OPTIMAL SCHEDULE REMAINS UNCLEAR
As with EBRT, HDR brachytherapy can be hypofractionated for accelerated delivery of total therapeutic dose in fewer fractions, and the published literature includes a much wider range of fraction and total doses for HDR brachytherapy than LDR.1
Defining optimum dose fraction schedules remains a pressing challenge for proponents of HDR monotherapy, experts agree.1 But despite the wide range of radiation doses reported for HDR, most studies report similar outcomes, making it difficult to identify the best hypofractionation schedule.1,7
Older studies involved delivery of HDR brachytherapy in four to six, and as many as nine, fractions because of concern about possible toxicities arising from higher dose fractions, but Morton and Hoskin report that growing evidence exists to supports the delivery of HDR in three or even two fractions.1
The two most frequently employed fractionation schedules in the published literature are 54 Gy delivered in six fractions, or 38 Gy in four fractions, according to Morton and Hoskin.1 “More recently there has been a trend of using fewer fractions, with several series reporting favorable results with the use of a single HDR dose,” they note. Single-fraction HDR monotherapy would have considerable logistic and cost advantages over the alternatives.
KEYS TO TREATMENT DURATION
Image guidance with TRUS guides the transperineum placement of temporary catheters at the base of the prostate, and then TRUS or an alternative imaging modality like computed tomography (CT) or magnetic resonance imaging (MRI) is used to acquire data for treatment planning. (“Computed tomography contouring of soft-tissue anatomy can be challenging, but MRI provides optimal soft-tissue imaging and definition of the clinical target volume,” Morton and Hoskin note.1 However, TRUS and CT are far more widely available than MRI, they acknowledge.)
Treatment plans specify bead placement and dwell times along target tissue (tumor) contours to minimize irradiation of nearby nontarget healthy but radiosensitive rectal and urethral tissue.1 Treatment delivery usually requires about 10 minutes, but depending on imaging modalities employed, HDR brachytherapy can require 90 minutes (with TRUS) to several hours (with CT or MRI).1
If longer follow-up studies confirm the early promise of single-fraction HDR monotherapy, this “may well become the treatment of choice for many men with localized prostate cancer,” Morton and Hoskin predict.
Bryant Furlow is a medical journalist based in Albuquerque, New Mexico.
1. Morton GC, Hoskin PJ. Brachytherapy: current status and future strategies—can high dose rate replace low dose rate and external beam radiotherapy? Clin Oncol (R Coll Radiol). 2013;25(8):474-482. doi:10.1016/j.clon.2013.04.009.
2. Morton G, Loblaw A, Cheung P, et al. Is single fraction 15 Gy the preferred high dose-rate brachytherapy boost dose for prostate cancer? Radiother Oncol. 2011;100(3):463-467.
3. Hoskin PJ, Rojas AM, Bownes PJ, et al. Randomised trial of external beam radiotherapy alone or combined with high-dose-rate brachytherapy boost for localized prostate cancer. Radiother Oncol. 2012;103(2):217-222. doi:10.1016/j.radonc.2012.01.007.
4. Zaorsky NG, Doyle LA, Yamoah K, et al. High dose rate brachytherapy boost for prostate cancer: a systematic review. Cancer Treat Rev. 2014;40(3):414-425. doi:10.1016/j.ctrv.2013.10.006.
5. Tselis N, Tunn UW, Chatzikonstantinou G, et al. High dose rate brachytherapy as monotherapy for localised prostate cancer: a hypofractionated two-implant approach in 351 consecutive patients. Radiat Oncol. 2013;8:115. doi:10.1186/1748-717X-8-115.
6. Yoshioka Y, Konishi K, Suzuki O, et al. Monotherapeutic high-dose-rate brachytherapy for prostate cancer: a dose-reduction trial. Radiother Oncol. 2014;110(1):114-119. doi:10.1016/j.radonc.2013.10.015.
7. Yamada Y, Rogers L, Demanes DJ, et al; American Brachytherapy Society. American Brachytherapy Society consensus guidelines for high-dose-rate prostate brachytherapy. Brachytherapy. 2012;11(1):20-32. doi:10.1016/j.brachy.2011.09.008.