A dosimetric comparison of non-coplanar volumetric modulated arc therapy and non-coplanar fixed field intensity modulated radiation therapy in hippocampus-avoidance whole-brain radiation therapy with a simultaneous integrated boost for brain metastases.

The aim of this study was to investigate the dosimetric differences between non-coplanar volumetric modulated arc therapy (VMAT) and non-coplanar fixed-field intensity-modulated radiotherapy (IMRT) in hippocampus-avoidance whole-brain radiation therapy with a simultaneous integrated boost (HA-WBRT+SIB) for brain metastases using the Monaco treatment planning system (TPS). A total of 22 patients with brain metastases were retrospectively enrolled. Two radiotherapy treatment plans were designed for each patient: non-coplanar VMAT and non-coplanar fixed field IMRT. The dose distribution of targets and organs at risk (OAR), the number of monitor units (MUs), and pre-treatment plan verification were compared between the two plans while meeting the prescribed dose requirements of the target volume. There were no significant differences in V50, V55, Dmax, heterogeneity index (HI) and conformity index (CI) of target PGTV between the two plans (p>0.05). For PTV-brain-SIB, there was no significant difference in D98% between IMRT and VMAT (p=0.103). VMAT significantly improved the V30 of PTV-brain-SIB (p<0.001), decreased HI (p=0.003), and increased CI (p<0.001). There were no significant differences in the Dmax to the brain stem, left and right lens, optic chiasm, pituitary gland, and left and right hippocampus between the two plans (p>0.05). Compared with IMRT, VMAT significantly reduced the Dmax to the left and right eyes (p<0.001) and significantly increased the Dmax to the right inner ear (p=0.010). There was no significant difference in the Dmax to the left inner ear between VMAT and IMRT (p=0.458). Compared with IMRT, VMAT significantly reduced the Dmax to the left optic nerve (p=0.006), but significantly increased the Dmax to the right optic nerve (p=0.001). There was no significant difference in the Dmax to the left and right hippocampus between VMAT and IMRT (p>0.05), but VMAT significantly increased the D100% (p<0.05) compared with IMRT. Compared with VMAT, IMRT significantly reduced the MU (p<0.001) but VMAT has a higher treatment efficiency than IMRT, with an average reduction of 41 seconds (294.1 ± 16.4 s for VMAT, 335.8 ± 34.9 s for IMRT, p<0.001). Under the conditions of 3%/2 mm, and 2%/2 mm, the gamma passing rate of the IMRT QA was improved compared to VMAT, with an average increase of 0.6%, p=0.013, and 1.7%, p<0.001, respectively. Both non-coplanar VMAT and non-coplanar fixed field IMRT based on the Monaco TPS produce clinically acceptable results for HA-WBRT+SIB in patients with brain metastases. Compared with IMRT, VMAT has better dose distribution in the target volume and treatment efficiency, but IMRT can better protect the hippocampus and reduce the number of MUs.

Zeng H ，Zhong M ，Chen Z ，Tang S ，Wen Z ... -  《Frontiers in Oncology》

Retrospective Analysis of Dosimetric Comparison Between Intensity-Modulated Radiation Therapy and Volumetric-Modulated Arc Therapy in Patients With Esophageal Cancer.

Introduction Esophageal cancer is a significant global health concern, with high incidence and mortality rates, particularly in India, where it ranks among the top causes of cancer-related deaths. Radiotherapy plays a critical role in the treatment of advanced-stage esophageal cancer. This study aims to compare the dosimetric outcomes of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) to evaluate their efficacy and safety in managing mid-esophageal carcinoma.  Materials and methods A retrospective study was carried out on thirty patients with middle-third esophageal cancer who received treatment at Rohilkhand Medical College and Hospital, Bareilly, India. The patients, aged between 50 and 70 years (mean age of 66.5 years), were in stages II to III of cancer according to the American Joint Committee on Cancer (AJCC) 2018 guidelines. All patients had histologically confirmed cases of moderately differentiated squamous cell carcinoma. The treatment procedure included immobilization using a thoracic mold, CT simulation with intravenous and oral contrast, and contouring of the gross tumor volume (GTV), clinical target volume (CTV), planning target volume (PTV), and organs at risk (OARs) following the Radiation Therapy Oncology Group (RTOG) 0436 protocol. VMAT planning was done using the Varian Eclipse™ Treatment Planning System, while IMRT planning employed a seven-field non-coplanar beam setup. Comparative virtual IMRT plans were generated for these patients. Both VMAT and IMRT plans were evaluated based on dosimetric parameters for the PTV and OARs. Results Both VMAT and IMRT achieved sufficient PTV coverage, with no statistically significant differences in dosimetric parameters (dose to 99 % volume of PTV, dose to 95 %volume of PTV, maximum dose to PTV, minimum dose to PTV). VMAT demonstrated reduced lung and heart doses compared to IMRT; however, the observed differences were not statistically significant. There was a reduction in lung dose with VMAT when evaluating the dose-volume constraints: volume receiving 15 Gy dose (V15) by 11%, volume receiving 20 Gy dose (V20) by 20%, and volume receiving 25 Gy dose (V25) by 41%, though these differences were not statistically significant. The mean maximum spinal cord dose was significantly lower with VMAT (19.69 Gy) compared to IMRT (30.80 Gy, p=0.01). Heart dosimetry showed slight improvements with VMAT, particularly in volume receiving 30 Gy dose (V30), volume receiving 40 Gy dose (V40), and mean heart dose, though these differences were not statistically significant. Conclusion Both VMAT and IMRT provided similar PTV coverage. VMAT showed a reduction in spinal cord dose, which was statistically significant, and a trend toward lower lung and heart doses, though these differences were not statistically significant. VMAT appears to be an effective option for treating mid-esophageal carcinoma while reducing exposure to critical organs.

