Bulb of penis as a marker for prostatic apex in external beam radiotherapy of prostate cancer

Toxicity profile and Patient-Reported outcomes following salvage Stereotactic Ablative Radiation Therapy to the prostate Bed: The POPART multicentric prospective study

Background

While SBRT to the prostate has become a valuable option as a radical treatment, limited data support its use in the postoperative setting. Here, we report the updated results of the multicentric Post-Prostatectomy Ablative Radiation Therapy (POPART) trial, investigating possible predictors of toxicities and patient-reported outcomes.

Methods

Patients with PSA levels between 0.1-2.0 ng/mL after radical prostatectomy received Linac-based SBRT to the prostate bed in five fractions every other day for a total dose of 32.5 Gy (EQD21.5 = 74.3 Gy). Late toxicity was assessed using CTCAE v.5 scale, while EPIC-CP, ICIQ-SF, IIEF 5 questionnaires and PSA levels measured quality of life and biochemical control. Pre- and post-treatment scores were compared using a paired t-test, with MID established at > 0.5 pooled SD from the baseline. A logistic regression analysis was performed to evaluate potential associations between specific patient/tumor/treatment factors and outcome deterioration.

Results

From April 2021 to April 2023 a total of 50 pts were enrolled and treated. Median follow-up was 12.2 (3-27) months. No late ≥ G2 GI or GU toxicity was registered. Late G1 urinary and rectal toxicities occurred in 46 % and 4 % of patients, respectively. Among 47 patients completing all EPIC-CP domains, four (9 %) showed worsened QoL, and eleven (26 %) developed erectile dysfunction correlating with PTV D2% (P = 0.032). At Multivariate analysis bladder wall D10cc independently correlated with late G1 GU toxicity (P = 0.034). Median post-treatment PSA nadir was 0.04 ng/mL (0.00 - 0.84). At the last follow-up, six patients presented with biochemical failure, including two nodal relapses.

Conclusions

Our findings show that post-prostatectomy SBRT did not result in increased toxicity nor a significant decline in QoL measures, thus showing that it can be safely extended to the postoperative setting. Long-term follow-up and randomized comparisons with different RT schedules are needed to validate this approach.

Prostate Bed Delineation Guidelines for Postoperative Radiation Therapy: On Behalf Of The Francophone Group of Urological Radiation Therapy

PURPOSE

Prostate bed (PB) irradiation is considered the standard postoperative treatment after radical prostatectomy (RP) for tumors with high-risk features or persistent prostate-specific antigen, or for salvage treatment in case of biological relapse. Four consensus guidelines have been published to standardize practices and reduce the interobserver variability in PB delineation but with discordant recommendations. To improve the reproducibility in the PB delineation, the Francophone Group of Urological Radiotherapy (Groupe Francophone de Radiothérapie Urologique [GFRU]) worked to propose a new and more reproducible consensus guideline for PB clinical target volume (CTV) definition.

METHODS AND MATERIALS

A 4-step procedure was used. First, a group of 10 GFRU prostate experts evaluated the 4 existing delineation guidelines for postoperative radiation therapy (European Organization for Research and Treatment of Cancer; the Faculty of Radiation Oncology Genito-Urinary Group; the Radiation Therapy Oncology Group; and the Princess Margaret Hospital) to identify divergent issues. Second, data sets of 50 magnetic resonance imaging studies (25 after RP and 25 with an intact prostate gland) were analyzed to identify the relevant anatomic boundaries of the PB. Third, a literature review of surgical, anatomic, histologic, and imaging data was performed to identify the relevant PB boundaries. Fourth, a final consensus on PB CTV definition was reached among experts.

RESULTS

Definitive limits of the PB CTV delineation were defined using easily visible landmarks on computed tomography scans (CT). The purpose was to ensure a better reproducibility of PB definition for any radiation oncologist even without experience in postoperative radiation therapy.

CONCLUSIONS

New recommendations for PB delineation based on simple anatomic boundaries and available as a CT image atlas are proposed by the GFRU. Improvement in uniformity in PB CTV definition and treatment homogeneity in the context of clinical trials are expected.

The Utility of Penile Bulb Contouring to Localise the Prostate Apex as Compared to Urethrography

PURPOSE

High-precision radiotherapy relies on accurate anatomic localisation. Urethrography is often used to localise the prostatic apex. However, urethrography is an invasive localisation procedure and may introduce a systemic error. The penile bulb (PB) is contoured to minimise the risk of erectile dysfunction. The purpose of this study is to assess the value of using the PB, as an alternative to urethrography, to localise the prostate.

