There is a growing body of evidence supporting the use of radiation therapy in the postoperative setting for men with prostate cancer. Clinical trials and retrospective series have generally used non-conformal methods to administer this therapy.1, 2, 4
Three dimensional conformal radiation therapy and intensity modulated radiation therapy allow a reduction in the volume of bladder and rectum irradiated in the postoperative setting.6
This may improve treatment tolerance to the treatment and may open up the opportunity for radiation dose escalation in the postoperative setting.12
Patterns of clinical local failure following radical prostatectomy have been reported using a variety of imaging modalities. Using ultrasound, Connolly reported 53.5% of patients had biopsy evidence of local tumor recurrence in the anastomotic site (66%), the bladder neck (16%), and the retrotrigone region (13%).13
In a series of 35 patients with clinical suspicion of local recurrence, Silverman reported a sensitivity and specificity of 100% using transrectal contrast enhanced surface coil MRI to detect 31 recurrences. In that series the locations of the recurrences were at the posterior aspect of the VUA in 16, anterior to the VUA in 9 and both anterior and posterior to the VUA in 6 cases.14
Sella reported similarly high rates of sensitivity and specificity using endorectal coil MR imaging to detect 39 of 41 local recurrences in the prostate bed. Local recurrences were at the VUA in 19%, retrovesical in 40%, in retained seminal vesicles in 22% and at the anterior or lateral surgical margin in 9%.15
Leventis reported the location of local recurrences by ultrasound to commonly involve the VUA, bladder neck and retrovesical space.16
Several other groups have defined a 0radiation clinical target volume for patients following radical prostatectomy. 17-19
While there are some similarities to the current study, there are also many differences. As in our study, the published patterns of failure were reviewed by these investigators. In addition, some groups examined their own institutional experience with local recurrences and their locations by imaging. In the consensus paper by Wiltshire et al19
, they identified at least one gross local recurrence in the retropubic region, anterior to the VUA. In the series from Miralbell17
, sixty patients had abnormalities on contrast enhanced endorectal MRI. The location of the MRI abnormalities was determined to be at or near the VUA in all cases. They concluded that a cylindrically shaped (4cm high and 3cm) diameter CTV centered 0.5cm posterior and 3mm inferior to the VUA would encompass all these visualized sites of gross recurrence. Interestingly, they did not see recurrences in sites previously described by other authors such as the retrovesical space and their recommended CTV does not include these sites. Poortmans18
reported a similar consensus panel target volume for postoperative irradiation of prostate cancer patients to be utilized by EORTC sites. As in other published series, they used a pattern of failure review to determine the appropriate CTV in the postoperative setting. The published CTV from that series is subjectively smaller than that proposed by this group.
In this study, the approach differed from other groups because a consensus for the postoperative CTV was established by clinical investigators specializing in the treatment of prostate cancer. Anonymized clinical CT data sets were distributed to thirteen GU experts from RTOG institutions. While there was qualitatively substantial variation in the target volumes there were significant areas of agreement amongst these physicians. We then derived a CTV model using a statistically derived imputation method from the independently submitted contours. Starting from these STAPLE contours, a subgroup of participating investigators convened to define a consensus CTV for the two submitted clinical scenarios. This consensus CTV was then distributed for review and comments to the group of participants from the RTOG GU Committee. Whereas other CTV contours used a “bottom up” approach to create postoperative CTV from patterns of failure, our group used a “top down” approach to create a consensus CTV from individual submitted expert contours. It is possible that this method of target volume development could be applied to other disease sites. We are currently investigating this in breast and anal cancers.
The CTV defined by this group represents a minimum volume to be irradiated in a typical postoperative scenario. It is recognized that clinical judgment may require modification of the described CTV. As with any set of treatment guidelines, individual practitioners will have to consider individual patient characteristics. Variability in anatomy and co-morbidities are factors which may need to be considered in individual cases. The panelists felt that the pathology report should be available when defining the CTV with careful attention to areas of extraprostatic extension, seminal vesicle invasion or positive margins. Preoperative imaging, when available, can also help establish the superior limit of the CTV by referencing the superior extent of the prostate gland and seminal vesicles.
The inferior aspect of the CTV generated the most discussion and some disagreement amongst the participants. Wiltshire et al included urological surgeons in the development of their published postoperative CTV and they were emphatic that the penile bulb is never exposed to the surgical cavity.19
On the other hand, some of the radiation oncologists in our group expressed concern that apical tumors can extend into the GU diaphragm and inferior urethral sphincter. Tumor recurrences in this region are possible after either surgery or radiation therapy. For this reason, we agreed that the inferior aspect of the CTV should be allowed to extend to a level just above the penile bulb. This creates a CTV that could be 3 to 6 mm inferior to that described by Wiltshire.