Volumetric Arc Therapy Technique Research Articles

Long-term outcomes of definitive radiation with volumetric modulated arc therapy and concurrent chemotherapy for squamous cell carcinoma of the anus in a regional Australian cancer centre.

Concurrent chemoradiotherapy is the standard of care in the curative intent treatment of squamous cell carcinoma (SCC) of the anus. Volumetric arc therapy (VMAT) is a highly conformal radiation therapy technique that has been implemented to reduce toxicity for these patients. However, there are few reports evaluating the long-term outcomes of VMAT. Thus, we evaluated the survival and toxicity outcomes of anal cancer patients treated in our regional cancer centre undergoing curative intent chemoradiotherapy using VMAT and following the Australian EviQ guidelines. All consecutive patients treated with the VMAT technique for curative-intent definitive chemoradiotherapy for anal SCC at our institution from 2013 until 2022 were retrospectively reviewed for survival and toxicity outcomes. Kaplan-Meier estimates of locoregional control, distant metastasis-free survival, disease-free survival, anal cancer-specific survival and overall survival were obtained. In total, 44 patients were analysed. The median follow-up was 48.9 months (Range 7.8-107). 97.7% of patients completed the prescribed radiation therapy and 88.6% chemotherapy. Five patients (11.4%) recurred. Four (9.1%) had isolated local failures, and one (2.3%) had an isolated distant failure. There were no regional nodal failures. The Kaplan-Meier estimates for locoregional control, distant metastasis-free survival, disease-free survival, anal cancer-specific survival and overall survival were 90.3%, 97.7%, 88.1%, 97.1% and 87% at 3 years, and 90.3%, 97.7%, 88.1%, 93.0% and 72.3% at 5 years, respectively. Acute grade 3 genitourinary (GU), gastrointestinal (GI) and skin toxicities occurred in 2.2%, 6.8% and 13.6% of patients, respectively. There were no acute grade 4 toxicities. Late grade 2 GU and GI toxicities occurred in 6.8% and 11.3% of patients, respectively. There were no late grade 3 or 4 toxicities or treatment-related deaths. The 5 -year colostomy-free survival rate was 86.4%. Outcomes for anal SCC after definitive chemoradiotherapy using VMAT in our regional cancer centre results in low rates of grade 3/4 toxicity, high rates of organ preservation and excellent survival outcomes.

The Impact of Deep Inspiration Breath Hold (DIBH) Implementation on the Hybrid Technique in Left-Sided Whole Breast Irradiation: A Dosimetric Characteristic Study of 3D-CRT Hybrid VMAT in DIBH and Free Breathing Conditions, and VMAT in Free Breathing Conditions.

To investigate the impact of DIBH for heart sparing effect on left sided breast postoperative whole breast irradiation by comparing the dosimetric characteristics of 3D-CRT hybrid VMAT and pure VMAT treatment planning under DIBH condition. The primary CT data sets from previously treated left sided early breast cancer were used for pure volumetric arc therapy (VMAT) technique re-planning for the dosimetric characteristics comparison. A treatment plan of 3D-CRT hybrid VMAT technique was re-planned on the free breath (FB) condition for the investigation of the dosimetric characteristics comparison on DIBH condition. The prescribed dose for all the treatment plans was 42.5Gy in 16 fractions. All plans were optimized to cover 100% of the PTV by 95% of prescribed dose. The dosimetric differences among the 3 treatment plans for the 20 patients were analyzed using Wilcoxon signed-rank test, with p value<0.05 considered statistically significant. 3D-CRT hybrid VMAT using DIBH technique yielded the best results on the conformity index (CI) and homogeneity index (HI). By comparing this 3D-CRT hybrid VMAT technique using FB and DIBH technique, the mean heart dose (MHD) was reduced from 5.38Gy to 1.65Gy, respectively (p =0.001) and the left anterior descending coronary artery (LAD)0.03cc dose was reduced from 27.87Gy to 9.41Gy, respectively (p =0.001). 3D-CRT hybrid VMAT using DIBH technique significantly reduced the V5, V20 and D mean of the ipsilateral lung and D mean of the contralateral lung. The D5 of right breast was significantly reduced by 3D-CRT hybrid VMAT compared with VMAT using DIBH technique. The incorporation of DIBH into 3D-CRT hybrid VMAT technique provides the best benefits for the heart and the OAR with respect to the radiation dose-sparing effect without compromising the target conformity and homogeneity in the treatment planning.

