Intensity Modulated Radiation Therapy Fields Research Articles

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

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

A feasibility study of using advanced external beam techniques to create a vaginal cuff brachytherapy-like endometrial boost plan

The purpose of this study was to explore the feasibility of using advanced external beam radiation therapy (EBRT) planning techniques for creating plans that could be used as a possible alternative for high-dose rate (HDR) vaginal cuff brachytherapy (VCBT) boost in treating endometrial cancer. The computed tomography (CT) images of a total of 4 female patients who had endometrial cancer treated with HDR-VCBT were selected for this study. A typical HDR-VCBT target volume, 0.5-cm-thick shell volume around the cylinder applicator in the prescribed treatment length was contoured and used as the planning target volume (PTV) in both the HDR VCBT and the EBRT VCBT-like plans. HDR-VCBT plans were made based on the clinical protocol, 6 Gy given at the cylinder surface. The EBRT plans were generated using either a 7-field intensity-modulated radiation therapy (IMRT) or a 2-arc volumetric-modulated arc therapy (VMAT) techniques for different cylinder sizes and treatment lengths, with the prescription dose of 5 Gy. Organs at risk (OARs) such as bladder, femoral heads, rectum, and sigmoid were also contoured and used in dosimetric evaluations. Dose-to-target metrics included mean dose, the dose covering 90% of target volume (D90) and the percentage of target volume covered by 90% of prescription dose (V90 or V13.5 Gy). Dose to OAR metrics included the maximum dose received by 0.1 cc (D0.1cc), 1.0 cc (D1.0cc), and 2.0 cc (D2.0cc) of OARs. These metrics were calculated and compared between all techniques. After the EBRT plans were normalized to achieve a comparable mean dose to target as HDR-VCBT, the EBRT plans were found to have superior target coverage and increased dose homogeneity compared with HDR-VCBT. V90s of EBRT plans were 95%, compared with 50% to 58% of the HDR plans. However, D0.1cc, D1.0cc, and D2.0cc of OARs were 2% to 38% lower in HDR-VCBT than in EBRT. Although HDR-VCBT plans demonstrated superior normal tissue sparing, both EBRT and HDR-VCBT plans produce plans that met clinical dose constraints on normal tissues. Advanced EBRT techniques such as IMRT and VMAT are capable of making plans, which closely resemble HDR-VCBT. Although the doses of OARs are greater in EBRT than in HDR-VCBT, the prescription dose coverage and dose homogeneity of the EBRT plans are greater than that of HDR-VCBT plans at the similar mean dose, and the OAR dose is still acceptable with EBRT plans. The detailed dosimetric approaches are provided in the study.

Which simultaneous-integrated boost (SIB) intensity-modulated radiotherapy (IMRT) technique is dosimetrically superior in the treatment of breast cancer; volumetric-modulated arc therapy (VMAT) or fixed field (ff) IMRT?

AbstractBackground and purposeTo determine which concomitant boost technique is dosimetrically superior in the treatment of breast cancer; volumetric-modulated arc therapy (VMAT) or fixed field intensity-modulated radiotherapy (ff-IMRT).Materials and methodsIn total, 30 breast patients were re-planned with both VMAT and fixed field concomitant boost intensity-modulated radiotherapy techniques. A hybrid technique was used delivering 80% of the dose through tangential beams and 20% through an integrated boost. A two-tailed t-test sample for means was used to compare the dosimetric differences between the techniques.ResultsMaximum dose was statistically lower for VMAT; 103·2 versus 103·7% for ff-IMRT along with statistically lower V2 Gy doses to the contralateral lung (0·7 versus 1·6%) and heart for both left- (19·0%/22·6%), and right- (5·5%/8·8%) sided patients, respectively. ff-IMRT boasted significantly lower ipsilateral lung V20, V18 and V10 Gy (7·9/8·6/13·1 versus 8·1/8·8/13·4%) than VMAT, respectively. No differences were found with minimum coverage, mean dose and V5 Gy to all organs at risk (OARs).ConclusionVMAT and ff-IMRT techniques demonstrate excellent target coverage and OAR sparing facilitated by the hybrid planning technique and deep inspiration breath hold. There is no obvious dosimetrically superior option between the two techniques. Reduced treatment times with VMAT make it more desirable to implement clinically.

