Radiotherapy Treatment Position Research Articles

Abstract A008: Imaging response to induction PD-1 and PARP inhibition in patients with locally advanced head and neck squamous cell carcinoma

Abstract Introduction: Patients with locally advanced head and neck squamous cell carcinoma (LA-HNSCC) have high risk of disease progression and death after standard concurrent chemoradiotherapy (CCRT). We are conducting a prospective trial to investigate the efficacy of combining immune checkpoint blockade (ICB) with PARP inhibition prior to and following CCRT. Here we report the feasibility of utilizing pre- and post-induction CT simulations to assess early imaging response in patients treated on trial. Methods: NCT05366166 is an ongoing multi-institution, phase II trial. Patients with HPV negative or high-risk HPV positive LA-HNSCC were eligible. All received induction pembrolizumab 400mg IV and olaparib 150mg BID for 3 weeks followed by CCRT to 70Gy with weekly cisplatin (40mg/m2) followed by one year of maintenance pembrolizumab 400mg every 6 weeks and olaparib 150mg BID. Per protocol, all patients underwent CT simulation in the radiation treatment position with intravenous contrast pre- and post-induction. Dedicated post-induction imaging by radiology was not obtained. Gross tumor volumes of the primary (GTVp) and nodal (GTVn) disease were contoured on the pre- and post-induction simulation CTs by the treating physician in RayStation (RaySearch Laboratories). Pre- and post-induction simulation CTs were evaluated by two neuroradiologists independently using the RECIST criteria (v1.1). Statistical analyses were conducted in Microsoft Excel. Results: We evaluated the first 9 patients treated on-study at our center only. Median age was 67 years (range 59-76) and 78% were male. Location of primary site was oropharynx (N=6; 4 were HPV-positive), oral cavity (N=2), and larynx (N=1). 78% were T3-T4 and 89% had N2-N3 nodal disease. The median duration from the start of induction therapy to post-induction simulation was 22 days (range 7-51). Following induction, all patients experienced symptomatic benefit and had stable disease without progression per RECIST. Comparing pre- and post-induction GTVp and GTVn, overall mean volumes were not statistically different (mean±standard deviation -- 34.0±17.9 vs 35.6±19.5 cm3 for GTVp and 38.7±51.8 vs 39.5±54.2 cm3 for GTVn, respectively). At the individual patient level, the percent volume change after induction ranged from -21.9 to +16.5% (GTVp) and -48.7 to +53.2% (GTVn). Two patients (22%) had a decrease in GTVp, while five (56%) had a decrease in GTVn. There was a positive correlation (Pearson coefficient 0.77) between the percent volume changes in GTVp and GTVn (p=0.016). No differences in response by TNM stage or HPV status were observed. Conclusion: Favorable clinical and radiographic responses to three weeks of induction pembrolizumab and olaparib suggest anti-tumor activity. Performing pre- and post-induction radiation CT simulations is necessary to ensure adequate and accurate assessment of tumor extent for radiation planning. Therefore, omitting conventional post-induction scans by radiology to assess tumor response may be feasible. Formal cost-effective analysis will be conducted. Citation Format: Xuguang S. Chen, Colette J. Shen, Benjamin Y. Huang, Valerie L. Jewells, Michael C. Repka, Travis P. Schrank, Christopher B. Sullivan, Wendell G. Yarbrough, Trevor G. Hackman, Catherine Lumley, Jeffrey M. Blumberg, Shetal A. Patel, Sumita Trivedi, Jared Weiss, Bhisham Chera, Siddharth Sheth. Imaging response to induction PD-1 and PARP inhibition in patients with locally advanced head and neck squamous cell carcinoma. [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Translating Targeted Therapies in Combination with Radiotherapy; 2025 Jan 26-29; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(2_Suppl):Abstract nr A008.

The application of multiple metrics in deformable image registration for target volume delineation of breast tumor bed.

