3D CRT Research Articles

Dosimetric study of the protection level of the bone marrow in patients with cervical or endometrial cancer for three radiotherapy techniques - 3D CRT, IMRT and VMAT. Study protocol.

Abstract Background: The paper shows the methodology of an in-phantom study of the protection level of the bone marrow in patients with cervical or endometrial cancer for three radiotherapy techniques: three-dimensional conformal radiotherapy, intensity modulated radiotherapy, and volumetric modulated arc therapy, preceded by the procedures of image guidance. Methods/Design: The dosimetric evaluation of the doses will be performed in an in-house multi-element anthropomorphic phantom of the female pelvic area created by three-dimensional printing technology. The volume and position of the structures will be regulated according to the guidelines from the Bayesian network. The input data for the learning procedure of the model will be obtained from the retrospective analysis of imaging data obtained for 96 patients with endometrial cancer or cervical cancer treated with radiotherapy in our centre in 2008-2013. Three anatomical representations of the phantom simulating three independent clinical cases will be chosen. Five alternative treatment plans (1 × three-dimensional conformal radiotherapy, 2 × intensity modulated radiotherapy and 2 × volumetric modulated arc therapy) will be created for each representation. To simulate image-guided radiotherapy, ten specific recombinations will be designated, for each anatomical representation separately, reflecting possible changes in the volume and position of the phantom components. Discussion: The comparative analysis of planned measurements will identify discrepancies between calculated doses and doses that were measured in the phantom. Finally, differences between the doses cumulated in the hip plates performed by different techniques simulating the gynaecological patients' irradiation of dose delivery will be established. The results of this study will form the basis of the prospective clinical trial that will be designed for the assessment of hematologic toxicity and its correlation with the doses cumulated in the hip plates, for gynaecologic patients undergoing radiation therapy.

A Prospective Study to Evaluate Clinical Radiation Induced Pneumonitis in Lung Cancer Patients and its Dose Response Relationship with Radiotherapy

Purpose: This study was initiated to evaluate incidence, grade and dosimetric correlation of Clinical Radiation Induced Pneumonitis (RIP) (≥ grade 2) in lung cancer patients undergoing radical radiotherapy. Methods and Materials: From August, 2012 to November, 2013, 85 lung cancer patients received curative 3D CRT. On follow up 14 patients developed symptomatic pneumonitis (≥ Grade 2 as per RTOG Toxicity criteria). They underwent CT thorax/PET-CT at 3 monthly follow-up which were co-registered with planning CT images. Changes in lung density were graded as patchy, discrete and solid consolidation and contoured. Isodose surface enveloping these contours and mean doses received were noted. Result: At a median follow up of 12.5 months, incidence of clinical ≥Grade 2 RIP was 16.5%. Inclusion of mediastinum in the target volume and higher stage of disease were found to be indicators of increased risk of ≥Grade 2 RIP. Lung volumes showing patchy/discrete consolidation decreased from 3rd to 6th month and then plateaued while solid consolidation appeared at 6 months, increased at 9 months but then decreased at 12 months. Percentage isodoses encompassing grade 2 radiological RIP were between 80-85% and mean doses were between 45-48Gy. However for grade 3/4 RIP corresponding values were 90-95% and 50-54Gy. Conclusion: Incidence of ≥Grade 2 RIP with conformal RT was 16.5%. V20 alone may not be a sufficient predictor for RIP and one should consider conformal RT planning to restrict even higher isodoses beyond the PTV.

Toxicity Profile of IMRT Vs. 3D-CRT in Head and Neck Cancer: A Retrospective Study.

