Biomedical subjects

Gert J Meijer

Publications and source records attributed to Gert J Meijer.

4 recordsLinked to original sources

PubMed2006

Dosimetric comparison of interactive planned and dynamic dose calculated prostate seed brachytherapy.

PURPOSE: To compare the dosimetrical results of an interactive planning procedure and a procedure based on dynamic dose calculation for permanent prostate brachytherapy. MATERIALS AND METHODS: Between 6/2000 and 11/2005, 510 patients underwent (125)I implants for T1-T2 prostate cancer. Before 4/2003, 187 patients were treated using an interactive technique that included needle updating. After that period, 323 patients were treated with a more refined dynamic technique that included constant updating of the deposited seed position. The comparison is based on postimplant dose - volume parameters such as the V(100) and d(90) for the target, V(100)(r) for the rectum and d(10)(u) for the urethra. Furthermore, the target volume ratios (TVR identical with V(100)(body)/V(100)), and the homogeneity indices (HI identical with [V(100)-V(150)]/V(100)) were calculated as additional quality parameters. RESULTS: The dose outside the target volume was significantly reduced, the V(100)(r) decreased from 1.4 cm(3) for the interactive technique to 0.6 cm(3) for the dynamic technique. Similarly the mean TVR reduced from 1.66 to 1.44. In addition, the mean V(100) increased from 92% for the interactive procedure to 95% for the dynamic procedure. More importantly, the percentage of patients with a V(100) < 80% reduced from 5% to 1%. A slight decline was observed with regard to the d(10)(u) (136% vs. 140%) and the HI (0.58 vs. 0.51). CONCLUSION: The dynamic implant procedure resulted in improved implants. Almost ideal dose coverage was achieved, while minimizing the dose outside the prostate.

Algorithms↗

PubMed2006

High-dose simultaneously integrated breast boost using intensity-modulated radiotherapy and inverse optimization.

PURPOSE: Recently a Phase III randomized trial has started comparing a boost of 16 Gy as part of whole-breast irradiation to a high boost of 26 Gy in young women. Our main aim was to develop an efficient simultaneously integrated boost (SIB) technique for the high-dose arm of the trial. METHODS AND MATERIALS: Treatment planning was performed for 5 left-sided and 5 right-sided tumors. A tangential field intensity-modulated radiotherapy technique added to a sequentially planned 3-field boost (SEQ) was compared with a simultaneously planned technique (SIB) using inverse optimization. Normalized total dose (NTD)-corrected dose volume histogram parameters were calculated and compared. RESULTS: The intended NTD was produced by 31 fractions of 1.66 Gy to the whole breast and 2.38 Gy to the boost volume. The average volume of the PTV-breast and PTV-boost receiving more than 95% of the prescribed dose was 97% or more for both techniques. Also, the mean lung dose and mean heart dose did not differ much between the techniques, with on average 3.5 Gy and 2.6 Gy for the SEQ and 3.8 Gy and 2.6 Gy for the SIB, respectively. However, the SIB resulted in a significantly more conformal irradiation of the PTV-boost. The volume of the PTV-breast, excluding the PTV-boost, receiving a dose higher than 95% of the boost dose could be reduced considerably using the SIB as compared with the SEQ from 129 cc (range, 48-262 cc) to 58 cc (range, 30-102 cc). CONCLUSIONS: A high-dose simultaneously integrated breast boost technique has been developed. The unwanted excessive dose to the breast was significantly reduced.

Breast Neoplasms↗

PubMed2004

A prospective evaluation of Frialoc implants with ball-abutments in the edentulous mandible: 1-year results.

Several surgical and prosthetic concepts for the treatment of patients with mandibular atrophy and related lower denture problems are proposed and described in the literature. The present study discusses and evaluates the use of a new single-stage implant and overdenture with ball-attachment for this purpose. This study evaluates the clinical performance of the implants and abutments and addresses surgical and prosthetic complications that were encountered. Eighteen fully edentulous patients received two, single-stage Frialoc implants (Friadent, Mannheim, Germany). The implants were left to osseointegrate for 3 months and were subsequently provided with ball-abutments and loaded through a mandibular overdenture. After 1-year of clinical service, two implants were lost, which accumulated to a 1-year survival rate of 93.9% (SE 4.2%). Patient satisfaction was high, and prosthetic complications and postinsertion maintenance were minimal. Three abutments loosened, one of which subsequently broke after 5 months of loading. Retightening of the attachment (gold matrix) was performed on seven occasions in four patients. Soft tissue response was excellent. Although minor hypertrophy of the peri-implant mucosa was observed, hardly any marginal bone loss between baseline and 1-year observations occurred. Short-term results indicate that mandibular implant overdenture treatment by means of two ball-abutments, using Frialoc implants and prosthetic components, leads to good clinical results, both from an objective and a subjective perspective.

Aged↗

PubMed2003

Three-dimensional analysis of delineation errors, setup errors, and organ motion during radiotherapy of bladder cancer.

PURPOSE: To quantify in three dimensions the geometric uncertainties of bladder irradiation (i.e., uncertainties in target delineation, organ motion, and patient setup). METHODS AND MATERIALS: Pelvic CT images were obtained for 10 male bladder cancer patients. Apart from the initial planning CT scan, three follow-up scans were made for each of the patients. The bladder volumes in the planning CT scan were outlined by seven radiation oncologists. One observer also delineated the bladder volumes in the follow-up scans. Two-dimensional scalar maps of the interobserver variation and organ motion of the bladder surfaces were constructed. The setup errors were derived from the portal imaging results of the pooled group of bladder and prostate patients. RESULTS: All bladder volumes were consistently outlined by all observers. Generally small variations occurred (1.5-3 mm, 1 SD), although in 50% of the patients, larger discrepancies were observed in discriminating the bladder from the base of the prostate. Analysis of the portal imaging data showed setup errors of up to 3 mm (1 SD). Organ motion is the predominant geometric uncertainty in the radiotherapy process (5 mm, 1 SD, at the cranial side of the bladder), although 9 of 10 patients were able to preserve a fairly reproducible bladder volume during the complete treatment course. CONCLUSION: Anisotropic margins between the clinical target volume and planning target volume are needed in conformal radiotherapy of the bladder. Especially at the cranial side of the bladder, larger margins are needed because of the impact of bladder shape variation.

Aged↗