High-risk Clinical Tumor Volume Research Articles

Dosimetric Comparison of Inverse Planning Simulated Annealing and Manual Optimization for Intracavitary Cervix Brachytherapy

Background/Aims: Different optimization methods in brachytherapy treatment planning is used. The aim of this study is to evaluate dosimetric differences between manual optimization (MO) and inverse planning simulated annealing (IPSA) planning techniques commonly used in brachytherapy of cervical cancer. Methods: Fifteen cervical cancer patients were included in this study. Nucletron standard tandem-ovoid (TO) applicators were used for treatment. High-risk clinical tumor volume (HR-CTV), bladder, rectum, and sigmoid contouring were performed according to GEC-ESTRO recommendations. Two plans were created for each patient using IPSA and MO techniques. While a dose of 700 cGy was prescribed to the target volume during the planning phase, an effort was made to protect the organs at risk in the best way possible. IPSA and MO planning techniques were compared via dose volume histogram (DVH). Results: There was no significant difference between HR-CTV and CI values for MO and IPSA techniques. There was a significant difference between IPSA and MO techniques for the 2cm3 volume of the rectum (p= 0.002). It was observed that the bladder was better protected by the IPSA technique. There was a 6.26% dose difference between IPSA and MO for the bladder. A significant difference was found between IPSA and MO techniques for the 2cm3 volume of the sigmoid (p= 0.002). The IPSA technique was superior to the MO technique in terms of time. Conclusions: The IPSA technique was superior to the MO technique in terms of protecting organs at risk (OARs). IPSA provides a faster and higher quality plan in cervical brachytherapy.

Dosimetric Benefits of Online Adaptive Radiotherapy in Nasopharyngeal Carcinoma

Online adaptive radiotherapy (ART) has the advantage of compensating for potential underdosing to targets and overdosing to organs-at-risk (OARs) caused by variations in patient anatomy and tumor geometry. Artificial intelligence (AI)-assisted rapid generation of new plans makes online ART possible. We aimed to evaluate the dosimetric benefits of online ART on tumor coverage and OARs sparing in nasopharyngeal carcinoma (NPC). Twenty patients diagnosed with NPC (19 with stage III and 1 with stage II according to the 8th edition of the AJCC/UICC staging system) who underwent definitive radiotherapy or concurrent chemoradiotherapy and received online ART on CT-Linac between April 2022 and December 2022 were included in this study, consisting of 14 males and 6 females with a median age of 48 years (range: 29-68 years). The prescription dose was 6996 cGy/33 fractions for primary gross tumor volume (GTVp), 6600-6996 cGy/33 fractions for gross tumor volume of nodes (GTVn), 6006 cGy/33 fractions for high-risk clinical tumor volume (CTV1), 5412 cGy/33 fractions for low-risk clinical tumor volume (CTV2). The majority of the patients (15/20) received online ART during the fourth to fifth week of their radiotherapy treatment The auto-segmented contours and auto-plan generated by AI were manually reviewed and edited by radiotherapists and physicists. The paired samples t-test was used to compare the dose and volumes metrics of targets and OARs between scheduled plan and online ART plan. The results of this study showed that compared to the scheduled plan, the online ART plan resulted in significant reductions in the volumes of all targets and 8/12 OARs (temporal lobes, optic nerves, lenses, eyes, parotids, submandibulars, mandibles, and thyroid) (P<0.05). The online ART plan also improved target coverage, with D98% for GTVp in the scheduled plan compared to the online ART plan being 7063.4 ± 76.1 cGy and 7096.1 ± 53.9 cGy (P = 0.1), CTV1 being 6266.7 ± 114.9 cGy and 6208.7 ± 54.7 cGy (P<0.05), and CTV2 being 4142.5 ± 1700.9 cGy and 5416.4 ± 23.8 cGy (P<0.01), respectively. The dose to all 12 OARs was reduced with the use of online ART, with 5/12 OARs showing statistical significance. The D0.03cm3 for the spinal cord in the scheduled plan and online ART plan were 3630.9 ± 197.6 and 3454.1 ± 132.0 cGy; for the temporal lobes were 7075.2 ± 303.0 and 6994.2 ± 345.1 cGy; and 4396.0 ± 2575.0 and for the pituitary were 4214.5 ± 2499.2 cGy. Meanwhile the Dmean for the eyes in the scheduled plan and online ART plan was 769.0 ± 232.0 and 714.8 ± 200.1 cGy; and for the mandibles were 3187.7 ± 211.5 and 3066.0 ± 152.1 cGy. Online ART was effective in protecting most of the OARs in NPC patients, while simultaneously indicating a trend towards enhancing target coverage. This study demonstrated the promising potential of online ART for patients with NPC. This approach will be tested in an upcoming phase III trial.

