) cor and CF (θ) def were different, and the difference was significant between 85° and 95°, with a maximum of 7.5%(P<0.05). The CF (θ) cor correction method had a higher gamma pass rate than the CF (θ) def correction method, with a maximum of 17%(P<0.05). Conclusions The ionization chamber array MatriXX has an angular dependence and the angle correction should be performed. The angle correction factors have the individual characteristics and are different in every unit ionization chamber of the MatriXX. Therefore, it is necessary to do angle correction for every unit ionization chamber of the MatriXX and the possible errors caused by various factors should be considered in order to improve the accuracy rate and gamma pass rate of the plan verification. Key words: Ionization chamber matrix; Angle correction factor; Volumetric modulated arc radiotherapy; Plan verification

Phase 1/2 Study on Stereotactic Hypofractionated Once-Weekly Radiation Therapy for Nonmetastatic Prostate Cancer

Stereotactic radiotherapy has shown promising results in Phase II studies, but has been investigated predominantly in patients with low-intermediate risk disease. We conducted a clinical trial of stereotactic hypofractionated radiotherapy delivered in once-weekly fractions on patients with non-metastatic disease to test feasibility, acute toxicities, patient reported outcomes, and biochemical control in a cohort with predominantly high-risk disease. Patients with prostatic adenocarcinoma, Gleason 6-10, T1-4N0 (staged with multiparametric MRI and bone scans) and PSA <=60 ng/ml were eligible for enrolment into this Phase I/II trial. A planned sample of 30 patients were treated with volumetric intensity modulated arc radiation therapy to a dose of 35 Gy in 5 fractions delivered once-weekly with an overall treatment time of 29 days. Patients with high-risk disease also received elective nodal irradiation to a dose of 25 Gy in 5 fractions simultaneously. Androgen deprivation was offered to intermediate and high risk patients. Trial specific dose constraints were ensured. The primary outcome was acute toxicity with NCI CTC v4. Secondary outcome measures included biochemical control and late toxicity. Patient reported outcomes were measured with the IPSS score and EORTC QLQ-C30 and PR25 questionnaires. Clinically meaningful worsening of quality of life scores was defined as a 10 point reduction (out of 100) in any scale. All 30 patients completed treatment per-protocol. The majority of patients had T3 (60%) and Gleason 7 (50%) tumors. The median PSA was 17 ng/ml. High risk disease was present in 20 patients (66.7%). There was low incidence of acute toxicities (Grade 2+ urinary toxicities in 1 -3.3%, and grade 2+ rectal toxicities in none). The mean IPSS scores increased from baseline 8.6 to 14.6 at the end of treatment (P < 0.001) but reduced to 10.9 at 6 months (P = 0.05). Of the 21 parameters studied in the EORTC QLQ framework, only the urinary symptom score showed a clinically meaningful worsening from a mean of 20/100 at baseline to 34/100 at end of treatment (P < 0.001), but reduced to 24/100 at 6 months (P = 0.08). Other functional or symptomatic scales did not show any clinically meaningful worsening. There was 1 patient each with late grade 2 rectal bleeding and grade 2 urinary toxicity. With a median follow-up of 25 months, 1 patient developed a distant failure at 10 months, with a 2 year biochemical control rate of 96.7%. In a cohort of mainly high risk cancers in a developing country, stereotactic once-weekly radiation therapy was easy to implement, safe and well tolerated with a low incidence of acute toxicity. Preliminary biochemical control and late toxicity profiles are encouraging. This paves the way for further prospective evaluation in a larger cohort of patients with high-risk disease.

