Intensity Modulated Radiation Therapy Fields Research Articles

Dosimetric feasibility of magnetic resonance imaging‐guided tri-cobalt 60 preoperative intensity modulated radiation therapy for soft tissue sarcomas of the extremity

PurposeThe purpose of this study was to investigate the dosimetric differences of delivering preoperative intensity modulated radiation therapy (IMRT) to patients with soft tissue sarcomas of the extremity (ESTS) with a teletherapy system equipped with 3 rotating 60Co sources and a built-in magnetic resonance imaging and with standard linear accelerator (LINAC)‐based IMRT. Methods and materialsThe primary study population consisted of 9 patients treated with preoperative radiation for ESTS between 2008 and 2014 with LINAC-based static field IMRT. LINAC plans were designed to deliver 50 Gy in 25 fractions to 95% of the planning target volume (PTV). Tri-60Co system IMRT plans were designed with ViewRay system software. ResultsTri-60Co‐based IMRT plans achieved equivalent target coverage and dosimetry for organs at risk (long bone, skin, and skin corridor) compared with LINAC-based IMRT plans. The maximum and minimum PTV doses, heterogeneity indices, and ratio of the dose to 50% of the volume were equivalent for both planning systems. One LINAC plan violated the maximum bone dose constraint, whereas none of the tri-60Co plans did. ConclusionsUsing a tri-60Co system, we were able to achieve equivalent dosimetry to the PTV and organs at risk for patients with ESTS compared with LINAC-based IMRT plans. The tri-60Co system may be advantageous over current treatment platforms by allowing PTV reduction and by elimination of the additional radiation dose associated with daily image guidance, but this needs to be evaluated prospectively.

Bidimensional polycrystalline CVD diamond detector for Intensity Modulated Radiation Therapy pre-treatment verifications

This study aims at investigating the possible employment for pre-treatment verifications in Intensity Modulated Radiation Therapy (IMRT) of a polycrystalline Chemical Vapour Deposited (pCVD) diamond bidimensional detector.The pCVD device, with an area of 2.5 × 2.5 cm2 (12 × 12 pixels), has been used to measure dose maps of a 10 MVRX prostatic IMRT field. Its response was compared both with a commercial bi-dimensional detector made with silicon and with Treatment Planning System (TPS) calculations.Measurement provided promising results on a map of 1.8 × 12.6 cm2. Absorbed doses measured along IMRT profiles by our device are consistent with the ones acquired with the commercial device and an overall good agreement with respect to the TPS was found for the diamond dosimeter.

Impact of head immobilization position on dose distribution in patients of brainstem glioma

Purpose:The purpose of this study is to investigate the impact of patient position (supine and prone) on conventional bilateral field, three dimensional conformal radiotherapy (3DCRT) and inte nsity modulated radiotherapy (IMRT) treatment plans in patients of brainstem glioma with a view to exploring the possibility of avoiding beam entry through immobilization access o- ries.Methods:Five patients of brainstem glioma were immobilized and scanned in supine and prone positions with a combin a- tion of head rest and thermoplastic cast. Each patient was planned with three techniques: (i) 2 -fields bilateral (ii) 3 -fields 3DCRT, and (iii) 5 -fields IMRT. Plan quality was analyzed in terms of planning target volume (PTV) coverage and dose to var i- ous critical organs at risk (OAR) for both the supine and prone treatment positions. Results:In case of bilateral fields (parallel opposed) planning, th e PTV coverage and dose to the OAR were almost similar for both the supine and prone positions. In 3DCRT plan, although the PTV coverage and dose to critical structures were comparable for both the supine and prone pos i- tion, dose to cochlea was lower for t he prone position plan. A modest decrease in maximum dose to optic nerves and mean dose to temporal lobes were also observed for the prone position plan. In IMRT plans, the PTV coverage and homogeneity were comparable in both the supine and prone positions . Reduction in average maximum and mean doses to all OAR swith function- al subunit (FSU) in series and parallel respectively was observed in the IMRT plan for prone position when compared to the supine position.Conclusion:Supine and prone positions result ed in almost similar dose distribution in all the three techniques applied. At some instances, the prone position showed better normal tissues sparing when compared to supine. Moreover, prone position is more likely to avoid attenuation due to immobilizati on devices and uncertainty in dose calculation under large i n- homogeneities.

