Biomedical subjects

Jacob Christian Lindegaard

Publications and source records attributed to Jacob Christian Lindegaard.

3 recordsLinked to original sources

PubMed2006

Dose optimisation in single plane interstitial brachytherapy.

BACKGROUND AND PURPOSE: Brachytherapy dose distributions can be optimised by modulation of source dwell times. In this study dose optimisation in single planar interstitial implants was evaluated in order to quantify the potential benefit in patients. MATERIAL AND METHODS: In 14 patients, treated for recurrent rectal and cervical cancer, flexible catheters were sutured intra-operatively to the tumour bed in areas with compromised surgical margin. Both non-optimised, geometrically and graphically optimised CT -based dose plans were made. The overdose index (OI), homogeneity index (HI), conformal index (COIN), minimum target dose, and high dose volumes were evaluated. The dependence of OI, HI, and COIN on target volume and implant regularity was evaluated. In addition, 12 theoretical implant configurations were analyzed. RESULTS: Geometrical and graphical optimisation improved the dose plans significantly with graphical optimisation being superior. Graphically optimised dose plans showed a significant decrease of 18%+/-9% in high dose volume (p<0.001). HI, COIN, and OI were significantly improved from 0.50+/-0.05 to 0.60+/-0.05, from 0.65+/-0.04 to 0.71+/-0.04, and from 0.19+/-0.03 to 0.15+/-0.03, respectively (p<0.001 for all). Moreover, minimum target dose increased significantly from 71%+/-5% to 80%+/-5% (p<0.001). The improvement in OI and HI obtained by optimisation depended on the regularity of the implant, such that the benefit of optimisation was larger for irregular implants. OI and HI correlated strongly with target volume limiting the usability of these parameters for comparison of dose plans between patients. CONCLUSIONS: Dwell time optimisation significantly improved the dose distribution regarding homogeneity, conformity, minimum target dose, and size of high dose volumes. Graphical optimisation is fast, reproducible and superior to geometric optimisation.

Brachytherapy↗

PubMed2006

Geometric stability of intracavitary pulsed dose rate brachytherapy monitored by in vivo rectal dosimetry.

BACKGROUND AND PURPOSE: To evaluate geometric stability of applicator and rectum during pulsed dose rate (PDR) intracavitary brachytherapy. PATIENTS AND METHODS: A total of 14 patients with cervical cancer (stages IIB-IVA) were analysed retrospectively. A dose of 10 Gy to point A was prescribed per brachytherapy session, and PDR was given with 1 Gy/pulse, 1 pulse/h, using a ring applicator (Varian). A rectal dosimeter consisting of five diodes spaced by 1.5 cm was routinely placed in the rectum. The diodes detected the progression of each pulse of radiation, as the stepping source was advanced through the applicator. A mathematical model has been developed for spatial analysis of the pattern of the dose readings. The model transforms dose measurement into a quantification of the geometric relationship between rectum diodes and applicator. RESULTS: The model could be used for all treatment sessions, and the relative positions of diodes and applicator were calculated for each pulse of radiation. The SD of displacements during the treatment was below 2.8mm in all directions for all patients. The mean SD in lateral, longitudinal and anterior-posterior directions were 1.2 +/- 0.7, 1.2 +/- 0.7 and 0.9 +/- 0.6 mm, respectively. The mean measurement uncertainty was below 0.8 +/- 0.5 mm in all directions. CONCLUSIONS: A new mathematical method has been developed, enabling us to quantitate and monitor relative positions of applicator and rectal diodes during a PDR treatment. The spatial relation between rectal dosimeter and applicator was very stable during extended PDR treatments suggesting that the geometric stability of PDR treatment is at the same level as the stability reported for HDR brachytherapy.

Algorithms↗

PubMed2003

Chemical radioprotection: a critical review of amifostine as a cytoprotector in radiotherapy.

The use of chemical radioprotectors represents an obvious strategy to improve the therapeutic index in radiotherapy. Amofostine (WR-2721) has recently been approved for use in head and neck cancer to protect against radiation-induced xerostomia. Currently, the question has arisen whether amifostine could be used for radioprotection in broader terms. Amifostine may have the potential to enable intensified treatment by ameliorating mucosal reactions that are often a limiting factor in accelerated fractionation or concomitant chemoradiation. However, it has as yet not been clarified whether sufficient amifostine to reduce mucositis can be administered before each radiation fraction without causing unacceptable toxicity. Also, the optimal dosage and schedule of amifostine in chemoradiation combinations have not yet been established. The major concern related to radioprotectiors is the potential hazard of collateral tumor protection. A number of clinical studies have concluded that amifostine does not reduce antitumor efficacy. However, not even the largest study conducted, with over 300 patients, has sufficient statistical power to detect a clinically significant reduction in tumor control rate. To put this issue ultimately to a rest, a clinical trial with a sufficient accrual to definitely rule out a tumor protective effect of amifostine needs to be conducted. Substances reducing radiation-induced toxicity by modulating the biological response to radiation injury may represent an alternative concept in radioprotection. However, such agents are still at a developmental stage.

Amifostine↗