Postoperative radiotherapy for prostate cancer

PurposeThe aim of this work was to characterise actuarial incidence and prevalence of early and late side effects of local versus pelvic three-dimensional conformal postoperative radiotherapy for prostate cancer.Materials and methodsBased on a risk-adapted protocol, 575 patients received either local (n = 447) or local-plus-pelvic (n = 128) radiotherapy. Gastrointestinal (GI) and genitourinary (GU) side effects (≥grade 2 RTOG/EORTC criteria) were prospectively assessed. Maximum morbidity, actuarial incidence rate, and prevalence rates were compared between the two groups.ResultsFor local radiotherapy, median follow-up was 68 months, and the mean dose was 66.7 Gy. In pelvic radiotherapy, the median follow-up was 49 months, and the mean local and pelvic doses were 66.9 and 48.3 Gy respectively. Early GI side effects ≥ G2 were detected in 26% and 42% of patients respectively (p < 0.001). Late GI adverse events were detected in 14% in both groups (p = 0.77). The 5‑year actuarial incidence rates were 14% and 14%, while the prevalence rates were 2% and 0% respectively. Early GU ≥ G2 side effects were detected in 15% and 16% (p = 0.96), while late GU morbidity was detected in 18% and 24% (p = 0.001). The 5‑year actuarial incidence rates were 16% and 35% (p = 0.001), while the respective prevalence rates were 6% and 8%.ConclusionsDespite the low prevalence of side effects, postoperative pelvic radiotherapy results in significant increases in the actuarial incidence of early GI and late GU morbidity using a conventional 4‑field box radiotherapy technique. Advanced treatment techniques like intensity-modulated radiotherapy (IMRT) or volumetric modulated arc radiotherapy (VMAT) should therefore be considered in pelvic radiotherapy to potentially reduce these side effects.

Mid-term outcomes of a prospective phase II trial of preoperative sandwich-like neoadjuvant chemoradiotherapy for locally advanced rectal cancer

Objective To evaluate the mid-to long-term survival benefits of preoperative sandwich-like neoadjuvant chemoradiotherapy (CRT) in patients with locally advanced rectal cancer (LARC). Methods A total of 45 LARC patients who underwent neoadjuvant sandwich CRT in the form of XELOX regimen prior to, concurrently with, and following volumetric modulated arc radiotherapy (VMAT) in 2012 were enrolled in this study. VMAT was given at a gross tumor volume dose of 50 Gy in 25 fractions, and a clinical target volume dose of 45-46 Gy in 25 fractions. Total mesorectal excision was performed 6 to 8 weeks after completion of VMAT.The overall survival (OS) and disease-free survival (DFS) were determined by the Kaplan-Meier method, and survival comparison and univariate prognostic analysis were performed using the log-rank test. Results The median follow-up time was 46.7 months. There was no local recurrence detected among the patients. The 3-year distant metastasis (DM) rate was 18%, and the 3-year OS and DFS were 96% and 84%, respectively. Univariate analysis indicated that perineural invasion, N1-N2 pathology (pathological stage Ⅲ), and Ca-199>35 U/ml before treatment were risk factors for DM (P=0.000, 0.000, and 0.013, respectively). Conclusions The significant short-term efficacy of preoperative sandwich-like neoadjuvant CRT can be extended to a positive mid-term survival in LARC patients. However, further phase Ⅲ clinical studies will be needed to confirm this finding. Key words: Rectal neoplasms/chemoradiotherapy; Chemoradiotherapy, neoadjuvant; Prognosis

Frameless stereotactic radiotherapy alone and combined with temozolomide for presumed canine gliomas.

We evaluated stereotactic volume modulated arc radiotherapy (VMAT) for canine gliomas, alone (radiotherapy [RT]) and in combination with temozolomide (RT + TMZ), compared with palliation. Overall and disease-specific survival times were estimated. Thirty dogs were palliated, 22 dogs were treated with RT and 20 with RT + TMZ. Complete and partial responses were observed in 63.2% and 90.9% of patients in the RT and RT + TMZ arms, respectively, that were alive at 1 year. Median survival in the palliation arm was 94 days (95% conformity index [CI] 87÷101). Median survivals of the RT arm (383 days, 95% CI 276÷490) and RT+TMZ arm (420 days, 95% CI 280÷560) were not significantly different (P = .61). Positive correlation with survival was found both for the ratio between target and brain (relative) volume of the tumour of <5% (P = .013) and for a clinical presentation with normal mentation (P = .032). VMAT is feasible and effective for canine brain gliomas. Combining this therapy with TMZ did not elicit any additional improvement in survival time.