Pre-Radiation CT-Based Radiomic Features Predict Locoregional and Distant Failure in Locally Advanced Head and Neck Cancer

<h3>Purpose/Objective(s)</h3> Locally advanced head and neck cancer treatment often involves aggressive multimodal therapy. While outcomes have improved in certain groups (HPV-positive disease), locoregional (LRF) and distant failure (DF) remain persistent problems. Accurate prediction of these risks would provide vital clinical insight; for instance, a patient with low LRF risk could be de-escalated, while a patient at high-risk for DF could be offered systemic options in lieu of aggressive local therapy. In this study we explore the use of CT-based radiomic features (quantitative sub-visual cues) for this purpose. <h3>Materials/Methods</h3> We identified patients with primary or recurrent locally advanced head/neck cancer treated between 2014-2020 who received a definitive or adjuvant RT course (naïve to RT prior). Histologies included squamous cell carcinoma (SCC), poorly differentiated carcinoma (nasopharyngeal or salivary origin), high-risk parotid malignancies, and skin SCC metastatic to the parotid/neck. Patients had at least 12 months of follow-up and charts were assessed for LRF and DF. CT simulation images were extracted from our treatment planning system, and specific contoured regions of interest (ROIs) were selected including the peritumoral region or post-surgical tumor bed (high-risk clinical tumor volume, CTV HR) and involved/elective neck levels (CTV Necks). CT scans were resampled to be isotropic and 3D radiomic features (Gabor wavelet, Hara lick, and CoLlAGe) were extracted from within CTV HR and CTV Necks ROIs. Using a Wilcoxon rank sum test, differential expression for each feature was calculated between patients experiencing treatment failure (LRF and DF) and those with no evidence of disease progression. A similar process was done with baseline clinical features including performance status, tumor stage, age, p16 status and smoking history. Where required, a chi-squared test was used for categorical clinical variables. <h3>Results</h3> 95 patients were analyzed (45 definitive, 50 adjuvant). There were 17 LRF (17.9%) and 16 DF (16.8%) events. 304 radiomic features were extracted from CTV HR and CTV Necks (the latter was only performed for patients with bilateral neck contours). 2 features extracted from CTV HR ROIs were significantly associated with LRF and 29 features with DF (p < 0.05). 30 features extracted from CTV Necks ROIs were significantly associated with LRF and 0 features with DF (p < 0.05). There were no statistically significant clinical features associated with LRF or DF. <h3>Conclusion</h3> CT-based radiomic features derived from specific ROIs in simulation images were associated with both LRF and DF events, which was not the case for canonical clinical features. Interestingly, the CTV HR was more prominently associated with DF, whereas the CTV Necks was associated with LRF. Further studies with larger, more diverse datasets are needed to refine this model and provide a path for clinical validation.

A deep learning-based self-adapting ensemble method for segmentation in gynecological brachytherapy