Intensity-Modulated Proton Therapy (IMPT) Offered Advantageous Dosimetry Compared to Volumetric Arc Therapy (VMAT) or Helical Tomotherapy (HT) in Patients with Synchronous Bilateral Breast Cancer

Radiotherapy of synchronous bilateral breast cancer poses some technical challenges with regards to dose coverage and sparing of organs at risk (OAR). In this study, we aimed to evaluate dosimetric characteristics of 3 different techniques, IMPT vs photon (VMAT and HT). We hypothesized that IMPT would result in lower doses to organs at risk, as compared to the other 2 techniques. A total of 10 patients with synchronous bilateral breast cancer who were treated with VMAT at our institution were retrospectively analyzed. Clinical target volume (CTV) included chest wall and regional nodes (supraclavicular fossa and internal mammary chain) and prescription dose was 40.05 Gy in 15 daily fractions. HT and IMPT plans were generated for each patient. Dose-volume statistics, including planning target volume (PTV) coverage and dose to OAR: lungs, heart, thyroid, spinal cord, brachial plexus and esophagus, were compared between modalities using a paired T-test. Mean age of patients was 61 years (43-84). Majority of the patients (80%) were ER+ PR+ and HER2-. 40% of patients underwent breast reconstruction following surgery. All 3 techniques provided adequate target volume distribution and OAR sparing. Compared to VMAT and HT plans, IMPT had better heart and lung sparing effects, resulting in lower mean and V25 Gy heart dose; mean, V20 Gy and V5 Gy lung dose (p<0.0001). There was no significant difference in VMAT and HT plans for mean heart and lung dose. VMAT plans showed significantly lower V25 Gy heart dose on average (p = 0.04). V5 Gy lung dose was slightly lower in HT compared to VMAT plans, approaching statistical significance (p = 0.08). PTV coverage was adequate for all 3 techniques. All techniques fulfilled cord, esophagus, thyroid and brachial plexus constraints. IMPT plans showed significantly better OAR sparing compared to photon techniques. All 3 techniques met OAR constraints, and resulted in adequate target volume coverage. As IMPT is significantly more costly than VMAT or HT techniques, appropriate patient selection is important to deliver treatment in the most resource-effective manner for patients who would derive the most benefit, for example those with young age or existing heart or lung comorbidities.

Experience of the Hybrid technique for breast cancer planning in an oncology care center in Lima-Peru

ObjectiveTo investigate, describe and evaluate the dosimetric parameters of the hybrid technique as a combination of the 3D Irregular Surface Compensator (3D-ISC) technique and modulated volumetric arc therapy (VMAT) for breast cancer planning. MethodsThe study involved planning a patient with left breast cancer. Planning was carried out with 3D-ISC, VMAT and Hybrid techniques. The 3 techniques were compared with respect to the target volume (PTV), coverage, gradient and protection of organs at risk (OARs). The Eclipse version 13.6 planning system was used and the prescription of the dose obeyed the hypofractionated scheme of 40.05Gy in 15 sessions (267 cGy per fraction) followed by a 13.35Gy boost in 5 sessions. ResultsThe tangential field technique was the one with the lowest dose values delivered to healthy organs. However, with respect to the gradient, the VMAT technique was better. The Hybrid technique was the balance between the 3D-ISC and VMAT technique because after the evaluation of dosimetric parameters for both the OARs and the PTV coverage, values were found within the limits allowed according to the RTOG. ConclusionThe hybrid 3D-ISC and VMAT technique can be considered as a viable option for breast planning, achieving better control in OARs without losing priority over PTV coverage in addition to obtaining a good plan quality.

A phase 2 trial of deep-inspiration breath hold in radiotherapy of gastric lymphomas.

Radiotherapy (RT) is an important part in the treatment of gastric lymphomas and the prognosis after radiotherapy is very good with a good chance of long-term survival, so prevention of long-term adverse effects is important. In patients with gastric lymphomas cardiac late effects are of most concern. The aim of this study was to assess if the dose to the heart could be reduced with deep inspiration breath-hold (DIBH) without compromising the dose to the target or increasing the risk of other late effects. Fifteen patients with gastric lymphoma were included. RT plans were made using DIBH and Free breathing (FB)scans. Clinical target volume (CTV) was the stomach plus 1cm margin. The heart and surrounding organs at risk (OAR) were contoured. Two sets of plan comparisons were made, one with 1cm CTV to planning target volume (PTV) margin in both DIBH and FB and one set with an additional 5mm CTV to PTV margin in cranio-caudal direction with FB. Datasets were analysed with Wilcoxon signed rank test for non-parametric paired data. All patients tolerated the procedures and were treated with volumetric arc therapy technique in DIBH. Target coverage was kept equal between FB and DIBH, while a statistically significant reduction of the estimated does to the heart was seen with DIBH. Median mean heart dose was reduced from 7.1Gy (5.7-12) to a median of 3.2Gy (1.2-7.0) and heart V20 from a median of 54 (17-106) cm3 to 15. (0.0-78) cm3. The estimated mean doses to the liver, duodenum, pancreas and spinal cord were at the same level. This clinical trial of RT with DIBH for gastric lymphomas showed that the heart dose could be reduced without compromising PTV coverage. The doses to abdominal OARs were similar with FB and DIBH.