Trajectory modulated arc therapy using quasi-continuous couch motion layered on top of volumetric modulated arc therapy in left breast and chest wall irradiation: a feasibility study

AbstractAimTo investigate the dosimetric advantage of quasi-continuous couch motion-enabled trajectory modulated arc radiotherapy therapy (TMAT) over the coplanar tangential partial arcs volumetric modulated arc radiotherapy (VMAT) for treating left breast and chest wall patients.MethodTreatment plans of 43 patients who received radiotherapy for left breast (17) or for left chest wall (26) using coplanar partial tangential arcs VMAT (reference plan) were considered for this study. For each patient, in addition to the treatment plan, a TMAT plan was also generated using quasi-continuous couch rotation. The TMAT plan consisted of original two 30° tangential arc beams and two supplementary beams having a couch rotation of ±10°, ±20° and ±30°, respectively. The difference in PTV volume coverage (PTV V95%) between TMAT plan and VMAT plan was calculated for all the cases and normalised to the plan’s prescription dose. Similarly, differences in PTV_V105% and several dose-volume parameters related to organs at risk (OAR) were also computed and tabulated.ResultTMAT shows an increment in the PTV dose coverage V95% with respect to reference plan by 4·7±2·5% when averaged overall prescription dose levels. Mean PTV dose (averaged overall prescription levels) for reference and TMAT plan was 4638·6±423·8 and 4793·5±447·2 cGy, respectively, and statistically insignificant (p=0·06). However mean PTV_V105% values for TMAT and for reference plans were 6·7±4·8 and 7·2±5·2%, respectively, and were not statistically different (p=0·85). Mean heart dose in TMAT was less than in VMAT plans, but not significantly. As regarding D1% to heart, TMAT plan was again found to be better with a mean difference of 137·1 cGy over VMAT plan. Other parameters evaluated were: mean dose and D1% to contralateral breast, and V20 Gy and V5 Gy for lung.ConclusionTMAT plans were found to be better than VMAT plans in terms of PTV coverage and D1% for heart. For evaluated dose parameters apart from PTV coverage and D1% to the heart, no significant differences were observed. Thus, TMAT plans yielded better dose distribution in terms of PTV dose coverage, hot spots and OAR doses.

Actual gains in dosimetry and treatment delivery efficiency from volumetric modulated arc radiotherapy for inoperable, locally advanced lung cancer over five-field forward-planned intensity-modulated radiotherapy

Volumetric modulated arc radiotherapy (VMAT) is used for inoperable, locally advanced nonsmall cell lung cancer, where three-dimensional conformal radiotherapy (3D-CRT) cannot yield an acceptable plan. The planning and treatment data were prospectively collected on the first 18 patients treated using VMAT plans. We analyzed the actual dosimetric gain and impact on treatment, compared with complex multisegment 3D-CRT (five-field forward-planned intensity-modulated radiotherapy [IMRT]) that were generated for treatment. Proportion of planning target volume (PTV) receiving 95% dose (PTV-V95%) conformity index (CI), conformity number (CN), dose homogeneity index (DHI), monitor units (MUs), and treatment time were also analyzed. The PTV coverage (PTV-V95%) was improved from a median of 91.41% for 5-F forward-IMRT to 98.25% for VMAT (P < 0.001). The CI improved with a mean of 1.12 for VMAT and 1.31 for 5-F forward-IMRT (P < 0.001). The mean DHI improved from 1.15 for forward-IMRT to 1.08 for VMAT (P < 0.001). The mean CN improved from 0.62 for forward-IMRT to 0.87 for VMAT (P < 0.001). No significant increase in the low-dose bath (V5, V10 and mean lung dose) to the lung was seen. Significantly higher number of MUs (P < 0.001) and shorter treatment delivery times (P = 0.03) were seen with VMAT. VMAT resulted in improvement in target volume coverage, demonstrated by PTV-V95%, CI, CN, and DHI, without any increase in the low-dose bath to the lung. For conventional fractionation, VMAT requires more MUs (P < 0.001) but has a shorter treatment delivery time (P = 0.03) per fraction.