PurposeFast and accurate outlining of the organs at risk (OARs) and high-risk clinical tumor volume (HRCTV) is especially important in high-dose-rate brachytherapy due to the highly time-intensive online treatment planning process and the high dose gradient around the HRCTV. This study aims to apply a self-configured ensemble method for fast and reproducible auto-segmentation of OARs and HRCTVs in gynecological cancer.Materials and methodsWe applied nnU-Net (no new U-Net), an automatically adapted deep convolutional neural network based on U-Net, to segment the bladder, rectum and HRCTV on CT images in gynecological cancer. In nnU-Net, three architectures, including 2D U-Net, 3D U-Net and 3D-Cascade U-Net, were trained and finally ensembled. 207 cases were randomly chosen for training, and 30 for testing. Quantitative evaluation used well-established image segmentation metrics, including dice similarity coefficient (DSC), 95% Hausdorff distance (HD95%), and average surface distance (ASD). Qualitative analysis of automated segmentation results was performed visually by two radiation oncologists. The dosimetric evaluation was performed by comparing the dose-volume parameters of both predicted segmentation and human contouring.ResultsnnU-Net obtained high qualitative and quantitative segmentation accuracy on the test dataset and performed better than previously reported methods in bladder and rectum segmentation. In quantitative evaluation, 3D-Cascade achieved the best performance in the bladder (DSC: 0.936 ± 0.051, HD95%: 3.503 ± 1.956, ASD: 0.944 ± 0.503), rectum (DSC: 0.831 ± 0.074, HD95%: 7.579 ± 5.857, ASD: 3.6 ± 3.485), and HRCTV (DSC: 0.836 ± 0.07, HD95%: 7.42 ± 5.023, ASD: 2.094 ± 1.311). According to the qualitative evaluation, over 76% of the test data set had no or minor visually detectable errors in segmentation.ConclusionThis work showed nnU-Net’s superiority in segmenting OARs and HRCTV in gynecological brachytherapy cases in our center, among which 3D-Cascade shows the highest accuracy in segmentation across different applicators and patient anatomy.

A prospective comparative dosimetric study between diffusion weighted MRI (DWI) & T2-weighted MRI (T2W) for target delineation and planning in cervical cancer brachytherapy.

To evaluate the difference between GTVBT (Gross Tumor Volume at Brachytherapy) and HR CTV (High Risk Clinical Tumor Volume) delineated with DWI and T2W MRI. To evaluate doses to organs at risk and targets from plans generated using T2W and DWI. Functional imaging with DWI can improve cervical tumor distinction as it is more sensitive than T2W MRI even in detecting parametrial invasion. This study does a dosimetric comparison between a T2W and DWI based plan. Fifty carcinoma cervix patients were subjected to MRI based brachytherapy. T2W and a diffusion weighted sequence were acquired. Target delineation and brachytherapy planning was done on both T2W and DWI. Standard DVH parameters were recorded and the treatment was given using the plan generated from T2W images. GTVBT and HRCTV contours on DWI were different when compared with T2W. Mean GTVBT volume on T2W and DWI was 5.25 and 5.23, respectively (p value 0.8). Mean HRCTV on T2W and DWI was 28.3 and 27 cc, respectively (p value 0.003). Planning on the above volumes resulted in a superior coverage in terms of HRCTV D90 and D100 for DWI based plan, HRCTV D90 - 735.1 and 741 cGy for T2W and DWI, respectively (p value 0.006), HRCTV D100 - 441.05 and 444.5 for T2W and DWI plans, respectively (p value = 0.006). Doses to the OAR were not significantly increased. GEC ESTRO based contouring guidelines cover all the functionally abnormal areas on DWI. DWI should only be used as a supplement to T2W for contouring target volumes.

Local Control and Overall Survival of Patients with Stage IIB–IVA Cervical Cancer after Definitive External Beam Chemoradiation and High-Dose-Rate Cobalt-60 Intracavitary Brachytherapy

The present study aimed to assess the local control and overall survival of patients with stage IIB–IVA cervical cancer after definitive external beam chemoradiation and high-dose-rate miniaturized Cobalt-60 (Co-60) intracavitary BT. This was a cross-sectional study that prospectively enrolled patients with cervical squamous cell carcinoma referred for BT as a part of their definitive treatment to Reza Radiotherapy & Oncology Center of Mashhad, Razavi Khorasan, Iran, between 2017 and 2018. The optimal dose of treatment was determined, and survival analysis was performed using the log-rank test at the level of p ≤ 0.05. A total of 65 patients were enrolled, and most of them had stage IIB (76.9%). With a median follow-up of 18 months, the 6-, 12-, 18-, and 24-month overall survival was 98%, 86%, 75%, and 50%, respectively. The optimal cutoff dose of high-risk clinical target volume (HR-CTV) was 85.06 gray (Gy). There was a trend in the reduction of survival in patients with higher stages and receiving lower doses to tumor; however, the results were not significant. Based on the results of this study, a minimum total dose of 85 Gy to high-risk clinical tumor volume is essential to achieve an optimal local control.