Role of radiotherapy in comprehensive management of head and neck cancer for achieving tumour control and organ preservation is now well established and radiotherapy is routinely used in adjuvant setting after surgery, concurrently with chemotherapy or targeted agents and for palliation. Development of linear accelerator with Multileaf Collimator (MLC) have revolutionized radiation delivery techniques, allowing conformal and Intensity Modulated Radiotherapy (IMRT) to deliver highly conformal sculpted radiation dose to a very complex structure with improved sparing of adjoining critical structures like salivary glands, spinal cord, eyes, brainstem and larynx amounting to better therapeutic gain. This retrospective study was to compare toxicity profile of IMRT with Three Dimensional Conformal Radiotherapy (3D CRT) in head and neck cancer. Total of 80 patients from January 2013 to July 2015 with proven head and neck cancer who underwent radiotherapy on linac 2300 C/D machine were included in the study, IMRT group and 3D-CRT group comprised of 40 patients each. We have searched patient's radiotherapy details in record section of our institute and observations were noted down. Patients received 70Gy/35 fractions, Monday to Friday as radical treatment and 60 Gy/30 fractions as adjuvant treatment were included. The 3D-CRT group demonstrated significantly more acute toxic effects compared with the IMRT group in our analysis. Acute Grade 3 or greater toxic effects to the skin occurred in 5 of 40 (12.5%), patients in the 3D-CRT group compared with 3 of 40 (7.5%) patients in the IMRT group. Acute Grade 3 or greater toxic effects to the mucous membranes occurred in 23 of 40 (57.5%) patients in the 3D-CRT group and only 16 of 40 (40%) patients in the IMRT group. Statistically significant dysphagia developed in 34 of 40 (85%), patients in 3D-CRT group compared with 23 of 40 (57.5%) patients in IMRT group, while statistically significant xerostomia developed in 29 of 40 patients in 3D-CRT group (72.5%), compared with18 of 40 (45%) patients in IMRT group. In our analysis, IMRT was associated with a significantly lower incidence of Grade 3 or greater xerostomia, acute toxic effects to skin and mucous membranes than 3D-CRT. In addition, compared to 3D-CRT, IMRT had lower rates of Grade 3 or greater mucositis and skin toxicity as well as less feeding tube use during radiotherapy. Our analysis showed potentially less toxicity in patients treated with IMRT in comparision to 3D-CRT.

Radiation induced toxicity in rectal cancer patients

Preoperative radiotherapy ? chemotherapy became the standard treatment for locally advanced rectal cancer. Despite better local control with this approach, there was not seen a significant improvement in overall survival and disease free survival, yet. The main disadvantage is toxicity that can be developed, especially concomitantly with chemotherapy. Toxicity can be acute and late. Acute complications are transitory, but late might lead to permanent damage and consequently are more significant for patients. Today, there are technical opportunities in reduction of acute and late radiation toxicity in the treatment of rectal cancer. With the implementation of 3D conformal radiotherapy (3D CRT) and intensity modulated radiation therapy (IMRT) techniques in clinical practice significant accuracy, better dose distribution and safety in the treatment of rectal cancer patients is achieved, with maximal sparing of surrounding normal tissue. Utilization of advanced techniques and new software solutions can keep adverse effects on satisfactory levels with excellent local control.

Quantification of interplay and gradient effects for lung stereotactic ablative radiotherapy (SABR) treatments

This study quantified the interplay and gradient effects on GTV dose coverage for 3D CRT, dMLC IMRT, and VMAT SABR treatments for target amplitudes of 5–30 mm using 3DVH v3.1 software incorporating 4D Respiratory MotionSim (4D RMS) module. For clinically relevant motion periods (5 s), the interplay effect was small, with deviations in the minimum dose covering the target volume (D99%) of less than ±2.5% for target amplitudes up to 30 mm. Increasing the period to 60 s resulted in interplay effects of up to ±15.0% on target D99% dose coverage. The gradient effect introduced by target motion resulted in deviations of up to ±3.5% in D99% target dose coverage. VMAT treatments showed the largest deviation in dose metrics, which was attributed to the long delivery times in comparison to dMLC IMRT. Retrospective patient analysis indicated minimal interplay and gradient effects for patients treated with dMLC IMRT at the NCCI.PACS numbers: 87.55.km, 87.56.Fc

Estimating and reducing dose received by cardiac devices for patients undergoing radiotherapy.

The objectives of this project are to quantify the dose reduction effect provided by a lead shield for patients with cardiac implantable electronic devices (CIED) during a clinically realistic radiation treatment on phantom and to provide a simple model of dose estimation to predict dose received by CIED in a wide range of situations. The shield used in this project is composed of a lead sheet wrapped in thermoplastic. Dose measurements were made with a plastic scintillation detector (PSD). The phantom was treated with ten different plans. Three of these cases were treated with intensity‐modulated radiation therapy (IMRT) and the others received standard 3D conformal radiation therapy (3D CRT). Lateral dose measurement for photon fields was made to establish a dose prediction model. On average, the use of the lead shield reduced the dose to CIEDs by 19%±13%. Dose reduction was most important for breast cases, with a mean reduction of 31%±15%. In three cases, the total dose reduction was more than 25 cGy over the complete treatment. For the three IMRT cases, the mean dose reduction was 11%±9%. On average, the difference between the TPS prediction and the measurement was 71%, while it was only 14% for the dose prediction model. It was demonstrated that a lead shield can be efficiently used for reducing doses to CIED with a wide range of clinical plans. In patients treated with IMRT modality treatment, the shielding should be used only for those with more than two anterior fields over seven fields. In the case of 3D CRT patients, the shielding should be used for those with a dose on the CIED higher than 50 cGy and with a reduction of dose higher than 10 cGy. The dose prediction model developed in this study can be an easy way to have a better estimation of the out‐of‐field dose than the TPS.PACS number(s): 87.55.N, 87.55.km

Analysis of direct clinical consequences of MLC positional errors in volumetric-modulated arc therapy using 3D dosimetry system.

