Dose-escalated volumetric modulated arc therapy for total marrow irradiation: A feasibility dosimetric study with 4DCT planning and simultaneous integrated boost

PurposeTo evaluate the planning feasibility of dose-escalated total marrow irradiation (TMI) with simultaneous integrated boost (SIB) to the active bone marrow (ABM) using volumetric modulated arc therapy (VMAT), and to assess the impact of using planning organs at risk (OAR) volumes (PRV) accounting for breathing motion in the optimization.MethodsFive patients underwent whole-body CT and thoraco-abdominal 4DCT. A planning target volume (PTV) including all bones and ABM was contoured on each whole-body CT. PRV of selected OAR (liver, heart, kidneys, lungs, spleen, stomach) were determined with 4DCT. Planning consisted of 9–10 full 6 MV photon VMAT arcs. Four plans were created for each patient with 12 Gy prescribed to the PTV, with or without an additional 4 Gy SIB to the ABM. Planning dose constraints were set on the OAR or on the PRV. Planning objective was a PTV D_mean < 110% of the prescribed dose, a PTV V_110% < 50%, and OAR D_mean ≤ 50–60%.ResultsPTV D_mean < 110% was accomplished for most plans (n = 18/20), while all achieved V_110%<50%. SIB plans succeeded to optimally cover the boost volume (median ABM D_mean = 16.3 Gy) and resulted in similar OAR sparing compared to plans without SIB (median OAR D_mean = 40–54% of the ABM prescribed dose). No statistically significant differences between plans optimized with constraints on OAR or PRV were found.ConclusionsAdding a 4 Gy SIB to the ABM for TMI is feasible with VMAT technique, and results in OAR sparing similar to plans without SIB. Setting dose constraints on PRV does not impair PTV dosimetric parameters.     

Static and rotational intensity modulated techniques for head-neck cancer radiotherapy: A planning comparison

PurposeTo compare helical Tomotherapy (HT), two volumetric-modulated arc techniques and conventional fixed-field intensity modulated techniques (S-IMRT) for head-neck (HN) cancers.Methods and materialsEighteen HN patients were considered. Four treatment plans were generated for each patient: HT, S-IMRT optimised with Eclipse treatment planning system and two volumetric techniques using Elekta–Oncentra approach (VMAT) and Varian-RapidArc (RA), using two full arcs. All techniques were optimised to simultaneously deliver 66Gy to PTV1 (GTV and enlarged nodes) and 54Gy to PTV2 (subclinical and electively treated nodes). Comparisons were assessed on several dosimetric parameters and, secondarily, on planned MUs and delivery time.ResultsConcerning PTV coverage, significantly better results were found for HT and RA. HT significantly improved the target coverage both compared to S-IMRT and VMAT. No significant differences were found between S-IMRT and volumetric techniques in terms of dose homogeneity. For OARs, all the techniques were able to satisfy all hard constraints; significantly better results were found for HT, especially in the intermediate dose range (15–30 Gy). S-IMRT reached a significantly better OARs sparing with respect to VMAT and RA. No significant differences were found for body mean dose, excepting higher values of V5–V10 for HT. A reduction of planned MUs and delivery treatment time was found with volumetric techniques.ConclusionsThe objectives of satisfying target coverage and sparing of critical structures were reached with all techniques. S-IMRT techniques were found more advantageous compared to RA and VMAT for OARs sparing. HT reached the best overall treatment plan quality.     

