Biological effective doses in the intracavitary high dose rate brachytherapy of cervical cancer

Abstract

PurposeThe aim of this study is to evaluate the decrease of biological equivalent dose and its correlation with local/loco-regional control of tumour in the treatment of cervical cancer when the strength of the Ir-192 high dose rate (HDR) brachytherapy (BT) source is reduced to single, double and triple half life in relation to original strength of 10 Ci (∼ 4.081 cGy x m2 x h−1).Material and methodsA retrospective study was carried out on 52 cervical cancer patients with stage II and III treated with fractionated HDR-BT following external beam radiation therapy (EBRT). International Commission on Radiation Units and Measurement (ICRU) points were defined according to ICRU Report 38, using two orthogonal radiograph images taken by Simulator (Simulix HQ). Biologically effective dose (BED) was calculated at point A for different Ir-192 source strength and its possible correlation with local/loco-regional tumour control was discussed.ResultThe increase of treatment time per fraction of dose due to the fall of dose rate especially in HDR-BT of cervical cancer results in reduction in BED of 2.59%, 7.02% and 13.68% with single, double and triple half life reduction of source strength, respectively. The probabilities of disease recurrence (local/loco-regional) within 26 months are expected as 0.12, 0.12, 0.16, 0.39 and 0.80 for source strength of 4.081, 2.041, 1.020, 0.510 and 0.347 cGy x m2 x h−1, respectively. The percentages of dose increase required to maintain the same BED with respect to initial BED were estimated as 1.71, 5.00, 11.00 and 15.86 for the dose rate of 24.7, 12.4, 6.2 and 4.2 Gy/hr at point A, respectively.ConclusionsThis retrospective study of cervical cancer patients treated with HDR-BT at different Ir-192 source strength shows reduction in disease free survival according to the increase in treatment time duration per fraction. The probable result could be associated with the decrease of biological equivalent dose to point A. Clinical end point of this study is more significant from double half life reduction of original source strength.

AAPM Task Group Report 267: A joint AAPM GEC‐ESTRO report on biophysical models and tools for the planning and evaluation of brachytherapy

“…The clinical endpoint was more significant from double half‐life reduction of source strength onwards. The reduced local tumor control could be associated with the decrease of biological equivalent dose to point A 290 . This modeling analysis did not consider the effect of time‐variable dose rate during the HDR brachytherapy dose delivery using a stepping source which could be different from that of a constant average dose rate used in this study 19 …”

“…When the dose rate decreases below 12 Gy/h, for example, due to decaying sources that are not replaced in time, estimation of the loss in biological effect should consider the repair processes during the prolonged irradiation time. 7 Sharma et al 290 evaluated the decrease of biological equivalent dose and its correlation with local/locoregional control of tumor in the treatment of cervical cancer when the source strength of the 192 Ir is reduced to single,double,and triple half -life in relation to original strength of approximately 41,000 U. A retrospective study was also carried out on 52 cervical cancer patients with stages II and III diseases treated with fractionated HDR brachytherapy following EBRT.…”

“…Cell repopulation occurring between fractions could potentially affect the biological effect of the overall treatment depending on the total elapsed time and the cell proliferation rate. While intrafraction dose‐rate effects is small when the dose delivery time per fraction is much less than the DNA repair half‐time (∼1.5 h), the source decay coupled with large dose per fraction could make the influence of DNA repair nonnegligible for certain HDR cervical brachytherapy treatments 290 . The drastically different temporal dose delivery patterns of LDR and HDR cervical brachytherapy can also affect the determination of their biological equivalency.…”

Image-guided interstitial high-dose-rate brachytherapy in the treatment of inoperable recurrent head and neck malignancies: An effective option of reirradiation

“…8,9 From this perspective, retreatment with a second course of dose-escalated EBRT to the same localized site, although technically feasible, is not unreservedly implemented because of the high risk of severe side effects because of previous RT. 11,12 Three-dimensional (3D) treatment planning in highdose-rate (HDR) and pulsed-dose-rate (PDR) brachytherapy enables for anatomy-oriented dose optimization, 13,14 whereas the versatility of intratarget dose modulation inherent to brachytherapy can be controlled and directed to deliver higher doses to gross disease or to selectively reduce the dose to organs at risk. 11,12 Three-dimensional (3D) treatment planning in highdose-rate (HDR) and pulsed-dose-rate (PDR) brachytherapy enables for anatomy-oriented dose optimization, 13,14 whereas the versatility of intratarget dose modulation inherent to brachytherapy can be controlled and directed to deliver higher doses to gross disease or to selectively reduce the dose to organs at risk.…”

“…10 Thinking with the wisdom of hindsight, image-based interstitial brachytherapy has proven to be an effective alternative for this poor-prognosis population by escalating the biologically effective dose (BED) to the treatment target while ameliorating conformity. 11,12 Three-dimensional (3D) treatment planning in highdose-rate (HDR) and pulsed-dose-rate (PDR) brachytherapy enables for anatomy-oriented dose optimization, 13,14 whereas the versatility of intratarget dose modulation inherent to brachytherapy can be controlled and directed to deliver higher doses to gross disease or to selectively reduce the dose to organs at risk. A number of publications have reported good local control associated with acceptable complication rates in the treatment of recurrent head and neck cancer with afterloaded brachytherapy.…”