Dosimetric comparison and time consuming evaluations for neoadjuvant 5-fields versus 7-fields Intensity-Modulated Radiation Therapy for locally advanced rectal cancer.

Aims and background. Preoperative – multidrug - chemoradiotherapy schedule (PCR) is proven to be the standard approach in patients with locally advanced rectal cancer (LARC). The main limiting factor of PCR delivery is severe acute gastrointestinal (GI) toxicity due to the small bowel irradiated volume. Compared to 3-dimensional conformal radiation therapy (3DCRT), intensity-modulated radiotherapy (IMRT) plans, with 7 or more fields, by highly conformal dose distributions, will minimize the dose received by small bowel, but required an increase in overall treatment time. The purpose of this study was to investigate if simple IMRT plans were comparable to conventional 7-fields IMRT in terms of dose distribution, with the advantage of reducing time delivery. Methods. Twelve patients with histologically proved LARC underwent PCR with concurrent chemotherapy with Oxaliplatin 50 mg/m2 intravenously weekly x 6 weeks + Capecitabine 1500 mg/mq day (on days 1,14 every 21 days) and 7-field IMRT step-and -shoot technique at the cumulative dose of 50.4 Gy to the target volume, with conventional fractionation schedule of 1.8 Gy each day. Dose calculation for selected Organ at Risks (OARs) such as femoral heads, bladder and small bowel, were performed. Without exceeding OARs dose constraints or compromising target coverage, for each treated patients, a “simple” IMRT plan with 5 fields was computed and retrospectively compared with 7-field IMRT. Dosimetric parameters and treatment time data were analized. Results. As expected, homogeneity of dose distribution was significantly better for 7F-IMRT than 5F-IMRT; while in terms of Conformation Number, as proposed by van’t Riet et. Al, we registered no statistically significant differences between the two IMRT techniques resulting in equal sparing of healthy tissues. We recorded a median delivering treatment time of 7.9 minutes for 5F-IMRT and of 12.3 minutes for 7F-IMRT, with a difference statistically significant. Conclusions.This preliminary study demonstrated that the reduction in the number of fields obtained with the 5F-IMRT is a strategy to improve treatment time delivery without a detriment in target coverage and normal tissue sparing in PCR for LARC patients.

New method for estimation of fluence complexity in IMRT fields and correlation with gamma analysis

A new method for estimation of fluence complexity in Intensity Modulated Radiation Therapy (IMRT) fields is proposed. Unlike other previously published works, it is based on portal images calculated by the Portal Dose Calculation algorithm in Eclipse (version 8.6, Varian Medical Systems) in the plane of the EPID aS500 detector (Varian Medical Systems). Fluence complexity is given by the number and the amplitudes of dose gradients in these matrices. Our method is validated using a set of clinical plans where fluence has been smoothed manually so that each plan has a different level of complexity. Fluence complexity calculated with our tool is in accordance with the different levels of smoothing as well as results of gamma analysis, when calculated and measured dose matrices are compared. Thus, it is possible to estimate plan complexity before carrying out the measurement. If appropriate thresholds are determined which would distinguish between acceptably and overly modulated plans, this might save time in the re-planning and re-measuring process.

An IMRT/VMAT Technique for Nonsmall Cell Lung Cancer.

The study is to investigate a Hybrid IMRT/VMAT technique which combines intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) for the treatment of nonsmall cell lung cancer (NSCLC). Two partial arcs VMAT, 5-field IMRT, and hybrid plans were created for 15 patients with NSCLC. The hybrid plans were combination of 2 partial arcs VMAT and 5-field IMRT. The dose distribution of planning target volume (PTV) and organs at risk (OARs) for hybrid technique was compared with IMRT and VMAT. The monitor units (MUs) and treatment delivery time were also evaluated. Hybrid technique significantly improved the target conformity and homogeneity compared with IMRT and VMAT. The mean delivery time of IMRT, VMAT, and hybrid plans was 280 s, 114 s, and 327 s, respectively. The mean MUs needed for IMRT, VMAT, and hybrid plans were 933, 512, and 737, respectively. Hybrid technique reduced V 5, V 10, V 30, and MLD of normal lung compared with VMAT and spared the OARs better with fewer MUs with the cost of a little higher V 5, V 10, and mean lung dose (MLD) of normal lung compared with IMRT. Hybrid IMRT/VMAT can be a viable radiotherapy technique with better plan quality.