In advanced, intensity‐modulated external radiotherapy facility, the multileaf collimator has a decisive role in the beam modulation by creating multiple segments or dynamically varying field shapes to deliver a uniform dose distribution to the target with maximum sparing of normal tissues. The position of each MLC leaf has become more critical for intensity‐modulated delivery (step‐and‐shoot IMRT, dynamic IMRT, and VMAT) compared to 3D CRT, where it defines only field boundaries. We analyzed the impact of the MLC positional errors on the dose distribution for volumetric‐modulated arc therapy, using a 3D dosimetry system. A total of 15 VMAT cases, five each for brain, head and neck, and prostate cases, were retrospectively selected for the study. All the plans were generated in Monaco 3.0.0v TPS (Elekta Corporation, Atlanta, GA) and delivered using Elekta Synergy linear accelerator. Systematic errors of +1,+0.5,+0.3,0,−1,−0.5,−0.3 mm were introduced in the MLC bank of the linear accelerator and the impact on the dose distribution of VMAT delivery was measured using the COMPASS 3D dosimetry system. All the plans were created using single modulated arcs and the dose calculation was performed using a Monte Carlo algorithm in a grid size of 3 mm. The clinical endpoints D95%,D50%,D2%, and Dmax,D20%, D50% were taken for the evaluation of the target and critical organs doses, respectively. A significant dosimetric effect was found for many cases even with 0.5 mm of MLC positional errors. The average change of dose D95% to PTV for ±1 mm,±0.5 mm, and ±0.3 mm was 5.15%, 2.58%, and 0.96% for brain cases; 7.19%, 3.67%, and 1.56% for head and neck cases; and 8.39%, 4.5%, and 1.86% for prostate cases, respectively. The average deviation of dose Dmax was 5.4%, 2.8%, and 0.83% for brainstem in brain cases; 8.2%, 4.4%, and 1.9% for spinal cord in H&N; and 10.8%, 6.2%, and 2.1% for rectum in prostate cases, respectively. The average changes in dose followed a linear relationship with the amount of MLC positional error, as can be expected. MLC positional errors beyond ±0.3 mm showed a significant influence on the intensity‐modulated dose distributions. It is, therefore, recommended to have a cautious MLC calibration procedure to sufficiently meet the accuracy in dose delivery.PACS number: 87.56

Late radiation toxicity in Hodgkin lymphoma patients: proton therapy's potential.

In 2010, all young patients treated for intrathoracic Hodgkin lymphoma (HL) at one of 10 radiotherapy centers in the province of Quebec received 3D conformal photon therapy. These patients may now be at risk for late effects of their treatment, notably secondary malignancies and cardiac toxicity. We hypothesized that more complex radiotherapy, including intensity‐modulated proton therapy (IMPT) and possibly IMRT (in the form of helical tomotherapy (HT)), could benefit these patients. With institutional review board approval at 10 institutions, all treatment plans for patients under the age of 30 treated for HL during a six‐month consecutive period of 2010 were retrieved. Twenty‐six patients were identified, and after excluding patients with extrathoracic radiation or treatment of recurrence, 20 patients were replanned for HT and IMPT. Neutron dose for IMPT plans was estimated from published measurements. The relative seriality model was used to predict excess risk of cardiac mortality. A modified linear quadratic model was used to predict the excess absolute risk for induction of lung cancer and, in female patients, breast cancer. Model parameters were derived from published data. Predicted risk for cardiac mortality was similar among the three treatment techniques (absolute excess risk of cardiac mortality was not reduced for HT or IMPT (p>0.05,p>0.05) as compared to 3D CRT). Predicted risks were increased for HT and reduced for IMPT for secondary lung cancer (p<0.001,p<0.001) and breast cancers (p<0.001,p<0.001) as compared to 3D CRT.PACS numbers: 87.55.dh, 87.55.dk

SU-E-T-294: Dosimetric Analysis of Planning Phase Using Overlap Volume Histogram for Respiratory Gated Radiotherapy