A new split arc VMAT technique for lymph node positive breast cancer

PurposeTo investigate different volumetric modulated arc therapy (VMAT) field designs for lymph node positive breast cancer patients when compared to conventional static fields and standard VMAT designs.MethodsNineteen breast cancer patients with lymph node involvement (eleven left and eight right sided) were retrospectively analyzed with different arc designs. Proposed split arc designs with total rotations of 2 × 190° and 2 × 240° were compared to conventional field in field (FinF) and previously published non-split arc techniques with the same amount of total rotations.ResultsAll VMAT plans were superior in dose conformity, when compared to the FinF plans. Split arc design decreased significantly ipsilateral lung dose and heart V5Gy for both left and right sided cases, when compared to non-split VMAT designs. For left sided cases no significant differences were seen in contralateral lung mean dose or V5Gy between different VMAT designs. For right sided cases the contralateral lung dose V5Gy was significantly higher in split VMAT group, when compared to non-split VMAT designs. The contralateral breast dose V5Gy increased significantly for split VMAT plans for both sides, when compared to non-split VMAT designs or FinF plans.ConclusionsThe proposed split VMAT technique was shown to be superior to previously published non-split VMAT and conventional FinF techniques significantly reducing dose to the ipsilateral lung and heart. However, this came with the expense of an increase in the dose to the contralateral breast and for right-sided cases to the contralateral lung.     

Is dose escalation achievable for esophageal carcinoma?

Aim

To investigate the feasibility of dose escalation using rapid arc (RA) and Helical Tomotherapy (HT) for patients with upper, middle and distal esophageal carcinomas, even for large tumor volumes.

Background

In esophageal cancer, for patients with exclusive radio-chemotherapy, local disease control remains poor. Planning study with dose escalation was done for two sophisticated modulated radiotherapy techniques: Rapid arc against Tomotherapy.

Materials and methods

Six patients treated with a RA simultaneous integrated boost (SIB) of 60 Gy were re-planned for RA and HT techniques with a SIB dose escalated to 70 Gy. Dose volume histogram statistics, conformity indices and homogeneity indices were analyzed. For a given set of normal tissue constraints, the capability of each treatment modality to increase the GTV dose to 70 Gy was investigated.

Results

Either HT or VMAT may be used to escalate the dose delivered in esophageal tumors while maintaining the spinal cord, lung and heart doses within tolerance. Adequate target coverage was achieved by both techniques. Typically, HT achieved better lung sparing and PTV coverage than did RA.

Conclusions

Dose escalation for esophageal cancer becomes clinically feasible with the use of RA and HT. This promising result could be explored in a carefully controlled clinical study which considered normal tissue complications and tumor control as endpoints.     

Advanced optimization methods for whole pelvic and local prostate external beam therapy

PurposeRadiation treatment planning inherently involves multiple conflicting planning goals, which makes it a suitable application for multicriteria optimization (MCO). This study investigates a MCO algorithm for VMAT planning (VMAT–MCO) for prostate cancer treatments including pelvic lymph nodes and uses standard inverse VMAT optimization (sVMAT) and Tomotherapy planning as benchmarks.MethodsFor each of ten prostate cancer patients, a two stage plan was generated, consisting of a stage 1 plan delivering 22 Gy to the prostate, and a stage 2 plan delivering 50.4 Gy to the lymph nodes and 56 Gy to the prostate with a simultaneous integrated boost. The single plans were generated by three planning techniques (VMAT–MCO, sVMAT, Tomotherapy) and subsequently compared with respect to plan quality and planning time efficiency.ResultsPlan quality was similar for all techniques, but sVMAT showed slightly better rectum (on average D_mean −7%) and bowel sparing (D_mean −17%) compared to VMAT–MCO in the whole pelvic treatments. Tomotherapy plans exhibited higher bladder dose (D_mean +42%) in stage 1 and lower rectum dose (D_mean −6%) in stage 2 than VMAT–MCO. Compared to manual planning, the planning time with MCO was reduced up to 12 and 38 min for stage 1 and 2 plans, respectively.ConclusionMCO can generate highly conformal prostate VMAT plans with minimal workload in the settings of prostate-only treatments and prostate plus lymph nodes irradiation. In the whole pelvic plan manual VMAT optimization led to slightly improved OAR sparing over VMAT–MCO, whereas for the primary prostate treatment plan quality was equal.     