METHODS AND MATERIALS

The PB was localised on 10 patients treated with simplified intensity-modulated arc radiotherapy at computed tomography simulation during treatment weeks 1 and 7. All patients underwent placement of fiducial markers. Urethrography was used only at simulation. Distances from the superior PB contour to the inferior prostate contour, the apex fiducial marker, and to the inferior prostate contour were obtained as well. The PB was contoured by two observers independently. Agreement coefficients and analysis of variance were used to assess reliability between rates and consistency of measurements over time.

RESULTS

The PB-apex distance was greater than or equal to the urethrogram-apex distance in 24/30 (80%) measurements, and the median difference was 3 mm and was consistent between raters. The greatest variation in PB-IM distance between weeks was 6 mm, the median was 3 mm, and the agreements of measurements between weeks for raters 1 and 2 were 0.79 and 0.69, respectively. These differences were not statistically different and were consistent with the computed tomography slice thickness.

CONCLUSIONS

The PB can be used to identify the prostate apex and can be reliably contoured between observers. Measurements are consistent between patients and through the duration of treatment. The PB distance measurements support studies indicating that urethrography causes a shift of the prostate superiorly. The distance from the PB to prostate apex remains stable during treatment for individual patients but varies between patients.

An interobserver study of prostatic fossa clinical target volume delineation in clinical practice: are regions of recurrence adequately targeted?

OBJECTIVES

To study interphysician variability of delineation of the prostatic fossa clinical target volume (pfCTV) to be irradiated in patients with residual or recurrent microscopic prostate cancer following radical prostatectomy and to estimate the risk for a geographical miss.

METHODS

Thirty-eight pfCTV were delineated on postradical prostatectomy computerized tomography scans of 8 patients by 5 observers. To estimate the risk of a geographical miss, a high risk volume (HRV) was defined and the percentage of "missed" HRV was calculated for each pfCTV.

RESULTS

Interphysician variability was considerable with a mean pfCTV of 39.09 cm (range, 11.8-72.5 cm). At least 25% of the HRV at the bladder neck/anastomosis and the retro-vesical space was excluded in 11 pfCTVs. The mean "missed" HRV was 27.5% (range, 2.3%-78.7%). A pfCTV of less than 30 cm was associated with a geographical miss in 66% of cases versus 17.2% for pfCTV of 30 cm or more (P = 0.006). Observer identity was significantly associated with excluded HRV (P = 0.03).

CONCLUSIONS

pfCTV delineation is subject to considerable interobserver variability associated with a significant risk of inadequate targeting of the anastomosis/bladder neck region and the retrovesical space. The failure to recognize regions at high risk for harboring microscopic disease may be due to a lack of familiarity with tissue redistribution following radical surgery, and a lack of literature-based guidelines for pfCTV delineation. A strategy to improve pfCTV delineation is proposed.

Guidelines for target volume definition in post-operative radiotherapy for prostate cancer, on behalf of the EORTC Radiation Oncology Group

The appropriate application of 3-D conformal radiotherapy, intensity modulated radiotherapy or image guided radiotherapy for patients undergoing post-operative radiotherapy for prostate cancer requires a standardisation of the target volume definition and delineation as well as standardisation of the clinical quality assurance procedures. Recommendations for this are presented on behalf of the European Organisation for Research and Treatment of Cancer (EORTC) Radiation Oncology Group and in addition to the already published guidelines for radiotherapy as the primary treatment.

Déplacements de la prostate et des vésicules séminales suite à l'uréthrographie : une étude par tomographie axiale

PURPOSE

It has been suggested that urethrography used for localization of the prostate apex may cause a systematic cranial displacement of the organ. Our objective was to use CT-CT image registration to identify if a clinically relevant systematic shift occurs in the position of the prostate and seminal vesicles following retrograde urethrography.

PATIENTS AND METHODS

Patients were scanned twice at the time of simulation. They were imaged supine, bladder empty. Scan resolution was 512x512 with 5 mm cuts. After the first CT sequence, with the patient still on the CT couch, an urethrogram was performed. The patients were then re-scanned. The image sets were registered through the use of external skin fiducials. A single author reviewed x, y and z-axis displacement. Z-axis motion of the prostate was also assessed by having three blinded radiation oncologists mark the cranial limit of the prostate on all 104 image sets.