A Dosimetric Comparison of Double Arc Volumetric Modulated Arc Therapy with Large Field Intensity Modulated Radiation Therapy for Head and Neck Cancer

Background: This Study Evaluate two state of Art techniques, Rapid Arc and large-field sliding window IMRT in terms of dosimetric end points and delivery time for head and neck cancer. Materials and Methods: 22 patients with head and neck cancer were selected for a planning comparative study. All patients went to CT-simulation in supine position. PTVs were delineated for two dose level of prescription 70 Gy to the boost-PTV70Gy and 54 Gy to the elective-PTV54Gy in 35 equal fraction/day. Simultaneous Integrated Boost (SIB) technique plan was generated for all patients and optimized with both techniques, Rapid Arc and IMRT with similar planning objectives. Dose of all plans of both techniques were calculated for 6MV photon using AAA implemented in Eclipse treatment planning system (10.0.39) with calculating grid size of 2.5 mm. Results: Comparison of Rapid Arc and IMRT plans in every patient showed significantly higher conformity index (CI95%) (p = 0.021) and sparing of the all OARs with Rapid Arc. The average homogeneity Index (HI95%) of lower prescribed dose target PTV54Gy which is in proximity to Higher dose prescribed target PTV70Gy was improved significantly with rapid Arc (p = 0.0001). D1% of spinal cord dose reduced significantly (p = 0.047) with Rapid Arc and the average mean dose of both left-parotid (21.26 ± 8.5 Gy), right-parotid (22.37 ± 7.44 Gy) were received lesser than with IMRT (22.78 ± 11.2 Gy and 24.1 ± 7.96 Gy) respectively. A significantly less monitor unit (MU) was required to deliver the plan (p p

A hybrid IMRT/VMAT technique for the treatment of nasopharyngeal cancer.

Hybrid IMRT/VMAT technique which combined intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) was developed for the treatment of nasopharyngeal cancer (NPC). Two-full-arc VMAT (2ARC-VMAT), 9-field IMRT (9F-IMRT), and Hybrid IMRT/VMAT plans for NPC were compared in terms of the dosimetric quality, sparing of organs at risk (OARs), and delivery efficiency. The Hybrid IMRT/VMAT technique can improve the target dose homogeneity and conformity compared with 9F-IMRT and 2ARC-VMAT. It can reduce the dose delivered to the TMJ, mandible, temporal lobe, and unspecified tissue with fewer MUs compared with 9F-IMRT and dose delivered to parotids, brainstem, and spinal cord compared with 2ARC-VMAT technique. The mean delivery time of Hybrid plans was shorter than that of 9F-IMRT plans (408 s versus 812 s; P = 0.00) and longer than that of 2ARC-VMAT plans (408 s versus 179 s; P = 0.00). Hybrid IMRT/VMAT technique could be a viable radiotherapy technique with better plan quality.

Impact of dose rate on accuracy of intensity modulated radiation therapy plan delivery using the pretreatment portal dosimetry quality assurance and setting up the workflow at hospital levels.

The aim of this study was to examine the impact of dose rate on accuracy of intensity modulated radiation therapy (IMRT) plan delivery by comparing the gamma agreement between the calculated and measured portal doses by pretreatment quality assurance (QA) using electronic portal imaging device dosimetry and creating a workflow for the pretreatment IMRT QA at hospital levels. As the improvement in gamma agreement leads to increase in the quality of IMRT treatment delivery, gamma evaluation was carried out for the calculated and the measured portal images for the criteria of 3% dose difference and 3 mm distance-to-agreement (DTA). Three gamma parameters: Maximum gamma, average gamma, and percentage of the field area with a gamma value>1.0 were analyzed. Three gamma index parameters were evaluated for 40 IMRT plans (315 IMRT fields) which were calculated for 400 monitor units (MU)/min dose rate and maximum multileaf collimator (MLC) speed of 2.5 cm/s. Gamma parameters for all 315 fields are within acceptable limits set at our center. Further, to improve the gamma results, we set an action level for this study using the mean and standard deviation (SD) values from the 315 fields studied. Forty out of 315 IMRT fields showed low gamma agreement (gamma parameters>2 SD as per action level of the study). The parameters were recalculated and reanalyzed for the dose rates of 300, 400 and 500 MU/min. Lowering the dose rate helped in getting an enhanced gamma agreement between the calculated and measured portal doses of complicated fields. This may be attributed to the less complex motion of MLC over time and the MU of the field/segment. An IMRT QA work flow was prepared which will help in improving the quality of IMRT delivery.

