A comparison of HDR brachytherapy and IMRT techniques for dose escalation in prostate cancer: A radiobiological modeling study

Abstract

A course of one to three large fractions of high dose rate ͑HDR͒ interstitial brachytherapy is an attractive alternative to intensity modulated radiation therapy ͑IMRT͒ for delivering boost doses to the prostate in combination with additional external beam irradiation for intermediate risk disease. The purpose of this work is to quantitatively compare single-fraction HDR boosts to biologically equivalent fractionated IMRT boosts, assuming idealized image guided delivery ͑igIMRT͒ and conventional delivery ͑cIMRT͒. For nine prostate patients, both seven-field IMRT and HDR boosts were planned. The linear-quadratic model was used to compute biologically equivalent dose prescriptions. The cIMRT plan was evaluated as a static plan and with simulated random and setup errors. The authors conclude that HDR delivery produces a therapeutic ratio which is significantly better than the conventional IMRT and comparable to or better than the igIMRT delivery. For the HDR, the rectal gBEUD analysis is strongly influenced by high dose DVH tails. A saturation BED, beyond which no further injury can occur, must be assumed. Modeling of organ motion uncertainties yields mean outcomes similar to static plan outcomes.

External beam radiotherapy plus single-fraction high dose rate brachytherapy in the treatment of locally advanced prostate cancer

“…Prostate cancer cells are believed to be highly sensitive to the dose per fraction. It is estimated that, unlike most cancer cells, prostate cancer cells have a low a/b ratio (between 1.2-3 Gy) [40][41][42], and this implies that such cells should be more responsive to high dose radiation. Thus, a hypofractionated irradiation schedule, theoretically, offers an improved radiobiological advantage in terms of selective tumour-cell killing without a concomitant increase in the development of late side effects [43].…”

Comp Plan: A computer program to generate dose and radiobiological metrics from dose-volume histogram files

“…SED used with equivalent uniform dose (EUD) will generate EUBED, 25 also named equivalent survival dose (ESD). 23 Although dose distributions cannot be added together, because of the …”

“…This accounts for the possibility of an isoeffect threshold beyond which any further damage has no further clinical significance. 23 For each of the structures considered a homogeneous boost dose, of a specified total dose and fraction number, can also be added. In most circumstances, it is expected that the SED conversion will be used with the boost option to account for changes in fractionation.…”

An Overview on the Clinical Application of Radiobiological Modeling in Radiation Therapy of Cancer

“…Although, the main purpose of TCP/NTCP calculations has been to provide a surrogate tool for plan comparisons and optimum plan selection for a given treatment, there are many other investigations that have employed this approach to quantize the radiobiological consequences for different available modalities, and geometric errors, as well as comparing novel techniques for radiation therapy [2,[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. Moreover, several studies have utilized radiobiological modeling to evaluate the effect of geometric errors in image guided radiation therapy (IGRT), while others have applied this modeling for brachytherapy planning as well as radiation therapy with heavy ion beams [25][26][27][28][29][30][31][32].…”

“…Also, it was dosimetrically and radiobiologically comparable to or even better than the image guided IMRT delivery. [12] In another recent study, a comparison of two different optimization algorithms in brachytherapy has been reported. In this study inverse planning simulated annealing (IPSA) and hybrid inverse treatment planning optimization (HIPO) algorithms were compared for brachytherapy plans of prostate cancer.…”