Critical Structure Sparing in Stereotactic Ablative Radiotherapy for Central Lung Lesions: Helical Tomotherapy vs. Volumetric Modulated Arc Therapy

Background

Helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT) are both advanced techniques of delivering intensity-modulated radiotherapy (IMRT). Here, we conduct a study to compare HT and partial-arc VMAT in their ability to spare organs at risk (OARs) when stereotactic ablative radiotherapy (SABR) is delivered to treat centrally located early stage non-small-cell lung cancer or lung metastases.

Methods

12 patients with centrally located lung lesions were randomly chosen. HT, 2 & 8 arc (Smart Arc, Pinnacle v9.0) plans were generated to deliver 70 Gy in 10 fractions to the planning target volume (PTV). Target and OAR dose parameters were compared. Each technique’s ability to meet dose constraints was further investigated.

Results

HT and VMAT plans generated essentially equivalent PTV coverage and dose conformality indices, while a trend for improved dose homogeneity by increasing from 2 to 8 arcs was observed with VMAT. Increasing the number of arcs with VMAT also led to some improvement in OAR sparing. After normalizing to OAR dose constraints, HT was found to be superior to 2 or 8-arc VMAT for optimal OAR sparing (meeting all the dose constraints) (p = 0.0004). All dose constraints were met in HT plans. Increasing from 2 to 8 arcs could not help achieve optimal OAR sparing for 4 patients. 2/4 of them had 3 immediately adjacent structures.

Conclusion

HT appears to be superior to VMAT in OAR sparing mainly in cases which require conformal dose avoidance of multiple immediately adjacent OARs. For such cases, increasing the number of arcs in VMAT cannot significantly improve OAR sparing.     

Efficacy of tangential irradiation with volumetric modulated arc therapy on scalp angiosarcoma using medical linac

PurposeTo increase the superficial dose and reduce the brain dose for radiotherapy of scalp angiosarcoma, we propose a novel irradiation technique of tangential irradiation volumetric modulated arc therapy (TI-VMAT).MethodsTI-VMAT and the conventional VMAT treatment plans for thirteen scalp angiosarcoma patients were created with a prescribed dose of 70 Gy. Each treatment was normalized to cover 95% of the planning target volume (PTV) with its prescribed dose. To realize TI-VMAT, an avoidance structure (AS) function was applied. AS was defined as a contour subtracted PTV by a certain space from the brain contour. TI-VMAT treatment plans for six different spaces between PTV and AS were developed and compared with the conventional VMAT treatment plan with respect to the following dosimetric parameters: homogeneity index (HI) and conformity index (CI) of the PTV, mean brain dose, and brain volume irradiated with 20% (V_20% [cc]), 40% (V_40% [cc]), 60% (V_60% [cc]), 80% (V_80% [cc]), and 100% (V_100% [cc]) of the prescribed dose.ResultsHI and CI were comparable between TI-VMAT and the conventional VMAT, the mean brain dose for TI-VMAT with AS defined by a space of 2.0 cm and jaw tracking was 14.27 Gy, which was significantly lower than that for the conventional VMAT (21.20 Gy). In addition, dosimetric parameters such as V_20% [cc] were significantly suppressed compared to those for high doses.ConclusionOur proposed irradiation technique TI-VMAT shows the potential to reduce radiation doses in the brain with maintaining higher dose coverage on the PTV.     

Comparison between two treatment planning systems for volumetric modulated arc therapy optimization for prostate cancer