For postoperative breast cancer patients, deformable image registration (DIR) is challenged due to the large deformations and non-correspondence caused by tumor resection and clip insertion. To deal with it, three metrics (fiducial-, region-, and intensity-based) were jointly used in DIR algorithm for improved accuracy. Three types of metrics were combined to form a single-objective function in DIR algorithm. Fiducial-based metric was used to minimize the distance between the corresponding point sets of two images. Region-based metric was used to improve the overlap between the corresponding areas of two images. Intensity-based metric was used to maximize the correlation between the corresponding voxel intensities of two images. The two CT images, one before surgery and the other after surgery, were acquired from the same patient in the same radiotherapy treatment position. Twenty patients who underwent breast-conserving surgery and postoperative radiotherapy were enrolled in this study. For target registration error, the difference between the proposed and the conventional registration methods was statistically significant for soft tissue (2.06 vs. 7.82, p=0.00024<0.05) and body boundary (3.70 vs. 6.93, p=0.021<0.05). For visual assessment, the proposed method achieved better matching result for soft tissue and body boundary. Comparing to the conventional method, the registration accuracy of the proposed method was significantly improved. This method provided a feasible way for target volume delineation of tumor bed in postoperative radiotherapy of breast cancer patients.

Characterization of positioning uncertainties in PET-CT-MR trimodality solutions for radiotherapy.

The purpose of this study was to evaluate the positioning uncertainties of two PET/CT‐MR imaging setups, C1 and C2. Because the PET/CT data were acquired on the same hybrid device with automatic image registration, experiments were conducted using CT‐MRI data. In C1, a transfer table was used, which allowed the patient to move from one imager to another while maintaining the same position. In C2, the patient stood up and was positioned in the same radiotherapy treatment position on each imager. The two setups provided a set of PET/CT and MR images. The accuracy of the registration software was evaluated on the CT‐MRI data of one patient using known translations and rotations of MRI data. The uncertainties on the two setups were estimated using a phantom and a cohort of 30 patients. The accuracy of the positioning uncertainties was evaluated using descriptive statistics and a t‐test to determine whether the mean shift significantly deviated from zero (p < 0.05) for each setup. The maximum registration errors were less than 0.97 mm and 0.6° for CT‐MRI registration. On the phantom, the mean total uncertainties were less than 2.74 mm and 1.68° for C1 and 1.53 mm and 0.33° for C2. For C1, the t‐test showed that the displacements along the z‐axis did not significantly deviate from zero (p = 0.093). For C2, significant deviations from zero were present for anterior‐posterior and superior‐inferior displacements. The mean total uncertainties were less than 4 mm and 0.42° for C1 and less than 1.39 mm and 0.27° for C2 in the patients. Furthermore, the t‐test showed significant deviations from zero for C1 on the anterior‐posterior and roll sides. For C2, there was a significant deviation from zero for the left‐right displacements.This study shows that transfer tables require careful evaluation before use in radiotherapy.

Delineation guidelines for the lymphatic target volumes in \u2018prone crawl\u2019 radiotherapy treatment position for breast cancer patients

Our recently developed prone crawl position (PCP) for radiotherapy of breast cancer patients with lymphatic involvement showed promising preliminary data and it is being optimized for clinical use. An important aspect in this process is making new, position specific delineation guidelines to ensure delineation (for treatment planning) is uniform across different centers. The existing ESTRO and PROCAB guidelines for supine position (SP) were adapted for PCP. Nine volunteers were MRI scanned in both SP and PCP. Lymph node regions were delineated in SP using the existing ESTRO and PROCAB guidelines and were then translated to PCP, based on the observed changes in reference structure position. Nine PCP patient CT scans were used to verify if the new reference structures were consistently identified and easily applicable on different patient CT scans. Based on these data, a team of specialists in anatomy, CT- and MRI radiology and radiation oncology postulated the final guidelines. By taking the ESTRO and PROCAB guidelines for SP into account and by using a relatively big number of datasets, these new PCP specific guidelines incorporate anatomical variability between patients. The guidelines are easily and consistently applicable, even for people with limited previous experience with delineations in PCP.