Long-term results of 3-D brachytherapy treatment in locally advanced cervical cancer

In many advanced studies, image-guided 3D brachytherapy (BT) treatment has been shown to improve survival and reduce treatment-related toxicity in locally advanced cervical cancer. In this study, long-term treatment results, risky organ doses and toxicity results of patients who were admitted to our clinic with the diagnosis of cervical cancer and treated with 3D brachytherapy were examined. Between 2012 and 2015, 152 inoperable cervical cancers were admitted, and long-term (> 12 months) follow-up of our clinic107 cases of inoperable cervical cancer was included in the study. After pelvic radiotherapy, pelvic MRI was performed, and target volumes were determined on CT. Volumes defined by the GEC-ESTRO guideline were, Gross tumor volume (GTV); residual tumor volume after external RT, High-risk clinical tumor volume (HRCTV); entire cervix and residual lesion, Intermediate-risk clinical tumor volume (IRCTV) low-risk volume and rectum, sigmoid and bladder contouring as risky organs, respectively. 3D brachytherapy treatment was performed with the microselectron device of 192 high-dose-rate (HDR) Ir 192 source. The median age was 53 years, and the median follow-up was 45 months. All patients were diagnosed by biopsy, and 81.9% of these patients were diagnosed as squamous cell carcinoma. According to the stages;IB1 was 2 (2%), II was 65 (61%), III was 31 (29%), and IV was 9 (8%). 96% of the patients received cisplatin-based chemotherapy with pelvic 3 D RT. When 3D RT doses of all patients were examined; Median HRCTV was calculated as 90% 6 Gy, EQD2 value 84.7 Gy, IRCTV 95% 3.03 Gy. When we look at risky organ doses; The median rectum 2cc 2.4Gy, EQD2 58.4Gy value, median bladder 2cc 3.52Gy, EQD2 value was 68.8 Gy, median sigmoid 2cc 2.60 Gy, EQD2 value was found to be 60.3 Gy. During the follow-up period, 4 patients had local recurrence, 11 patients had both local and distant metastasis, and 21 patients had only distant metastasis. The overall survival rate of 3 and 5 years was 78.1% and 72.2%. The 3 and 5-year local control rates were 87.4% and 77.3%, respectively. The survival rates of 3 and 5 years without distant metastasis were 66.5% and 61.2%. Rectovaginal fistula developed in 5 patients as late side effects and tumor progression was found in three of these patients. In the treatment of locally advanced cervical cancer 3D BRT, the volumes defined by the GEC-ESTRO guidance are individual. Thanks to the development of imaging techniques during the treatment of these volumes, the survival rates have increased compared to the previous series, and a shallow rate of GIS and GUS side effects are observed.

Dosimetric effects of the Smit sleeve on high-dose-rate brachytherapy tandem and ovoids plans for patients with locally advanced cervical cancer.

PurposeSmit sleeves are used to facilitate insertion of the intrauterine tandem during brachytherapy for cervical cancer. When a tandem and ovoids system is used the base of the Smit sleeve displaces the ovoids distally. The dosimetric impact of this displacement is not known. Herein we performed a dosimetric analysis to quantify this impact on the integral dose and dose delivered to the organs at risk (OARs).Material and methodsEleven high-dose-rate brachytherapy plans in which a Smit sleeve was used with a tandem and ovoids were reviewed. A second set of plans was generated modifying the position of the ovoids to simulate absence of the Smit sleeve. The high-risk clinical tumor volume (HR-CTV) dose coverage was maintained the same for both sets of plans by appropriately rescaling the dwell times of the simulated plan. The mean integral dose, D2cc to the OARs (bladder, bowel, sigmoid and rectum) and the ICRU rectum point dose were compared between the original and modified plans using a paired two-sample t-test.ResultsSimulating removal of the Smit sleeve was associated with an average reduction in the mean integral dose of 6.1% (p < 0.001) and an average reduction of 10.9% (p = 0.004) to the rectal D2cc. Doses to the remaining OARs decreased to a lesser magnitude with only that of the sigmoid being statistically significant.ConclusionsThe use of a Smit sleeve with a tandem and ovoids system could lead to the delivery of a higher mean integral dose to achieve similar HR-CTV coverage. In addition, it could increase the dose to surrounding OARs, primarily the rectum. The clinical significance of these findings is unknown, but the potential dosimetric impact of using a Smit sleeve should be taken into consideration during the planning when this device is used.

