The penis lends itself well to the application of interstitial brachytherapy and has been successfully treated with LDR brachytherapy for decades with reports from Europe, India, and Canada. Interstitial brachytherapy can deliver the required dose precisely and accurately to the target without excessive treatment of the penile shaft or concerns about daily set-up. Furthermore, for well lateralized lesions it is not necessary to treat the full thickness of the penis and some sparing of the contra-lateral glans is possible [25]. Technique and dose prescription have been more consistent over time with LDR brachytherapy than in the external beam literature.

LDR interstitial brachytherapy is performed with sterile technique in a dedicated brachytherapy procedure room or operating room under general anesthesia or penile block. The procedure generally takes 45 min to 1 h with the patient admitted afterward for the duration of the brachytherapy (4–6 days). After skin cleansing and creation of a sterile field, the penis is examined carefully and the visible/palpable lesion is delineated with sterile pen and the appropriate margins chosen. The patient is catheterized and an in-dwelling Foley catheter is left in situ until completion of treatment and removal of the brachytherapy needles. The position and spacing of the interstitial needles is chosen so as to avoid the urethra, and to have the superficial needles within 3 mm of the treated surface. If they are too deep, the surface will be underdosed, while if they are too shallow, skin ulceration and scarring will result. A minimum of a two-plane implant is required (Fig. 9.2). The needle direction can be either antero-posterior for a lateral lesion, or right–left for a thicker infiltrating lesion. If the anatomy does not allow both avoidance of the urethra and optimal depth under the surface, then a plesiotherapy plane can be added externally on the side of the cancer with the air gap filled with appropriate bolus material such as “superflab”, available from several radiotherapy supply companies (Fig. 9.3).

Guide templates are required to ensure parallelism and equal spacing. Both the needles and planes should be equidistant in an LDR implant. Ideal spacing is 12–18 mm with 15 mm most commonly used. Pairs of templates should be available, predrilled with an appropriate range of needle spacing but a “universal template” with holes drilled every 3 mm allows more flexibility once the first couple of needles have been placed (Fig. 9.4). Once positioned, the needles are fixed in place with washers against the template with a single set-screw in each to tighten against the shaft of the needle. Since the implant geometry is totally stable throughout the duration of the treatment, dosimetry can be calculated based on measurements of spacing and treated lengths but more commonly a CT scan is performed and the needles reconstructed from the scan.

The basic rules of geometry of the Paris System of Dosimetry should be appreciated in order to place the needles optimally [26]. When using classic LDR treatment with Iridium wire, it is essential to be aware that the length of your treated volume along the axis of the needles is 0.75 of the active length of the wire sources and to allow for the consequent in-drawing of the isodoses between the ends of the wires. Similarly, the spacing between the needles determines the lateral margin treated beyond the sources (0.27 × spacing; i.e.: 4 mm for 15 mm spacing; Fig. 9.5). If a stepping source is used from an automated afterloader, such as in Pulse Dose Rate Brachytherapy, then dose optimization is possible. Nonetheless, the prescribing rules of the Paris System give guidance as to desirable homogeneity, such that dose rate minima between the sources are 115 % of the prescription isodose, and the sum of the high dose sleeve around each source (V200) is <10 % of the treated volume.

Classic continuous LDR brachytherapy aims for a dose rate of 50–60 cGy per hour. Pulse dose rate brachytherapy (Fig. 9.6) is radiobiologically equivalent if hourly fractions of 0.5–0.6 Gy are delivered, 24 h per day [27–29]. Most PDR results are mixed with classic LDR in single institution reports but Kamsu-Kom et al. from Institut Gustav Roussy recently reported on 27 patients treated from 2008 to 2013 exclusively with PDR brachytherapy to a dose of 60–70 Gy with 0.4–0.5 Gy per hour, with results indistinguishable from those reported with classic LDR [30]. The total dose recommended is generally 60–65 Gy over 5 days. Minimal analgesia is required during the duration of the implant and the patient can even mobilize within the hospital room, disconnected from the afterloader between fractions for PDR cases. If the patient is less mobile, then anti-embolic stockings and low molecular weight heparin are advised as anti-thrombotic measures. Needle removal can occur at the bedside after premedication with a narcotic analgesic such as Demerol or morphine. Bleeding is usually minimal and the patient can be discharged the same day.

Selected results from the literature for interstitial brachytherapy are shown in Table 9.2. Five-year local control ranges from 70 to 96 % and 10-year from 70 to 80 %, with penile preservation at 10 years being 70 %. Local failures can be salvaged surgically and, as they can occur late, up to 8–10 years after treatment, continued surveillance and patient-awareness are essential. Crook et al. found that although five of eight local recurrences occurred in the first 2 years, the remaining three occurred at 4.5, 7, and 8 years after brachytherapy [18]. Similarly, Mazeron et al. [31] reported that 18 % of local recurrences occurred between 5 and 8 years and DeCrevoisier et al. found that with longer follow-up, 20 % were diagnosed beyond 8 years [19].

The use of manually afterloaded sources such as Iridium 192 wires is no longer available in most departments due to reasons of staff exposure, logistics of source disposal after use, and risks of contamination from having to cut brittle wire to the correct length. On the contrary, HDR afterloaders are available in most radiotherapy centers for use in more common malignancies such as breast and prostate, and as an essential component of curative treatment of cervical cancer. Recently, there has been renewed interest in brachytherapy for penile cancer using HDR. The technique is very similar to that described above for LDR but with a few notable exceptions.

Recent publications indicate that 3 Gy bid, 6 h apart is safe and effective for a total dose of 45–51 Gy delivered over 7.5–8.5 days [32, 33]. Penile preservation rates are reported between 80 and 100 %. Kellas-Slezka et al. report the largest series of 55 patients with median follow-up of 4.5 years [34]. A freehand flexible catheter technique was used to place 2–7 catheters to create either a single plane implant (n = 31) or two-plane (n = 24). Fraction size was 3.0–3.5 Gy with a median total dose of 49 Gy after biopsy (range 30–54 Gy) or 36 Gy (range 30–45.5) after previous total gross excision. Median duration of implant was 11 days and median follow-up was 59 months (8–152 months). Persistent tumors were seen in four patients and seven had a subsequent local recurrence. Regional failures were seen in 22 % and distant metastases in 5 %. Penile preservation was achieved in 80 % [34]. Although this is a large series with mature follow-up, at the time of writing, HDR brachytherapy for penile cancer must still be considered to be in evolution, as optimal fractionation and homogeneity parameters are yet to be established.