Radiotherapy plan evaluation indices: A dosimetrical suitability check

To classify the available plan evaluation indices and compare the dosimetric suitability of these indices. Available published plan evaluation indices were categorized. Conformity index (CI) into two groups, one group contains those CI formulas which do not consider critical structure and other group contains those CI formulas which consider planning target volume (PTV) coverage, normal tissue and critical structure sparing simultaneously. Various homogeneity index (HI) formulas extracted from literature. Structure data sets of 25 patients were taken under consideration comprising of various sites. For each patient, two plans were created using Volumetric Arc Therapy technique. First type of plan (Plan-A) were generated considering all tissue objectives for targets and Organ at Risks (OARs) whereas second type of plan (Plan-B) were generated considering only targets tissue objectives and excluding OARs tissue objectives during plan optimization and dose calculation. Planning evaluation parameters were compared between Plan-A and Plan-B. CI calculated by various formulas in two different scenarios presented <2% variation. Any commonly used CI formula failed to differentiate the two different planning situations. On comparison between HI of two different scenario, it is observed that there are four formulas of HI which showed negligible variation but two formulae: S-index and HI (D) showed marginal variation. It is also observed that when OARs are removed from optimization dose homogeneity improved which is specifically pointed by sigma index formula. CI, which has assimilated the presence of OAR in their formulation, shows more reliability in plan evaluation. Sigma index was found to be more efficient formula while evaluating homogeneity of a treatment plan.

Point dose verification of Cranial Stereotactic Radiosurgery using micro Ionization Chamber and EBT3 film for 6MV FF and FFF beams in Varian TrueBeam® LINAC

Abstract Introduction: Achieving high positional and dosimetric accuracy in small fields is very challenging due to the imbalance of charged particle equilibrium (CPE), occlusion of the primary radiation source, and overlapping penumbra regions. These factors make the choice of the detector for Stereotactic Radiosurgery (SRS) patient-specific quality assurance (PSQA) difficult. The aim of the study is to compare the suitability of EBT3 Gafchromic film against CC01 pinpoint chamber for the purpose of SRS and stereotactic Radiotherapy (SRT) dose verification. Material and Method: EBT3 Gafchromic film was calibrated against Treatment Planning System (TPS) doses (1 Gy – 35 Gy). CC01 pinpoint chamber and EBT3 film was used to verify Patient-Specific point doses of 21 intracranial lesions each planned with Static, Dynamic Conformal Arc (DCA), and Volumetric Arc Therapy (VMAT) using Varian TrueBeam Accelerator 6MV Flattening Filter (FF) and 6MV Flattening Filter Free (FFF) beams. The lesion sizes varied from 0.4 cc to 2.9 cc. The lesions were categorized into &lt;1cc, 1cc-2cc and 2cc-3cc. Results: High variations in measured doses from TPS calculated dose were observed with small lesion volumes irrespective of the dosimeter. As the sizes decreased high uncertainty was observed in ion chamber results. CC01 was observed under-responding to film in small lesion sizes (&lt;1cc), where nearly 50% of results under-responded in comparison with Film results. Film results were more or less consistent for static and DCA plans. Static and DCA plans were consistent passing more than 73% of the plans of the smallest lesion size category. VMAT showed very poor PSQA agreement for all three volumes (32.1% for &lt;1cc, 14.3% for 2cc-3cc and 39.3% for 2cc-3cc). No significant difference was observed between 6MVFF and 6MVFFF beams from the chi-squared test. Conclusion: EBT3 Film was observed to be a more suitable detector for small lesion sizes less than 1cc, compared to CC01. As the volume increases, the response of CC01 and EBT3 film have no significant difference in performing PSQA for intracranial SRS/SRT. VMAT techniques for intra cranial SRS shows deviation from TPS planned dose for both EBT3 film and CC01 and should not be preferred choice of verification tools.

An institutional review: dosimetry comparison between simultaneous integrated boost IMRT and VMAT for prostate cancer