PurposeTo investigate the performances of two commercial treatment planning systems (TPS) for Volumetric Modulated Arc Therapy (VMAT) optimization regarding prostate cancer. The TPS were compared in terms of dose distributions, treatment delivery parameters and quality control results.Materials and methodsFor ten patients, two VMAT plans were generated: one with Monaco TPS (Elekta) and one with Pinnacle TPS (Philips Medical Systems). The total prescribed dose was 78 Gy delivered in one 360° arc with a Synergy^® linear accelerator equipped with a MLCi2^®.ResultsVMAT with Monaco provided better homogeneity and conformity indexes but lower mean dose to PTVs than Pinnacle. For the bladder wall (p = 0.019), the femoral heads (p = 0.017), and healthy tissues (p = 0.005), significantly lower mean doses were found using Monaco. For the rectal wall, VMAT with Pinnacle provided a significantly (p = 0.047) lower mean dose, and lower dose into 50% of the volume (p = 0.047) compared to Monaco. Despite a greater number of monitor units (factor 1.5) for Monaco TPS, the total treatment time was equivalent to that of Pinnacle. The treatment delivery parameter analysis showed larger mean MLC area for Pinnacle and lower mean dose rate compared to Monaco. The quality control results gave a high passing rate (>97.4%) for the gamma index for both TPS but Monaco provided slightly better results.ConclusionFor prostate cancer patients, VMAT treatment plans obtained with Monaco and Pinnacle offered clinically acceptable dose distributions. Further investigations are in progress to confirm the performances of the two TPS for irradiating more complex volumes.     

Time motion study to evaluate the impact of flattening filter free beam on overall treatment time for frameless intracranial radiosurgery using Varian TrueBeam® linear accelerator

BackgroundThe aim was to study the impact of the flattening filter free (FFF) beam on overall treatment time for frameless intracranial radiosurgery using TrueBeam^® LINAC.The development of frameless stereotactic radiosurgery (SRS) is possible due to the incorporation of image guidance in the delivery of treatment. It is important to analyze the cost and benefits of FFF beams for treating SRS by understanding the impact of FFF beams in reducing the treatment time.Materials and methodsDynamic conformal arc (DCA ) and volumetric arc therapy (VMAT) plans were generated using 6 MV with a flattening filter (FF) and FFF beams. Overall treatment time was divided into beam on time (BOT) and beam off time (BFT). Percentage beam on time reduction (PBOTR) and Percentage total time reduction (PTTR) factors were defined for the comparison.ResultsBOT reduction was observed to be significant for higher dose per fraction but subjected to the treatment technique and modulation differences. PBOTR values are much higher than PTTR values. The 39.9% of PBOTR resulted in only 8% PTTR for DCA and 65.3% resulted in 15.9% PTTR for VMAT.ConclusionMajor BFT was utilized for imaging and verification. FFF beam significantly reduced the beam on time and was found to be most effective if the fractional dose was as high as that for SRS. Newly defined PBOTR and PTTR factors are very useful indicators to evaluate the efficacy of FFF beams in terms of time reduction.     

The robustness of dual isocenter VMAT radiation therapy for bilateral lymph node positive breast cancer

PurposeTo investigate the use of dual isocenters for VMAT planning in patients with lymph node positive synchronous bilateral breast cancer (BBC) compared to a single isocenter option.MethodsTreatment plans of 11 patients with lymph node positive BBC were retrospectively analyzed using two different VMAT planning techniques: dual-isocenter split-arc VMAT plans (Iso2) were compared with mono-isocenter VMAT plans (Iso1). For Iso2 plans, PTV dose was investigated after introducing ±2 and ±5 mm couch shift errors between the two isocenters in the lateral, longitudinal and vertical direction.ResultsFor both techniques the planning aims for PTV coverage and OARs were met. The mean dose for the bilateral lungs and heart was reduced from 11.3 Gy and 3.8 Gy to 10.9 Gy (p < .05) and 3.6 Gy (p < .05), respectively, for Iso2 plans when compared to Iso1 plans. Positive statistically significant correlation (rho = 0.76, p = .006) was found between PTV volume and D2cc_PTV for Iso1 plans. No clinically significant change was seen in the D98_CTV or D2cc_PTV after the 2 and 5 mm errors were introduced between isocenters for Iso2 plans.ConclusionsThe split arc method was shown to be a feasible treatment technique in the case of synchronous BBC for both mono and dual isocenter techniques. The dose parameters were slightly favoring dual-isocenter option instead of mono-isocenter. The dual-isocenter method was shown to be a robust treatment option in the presence of ≤5 mm errors in the shifts between the two isocenters.     

