The effect of on-line position correction on the dose distribution in focal radiotherapy for bladder cancer

<p>Abstract</p> <p>Background</p> <p>The purpose of this study was to determine the dosimetric effect of on-line position correction for bladder tumor irradiation and to find methods to predict and handle this effect.</p> <p>Methods</p> <p>For 25 patients with unifocal bladder cancer intensity modulated radiotherapy (IMRT) with 5 beams was planned. The requirement for each plan was that 99% of the target volume received 95% of the prescribed dose. Tumor displacements from -2.0 cm to 2.0 cm in each dimension were simulated, using 0.5 cm increments, resulting in 729 simulations per patient. We assumed that on-line correction for the tumor was applied perfectly. We determined the correlation between the change in D_99%and the change in path length, which is defined here as the distance from the skin to the isocenter for each beam. In addition the margin needed to avoid underdosage was determined and the probability that an underdosage occurs in a real treatment was calculated.</p> <p>Results</p> <p>Adjustments for tumor displacement with perfect on-line position correction resulted in an altered dose distribution. The altered fraction dose to the target varied from 91.9% to 100.4% of the prescribed dose. The mean D_99%(± SD) was 95.8% ± 1.0%. There was a modest linear correlation between the difference in D_99%and the change in path length of the beams after correction (R²= 0.590). The median probability that a systematic underdosage occurs in a real treatment was 0.23% (range: 0 - 24.5%). A margin of 2 mm reduced that probability to < 0.001% in all patients.</p> <p>Conclusion</p> <p>On-line position correction does result in an altered target coverage, due to changes in average path length after position correction. An extra margin can be added to prevent underdosage.</p

Intensity-modulated radiation therapy (IMRT) vs. 3D conformal radiotherapy (3DCRT) in locally advanced rectal cancer (LARC): dosimetric comparison and clinical implications

<p>Abstract</p> <p>Purpose</p> <p>To compare target dose distribution, comformality, normal tissue avoidance, and irradiated body volume (IBV) in 3DCRT using classic anatomical landmarks (c3DCRT), 3DCRT fitting the PTV (f3DCRT), and intensity-modulated radiation therapy (IMRT) in patients with locally advanced rectal cancer (LARC).</p> <p>Materials and methods</p> <p>Fifteen patients with LARC underwent c3DCRT, f3DCRT, and IMRT planning. Target definition followed the recommendations of the ICRU reports No. 50 and 62. OAR (SB and bladder) constraints were D5 ≤ 50 Gy and Dmax < 55 Gy. PTV dose prescription was defined as PTV95 ≥ 45 Gy and PTVmin ≥ 35 Gy. Target coverage was evaluated with the D95, Dmin, and Dmax. Target dose distribution and comformality was evaluated with the homogeneity indices (HI) and Conformity Index (CI). Normal tissue avoidance of OAR was evaluated with the D5 and V40. IBV at 5 Gy (V5), 10 Gy (V10), and 20 Gy (V20) were calculated.</p> <p>Results</p> <p>The mean GTV95, CTV95, and PTV95 doses were significantly lower for IMRT plans. Target dose distribution was more inhomogeneous after IMRT planning and 3DCRTplans had significantly lower CI. The V40 and D5 values for OAR were significantly reduced in the IMRT plans .V5 was greater for IMRT than for f3DCRT planning (p < 0.05) and V20 was smaller for IMRT plans(p < 0.05).</p> <p>Conclusions</p> <p>IMRT planning improves target conformity and decreases irradiation of the OAR at the expense of increased target heterogeneity. IMRT planning increases the IBV at 5 Gy or less but decreases the IBV at 20 Gy or more.</p

Recent advances in radiotherapy

Radiation therapy has come a long way from treatment planning based on orthogonal radiographs with large margins around tumours. Advances in imaging and radiation planning software have led to three-dimensional conformal radiotherapy and, further, to intensity modulated radiotherapy (IMRT). IMRT permits sparing of normal tissues and hence dose-escalation to tumours. IMRT is the current standard in treatment of head and prostate cancer and is being investigated in other tumour sites. Exquisitely sculpted dose distributions (increased geographical miss) with IMRT, plus tumour motion and anatomical changes during radiotherapy make image guided radiotherapy an essential part of modern radiation delivery. Various hardware and software tools are under investigation for optimal IGRT