Synthetic CT Generation From Multi-Sequence MR Images for Head and Neck MRI-Only Radiotherapy via Cycle-Consistent Generative Adversarial Network

Synthetic CT (sCT) generation with MR image plays an essential role in MR-only radiotherapy, which can be used for electron density estimation and dose calculation in treatment planning. Currently, the reliability of deep learning-based methods for sCT generation depends on two aspects: the MR-CT registration errors, which can eliminate by a cycle-consistent generative adversarial network (CycleGAN) with unpaired training data, and the different anatomy information and contract divergence of various tissue in different sequences MRI which will significantly affect the nonlinear mapping of MR-CT. The purpose of this study is to investigate the effect of different sequence MRI by evaluating the image quality of corresponded sCTs.Multi-sequence MR images (T1, T2, T1C) and plan CT images of 151 patients with nasopharyngeal carcinoma were acquired on the same day in the radiation treatment position. 126 cases were randomly selected as the training set with the same preprocessing. Three unsupervised CycleGAN-based models were respectively trained with different sequence MRI with Architecture, which consists of 2 ResUnet-based generators and 2 Patch-GAN-based discriminators. The remaining 25 CT-MR cases with non-rigid registration were selected as the independent paired testing set. The mean error (ME) and mean absolute error (MAE) between plan CT and sCT of each model were used to measure the CT value estimation accuracy, which was calculated within air (Hounsfield Unit, HU < 100), soft tissue (-100 < HU < 150), bone (HU > 150) and whole body, respectively. Structural similarity index (SSIM) was applied to evaluate the similarity between error (plan CT and sCT.The MEs calculated between plan CT and T1, T2, T1C-based sCT images, were (-0.62 ± 3.06) vs. (-1.81 ± 3.13) vs. (0.13 ± 2.56) within air, (154.92 ± 87.93) vs. (173.27 ± 97.62) vs. (262.78 ± 91.74) within soft tissue, (1363.99 ± 294.94) vs. (337.21 ± 50.4) vs. (661.63 ± 168.43) within bone, (22.12 ± 29.47) vs. (17.05 ± 10.51) vs. (35.28 ± 20.75) within the whole body. The MAEs correspondingly were (4.49 ± 3.13) vs. (4.6 ± 3.47) vs. (4.6 ± 3.47) within air, (186.41 ± 61.75) vs. (197.33 ± 58.62) vs. (293.56 ± 72.72) within soft tissue, (186.41 ± 61.75) vs. (197.33 ± 58.62) vs. (293.56 ± 72.72) within bone, (31.28 ± 28.1) vs. (27.64 ± 10.41) vs. (42.6 ± 23.82) within the whole body. The quantitative analysis between T1, T2, T1C-sCTs indicates that the T1C based generated model achieves higher accuracy than the other models in nasopharyngeal carcinoma.The T1C MRI can provide sufficient anatomy information and tissue contract in synthetic CT prediction of head and neck region, which offers a substantial potential for density estimation and dose calculation in radiotherapy. The generation method and evaluation will investigate synthetic CT prediction with more complex tissue in various body parts.

PO-1908: Comparing soft tissue and bone to verify radiotherapy treatment position for lung cancer patients

PO-1908: Comparing soft tissue and bone to verify radiotherapy treatment position for lung cancer patients

A pilot study of 13N-ammonia cardiac PET imaging to assess subacute cardiotoxicity following adjuvant intensity-modulated radiotherapy for locally advanced breast cancer

Objective(1) Assess the feasibility of 13 N-ammonia cardiac PET (13 N-ammonia-PET) imaging in radiotherapy (RT) treatment position in locally-advanced breast cancer (LABC) patients. (2) Correlate pre−/post-RT changes in myocardial flow reserve (MFR) with the corresponding radiation heart dose. MethodsTen left-sided LABC patients undergoing Volumetric Modulated-Arc-Therapy (VMAT) to chest wall and regional lymph nodes underwent a rest/stress 13 N-ammonia-PET at baseline and (median) 13 months post-RT. Changes in cardiac functions and coronary artery Ca2+ scoring between baseline and follow-up were correlated with average RT dose to the myocardium,3 coronary territories, and 17 myocardial segments. ResultsEight (of 10) patients successfully completed the study. The average rest (stress) global MBF (ml.g-1.min-1) for baseline (follow-up) were 0.83 ± 0.25 (2.4 ± 0.79) and 0.92 ± 0.30 (2.76 ± 0.71), respectively. Differences in MBF, heart rate, blood pressure, and rate-pressure product (RPP) between baseline and follow-up were insignificant (P > 0.1).Strong (R = 0.79; P < 0.01) and moderate (R = 0.53; P = 0.37) correlation existed between MBF Rest and MBF Stress, and RPP respectively. Four patients showed a reduction in MFR of up to ~41% in follow-up studies, increasing to ~52% in myocardial segments close to high-radiation isodose lines in 5/8 patients. Agatston Ca + 2 scoring were zero in both baseline and follow-up in six patients; two patients exhibited mild increase in Ca + 2 on follow-ups (range:10–20).Rest and stress LVEF's were normal (>50) for all patients in both studies. ConclusionThe feasibility of 13 N-ammonia-PET imaging in treatment position of LABC patients was demonstrated. MFR at 1-year post-irradiation of the heart decreased in 50% of the patients. MFR may be a potential index for early detection of cardiotoxicity in BC patients receiving RT to the chest wall.