Purpose: End-of-exhale (EOE) phase is generally preferred for gating window because tumor position is more reproducible. However, other gating windows might be more appropriate for dose distribution perspective. In this pilot study, we proposed to utilize overlap volume histogram (OVH) to search optimized gating window and demonstrated its feasibility. Methods: We acquired 4DCT of 10 phases for 3 lung patients (2 with a target at right middle lobe and 1 at right upper lobe). After structures were defined in every phase, the OVH of each OAR was generated to quantify the three dimensional spatial relationship between the PTV and OARs (bronchus, esophagus, heart and cord etc.) at each phase. OVH tells the overlap volume of an OAR according to outward distance from the PTV. Relative overlap volume at 20 mm outward distance from the PTV (ROV-20) was also defined as a metric for measuring overlap volume and obtained. For dose calculation, 3D CRT plans were made for all phases under the same beam angles and objectives (e.g., 95% of the PTV coverage with at least 100% of the prescription dose of 50 Gy). The gating window phase was ranked according to ROV-20, and the relationship between the OVH and dose distribution at each phase was evaluated by comparing the maximum dose, mean dose, and equivalent uniform dose of OAR. Results: OVHs showed noticeable difference from phase to phase, implying it is possible to find optimal phases for gating window. For 2 out of 3 patients (both with a target at RML), maximum dose, mean dose, and EUD increased as ROV-20 increased. Conclusion: It is demonstrated that optimal phases (in dose distribution perspective) for gating window could exist and OVH can be a useful tool for determining such phases without performing dose optimization calculations in all phases. This work was supported by the Radiation Technology R&D program (No. 2013M2A2A7043498) and the Mid-career Researcher Program (2012-007883) through the National Research Foundation (NRF) funded by the Ministry of Science, ICT & Future Planning (MSIP) of Korea.

SU‐E‐T‐103: An Evaluation of Multiple Irradiations of the IROC Houston QA Center Anthropomorphic Liver Phantom

Purpose:Analyze the results from irradiations of an anthropomorphic liver phantom based on irradiation technique and number of isocenters used for the SBRT delivery.Methods:The phantom consists of a water‐fillable plastic shell that has a polystyrene insert, representing the liver which includes two Solid WaterTM targets (PTV1 and PTV2) mimicking liver metastases. The two targets, PTV1 and PTV2 are non‐coplanar and are an ovoid 2 cm in diameter and 2.5 cm long and a 3 cm diameter sphere, respectively. Each PTV houses one TLD and 2 planes of radiochromic film. The phantom and a motion table to simulate respiratory motion is sent to institutions sthat are instructed to design and deliver a stereotactic treatment plan that delivers 6 Gy to ≥ 95% of each PTV. The maximum motion of the phantom on the motion table was 1 cm in the superior‐inferior direction.Results:Irradiations from 93 institutions have been analyzed. The acceptance criteria are ±7% for the TLD and 85% of the pixels in a region surrounding each PTV passing a ±7%/4 mm global gamma analysis. Sixty‐seven (71%) irradiations meet this criteria. The majority, 74 (80%), of the irradiations were performed with IMRT. 73% of the IMRT deliveries were within criteria and 68% of the 3D CRT delivery were within criteria. 32 of the irradiations had a single isocenter plan, 50 were performed with two isocenters and 11 irradiations were performed with CyberKnife and TomoTherapy units where the concept of isocenter is not applicable. The pass rate for the single, dual and no isocenter irradiations were 69%, 74% and 73%, respectively and are not statistically different.Conclusion:The pass rate for the anthropomorphic liver phantom is approximately 70%. There does not seem to be any correlation with number of isocenters used or irradiation technique used for the delivery.This work was supported by PHS CA180803 awarded by NCI, DHHS

MO‐F‐CAMPUS‐T‐04: Development and Evaluation of a Knowledge‐Based Model for Treatment Planning of Lung Cancer Patients Using Stereotactic Body Radiotherapy (SBRT)

Purpose:To describe the development of a knowledge‐based treatment planning model for lung cancer patients treated with SBRT, and to evaluate the model performance and applicability to different planning techniques and tumor locations.Methods:105 lung SBRT plans previously treated at our institution were included in the development of the model using Varian's RapidPlan DVH estimation algorithm. The model was trained with a combination of IMRT, VMAT, and 3D–CRT techniques. Tumor locations encompassed lesions located centrally vs peripherally (43:62), upper vs lower (62:43), and anterior vs posterior lobes (60:45). The model performance was validated with 25 cases independent of the training set, for both IMRT and VMAT. Model generated plans were created with only one optimization and no planner intervention. The original, general model was also divided into four separate models according to tumor location. The model was also applied using different beam templates to further improve workflow. Dose differences to targets and organs‐at‐risk were evaluated.Results:IMRT and VMAT RapidPlan generated plans were comparable to clinical plans with respect to target coverage and several OARs. Spinal cord dose was lowered in the model‐based plans by 1Gy compared to the clinical plans, p=0.008. Splitting the model according to tumor location resulted in insignificant differences in DVH estimation. The peripheral model decreased esophagus dose to the central lesions by 0.5Gy compared to the original model, p=0.025, and the posterior model increased dose to the spinal cord by 1Gy compared to the anterior model, p=0.001. All template beam plans met OAR criteria, with 1Gy increases noted in maximum heart dose for the 9‐field plans, p=0.04.Conclusion:A RapidPlan knowledge‐based model for lung SBRT produces comparable results to clinical plans, with increased consistency and greater efficiency. The model encompasses both IMRT and VMAT techniques, differing tumor locations, and beam arrangements.Research supported in part by a grant from Varian Medical Systems, Palo Alto CA.

