Gy For Volumetric Modulated Arc Therapy Research Articles

Optimising craniospinal irradiation for medulloblastoma: a dosimetric comparison of two VMAT planning methods.

Craniospinal irradiation (CSI) poses a challenging planning process because of the complex target volume. Traditional 3D conformal CSI does not spare any critical organs, resulting in toxicity in patients. Here the dosimetric advantages of volumetric-modulated arc therapy (VMAT) using partial arc and avoidance sectors are compared with each other in planning in adult patients undergoing CSI to develop a clinically feasible technique that is both effective and efficient. Eight adult patients treated with CSI were retrospectively identified. In total 16 plans were made. We generated two plans for each patient: 1. VMAT plan using partial arc, namely VMAT_pa. 2. VMAT plan using avoidance sectors, namely VMAT_as. The dose prescribed was 36 Gy in 20 fractions. The dose-volume histogram for planning target volume (PTV) and organs at risk (OAR) (lens, eye, heart, thyroid, lungs, liver, gonads and kidneys) were analysed and compared. Dose parameters of mean dose, V95%, and V107% for the PTV were evaluated. The median length of PTV is 65.58 cm (45.8-79.5). The volume of PTV receiving 95% of the dose (V95%) in both the plans are 97.51% (VMAT_as) and 97.99% (VMAT_pa) (p = 0.121) while V107% are 0.733 and 0.742 for VMAT_as and VMAT_pa, respectively (p = 0.969). The doses of OARs such as lens, eye, liver and gonads were comparable. The mean heart dose was 10.4 and 9.0 Gy in VMAT_as and VMAT_pa plans, respectively (p = 0.005). Significant lower doses to the thyroid, kidneys and lungs were seen in VMAT plans using avoidance sectors. This study provides a practically useful VMAT planning method for the treatment of CSI and illustrates the ability of VMAT using avoidance sectors to generate highly conformal and homogeneous treatment plans for CSI, while limiting the dose to the relevant OARs.

Comparative Analysis of External and Internal Radiotherapy- Dependent Plans in Patients with Gynecological Cancer.

Radiotherapy plays a key role in the treatment of gynecological cancer. Modern radiotherapy techniques with external beams (e-RT) are applied in a broad spectrum of gynecological cancer cases. However, high radiation doses, affecting normal tissue adjacent to cancer, represent the main disadvantage of e-RT regimens. For this reason, brachytherapy (BT), an internal beam-based technique (i-RT), is suggested following e-RT. Our purpose was to compare e-RT plans using volumetric-modulated arc therapy (VMAT) with those using 3D conformal techniques (3D-CRT) and compare BT plans guided by 3D or 2D imaging based on the potential corresponding toxicity levels. In this preliminary, non-randomized comparative retrospective study, 15 females suffering gynecological cancer were enrolled. Modern e-RT and i-RT (BT) techniques were applied. Concerning e-RT, D95/D99/rectum 2cc/bladder 2cc and small intestine 2cc were measured and compared; in i-RT, rectum 2cc/bladder 2cc were measured and compared. The median dose to the planning target volume in VMAT was 97.4 Gy compared with 92.9 Gy in 3D-CRT. Τhe rectum received almost 5 Gy less in VMAT compared to 3D-CRT (median of 43.5 Gy vs. 48.6 Gy; p=0.001). In the bladder, dose differences were minimal, while the small intestine received 47.6 Gy in VMAT (p=0.001). Regarding 3D-BT, the rectum received 63.1 Gy compared with 49.9 Gy (p=0.009) in 2D-BT. Concerning the bladder, mean 2D-BT and 3D-BT doses were 71.9 and 65 Gy, respectively, differing non-significantly. VMAT was found to be superior to 3D-CRT, especially in dose distribution, volume coverage and protection of critical organs. Similarly, 3D-BT should be preferred over 2D-BT due to critical advantages.

Comparative Evaluation of Brachial Plexus Sparing for Comprehensive Reirradiation of High Risk Recurrent or New Primary Breast Cancer