AbstractPurpose:A comparative study was performed about the plan parameters and quality indices between volumetric arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT) for the treatment of high-risk prostate cancer patients. The aim of this retrospective study was to compare the two methods of external beam radiotherapy IMRT and VMAT in terms of plan quality and efficacy.Material and method:Fifteen high-risk prostate patients were planned for radiotherapy using 6 MV photon. Three dose levels were contoured having Planning Tumour Volume 1 (PTV1 = 48 Gy), Planning Tumour Volume 2 (PTV2 = 57.6 Gy) and Planning Tumour Volume 3 (PTV3 = 60 Gy). Setup margins were given using the CHIP trial method. The prescribed PTV3 dose was 60 Gy in 20 fractions which is biologically equivalent to 74 Gy in 37 fractions using α/β = 3. In case of IMRT, seven fixed beam angles 30, 60, 105, 180, 255, 300 and 330 were used and the dose was optimised using the sliding window method. In case of rapid arc technique, one or two full arcs were used for dose optimisation while keeping all the dose constraints and other planning parameters same used in IMRT. The plan evaluation parameters and Organ at risks (OARs) doses were calculated using a dose volume histogram (DVH).Results:The average D2, D5, D95 and PTVmean for PTV3 were 61.22, 61.13, 58.12, 60.00 Gy and 62.41 62.24 59.53 61.12 Gy for IMRT and VMAT, respectively. The averages V60 for bladder and V30 for rectum were 22.81, 25 and 67, 65% for IMRT and VMAT, respectively. The average homogeneity index (HI), conformity index (CI) and gradient index (GI) were 1.04, 1.4833, 14.79 and 1.04, 1.704, 7.89 for IMRT and VMAT, respectively.Conclusion:VMAT takes less dose-delivery time and lesser number of monitoring units than IMRT, thus it compensates the intrafractional movements during dose delivery. The Dose GI in VMAT was much better than IMRT. This indicates sharper dose fall off near the normal tissue. No other major differences were observed in terms of plan evaluation parameters between IMRT and VMAT techniques. So, we conclude that VMAT technique is more efficient than IMRT in terms of plan quality and dose delivery.

Plasmocytome solitaire osseux : expérience du service de radiothérapie de l’hôpital militaire d’instruction Mohammed-V de Rabat (Maroc)

PurposeThe primary objective was to determine in our department the progression-free survival rate of patients with solitary bone plasmocytoma and secondarily to evaluate its diagnostic, therapeutic and evolutionary aspects. Patients and methodsThis is a retrospective review of 12 patients monitored and treated in the radiotherapy department of the Mohammed-V military medical teaching hospital in Rabat for a solitary bone plasmocytoma between January 2012 and December 2018. The average age of our patients were 53.8 years old (range: 31-72 years old). Pain was the most common telltale sign. The site of the lesions was spinal in four cases, iliac in four cases, mandibular, ribal, humeral and at the level of the astragalus in one case respectively. All patients received radiotherapy. This irradiation was delivered alone in 60% of cases or associated with surgery in 40% of cases. The average dose of radiotherapy was 47.3Gy (range: 45 to 50.4Gy) and this was delivered by a modulated volumetric arc therapy technique in ten patients and conformal tridimensional radiotherapy in two patients. ResultsLocal control, defined by stability or radiological regression, was obtained in ten patients and four patients progressed to multiple myeloma, two of whom died. The average duration of follow-up was 51 months. ConclusionRadiation therapy is the standard treatment for solitary bone plasmocytoma. It ensures good local control in 90% of cases. The prognosis is affected by progression to multiple myeloma, which justifies rigorous monitoring after treatment and suggests a reflection on the exact place of chemotherapy.

Dosimetric comparison between volumetric-modulated arc therapy and a hybrid volumetric-modulated arc therapy and segmented field-in-field technique for postmastectomy chest wall and regional lymph node irradiation

Decreasing radiotoxicity to the heart, lungs, and contralateral breast has proven to lower the risk of secondary malignancy and improve overall outcomes when treating chest wall (CW) and regional lymph nodes in postmastectomy breast cancer patients. In this retrospective study, 11 postmastectomy patients were selected and planned with a novel hybrid treatment method and a traditional volumetric arc therapy (VMAT) approach for comparison. This hybrid technique was able to optimize tangential beams to minimize heart dose and the VMAT contribution to improve dose conformity around the planning target volume (PTV). Overall, this hybrid technique produced more homogenous target dose coverage and demonstrated a decrease of integral dose to organs at risk (OAR), while the VMAT technique demonstrated a higher affinity for maintaining dose conformity. Further observation of dose distributions also revealed that the hybrid plans were more effective in sparing low-dose spread to healthy tissue in both right- and left-sided cases. This observation was made evident by the reduction in heart V5 and Dmean, decreases in all parameters regarding the contralateral lung, as well as all values other than the V20 of the ipsilateral lung. This unique hybrid planning technique could present an alternative to standard intensity-modulated radiation therapy (IMRT) planning when treating postmastectomy CW and regional lymph nodes, as it has shown the capacity to decrease cardiac, lung, and contralateral breast toxicity while maintaining quality PTV coverage.

