J.R. Robbins

Interfractional Target Variations for Partial Breast Irradiation

PURPOSEnIn this work, we quantify the interfractional variations in the shape of the clinical target volume (CTV) by analyzing the daily CT data acquired during CT-guided partial breast irradiation (PBI) and compare the effectiveness of various repositioning alignment strategies considered to account for the variations.nnnMETHODS AND MATERIALSnThe daily CT data for 13 breast cancer patients treated with PBI in either prone (10 patients) or supine (3 patients) with daily kV CT guidance using CT on Rails (CTVision, Siemens, Malvern, PA) were analyzed. For approximately 25 points on the surface of the CTV, deformation vectors were calculated by means of deformable image registration and verified by visual inspection. These were used to calculate the distances along surface normals (DSN), which directly related to the required margin expansions for each point. The DSN values were determined for seven alignment methods based on volumetric imaging and also two-dimensional projections (portal imaging).nnnRESULTSnThe margin expansion necessary to cover 99% of all points for all days was 2.7 mm when utilizing the alignment method based on deformation field data (the best alignment method). The center-of-mass based alignment yielded slightly worse results (a margin of 4.0 mm), and shifts obtained by operator placement (7.9 mm), two-dimensional-based methods (7.0-10.1 mm), and skin marks (13.9 mm) required even larger margin expansions. Target shrinkage was evident for most days by the negative values of DSN. Even with the best alignment, the range of DSN values could be as high as 7 mm, resulting in a large amount of normal tissue irradiation, unless adaptive replanning is employed.nnnCONCLUSIONnThe appropriate alignment method is important to minimize the margin requirement to cover the significant interfractional target deformations observed during PBI. The amount of normal tissue unnecessarily irradiated is still not insignificant, and can be minimized if adaptive radiotherapy is applied.

Palliative interventions for hepatocellular carcinoma patients: Analysis of the National Cancer Database

BACKGROUNDnPalliative therapies are provided to a subset of hepatocellular carcinoma (HCC) patients with the aim of providing symptomatic relief, better quality of life and improved survival. The present study sought to assess and compare the efficacy of different palliative therapies for HCC.nnnMETHODSnThe National Cancer Database (NCDB), a retrospective national database that captures approximately 70% of all patients treated for cancer in the US, was queried for patients with HCC who were deemed unresectable from 1998-2011. Patients were stratified by receipt of palliative therapy. Survival analysis was examined by log-rank test and Kaplan Meier curves, and a multivariate proportional hazards model was utilized to identify the predictors of survival.nnnRESULTSnA total of 3,267 patients were identified; 287 (8.7%) received surgical palliation, 827 (25.3%) received radiotherapy (RT), 877 (26.8%) received chemotherapy, 1,067 (32.6%) received pain management therapy, while 209 (6.4%) received a combination of the previous three modalities. On multivariate analysis palliative RT was identified as a positive predictor of survival [hazards ratio (HR) 0.65; 95% CI, 0.50-0.83]. Stratifying by disease stage, palliative RT provided a significant survival benefit for patients with stage IV disease.nnnCONCLUSIONSnPalliative RT appears to extend survival and should be considered for patients presenting with late stage HCC.

Reducing radiation dose and enhancing imaging quality of 4DCT for radiation therapy using iterative reconstruction algorithms