<h3>Purpose/Objective(s)</h3> Recurrent or new primary breast cancer with an indication for comprehensive regional nodal irradiation (RNI) in the setting of prior radiotherapy (RT) to the supraclavicular area (SCV) and upper axilla presents a unique treatment challenge due to cumulative brachial plexus (BP) dose tolerance. Brachial plexopathy is a debilitating potential consequence of RT, and BP dose monitoring is needed for comprehensive reirradiation (reRT). We hypothesize that pencil beam scanning proton therapy (PBS-PT) and photon volumetric-modulated arc therapy (VMAT) are conformal techniques that allow BP relative dose-sparing, while maintaining target volume (TV) dose. A comparative evaluation was performed to assess each approach. <h3>Materials/Methods</h3> In this IRB-approved retrospective study, all patients with ipsilateral recurrent or new primary breast cancer previously treated with photon RT, then receiving PBS-PT reRT to TV with at least partial BP overlap, were identified. VMAT plans were developed by photon breast dosimetrists using matched individualized BP dose constraints (BP maximum 17.1-53.9 Gy) used in the PBS-PT course. BP and TV DVH parameters were assessed. Patient and tumor characteristics, treatment parameters, clinical outcomes, and toxicities were collected. The median follow-up from the start of reRT was 10.5 months. <h3>Results</h3> Ten consecutive patients were identified. Median patient age was 58 years (41-82), with median time between RT courses of 48 months (15-276). Median first, second, and cumulative RT doses were 50.4 Gy (42.6-60.0), 50.4 Gy(RBE) (45.0-64.4), and 102.4 Gy(RBE) (95.0-120.0), respectively. PBS-PT and VMAT plans matched BP doses, with the median maximum and mean BP cumulative doses 86.6 Gy (RBE) and 60.7 Gy (RBE) for PBS-PT and 87.5 Gy and 60.2 Gy for VMAT, respectively. TV coverage of V85% (volume receiving 85% of prescription dose), V90%, and V95% were generally lower for VMAT vs. IMPT plans: axilla level II were 84.8%, 91.8%, and 75.7% vs. 90.9% (p=0.17), 88.3% (p=0.04), and 84.5% (p<0.01); axilla level III were 89.8%, 75.1%, and 64.0% vs. 95.4% (p=0.39), 91.8% (p=0.12), and 86.5% (p=0.32); and SCV were 83.0%, 74.3%, and 67.2% vs. 90.9% (p=0.41), 82.1% (p=0.13), and 68.2% (p=0.76), respectively. One patient developed symptoms of brachial plexopathy with neuropathy in the ulnar nerve distribution without pain or weakness. This patient had the highest maximum cumulative BP dose of the entire cohort (106.1 Gy(RBE)). <h3>Conclusion</h3> VMAT and PBS-PT provide conformal RT plans that can provide BP dose sparing but some surrounding compromise of the adjacent TV at risk. In this cohort, PBS-PT improved BP sparing and TV coverage versus VMAT. Further study with uniform TV and prescription parameters will be useful for direct comparison of the two modalities as the approach to this clinical situation continues to be refined. Longer follow-up will be needed to characterize the implication of cumulative BP dose on risk of developing clinically-significant brachial plexopathy.

A Randomised Phase II Clinical Trial Comparing the Deliverability and Acute Toxicity of Wide Tangent versus Volumetric Modulated Arc Therapy to the Breast and Internal Mammary Chain

AimsInclusion of the internal mammary chain in the radiotherapy target volume (IMC-RT) improves disease-free and overall survival in higher risk breast cancer patients, but increases radiation doses to heart and lungs. Dosimetric data show that either modified wide-tangential fields (WT) or volumetric modulated arc therapy (VMAT) together with [AQ1]voluntary deep inspiration breath hold (vDIBH) keep mean heart doses below 4 Gy in most patients. However, the impact on departmental resources has not yet been documented. This phase II clinical trial compared the time taken to deliver IMC-RT using either WT and vDIBH or VMAT and vDIBH, together with planning time, dosimetry, set-up reproducibility and toxicity. Materials and methodsLeft-sided breast cancer patients requiring IMC-RT were randomised to receive either WT(vDIBH) or VMAT radiotherapy. The primary outcome was treatment time, powered to detect a minimum difference of 75 min (5 min/fraction) between techniques. The population mean displacement, systematic error and random error for cone beam computed tomography chest wall matches in three directions of movement were calculated. Target volume and organ at risk doses were compared between groups. Side-effects, including skin (Radiation Therapy Oncology Group), lung and oesophageal toxicity (Common Terminology Criteria for Adverse Events v 4.03) rates, were compared between the groups over 3 months. Patient-reported outcome measures, including shoulder toxicity at baseline, 6 months and 1 year, were compared. ResultsTwenty-one patients were recruited from a single UK centre between February 2017 and January 2018. The mean (standard deviation) total treatment time per fraction for VMAT treatments was 13.2 min (1.7 min) compared with 28.1 min (3.3 min) for WT(vDIBH). There were no statistically significant differences in patient set-up errors in between groups. The average mean heart dose for WT(vDIBH) was 2.6 Gy compared with 3.4 Gy for VMAT(vDIBH) (P = 0.13). The mean ipsilateral lung V17Gy was 32.8% in the WT(vDIBH) group versus 34.4% in the VMAT group (P = 0.2). The humeral head (mean dose 16.8 Gy versus 2.8 Gy), oesophagus (maximum dose 37.3 Gy versus 20.1 Gy) and thyroid (mean dose 22.0 Gy versus 11.2 Gy) all received a statistically significantly higher dose in the VMAT group. There were no statistically significant differences in skin, lung or oesophageal toxicity within 3 months of treatment. Patient-reported outcomes of shoulder toxicity, pain, fatigue, breathlessness and breast symptoms were similar between groups at 1 year. ConclusionVMAT(vDIBH) and WT(vDIBH) are feasible options for locoregional breast radiotherapy including the IMC. VMAT improves nodal coverage and delivers treatment more quickly, resulting in less breath holds for the patient. This is at the cost of increased dose to some non-target tissues. The latter does not appear to translate into increased toxicity in this small study.

