Biomedical subjects

A Rijnders

Publications and source records attributed to A Rijnders.

23 records · Page 2Linked to original sources

PubMed1988

Practical implications of backscatter from outside the patient on the dose distribution during total body irradiation.

Total body irradiation (TBI) sometimes requires the set-up of the patient very close to the wall of the treatment room in order to obtain sufficiently large irradiation fields. Under these conditions, backscattered electrons can become clinically important. In the present study, an attempt was made to quantify the dose contribution to the patient from these electrons. Measurements were performed both in experimental conditions and on patients during their TBI treatment. It is concluded that, with the patient close to the wall, backscattered electrons constitute a significant (up to 20% of the dose obtained under electronic equilibrium at the exit port of the beam) radiation dose which can (under certain conditions) influence measurements of exist dose leading to an overestimation of the midline dose and contribute a superficial irradiation of the patient without therapeutic benefit. This problem can be solved by interposing a 2 cm thick low-Z absorber between wall and patient.

Construction Materials↗

PubMed1987

Tumor excision and radiotherapy as primary treatment of breast cancer. Analysis of patient and treatment parameters and local control.

From 1966 to 1979, 235 patients with operable breast cancer were treated by tumor excision and radiotherapy. The actuarial survival at 10 years was 94.8% for stage I and 58% for stage II tumors. Local recurrent cancer was seen in 23/235 patients and was related to T stage, N stage, width of surgical excision, radiation dose to the tumor bed and anatomopathological differentiation. Recurrences were seen in 1/7 of T0, 3/57 (5.2%) of T1, 11/102 (10.8%) of T2 and 2/6 of T3 tumors. Local control in the breast decreased significantly in N1b cases (p = 0.005) or when 3 or more axillary lymph nodes were positive (p = 0.0074). Local control after segmentectomy or tumorectomy was identical. However, a poorer local control was found in 20 cases treated with subtotal resection (p less than 0.05). A clear dose-local control relationship was found in this material, with a 100% local control in all T0, T1 tumors which received more than 1800 ret and all T2 tumors which received more than 2000 ret. As 19 of 23 breast recurrences were seen at the primary site in the breast we believe that booster doses should be given in order to maximise local control.

Adult↗

PubMed1985

Determination of ionisation chamber collection efficiency in a swept electron beam by means of thermoluminescent detectors and the "two-voltage" method.

Two methods for determining the collection efficiency of a 0.6 cm3 thimble ionisation chamber exposed to the swept electron beam of a linear accelerator Therac 20 Saturne (CGR MeV) have been compared. In one method the chamber signal has been compared to that of simultaneously exposed thermoluminescent LiF dosemeters (TLD), in the other the "two-voltage" method of Boag, adapted for swept beams, has been used. By variation of the electron energy between 20 and 13 MeV, of the focus-skin-distance (FSD) between 200 and 100 cm and of the monitor rate between 400 monitor units (m.u.) and 100 m.u. per minute, different values could be produced for the peak charge density M. The collection efficiency of the chamber, operating at a standard voltage of 250 V, decreases from 0.99 to 0.84 for a charge density increasing from 0.3 X 10(-4) C/m3 to 7.5 X 10(-4) C/m3, respectively. The maximum deviation observed between the TLD and the "two-voltage" method adopted for similar M is never more than 2% and mostly smaller than 1%. It can be concluded that, under the present experimental conditions, the calculated ionisation chamber collection efficiency is confirmed by the experimental method using TL dosimetry.

Animals↗

PubMed1984

A modified radiotherapy technique in the treatment of medulloblastoma.

Craniospinal irradiation is a standard treatment technique in patients who receive surgery for medulloblastoma. In most centers megavoltage photon irradiation is used, resulting in significant irradiation exposure to critical organs. In order to overcome this difficulty, we recently modified the technique applied in our center, by using high energy electrons (20 MeV) for irradiation of the spinal cord. The reliability of this technique was checked by performing dosimetry in a specially constructed wax phantom. Attention was focused upon dose variations at the junction of fields. Furthermore, the influence of vertebrae on the absorbed dose distribution of high energy electrons is presented. This technique seems to be safe and reliable in selected patients (children and teenagers).

Adolescent↗

PubMed1984

Differences in repopulation kinetics in mouse skin during split course multiple fractions per day (MFD) or daily fractionated irradiations.

The influence of protraction and distribution of irradiation as a function of time on the repopulation kinetics of mouse skin have been evaluated. Twenty fractions have been given either daily for 5 days per week during 4 weeks, or thrice a day to 10 irradiations in 3 days, repeated after a rest period of 19 days, resulting also in an overall time of 4 weeks. The acute skin reaction was scored. It was found that the split course multiple fractions per day (MFD) schedule induced less skin reaction than continuous daily fractionation, which was mainly attributable to recovery of skin damage during the rest period. Therefore, it can be postulated that the repopulation of the surviving clonogenic epidermal cells is less efficient during continuous daily irradiation than during split course MFD schedule given in the same overall treatment time.

Animals↗