Tangential beam IMRT versus tangential beam 3D-CRT of the chest wall in postmastectomy breast cancer patients: A dosimetric comparison

<p>Abstract</p> <p>Background</p> <p>This study evaluates the dose distribution of reversed planned tangential beam intensity modulated radiotherapy (IMRT) compared to standard wedged tangential beam three-dimensionally planned conformal radiotherapy (3D-CRT) of the chest wall in unselected postmastectomy breast cancer patients</p> <p>Methods</p> <p>For 20 unselected subsequent postmastectomy breast cancer patients tangential beam IMRT and tangential beam 3D-CRT plans were generated for the radiotherapy of the chest wall. The prescribed dose was 50 Gy in 25 fractions. Dose-volume histograms were evaluated for the PTV and organs at risk. Parameters of the dose distribution were compared using the Wilcoxon matched pairs test.</p> <p>Results</p> <p>Tangential beam IMRT statistically significantly reduced the ipsilateral mean lung dose by an average of 21% (1129 cGy versus 1437 cGy). In all patients treated on the left side, the heart volume encompassed by the 70% isodose line (V70%; 35 Gy) was reduced by an average of 43% (5.7% versus 10.6%), and the mean heart dose by an average of 20% (704 cGy versus 877 cGy). The PTV showed a significantly better conformity index with IMRT; the homogeneity index was not significantly different.</p> <p>Conclusions</p> <p>Tangential beam IMRT significantly reduced the dose-volume of the ipsilateral lung and heart in unselected postmastectomy breast cancer patients.</p

Imaging of normal lung, liver and parotid gland function for radiotherapy.

There is growing clinical evidence that functional imaging is useful for target volume definition and early assessment of tumour response to external beam radiotherapy. A subject that has perhaps received less attention, but is no less promising, is the application of functional imaging to the prediction or measurement of radiation adverse effects in normal tissues. In this manuscript, we review the current published literature describing the use of positron emission tomography (PET), four-dimensional computed tomography (4D-CT), single photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI) to study normal tissue function in the context of radiotherapy to the lung, liver and head and neck. Published results to date demonstrate that functional imaging can be used to preferentially avoid normal tissues not easily identifiable on solely anatomical images. It is also a potentially very powerful tool for the early detection of radiotherapy-induced normal tissue adverse effects and could provide valuable data for building predictive models of outcome. However, one of the major challenges to building useful predictive models is that, to date, there are very little data available with combined images of normal function, 3D delivered radiation dose and clinical outcomes. Prospective data collection through well-constructed studies which use established morbidity scores is clearly a priority if significant progress is to be made in this area

Recommendations on how to establish evidence from auto-segmentation software in radiotherapy

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Bladder runner:visual analytics for the exploration of RT-induced bladder toxicity in a cohort study

\u3cp\u3eWe present the Bladder Runner, a novel tool to enable detailed visual exploration and analysis of the impact of bladder shape variation on the accuracy of dose delivery, during the course of prostate cancer radiotherapy (RT). Our tool enables the investigation of individual patients and cohorts through the entire treatment process, and it can give indications of RT-induced complications for the patient. In prostate cancer RT treatment, despite the design of an initial plan prior to dose administration, bladder toxicity remains very common. The main reason is that the dose is delivered in multiple fractions over a period of weeks, during which, the anatomical variation of the bladder – due to differences in urinary filling – causes deviations between planned and delivered doses. Clinical researchers want to correlate bladder shape variations to dose deviations and toxicity risk through cohort studies, to understand which specific bladder shape characteristics are more prone to side effects. This is currently done with Dose-Volume Histograms (DVHs), which provide limited, qualitative insight. The effect of bladder variation on dose delivery and the resulting toxicity cannot be currently examined with the DVHs. To address this need, we designed and implemented the Bladder Runner, which incorporates visualization strategies in a highly interactive environment with multiple linked views. Individual patients can be explored and analyzed through the entire treatment period, while inter-patient and temporal exploration, analysis and comparison are also supported. We demonstrate the applicability of our presented tool with a usage scenario, employing a dataset of 29 patients followed through the course of the treatment, across 13 time points. We conducted an evaluation with three clinical researchers working on the investigation of RT-induced bladder toxicity. All participants agreed that Bladder Runner provides better understanding and new opportunities for the exploration and analysis of the involved cohort data.\u3c/p\u3