Mishra V ，Yadav R ，Chaudhary S ，Pandey L ，Pandey A ... -  《-》

Adjuvant Radiotherapy in Bladder Cancers: A Dosimetric Study Focusing on Ileal Conduit Sparing.

To compare ileal conduit (IC) and other organ at risk (OAR) dosimetry between treatment techniques in a prospective cohort of patients planned for adjuvant radiotherapy (RT) after radical cystectomy and IC reconstruction. Computed tomography (CT datasets of twenty patients who underwent adjuvant RT were obtained and used prospectively for delineation of target volumes (primary and nodal) and OARs, including IC, uretero-ileal anastomosis and ileal stoma using a specified protocol for simulation including a delayed CT to identify IC. Three RT plans were generated for each patient for a dose of 54 gray (Gy) in 27 fractions (PTV V95% >95%): 3-dimensional conformal radiotherapy (3DCRT) with (3DCRT_S) and without (3DCRT_N) stoma shielding, and volumetric modulated arc therapy (VMAT), with OAR constraints specified for VMAT plans (IC: Dmax<54Gy, V50Gy < 20 cc). Constraints were given for other pelvic OARs (bowel, rectum, femur heads) as per published literature. Plans were evaluated for target coverage as well as OAR doses; in particular, IC and ileal stoma). ANOVA test was used to compare medians of achieved doses, and a p-value <0.05 was statistically significant. The median IC volume was 63.34 (55.29-82.93) cc. The cranial end of IC was at L5 or L4 vertebral level in 95% of patients and caudal level at S2 or S3 in 80% of patients. In contrast, the ileal stoma spanned from L4 or L5 vertebral level cranially (100%) to L5 level caudally (80%). PTV V95% was similar for 3DCRT_N and VMAT plans while it was significantly lower for 3DCRT_S in areas of ileal stoma shielding (99.95% vs 99.01% vs 96.29%, p < 0.01). Median IC V50Gy was comparable in 3DCRT_N (38.81 cc) and 3DCRT_S (35.62 cc) while it was significantly lower in the VMAT plan (17.05 cc, p < 0.01). IC Dmax did not differ significantly between the three plans. On the other hand, when 3DCRT_N, 3DCRT_S, and VMAT plans were compared for ileal stoma doses, Dmean was comparable (11.93 Gy vs 7.41 Gy vs 9.54 Gy, p = 0.06) while Dmax was significantly higher for 3DCRT_N plan and least for VMAT plan (35.32 Gy vs 27.57 Gy vs 24.22 Gy, p < 0.01). VMAT plans fared significantly better than both 3DCRT plans for uretero-ileal anastomosis, bowel, and rectal dosimetry. Ileal stoma shielding in 3DCRT compromises PTV coverage but does not spare IC effectively. Sparing IC with VMAT is feasible without compromising PTV coverage. Dosimetric gains with VMAT are expected to benefit patients needing higher pelvic RT doses and nodal RT by reducing the risk of anastomotic and mucosal complications. Clinical benefits should be evaluated in a prospective protocol.

Goyal S ，Periasamy K ，Dey T ，Vias P ，Trivedi G ，Ghera G ，Madan R ，Prashar H ，Khosla D ，Mavuduru R ，Bora GS ... -  《-》

Automated hippocampal sparing whole brain radiotherapy with simultaneous integrated boost for multiple brain metastases: Halcyon, HyperArc on TrueBeam, and coplanar TrueBeam.