Primary Tumor Extension Probability-based Prediction of Individualized Clinical Target Volume for Nasopharyngeal Carcinoma

To establish a primary tumor extension probability knowledge base and develop a probability-based clinical tumor volume (CTV) prediction model for nasopharyngeal carcinoma (NPC). One thousand patients with newly histologically confirmed, non-disseminated NPC between January 2010 and December 2011 were included in this study. For all patients, primary gross tumor volumes (GTVp) displayed on pre-treatment magnetic resonance (MR) images were manually superimposed onto a single computed tomography (CT) scan. Tumor extension probability of each CT voxel was calculated to form a knowledge base. Then association rules mining algorithm was implemented to develop a probability-based CTV prediction model. One hundred cases were randomly selected from the patient cohort to evaluate similarity and variance between predicted CTV and expert delineation, which were manually completed by 2 radiation oncologists by consensus. Similarity was evaluated using Dice similarity coefficient (DSC), and variance using mean distances from GTVp to CTV in anterior, posterior, lateral, superior and inferior directions. Five multicenter radiation oncologists and another randomly selected 16 cases were included in a multicenter setting to evaluate the similarity between edited predicted CTV and expert delineation against that between manual delineation and expert delineation. Besides, inter-observer variance of 5 oncologists’ delineation was assessed using multi-observer DSC, and time spent on manual delineation and in editing predicted CTV were also reported. For 1000 patients, 58 developed local recurrence after median follow up of 67.3 months, and all recurrences were in-field or marginal. Probability heat map and equiprobability contours were generated to demonstrate the tumor extension probability. Based on proposed prediction model, CTV10% and CTV5% were defined to encompass corresponding subclinical disease. For 100 cases, mean DSC between predicted CTV and expert delineation were 0.89 ± 0.031 and 0.90 ± 0.020 for high-risk and low-risk CTV, indicating high similarity. Distances from GTV to predicted CTV were comparable to or slightly smaller than that to expert delineation in most directions. In multicenter evaluation, with assistance of predicted CTV, increased delineation accuracy was observed in all 5 oncologists, with mean DSC increased from 0.85 to 0.91 for high risk CTV and 0.87 to 0.93 for low risk CTV (P < 0.001 for 5 oncologists). Moreover, mean multi-observer DSC increased from 0.73 to 0.80 for high risk CTV, and 0.78 to 0.83 for low risk CTV (both P < 0.001) and average time spent on CTV delineation decreased from 30.3 to 14.9 min (P < 0.001). The probability-based predicted CTV was comparable to experienced expert delineation and might be enough for treating NPC. Predicted CTV significantly improved delineation accuracy in less experienced radiation oncologist and reduced inter-observer variance and time spent on CTV delineation.

Advantage of PET/CT in Target Delineation of MRI-negative Cervical Lymph Nodes In Intensity-Modulated Radiation Therapy Planning for Nasopharyngeal Carcinoma.

Introduction: In intensity-modulated radiation therapy (IMRT) planning for nasopharyngeal carcinoma (NPC), cervical lymph nodes (CLNs) that appear negative on magnetic resonance imaging (MRI) scans can be difficult to target. The purpose of this study was to assess the advantage of 18F-fluorodeoxyglucose positron emission tomography with computed tomography (18F-FDG PET/CT) for distinguishing MRI-negative CLNs and the effect of 18F-FDG PET/CT on diagnosis, target delineation, and dose prescription in IMRT planning for NPC.Methods: Thirty-five NPC patients with 37 MRI-negative CLNs underwent 18F-FDG PET/CT imaging before treatment. Ultrasonography-guided fine-needle aspiration cytology (USgFNAC) was performed to examine the pathology of CLNs. The 18F-FDG PET/CT and cytopathological results were compared, and the diagnostic accuracy of 18F-FDG PET/CT was calculated. The cytopathologically confirmed CLNs were delineated and treated as the gross tumor volume of lymph nodes (denoted as GTVnd).Results: Nineteen of the 37 MRI-negative CLNs were positive on 18F-FDG PET/CT, and metastasis was confirmed by USgFNAC in 16 CLNs. Of the remaining 18 18F-FDG PET/CT-negative lymph nodes, metastasis was confirmed in one. The diagnostic accuracy, sensitivity, and specificity of 18F-FDG PET/CT were 89.2%, 94.1%, and 85.0%, respectively. The positive and negative predictive values were 84.2% and 94.4%, respectively. With a median follow-up of 48.3 months, no relapse was observed among the 18F-FDG PET/CT-positive CLNs with metastasis confirmed by USgFNAC and treated as GTVnd.Conclusion: 18F-FDG PET/CT had high accuracy, sensitivity, and specificity for distinguishing MRI-negative CLNs. 18F-FDG PET/CT-positive CLNs could reasonably be categorized as high-risk clinical tumor volume in IMRT planning for NPC.