Correlation Between FDG Hotspots on Pre-radiotherapy PET/CT and Areas of HNSCC Local Relapse: Impact of Treatment Position and Images Registration Method.

Aim: Several series have already demonstrated that intratumoral subvolumes with high tracer avidity (hotspots) in 18F-flurodesoxyglucose positron-emission tomography (FDG-PET/CT) are preferential sites of local recurrence (LR) in various solid cancers after radiotherapy (RT), becoming potential targets for dose escalation. However, studies conducted on head and neck squamous cell carcinoma (HNSCC) found only a moderate overlap between pre- and post-treatment subvolumes. A limitation of these studies was that scans were not performed in RT treatment position (TP) and were coregistred using a rigid registration (RR) method. We sought to study (i) the influence of FDG-PET/CT acquisition in TP and (ii) the impact of using an elastic registration (ER) method to improve the localization of hotpots in HNSCC.Methods: Consecutive patients with HNSCC treated by RT between March 2015 and September 2017 who underwent FDG-PET/CT in TP at initial staging (PETA) and during follow-up (PETR) were prospectively included. We utilized a control group scanned in non treatment position (NTP) from our previous retrospective study. Scans were registered with both RR and ER methods. Various sub-volumes (AX; x = 30, 40, 50, 60, 70, 80, and 90%SUVmax) within the initial tumor and in the subsequent LR (RX; x = 40 and 70%SUVmax) were overlaid on the initial PET/CT for comparison [Dice, Jaccard, overlap fraction = OF, common volume/baseline volume = AXnRX/AX, common volume/recurrent volume = AXnRX/RX].Results: Of 199 patients included, 43 (21.6%) had LR (TP = 15; NTP = 28). The overlap between A30, A40, and A50 sub-volumes on PETA and the whole metabolic volume of recurrence R40 and R70 on PETR showed moderate to good agreements (0.41–0.64) with OF and AXnRX/RX index, regardless of registration method or patient position. Comparison of registration method demonstrated OF and AXnRX/RX indices (x = 30% to 50%SUVmax) were significantly higher with ER vs. RR in NTP (p < 0.03), but not in TP. For patient position, the OF and AXnRX/RX indices were higher in TP than in NTP when RR was used with a trend toward significance, particularly for x=40%SUVmax (0.50±0.22 vs. 0.31 ± 0.13, p = 0.094).Conclusion: Our study suggested that PET/CT acquired in TP improves results in the localization of FDG hotspots in HNSCC. If TP is not possible, using an ER method is significantly more accurate than RR for overlap estimation.

Role of PET imaging in adaptive radiotherapy for lymphoma.

Positron emission tomography/Computed tomography (PET/CT) is an essential part of modern radiotherapy for patients with lymphoma. PET/CT can be used to adapt treatment algorithms in Hodgkin lymphoma, reserving consolidation radiotherapy for patients with residual fluoro-D-glucose (FDG) avidity after treatment with intensive chemotherapy such as escalated BEACOPP and limiting the need for radiotherapy for some patients with complete metabolic response on PET if radiotherapy may be associated with increased toxicity. More importantly, PET/CT is now mandatory to define sites of initial disease for radiotherapy planning where smaller volumes are to be used rather than historical extended field treatments, such as mantle radiotherapy or even involved field radiotherapy. Involved node radiotherapy (INRT) treats only the initially involved nodes and is possible when the pretreatment PET/CT scan has been performed in the radiotherapy treatment position. Involved site radiotherapy (ISRT) builds in a margin for uncertainty when a pretreatment PET/CT is available, but has not been performed in the radiotherapy treatment position. Studies suggest that PET/CT changes radiotherapy volumes in approximately one third of patients by mapping the extent of initial disease better than using CT alone. PET/CT has also been used to adjust radiotherapy dose for patients who may be at increased risk of radioresistance, by virtue of residual FDG avidity post chemotherapy or patients with relapsed disease. This article will discuss the role of PET in selecting patients for radiotherapy, its influence on the choice of target volume and radiotherapy dose and the practicalities of how PET/CT scanning is incorporated into the radiotherapy planning process.