Dosimetric Comparison of Volumetric-Modulated Arc Therapy and Proton Therapy for Postmastectomy Radiation Using the New ESTRO-ACROP Breast Reconstruction Contouring Guidelines

In 2019, ESTRO-ACROP released new consensus guidelines for postmastectomy radiation therapy (PMRT) in the setting of breast reconstruction. In particular, the chest wall (CW) target was redefined to exclude the breast prosthesis and underlying tissue. In this study, we assess the impact of these changes on treatment planning and compare the dosimetric outcomes using both volumetric-modulated arc therapy (VMAT) and pencil-beam scanning (PBS) proton therapy. We performed a treatment planning study of 10 women with left sided breast cancer who received PMRT after implant-based breast reconstruction. All target structures and organs-at-risk (OARs) were delineated first using current RTOG breast contouring guidelines and then separately delineated using the updated ESTRO-ACROP consensus guidelines. Four sets of plans were then generated; 1) VMAT using RTOG contours, 2) VMAT using new ESTRO-ACROP contours, 3) PBS using RTOG contours, and 4) PBS using new ESTRO-ACROP contours. All plans prescribed a dose of 50.4 Gy or GyRBE to the CW and 45 Gy or GyRBE to the regional lymphatics, inclusive of the internal mammary nodes. Similar target coverage objectives and normal tissue (OAR) constraints were utilized, applying the concept of ALARA. Dosimetric goals between the RTOG and updated ESTRO-ACROP contoured plans and across treatment modalities were compared. Utilizing the updated ESTRO-ACROP contouring guidelines, VMAT and PBS plans were able to generate equivalent coverage for all targets. The mean CW D95 was 49.9 Gy for VMAT vs. 48.4 GyRBE with PBS, and the mean regional lymphatic D95 was 45.1Gy (VMAT) vs. 42.8 GyRBE (PBS). Despite the more limited CW volume, proton PBS plans still demonstrated superior OAR metrics compared to VMAT: ipsilateral lung V20 of 16.1% (VMAT) vs. 5.3% (PBS), mean heart doses of 4.6 Gy (VMAT) vs. 0.51 GyRBE (PBS), LAD 1cc dose of 7.43 Gy (VMAT) vs. 5.95 GyRBE (PBS). Compared to plans generated with RTOG guidelines, the updated guideline plans were able to achieve equivalent target coverage with similar, but modestly improved sparing of most OARs: ipsilateral lung V20 7.3% (RTOG PBS) vs. 5.3% (ESTRO PBS) and 24% (RTOG VMAT) vs. 20% (ESTRO VMAT), mean heart dose 0.49 GyRBE (RTOG PBS) vs. 0.51 GyRBE (ESTRO PBS) and 4.95 Gy (RTOG VMAT) vs. 4.82 Gy (ESTRO VMAT). Notably, contralateral lung doses with VMAT were higher using the updated ESTRO-ACROP guidelines compared to RTOG guidelines with a mean V10 of 19.6%. PMRT with reconstruction utilizing the updated ESTRO-ACROP consensus contouring guidelines is feasible with both VMAT and PBS proton therapy. Treatment plans utilizing the updated contouring guidelines provided equivalent target coverage compared to conventional guidelines, while modestly further sparing cardiopulmonary structures. Care must be taken with new contouring guidelines when utilizing VMAT to minimize undue contralateral lung exposure.

Dosimetric Comparison of the Newest Version Tomotherapy, Volumetric-Modulated Arc Therapy, and Intensity-Modulated Proton Therapy Plans for Angiosarcoma of the Scalp

Patients with angiosarcoma of the scalp (AS) have an extremely unfavorable prognosis. As local recurrence is one of the main causes of failure, radiotherapy is established as an integral component of the treatment for AS. Delivering an adequate dose to the target while limiting the dose to the surrounding organs at risk (OARs) such as the brain is challenging. We aimed to compare treatment plans among the newest version of tomotherapy (Tomo), volumetric-modulated arc therapy (VMAT), and intensity-modulated proton therapy (IMPT) for AS patients. We created radiotherapy plans using Tomo, VMAT, and IMPT for 19 AS patients treated at our institution and conducted a pilot study comparing the three methods. The clinical target volume (CTV) 1 included the gross tumor volume plus 3.0 cm and CTV2 was defined as the total scalp. The planning target volume (PTV) 1 and PTV2 were defined as CTV1 plus 0.5 cm and CTV2 plus 0.5 cm other than PTV1, respectively. For IMPT, a setup robustness of ± 0.2 cm was used for the setting of PTV. 70 Gy and 56 Gy were prescribed to D95% (i.e., dose to 95% volume of PTV) of PTV1 and PTV2, respectively, using the simultaneous integrated boost technique. Other constraint goals and acceptable ranges of PTV1, PTV2, and OARs were also set. PTV1 and PTV2 with Tomo, VMAT, and IMPT met the dose constraints of D95% and D98% at least within acceptable ranges for all patients. D95% and D98% of PTV1 and PTV2 were similar among the three methods. D2% of PTV1 and PTV2 were significantly higher in IMPT than in Tomo and VMAT. HI for the IMPT plans was significantly higher than for the other plans; HI was 1.22±0.10 (SD) for the IMPT plans, 1.13±0.04 for the Tomo plans, and 1.14±0.04 for the VMAT plans (p < 0.001). D1% and Dmean of the spinal cord (planning organ at risk volume, PRV), brain, brainstem (PRV), optic pathway (PRV), and both inner ears were significantly lower in IMPT than in Tomo and VMAT. Dmax of the spinal cord (PRV) and optic pathway (PRV) and Dmean of the brain, brainstem (PRV), and optic pathway (PRV) were lower in VMAT than in Tomo. Dmean of the brain was 37.4±6.6 Gy in Tomo, 29.7±3.6 Gy in VMAT, and 17.9±2.0 Gy in IMPT (p < 0.001). The three methods could provide adequate coverage of the PTV while compromising the dose constraint of OARs. Although the dose homogeneity within the PTV was worse in IMPT than in Tomo and VMAT, the three methods could provide a well acceptable homogeneity. Among the three methods, IMPT achieved the best OAR sparing, especially for the brain.

