Utility of Smart Arc CDR for intensity-modulated radiation therapy for prostate cancer.

Volumetric-modulated arc therapy (VMAT) is a widespread intensity-modulated radiation therapy (IMRT) method, however, VMAT requires adaptation of the radiation treatment planning system (RTPS) and linear accelerator (linac); these upgrades are quite expensive. The Smart Arc of Pinnacle(3) (Philips), which is the software used in VMAT calculations, can select constant dose rate (CDR) mode. This approach has a low initial cost because the linac upgrade is not required. The objective of this study was to clarify the utility of CDR mode for prostate IMRT. Pinnacle(3) and Clinac 21EX linac (Varian, 10 MV X-rays) were used for planning. The plans were created for 28 patients using a fixed multi-field IMRT (f-IMRT), VMAT and CDR techniques. The dose distribution results were classified into three groups: optimal, suboptimal and reject. For the f-IMRT, VMAT and CDR results, 25, 26 and 21 patients were classified as 'optimal', respectively. Our results show a significant reduction in the achievement rate of 'optimal' for a CDR when the bladder volume is <100 cm(3). The total numbers of monitoring units (MUs) (average ± 1σ) were 469 ± 53, 357 ± 35 and 365 ± 33; the average optimization times were ∼50 min, 2 h and 2 h 40 min, and the irradiation times were ∼280 s, 60 s and 110 s, respectively. CDR can reduce the total MUs and irradiation time compared with f-IMRT, and CDR has a lower initial cost compared with VMAT. Thus, for institutions that do not currently perform VMAT, CDR is a useful option. Additionally, in the context of patient identification, bladder volume may be useful.

Gas in the rectum tends to reduce during radical external beam radiotherapy for localised prostate cancer.

PURPOSE: This study aims to clarify the time-course of gas accumulation in the rectum during treatment as guidance for the management of rectal volumes. MATERIALS AND METHODS: We reviewed 2042 sets (35.2 sets per patient) of anteroposterior and right-left mega voltage (MV) images obtained for daily set-up from 58 patients who underwent radical external beam radiotherapy for localised prostate cancer. The patients were instructed to take magnesium oxide tablets during radiotherapy. They were also encouraged to avoid foods that might cause intestinal gas during radiotherapy. Gas accumulation in the rectum was graded into three classes by the same radiation oncologist. If no gas was seen in the rectum, it was classified as grade 0. A small amount of gas was classified as grade 1, whereas a marked amount of gas that required removal was classified as grade 2. RESULTS: Of the 2042 sets of MV images, grades 1 and 2 gas accumulation were seen in 332 (16%) and 156 (8%), respectively. By the trend test, gas accumulation significantly decreased towards the end of treatment (P = 0.02 for grade 1 or 2 and P = 0.02 for grade 2). On multivariate analysis, we did not identify any significant independent predictors for either baseline gas accumulation or gas reduction. CONCLUSION: Gas accumulation tended to decrease until the end of treatment. This tendency should be reconfirmed by other institutions.

Effects of geometrical uncertainties on whole breast radiotherapy: a comparison of four different techniques.

PURPOSE: The purpose of this study was to quantify the target coverage, homogeneity, and robustness of the dose distributions against geometrical uncertainties associated with four whole breast radiotherapy techniques. METHODS: The study was based on the planning-computed tomography-datasets of 20 patients who underwent whole breast radiotherapy. A total of four treatment plans (wedge, field-in-field [FIF], hybrid intensity-modulated radiotherapy [IMRT], and full IMRT) were created for each patient. The hybrid IMRT plans comprised two opposed tangential open beams plus two IMRT beams. Setup errors were simulated by moving the beam isocenters by 5 mm in the anterior or posterior direction. RESULTS: With the original plan, the wedge technique yielded a high volume receiving ≥107% of the prescription dose (V107; 7.5%±4.2%), whereas the other three techniques yielded excellent target coverage and homogeneity. A 5 mm anterior displacement caused a large and significant increase in the V107 (+5.2%±4.1%, p<0.01) with the FIF plan, but not with the hybrid IMRT (+0.4%±1.2%, p=0.11) or full IMRT (+0.7%±1.8%, p=0.10) plan. A 5-mm posterior displacement caused a large decrease in the V95 with the hybrid IMRT (-2.5%±3.7%, p<0.01) and full IMRT (-4.3%±5.1%, p<0.01) plans, but not with the FIF plan (+0.1%±0.7%, p=0.74). The decrease in V95 was significantly smaller with the hybrid IMRT plan than with the full IMRT plan (p<0.01). CONCLUSION: The FIF, hybrid IMRT, and full IMRT plans offered excellent target coverage and homogeneity. Hybrid IMRT provided better robustness against geometrical uncertainties than full IMRT, whereas FIF provided comparable robustness to that of hybrid IMRT.

Markerless Lung Tumor Motion Tracking by Dynamic Decomposition of X-Ray Image Intensity.

We propose a new markerless tracking technique of lung tumor motion by using an X-ray fluoroscopic image sequence for real-time image-guided radiation therapy (IGRT). A core innovation of the new technique is to extract a moving tumor intensity component from the fluoroscopic image intensity. The fluoroscopic intensity is the superimposition of intensity components of all the structures passed through by the X-ray. The tumor can then be extracted by decomposing the fluoroscopic intensity into the tumor intensity component and the others. The decomposition problem for more than two structures is ill posed, but it can be transformed into a well-posed one by temporally accumulating constraints that must be satisfied by the decomposed moving tumor component and the rest of the intensity components. The extracted tumor image can then be used to achieve accurate tumor motion tracking without implanted markers that are widely used in the current tracking techniques. The performance evaluation showed that the extraction error was sufficiently small and the extracted tumor tracking achieved a high and sufficient accuracy less than 1 mm for clinical datasets. These results clearly demonstrate the usefulness of the proposed method for markerless tumor motion tracking.