Multimodality imaging using PET/CT (18F)-fluorodeoxyglucose for radiotherapy field delineation of localized Hodgkin lymphoma

It is now well demonstrated that (18F)-fluorodeoxyglucose PET/CT is the most accurate imaging method for determining disease extent in Hodgkin lymphoma. Thus, up-front PET/CT is mandatory for involved node radiation therapy design. For a proper use of this new imaging modality for radiotherapy, some adaptations should be made to the PET/CT acquisition as well as to the report. Initial PET/CT should be performed in the radiotherapy treatment position. Nuclear medicine physicians should report to the radiation oncologist the precise location of each involved lymph node, for which the use of a common atlas of upper diaphragmatic nodal stations could be useful. All these new procedures have to be implemented in close collaboration among the different medical specialists providing care to Hodgkin lymphoma patients. We report here the usual procedures of PET/CT acquisition in the radiotherapy environment and propose a more sophisticated description of the different lymph nodes for a more efficient nuclear medicine report to the radiation oncologist.

EP-2348: MRI acquisition in radiotherapy treatment position: sequence optimization for head and neck cancer

EP-2348: MRI acquisition in radiotherapy treatment position: sequence optimization for head and neck cancer

Prospective analysis of in vivo landmark point-based MRI geometric distortion in head and neck cancer patients scanned in immobilized radiation treatment position: Results of a prospective quality assurance protocol

PurposeUncertainties related to geometric distortion are a major obstacle for effectively utilizing MRI in radiation oncology. We aim to quantify the geometric distortion in patient images by comparing their in-treatment position MRIs with the corresponding planning CTs, using CT as the non-distorted gold standard. MethodsTwenty-one head and neck cancer patients were imaged with MRI as part of a prospective Institutional Review Board approved study. MR images were acquired with a T2 SE sequence (0.5×0.5×2.5mm voxel size) in the same immobilization position as in the CTs. MRI to CT rigid registration was then done and geometric distortion comparison was assessed by measuring the corresponding anatomical landmarks on both the MRI and the CT images. Several landmark measurements were obtained including; skin to skin (STS), bone to bone, and soft tissue to soft tissue at specific levels in horizontal and vertical planes of both scans. Inter-observer variability was assessed and interclass correlation (ICC) was calculated. ResultsA total of 430 landmark measurements were obtained. The median distortion for all landmarks in all scans was 1.06mm (IQR 0.6–1.98). For each patient 48% of the measurements were done in the right-left direction and 52% were done in the anteroposterior direction. The measured geometric distortion was not statistically different in the right-left direction compared to the anteroposterior direction (1.5±1.6 vs. 1.6±1.7mm, respectively, p=0.4). The magnitude of distortion was higher in the STS peripheral landmarks compared to the more central landmarks (2.0±1.9 vs. 1.2±1.3mm, p<0.0001). The mean distortion measured by observer one was not significantly different compared to observer 2, 3, and 4 (1.05, 1.23, 1.06 and 1.05mm, respectively, p=0.4) with ICC=0.84. ConclusionMRI geometric distortions were quantified in radiotherapy planning applications with a clinically insignificant error of less than 2mm compared to the gold standard CT.