Comparative study on dosimetry of VMAT and IMRT in assisted radiotherapy after radical resection of rectal cancer.

The present study compared the dosimetric differences of volumetric modulated arc therapy (VMAT) and 7-field intensity modulated radiation therapy technology (7F-IMRT) in assisted radiotherapy plan after resection of rectal carcinoma. Ten cases of patients at stages II–III of rectal cancer transabdominal resection with postoperative pelvic radiotherapy underwent 7F-IMRT and VMAT radiotherapy plan design using the CMS Monaco treatment planning system. We compared the dose distribution, the number of organs at risk and the number of machines in the two groups. The 7F-IMRT plans conformal index (CI) was 0.8319±0.0143 and VMAT plans CI was 0.838±0.164. Both plans reached up to the 95% isodose line at a volume of 100% planning target volume (PTV), the 7F- IMRT plans homogeneity index (HI) was 1.0760±0.0179, and the VMAT plans HI was 1.0821±0.0143. CI and HI had no statistical difference. With regard to S40, the V50 dose volume of the small intestine was endangered, and the VMAT plan was better than that of the 7F-IMRT plan, and the difference was statistically significant (P<0.05). The machine hop numbers of the two types of plans were 594.1±36.1 and 793.2 ±56.6 for for VMAT and 7F-IMRT, respectively. The VMAT plan was less than htat of the 7F-IMRT and the difference was statistically significant (P<0.05). Patients to whom VMAT techniques were utilized after resection of rectal cancer obtained an equal or a superior dose distribution compared with the IMRT plan. VMAT had important significance in protecting the small intestine, while significantly reducing treatment time.

Safety and efficacy of semiextended field intensity-modulated radiation therapy and concurrent cisplatin in locally advanced cervical cancer patients: An observational study of 10-year experience.

Patients with locally advanced cervical cancer (LACC) are at risk of para-aortic lymph node (PALN) metastasis. Pelvic concurrent chemoradiotherapy, the current standard treatment for LACC, has a PALN failure rate of 9% according to the Radiation Therapy Oncology Group Trial 90–01, suggesting that it may not completely eliminate all microscopic tumors in the PALNs. To minimize the toxicities associated with conventional prophylactic extended-field radiotherapy, our institute use prophylactic semiextended field radiotherapy that includes only the PALNs below the level of the renal vessels. Use of intensity-modulated radiotherapy (IMRT) is another means of reducing the incidence of toxicity. This study evaluated the safety and efficacy of prophylactic semiextended field IMRT (SEF-IMRT) and concurrent cisplatin chemotherapy in patients with LACC.We retrospectively assessed survival and toxicity in 76 patients with stage IB2–IVA cervical cancer and negative PALNs who received prophylactic SEF-IMRT and concurrent weekly cisplatin (40 mg/m2) between 2004 and 2013. The region targeted by SEF-IMRT included the PALNs below the level of the renal vessels, and the prescribed dose was 50.4 Gy in 28 fractions. Brachytherapy was administered at a dose of 30 Gy in 6 fractions. Survival outcomes were calculated by using the Kaplan–Meier method, and acute and late toxicities were scored according to the Common Terminology Criteria for Adverse Events, version 3.0.All patients completed the planned SEF-IMRT, as well as brachytherapy. Acute grade ≥3 gastrointestinal, genitourinary, and hematologic toxicities were observed in 2, 0, and 41 patients, respectively. The median follow-up time after SEF-IMRT was 55 (range, 11–124) months. Eight patients developed out-field distant recurrences without PALN failure, and 1 patient experienced out-field PALN failure with simultaneous distant metastasis. No patients had late genitourinary toxicities, and 3 patients had late grade 3 gastrointestinal toxicities. The 5-year overall survival, disease-free survival, local failure-free survival, regional failure-free survival, PALN failure-free survival, and distant metastasis-free survival rates were 85.0%, 84.4%, 96.0%, 97.3%, 98.6%, and 88.4%, respectively.For patients with LACC, prophylactic PALN irradiation up to the level of the renal vessels reduced PALN recurrence and resulted in favorable outcomes with few severe toxicities.

Verification of Dosimetric Commissioning Accuracy of Intensity Modulated Radiation Therapy and Volumetric Modulated Arc Therapy Delivery using Task Group-119 Guidelines.