SU‐F‐T‐37: Dosimetric Evaluation of Planned Versus Decay Corrected Treatment Plans for the Treatment of Tandem‐Based Cervical HDR Brachytherapy

Purpose:This study evaluated dosimetric parameters for actual treatment plans versus decay corrected treatment plans for cervical HDR brachytherapy.Methods:125 plans of 25 patients, who received 5 fractions of HDR brachytherapy, were evaluated in this study. Dose was prescribed to point A (ICRU‐38) and High risk clinical tumor volume (HR‐CTV) and organs at risk (OAR) were, retrospectively, delineated on original CT images by treating physician. First HDR plan was considered as reference plan and decay correction was applied to calculate treatment time for subsequent fractions, and was applied, retrospectively, to determine point A, HR‐CTV D90, and rectum and bladder doses.Results:The differences between mean point A reference doses and the point A doses of the plans computed using decay times were found to be 1.05%±0.74% (−2.26% to 3.26%) for second fraction; −0.25%±0.84% (−3.03% to 3.29%) for third fraction; 0.04%±0.70% (−2.68% to 2.56%) for fourth fraction and 0.30%±0.81% (−3.93% to 2.67%) for fifth fraction. Overall mean point A dose difference, for all fractions, was 0.29%±0.38% (within ± 5%). Mean rectum and bladder dose differences were calculated to be −3.46%±0.12% and −2.47%±0.09%, for points, respectively, and −1.72%±0.09% and −0.96%±0.06%, for D2cc, respectively. HR‐CTV D90 mean dose difference was found to be −1.67% ± 0.11%. There was no statistically significant difference between the reference planned point A doses and that calculated using decay time to the subsequent fractions (p&lt;0.05).Conclusion:This study reveals that a decay corrected treatment will provide comparable dosimetric results and can be utilized for subsequent fractions of cervical HDR brachytherapy instead of actual treatment planning. This approach will increase efficiency, decrease workload, reduce patient observation time between applicator insertion and treatment delivery. This would be particularly useful for institutions with limited resources or large patient populations with limited access to care.

SU‐C‐202‐02: A Comprehensive Evaluation of Adaptive Daily Planning for Cervical Cancer HDR Brachytherapy

Purpose:To evaluate adaptive daily planning for cervical cancer patients who underwent high‐dose‐rate intra‐cavitary brachytherapy (HDR‐ICBT).Methods:This study included 22 cervical cancer patients who underwent 5 fractions of HDR ICBT. Regions of interest (ROIs) including high‐risk clinical tumor volume (HR‐CTV) and organs‐at‐risk (OARs) were manually contoured on daily CT images. All patients were treated with adaptive daily plans, which involved ROI delineation and dose optimization at each treatment fraction. Single treatment plans were retrospectively generated by applying the first treatment fraction's dwell times adjusted for decay and dwell positions of the applicator to subsequent treatment fractions. Various existing similarity metrics were calculated for the ROIs to quantify interfractional organ variations. A novel similarity score (JRARM) was established, which combined both volumetric overlap metrics (DSC, JSC, and RVD) and distance metrics (ASD, MSD, and RMSD). Linear regression was performed to determine a relationship between inter‐fractional organ variations of various similarity metrics and D2cc variations from both plans. Wilcoxon Signed Rank Tests were used to assess adaptive daily plans and single plans by comparing EQD2 D2cc (α/β=3) for OARs.Results:For inter‐fractional organ variations, the sigmoid demonstrated the greatest variations based on the JRARM and DSC similarity metrics. Comparisons between paired ROIs showed differences in JRARM scores and DSCs at each treatment fraction. RVD, MSD, and RMSD were found to be significantly correlated to D2cc variations for bladder and sigmoid. The comparison between plans found that adaptive daily planning provided lower EQD2 D2cc of OARs than single planning, specifically for the sigmoid (p=0.015).Conclusion:Substantial inter‐fractional organ motion can occur during HDR‐BT, which may significantly affect D2cc of OARs. Adaptive daily planning provides improved dose sparing for OARs compared to single planning.