Volumetric modulated arc therapy versus intensity-modulated proton therapy in the postoperative irradiation of thymoma.

To investigate the role of intensity-modulated proton therapy (IMPT) compared to volumetric modulated arc therapy (VMAT) for the radiation treatment of thymoma cancer. Twenty patients were retrospectively planned for IMPT [with (IMPT_R1 or IMPT_R2 according to the approach adopted) and without robust optimization] and VMAT. The results were compared according to dose-volume metrics on the clinical and planning target volumes (CTV and PTV) and the main organs at risk (heart, breasts, lungs, spinal cord and oesophagus). Estimates of the excess absolute risk (EAR) of secondary cancer induction were determined for the oesophagus, the breasts and the composite lungs. For the heart, the relative risk (RR) of chronic heart failure (CHF) was assessed. IMPT and VMAT plans resulted equivalent in terms of target coverage for both the CTV and the PTV. The CTV homogeneity index resulted in 0.03 ± 0.01 and 0.04 ± 0.01 for VMAT and all IMPT plans, respectively. The conformality index resulted in 1.1 ± 0.1 and 1.2 ± 0.1 for VMAT and all IMPT plans. The mean dose to the breasts resulted in 10.5 ± 5.0, 4.5 ± 3.4, 4.7 ± 3.5 and 4.6 ± 3.4Gy for VMAT, IMPT, IMPT_R1 and IMPT_R2. For the lungs, the mean dose was 9.6 ± 2.3, 3.5 ± 1.5, 3.6 ± 1.6 and 3.8 ± 1.4Gy; for the heart: 8.7 ± 4.4, 4.3 ± 1.9, 4.5 ± 2.0 and 4.4 ± 2.4Gy and for the oesophagus 8.2 ± 3.5, 2.2 ± 3.4, 2.4 ± 3.6 and 2.5 ± 3.5Gy. The RR for CHF was 1.6 ± 0.3 for VMAT and 1.3 ± 0.2 for IMPT (R1 or R2). The EAR was 3.6 ± 0.v vs 1.0 ± 0.6 or 1.2 ± 0.6 (excess cases/10,000 patients year) for the oesophagus; 17.4 ± 6.5 vs 5.7 ± 3.2 or 6.1 ± 3.8 for the breasts and 24.8 ± 4.3 vs 8.1 ± 2.7 or 8.7 ± 2.3 for the composite lungs for VMAT and IMPT_R, respectively. The data from this in-silico study suggest that intensity-modulated proton therapy could be significantly advantageous in the treatment of thymoma patients with particular emphasis to a substantial reduction of the risk of cardiac failure and secondary cancer induction. Robust planning is a technical pre-requisite for the safety of the delivery.

Functional cranio-spinal irradiation: A hippocampal and hypothalamic-pituitary axis sparing radiation technique using two IMRT modalities

Cranio-spinal irradiation (CSI) treatment of embryonal tumors is associated with long-term endocrine and neuro-cognitive sequelae. As an example, the radiation regiment for standard risk medulloblastoma is 23.4 Grays (Gy) CSI followed by a boost of 30.6Gy to the tumor bed. We hypothesize that a novel CSI technique, which we named “Functional” CSI (F-CSI) can reduce the dose to the hypothalamic-pituitary axis (HPA) and hippocampi compared to standard CSI (S-CSI) without sacrificing coverage. In this study, we compared the efficacy of Volumetric Modulated Arc Therapy (VMAT) and Helical Tomotherapy (HT) in delivering this novel CSI technique. Plans were constructed from 10 patients with embryonal tumors previously treated at our institution. Target volumes and organs at risk were delineated as per our local protocol and the ACNS0331 Atlas. The HPA and hippocampi contours were verified by an experienced neuro-radiologist. Primary objective was to achieve a D95% to the prescribed dose of 23.4Gy for CSI and 30.6Gy for the boost. Dmean ≤18Gy was assigned to the HPA and hippocampi. A two-sided t-test was used for comparison. F-CSI in both modalities were able to achieve the D95% target coverage. Hot spots (D2%) were lower with HT for both the CSI component (p = 0.03) and boost component (p < 0.01). VMAT was able to achieve better conformality (p < 0.01). Compared to S-CSI, both F-CSI modalities were able to achieve a significant decrease in dose to the HPA and Hippocampi. The average S-CSI HPA and Hippocampi Dmean were 23.9Gy and 23.8Gy. In contrast, respective F-CSI Dmean were 13.9Gy and 17.2Gy in VMAT and 15Gy and 15.9Gy in HT. The average composite (F-CSI plus boost) Dmean to the HPA and hippocampi often exceeded 18Gy. Compared to S-CSI, F-CSI with VMAT and HT were capable of achieving acceptable coverage while sparing the HPA and hippocampi. However, the addition of the boost component often exceeded the mean dose of 18Gy. This may be overcome with more conformal modalities for the boost phase such as stereotactic radiotherapy or proton therapy.