Comparison of dose statistics for bladder wall and rectum wall vs whole organs for VMAT prostate treatment

Dose-wall histograms (DWHs) have been used as alternatives to dose-volume histograms (DVHs) for hollow organs, with the rationale that the dose delivered to the interior of a hollow organ would be unrelated to the level of radiation damage. The purpose of this study is to conduct a statistical comparison of dose statistics for both walled and solid structure contours for both bladder and rectum in the treatment of intermediate risk prostate cancer with volumetric arc therapy (VMAT). Ten intermediate risk prostate cases were randomly selected. Rectum and bladder were first contoured as solid structures, and then the corresponding wall structures were generated using either a slice-by-slice cropping (2D method), or with a full 3D cropping tool (3D method). Each case was then inverse planned using a 2-arc VMAT technique. Two plans per case were created, 1 with a hypofractionated treatment and 1 with a standard fractionated treatment. DVHs were calculated for solid structure contours, and DWHs were calculated for the walled structure contours generated using 2D and 3D contouring tools. A nonparametric Spearman statistic correlation test was used to compare a large number of relevant dose histogram points, and to establish the relationship between dose statistics for walled and solid structures. Several notable relationships were observed. Maximum rectal dose was strongly correlated between the solid structure and both the 2D-generated (Spearman's correlation rs = 0.988, p < 0.01) and 3D-generated (rs = 0.952 p< 0.01) wall structures. This indicates that the rectal hot spot occurred in or near the wall for all cases, suggesting that both structure types give similar maximum dose information for rectum. Maximum bladder dose was not significantly correlated between solid structures and the 2D (rs = 0.596, p= 0.069) and 3D-generated (rs = 0.681, p= 0.03) counterparts. This suggests that the maximum dose is not consistently in or near the bladder wall. This favors the use of bladder wall contours when considering bladder toxicity, with the maximum dose to the wall potentially being more relevant radiobiologically. This analysis was extended to many other relevant points on the rectum and bladder histogram curves. Where correlations are strong, equations of best-fit are presented. This work establishes several statistically-significant relationships between bladder and rectum DVHs and DWHs for VMAT irradiation of intermediate-risk prostate cancer. This information may be used to inform contouring requirements for clinical trial design as well as for standard patient care.

Modulated volumetric arc therapy for total marrow irradiation: A feasibility study in the oncology hospital of CMN SXXI from a medical physics approach.

The objective of this study is to explore the use of volumetric arc therapy (VMAT) to perform total marrow irradiation (TMI) and compare its results to the standard TBI technique in the Mexican public health system. The standard total body irradiation (TBI) technique is used with chemotherapy as a method of a pre-transplant conditioning of the bone marrow. In this technique, the whole body of the patient is considered to be PTV and irradiated generating toxicities and raising concerns about possible development of radio-induced tumors. Through the use of simulation tomography of 12 patients previously treated with TBI, twelve different treatment plans were created with the proposed TMI technique and compared with the conventional protocol, the treatment plans were evaluated with a dose volume histogram analysis and quality assurance was evaluated with a portal dosimetry system using the gamma index criteria 3%/3mm. Experimental results show an increasing dose to 99% of PTV of up to 41.1% by using TMI with the VMAT technique. The mean average dose to PTV was increased up to 19.3%. The use of the new TMI technique caused an improvement in the mean average dose to 99% of the PTV as well the homogeneity of the dose distribution prescribed at the PTV while leading to a better reproducibility of the treatment. The Qa of all the plans met the criterion of gamma index 3mm-3%. The results analysis shows that the proposed TMI technique is feasible and applicable in the Mexican public health system.

Dosimetric evaluation of the gantry sag effect in clinical SRS plans.

Objectives:The gantry sag introduces a largely reproducible variation of the radiation field center around the radiation isocenter. The purpose of this work is to assess the change of the dose distribution caused by the gantry sag in clinical stereotactic plans.Methods:Brain stereotactic radio surgery treatment plans were evaluated and grouped according to radiation therapy planning technique. Group 1 was planned with volumetric arc therapy technique using coplanar arcs while Group 2—non-coplanar arcs. To simulate the gantry sag effect in the treatment planning system, the original plan segments were divided into four groups according to corresponding gantry angles: upper, lower, left and right quadrants. Then, isocenter of the upper quadrant was shifted towards “Gun”, isocenter of the lower quadrant was shifted towards “Target” and isocenter of the left and right quadrants was left at its original positions. The magnitude of the shift was 0.5, 1 and 1.5 mm in each direction, corresponding to 1, 2 and 3 mm of gantry isocenter diameter. To estimate the changes in dose distribution between the original and modified plans, the following dose–volume metrics were tracked: planning target volume (PTV) coverage (V99;PTV), hotspot dose in PTV (DPTV;0.015cc)), coldspot doses in PTV (DPTV;(V-0.015cc)), conformity and gradient indexes, maximum point doses in organs at risk (OAR, DOAR;0.015cc) and outside PTV (DoutsidePTV;0,015cc). For the second group of patients volume of brain receiving 12 Gy (V12Gy) was analyzed.Results:The mean relative change of all metrics was within −2%/+2.5% range for both techniques for isocenter diameter up to 2 mm. Isocenter diameter of 3 mm causes significant changes in V99;PTV, conformity and gradient indexes for coplanar, and additionally in DPTV;(V-0.015cc) for non-coplanar plans. The largest increase of maximum point dose in OAR was 1.1, 2.1 and 3.2% for ±0.5, ±1 and ±1.5 mm shift, respectively.Conclusion:The results demonstrate dosimetric effect of gantry sag depending on its value. By itself, the gantry sag effect does not produce clinically perceptible dose changes neither for PTV nor for OARs for shift ranges up to ±1 mm, both for coplanar and non-coplanar delivery techniques. For the larger gantry sag magnitude dosimetric changes can become significant, especially for non-coplanar plans. It indicates that 2 mm diameter tolerance of gantry isocenter postulated in TG-142 is reasonable, as variations in excess of this value start to affect the overall dosimetric and spatial uncertainty.Advances in knowledge:Dosimetric evaluation of the gantry sag effect in clinical stereotactic radio surgery plans is presented for the first time.