Results from a clinical trial evaluating the efficacy of real-time body surface visual feedback in reducing patient motion during lung cancer radiotherapy

Introduction: Optical surface measurement devices are a maturing technology in radiotherapy. The challenge for such devices is to demonstrate how they can improve clinical care. We present results from a phase 1 clinical trial designed to test the hypothesis that if presented with live data from a novel optical measurement device, showing their deviation from an ideal radiotherapy treatment position, patients will be able to better control their motion and increase their geometrical conformance.Method and materials: Fourteen lung cancer patients were enrolled in a prospective clinical study and asked to use a variety of visual feedback schema from a novel in-house developed optical surface measurement device. The magnitude and regularity of their body surface motion using the different schema was compared to that when free-breathing at three time-points throughout their radiotherapy treatment schedule. Additionally, 4D Cone Beam CT data, acquired simultaneously with the optical measurements, was used to test if improvements in external motion are reflected in changes in internal tumor motion.Results: The primary endpoint of the trial, device tolerability assessed by the fraction of participants completing all study sessions, was 86%. Secondary endpoints showed that use of the visual feedback device was found to statistically significantly decrease body surface motion magnitude by an average of 17% over the study cohort, although not universally. Similarly body surface motion variability was decreased by 18% on average. Internal tumor motion magnitude was also found to be statistically significantly decreased by an average of 14% when using the feedback device. Reduction in external motion was predictive of reduced internal motion but no evidence of a simple correlation between changes in internal and external motion magnitude was found.Conclusions: Visual feedback of live motion is well tolerated by lung cancer patients and can reduce both body surface and tumor motion.

Evaluation of clinical target volume expansion required for involved site neck radiotherapy for lymphoma to account for the absence of a pre-chemotherapy PET-CT in the radiotherapy treatment position

Background and purposeInvolved site radiotherapy clinical target volume (CTV) for lymphoma requires an expansion to account for the absence of radiotherapy treatment-position pre-chemotherapy imaging, which is not widely implemented. This prospective imaging study aims to quantify CTV expansion required for neck radiotherapy. Materials and methods10 patients from a prospective single centre imaging study underwent a pre-chemotherapy FDG-PET-CT in both the diagnostic and radiotherapy treatment position, and subsequently received neck radiotherapy post-chemotherapy. CTVINRT and CTVdiagPET were delineated on the planning CT, following co-registration of the radiotherapy position PET-CT and side-by-side assessment of diagnostic PET-CT respectively. ResultsIntra-observer variability was limited, with delineation of CTVINRT highly reproducible and slightly lower for CTVdiagPET (mean DICE 0.88 and 0.8 respectively). Superiorly, CTVdiagPET varied by −10 to +15mm from CTVINRT. Inferiorly, CTVdiagPET varied by −18 to +6mm from CTVINRT. Comparing CTVINRT and CTVdiagPET in the axial plane, the mean DICE was 0.74. Mean sensitivity index was 0.75 (range 0.59–0.91), showing that on average 75% of the CTVINRT was encompassed by the CTVdiagPET. ConclusionsIn the absence of treatment-position PET-CT, CTV expansion cranially and caudally by 10mm and 18mm respectively, along with generous contouring in the axial plane, was required to encompass pre-chemotherapy disease.

Follow up results of a prospective study to evaluate the impact of FDG-PET on CT-based radiotherapy treatment planning for oesophageal cancer

BackgroundThis prospective study aims to determine the impact of PET/CT on radiotherapy planning and outcomes in patients with oesophageal cancer. MethodsAll patients underwent PET/CT scanning in the radiotherapy treatment position, and received treatment planned using the PET/CT dataset. GTV was defined separately on PET/CT (GTV-PET) and CT (GTV-CT) datasets. A corresponding PTV was generated for each patient. Volumetric and spatial analysis quantified the proportion of FDG-avid disease not included in CT-based volumes. Clinical data was collected to determine locoregional control and overall survival rates. Results13 (24.1%) of 57 accrued patients had metastatic disease detected on PET. Median follow up was 4years. FDG-avid disease would have been excluded from GTV-CT in 29 of 38 patients (76%). In 5 patients, FDG-avid disease would have been completely excluded from the PTV-CT. GTV-CT underestimated the cranial and caudal extent of FDG-avid tumour in 14 (36%) and 10 (26%) patients. 4-Year overall survival and locoregional failure free survival were 37% and 65%. ConclusionsPET/CT altered the delineation of tumour volumes when compared to CT alone, and should be considered standard for treatment planning. Although clinical outcomes were not improved with PET/CT planning, it did allow the use of smaller radiotherapy volumes.