MP62-17 PREDICTIVE FACTORS OF OUTCOME FOLLOWING SALVAGE RADIOTHERAPY ALONE FOR PATIENTS WITH BIOCHEMICAL RECURRENCE AFTER RADICAL PROSTATECTOMY

You have accessJournal of UrologyProstate Cancer: Localized V1 Apr 2015MP62-17 PREDICTIVE FACTORS OF OUTCOME FOLLOWING SALVAGE RADIOTHERAPY ALONE FOR PATIENTS WITH BIOCHEMICAL RECURRENCE AFTER RADICAL PROSTATECTOMY Wan Song, Hwang Gyun Jeon, Hyun Hwan Sung, Deok Hyun Han, Joon Hyung Park, Young Hyo Choi, Sang Eun Lee, Byong Chang Jeong, Seong Il Seo, Seong Soo Jeon, Han Yong Choi, and Hyun Moo Lee Wan SongWan Song More articles by this author , Hwang Gyun JeonHwang Gyun Jeon More articles by this author , Hyun Hwan SungHyun Hwan Sung More articles by this author , Deok Hyun HanDeok Hyun Han More articles by this author , Joon Hyung ParkJoon Hyung Park More articles by this author , Young Hyo ChoiYoung Hyo Choi More articles by this author , Sang Eun LeeSang Eun Lee More articles by this author , Byong Chang JeongByong Chang Jeong More articles by this author , Seong Il SeoSeong Il Seo More articles by this author , Seong Soo JeonSeong Soo Jeon More articles by this author , Han Yong ChoiHan Yong Choi More articles by this author , and Hyun Moo LeeHyun Moo Lee More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2015.02.2391AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES In patient with biochemical recurrence (BCR) after radical prostatectomy (RP), salvage radiotherapy (SRT) is recommended as curative treatment option for patient with documented or presumed local recurrence. The aim of this study was to evaluate the oncologic outcomes of SRT and to investigate the predictive factors of SRT failure for patients with BCR after RP. METHODS We reviewed our prospectively maintained database of 2,043 patients who underwent RP at single institute between September 1995 and December 2011. Of the 297 (14.5%) patients with BCR defined as two consecutive serum prostate specific antigen (PSA) level of > 0.2ng/ml, 149 patients who received SRT and performed prostate magnetic resonance imaging (MRI) before SRT were included. Positive result in prostate MRI was defined when there is a high signal intensity lesion in T2 weighted image (T2WI) that is suspicious for local recurrence. Three-dimensional conformal RT (3D CRT) or intensity-modulated RT (IMRT) was delivered with median dose of 70.0Gy (66.0-78.0Gy) or 67.2Gy (64.8 - 70.0Gy). Treatment failure of SRT was defined as a serum PSA level of ¡Ý0.2ng/ml or as initiation of androgen-deprivation therapy (ADT). Kaplan-Meier and Cox regression analysis was carried out to investigate predictive factors of SRT failure RESULTS The mean age was 62.8 years with median follow up of 82 (20-153) months. The mean pre-operative and pre-SRT PSA were 10.48 ng/ml and 0.54 ng/ml, respectively. Pathologic stage ¡ÜpT2 was in 106 patients, Pathologic Gleason score ¡Ý7 was in 130 patients and positive surgical margin was in 47 patients. In prostate MRI, 97 patients showed positive results. Of 149 patients, 55 (36.9%) patients showed SRT failure. The 5 year SRT failure free probability was 53.6 %. By multivariate analysis, pre-SRT PSA ¡Ý1.0 (p = 0.003, hazard ratio [HR]: 3.657, 95% confidence interval [CI]: 1.570-8.517), pathologic stage ¡ÝT3a (p = 0.005, HR: 2.231, 95% CI: 1.278-3.896), pathologic Gleason score ¡Ý7 (p = 0.019, HR: 5.443, 95% CI: 1.320-22.443), and positive result in prostate MRI (p = 0.010, HR: 0.494, 95% CI: 0.289-0.843) were independent predictors of SRT failure after RP. CONCLUSIONS SRT provided excellent long term control of disease for patients with BCR after RP. Higher pre-SRT PSA, pathologic stage, pathologic Gleason score and negative result in prostate MRI are prognostic factors of SRT failure after RP © 2015 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 193Issue 4SApril 2015Page: e787 Advertisement Copyright & Permissions© 2015 by American Urological Association Education and Research, Inc.MetricsAuthor Information Wan Song More articles by this author Hwang Gyun Jeon More articles by this author Hyun Hwan Sung More articles by this author Deok Hyun Han More articles by this author Joon Hyung Park More articles by this author Young Hyo Choi More articles by this author Sang Eun Lee More articles by this author Byong Chang Jeong More articles by this author Seong Il Seo More articles by this author Seong Soo Jeon More articles by this author Han Yong Choi More articles by this author Hyun Moo Lee More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

