Anneyuko I. Saito

Cine-magnetic resonance imaging assessment of intrafraction motion for prostate cancer patients supine or prone with and without a rectal balloon.

Purpose:Determine prostate intrafraction motion with Cine-magnetic resonance imaging (MRI) and deformable registration. Methods:A total of 68 cine-MRI studies were done in 17 different series with 4 scans per series in 7 patients. In without rectal balloon (WORB) scans, 100 mL of water was infused in the rectum. Each series consisted of supine and prone, with a rectal balloon (WRB) and WORB. Each scan was performed over 4 minutes. Automatic deformable registration software developed by View Ray, Inc., Cleveland, Ohio was employed to segment the prostate for each cine-MRI image. A time-based analysis was done for the different positions and the use of the rectal balloon. Results:The variation/standard deviation of the prostate position during 240 seconds was: supine WRB: 0.55 mm, WORB: 1.2 mm, and prone WRB: 1.48 mm, WORB: 2.15 mm (P < 0.001). A strong relationship was observed between time and prostate motion. For the initial 120 s the standard deviation was smaller than for the second 120 s supine WRB 0.54 mm versus 1.37 mm; supine WORB 0.61 mm versus 1.70 mm; prone WRB 0.85 mm versus 1.85 mm; and prone WORB 1.60 mm versus 2.56 mm. The probabilities for prostate staying within ±2 mm to its initial position are: 94.8% supine WRB; 91.5% supine WORB; 92.3% prone WRB; 79.2% prone WORB. Conclusions:Intrafraction prostate motion was found dependent on time, patient position, and the use of a rectal balloon. Relatively stable positions can be obtained for 4 minutes or less especially in the supine position with a rectal balloon.

The Dynamic Tumor Bed: Volumetric Changes in the Lumpectomy Cavity During Breast-Conserving Therapy

PURPOSE To characterize the magnitude of volume change in the postoperative tumor bed before and during radiotherapy, and to identify any factors associated with large volumetric change. METHODS AND MATERIALS Thirty-six consecutive patients with early-stage or preinvasive breast cancer underwent breast-conserving therapy at our institution between June 2006 and October 2007. Computed tomography (CT) scans of the breast were obtained shortly after surgery, before the start of radiotherapy (RT) for treatment planning, and, if applicable, before the tumor bed boost. Postoperative changes, seroma, and surgical clips were used to define the tumor bed through consensus agreement of 3 observers (B.P., D.I., and J.L.). Multiple variables were examined for correlation with volumetric change. RESULTS Between the first and last scan obtained (median time, 7.2 weeks), the tumor bed volume decreased at least 20% in 86% of patients (n = 31) and at least 50% in 64% of patients (n = 23). From the postoperative scan to the planning scan (median time, 3 weeks), the tumor bed volume decreased by an average of 49.9%, or approximately 2.1% per postoperative day. From planning scan to boost scan (median interval, 7 weeks), the median tumor bed volume decreased by 44.6%, at an average rate of 0.95% per postoperative day. No single factor was significantly associated with a change in tumor bed volume greater than 20%. CONCLUSIONS The average postlumpectomy cavity undergoes dramatic volumetric change after surgery and continues this change during RT. The rate of change is inversely proportional to the duration from surgery. In this study no factors studied predicted large volumetric change.

Accurate heterogeneous dose calculation for lung cancer patients without high-resolution CT densities.

