Biomedical subjects

A J Nederveen

Publications and source records attributed to A J Nederveen.

3 recordsLinked to original sources

PubMed2006

Patient position verification using small IMRT fields.

A commonly used approach to quantify and minimize patient setup errors is by using electronic portal imaging devices (EPIDs). The position of the tumor can be verified indirectly by matching the bony anatomy to a reference image containing the same structures. In this paper we present two off-line methods for detecting the position of the bony anatomy automatically, even if every single portal image of each segment of an IMRT treatment beam contains insufficient matching information. Extra position verification fields will no longer be necessary, which reduces the total dose to the patient. The first method, the stack matching method (SMM), stacks the portal image of each segment of a beam to a three dimensional (3D) volume, and this volume is subsequently used during the matching phase. The second method [the averaged projection matching method (APMM)], is a simplification of the first one, since the initially created volume is reduced again to a 2D artificial image, which speeds up the matching procedure considerably, without a significant loss of accuracy. Matching is based on normalized mutual information. We demonstrate our methods by comparing them to existing matching routines, such as matching based on the largest segment. Both phantom and patient experiments show that our methods are comparable with the results obtained from standard position verification methods. The matches are verified by means of visual inspection. Furthermore, we show that when a distinct area of 40-60 cm2 of the EPID is exposed during one treatment beam, both SMM and APMM are able to deliver a good matching result.

Humans↗

PubMed2001

Partial boosting of prostate tumours.

BACKGROUND AND PURPOSE: In this planning study we propose a class solution for partial boosting of prostate tumours. Treatment margins and rectum dose are similar to that of the conventional treatment and are supposed to have no direct link to the level of dose escalation. We also study the robustness of our class solution in the presence of geometrical deviations. METHODS AND MATERIALS: To study the specifications of the class solution ten patients with histologically confirmed prostate cancer were replanned. Besides a conventional plan for each patient, different partial boost plans were produced with an inverse treatment-planning tool. We also simulated treatment geometrical deviations to estimate their effect on partial boost plans. RESULTS: In our class solution we use three contours in our inverse treatment planning, which are based on the classical CTV. A three beam arrangement appeared to produce a dose distribution, which is comparable to that of a five or seven beam geometry. Comparison of partial boost plans and conventional plans indicated that all conditions for a partial boost plan could be satisfied with the proposed class solution. Simulation of treatment geometrical deviations showed that large random deviations have a minor effect on the overall dose distributions, while systematic deviations may decrease the boost dose and increase the rectal dose. CONCLUSIONS: We presented a class solution for partial boosting of prostate tumours in which the level of dose escalation is dealt with separately from the margin size and the nominal rectum dose. The framework put forward in this study allows practical introduction of intensity modulated radiotherapy in routine clinical practice using current standards of imaging and position verification.

Humans↗

PubMed2001

Feasibility of automatic marker detection with an a-Si flat-panel imager.

Here we study automatic detection of implanted gold markers relative to the field boundary in portal images for on-line position verification. Portal images containing 1-2 MU were taken with an amorphous silicon flat-panel imager. The images were obtained with lateral field at 18 MV. Both the detection success rate and the localization accuracy of markers of 1.0 and 1.2 mm diameter were determined with the help of a marker detection method based on a marker extraction kernel. A method for determining a fiducial reference point related to the field boundary was developed. Detection success rates were 0.99, 0.90 and 0.95 for markers of 1.2 mm diameter and 5 mm length, 1.0 mm diameter and 5 mm length and 1.0 mm diameter and 10 mm length respectively. The localization accuracy appeared to be better than 0.3 mm. The reference point could be reproduced with an accuracy equal to 1 pixel (0.5 mm at isocentre) within one fraction. During the first few seconds of a treatment fraction the field edge was not stable, which appeared to be an effect of the motion of the radiation source. Thanks to the use an a-Si flat-panel imager, on-line position verification using implanted gold markers becomes clinically feasible. We can use a clinically acceptable marker diameter as small as 1.0 mm. These markers can be automatically detected in portal images obtained with 1-2 MU relative to a stable reference point related to the field boundary.

Algorithms↗