Feasibility study on the verification of actual beam delivery in a treatment room using EPID transit dosimetry.

PurposeThe aim of this study is to evaluate the ability of transit dosimetry using commercial treatment planning system (TPS) and an electronic portal imaging device (EPID) with simple calibration method to verify the beam delivery based on detection of large errors in treatment room.Methods and materialsTwenty four fields of intensity modulated radiotherapy (IMRT) plans were selected from four lung cancer patients and used in the irradiation of an anthropomorphic phantom. The proposed method was evaluated by comparing the calculated dose map from TPS and EPID measurement on the same plane using a gamma index method with a 3% dose and 3 mm distance-to-dose agreement tolerance limit.ResultsIn a simulation using a homogeneous plastic water phantom, performed to verify the effectiveness of the proposed method, the average passing rate of the transit dose based on gamma index was high enough, averaging 94.2% when there was no error during beam delivery. The passing rate of the transit dose for 24 IMRT fields was lower with the anthropomorphic phantom, averaging 86.8% ± 3.8%, a reduction partially due to the inaccuracy of TPS calculations for inhomogeneity. Compared with the TPS, the absolute value of the transit dose at the beam center differed by −0.38% ± 2.1%. The simulation study indicated that the passing rate of the gamma index was significantly reduced, to less than 40%, when a wrong field was erroneously irradiated to patient in the treatment room.ConclusionsThis feasibility study suggested that transit dosimetry based on the calculation with commercial TPS and EPID measurement with simple calibration can provide information about large errors for treatment beam delivery.

Evaluations of secondary cancer risk in spine radiotherapy using 3DCRT, IMRT, and VMAT: A phantom study

This study evaluated the secondary cancer risk from volumetric-modulated arc therapy (VMAT) for spine radiotherapy compared with intensity-modulated radiotherapy (IMRT) and 3-dimensional conformal radiotherapy (3DCRT). Computed tomography images of an Radiological Physics Center spine anthropomorphic phantom were exported to a treatment planning system (Pinnacle3, version 9.4). Radiation treatment plans for spine were prepared using VMAT (dual-arc), 7-field IMRT (beam angles: 110°, 130°, 150°, 180°, 210°, 230°, and 250°), and 4-field 3DCRT technique. The mean and maximum doses, dose-volume histograms, and volumes receiving more than 2 and 4Gy to organs at risk (OARs) were calculated and compared. The lifetime risk for secondary cancers was estimated according to the National Cancer Registry Programme Report 116. VMAT delivered the lowest maximum dose to the esophagus (4.03Gy), bone (8.11Gy), heart (2.11Gy), spinal cord (6.45Gy), and whole lung (5.66Gy) as compared with other techniques (IMRT and 3DCRT). The volumes of OAR (esophagus) receiving more than 4Gy were 0% for VMAT, 27.06% for IMRT, and up to 32.35% for 3DCRT. The estimated risk for secondary cancer in the respective OAR is considerably lower in VMAT compared with other techniques. The results of maximum doses and volumes of OARs suggest that the risk of secondary cancer induction for the spine in VMAT is lower than IMRT and 3DCRT, whereas VMAT has the best target coverage compared with the other techniques.

Extended field intensity modulated radiation therapy for gynecologic cancers: Is the risk of duodenal toxicity high?