Aim:The purpose of this study is to verify the accuracy of the commissioning of intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) based on the recommendation of the American Association of Physicists in Medicine Task Group 119 (TG-119).Materials and Methods:TG-119 proposes a set of clinical test cases to verify the accuracy of IMRT planning and delivery system. For these test cases, we generated two sets of treatment plans, the first plan using 7–9 IMRT fields and a second plan utilizing two-arc VMAT technique for both 6 MV and 15 MV photon beams. The template plans of TG-119 were optimized and calculated by Varian Eclipse Treatment Planning System (version 13.5). Dose prescription and planning objectives were set according to the TG-119 goals. The point dose (mean dose to the contoured chamber volume) at the specified positions/locations was measured using compact (CC-13) ion chamber. The composite planar dose was measured with IMatriXX Evaluation 2D array with OmniPro IMRT Software (version 1.7b). The per-field relative gamma was measured using electronic portal imaging device in a way similar to the routine pretreatment patient-specific quality assurance.Results:Our planning results are compared with the TG-119 data. Point dose and fluence comparison data where within the acceptable confident limit.Conclusion:From the obtained data in this study, we conclude that the commissioning of IMRT and VMAT delivery were found within the limits of TG-119.

Quick, efficient and effective patient-specific intensity-modulated radiation therapy quality assurance using log file and electronic portal imaging device.

The aim of work is to explore a quick, efficient, and effective patient-specific intensity-modulated radiation therapy (IMRT) quality assurance (QA). Software tools were developed to extract and analyze the multi-leaf collimator (MLC) leaf positions (LPs) from electronic portal imaging device (EPID) images for Varian C-series machine and TrueBeam, to extract useful data from MLC log file of C-series linear accelerator (LINAC), to extract useful information from the trajectory log binary file of TrueBeam LINAC, to compare LPs derived from EPID images with log file/trajectory log data, and to analyze IMRT treatment files using the MATLAB programming language. The difference in LP determined from the trajectory log and EPID images was proposed for patient-specific QA. It was found that the differences in LP for regular radiation fields generated using stationary leaves are <0.5 mm for all the field sizes while for regular radiation fields generated using the moving leaves are more but <2 mm. The differences in LPs for IMRT field were also determined and found to be <2 mm. The methodology demonstrated can be used for establishing the accuracy of trajectory log data and for independent routine IMRT QA by generating single number like gamma index to indicate pass or fail of an IMRT treatment plan. The QA indices such as numbers of occurrences of ≥2 mm error in LPS are found more than 5% of total number of occurrences; the dosimetric review of planned treatment is advisable.

Dosimetric Comparison of Static Field Intensity-Modulated Radiotherapy and Volumetric Modulated Arc Therapy for Adjuvant Treatment of Patients with Endometrial Cancer

Dosimetric Comparison of Static Field Intensity-Modulated Radiotherapy and Volumetric Modulated Arc Therapy for Adjuvant Treatment of Patients with Endometrial Cancer

Dosimetric analysis of 3D-conformal radiotherapy and intensity modulated radiotherapy for treatment of advanced stage cervical cancer: A comparative study

Purpose: The purpose of this study is to analyze the dosimetric parameters of three dimensional conformal radiotherapy (3DCRT), intensity modulated radiotherapy (IMRT) with seven and nine fields (7F-IMRT, 9F-IMRT) in selected advanced stage cervical cancer cases. Methods: Fifteen cases of cervical cancer (IIB to IIIB) were selected for retrospective analysis. All the cases were previously treated with 3DCRT technique with prescribed dose of 50 Gy in 25 fractions. For this study, plans with seven fields IMRT and nine fields IMRT were generated for all patients following Radiation Therapy Oncology Group (RTOG) guidelines. The plans were compared on the basis of planning target volume (PTV) coverage (dose to 1%, 5%, 95% and 99% of target), maximum dose and mean dose to organs at risk (OARs) and also doses at different volumes of OARs. Apart from this, uniformity index (UI), homogeneity index (HI), conformity index (CI) and dose spillage index (R50%) were also calculated with respect to PTV coverage. Results: The average dose value of PTV coverage for all three techniques were comparable and all the DVH indices for 7field IMRT (UI (1.04±0.01), HI (0.07 ±0.02), CI (0.75±0.03) and R50% (4.47±0.36)) were better than 3DCRT and 9F-IMRT techniques. All OAR doses were significantly reduced in 7F- IMRT compared to 3DCRT and 9F- IMRT. The target volumes ranged from 769.2 ml to 1375.6 ml with average target volume of 1071.9 ml (SD: 205.38 ml). Conclusion: This study showed that significant dose reduction to OARs could be achieved with seven field IMRT plans by maintaining the PTV coverage compared to 3DCRT or 9F- IMRT for treating cervical cancer in advanced stages particularly from IIB to IIIB.