Treatment planning for non-small cell lung tumours: VMAT versus 3DCRT a quantitative dosimetric study

AbstractPurpose:The dosimetric impact of volumetric modulated arc therapy (VMAT) in lung cancer compared with 3D conformal radiotherapy (3DCRT) is well known. However, this improvement is often associated with an increase in low doses. The aim of this study is to quantify these results more accurately.Methods:For each patient treated with 3DCRT, a second VMAT treatment plan was calculated. Usual dosimetric parameters such as target coverage or dose to the organs at risk were used to achieve the comparisons.Results:For planning target volume, homogeneity and conformity indices showed superiority of VMAT (respectively 0·07 and 0·87) compared to 3DCRT (0·11 and 0·57). For spinal cord planning organ at risk volume, the median maximum dose was 45·6 Gy in 3DCRT against 19·3 Gy in VMAT. Heart volume receiving at least 35 Gy (V35) decreased from 15·64% in 3DCRT to 8·28% in VMAT. Oesophagus V50 was higher in 3DCRT (25·45%) than in VMAT (14·03%). The mean lung dose was 17·9 Gy in 3DCRT versus 15·5 Gy in VMAT. Moreover, volumes receiving 5, 10 and 15 Gy were not significantly different between the two techniques when VMAT was performed with partial arcs.Conclusion:All the dosimetric parameters were improved with VMAT compared to the 3DCRT without increasing low doses when using partial arcs.

Dosimetric comparison between intensity-modulated radiotherapy and volumetric-modulated arc therapy in hippocampus sparing in brain metastasis treated by whole-brain irradiation and simultaneous integrated boost

AbstractBackground:While treating brain metastasis with whole-brain radiotherapy incorporating a simultaneous integrated boost (WBRT-SIB), the risk of hippocampus injury is high. The aim of this study is to compare dosimetrically between intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) in sparing of hippocampus and organs at risk (OARs) and planning target volume (PTV) coverage.Methods:In total, 16 patients presenting with more than one brain metastases were previously treated and then retrospectively planned using VMAT and IMRT techniques. For each patient, a dual-arc VMAT and another IMRT (five beams) plans were created. For both techniques, 30 Gy in 10 fractions was prescribed to the whole brain (WB) minus the hippocampi and 45 Gy in 10 fractions to the tumour with 0·5 cm margin. Dose–volume histogram (DVH), conformity index (CI) and homogeneity index (HI) of PTV, hippocampus mean and maximum dose and other OARs for both techniques were calculated and compared.Results:A statistically significant advantage was found in WB-PTV CI and HI with VMAT, compared to IMRT. There were lower hippocampus mean and maximum doses in VMAT than IMRT. The maximum hippocampus dose ranged between 15·5 and 19·2 Gy and between 18·4 and 20·6 Gy in VMAT and IMRT, respectively. The mean dose of the hippocampus ranged between 11·5 and 17·7 Gy and between 13·2 and 18·3 Gy in VMAT and IMRT, respectively.Conclusion:Using WBRT-SIB technique, VMAT showed better PTV coverage with less mean and maximum doses to the hippocampus than IMRT. Clinical randomised studies are needed to confirm safety and clinical benefit of WBRT-SIB.

A study of the dosimetric characteristics between different fixed-field IMRT and VMAT in early-stage primary mediastinal B-cell lymphoma

This analysis was designed to compare dosimetric parameters among different fixed-field intensity-modulated radiation therapy (IMRT) solutions and volumetric-modulated arc therapy (VMAT) to identify which can achieve the lowest risk of organs at risk (OARs) and treatment delivery efficiently. A total of 16 patients (8 male and 8 female) with early-stage primary mediastinal large B-cell lymphoma (PMBCL) were enrolled with planned gross tumor volume (PGTV) 45 Gy and planning target volume (PTV) 40 Gy. Four different plans were generated: 5-, 7, 9-field IMRT, and VMAT. The dose distributions for PGTV and PTV OARs (lungs, left ventricle, heart, thyroid gland, and breasts) were compared. The monitor units (MUs) and treatment delivery time were also evaluated. Mean conformity index (CI) and homogeneity index (HI) for PGTV in 5F-, 7F-, 9F-IMRT, and VMAT were 1.01 and 1.10, 1.01 and 1.10, 1.01 and 1.10, and 1.01 and 1.11 (p = 0.963 and 0.843), whereas these 2 indices for PTV were 1.04 and 1.22, 1.03 and 1.19, 1.03 and 1.17, and 1.08 and 1.14 (p = 0.964 and 0.969), respectively. Dmean (Gy), V4 (%), D50 (Gy), and D80 (Gy) to the left and right breasts increased by 0.7 Gy and 0.1 Gy, 6.8% and 7.7%, 0.9 Gy and 1.7 Gy, and 1.0 Gy and 1.5 Gy in VMAT, respectively. The 9-beam IMRT plan had the highest MUs (25,762.4 MUs) and the longest treatment delivery time (10.7 minutes); whereas, the VMAT had the lowest MUs (13,345.0) and the shortest treatment delivery time (5.9 minutes). Seven- and 9-field IMRT and VMAT provide improved tumor coverage compared with 5F-IMRT, whereas VMAT shows higher treatment delivery efficiency than IMRT technique. Seven- and 9-field IMRT slightly reduce the low dose radiation exposure of breasts compared with VMAT technique. The 7- and 9-field IMRT and VMAT techniques both can be safely and efficiently delivered to patients with PMBCL.