The role of hypofractionated radiotherapy for the definitive treatment of localized prostate cancer: early results of a randomized trial.

Background: Prostate cancer is considered to have a special biology which could affect the radiation therapy result based on the selected fractionation scheme. We present the preliminary results of a randomized trial comparing conventionally and hypofractionated radiation therapy for prostate cancer.Methods: Patients included in the study had localized prostate cancer (cT1c-T3bN0M0) and were randomly assigned to mild hypofractionated (72 Gy in 32 fractions, arm1) or conventionally fractionated (74 Gy in 37 fractions, arm2) radiation therapy treatment with Volumetric Arc Therapy technique. The treatment was delivered only to the prostate with or without the seminal vesicles according to physician's discretion and hormone therapy was optional according to the disease stage and comorbidities. Here we present the preliminary results of acute toxicity from the gastrointestinal (GI) and genitourinary (GU) system.Results: Between 2015 and 2016, 139 patients were enrolled. 67 patients were treated with conventional fractionation and 72 were treated with hypofractionation. Grade≥ 2 toxicity from GU and GI was observed in 23 and 21 patients (31,9% vs 31,3%, p=0,79) and 15 and 12 (20,8% vs 17,9%, p=0,6) for arm1 and arm2 respectively. No statistically significant differences were observed between arms in the incidence of early toxicity. There was no correlation observed between patient characteristics and toxicity from either GU or GI.Conclusions: Hypofractionated radiotherapy appears to be equally tolerated compared to conventional fractionation in the early setting. Longer follow up is needed to assess the late toxicity profile of the patients and any potential differences between the control and experimental arm.

P255] Comparison of finf and vmat plans prepared using breath-hold technique in early stage left breast irradiation

Purpose Breath-hold RT (BHRT), in which organ movements can be controlled, is one of the recommended methods for treating left breast cancer. In radiotherapy planning of left breast cancer, the risky organs in the radiation field make it difficult to obtain a homogeneous dose distribution. The aim of this study was to compare the volumetric arc therapy (VMAT) plans with the Field-in-Field (FinF) plans prepared for the early stage left breast cancer patients using BHRT. Treatment plans were compared in terms of plan quality and doses received by organs at risk. Methods In the study, 10 tomography images of the patients were taken using breath-hold technique. VMAT and FinF plans were prepared in Eclipse Treatment Planning System (TPS). The dose was defined as 50 Gy/25 fractions. For all plans, 95% of the CTV breast volume was targeted to receive 46 Gy. In both techniques, target volume homogeneity index (HI) and conformity index (CI), critical organ doses and MUs were compared. Result For the VMAT and FinF techniques, CI was found as 1.02 ± 0.04 and 1.341 ± 0.08; HI was found as 0.101 ± 0.02 and 0.147 ± 0.03, respectively. The differences between the treatment techniques are statistically significant for CI and HI values. The CTV breast maximum and mean doses were found to be lower in the VMAT technique (p 0.05). The LAD mean doses were lower in the FinF technique compared to the VMAT technique (p 0.05). The volume of the ipsilateral lung receiving 5, 10, 20 and 30Gy; the volume of the heart receiving 5 and 10 Gy and mean dose of the heart; the maximum doses of contralateral lung and breast were found lower in FinF technique (p 0.05). MU differences are also statistically significant in favor of FinF. Conclusion In patients with early stage left breast cancer, better CI and HI values were obtained with VMAT than with FinF in the case of irradiation using BHRT technique . But on the other hand, critical organ doses were found to be higher with VMAT technique. This result should not be overlooked in young patients who are thought to have longlife expectancy. This work was supported by Scientific Research Projects Coordination Unit of Istanbul University (Project Number: I.U.BAP-23057).