Can a commercially available EPID dosimetry system detect small daily patient setup errors for cranial IMRT/SRS?

PurposeThe purpose of this study was to determine if the Sun Nuclear PerFRACTION electronic portal imager device dosimetry software would be able to detect setup errors in a clinical setting and would be able to correctly identify the direction in which the setup error was introduced. Methods and materialsA 7-field intensity modulated radiation therapy (IMRT) treatment plan for a centrally located tumor was developed for 1 phantom and 5 canine cadaver heads. Systematic setup errors were introduced by manually moving the treatment couch by 1, 3, and 5 mm in each translational direction to assess stereotactic radiation surgery (SRS), IMRT, and 3-dimensional (3D) treatment tolerances after the initial alignment was performed. An angular setup error of 5° yaw was also assessed. The delivered treatment fluence was automatically imported in the PerFRACTION software and compared with the baseline fluence. ResultsIn the canine phantom, a 5-mm shift was undetected by gamma analysis, and up to a 2-cm shift had to be introduced for the gamma pass rate of 3%/3 mm to fall below a 95% pass rate criterion. The same 5-mm shift using 3% difference caused the pass rates for 2 fields to drop below the 95% tolerance. For each respective translational shift, the affected beam angles were consistent across the cadaver heads and correlated with the direction of translational shift. The best field pass rate, worst field pass rate, and average pass rate across all 7 fields was analyzed to develop clinical guidance on parameter settings for SRS, IMRT, and 3D tolerances. ConclusionsPerFRACTION 2-dimensional mode successfully detected setup errors outside the systematic error tolerance for SRS, IMRT, and 3D when an appropriate analysis metric and pass/fail criteria was implemented. Our data confirm that percent difference may be more sensitive in detecting plan failure than gamma analysis.

Relationship between acute radiation pneumonitis and dosimetric factors in intensity-modulated radiotherapy for lung caner: a study based on different lesion locations

Objective To explore the dosimetric factors for acute radiation pneumonitis (ARP) after restricted field intensity-modulated radiotherapy (IMRT) for lung caner based on different lesion locations. Methods A retrospective study of ARP was performed among 113 patients with lung cancer undergoing restricted field IMRT from 2013 to 2015. The Radiation Therapy Oncology Group criteria were used to grade ARP. Comparison was made by χ2 test and independent sample t-test. The logistic regression model was used for multivariate analysis. The receiver operating characteristic curve was used to predict the optimal cut-off value. Results The statistical analysis showed that the incidence of ARP was not related to clinical factors. The V5 of the diseased lung was an independent predictor of the incidence of grade>2 ARP (P=0.016). The optimal cut-off value of V5 was 71.6%. According to the lesion locations in patients, the rV5 was an independent predictor of the incidence rates of ARP in the right lung, upper right lung, and right middle/lower lung (P=0.020, 0.020, 0.049) with optimal cut-off values of 66.2%, 74.7%, and 87.5%, respectively. The aV5 was an independent predictor of the incidence of ARP in mediastinal lung cancer (P=0.009) with an optimal cut-off value of 66.73%. Conclusions The V5 of the diseased lung is an independent predictor of the incidence of grade>2 ARP. In terms of the different lesion locations, the rV5 is an independent predictor of the incidence rates of grade>2 ARP in the right lung, upper right lung, and right middle/lower lung. The aV5 is an independent predictor of the incidence of ARP in mediastinal lung cancer. Key words: Lung neoplasms/intensity-moduliated radiotherapy; Different lesion location; Acute radiation pneumonitis; Dosimetry