Functional image-guided dose escalation in gliomas using of state-of-the-art photon vs. proton therapy

Background: Recurrences of glioma are usually local, suggesting the need for higher tumor dose. We investigated the boundaries for dose escalation of an 18F-fluoro-ethyl-tyrosine positron emission tomography defined target by intensity-modulated photon therapy (IMRT), volumetric modulated arc therapy (VMAT) and intensity-modulated proton therapy (IMPT).Materials and methods: Standard dose (60 Gy) and dose-escalated plans were calculated for seven patients using IMRT, VMAT and IMPT. The achieved boost dose, the dose to the organs at risk (OAR), the dose homogeneity (defined as overdose volume, ODV) and the ratio of the 30 Gy isodose curve and the boost volume (R30) were compared. The risk of radionecrosis was estimated using the ratio of the dose volume histograms of the brain (range 30–60 Gy).Results: The mean boost dose was 77.1 Gy for IMRT, 79.2 Gy for VMAT and 85.1 GyE for IMPT. Compared with the standard plan, the ODV was unchanged and the R30 increased (17%) for IMRT. For VMAT, the ODV decreased (7%) and the R30 was unchanged whereas IMPT substantially decreased ODV (61%), R30 (22%), OAR doses as well as the risk of radionecrosis.Conclusions: Dose escalation can be achieved with IMRT, VMAT and IMPT while respecting normal tissue constraints, yet with IMPT being most favorable.

Dosimetric comparison of intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) in total scalp irradiation: a single institutional experience.

PurposeTotal scalp irradiation (TSI) is a rare but challenging indication. We previously reported that non-coplanar intensity-modulated radiotherapy (IMRT) was superior to coplanar IMRT in organ-at-risk (OAR) protection and target dose distribution. This consecutive treatment planning study compared IMRT with volumetric-modulated arc therapy (VMAT).Materials and MethodsA retrospective treatment plan databank search was performed and 5 patient cases were randomly selected. Cranial imaging was restored from the initial planning computed tomography (CT) and target volumes and OAR were redelineated. For each patients, three treatment plans were calculated (coplanar/non-coplanar IMRT, VMAT; prescribed dose 50 Gy, single dose 2 Gy). Conformity, homogeneity and dose volume histograms were used for plan.ResultsVMAT featured the lowest monitor units and the sharpest dose gradient (1.6 Gy/mm). Planning target volume (PTV) coverage and homogeneity was better in VMAT (coverage, 0.95; homogeneity index [HI], 0.118) compared to IMRT (coverage, 0.94; HI, 0.119) but coplanar IMRT produced the most conformal plans (conformity index [CI], 0.43). Minimum PTV dose range was 66.8% –88.4% in coplanar, 77.5%–88.2% in non-coplanar IMRT and 82.8%–90.3% in VMAT. Mean dose to the brain, brain stem, optic system (maximum dose) and lenses were 18.6, 13.2, 9.1, and 5.2 Gy for VMAT, 21.9, 13.4, 14.5, and 6.3 Gy for non-coplanar and 22.8, 16.5, 11.5, and 5.9 Gy for coplanar IMRT. Maximum optic chiasm dose was 7.7, 8.4, and 11.1 Gy (non-coplanar IMRT, VMAT, and coplanar IMRT).ConclusionTarget coverage, homogeneity and OAR protection, was slightly superior in VMAT plans which also produced the sharpest dose gradient towards healthy tissue.

Dosimetric and radiobiological comparison of volumetric modulated arc therapy, high-dose rate brachytherapy, and low-dose rate permanent seeds implant for localized prostate cancer

To investigate the dosimetric and radiobiological differences among volumetric modulated arc therapy (VMAT), high-dose rate (HDR) brachytherapy, and low-dose rate (LDR) permanent seeds implant for localized prostate cancer. A total of 10 patients with localized prostate cancer were selected for this study. VMAT, HDR brachytherapy, and LDR permanent seeds implant plans were created for each patient. For VMAT, planning target volume (PTV) was defined as the clinical target volume plus a margin of 5mm. Rectum, bladder, urethra, and femoral heads were considered as organs at risk. A 78Gy in 39 fractions were prescribed for PTV. For HDR and LDR plans, the dose prescription was D90 of 34Gy in 8.5Gy per fraction, and 145Gy to clinical target volume, respectively. The dose and dose volume parameters were evaluated for target, organs at risk, and normal tissue. Physical dose was converted to dose based on 2-Gy fractions (equivalent dose in 2Gy per fraction, EQD2) for comparison of 3 techniques. HDR and LDR significantly reduced the dose to rectum and bladder compared with VMAT. The Dmean (EQD2) of rectum decreased 22.36Gy in HDR and 17.01Gy in LDR from 30.24Gy in VMAT, respectively. The Dmean (EQD2) of bladder decreased 6.91Gy in HDR and 2.53Gy in LDR from 13.46Gy in VMAT. For the femoral heads and normal tissue, the mean doses were also significantly reduced in both HDR and LDR compared with VMAT. For the urethra, the mean dose (EQD2) was 80.26, 70.23, and 104.91Gy in VMAT, HDR, and LDR brachytherapy, respectively. For localized prostate cancer, both HDR and LDR brachytherapy were clearly superior in the sparing of rectum, bladder, femoral heads, and normal tissue compared with VMAT. HDR provided the advantage in sparing of urethra compared with VMAT and LDR.