Impact of 18F-fluorodeoxyglucose position emission tomography/computed tomography on radiotherapy treatment planning and outcomes in esophageal cancer.

67 Background: Currently there is no universally accepted method to accurately delineate the gross tumor volume (GTV) of primary esophageal cancer in patients undergoing radiotherapy. This prospective study aims to determine the impact of PET/CT on radiotherapy planning and outcomes in patients with localized esophageal cancer. Methods: 54 patients were recruited between June 2003 - May 2008. All underwent PET/CT scanning in the radiotherapy treatment position and received treatment planned using the PET/CT dataset. Of these, 13 (24.1%) had metastatic disease detected on PET and 3 patients had no radical radiotherapy, while another 3 patients had missing planning PET/CT data (excluded from planning component analysis). GTV was defined separately on PET/CT (GTV-PET) and CT (GTV-CT) data sets. A corresponding planning target volume (PTV) was generated for each patient. Volumetric and spatial analysis quantified the proportion of FDG-avid disease not included in CT-based volumes. Clinical data was collected for 38 patients treated radically to determine locoregional control and overall survival rates. Results: Mean age was 67 years (range:32 - 88). Median follow up was 4 years (range:2.7 – 6.8). FDG-avid disease would have been excluded from GTV-CT in 29 patients (79%) with a mean volume of 17% (range:1-100%). In 5 patients, FDG-avid disease would have been completely excluded from the PTV-CT (median volume missed = 6%, range:2-92%). For 8 patients, less than 95% of PTV-PET would have received at least 95% of prescription dose based on the CT-based plan. GTV-CT underestimated the cranial and caudal extent of FDG-avid tumor in 14 (36%) and 10 (26%) patients respectively. There were no significant differences in radiation doses to the lungs and liver. 5-year overall survival and locoregional failure free survival were 24%, and 42% respectively. Conclusions: PET/CT prevented futile radiotherapy for 1 in 4 patients and avoided geographic misses without significant impact on normal tissues in apparently localized esophageal cancer. However, survival remains suboptimal and indicates the need for further improvement in planning and therapeutic paradigms.

SU‐E‐J‐220: Assessment of MRI Geometric Distortion in Head and Neck Cancer Patients Scanned in Immobilized Radiation Treatment Position

Purpose:Uncertainties about geometric distortion have somewhat hindered MRI simulation in radiation therapy. Most of the geometric distortion studies were performed with phantom measurements but another major aspect of MR distortion is patient related. We studied the geometric distortion in patient images by comparing their MRI scans with the corresponding CT, using CT as the non‐distorted gold standard.Methods:Ten H&amp;N cancer patients were imaged with MRI as part of a prospective IRB approved study. All patients had their treatment planning CT done on the same day or within one week of the MRI. MR Images were acquired with a T2 SE sequence (1×1×2.5mm voxel size) in the same immobilization position as in the CT scans. MRI to CT rigid registration was then done and geometric distortion comparison was done by measuring the corresponding anatomical landmarks on both the MRI and the CT images by two observers. Several skin to skin (9 landmarks), bone to bone (8 landmarks), and soft tissue (3 landmarks) were measured at specific levels in horizontal and vertical planes of both scans.Results:The mean distortion for all landmark measurements in all scans was 1.8±1.9mm. For each patient 11 measurements were done in the horizontal plane while 9 were done in the vertical plane. The measured geometric distortion were significantly lower in the horizontal axis compared to the vertical axis (1.3±0.16 mm vs 2.2±0.19 mm, respectively, P=0.003*). The magnitude of distortion was lower in the bone to bone landmarks compared to the combined soft tissue and skin to skin landmarks (1.2±0.19 mm vs 2.3±0.17 mm, P=0.0006*). The mean distortion measured by observer one was not significantly different compared toobserver 2 (2.3 vs 2.4 mm, P=0.4).Conclusion:MRI geometric distortions were quantified in H&amp;N patients with mean error of less than 2 mm.JW received a corporate sponsored research grant from Elekta

Involved Node, Site, Field and Residual Volume Radiotherapy for Lymphoma: A Comparison of Organ at Risk Dosimetry and Second Malignancy Risks