Development of a gimbal-swing irradiation technique for uniform expanded-field, wedged-beam, and intensity-modulated radiation therapy

The purpose of this study was to develop a new irradiation technique for a uniform expanded irradiation field (uniform expanded-field), wedged-beam, and intensity-modulated radiation therapy (IMRT) using the gimbaled x-ray head swing (gimbal-swing) of Vero4DRT. The gimbal has two orthogonal axes which provides tilt and pan movements. The Vero4DRT has a maximum field size of 150 × 150 mm2. By swinging the gimbaled x-ray head ±35 mm at the isocenter level, the field size was expanded from 150 to 220 mm in the tilt motion. In order to obtain a uniform dose distribution, continuous irradiation was delivered through a parallelogram-shaped radiation field by the gimbal-swing. Dosimetric characteristics of the uniform expanded-field were evaluated using irradiated film. In order to obtain a wedge-beam, continuous irradiation was delivered through a triangular-shaped radiation field by the gimbal-swing. Three different wedge angles: 15°, 30°, and 45°, were measured on the irradiated film and compared with the theoretical wedge angles. Additionally, the gimbal-swing irradiation technique was applied to IMRT for three clinical cases. The absolute point dose and relative dose distributions were evaluated. In the uniform field, the field size, penumbra, flatness, and symmetry were 220.1 mm, 6.3–6.4 mm, 3.2%, and −0.4% for the tilt motion. The differences between measured and theoretical wedge angles were within 0.2°. The absolute dose difference of the gimbal-swing IMRT field between the measured dose with an ion chamber and the calculated dose was within 2.3% for three cases. The passing rate of 3%/3 mm gamma analysis was larger than 93.7%. A new technique for gimbal-swing irradiation was developed. To extend the clinical application of the Vero4DRT for targets with a size over 150 × 150 mm2, the uniform expanded-field, wedged-beam, and gimbal-swing IMRT would be effective.

Sparing of high retropharyngeal nodal basins in patients with unilateral oropharyngeal carcinoma treated with intensity modulated radiation therapy

PurposeThe introduction of intensity modulated radiotherapy (IMRT) has facilitated dose painting and sparing of uninvolved/low-risk nodal basins in head and neck cancers. In oropharynx cancer (OPC), the need for elective coverage of uninvolved high contralateral retropharyngeal (RP) nodes and the risk associated with sparing this region remain unclear. We examined outcomes of OPC patients treated with IMRT and omission of contralateral high RP coverage. Methods and materialsWe identified 102 OPC patients with cN0-N2b disease treated with definitive IMRT with or without concurrent chemotherapy between 2010 and 2013. The contralateral RP nodal basins superior to the vertebral level of C1 were omitted from the elective IMRT field for all patients. Of the 67 patients (66%) with p16 status available, 63 (94%) were p16+. We used the Kaplan-Meier method to estimate overall survival, as well as freedom from local failure, regional failure, distant failure, and retropharyngeal failure. ResultsThe median follow-up was 26.9 months (range, 3.0-59.9 months). There were no failures in the treated ipsilateral RP nodes or the spared contralateral high RP nodes in the entire cohort. In the p16+ cohort and the entire cohort, the 2-year rates of overall survival and freedom from local, regional, distant, and retropharyngeal failure were 98.0% and 95.1%, 98.1% and 97.7%, 96.4% and 96.7%, 98.1% and 95.1%, and 100% and 100%, respectively. ConclusionsOmission of contralateral high RP nodes in patients with p16+ OPC with unilateral disease is safe.

EPID-based dosimetry to verify IMRT planar dose distribution for the aS1200 EPID and FFF beams.