The aim of this study was to investigate the relative accuracy of megavoltage photon‐beam dose calculations employing either five bulk densities or independent voxel densities determined by calibration of the CT Houndsfield number. Full‐resolution CT and bulk density treatment plans were generated for 70 lung or esophageal cancer tumors (66 cases) using a commercial treatment planning system with an adaptive convolution dose calculation algorithm (Pinnacle3, Philips Medicals Systems). Bulk densities were applied to segmented regions. Individual and population average densities were compared to the full‐resolution plan for each case. Monitor units were kept constant and no normalizations were employed. Dose volume histograms (DVH) and dose difference distributions were examined for all cases. The average densities of the segmented air, lung, fat, soft tissue, and bone for the entire set were found to be 0.14, 0.26, 0.89, 1.02, and 1.12 g/cm3, respectively. In all cases, the normal tissue DVH agreed to better than 2% in dose. In 62 of 70 DVHs of the planning target volume (PTV), agreement to better than 3% in dose was observed. Six cases demonstrated emphysema, one with bullous formations and one with a hiatus hernia having a large volume of gas. These required the additional assignment of density to the emphysemic lung and inflammatory changes to the lung, the regions of collapsed lung, the bullous formations, and the hernia gas. Bulk tissue density dose calculation provides an accurate method of heterogeneous dose calculation. However, patients with advanced emphysema may require high‐resolution CT studies for accurate treatment planning. PACS number: 87.53.Tf

Optimal Image-Guidance Scenario With Cone-Beam Computed Tomography in Conventionally Fractionated Radiotherapy for Lung Tumors

Purpose:To determine the residual setup errors of several image guidance scenarios, using cone-beam computed tomography (CBCT) in conventionally fractionated radiotherapy for lung tumors. Methods:Thirteen lung cancer patients were treated with conventionally fractionated radiotherapy, using daily image guidance with CBCT, resulting in 389 CBCT scans which were registered to the planning scan using automated soft-tissue registration. Using the resulting daily alignment data, 4 imaging frequency scenarios were analyzed: (A) no imaging; (B) weekly imaging with a 3-mm threshold; (C) first 5 fractions imaged, then weekly imaging with a patient-specific threshold; and (D) imaging every other day. Results:The systematic setup error (Σ) was reduced with increasing frequency of imaging from 3.4 mm for no imaging to 1.0 mm for imaging every other day. Random setup error (σ), however, varied little regardless of the frequency of imaging: 2.9, 3.0, 3.4, and 3.2 mm for scenarios A, B, C, and D, respectively. The setup margins required to account for the residual error of each imaging scenario were 1 to 1.6 cm for scenario A, 4 to 6 mm for scenarios B and C, and 4 to 5 mm for scenario D. As the residual error of daily CBCT was not included in this analysis, these margins compare with a margin of zero for daily CBCT. Conclusions:Daily image guidance is ideal as the setup margin can be reduced by about 5 mm versus a nondaily imaging scenario. However, if daily image guidance is not possible, there is little benefit in imaging more often than once a week.

An investigation of anxiety about radiotherapy deploying the Radiotherapy Categorical Anxiety Scale

BackgroundRadiotherapy is one of the major methods for treating cancer, but many patients undergoing radiotherapy have deep concerns about receiving radiation treatment. This problem is not generally appreciated and has not been adequately studied.MethodsThe objective of this investigation was to empirically investigate the anxieties that cancer patients feel towards radiotherapy by using questionnaires to classify and quantitatively measure their concerns. A preliminary interview to develop a questionnaire was carried out with 48 patients receiving radiotherapy to discover their anxieties about on-going treatments. Subsequently, a main study was performed using a questionnaire with 185 patients to classify their types of anxiety and to ascertain the reliability and validity of the responses. Confirmatory factor analysis was then carried out with a 17-item Radiotherapy Categorical Anxiety Scale.ResultsThree anxiety factors were abstracted by factor analysis: (1) adverse effects of radiotherapy, (2) environment of radiotherapy, and (3) treatment effects of radiotherapy. Reliability, content validity, and concurrent validity were obtained. The adequacy of the three-factor model of anxiety concerning radiotherapy was confirmed.ConclusionA 17-item Radiotherapy Categorical Anxiety Scale was formulated to quantitatively measure the specific types of anxiety among cancer patients receiving radiotherapy.

A new two-step accurate CT-MRI fusion technique for post-implant prostate cancer.