PurposeThere have been conflicting reports regarding the incidence of duodenal toxicity in patients receiving intensity modulated radiation therapy (IMRT) with an extended field covering the para-aortic (PA) lymph nodes for gynecologic cancers. We reviewed our experiences and rates of duodenal toxicity in patients treated with extended field IMRT. Methods and materialsPatients with either cervical or endometrial cancer who were treated with IMRT to the PA nodes for involved lymph nodes or for prophylactic intent between 2005 and 2013 were included. For prophylactic intent, the radiation dose to the PA nodes was 45 Gy in 25 fractions. For involved lymph nodes, a boost was delivered to the gross disease with a 0.7-cm expansion, with editing for critical structures. The entire duodenum was retrospectively contoured on all patients from the gastric outlet to the jejunal transition. ResultsWe identified 76 eligible patients with endometrial and cervical cancer. The PA region was treated prophylactically in 46.1% (n = 35) and for involved PA lymph nodes in 53.9% (n = 41). The duodenum was contoured on all patients with a median volume of 83.2 cm3 (range, 21.2-174.9 cm3). The mean volume of duodenum receiving 55 Gy (V55) for those treated prophylactically and for involved PA nodes was 0 cm3 and 0.8 cm3 (range, 0-10.6 cm3), respectively (P = .014). Specifically, no patient had a V55 >15 cm3. The mean V40 was 28.3 cm3 (range, 0-77.3 cm3) and 41.4 (range, 0-90.0 cm3), respectively (P = .016). The mean dose delivered to 2 cm3 of the duodenum was 34.9 Gy (range, 0-52.3 Gy) and 50.1 Gy (range, 31.3 - 58.3 Gy), respectively. Grade 3 acute gastrointestinal toxicity was recorded in 3.9% (n = 3) of patients. ConclusionsIn our experience, the treatment of PA lymph nodes using an IMRT technique is associated with a low duodenal toxicity profile and there has been no high-grade late duodenal toxicity.

Dose calibration of EPIDs for segmented IMRT dosimetry.

The purpose of this study was to investigate the dose response of amorphous silicon (a‐Si) electronic portal imaging devices (EPIDs) under different acquisition settings for both open jaw defined fields and segmented intensity‐modulated radiation therapy (IMRT) fields. Four different EPIDs were used. Two Siemens and one Elekta plus a standalone Perkin Elmer research EPID. Each was operated with different acquisition systems and settings. Dose response linearity was measured for open static jaw defined fields and ‘simple’ segmented IMRT fields for a range of equipment and system settings. Six ‘simple’ segmented IMRT fields were used. The segments of each IMRT field were fixed at 10×10cm2 field size with equal MU per segment, each field having a total of 20 MU. Simultaneous measurements with an ionization chamber array (ICA) and EPID were performed to separate beam and detector response characteristics. Three different pixel calibration methods were demonstrated and compared for an example ‘clinical IMRT field’. The dose response with the Elekta EPID for ‘simple’ segmented IMRT fields versus static fields agreed to within 2.5% for monitor unit (MU)≥2. The dose response for the Siemens systems was difficult to interpret due to the poor reproducibility for segmented delivery, at MU≤5, which was not observed with the standalone research EPID nor ICA on the same machine. The dose response measured under different acquisition settings and different linac/EPID combinations matched closely (≤1%), except for the Siemens EPID. Clinical IMRT EPID dosimetry implemented with the different pixel‐to‐dose calibration methods indicated that calibration at 20 MU provides equivalent results to implementing a ghosting correction model. The nonlinear dose response was consistent across both clinical EPIDs and the standalone research EPID, with the exception of the poor reproducibility seen with Siemens EPID images of IMRT fields. The nonlinear dose response was relatively insensitive to acquisition settings and appears to be primarily due to gain ghosting effects. No additional ghosting correction factor is necessary when the pixel‐to‐dose calibration factor at small MU calibration method is used.PACS numbers: 87.53.Bn, 87.55.Qr, 87.56.Fc, 87.57.uq

Radiotherapy for unresectable sinonasal cancers: Dosimetric comparison of intensity modulated radiation therapy with coplanar and non-coplanar volumetric modulated arc therapy

Background and purposeTo compare volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) plans for treatment of unresectable paranasal sinuses cancers (PNSCs) with different clinical presentations. Material and methodsFour patients treated for primary target volume only (group 1), four requiring elective nodal irradiation (group 2) and four with positive nodes in macroscopic disease (group 3) were selected. For each patient were generated 7 fields IMRT, coplanar VMAT (c-VMAT) and non-coplanar VMAT (nc-VMAT) treatment plans. Total doses were 70Gy and 54Gy to high dose planning target volume (HD-PTV) and low-dose-PTV, respectively. Dose–volume histogram, conformity and homogeneity index (CI and HI), and monitor units (MUs) per Gy were evaluated. ResultsVMAT provided significantly better target coverage, in terms of V100% (Volume encompassed by the isodose 100%), than IMRT, in particular when nc-VMAT was used. In general, organ at risk sparing is similar with the three approaches, although nc-VMAT can allow a statistically significant reduction of dose to contralateral parotid gland and cochlea for all three groups. ConclusionsVMAT can offer significant improvement of treatment for all unresectable PNSCs over existing IMRT techniques. In particular, nc-VMAT may be a further advantage for those patients with sinonasal cancers and involvement of the nodes in whom large volumes and complex/irregular shape have to be irradiated, even if clinical benefits should be established in the future.