We proposed to perform a basic dosimetry commissioning on a new imager system, the Varian aS1200 electronic portal imaging device (EPID) and TrueBeam 2.0 linear accelerator for flattened (FF) and flattening filter‐free (FFF) beams, then to develop an image‐based quality assurance (QA) model for verification of the system delivery accuracy for intensity‐modulated radiation therapy (IMRT) treatments. For dosimetry testing, linearity of dose response with MU, imager lag, and effectiveness of backscatter shielding were investigated. Then, an image‐based model was developed to convert images to planar dose onto a virtual water phantom. The model parameters were identified using energy fluence of the Acuros treatment planning system (TPS) and, reference dose profiles and output factors measured at depths of 5, 10, 15, and 20 cm in water phantom for square fields. To validate the model, its calculated dose was compared to measured dose from MapCHECK 2 diode arrays for 36 IMRT fields at 10 cm depth delivered with 6X, 6XFFF, 10X, and 10XFFF energies. An in‐house gamma function was used to compare planar doses pixel‐by‐pixel. Finally, the method was applied to the same IMRT fields to verify their pretreatment delivery dose compared with Eclipse TPS dose. For the EPID commissioning, dose linearity was within 0.4% above 5 MU and ∼1% above 2 MU, measured lag was smaller than the previous EPIDs, and profile symmetry was improved. The model was validated with mean gamma pass rates (standard deviation) of 99.0% (0.4%), 99.5% (0.6%), 99.3% (0.4%), and 98.0% (0.8%) at 3%/3 mm for respectively 6X, 6XFFF, 10X, and 10XFFF beams. Using the same comparison criteria, the beam deliveries were verified with mean pass rates of 100% (0.0%), 99.6% (0.3%), 99.9% (0.1%), and 98.7% (1.4%). Improvements were observed in dosimetric response of the aS1200 imager compared to previous EPID models, and the model was successfully developed for the new system and delivery energies of 6 and 10 MV, FF, and FFF modes.PACS number(s): 87.53.Oq, 87.53.Xd

OPTIMUM TREATMENT MODE APPLIED TO POST-OPERATIVE CERVICAL CANCER FOR 5F-IMRT PLAN BASED ON FOUR VARIABLES IN VARIAN ECLIPSE TPS

Purpose: This study aimed to determine the dosimetric effect on the target volume, organs at risk (OARs) and normal tissues based on the different choice for four types of mechanical variables, i.e., treatment position, dose calculation algorithm, mulitleaf collimator (MLC) motion mode and X-ray energy; and to investigate the optimum treatment mode applied to post-operative cervical cancer for 5-field intensity-modulated radiation therapy (5F-IMRT) technique. Methods: The dosimetric difference on the target volume and OARs under the influence of four types of variables were initially compared by changing one variable at a time. Then, based on the above compared results, we compared the dosimetric difference on planning target volume (PTV) and OARs between group A composed of the superior four variables and group B composed of the relatively inferior four variables. The dosimetric parameters included dose distribution of the target volume, OARs and normal tissues, conformal index (CI), homogeneity index (HI), monitor units (MU) and beam-on time ([Formula: see text]. The independent and paired t-tests were used for statistical analysis, and the threshold for statistical significance was [Formula: see text]. Results: Compared with the supine position, the maximum dose of PTV ([Formula: see text]), the maximum dose of small intestine ([Formula: see text]) and [Formula: see text] of bladder ([Formula: see text] were all lower in prone position. In contrast with the pencil beam convolution (PBC), CI of PTV (CI[Formula: see text]) was larger while HI of PTV (HI[Formula: see text]) was lower, both [Formula: see text] and the maximum dose of rectum ([Formula: see text]) were lower using anisotropic analytical algorithm (AAA). Moreover, the same results were obtained using sliding window (SW) compared with multiple static segments (MSS). The mean dose of PTV ([Formula: see text] and CI[Formula: see text] was larger while the maximum dose of the spinal cord ([Formula: see text]), [Formula: see text] and the maximum dose of femoral heads were lower with 15 MV X-rays compared with 6 MV X-rays. In comparison with group B comprising the supine position, PBC, MSS and 6 MV X-rays, [Formula: see text] and HI[Formula: see text] decreased 1.4% and 53.4% respectively, CI[Formula: see text] increased 5.8% medially, while [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] all decreased in group A comprising of prone position, AAA, SW and 15 MV X-rays. Conclusion: The treatment mode composed of prone position, AAA algorithm, SW and 15 MV X-rays is chosen for the post-operative cervical cancer of 5F-IMRT technique, which is more capable of meeting the target volume constraints and maximal protection of OARs.

