Andrew See | PubMed Health

PubMed2003

Exploring the effect of marked normal structure volume on normal tissue complication probability.

Radiation therapy dosimetry software now frequently incorporates biological predictions of the probability of normal tissue complications. This study investigates whether the length of normal structure outlined affects a normal tissue complication probability (NTCP) for that structure. It also researches the effect of any change in the dose parameter used to produce a 50% probability of a complication (the TD50) on the calculated NTCP, as this is related to the clinical observations. An NTCP was calculated for rectum and bladder on a sample of prostate cases receiving external beam radiation therapy. The length of the organs at risk was varied and the NTCP recalculated for each different length using the same treatment plan. Large variations of up to 80% in NTCP for different delineated lengths of organ for a given TD50 were observed. Changing the TD50 dose altered the calculated NTCP and the relative size of the variation in the values. This parameter will need further investigation; a standardized delineated length of 2 cm beyond the beam edge for normal structures is recommended. Interpatient and interinstitution plan comparison using dose volume histograms and/or normal tissue complication probabilities will be compromised until such standardization occurs.

Humans↗

PubMed2002

Dose distribution and morbidity after high dose rate brachytherapy for prostate cancer: influence of V150 and V200 parameters.

The purpose of this study is to identify factors predicting morbidity in patients undergoing high dose rate (HDR) brachytherapy boost with external beam irradiation for prostate cancer. Acute and late morbidity data were collected for 104 prostate cancer patients treated with an HDR boost together with external beam radiotherapy. Significant urinary and rectal morbidity were correlated with urethral and rectal point doses, and the proportions of the target volume receiving 100%, 150% and 200% (V200) or more of the prescribed dose. Rectal or urethral point doses did not predict morbidity. By contrast, the V200 was significantly higher for patients experiencing either acute or late urinary morbidity. The cut-off V200 was 15% of the target volume. Although theoretically beneficial for tumour cell kill, the treatment of significant proportions of the prostate to high dose might be associated with increased morbidity, and should preferably be avoided.

Brachytherapy↗