Outcome Assessment of Dose Adaptation of MRI-Guided Cervical Cancer Brachytherapy

Outcome Assessment of Dose Adaptation of MRI-Guided Cervical Cancer Brachytherapy

Dynamic rotating‐shield brachytherapy

To present dynamic rotating shield brachytherapy (D-RSBT), a novel form of high-dose-rate brachytherapy (HDR-BT) with electronic brachytherapy source, where the radiation shield is capable of changing emission angles during the radiation delivery process. A D-RSBT system uses two layers of independently rotating tungsten alloy shields, each with a 180° azimuthal emission angle. The D-RSBT planning is separated into two stages: anchor plan optimization and optimal sequencing. In the anchor plan optimization, anchor plans are generated by maximizing the D90 for the high-risk clinical-tumor-volume (HR-CTV) assuming a fixed azimuthal emission angle of 11.25°. In the optimal sequencing, treatment plans that most closely approximate the anchor plans under the delivery-time constraint will be efficiently computed. Treatment plans for five cervical cancer patients were generated for D-RSBT, single-shield RSBT (S-RSBT), and (192)Ir-based intracavitary brachytherapy with supplementary interstitial brachytherapy (IS + ICBT) assuming five treatment fractions. External beam radiotherapy doses of 45 Gy in 25 fractions of 1.8 Gy each were accounted for. The high-risk clinical target volume (HR-CTV) doses were escalated such that the D2cc of the rectum, sigmoid colon, or bladder reached its tolerance equivalent dose in 2 Gy fractions (EQD2 with α∕β = 3 Gy) of 75 Gy, 75 Gy, or 90 Gy, respectively. For the patients considered, IS + ICBT had an average total dwell time of 5.7 minutes∕fraction (min∕fx) assuming a 10 Ci(192)Ir source, and the average HR-CTV D90 was 78.9 Gy. In order to match the HR-CTV D90 of IS + ICBT, D-RSBT required an average of 10.1 min∕fx more delivery time, and S-RSBT required 6.7 min∕fx more. If an additional 20 min∕fx of delivery time is allowed beyond that of the IS + ICBT case, D-RSBT and S-RSBT increased the HR-CTV D90 above IS + ICBT by an average of 16.3 Gy and 9.1 Gy, respectively. For cervical cancer patients, D-RSBT can boost HR-CTV D90 over IS + ICBT and S-RSBT without violating the tolerance doses to the bladder, rectum, or sigmoid. The D90 improvements from D-RSBT depend on the patient, the delivery time budget, and the applicator structure.

Intensity-Modulated Radiation Therapy Without Concurrent Chemotherapy for Stage IIB Nasopharyngeal Cancer

To evaluate the treatment outcome of patients with stage IIB nasopharyngeal carcinoma (NPC) after definitive intensity-modulated radiotherapy (IMRT) without concurrent chemotherapy. Between August 2003 and December 2006, 107 patients with T1N1M0 (8%), T2N0M0 (13%), or T2N1M0 (79%) NPC were definitively treated with IMRT. Sixty-one received IMRT only, and 46 patients had various strategies of systemic treatment, consisting of abbreviated neoadjuvant (38 patients), concurrent (8 patients), or adjuvant (16 patients) chemotherapy. Radiation doses prescribed to the planning tumor volume of the gross disease, high-risk clinical tumor volume, and low-risk clinical tumor volume were 66 to 70 Gy, 54 to 60 Gy, and 50-54 Gy, respectively. With a median follow-up of 39 months (range, 7-77 months), 6 patients had locoregional relapse: 1 local only, 1 locoregional, and 4 regional only. Five patients had distant failure. Five of 6 total deaths were cancer related. The 3-year estimated local control, regional control, metastasis-free survival, disease-free survival, and overall survival were 96.5%, 98%, 94.8%, 90.7%, and 95.8%, respectively. No significant difference in treatment outcome was demonstrated in patients treated with or without chemotherapy of any schedule. IMRT without concurrent chemotherapy provides good outcome for patients with stage IIB NPC with acceptable toxicity. Neoadjuvant chemotherapy did not appear to provide significant additional benefit for this patient subgroup. Further investigation in the prospective setting is warranted to explore the role of systemic agents in the treatment of NPC with limited primary disease and cervical lymphadenopathy when IMRT is used.