A Comparison between Three-Dimensional Conformal Radiotherapy, Intensity-Modulated Radiotherapy, and Volumetric-Modulated Arc Therapy Techniques for Stereotactic Body Radiotherapy of Lung Tumors

Introduction: The aim of this study is to dosimetrically compare 3D CRT, IMRT, and VMAT techniques that employ coplanar and non-coplanar beams for the SBRT of lung tumors. Methods and Materials: Nine (n = 9) consecutive SBRT lung patients with ten tumor sites who were previously treated at our institution were selected for this study. Six (n = 6) treatment plans were created for each PTV: 1 coplanar and 1 non-coplanar 3D CRT, IMRT, and VMAT such that 98% of PTV received 100% of prescription dose, Rx of 50 Gy in 5 fractions. The data collected from each plan included the conformity index, R50%, and homogeneity index of the target as well as the volume of normal tissue irradiated by 5 Gy, 25 Gy isodose lines, V5 and V20 of total lung, and maximum dose to organs at risk. Beam angles and arc lengths were chosen in order to achieve the lowest total lung V5, V20 and R50% values. Results: According to the observed data, the mean total lung V5 and V20 values were lowest for the non-coplanar VMAT plans, but were not statistically different from the other planning techniques. Conformity values were similar for the IMRT and VMAT plans, and significantly lower than the 3D CRT plans. R50% values were lowest for the VMAT plans and significantly lower than both IMRT and 3D CRT plans in both coplanar and non-coplanar beam arrangements. However, dose homogeneity in the PTV is significantly higher in the IMRT coplanar plans than the corresponding 3D CRT and SmartArc (SA) coplanar plans. Coplanar VMAT plans were able to produce a significant 35.5% reduction in the maximum cord dose than coplanar 3D CRT plans (p-value < 0.03). VMAT plans also reduce the volume of the normal tissue irradiated to high doses, but the reduction is insignificant. Conclusion: Overall, the VMAT plans were able to produce highly conformal plans. No single planning technique can outclass the others in all of the SBRT planning indices significantly and a thorough review of each patient plan is needed.

Volumetric Modulated Arc Therapy in a Large Body Habitus Patient with Left Breast Cancer: A Dosimetric Study

Background: Women with large body habitus present unique challenges for breast cancer radiation planning. We describe volumetric modulated arc therapy (VMAT) planning and its associated challenges for loco-regional radiotherapy of left sided cancer; we also describe strategies to overcome these challenges. Methods: We performed a dosimetric comparison of loco-regional radiotherapy using three dimensional conformal radiotherapy (3D CRT) with VMAT. Our patient was a 49 year old female patient who underwent left modified radical mastectomy for stage IIB (pT1 pN1) breast cancer. She had a chest wall separation of >40 cm. Dose prescription to planning target volumes were 50 Gy of chest wall (PTV50_ eval), 45 Gy to levels II-III axilla (PTV45) and 40 Gy to internal mammary nodes (PTV40) – all in 25 fractions. To assess chest wall motion, we used fluoroscopy and breath hold scan; we fused breath hold scan to the free breathing planning scan, and slice by slice examined the chest wall motion. Results: In 3D CRT, 95% of PTV50_eval could be covered by 95% dose with hotspots of dose up to 115%. PTV40 could not be adequately covered because of excessive doses to the heart and lung. VMAT achieved planning objectives on target volumes and organs-at-risk. Breath hold scan revealed ≤ 5 mm chest wall motion. Conclusion: Compared to 3D CRT in woman with large body habitus, VMAT can produce superior dosimetric plan. Chest wall motion must be carefully assessed. Breath hold scan is a useful tool in addition to fluoroscopy to assess chest wall motion, and could be incorporated in VMAT for treatment delivery.