To demonstrate the ease and feasibility that hippocampal sparing whole brain (WB) simultaneous integrated boost (HSWB-SIB) plans can be generated using knowledge-based planning and Eclipse Scripting Application Programming Interface (ESAPI) for three different modalities, HyperArc on TrueBeam (TB-HA), a coplanar beam arrangement on TrueBeam (TB-Co), and the ring-mounted Halcyon LINAC (Hal). Twelve patients with 2-14 brain metastases were retrospectively replanned for HSWB-SIB using a published HSWB RapidPlan model with modifications for the automated addition of SIB to metastases. Prescribed dose was 30 Gy to the WB planning target volume (PTV) and 50 Gy to the metastases in 10 fractions. Eclipse treatment planning system (v16.1) was used with a 6 MV-FFF beam and Acuros XB dose algorithm. The methodology was successfully used for all modalities, generating plans in under 30 min. The plan doses were normalized to the WB PTV D95% receiving 30 Gy. Reporting values in the order of Hal, TB-Co, and TB-HA: The WB PTV received a V48 Gy of 4.58, 3.98, and 4.45 cc with statistically insignificant differences (p = 0.806). The boost PTVs received a D95% of 50.60, 50.43, and 51.13 Gy with statistically significant comparisons between TB-HA and the other two modalities (p = 0.005). The hippocampus maximum dose was 11.81, 11.51, and 11.13 Gy with no statistically significant comparisons (p = 0.105). All other oragns-at-risk (OAR) doses were clinically acceptable. The modalities were evaluated using a dosimetric scorecard, achieving average scores of 84.85%, 86.45%, and 87.39%. End-to-end testing ensured the deliverability of the HSWB-SIB plans for all modalities. The novel modification of the preexisting HSWB RapidPlan model with the automated inclusion of SIB objectives allows for easy, intuitive planning of complex HSWB-SIB treatments. All modalities demonstrated can be used with clinically comparable results. Other institutions are recommended to pursue and validate this HSWB-SIB technique to increase the accessibility of a single-course of high-quality treatment for patients with multiple brain lesions.

McCarthy S ，Clark R ，Magliari A ，St Clair W ，Pokhrel D ... -  《-》

Enhancing Delivery Efficiency on the Magnetic Resonance-Linac: A Comprehensive Evaluation of Prostate Stereotactic Body Radiation Therapy Using Volumetric Modulated Arc Therapy.

Long treatment sessions are a limitation within magnetic resonance imaging guided adaptive radiation therapy (MRIgART). This work aims for significantly enhancing the delivery efficiency on the magnetic resonance linear accelerator (MR-linac) by introducing dedicated optimization and delivery techniques for volumetric modulated arc therapy (VMAT). VMAT plan and delivery quality during MRIgART is compared with step-and-shoot intensity-modulated radiation therapy (IMRT) for prostate stereotactic body radiation therapy. Ten patients with prostate cancer previously treated on a 1.5T MR-linac were retrospectively replanned to 36.25 Gy in 5 fractions using step-and-shoot IMRT and the clinical Hyperion optimizer within Monaco (Hyp-IMRT), the same optimizer with a VMAT technique (Hyp-VMAT), and a research-based optimizer called optimal fluence levels and pseudo gradient descent with VMAT (OFL+PGD-VMAT). The plans were then adapted onto each daily magnetic resonance imaging data set using 2 different optimization strategies to evaluate the adapt-to-position workflow: "optimize weights" (IMRT-Weights and VMAT-Weights) and "optimize shapes" (IMRT-Shapes and VMAT-Shapes). Treatment efficiency was evaluated by measuring optimization time, delivery time, and total time (optimization+delivery). Plan quality was assessed by evaluating organ at risk sparing. Ten patient plans were measured using a modified linac control system to assess delivery accuracy via a gamma analysis (2%/2 mm). Delivery efficiency was calculated as average dose rate divided by maximum dose rate. For Hyp-VMAT and OFL+PGD-VMAT, the total time was reduced by 124 ± 140 seconds (P = .020) and 459 ± 110 seconds (P < .001), respectively, as compared with the clinical Hyp-IMRT group. Speed enhancements were also measured for adapt-to-position with reductions in total time of 404 ± 55 (P < .001) for VMAT-Weights as compared with the clinical IMRT-Shapes group. Bladder and rectum dosimetric volume histogram (DVH) points were within 1.3% or 0.8 cc for each group. All VMAT plans had gamma passing rates greater than 96%. The delivery efficiency of VMAT plans was 89.7 ± 2.7 % compared with 50.0 ± 2.2 % for clinical IMRT. Incorporating VMAT into MRIgART will significantly reduce treatment session times while maintaining equivalent plan quality.

Snyder JE ，Fast MF ，Uijtewaal P ，Borman PTS ，Woodhead P ，St-Aubin J ，Smith B ，Shepard A ，Raaymakers BW ，Hyer DE ... -  《-》