SU‐E‐T‐700: Single Isocenter Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiotherapy (IMRT) for Intact Left Breast Cancer Patients with Internal Mammary (IM) and Supraclavicular (S/C) Nodes ‐ a Treatment Planning Study

Purpose:To investigate treatment plan quality and feasibility of VMAT for treatment delivery of intact left breast cancer patients with involved internal mammary (IM) and supraclavicular (S/C) nodes.Methods:Ten patients were selected for this retrospective study. All PTVs (Intact left breast, IM &amp; S/C nodes) were contoured by a single radiation oncologist. Four 200° partial arcs with 2cm overlapping jaws (two clockwise and two counterclockwise; gantry angle 300°–140°) and ten fixed‐field equally spaced coplanar modulated fields were used to optimize single isocenter VMAT (RapidArc) and IMRT treatment plans, respectively, using Eclipse TPS. Prescribed dose to PTV was 46Gy in 23 fractions with prescription dose covering 95% of the PTV.Results:Four of the 10 patients had PTV &gt; 1200cc. The mean PTV volume was 1200.17±571.51cc (findings are reported as mean ± 1 SD). All plans were judged clinically acceptable while satisfying dose‐volume constraints, with VMAT showing significantly better conformity than IMRT. The mean Paddick conformity index (PCI) was 0.88±0.03 for VMAT vs. 0.82±0.06 for IMRT plans (p=0.001). However, maximum doses were within ±1.0% of 111% of the prescription dose for both plans. The heart mean dose was 5.00±0.99Gy for VMAT vs. 7.09±1.70Gy for IMRT (p&lt;0.001), heart volume receiving &gt;30Gy was 0.18±0.29% for VMAT vs. 0.68±1.24% for IMRT (p=0.19), and V5Gy and V7Gy were 31.67±11.56% and 14.93±7.41% for VMAT vs. 67.15±17.66% and 36.55±16.59% for IMRT plans, respectively (p&lt;0.001). The mean total lung dose was 8.95±0.52Gy vs. 8.48±0.81Gy (p=0.06) and V20Gy was 10.65±2.00% vs. 8.12±1.37% (p=0.055) for VMAT and IMRT plans, respectively. The right breast mean dose was 2.83±0.46Gy for VMAT vs. 4.06±0.61Gy for IMRT plans (p&lt;0.001).Conclusion:VMAT plans achieved intended dose coverage to the intact left breast, IM &amp; S/C nodes at ≥ 95% with significantly lower dose to critical structures, especially, to heart and contralateral breast compared to IMRT plans.

ART for head and neck patients: On the difference between VMAT and IMPT

Anatomical changes in the head-and-neck (H&N) region during the course of treatment can cause deteriorated dose distributions. Different replanning strategies were investigated for volumetric modulated arc therapy (VMAT) and intensity-modulated proton therapy (IMPT).Material and methods. For six H&N patients two repeated computed tomography (CT) and magnetic resonance (MR) (CT1/MR1 at week 2 and CT2/MR2 at week 4) scans were acquired additionally to the initial planning CT/MR. Organs-at-risk (OARs) and three targets (CTV70Gy, CTV63Gy, CTV56Gy) were delineated on MRs and transferred to respective CT data set. Simultaneously integrated boost plans were created using VMAT (two arcs) and IMPT (four beams). To assess the need of replanning the initial VMAT and IMPT plans were recalculated on repeated CTs. Furthermore, VMAT and IMPT plans were replanned on the repeated CTs. A Demon algorithm was used for deformable registration of the repeated CTs with the initial CT and utilized for dose accumulation. Total dose estimations were performed to compare ART versus standard treatment strategies.Results. Dosimetric evaluation of recalculated plans on CT1 and CT2 showed increasing OAR doses for both, VMAT and IMPT. The target coverage of recalculated VMAT plans was considered acceptable in three cases, while for all IMPT plans it dropped. Adaptation of the treatment reduced D2% for brainstem by 6.7 Gy for VMAT and by 8 Gy for IMPT, for particular patients. These D2% reductions were reaching 9 Gy and 14 Gy for the spinal cord. ART improved target dose homogeneity, especially for protons, i.e. D2% decreased by up to 8 Gy while D98% increased by 1.2 Gy.Conclusion. ART showed benefits for both modalities. However, as IMPT is more conformal, the magnitude of dosimetric changes was more pronounced compared to VMAT. Large anatomic variations had a severe impact on treatment plan quality for both VMAT and IMPT. ART is justified in those cases irrespective of treatment modalities.