RT-12 * OUTCOMES IN MEDULLOBLASTOMA: SINGLE INSTITUTION CASE SERIES

BACKGROUND: We have seen a paradigm shift in terms of use of radiation technology for the treatment of patients with medulloblastoma, from conventional 2-D shifting fields to 3-D CRT, IMRT and proton therapy. Similarly from prone to supine position and reduced dose to the cranio-spinal axis with an intent to have equivalent outcomes with reduced probability of late sequelae including second malignancies. METHODS: We have analysed data of 21 consecutive patients in May 2014, registered and treated in our hospital between 2002 and 2011. The cohort consisted of 14 male and 7 female patients with a median age of 8 (Range 3-30) Years. With no known co-morbidities and median KPS of 70 they all had tumors mostly in the IV ventricle(43%) and cerebellum(38%), for which they underwent surgery including decompression(72%) subtotal excision(9%), near total or total excision(19%). All patients were histologically grade IV medulloblastoma who underwent adjuvant radiation alone (40%) or followed by chemotherapy (60%) based on the risk stratification. 57% received 3D CRT in supine position while rest are treated with conventional techniques, median dose given to cranio-spinal axis was 23.4 Gy, posterior fossa was 36 Gy and to the tumor bed was 55.8 Gy at 1.8Gy per fraction. Chemotherapy was usually procarbazine/cisplatin/vincristine based regimen. Regular IQ, endocrine, ophthalmic and auditory evaluation was done in all the patients on follow-up. RESULT: Overall survival at 5 year was documented at 45% and 10 year survival at 35% for the entire cohort taking worst case scenario.3/13 patients developed IQ problems, 7/13 developed endocrine dysfunction, 3/12 developed auditory abnormality. CONCLUSION: Outcome of this cohort is comparable to the literature on risk group stratification. More importantly, risk adapted strategy for the treatment was found to be technically and logistically feasible and effective for a comparatively rare tumor in our setup.

Overutilization of IMRT/IGRT in treatment of rectal cancer: Cost implications of deviation from evidence-based practices.

34 Background: Current evidence-based guidelines for management of rectal cancer (RC) caution against routine use of IMRT and do not address the role of IGRT. To explore patterns of care and cost implications for treatment of RC in commercially insured patients, we assessed treatment requests submitted for preauthorization through eviti Connect. Methods: A proprietary web-based application enables oncology providers to obtain automated precertification for patients insured by payers across the US that use the platform. All requests for pelvic radiation for treatment of RC submitted from 6/1/11-5/31/14 were reviewed. Treatment delivery costs for 3D CRT + weekly port films and for IMRT + IGRT were calculated based on average reimbursement rates from 3 payers for a typical course of 50.4 Gy/28 fractions. Results: A total of 195 cases for treatment of RC were submitted. At submission, 50.3% (98/195) of cases met evidence based standards and received automated preauthorization; 49.7% required treatment justification. Ninety-eight percent of deviations involved use of IMRT and/or IGRT. Upon review, 34.9% (68/195) had a medical rationale for the variance. Justification for IMRT/IGRT use included treatment volumes comparable to anal cancer, inadequate bowel displacement by routine techniques, and obesity. Fifteen percent (29/195) contained unwarranted deviations. In 23/29 cases peer to peer discussion resulted in the provider altering the plan to be compliant. Providers did not agree to changes in the other 6 cases. Cost for a course of 3D CRT + weekly port films was $6,591 vs. $32,292 for IMRT + daily IGRT. For these 195 cases, the estimated cost of overutilization of IMRT/IGRT was $745,000 ($25,700 X 29). Conclusions: Despite lack of endorsement by consensus group guidelines, IMRT and IGRT were prescribed for treatment of RC in nearly 50% of cases. Case review and peer to peer discussion clarified the rationale for treatment deviations from guidelines and allowed providers to bring plans into compliance with evidence based practices, reducing inappropriate use of IMRT/IGRT from 15% to 3%. Reduction in unwarranted use of high cost technologies can improve quality and yield significant cost savings.