Image-guided radiotherapy for prostate cancer with cone beam CT: dosimetric effects of imaging frequency and PTV margin

Background and purposeThis study assesses the effect of frequency of cone beam CT (CBCT) verification imaging on dose–volume parameters during image-guided radiotherapy (IGRT) for prostate cancer. It also investigates the dosimetric impact of reducing the planning target volume (PTV) margin, when daily imaging is used. Material and methods844 CBCT images from 20 patients undergoing radical prostate radiotherapy were included. Patients received a dose of 74Gy in 37 fractions using 7-field intensity-modulated radiotherapy (IMRT). Clinical target volume (CTV) and organs at risk were contoured manually on each slice of every CBCT image. A daily online CBCT verification schedule was compared with a protocol of verification on days 1–3 followed by weekly online imaging. PTV margins of 3mm, 5mm, and 7mm were compared for the daily imaging protocol. Results90% of patients had improved target coverage with daily online in comparison to weekly online imaging. A median of 37 fractions per treatment course achieved CTV coverage with daily imaging compared to 34 fractions with a weekly online protocol. 80% of patients had a reduction in rectal dose with the daily protocol. PTV margin reduction to 5mm with adequate target coverage was feasible with daily imaging. ConclusionsDaily online CBCT verification improves CTV coverage and reduces rectal dose during IGRT for prostate cancer. Tighter PTV margins could be considered with daily CBCT use.

The impact of positron emission tomography on primary tumour delineation and dosimetric outcome in intensity modulated radiotherapy of early T-stage nasopharyngeal carcinoma.

BackgroundIn intensity modulated radiotherapy (IMRT) of nasopharyngeal carcinoma (NPC), accurate delineation of the gross tumour volume (GTV) is important. Image registration of CT and MRI has been routinely used in treatment planning. With recent development of positron emission tomography (PET), the aims of this study were to evaluate the impact of PET on GTV delineation and dosimetric outcome in IMRT of early stage NPC patients.MethodsTwenty NPC patients with T1 or T2 disease treated by IMRT were recruited. For each patient, 2 sets of NP GTVs were delineated separately, in which one set was performed using CT and MRI registration only (GTVCM), while the other set was carried out using PET, CT and MRI information (GTVCMP). A 9-field IMRT plan was computed based on the target volumes generated from CT and MRI (PTVCM). To assess the geometric difference between the GTVCM and GTVCMP, GTV volumes and DICE similarity coefficient (DSC), which measured the geometrical similarity between the two GTVs, were recorded. To evaluate the dosimetric impact, the Dmax, Dmin, Dmean and D95 of PTVs were obtained from their dose volume histograms generated by the treatment planning system.ResultsThe overall mean volume of GTVCMP was greater than GTVCM by 4.4 %, in which GTVCMP was slightly greater in the T1 group but lower in the T2 group. The mean DSC of the whole group was 0.79 ± 0.05. Similar mean DSC values were also obtained from the T1 and T2 groups separately. The dosimetric parameters of PTVCM fulfilled the planning requirements. When applying this plan to the PTVCMP, the average Dmin (56.9 Gy) and D95 (68.6 Gy) of PTVCMP failed to meet the dose requirements and demonstrated significant differences from the PTVCM (p = 0.001 and 0.016 respectively), whereas the doses to GTVCMP did not show significant difference with the GTVCM.ConclusionIn IMRT of early stage NPC, PET was an important imaging modality in radiotherapy planning so as to avoid underdosing the PTV, although its effect on GTV delineation was not significant. It was recommended that PET images should be included in the treatment planning of NPC patients.

Acceptance testing of photon beam model in Axesse accelerator in two intensity-modulated treatment planning systems

Objective To investigate the acceptance testing the photon beam model in Axesse accelerator in Monaco Oncentra treatment planning systems (TPS), in order to establish an integral method for the acceptance both systems at the same time. Methods The conflicting parameters the two TPSs were determined before acceptance, the corresponding parameters in the accelerator were adjusted to the overlapping values. The acceptance test was performed from the aspects point dose, surface dose, characteristic simulation multi-leaf collimator (MLC). The test case for point dose was designed based on TRS430, TG53, practical situations. The test case for surface dose included conventional radiation field intensity-modulated radiotherapy (IMRT) cases. The test the characteristics MLC included concave-convex groove, leakage, values of and Gain . Results The error most point doses were within 4%, only some measuring points in the penumbra region outside the radiation field had an error of>4%. The γ pass rate the surface dose tests IMRT cases was>90% at a value 3 mm/3% except three test cases. Oncentra could only simulate the situation with a positive offset value MLC, but Monaco could simulate the situation with both positive negative offset values MLC. Conclusions The results show that this method can accurately validate all the parameters the two systems realize the accurate acceptance Monaco Oncentra systems with Axesse accelerator. Both Monaco Oncentra models can meet the needs for clinical calculation. Key words: Threatment planning system commission; Multi-leaf collimator test; Dose verification; Error analysis