Volumetric modulated arc therapy for synchronous bilateral whole breast irradiation – A case study

PurposeThe treatment planning of bilateral breast irradiation (BBI) is a challenging task. The overlapping of tangential fields is usually unavoidable without compromising the target coverage. The purpose of this study was to investigate the technical feasibility and benefits of a single isocentre volumetric modulated arc therapy (VMAT) in BBI.Methods and materialsTwo women with bilateral breast cancer were included in this case study. The first patient (Pat#1) underwent a bilateral breast-conserving surgery and sentinel lymph node biopsy. The second patient (Pat#2) underwent a bilateral ablation and axillary lymph node dissection. Planning target volumes (PTV) and organs at risk were delineated on CT images. VMAT plans were created with four (two for both sides, Pat#1) or two (one for each breast, Pat#2) separate VMAT fields. Subsequently, traditional tangential field plans were generated for each patient and the dosimetric parameters were compared.ResultsThe treatment times of the patients with VMAT were less than 15 min with daily CBCT imaging. When compared to the standard tangential field technique, the VMAT plans improved the PTV dose coverage and dose homogeneity with improved sparing of lungs and heart. With traditional field arrangement, the overlapping of the tangential fields was inevitable without significantly compromising the target coverage, whereas with VMAT the hotspots were avoided. The patients were treated with the VMAT technique and no acute skin toxicity was observed with either of the patients.ConclusionsA single isocentre VMAT technique has been implemented clinically for BBI. With the VMAT techniques, the dose delivery was quick and the hotspots in the field overlapping areas were avoided. The PTV dose coverage was superior in VMAT plans when compared with conventional tangential technique plans.     

Photon beam energy dependent single-arc volumetric modulated arc optimization

PurposeThe purpose of this work was to present a new single-arc mixed photon (6&18MV) VMAT (SAMP) optimization framework that concurrently optimizes for two photon energies with corresponding partial arc lengths.Methods and materialsOwing to simultaneous optimization of energy dependent intensity maps and corresponding arc locations, the proposed model poses nonlinearity. Unique relaxation constraints based on McCormick approximations were introduced for linearization. Energy dependent intensity maps were then decomposed to generate apertures. Feasibility of the proposed framework was tested on a sample of ten prostate cancer cases with lateral separation ranging from 34 cm (case no.1) to 52 cm (case no.6). The SAMP plans were compared against single energy (6MV) VMAT (SE) plans through dose volume histograms (DVHs) and radiobiological parameters including normal tissue complication probability (NTCP) and equivalent uniform dose (EUD).ResultsThe contribution of higher energy photon beam optimized by the algorithm demonstrated an increase for cases with a lateral separation >40 cm. SAMP–VMAT notably improved bladder and rectum sparing in large size cases. Compared to single energy, SAMP–VMAT plans reduced bladder and rectum NTCP in cases with large lateral separation. With the exception of one case, SAMP–VMAT either improved or maintained femoral heads compared to SE–VMAT. SAMP–VMAT reduced the nontarget tissue integral dose in all ten cases.ConclusionsA single-arc VMAT optimization framework comprising mixed photon energy partial arcs was presented. Overall results underline the feasibility and potential of the proposed approach for improving OAR sparing in large size patients without compromising the target homogeneity and coverage.     

Planning Study of Flattening Filter Free Beams for Volumetric Modulated Arc Therapy in Squamous Cell Carcinoma of the Scalp

Purpose

Flattening filter free (FFF) beams show the potential for a higher dose rate and lower peripheral dose. We investigated the planning study of FFF beams with their role for volumetric modulated arc therapy (VMAT) in squamous cell carcinoma of the scalp.

Methods and Materials

One patient with squamous cell carcinoma which had involvement of entire scalp was subjected to VMAT using TrueBeam linear accelerator. As it was a rare skin malignancy, CT data of 7 patients with brain tumors were also included in this study, and their entire scalps were outlined as target volumes. Three VMAT plans were employed with RapidArc form: two half-field full-arcs VMAT using 6 MV standard beams (HFF-VMAT-FF), eight half-field quarter-arcs VMAT using 6 MV standard beams (HFQ-VMAT-FF), and HFQ-VMAT using FFF beams (HFQ-VMAT-FFF). Prescribed dose was 25×2 Gy (50 Gy). Plan quality and efficiency were assessed for all plans.