Purpose To develop an accurate method of fusing computed tomography (CT) with magnetic resonance imaging (MRI) for post-implant dosimetry after prostate seed implant brachytherapy. Material and methods Prostate cancer patients were scheduled to undergo CT and MRI after brachytherapy. We obtained the three MRI sequences on fat-suppressed T1-weighted imaging (FST1-WI), T2-weighted imaging (T2-WI), and T2*-weighted imaging (T2*-WI) in each patient. We compared the lengths and widths of 450 seed source images in the 10 study patients on CT, FST1-WI, T2-WI, and T2*-WI. After CT-MRI fusion using source positions by the least-squares method, we decided the center of each seed source and measured the distance of these centers between CT and MRI to estimate the fusion accuracy. Results The measured length and width of the seeds were 6.1 ± 0.5 mm (mean ± standard deviation) and 3.2 ± 0.2 mm on CT, 5.9 ± 0.4 mm, and 2.4 ± 0.2 mm on FST1-WI, 5.5 ± 0.5 mm and 1.8 ± 0.2 mm on T2-WI, and 7.8 ± 1.0 mm and 4.1 ± 0.7 mm on T2*-WI, respectively. The measured source location shifts on CT/FST1-WI and CT/T2-WI after image fusion in the 10 study patients were 0.9 ± 0.4 mm and 1.4 ± 0.2 mm, respectively. The shift on CT/FST1-WI was less than on CT/T2-WI (p = 0.005). Conclusions For post-implant dosimetry after prostate seed implant brachytherapy, more accurate fusion of CT and T2-WI is achieved if CT and FST1-WI are fused first using the least-squares method and the center position of each source, followed by fusion of the FST1-WI and T2-WI images. This method is more accurate than direct image fusion.

Lung tumor motion change during stereotactic body radiotherapy (SBRT): an evaluation using MRI

The purpose of this study is to investigate changes in lung tumor internal target volume during stereotactic body radiotherapy treatment (SBRT) using magnetic resonance imaging (MRI). Ten lung cancer patients (13 tumors) undergoing SBRT (48 Gy over four consecutive days) were evaluated. Each patient underwent three lung MRI evaluations: before SBRT (MRI‐1), after fraction 3 of SBRT (MRI‐3), and three months after completion of SBRT (MRI‐3m). Each MRI consisted of T1‐weighted images in axial plane through the entire lung. A cone‐beam CT (CBCT) was taken before each fraction. On MRI and CBCT taken before fractions 1 and 3, gross tumor volume (GTV) was contoured and differences between the two volumes were compared. Median tumor size on CBCT before fractions 1 (CBCT‐1) and 3 (CBCT‐3) was 8.68 and 11.10 cm3, respectively. In 12 tumors, the GTV was larger on CBCT‐3 compared to CBCT‐1 (median enlargement, 1.56 cm3). Median tumor size on MRI‐1, MRI‐3, and MRI‐3m was 7.91, 11.60, and 3.33 cm3, respectively. In all patients, the GTV was larger on MRI‐3 compared to MRI‐1 (median enlargement, 1.54 cm3). In all patients, GTV was smaller on MRI‐3m compared to MRI‐1 (median shrinkage, 5.44 cm3). On CBCT and MRI, all patients showed enlargement of the GTV during the treatment week of SBRT, except for one patient who showed minimal shrinkage (0.86 cm3). Changes in tumor volume are unpredictable; therefore, motion and breathing must be taken into account during treatment planning, and image‐guided methods should be used, when treating with large fraction sizes. PACS number: 87.53.Ly

Effect of dose fractionation on pulmonary complications during total body irradiation.