A Novel Integrated VMAT/IMRT Technique for the Treatment of Non-Small Cell Lung Cancer: Novel Therapies/Experimental Therapies

To investigate a novel Integrated VMAT/IMRT technique which combines volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) for non-small cell lung cancer (NSCLC). Two partial arcs VMAT, 5-field IMRT and Integrated VMAT/IMRT plans were created for 17 patients with NSCLC. The Integrated VMAT/IMRT technique consisted of 2 partial VMAT arcs and 5 IMRT fields. The dose distribution of planning target volume (PTV) and organs at risk (OARs) for Integrated VMAT/IMRT was compared with IMRT and VMAT. The monitor units (MUs) and treatment delivery time were also evaluated. For each plan, a dry run was performed to assess the dosimetric accuracy. Integrated VMAT/IMRT significantly improved the target conformity and homogeneity. The V30 of normal lung for Integrated plans was significantly lower than IMRT plans (8.4% vs 9.2%; P<.05). The V5 and mean lung dose (MLD) of normal lung for Integrated plans were 9.8% and 4.6% lower than VMAT plans (P<.05). The maximum dose of spinal cord for Integrated plans was 4.9 Gy lower than IMRT plans (P<.05). The mean delivery time of IMRT, VMAT and Integrated plans was 280 s, 114 s, and 327 s, respectively. The mean MUs needed for IMRT, VMAT, and Integrated plans were 933, 512, and 737, respectively. The gamma pass rates were beyond 90% at the 3%/3 mm criteria when the gantry angles were set to 0° for pretreatment verification. Integrated VMAT/IMRT technique significantly reduced V5, V10, and MLD of normal lung compared with VMAT, and the irradiated volume of the OARs receiving medium to high dose with fewer MUs compared with IMRT. Integrated VMAT/IMRT technique can be a feasible radiation therapy technique with better plan quality and accurately delivered on the linear accelerator.Thoracic Abstract 217; TableDosimetric comparison of PTV and OARs for IMRT, VMAT, and Integrated VMAT/IMRT plansIMRTmean±SDVMATmean±SDIntegratedmean±SDIMRT vs VMATP valueIMRTvs IntegratedP valueVMATvs IntegratedP valuePTV CN0.7±0.10.8±0.10.9±0.1<.05<.05<.05 HI (%)16.1±3.613.9±3.49.9±1.4<.05<.05<.05Normal lung V30 (%)9.2±4.28.9±4.98.4±4.4>.05<.05>.05 V10 (%)21.5±10.324.9±12.323.5±11.8<.05<.05<.05 V5 (%)34.1±15.842.9±19.138.7±18.1<.05<.05<.05 Mean (Gy)8.1±3.38.7±3.78.3±3.5<.05<.05<.05Spinal cord Dmax (Gy)36.4±13.430.6±10.431.5±10.4<.05<.05>.05Esophagus Dmax (Gy)51.2±16.151.8±14.950.6±13.9>.05>.05<.05 Mean (Gy)14.0±10.315.2±9.814.6±9.8<.05>.05<.05 Open table in a new tab

VMAT planning study in rectal cancer patients.