Results

There were no statistically significant differences among the three VMAT plans in target volume coverage, conformity, and homogeneity. For HFQ-VMAT-FF plans, there was a significant decrease by 12.6% in the mean dose to the brain compared with HFF-VMAT-FF. By the use of FFF beams, the mean dose to brain in HFQ-VMAT-FFF plans was further decreased by 7.4% compared with HFQ-VMAT-FF. Beam delivery times were similar for each technique.

Conclusions

The HFQ-VMAT-FF plans showed the superiority in dose distributions compared with HFF-VMAT-FF. HFQ-VMAT-FFF plans might provide further normal tissue sparing, particularly in the brain, showing their potential for radiation therapy in squamous cell carcinoma of the scalp.     

Treatment planning and dosimetric comparison study on two different volumetric modulated arc therapy delivery techniques

Aim

To compare and evaluate the performance of two different volumetric modulated arc therapy delivery techniques.

Background

Volumetric modulated arc therapy is a novel technique that has recently been made available for clinical use. Planning and dosimetric comparison study was done for Elekta VMAT and Varian RapidArc for different treatment sites.

Materials and methods

Ten patients were selected for the planning comparison study. This includes 2 head and neck, 2 oesophagus, 1 bladder, 3 cervix and 2 rectum cases. Total dose of 50 Gy was given for all the plans. All plans were done for RapidArc using Eclipse and for Elekta VMAT with Monaco treatment planning system. All plans were generated with 6 MV X-rays for both RapidArc and Elekta VMAT. Plans were evaluated based on the ability to meet the dose volume histogram, dose homogeneity index, radiation conformity index, estimated radiation delivery time, integral dose and monitor units needed to deliver the prescribed dose.

Results

RapidArc plans achieved the best conformity (CI_95% = 1.08 ± 0.07) while Elekta VMAT plans were slightly inferior (CI_95% = 1.10 ± 0.05). The in-homogeneity in the PTV was highest with Elekta VMAT with HI equal to 0.12 ± 0.02 Gy when compared to RapidArc with 0.08 ± 0.03. Significant changes were observed between the RapidArc and Elekta VMAT plans in terms of the healthy tissue mean dose and integral dose. Elekta VMAT plans show a reduction in the healthy tissue mean dose (6.92 ± 2.90) Gy when compared to RapidArc (7.83 ± 3.31) Gy. The integral dose is found to be inferior with Elekta VMAT (11.50 ± 6.49) × 10⁴ Gy cm³ when compared to RapidArc (13.11 ± 7.52) × 10⁴ Gy cm³. Both Varian RapidArc and Elekta VMAT respected the planning objective for all organs at risk. Gamma analysis result for the pre-treatment quality assurance shows good agreement between the planned and delivered fluence for 3 mm DTA, 3% DD for all the evaluated points inside the PTV, for both VMAT and RapidArc techniques.

Conclusion

The study concludes that a variable gantry speed with variable dose rate is important for efficient arc therapy delivery. RapidArc presents a slight improvement in the OAR sparing with better target coverage when compared to Elekta VMAT. Trivial differences were noted in all the plans for organ at risk but the two techniques provided satisfactory conformal avoidance and conformation.     

Dosimetric comparison of normal breathing and deep inspiration breath hold technique for synchronous bilateral breast cancer using 6MV flattened beam and flattening filter free beam