限局期smallcell肺癌における海馬温存予防的全脳照射の一次臨床研究【Powered by NICT】

Objective To preliminarily observe the clinical efficacy of hippocampal-sparing prophylactic cranial irradiation (HS-PCI) using helical tomotherapy (HT) in patients with limited-stage small-cell lung cancer (LS-SCLC) after chemoradiotherapy, and compare HT with intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) in dose distribution. Methods From April to June, 2014, six patients with LS-SCLC who had achieved a complete remission after chemoradiotherapy were assigned to HS-PCI using HT within a month after brain metastasis was ruled out using brain magnetic resonance imaging (MRI). After fusing CT images and MRI images, the hippocampus was contoured in the fusion images and hippocampal avoidance regions were created using a volumetric expansion of 3 mm around the hippocampus. A dose of 25 Gy in 10 fractions to 95%of planning target volume (PTV) was prescribed in HT, IMRT, and VMAT. The clinical efficacy, adverse reactions, neurocognitive function, and brain metastasis were evaluated for HT. The dose distribution in PTV and hippocampus were compared between HT, IMRT, and VMAT. Results There were one patient with abdominal wall and abdominal lymph node metastases, one patient with local recurrence, and no patient with brain metastasis during the observation period. The numbers of patients with grade 1 and grade 2 headache, dizziness, and hair loss reactions were 3 and 1, 3 and 1, and 4 and 2, respectively. There were no significant differences in the average score of the Mini-Mental State Examination before treatment and at 3and 6 months after treatment (29.7, 29.2, and 29.3; P=0.083, 0.317, and 0.157). The mean dose to the hippocampus was 16.85 Gy for IMRT and 17.59 Gy for VMAT. For HT, the mean doses to the hippocampus and avoidance regions were reduced to 5.26 Gy and 6.21 Gy, respectively. The prescribed dose for HT was reduced by 79% and 71% compared with IMRT and VMAT, respectively. The average coverage rate of the prescribed dose was 94.48% for HT. Conclusions HT achieves promising dose distribution and target coverage in sparing of the hippocampus. Moreover, HT dose not increase the incidence of adverse reactions. The change in neurocognitive function needs to be further studied with long-term observation and large-scale sampling. Key words: Carcinoma, small-cell lung, limited stage; Hippocampal-sparing prophylactic cranial irradiation; Helical tomotherapy; Neurocognitive function; Three-dimensional radiotherapy; Dosimetry

Correlation of Integral Dose, White Blood Cell Counts, and Radiation Therapy Techniques for Head and Neck Cancer Patients Under Radiation Therapy

Correlation of Integral Dose, White Blood Cell Counts, and Radiation Therapy Techniques for Head and Neck Cancer Patients Under Radiation Therapy

Accelerated partial breast irradiation (APBI): Are breath-hold and volumetric radiation therapy techniques useful?

Background. In a selective group of patients accelerated partial breast irradiation (APBI) might be applied after conservative breast surgery to reduce the amount of irradiated healthy tissue. The role of volumetric modulated arc therapy (VMAT) and voluntary moderately deep inspiration breath-hold (vmDIBH) techniques in further reducing irradiated healthy – especially heart – tissue is investigated.Material and methods. For 37 partial breast planning target volumes (PTVs), three-dimensional conformal radiotherapy (3D-CRT) (3–5 coplanar or non-coplanar 6 and/or 10 MV beams) and VMAT (two partial 6 MV arcs) plans were made on CTs acquired in free-breathing (FB) and/or in vmDIBH. Dose-volume parameters for the PTV, heart, lungs, and breasts were compared.Results. Better dose conformity was achieved with VMAT compared to 3D-CRT (conformity index 1.24 ± 0.09 vs. 1.49 ± 0.20). Non-PTV ipsilateral breast receiving ≥ 50% of the prescribed dose was on average reduced by 28% in VMAT plans compared to 3D-CRT plans. Mean heart dose (MHD) reduced from 2.0 (0.1–5.1) Gy in 3D-CRT(FB) to 0.6 (0.1–1.6) Gy in VMAT(vmDIBH). VMAT is beneficial for MHD reduction if MHD with 3D-CRT exceeds 0.5Gy. Cardiac dose reduction as a result of VMAT increases with increasing initial MHD, and adding vmDIBH reduces the cardiac dose further. Mean dose to the ipsilateral lung decreased from 3.7 (0.7–8.7) to 1.8 (0.5–4.0) Gy with VMAT(vmDIBH) compared to 3D-CRT(FB). VMAT resulted in a slight increase in the contralateral breast dose (DMean) always remaining < 1.9 Gy).Conclusions. For APBI patients, VMAT improves PTV dose conformity and delivers lower doses to the ipsilateral breast and lung compared to 3D-CRT. This goes at the cost of a slight but acceptable increase of the contralateral breast dose. VMAT reduces cardiac dose if MHD exceeds 0.5 Gy for 3D-CRT. Adding vmDIBH results in a further reduction of heart and ipsilateral lung dose.

Multi-institutional comparison of volumetric modulated arc therapy vs. intensity-modulated radiation therapy for head-and-neck cancer: a planning study

BackgroundCompared to static beam Intensity-Modulated Radiation Therapy (IMRT), the main advantage of Volumetric Modulated Arc Therapy (VMAT) is a shortened delivery time, which leads to improved patient comfort and possibly smaller intra-fraction movements. This study aims at a treatment planner-independent comparison of radiotherapy treatment planning of IMRT and VMAT for head-and-neck cancer performed by several institutes and based on the same CT- and contouring data.MethodsFive institutes generated IMRT and VMAT plans for five oropharyngeal cancer patients using either Pinnacle3 or Oncentra Masterplan to be delivered on Elekta linear accelerators.ResultsComparison of VMAT and IMRT plans within the same patient and institute showed significantly better sparing for almost all OARs with VMAT. The average mean dose to the parotid glands and oral cavity was reduced from 27.2 Gy and 39.4 Gy for IMRT to 25.0 Gy and 36.7 Gy for VMAT, respectively. The dose conformity at 95% of the prescribed dose for PTVboost and PTVtotal was 1.45 and 1.62 for IMRT and 1.37 and 1.50 for VMAT, respectively. The average effective delivery time was reduced from 13:15 min for IMRT to 5:54 min for VMAT.ConclusionsIndependently of institution-specific optimization strategies, the quality of the VMAT plans including double arcs was superior to step-and-shoot IMRT plans including 5–9 beam ports, while the effective treatment delivery time was shortened by ~50% with VMAT.