P256] The effect of different breathing stages on treatment plans prepared using VMAT technique in early stage left breast irradiation

Purpose Volumetric Arc Therapy (VMAT) has become one of the most frequently used techniques in the treatment of left breast cancer radiotherapy due to its ability to reduce critical organ doses.In patients with left breast cancer, it is very important to reduce the amount of irradiated heart dose-volume in order to prevent possible cardiovascular morbidity associated with radiotherapy. Deep inspiration breath-hold (DIBH) is a technique that delivered the radiotherapy to the left breast patients in a deep breath hold position.In this study, VMAT plans on computed tomography (CT) images taken at different breath phases for left sided breast cancer patients were compared in terms of plan quality and risky organ doses. Methods In the study, VMAT plans were prepared on the CT images taken both free-breathing (FB) and DIBH modes. Eclipse treatment planning system (TPS) was used in order to prepare radiotherapy plans. The Varian Real Time Position Management System (RPM) was used for the DIBH technique.The dose was defined as 50 Gy/25 fractions. For all plans, 95% of the CTV breast volume was targeted to receive 46 Gy. In both techniques, target volume homogeneity index (HI) and conformity index (CI), critical organ doses and MU values were compared. Result CI values of VMAT plans prepared for both FB and DIBH CT images was found as 1.02 ± 0.04 and 1.014 ± 0.03; HI was found as 0.101 ± 0.018 and 0.113 ± 0.016, respectively. In terms of dose homogeneity, DIBH-VMAT plans were found to be better than FB-VMAT plans; the difference is statistically significant. The LAD mean doses were found to be lower in the DIBH-VMAT technique (p Conclusion DIBH-VMAT technique should be preferred instead of FB-VMAT technique for early stage left breast cancer irradiation. This work was supported by Scientific Research Projects Coordination Unit of Istanbul University (Project Number: I.U.BAP-23057).

Frameless Volumetric Intracranial Stereotactic Radiosurgery with Non-coplanar Arcs: Clinical Experience, Accuracy, and Dosimetric Evaluation

In the last decades technological advances are increasing with the development of new treatment techniques and ways to deliver cranial radiosurgery(SRS), that is based into precision and accuracy, Volumetric Arc Therapy (VMAT) have been used in brain radio surgery in terms of non coplanar rotational arc beams with the aid of multi-leaf(MLC) to provide beam collimation. Using the traditional Leksell Stereotactic System, the time to do a treatment in average was around 6 hours; however the workflow using a frameless system decreases the mean treatment time in less than an hour, turning out to be a resources optimization for its realization, all this with the help of all accessories, quality assurance that should be made before deliver a proper treatment. The goal of this study is to show our clinical experience doing frameless SRS, with VMAT technique in the treatment of Arteriovenous Malformations(AVMs), Brain Metastases, Meningiomas, among others. The issues discussed in this study with regard to not only the clinical features, but also beam characteristics, and dosimetric features. 20 patients have been treated since May up to September 2016 with different diagnostics, doses given are related to each pathology treated, each prescription isodose was higher than 96%. Frameless system used was trUpoint ARCH™ SRS/SRT System, the Immobilization is accomplished utilizing multiple immobilization components - custom head support, bite tray, thermoplastic mask, and nasion cushion - allowing a truly custom hold from CIVCO, Patients were simulated in Computed tomography (CT) simulation General Electric(GE) Optima model, slides acquisition 1.25 mm; Magnetic Resonance was also done in a Siemens de 1.5T with 1 mm slices in contrast enhanced T1 MPR, T2 Flair, T2 Ciss, Diffusion, Perfusion, DTI Tractography, Angiography was done in GE Discovery; for image fusion for PTV and OAR contouring; calculation were done in Monaco® planning system version 5.10.02 with Monte Carlo algorithms; treatment delivery were make in a LINAC Elekta Infinity™ with Agility™ head with 160 interdigitating leaves with 0.5 cm width at isocenter; positioning verification XVI versión 4.5.1 b141. Treatment Delivery time 22 +/- 1.30 minutes for VMAT. Mean Monitor Units (MU) were 3795; For each patient IGRT is made with 3 XVI (Cone Beam CT), Pre and Post Treatment, what makes the procedure safe, confortable and accurate. With regard to CIRTOG a 0.9825 was obtained in average and QA was made using the OCTAVIUS® 1000 SRS with a Gamma Index 3mm/3% over 96%. Data found in this study with regard to the 20 patients treated; suggest that Frameless arch design provides a secure hold with no surgical attachment to the patient, displacements are less than 1 mm of patient movement permitted during intrafraction immobilization testing; also is safe, confortable and easy to use even allows us to rapid response for anxious patients with its release mechanism. Less treatment times and also excellent clinical outcomes.