RESULTS

Fifty-two pairs of CT scans were analyzed for post-urethrogram organ displacement. The mean x axis displacement of the prostate was 0.016 mm (P=0.8), the mean y-axis displacement was 1.3 mm anterior (P<0.001). Mean z-axis displacement of the prostate, using the blinded assessments, was a 1.35 mm cranial shift (P<0.0001). Analogous shifts were identified for the seminal vesicles.

CONCLUSION

Our results suggest a small cranial and anterior displacement of the prostate and seminal vesicles following retrograde urethrography.

Critical organ dosimetry in permanent seed prostate brachytherapy: Defining the organs at risk

PURPOSE

Although permanent seed prostate brachytherapy is associated with a low risk of serious morbidity, proctitis and prolonged irritative and obstructive urinary symptoms may occur. Data are accumulating to help establish thresholds or guidelines for minimizing toxicity, however, no uniform method of defining and calculating the dose to critical organs currently exists. We set out to examine the existing data and propose a uniform method of reporting such that results from different centers can more easily be compared.

METHODS AND MATERIALS

In preparation for a panel discussion at the American Brachytherapy Society 2004 Annual Meeting, four members with expertise in prostate dosimetry and critical organ assessment performed a literature search and, supplemented with their clinical experience, formulated a proposal for defining and reporting dose in a standardized fashion to the critical organs for permanent seed prostate brachytherapy.

RESULTS

As previously recommended by the American Brachytherapy Society, postimplant dosimetry should be performed on all patients undergoing permanent prostate brachytherapy. The standard imaging for postplan assessment is the CT scan. The interval between seed implantation and postplan assessment should be reported. For rectal and urinary morbidities, the critical organs are considered to be the anterior rectum and the prostatic urethra, respectively. For erectile dysfunction, both the neurovascular bundle and penile bulb have been implicated. The rectum should be contoured on all CT scan slices where radioactive seeds are visible. Both the inner and outer walls should be contoured. The dose should be reported as RV100 and RV150, the volumes in cubic centimeters of the rectal wall receiving 100% and 150% of the prescribed dose, respectively. The urethra should be contoured as a structure on each slice where seeds can be seen. The urethra should be identified by either catheterization or fusion with transrectal ultrasound. The dose should be reported as UrD5 and UrD30, which are, respectively, the dose to 5% and 30% of the urethra in Gray. As well, a UrV150 should be reported, which is the volume in cubic centimeters of the urethra receiving 150% of the prescribed dose. No recommendations can be made at this time for reporting neurovascular bundle or penile bulb doses.

CONCLUSIONS

It is essential that toxicity data be collected and reported in a uniform fashion. Thus, the critical organs for toxicity must be defined and the corresponding dosimetry reported in a standard fashion such that guidelines can be established in the future based on data from a cross-section of centers.

Factors predicting an increased dose to the penile bulb in permanent seed prostate brachytherapy

PURPOSE

Erectile dysfunction following permanent seed brachytherapy for prostate cancer may be related to the dose to the penile bulb. We investigated anatomic and dosimetric factors that might contribute to an increased dose to the penile bulb.

METHODS AND MATERIALS

One-month CT and MR images were examined for 50 consecutive patients treated with exclusive (125)I permanent seed prostate brachytherapy to a prescribed dose of 145 Gy. Implants were preplanned by transrectal ultrasound (TRUS). Postimplant dosimetry was performed at 1 month using an MRI-CT fusion. Spearman's correlation was used to establish a correlation between dosimetric parameters, anatomical factors, and the dose to the penile bulb.

RESULTS

Penile bulb volumes ranged from 1.2-8.5 cc (median, 3.9 cc). The distance from the penile bulb to the prostate apex ranged from 5-33 mm (median, 15.5 mm). D50 of the penile bulb ranged from 13-121 Gy. The range for the V45 (65 Gy) was 0-87%; only 3% of patients had >2 cc covered by this isodose and in 16% of patients the V45 covered more than 50% of the penile bulb. About one-third of the patients received a dose to the bulb that would put them at a high risk of erectile dysfunction after external beam radiation, if the dose were radiobiologically equivalent. There was a significant inverse correlation between the distance between the prostate apex and the penile bulb, and the dosimetric parameters of the bulb: r = -0.548, -0.656, p = < 0.01. The further caudal the apex was from the symphysis, the closer it was to the penile bulb (r = -0.564, p = <0.01). We could not find a correlation between the dose to the prostate or its apex and the dose to the penile bulb.

CONCLUSION

When the prostate apex is close to the penile bulb, care should be taken to limit the dose to the penile bulb, if possible. This may reduce the incidence of erectile dysfunction and urinary toxicity after permanent seed prostate brachytherapy.