BackgroundThe present study was to investigate the usefulness of deep inspiration breath hold (DIBH) in bilateral breast patients using 6MV flattened beam (FB) and flattening filter free beam (FFFB).Materials and methodsTwenty bilateral breast cancer patients were simulated, using left breast patients treated with DIBH technique. CT scans were performed in the normal breathing (NB) and DIBH method. Three-dimensional conformal radiotherapy (3DCRT) and volumetric arc therapy (VMAT) plans were generated.ResultsIn our study the best organ at risk (OAR) sparing is achieved in the 3DCRT DIBH plan with adequate PTV coverage (V₉₅ ≥ 47.5 Gy) as compared to 6MV FB and FFFB VMAT DIBH plans. The DIBH scan plan reduces the heart mean dose significantly at the rate of 49% in 3DCRT (p = 0.00) and 22% in VMAT (p = 0.010). Similarly, the DIBH scan plan produces lesser common lung mean dose of 18% in 3DCRT (p = 0.011) and 8% in VMAT (0.007) as compared to the NB scan. The conformity index is much better in VMAT FB (1.04 ± 0.04 vs. 1.04 ± 0.05), p =1.00 and VMAT FFFB (1.04 ± 0.05 vs. 1 ± 0.24, p = 0.345) plans as compared to 3DCRT (1.63 ± 0.2 vs. 1.47 ± 0.28, p = 0.002). The homogeneity index of all the plans is less than 0.15. The global dmax is more in VMAT FFFB DIBH plan (113.7%). The maximum MU noted in the NB scan plan (478 vs. 477MU, 1366 vs. 1299 MU and 1853 vs. 1788 MU for 3DCRT, VMAT FB and VMAT FFFB technique as compared to DIBH scan.ConclusionWe recommend that the use of DIBH techniques for bilateral breast cancer patients significantly reduces the radiation doses to OARs in both 3DCRT and VMAT plans.     

Monte Carlo investigation on the effect of air gap under bolus in post-mastectomy radiotherapy

ObjectivesTo investigate the dosimetric effect of air gaps under bolus on skin dose for left-sided post-mastectomy radiotherapy with loco regional involvement.MethodsEight patients were planned retrospectively with volume modulated arc therapy (VMAT) and conventional static Field-in-Field (FinF) methods. Three different setups were applied for the 5-mm bolus over the chest wall having 0, 5 or 10 mm air gap under the bolus. The dose calculation was performed using Monte Carlo (MC) simulation. In addition, Analytic Anisotropic Algorithm (AAA) was used to demonstrate the differences observed in clinical setting.ResultsThe investigated air gaps under the bolus had minimal effect on surface dose for FinF plans (relative difference ≤ 2.6%), whereas for VMAT plans the surface dose decreased 13.6% when compared to the case with no air gap. In both FinF and VMAT, the largest differences between AAA and MC were seen at the surface where AAA underestimated the dose by 1.5 Gy (p < 0.05) on average; while the dose in the target volume excluding the surface was relatively similar being on average 0.3 Gy (p > 0.05) larger with AAA than with MC calculations.ConclusionsThe surface dose was significantly lower with VMAT technique than with FinF technique. Possible air gaps under the bolus reduced the surface dose significantly further for VMAT but not for FinF treatments, which may have clinical impact on recurrence rate. AAA was shown to underestimate the surface dose when compared to MC calculation.     

Dosimetric comparison of conformal technique (3D) with volumetric modulated arc therapy with respect to doses obtained in the temporal lobe area in patients irradiated for brain meningioma

AimThe aim of the analysis was to compare doses obtained for temporal lobes in patients being irradiated for meningiomas of the brain using the conformal technique and volumetric modulated arc therapy (VMAT). We try to answer the question whether the application of VMAT would lead to higher doses within temporal lobes.BackgroundIn recent years a significant increase in the detection of meningiomas and effectiveness of treatment has been observed. Hence quality of life should be considered as an important aspect after a treatment course.Materials and methodsTreatment plans of 27 patients were evaluated retrospectively. Radiotherapy procedures were carried out from 2007 until 2016 at the Department of Radiation Oncology in Wroclaw, Poland. For individual patients, alternative treatment plans were generated in relation to the ones originally used, wherein from dynamic techniques, volumetric modulated arc therapy was selected for analysis. Evaluated dosimetric parameters for temporal lobes were: mean dose, V10 Gy, V20 Gy, V45 Gy.ResultsStatistically significant differences were observed for V45 Gy for both temporal lobes (p = 0.023) and for V45 Gy for the right (p = 0.001) and the left temporal lobe (p = 0.016) considered for VMAT. The mean values of the V45 Gy for both temporal lobes, for the right temporal lobe and for the left temporal lobe were lower for VMAT than for 3D, respectively: 7.54% and 7.90%, 6.82% and 9.47%, 5.67% and 7.14%.Analysis of the remaining results found no statistical differences.ConclusionApplication of VMAT in patients treated for meningioma of the brain is not related to higher doses of radiation in the temporal lobe area, compared with the conformal technique.     