SU‐D‐204‐03: Comparison of Patient Positioning Methods Through Modeling of Acute Rectal Toxicity in Intensity Modulated Radiation Therapy for Prostate Cancer. Does Quality of Data Matter More Than the Quantity?

Purpose:To determine if differences in patient positioning methods have an impact on the incidence and modeling of grade &gt;=2 acute rectal toxicity in prostate cancer patients who were treated with Intensity Modulated Radiation Therapy (IMRT).Methods:We compared two databases of patients treated with radiation therapy for prostate cancer: a database of 79 patients who were treated with 7 field IMRT and daily image guided positioning based on implanted gold markers (IGRTdb), and a database of 302 patients who were treated with 5 field IMRT and daily positioning using a trans‐abdominal ultrasound system (USdb). Complete planning dosimetry was available for IGRTdb patients while limited planning dosimetry, recorded at the time of planning, was available for USdb patients. We fit Lyman‐Kutcher‐Burman (LKB) model to IGRTdb only, and Univariate Logistic Regression (ULR) NTCP model to both databases. We perform Receiver Operating Characteristics analysis to determine the predictive power of NTCP models.Results:The incidence of grade &gt;= 2 acute rectal toxicity in IGRTdb was 20%, while the incidence in USdb was 54%. Fits of both LKB and ULR models yielded predictive NTCP models for IGRTdb patients with Area Under the Curve (AUC) in the 0.63 – 0.67 range. Extrapolation of the ULR model from IGRTdb to planning dosimetry in USdb predicts that the incidence of acute rectal toxicity in USdb should not exceed 40%. Fits of the ULR model to the USdb do not yield predictive NTCP models and their AUC is consistent with AUC = 0.5.Conclusion:Accuracy of a patient positioning system affects clinically observed toxicity rates and the quality of NTCP models that can be derived from toxicity data. Poor correlation between planned and clinically delivered dosimetry may lead to erroneous or poorly performing NTCP models, even if the number of patients in a database is large.

SU-F-T-616: Comparison of Different Techniques Using RTOG0631 Guidelines in Spine SBRT

Purpose: Stereotactic body radiosurgery (SBRT) for spine metastases involves irradiation using a single high dose fraction. The purpose of this study was to investigate a Hybrid VMAT/IMRT technique which combines volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) for spine SBRT in terms of its dosimetric quality and treatment efficiency using Radiation Therapy Oncology Group (RTOG) 0631 guidelines. Methods: 7 fields IMRT, 2 full arcs VMAT and Hybrid VMAT/IMRT were created for ten previously treated patients. The Hybrid VMAT/IMRT technique consisted of 1 full VMAT arc and 5 IMRT fields. Hybrid VMAT/IMRT plans were compared with IMRT and VMAT plans in terms of the dose distribution, spinal cord sparing, homogeneity, conformity and gradient indexies, monitor unit (MU) and beam on time (BOT). RTOG 0631 recommendations were applied for treatment planning. All plans were normalized and prescribed to deliver 18.0 Gy in a single fraction to 90% of the target volume. Results: The Hybrid VMAT/IMRT technique significantly improved target dose homogeneity and conformity compared with IMRT and VMAT techniques. Providing sharp dose gradient Hybrid VMAT/IMRT plans spare the spinal cord and healthy tissue more effectively. Although, both MU and BOT slightly increased in Hybrid VMAT/IMRT plans there is no statistically meaningful difference between VMAT and Hybrid VMAT/IMRT plans. Conclusion: In IMRT, a smaller volume of healthy tissue can be irradiated in the low dose region, VMAT plans provide better target volume coverage, favorable dose gradient, conformity and better OAR sparing and also they require a much smaller number of MUs and thus a shorter treatment time than IMRT plans. Hybrid plan offers a sinergy through combination of these two techniques with slightly increased number of MU and thus more treatment time.