Total body irradiation (TBI) is an important component of conditioning regimens for Allogeneic bone marrow transplantation (BMT). Interstitial pneumonitis (IP) and other pulmonary disorders are known regimen-related complications. The incidence of IP is related to the dose rate and dose fractionation; however, there is a paucity of clinical data regarding the optimal dose fractionation. This retrospective study evaluated patients to determine the influence of dose fractionation during TBI in preparation for allogeneic BMT on the subsequent development of IP and other pulmonary complications. Fifty-six patients were treated with TBI followed by BMT at our institute. All patients received a total TBI dose of 12 Gy given in 6 fractions over 3 days or in 4 fractions over 2 days. The prevalence of unrelated donors in the 4-fraction group was higher than that in the 6-fraction group. The overall and freedom from progression rates for patients in the 4-fraction group were better than those for patients in the 6-fraction group, but the difference did not reach significance. Clinically significant lung complications occurred in 19 (10: infectious and 9: non-infectious diseases) of 33 patients in the 6-fraction group and 12 (7: infectious and 5: non-infectious diseases) of 23 in the 4-fraction group. There was no significant difference between the two groups. There was no significant difference in pulmonary complications between patients treated with a TBI dose of 12 Gy in 6 fractions over 3 days and patients treated with a TBI dose of 12 Gy in 4 fractions over 2 days.

Differences between current and historical breast cancer axillary lymph node irradiation based on arm position: implications for radiation oncologists.

Purpose:To identify differences in regional node irradiation using historical treatment planning techniques between 2 arm positions. Materials and Methods:Sixteen breast cancer patients were scanned using a wide-bore computed tomography (CT) scanner. The patients were scanned in 2 arm positions: historical position (HP), in which the ipsilateral arm is at 90 degrees to the body axis; and standard-bore position (CT-P), in which the arms are above the head. The locations of the axillary lymph nodes were compared between the 2 positions. The dose distribution to the axillary lymph nodes was compared between the HP and the CT-P using fields designed based on bony landmarks. Results:When the arm position changed from the HP to the CT-P, level I lymph nodes moved anteriorly and medially. Level II and III axillary nodes moved posteriorly and medially. If historical treatment planning techniques are used to treat the axillary lymph nodes with the patient in the CT-P, level I nodes could receive a higher dose of radiation and levels II and III could be significantly underdosed as compared with treatment in the HP. The dose distribution for the CT-P was more homogeneous compared with that of the HP. Conclusion:Coverage of the axillary lymph nodes varies significantly with arm position when using historical treatment planning techniques. Physicians should accurately contour the lymph node levels on the treatment planning CT and not rely on bony landmarks to design the axillary fields. CT-based treatment planning should be used to ensure adequate coverage of these nodes.

An efficient approach to incorporating interfraction motion in IMRT treatment planning

Intensity modulated radiation therapy (IMRT) is one of the most widely used delivery modalities for radiation therapy for cancer patients. A patient is typically treated in daily fractions over a period of 5-9 weeks. In this paper, we consider the problem of accounting for changes in patient setup location and internal geometry between the treatment fractions, usually referred to as interfraction motion. The conventional method is to add a margin around the clinical tumor volume (CTV) to obtain a planning target volume (PTV). A fluence map optimization (FMO) model is then solved to determine the optimal intensity profiles to deliver to the patient. However, a margin-based method may not adequately model the changes in dose distributions due to the random nature of organ motion. Accounting for interfraction motion in the FMO model essentially transforms the deterministic optimization problem into a stochastic one. We propose a stochastic FMO model that employs convex penalty functions to control the treatment plan quality and uses a large number of scenarios to characterize interfraction motion uncertainties. Some effects of radiotherapy are impacted mainly by the dose distribution in a given treatment fraction while others tend to manifest themselves over time and depend mostly on the total dose received over the course of treatment. We will therefore formulate an optimization model that explicitly incorporates treatment plan evaluation criteria that apply to the total dose received over all treatment fractions and ones that apply to the dose per fraction. Particularly when many structures fall into the former category, this can lead to significant reductions in the dimension of the optimization model and therefore the time required to solve it. We test an example of our model on five clinical prostate cancer cases, showing the efficacy of our approach. In particular, compared to a traditional margin-based treatment plan, our plans exhibit significantly improved target dose coverage and clinically equivalent critical structure sparing at only a modest increase in computational effort.