Purpose Four-dimensional computed tomography (CT) images are typically used to quantify the necessary internal target volumes for thoracic and abdominal tumors. However, 4-dimensional CT is typically associated with excessive imaging dose to patients and the situation is exacerbated when using repeat 4-dimensional CT imaging on a weekly or daily basis throughout fractionated therapy. The aim of this work is to evaluate an iterative reconstruction (IR) algorithm that helps reduce the imaging dose to the patient while maintaining imaging quality as quantified by point spread function and contrast-to-noise ratios (CNRs). Methods and materials An IR algorithm, SAFIRE, was applied to CT data of a phantom and patients with varying CT doses and reconstruction kernels. Phantom data enable measurements of spatial resolution, contrast, and noise. The impact of SAFIRE on 4-dimensional CT was assessed with patient data acquired at 2 different dose levels during image guided radiation therapy with an in-room CT. Results Phantom data demonstrate that IR reduces noise approximately in proportion to the number of iterations indicated by the strength (SAFIRE 1 to SAFIRE 5). Spatial resolution and contrast are conserved independent of dose and reconstruction parameters. The CNR increases with an increase of imaging dose or an increase in the number of iterations. The use of IR on CT sets confirms the results that were derived from phantom scans. The IR significantly enhances single breathing phase CTs in 4-dimensional CT sets as assessed by CT number discrimination. Furthermore, the IR of the low dose 4-dimensional CT features a 45% increase in the CNR in comparison with the standard dose 4-dimensional CT. Conclusions The use of IR algorithms reduces noise while preserving spatial resolution and contrast, as evaluated from both phantom and patient CT data sets. For 4-dimensional CT, the IR can significantly improve image quality and reduce imaging dose without compromising image quality.

Technical Note: Enhancing soft tissue contrast and radiation‐induced image changes with dual‐energy CT for radiation therapy

PURPOSEnThe purpose of this work is to investigate the use of low-energy monoenergetic decompositions obtained from dual-energy CT (DECT) to enhance image contrast and the detection of radiation-induced changes of CT textures in pancreatic cancer.nnnMETHODSnThe DECT data acquired for 10 consecutive pancreatic cancer patients during routine nongated CT-guided radiation therapy (RT) using an in-room CT (Definition AS Open, Siemens Healthcare, Malvern, PA) were analyzed. With a sequential DE protocol, the scanner rapidly performs two helical acquisitions, the first at a tube voltage of 80 kVp and the second at a tube voltage of 140 kVp. Virtual monoenergetic images across a range of energies from 40 to 140 keV were reconstructed using an image-based material decomposition. Intravenous (IV) bolus-free contrast enhancement in pancreas patient tumors was measured across a spectrum of monoenergies. For treatment response assessment, the changes in CT histogram features (including mean CT number (MCTN), entropy, kurtosis) in pancreas tumors were measured during treatment. The results from the monoenergetic decompositions were compared to those obtained from the standard 120 kVp CT protocol for the same subjects.nnnRESULTSnData of monoenergetic decompositions of the 10 patients confirmed the expected enhancement of soft tissue contrast as the energy is decreased. The changes in the selected CT histogram features in the pancreas during RT delivery were amplified with the low-energy monoenergetic decompositions, as compared to the changes measured from the 120 kVp CTs. For the patients studied, the average reduction in the MCTN in pancreas from the first to the last (the 28th) treatment fraction was 4.09 HU for the standard 120 kVp and 11.15 HU for the 40 keV monoenergetic decomposition.nnnCONCLUSIONSnLow-energy monoenergetic decompositions from DECT substantially increase soft tissue contrast and increase the magnitude of radiation-induced changes in CT histogram textures during RT delivery for pancreatic cancer. Therefore, quantitative DECT may assist the detection of early RT response.

Early Prediction of Acute Xerostomia During Radiation Therapy for Head and Neck Cancer Based on Texture Analysis of Daily CT

PURPOSEnTo investigate radiation-induced changes of computed tomography (CT)xa0textures in parotid glands (PG) to predict acute xerostomia during radiotherapy (RT) for head and neck cancer (HNC).nnnMETHODS AND MATERIALSnDaily or fraction kilovoltage CTs acquired using diagnostic CT scanners (eg, in-room CTs) during intensity-modulated RT for 59 HNC patients at 3 institutions were analyzed. The PG contours were generated on selected daily/fraction CTs. A series of histogram-based texture features, including the mean CT number (MCTN) in Hounsfield units, volume, standard deviation, skewness, kurtosis, and entropy for PGs were calculated for each fraction. Correlations between the changes of the texture features, radiation dose, and observed acute xerostomia were analyzed. A classifier model and the incurred CT-based xerostomia score (CTXS) were introduced to predict xerostomia based on combined changes of MCTN and volume of PGs. The t test and Spearman and Pearson correlation tests were used in the analyses.nnnRESULTSnSubstantial changes in various CT texture features of PGs were observed during RT delivery. The changes of PG MCTN or volume are not strongly correlated with the observed xerostomia grades if they are considered separately. The CTXS showed a significant correlation to the observed xerostomia grades (rxa0=xa00.71, Pxa0<xa0.00001). The CTXS-based classifier can predict the xerostomia severity with a success rate ranging from 79% to 98%. The xerostomia severity at the end of treatment can be predicted based on the CTXS determined at the fifth week with a precision and sensitivity of 100%.nnnCONCLUSIONnSignificant changes in the CT histogram features of the parotid glands were observed during RT of HNC. A practical method of using the changes of MCTN and volume of PGs is proposed to predict radiation-induced acute xerostomia, which may be used to help design adaptive treatment.