Dosimetric Comparison between Single and Dual Arc-Volumetric Modulated Arc Radiotherapy and Intensity Modulated Radiotherapy for Nasopharyngeal Carcinoma Using a Simultaneous Integrated Boost Technique

Backround:Plan quality and performance of dual arc (DA) volumetric modulated arc therapy (VMAT), single arc (SA) VMAT and nine field (9F) intensity modulated radiotherapy were compared using a simultaneous integrated boost (SIB) technique.Methods:Twelve patients treated in Elekta Synergy Platform (mlci2) by 9F-IMRT were replanned with SA/DA-VMAT using a CMS Monaco Treatment Planning System (TPS) with Monte Carlo simulation. Target delineation was conducted as per Radiation Therapy Oncology Protocols (RTOG0225 and 0615). A 70Gy dose prescribed to PTV70 and 61Gy to PTV61 in 33 fractions was applied for the SIB technique. The conformity index (CI) and homogeneity index (HI) for targets and the mean dose and maximum dose for OAR’s, treatment delivery time (min), monitor units (MUs) per fraction, normal tissue integral dose and patient specific quality assurance were analysed.Results:Acceptable target coverage was achieved for PTV70 and PTV61 with all the planning techniques. No significant differences were observed except for D98 (PTV61), CI(PTV70) and HI(PTV61). Maximum dose (Dmax) to the spinal cord was lower in DA-VMAT than 9F-IMRT (p=0.002) and SA-VMAT (p=0.001). D50 (%) of parotid glands was better controlled by 9F-IMRT (p=0.001) and DA-VMAT (p=0.001) than SA-VMAT. A lower mean dose to the larynx was achieved with 9F-IMRT (P=0.001) and DA-VMAT (p=0.001) than with SA-VMAT. DA-VMAT achieved higher CI of PTV70 (P= 0.005) than SA-VMAT. For PTV61, DA-VMAT (P=0.001) and 9F-IMRT (P=0.001) achieved better HI than SA-VMAT. The average treatment delivery times were 7.67mins, 3.35 mins, 4.65 mins for 9F-IMRT, SA-VMAT and DA-VMAT, respectively. No significant difference were observed in MU/fr (p=0.9) and NTID (P=0.90) and the patient quality assurance pass rates were >95% (gamma analysis I3mm, 3%).Conclusion:DA-VMAT showed better conformity over target dose and spared the OARs better or equal to IMRT. SA-VMAT could not spare the OARs well. DA-VMAT offered shorter delivery time than IMRT without compromising the plan quality.

The Effectiveness of Volumetric Modulated arc Radiotherapy to Treat Patients with Metastatic Spinal Tumors

The Effectiveness of Volumetric Modulated arc Radiotherapy to Treat Patients with Metastatic Spinal Tumors

Evaluation of Acute Toxicity and Early Clinical Outcome in Head and Neck Cancers Treated With Conventional Radiotherapy and Simultaneous Integrated Boost Arc Radiotherapy.

BackgroundChemoradiotherapy plays an important role in management of locally advanced head and neck cancers. This retrospective analysis was done to evaluate and compare acute toxicity profiles and early clinical outcomes in patients treated with conventional and arc techniques.MethodsFifty-five patients of head and neck cancers were evaluated. Thirty patients received conventional radiotherapy with 6 MV or cobalt 60 and 25 patients were treated with simultaneous integrated boost-volumetric modulated arc radiotherapy (SIB-VMAT) with dose prescription of 66 - 70 Gy. Concurrent chemotherapy was given as cisplatin injection at 40 mg/m2 weekly or 100 mg/m2 thrice weekly.ResultsThe incidence of grade 3-4 mucositis was 56% versus 83.3% with SIB-VMAT and conventional treatments (P = 0.026). The incidence of grade 2-3 xerostomia was 44% versus 80% (P = 0.006) in the two groups. Grade 2 dysphagia was seen in 40% versus 80% (P = 0.008) favoring the arc treatments. Seventeen patients undergoing arc treatment had complete response compared to 14 in the conventional group (P = 0.040). The median disease-free survival (median ± standard error) was 16 months (11 ± 1.987 months) in the conventional and arc groups (P = 0.073).ConclusionSIB-VMAT shows a better toxicity profile and a trend towards better disease-free survival when compared to conventional radiotherapy in head and neck cancers.