AimsRecent radiotherapy guidelines for lymphoma have included involved site radiotherapy (ISRT), involved node radiotherapy (INRT) and irradiation of residual volume after full-course chemotherapy. In the absence of late toxicity data, we aim to compare organ at risk (OAR) dose-metrics and calculated second malignancy risks. Materials and methodsFifteen consecutive patients who had received mediastinal radiotherapy were included. Four radiotherapy plans were generated for each patient using a parallel pair photon technique: (i) involved field radiotherapy (IFRT), (ii) ISRT, (iii) INRT, (iv) residual post-chemotherapy volume. The radiotherapy dose was 30 Gy in 15 fractions. The OARs evaluated were: breasts, lungs, thyroid, heart, oesophagus. Relative and absolute second malignancy rates were estimated using the concept of organ equivalent dose. Significance was defined as P < 0.005. ResultsCompared with ISRT, IFRT significantly increased doses to lung, thyroid, heart and oesophagus, whereas INRT and residual volume techniques significantly reduced doses to all OARs. The relative risks of second cancers were significantly higher with IFRT compared with ISRT for lung, breast and thyroid; INRT and residual volume resulted in significantly lower relative risks compared with ISRT for lung, breast and thyroid. The median excess absolute risks of second cancers were consistently lowest for the residual technique and highest for IFRT in terms of thyroid, lung and breast cancers. The risk of oesophageal cancer was similar for all four techniques. Overall, the absolute risk of second cancers was very similar for ISRT and INRT. ConclusionsDecreasing treatment volumes from IFRT to ISRT, INRT or residual volume reduces radiation exposure to OARs. Second malignancy modelling suggests that this reduction in treatment volumes will lead to a reduction in absolute excess second malignancy. Little difference was observed in second malignancy risks between ISRT and INRT, supporting the use of ISRT in the absence of a pre-chemotherapy positron emission tomography scan in the radiotherapy treatment position.

Reducing interobserver variation of boost-CTV delineation in breast conserving radiation therapy using a pre-operative CT and delineation guidelines

AimsTo investigate whether using a pre-operative CT scan (Preop-CT) (1) decreases interobserver variation of boost-CTV delineation in breast conserving therapy (BCT), and (2) influences the size of the delineated volumes. Patients and methodsThirty cT1-2N0-1 breast cancer patients underwent a CT-scan in radiation treatment position, prior to and after lumpectomy. Five observers delineated a boost-CTV, both with and without access to the Preop-CT. For each patient and for each observer pair, the conformity index (CI) and the distance between the centres of mass (COMd) for both boost volumes were calculated. In addition, all delineated volumes including the standard deviation (SD) with respect to the median delineation were calculated. ResultsUsing a Preop-CT reduced the mean COMd of the boost-CTV from 1.1cm to 1.0cm (p<0.001). No effect was seen on the CI, but the boost-CTV volume reduced from 42cc to 36cc (p=0.005), implying a reduction of interobserver variation. We saw no significant change in the SD. ConclusionUse of a Preop-CT in BCT results in a modest but statistically significant reduction in interobserver variation of the boost-CTV delineations and in a significant reduction in the boost-CTV volume.

PET/CT aids the staging of and radiotherapy planning for early-stage extranodal natural killer/T-cell lymphoma, nasal type: A case series

Extranodal natural killer/T-cell lymphoma (ENKTL), nasal type, is a rare form of non-Hodgkin lymphoma. Treatment of ENKTL primarily relies on radiation; thus, proper delineation of target volumes is critical. Currently, the ideal modalities for delineation of gross tumor volume for ENKTL are unknown. We describe three consecutive cases of localized ENKTL that presented to the Nova Scotia Cancer Centre in Halifax, Nova Scotia. All patients had a planning CT and MRI as well as a planning FDG-PET/CT in the radiotherapy treatment position, wearing immobilization masks. All patients received radiation alone. In two patients, PET/CT changed not only the stage, but also the target volume requiring treatment. The third patient was unable to tolerate an MRI, but was able to undergo PET/CT, which improved the accuracy of the target volume. PET/CT aided the staging of and radiotherapy planning for our patients and appears to be a promising tool in the treatment of ENKTL.