Magnetic Resonance-based Response Assessment and Dose Adaptation in Human Papilloma Virus Positive Tumors of the Oropharynx treated with Radiotherapy (MR-ADAPTOR): An R-IDEAL stage 2a-2b/Bayesian phase II trial

Highlights • Treatment de-escalation in HPV+ oropharynx cancer is an active area of research.• A Bayesian phase II trial of MR-guided radiotherapy dose adaptation is proposed.• High dose volume will be adapted on weekly MRI based on tumor response.• The non-inferiority of dose adaptation compared to standard IMRT will be assessed.

Palliative care for hepatocellular carcinoma: Analysis of the National Cancer Data Base.

390 Background: Palliative care is provided to a subset of hepatocellular carcinoma (HCC) patients with the aim of symptomatic relief and improving quality of life. The present study sought to assess and compare the prevalence and efficacy of different palliative therapies for HCC from the National Cancer Database (NCDB). Methods: The NCDB, a retrospective national database that captures approximately 70% of all patients treated for cancer, was queried for patients with HCC who were deemed non-resectable from 1998-2011. Patients were stratified by receipt of palliative care. Descriptive analyses were performed. Survival analysis was examined by log-rank test and Kaplan Meier curves, and a multivariate proportional hazards model was utilized to identify the predictors of survival. Results: A total of 3,267 patients were identified; 287 (8.7%) received surgical palliation, 827 (25.3%) received radiotherapy, 877 (26.8%) received chemotherapy, 1,067 (32.6%) received pain therapy, while 209 (6.4%) received a c...

SU‐FF‐J‐83: Interfractional Geometric and Dosimetric Variations in Prone Breast Irradiation

Purpose: To quantitatively evaluate interfractional variations in treatment setup and their dosimetric effects, in prone breast irradiation based on daily kVCT acquired during IGRT.Materials/Methods: In‐house study enrolling patients with prone breast irradiation to be treated on linac and CT‐on‐Rails combination (CTVision, Siemens) is on going. Patients with surgical clips placed in the lumpectomy cavity who fit through standard bore CT with field of view sufficient to image the whole treated breast are selected. Patients were setup prone with shifts made from a PA set up point to the isocenter. Registration was adjusted manually to achieve visual agreement between the daily and planning CTs using the cavity in conjunction with surgical clips. Daily CT data and repositioning shifts acquired for 15 patients were analyzed. Dose plan delivered with CT guidance (IGRT plan) for each treatment was reconstructed in the planning system (Xio, CMS) by placing the original beams on CT of the day with the corresponding shifts. In addition, the dosimetric plan with the patient shifts based on 2D portal images (non‐IGRT plan), as conventionally practiced, was reconstructed. Dose‐Volume‐Histograms (DVH) for PTV and organs‐at‐risk (OAR) for the IGRT, non‐IGRT and original plans were compared. Results: The daily shifts are patient dependent. Comparison of variations of D95 and D50 values shows higher interfractional variability for non‐IGRT plan. Average D95 was 1–2% lower for non‐IGRT plans than IGRT plans, with some fractions receiving as low as 91% of planned dose. IGRT plans showed improvement with minimum D95 of 95% of planned D95. Effect of the repositioning on the OAR DVH is patient specific and depends on the location of the cavity.Conclusion: The interfractional variations in patient setup and anatomic changes, and their dosimetric impact, in prone breast irradiation are significant, and can be reduced with IGRT based on kV fan‐beam CT.