Intensity‐modulated chemoradiation for treatment of stage III and IV oropharyngeal carcinoma

Treatment outcomes for stage III and IV oropharyngeal carcinoma treated with intensity-modulated radiotherapy (IMRT) and concurrent chemotherapy without prior surgical resection were reviewed. Between April 2000 and September 2004, 71 patients underwent IMRT concurrent with chemotherapy without prior surgical resection for stage III and IV oropharyngeal carcinoma. Chemotherapy was platinum based. The gross tumor volume (GTV) received 70 Gy in 2.12 Gy per fraction. The high-risk clinical tumor volume (CTV) received 59.4 Gy in 1.80 Gy per fraction, and the low-risk CTV received 54 Gy in 1.64 Gy per fraction. With a median follow-up of 33 months, the 3-year local, regional, and locoregional progression-free probabilities were 94%, 94%, and 90%, respectively. The 3-year overall survival estimate was 83%. Locoregional failures occurred in the GTV in 7 patients. Acute grade 3 or 4 toxicity developed in 35 patients. A feeding gastrostomy was placed in 25 patients. Late xerostomia was grade 0 in 16 patients, grade 1 in 31 patients, and grade 2 in 24 patients at last follow-up. No patients experienced grade 3 or 4 late toxicity, except for 1 who developed osteoradionecrosis of the mandible. Excellent local and regional control was achieved with IMRT and concurrent chemotherapy without prior surgical resection in the treatment of stage III and IV oropharyngeal carcinoma. Significant sparing of the parotid glands and other critical normal tissues was possible using IMRT with moderate acute toxicities and minimal severe late effects.

Gabapentin for the treatment of pain related to radiation-induced mucositis in patients with head and neck cancers treated with intensity modulated radiation therapy (IMRT)

16513 Background: Gabapentin has been reported to effectively treat multiple neuropathic pain syndromes. This retrospective study evaluates the efficacy of gabapentin for the treatment of pain related to radiation induced mucositis, in patients with head and neck cancers, treated with radiation therapy (RT). Methods: This retrospective study includes 30 pts with head and neck cancers, treated with RT, without concomitant or induction chemotherapy. IMRT planning was performed using a concomitant boost technique with a median dose of 54 Gy, 63 Gy, and 66 Gy delivered to the low risk clinical tumor volume (CTV), high risk CTV and boost target volume, respectively, using 30- 34 fractions. The dose of gabapentin was gradually increased starting on the second week of RT from 600 mg/day to the dose of 2700 mg/d over the course of one week. Narcotic pain medication (Roxicodone) was prescribed as needed. Results: 26 (86%) pts required no pain medication during the first two weeks of RT, despite the presence of grade 1 and/or 2 mucositis in 24 of them. During the third and fourth weeks of RT, 28 (93%) pts were treated with a median dose of 2700 mg/day of gabapentin, with only 3 (10%) pts requiring low dose narcotic pain medication, 15–30 mg/day of Roxicodone, added to gabapentin for adequate pain control, despite grade 2 or higher mucositis in 22 pts. During weeks 5 and 6, 28 (93%) pts continued to be treated with a median dose of 2700 mg/day of gabapentin with only 10 (35%) pts requiring 15–40 mg/day of Roxicodone, in addition to gabapentin for pain control, despite the presence of grade 2 or higher mucositis in 23 pts. Only 3% of the pts in this group had delay in RT delivery. Gabapentin was well tolerated with only 13% of pts experiencing mild side effects (somnolence, nausea, or vomiting), which were managed with reducing the dose or changing the dosing schedule. Conclusions: Gabapentin is effective and well-tolerated for the treatment of mucositis-induced pain related to radiation treatment in patients with head and neck cancers, treated with IMRT. We further demonstrate that the use of gabapentin at doses of 2700 mg per day can reduce or eliminate the need for narcotic pain medication. No significant financial relationships to disclose.