BackgroundTo compare the dosimetric differences among fixed field intensity-modulated radiation therapy (IMRT), single-arc volumetric-modulated arc therapy (SA-VMAT) and double-arc volumetric-modulated arc therapy (DA-VMAT) plans in rectal cancer.MethodFifteen patients with rectal cancer previously treated with IMRT in our institution were selected for this study. For each patient, three plans were generated with the planning CT scan: one using a fixed beam IMRT, and two plans using the VMAT technique: SA-VMAT and DA-VMAT. Dose prescription to the PTV was 50 Gy in 2 Gy per fraction. Dose volume histograms (DVH) for the target volume and the organs at risk (small bowel, bladder, femoral heads and healthy tissue) were compared for these different techniques. Monitor units (MU) and delivery treatment time were also reported.ResultsDA-VMAT achieved the highest minimum planning target volume (PTV) dose and the lowest maximal dose, resulting in the most homogeneous PTV dose distribution. DA-VMAT also yielded the best CI, although the difference was not statistically significant. Between SA-VMAT and IMRT, the target dose coverage was largely comparable; however, SA-VMAT was able to achieve a better V95 and V107. VMAT showed to be inferior to IMRT in terms of organ at risk sparing, especially for the small bowel. Compared with IMRT, DA-VMAT increased the V15 of small bowel nearly 55 cc. The MU and treatment delivery time were significantly reduced by the use of VMAT techniques.ConclusionVMAT is a new radiation technique that combines the ability to achieve highly conformal dose distributions with highly efficient treatment delivery. Considering the inferior role of normal tissue sparing, especially for small bowel, VMAT need further investigation in rectal cancer treatment.

Dosimetric Evaluation of Different Intensity-Modulated Radiotherapy Techniques for Breast Cancer After Conservative Surgery.

Intensity-modulated radiotherapy (IMRT) potentially leads to a more favorite dose distribution compared to 3-dimensional or conventional tangential radiotherapy (RT) for breast cancer after conservative surgery or mastectomy. The aim of this study was to compare dosimetric parameters of the planning target volume (PTV) and organs at risk (OARs) among helical tomotherapy (HT), inverse-planned IMRT (IP-IMRT), and forward-planned field in field (FP-FIF) IMRT techniques after breast-conserving surgery. Computed tomography scans from 20 patients (12 left sided and 8 right sided) previously treated with T1N0 carcinoma were selected for this dosimetric planning study. We designed HT, IP-IMRT, and FP-FIF plans for each patient. Plans were compared according to dose-volume histogram analysis in terms of PTV homogeneity and conformity indices (HI and CI) as well as OARs dose and volume parameters. Both HI and CI of the PTV showed statistically significant difference among IP-IMRT, FP-FIF, and HT with those of HT were best (P < .05). Compared to FP-FIF, IP-IMRT showed smaller exposed volumes of ipsilateral lung, heart, contralateral lung, and breast, while HT indicated smaller exposed volumes of ipsilateral lung but larger exposed volumes of contralateral lung and breast as well as heart. In addition, HT demonstrated an increase in exposed volume of ipsilateral lung (except for fraction of lung volume receiving >30 Gy and 20 Gy), heart, contralateral lung, and breast compared with IP-IMRT. For breast cancer radiotherapy (RT) after conservative surgery, HT provides better dose homogeneity and conformity of PTV compared to IP-IMRT and FP-FIF techniques, especially for patients with supraclavicular lymph nodes involved. Meanwhile, HT decreases the OAR volumes receiving higher doses with an increase in the volumes receiving low doses, which is known to lead to an increased rate of radiation-induced secondary malignancies. Hence, composite factors including dosimetric advantage, clinical effect, and economic burden should be taken into comprehensive consideration when choosing an RT technique in clinical practice.

Extended Field Intensity Modulated Radiation Therapy With Concomitant Boost for Lymph Node–Positive Cervical Cancer: Analysis of Regional Control and Recurrence Patterns in the Positron Emission Tomography/Computed Tomography Era