Stereotactic radiotherapy in the treatment of local recurrences of esophageal cancer

Esophageal cancer (EC) consists of tumors with a generally poor prognosis, and treatment options for patients with disease recurrence are extremely limited. Due to this poor patient prognosis, the possible treatment toxicity should be carefully balanced against its potential benefit and patient quality of life. Stereotactic body radiotherapy (SBRT) is a rapidly expanding novel technique combining a short treatment time together with high local efficacy and an acceptable toxicity profile. There are no publications thus far presenting data regarding the usage of SBRT utilizing a conventional linear accelerator in locally recurrent EC patients. In the present study, 2 patients with recurrent EC in the neck lymph nodes were treated by SBRT in the Department of Oncology, University Hospital Olomouc, Czech Republic. The treatment dose was 30 and 40 Gy in 5 daily fractions, with a prescribed dose to 65 and 81% isodose, for each patient respectively, utilizing a volumetric arc therapy technique, a 6-MV photon beam and an Elekta Synergy linear accelerator. The treatment was delivered without any unintentional treatment interruptions and without any treatment-related acute toxicity. The maximum dose in the patients was 45.9 and 49.2 Gy, respectively. The maximum doses for the surrounding major blood vessels were 35.4 and 45.7 Gy, respectively. Maximum doses to the trachea and the esophagus in the first patient were 32.6 and 27.0 Gy. In the second patient, these doses were not clinically significant. SBRT utilizing linear accelerators should be considered in patients with localized recurrent EC, offering the patients the chance for local control with minimal treatment toxicity.

The Feasibility Study of a Hybrid Coplanar Arc Technique Versus Hybrid Intensity-modulated Radiotherapy in Treatment of Early-stage Left-sided Breast Cancer with Simultaneous-integrated Boost.

This study demonstrated the feasibility and advantages of a hybrid, volumetric arc therapy technique that used two 90° coplanar arcs and two three-dimensional conformal tangential beams in the simultaneous-integrated boost radiotherapy of left-sided breast cancer after breast-conserving surgery. A total of nine patients with stage I, left-sided breast cancer who underwent breast-conserving surgery were selected for this retrospective study. For each patient, a hybrid arc plan was generated and then compared with two hybrid intensity-modulated radiotherapy plans. All plans were optimized using the same objectives and dose constraints. The prescription dose was 50.4 Gy to the planning target volume with simultaneous boost to 60 Gy to the expanded gross target volume in 28 fractions. The differences among these hybrid plans were analyzed by the Kolmogorov–Smirnov test or the Wilcoxon rank sum test. The hybrid arc plans achieved the clinical requirements of target dose coverage and normal tissue (NT) dose constraints. It was found that the hybrid arc plans showed advantages in the conformity index of the expanded gross target volume, the V5 of the heart, the D2 of the left ventricle, and the D2 and V50.4 of NTs. The average beam-on time and monitor units of the hybrid arc plans were significantly lower (P < 0.001).

Dosimetric evaluation of volumetric modulated arc therapy for bilateral breast carcinoma

Introduction Patients with bilateral breast carcinoma are usually treated with two sets of tangential beams with different iso-centers. Single iso-center Volumetric Arc Therapy (VMAT) treatment plan can give several logistical advantages, avoiding also the overlapping of tangential fields. Purpose Perform a dosimetric study to evaluate the enforcement of Volumetric Modulated Arc Therapy (VMAT) on bilateral breast carcinoma radiotherapy. Materials and methods Treatment plans for 5 patients, previously treated with 50.4 Gy/28 fractions, using 3D Conformal Radiotherapy planned with a standard tangential field technique, were replanned with VMAT technique. The PTV used in the optimization was expanded 2 cm to the external direction, in order to correct respiratory movement. VMAT plans were optimized with 2-arcs, 3-arcs and 4-arcs, all plans using one iso-center, avoiding angles between 140° and 220°. Results VMAT presents evident logistical advantages for bilateral breast treatment; one iso-center reduces patient setup time, and treatment time. 4-arcs plan and 3-arcs plan had similar dosimetric results, being 2-arcs plan the worst solution. Comparing to the standard tangential field technique, VMAT had better PTV dose coverage (Conformity Index improved in a 13%), avoiding hotspots, which can appear on 3DCRT standard tangential field technique. VMAT also reduces high doses to OARs. On the other hand, VMAT increase lower doses to the whole body, increasing slightly the mean heart dose. Conclusion VMAT technique showed logistical advantages for the treatment of bilateral breast carcinoma, but also dosimetric improvements. 3DCRT had greater high doses to OARs, but save lower doses to the whole body.