Impact of 3D CRT Versus IMRT on Post operative Wound Complications

Impact of 3D CRT Versus IMRT on Post operative Wound Complications

P0107 Dose to dysphagia aspiration-related structures and its effect on swallowing: Comparison of 3D CRT and IMRT plans

Background Advances in radiotherapy techniques have improved clinical outcomes, but have also lead to concerns over subsequent acute and late effects. Dysphagia is one such complication that has garnered much attention. This retrospective study, conducted at a tertiary cancer care centre, aimed to analyse swallowing profiles of patients with cancer of anterior two-thirds of tongue, who had undergone surgery and had received adjuvant radiation using either IMRT or 3D CRT, as a surrogate of dose received by dysphagia aspiration-related structures (DARS). Methods The treatment plans of patients treated using IMRT and 3D CRT, from November 2011 to December 2012, were retrieved from the planning system. The swallowing structures (DARS), namely superior, middle and inferior constrictors, base of tongue, larynx with supraglottis, and length of oesophagus, included in treatment volume with cricopharyngeous muscle, were contoured according to RTOG guidelines. Dose volume histograms were generated for these. Constraint doses were statistically derived. University of Washington Head-and-Neck-related Quality-of-Life questions addressing swallowing was used to evaluate swallowing status of patients. Findings A statistically significant subjective correlation was found to exist between doses of swallowing structures, especially the constrictor muscles, base of tongue, and the larynx. Statistically derived probable mean dose-constraints correlated clinically with swallowing status of patients. IMRT had a statistically significant advantage over 3D CRT, in terms of V30 (p = 0.051), V50 (p = 0.002), V60 (p = 0.002), and D80 (p = 0.023) for the swallowing structures taken together. The probable limiting dose for dysphagia was 63 Gy for the superior constrictor and base of tongue, and 55 Gy for the larynx. Interpretation Our study predicted possible mean dose constraints for the superior constrictor, base of tongue, and larynx. Further prospective studies are required to confirm these findings. Dysphagia-optimised IMRT is needed to improve swallowing status and quality of life in these patients.

Optimization strategies for pulsed low-dose-rate IMRT of recurrent lung and head and neck cancers.

Pulsed low‐dose‐rate radiotherapy (PLDR) has been proven to be a valid method of reirradiation. Previous studies of recurrent cancer radiotherapy were mainly based on conventional 3D CRT and VMAT delivery techniques. There are difficulties in IMRT planning using existing commercial treatment planning systems (TPS) to meet the PLDR protocol. This work focuses on PLDR using ten‐field IMRT and a commercial TPS for two specific sites: recurrent lung cancers and head and neck cancers. Our PLDR protocol requires that the maximum dose to the PTV be less than 0.4 Gy and the mean dose to be 0.2 Gy per field. We investigated various planning strategies to meet the PLDR requirements for 20 lung and head and neck patients. The PTV volume for lung cases ranged from 101.7 to 919.4 cm3 and the maximum dose to the PTV ranged from 0.22 to 0.39 Gy. The PTV volume for head and neck cases ranged from 66.2 to 282.1 cm3 and the maximum dose to the PTV ranged from 0.21 to 0.39 Gy. With special beam arrangements and dosimetry parameters, it is feasible to use a commercial TPS to generate quality PLDR IMRT plans for lung and head and neck reirradiation.PACS number: 87.55.D‐

A Study of the Anatomic Changes and Dosimetric Consequences in Adaptive CRT of Non-Small-Cell Lung Cancer Using Deformable CT and CBCT Image Registration

The aim of this study is to evaluate anatomic lung tumor changes and dosimetric consequences utilizing the deformable daily kilovolt (KV) cone-beam computer tomography (CBCT) image registration. Five patients diagnosed with NSCLC were treated with three-dimensional conformal radiotherapy (3D CRT) and 10 daily KV CBCT image sets were acquired for each patient. Each CBCT image and plan CT were imported into the deformable image registration (DIR) system. The plan CT image was deformed by the DIR system and a new contour on CBCT was obtained by using the auto-contouring function of the DIR. These contours were individually marked as CBCT f1, CBCT f2,..., and CBCT f10, and imported into a treatment planning system (TPS). The daily CBCT plan was individually generated with the same planning criteria based on new contours. These plans were individually marked as CBCTp1, CBCTp2,..., and CBCTp10, followed by generating a dose accumulation plan (DA plan) in original pCT image contour sets by adding all CBCT plans using Varian Eclipse TPS. The maximum, minimum and mean doses to the plan target volume (PTV) in the 5 DA plans were the same with the CT plans. However, the volume of radiation 5, 10, 20, 30, and 50 Gy of the total lungs in DA plans were less than those of the CT plans. The maximum dose of the spinal cord in the DA plans were average 27.96% less than the CT plans. The mean dose for the left, right, and total lungs in the DA plans were reduced by 13.80%, 23.65%, and 12.96%, respectively. The adaptive 3D CRT based on the deformable registration can reduce the dose to the lung and the spinal cord with the same PTV dose coverage. Moreover, it provides a method for further adaptive radiotherapy exploration.