Biological effective dose evaluation in gynaecological brachytherapy: LDR and HDR treatments, dependence on radiobiological parameters, and treatment optimisation.
OBJECTIVE
This study was undertaken to compare the biological efficacy of different high-dose-rate (HDR) and low-dose-rate (LDR) treatments of gynaecological lesions, to identify the causes of possible nonuniformity and to optimise treatment through customised calculation.


METHODS
The study considered 110 patients treated between 2001 and 2006 with external beam radiation therapy and/or brachytherapy with either LDR (afterloader Selectron, (137)Cs) or HDR (afterloader microSelectron Classic, (192)Ir). The treatments were compared in terms of biologically effective dose (BED) to the tumour and to the rectum (linear-quadratic model) by using statistical tests for comparisons between independent samples.


RESULTS
The difference between the two treatments was statistically significant in one case only. However, within each technique, we identified considerable nonuniformity in therapeutic efficacy due to differences in fractionation schemes and overall treatment time. To solve this problem, we created a Microsoft Excel spreadsheet allowing calculation of the optimal treatment for each patient: best efficacy (BED(tumour)) without exceeding toxicity threshold (BED(rectum)).


CONCLUSIONS
The efficacy of a treatment may vary as a result of several factors. Customised radiobiological evaluation is a useful adjunct to clinical evaluation in planning equivalent treatments that satisfy all dosimetric constraints.
Bianchi
C
C
Servizio di Fisica Sanitaria, Ospedale di Circolo, Viale Borri 57, 21100 Varese, Italy. fisica.sanitaria@ospedale.varese.it
Botta
F
F
Conte
L
L
Vanoli
P
P
Cerizza
L
L
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001918:Brachytherapy / Q000379:methods; D002584:Cervix Uteri / Q000473:pathology; D004307:Dose-Response Relationship, Radiation; D016889:Endometrial Neoplasms / Q000473:pathology / Q000532:radiotherapy; D004717:Endometrium / Q000473:pathology; D005260:Female; D005833:Genital Neoplasms, Female / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D008875:Middle Aged; D008954:Models, Biological; D015233:Models, Statistical; D009367:Neoplasm Staging; D011853:Radiobiology / Q000379:methods; D011879:Radiotherapy Dosage; D018714:Radiotherapy, Adjuvant; D012062:Relative Biological Effectiveness; D012984:Software; D002583:Uterine Cervical Neoplasms / Q000473:pathology / Q000532:radiotherapy; D014621:Vagina / Q000473:pathology; D014625:Vaginal Neoplasms / Q000473:pathology / Q000532:radiotherapy