Dosimetric study of a hybrid plan technique for external beam radiotherapy in patients with cervical cancer

The aim of this study was to investigate the effect of a hybrid technique which results from combining intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) for the treatment of cervical cancer patients. Plans made with the hybrid technique and pure IMRT and VMAT were retrospectively compared in 20 patients with cervical cancer at different stages. All plans were made using the same contours based on the original computed tomography (CT) scans. Conformity (CI) and homogeneity (HI) indices of the planning target volumes (PTVs) were calculated for each technique in order to evaluate plan quality. All techniques were compared in terms of dose to organs at risk (OARs), number of monitor units (MUs) and treatment time. It turned out that plans made with the hybrid technique had improved dose conformity and homogeneity compared to plans made only with IMRT and VMAT (p < 0.001). Regarding the OARs, the maximum dose (D_max) delivered to the bladder, rectum and femoral heads was lower for the hybrid plans compared to the IMRT and VMAT plans (p < 0.001). The volumes irradiated to doses of 50 Gy (V_50Gy) for rectum, bladder and bowel were lower for the hybrid plans (p < 0.001, p = 0.002). Furthermore, the treatment time and MU values for the hybrid plans were found to be between of the values for the IMRT and VMAT plans. It is concluded that, as compared to IMRT and VMAT plans, the hybrid plan technique allowed a better conformity and homogeneity for the dose distribution in the PTV and a dose reduction to the OARs.

     

Hippocampal dose during Linac-based stereotactic radiotherapy for brain metastases: An observational study

IntroductionAim of the present study is to evaluate homolateral and contralateral hippocampus (H-H, C-H, respectively) dose during Fractionated Stereotactic Radiotherapy (FSRT) or Radiosurgery (SRS) for brain metastases (BM).Materials & methodsPatients with BM < 5, size ≤ 30 mm, KPS ≥ 80 and a life expectancy > 3 months, were considered for SRS/FSRT (total dose 15–30 Gy, 1–5 fractions). For each BM, a Flattening Filter Free (FFF) Volumetric Modulated Arc Therapy (VMAT) plan was generated with one or two arcs. Hippocampi were not considered during optimizations phase and were contoured and evaluated retrospectively in terms of dose: the Dmedian, Dmean, D0.1cc and the V1Gy, V2Gy, V5Gy and V10Gy were analyzed.ResultsFrom April 2014 to December 2015, 81 BM were treated with FFF-FSRT/SRS. For the H-H, the average values of Dmedian, Dmean and D0.1cc were 1.5Gy, 1.54Gy and 2.2Gy, respectively, while the V1Gy, V2Gy, V5Gy and V10Gy values were 25%, 8.9%, 8.9% and 2.1%, respectively. For the C–H, the average Dmedian, Dmean and D0.1 cc were 0.7Gy, 0.7Gy, 0.9Gy, respectively, while the average values of V1Gy, V2Gy, V5Gy and V10Gy were 18%, 10.2%, 2.8% and 1.4%, respectively. Tumor dimension, tumor cranial-caudal length and the distance between BM and H-H were correlated to Dmedian, Dmean and D0.1cc. For C-H, only the distance from PTV was correlated with a dose reduction.ConclusionDuring FFF-FSRT/SRS, hippocampus received a negligible dose. Despite its clinical significance is still under evaluation, in patients with a long life expectancy, H-H should be considered during Linac-based FSRT/SRS.