Positron emission tomography/computed tomography (PET/CT) is commonly used for nodal staging in locally advanced cervical cancer; however the false negative rate for para-aortic disease are 20% to 25% in PET-positive pelvic nodal disease. Unless surgically staged, pelvis-only treatment may undertreat para-aortic disease. We have treated patients with PET-positive nodes with extended field intensity modulated radiation therapy (IMRT) to address the para-aortic region prophylactically with concomitant boost to involved nodes. The purpose of this study was to assess regional control rates and recurrence patterns. Sixty-one patients with cervical cancer (stage IBI-IVA) diagnosed from 2003 to 2012 with PET-avid pelvic nodes treated with extended field IMRT (45 Gy in 25 fractions with concomitant boost to involved nodes to a median of 55 Gy in 25 fractions) with concurrent cisplatin and brachytherapy were retrospectively analyzed. The nodal location was pelvis-only in 41 patients (67%) and pelvis + para-aortic in 20 patients (33%). There were a total of 179 nodes, with a median number of positive nodes of 2 (range, 1-16 nodes) per patient and a median nodal size of 1.8 cm (range, 0.7-4.5 cm). Response was assessed by PET/CT at 12 to 16 weeks. Complete clinical and imaging response at the first follow-up visit was seen in 77% of patients. At a mean follow-up time of 29 months (range, 3-116 months), 8 patients experienced recurrence. The sites of persistent/recurrent disease were as follows: cervix 10 (16.3%), regional nodes 3 (4.9%), and distant 14 (23%). The rate of para-aortic failure in patients with pelvic-only nodes was 2.5%. There were no significant differences in recurrence patterns by the number/location of nodes, largest node size, or maximum node standardized uptake value. The rate of late grade 3+ adverse events was 4%. Extended field IMRT was well tolerated and resulted in low regional recurrence in node-positive cervical cancer. The dose of 55 Gy in 25 fractions was effective in eradicating disease in involved nodes, with acceptable late adverse events. Distant metastasis is the predominant mode of failure, and the OUTBACK trial may challenge the presented paradigms.

Development of an expanded-field irradiation technique using a gimbaled x-ray head.

The Vero4DRT has a maximum field size of 150.0 × 150.0 mm. The purpose of the present study was to develop expanded-field irradiation techniques using the unique gimbaled x-ray head of the Vero4DRT and to evaluate the dosimetric characteristics thereof. Two techniques were developed. One features gimbal swing irradiation and multiple static segments consisting of four separate fields exhibiting 2.39° gimbal rotation around two orthogonal axes. The central beam axis for each piecewise-field is shifted 40 mm from the isocenters of the left-right (LR) and superior-inferior (SI) directions, and, thus, the irradiation field size is expanded to 230.8 × 230.8 mm. Adjacent regions were created at the isocenter (a center-adjacent expandedfield) and 20 mm from the isocenter (an off-adjacent expandedfield). The field gaps or overlaps of combined piecewise-fields were established by adjustment of gimbal rotation and movement of the multileaf collimator (MLC). Another technique features dynamic segment irradiation in which the beam is delivered while rotating the gimbal. The dose profile is controlled by a combination of gimbal swing motion and opening and closing of the MLC. This enabled the authors to expand the irradiation field on the LR axis because the direction of MLC motion is parallel to that axis. A field 220.6 × 150.0 mm in dimensions was configured and examined. To evaluate the dosimetric characteristics of the expandedfields, films inserted into water-equivalent phantoms at depths of 50, 100, and 150 mm were irradiated and field sizes, penumbrae, flatness, and symmetry analyzed. In addition, the expanded-field irradiation techniques were applied to intensity-modulated radiation therapy (IMRT). A head-and-neck IMRT field, created using a conventional Linac (the Varian Clinac iX), was reproduced employing an expanded-field of the Vero4DRT. The simulated dose distribution for the expanded-IMRT field was compared to the measured dose distribution. The field sizes, penumbrae, flatness, and symmetry of the center- and off-adjacent expanded-fields were 230.2-232.1 mm, 6.8-10.7 mm, 2.3%-5.1%, and -0.5% to -0.4%, respectively, at a depth of 100 mm. Similarly, the field sizes, penumbrae, flatness, and symmetry of dynamic segment irradiation on the LR axis were 219.2 mm, 6.0-6.2 mm, 3.4%, and -0.1%, respectively, at a depth of 100 mm. In the area of expanded-IMRT dose distribution, the passing rate of 5% dose difference was 85.8% between measurements and simulation, and the 3%/3 mm gamma passing rate was 96.4%. Expanded-field irradiation techniques were developed using a gimbaled x-ray head. The techniques effectively extend target areas, as required when whole-breast irradiation or head-and-neck IMRT is contemplated.

Changes in Kidney Position and Dose Due to Respiratory Motion in Gynecologic Patients Receiving Extended Field Intensity Modulated Radiation Therapy

Optimization of extended field radiation therapy is usually based on organs contoured on a static scan. This work aims (i) to evaluate kidney motion due to patient breathing in patients without chest compression; and (ii) to evaluate kidney dosimetric variability associated with breathing motion for optimizations based only on free-breathing (FB) scans and for optimizations based on the maximum intensity projection (MIP) of 4DCT scans.