In bladder cancer target delineation, planning only works when target definition, bladder filling reproducibility, and daily verification stay aligned from the first pelvic field to the final boost. This detailed article rewrites the chapter in a practical voice; for the broader framework, see our complete guide to target volume delineation and field setup.
The chapter’s central message is straightforward. Organ preservation is not driven by dose prescription alone. It depends on maximal TURBT, concurrent chemoradiotherapy, margins that respect bladder motion, and a boost strategy that matches the anatomy treated in each phase.
Bladder cancer target delineation: general principles
The starting point is the definitive organ-preservation setting. For node-negative, muscle-invasive bladder cancer, bladder-sparing trimodality therapy is presented as a standard treatment option. That approach combines maximal, ideally complete, TURBT with concurrent chemoradiotherapy. In node-positive disease, systemic chemotherapy remains the mainstay, but chemoradiation is still reasonable when disease is confined to pelvic or para-aortic nodes.
The chapter also reflects a technical transition. Classical RTOG/NRG protocols used three-dimensional conformal radiation therapy, but future NRG studies, including the phase III SWOG/NRG 1806 trial (NCT03775265), allow IMRT during concurrent chemoradiotherapy. That shift is not framed as a purely technological upgrade. It appears because IMRT can reduce dose to adjacent normal tissue, especially bowel, when protocol constraints cannot be achieved with 3D-CRT planning.
At the same time, the text avoids pretending that one layout fits every patient. It states that there is no consensus on the optimal field design – whole bladder with or without prostate, partial bladder treatment, or elective nodal coverage – and no consensus on fractionation, which may involve daily treatment, BID hyperfractionation, or hypofractionation. The practical consequence is that field design has to follow disease extent and the team’s ability to reproduce anatomy throughout the course, not habit.
The chapter is equally firm about radiosensitization. Definitive treatment should include radiosensitizing therapy in all eligible patients. Several regimens are cited, but the agents used most often are cisplatin, fluorouracil (5 FU)/mitomycin C, and gemcitabine. Adjuvant radiotherapy after radical cystectomy is still under investigation and is considered most appropriate for pT3 disease, pN+ disease, and/or positive surgical margins. In selected locally advanced cases with a high likelihood of positive margins, intraoperative radiotherapy may also be appropriate. Throughout all of this, the organs at risk that stay in focus are small bowel, large bowel, rectum, and femoral heads.
If you want a comparison point from the same series, read our dedicated lung cancer article.
Three-dimensional conformal radiation therapy (3D-CRT)
In RTOG 0712 and 0926, the planning logic is sequential. Treatment begins with a small pelvic field that includes the whole bladder, the prostate and prostatic urethra in men, the proximal urethra in women, and the regional lymphatics. That is followed by a cone down to a whole-bladder field focused on the entire bladder plus any gross tumor volume. The chapter is careful here because the distinction between elective pelvic coverage and the high-dose phase drives the rest of the design.
The small pelvic field is generally planned with a four-field box. The whole-bladder field is usually planned either with a four-field box or with parallel opposed laterals. The intent is clear: preserve reliable target coverage while keeping control of rectal, bowel, and femoral head dose. The text also notes that multi-leaf collimation can improve conformality when the planner needs to shape the field more tightly around the intended volume.
Table 26.1. Dose constraints for selective bladder preservation with 3D-CRT
The protocol summary below concentrates the organ-at-risk constraints cited for RTOG 0712 and 0926. These values set the practical limits of conformal planning and help define when 3D-CRT remains acceptable and when IMRT may offer a better solution.
| Organ at risk | Constraints |
|---|---|
| Rectum | V30 < 50% (0712) or V55 < 50% (0926) V55 < 10% (0712) |
| Femoral heads | V50 < 20% (0712) Dmax < 45 Gy (0712, 0926) |
| Small bowel | D45 < 300 cm3 |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 26.1)
Table 26.2. Field design for selective bladder preservation with 3D-CRT
This table matters because it goes beyond naming the fields. It defines borders, expansions, and adjustments that make standard pelvic coverage actually correspond to the lymphatics and bladder volumes the protocol intends to treat.
| Field | Definition and limits |
|---|---|
| Small pelvic field | Designed to cover the whole bladder and regional pelvic nodes, as well as the prostate/prostatic urethra in men and the proximal urethra in women, using a four-field box arrangement. AP/PA fields: superior extent to the S1/S2 junction anteriorly and inferior extent 1 cm below the obturator foramen. Laterally, extend 1.5 cm beyond the bony pelvis at its widest diameter. Block the femoral heads. Parallel opposed laterals: same superior and inferior extent as the AP/PA fields. Anteriorly, 1 cm anterior to the symphysis pubis or 1.5 cm anterior to the whole-bladder CTV. Posteriorly, extend 3 cm beyond the whole-bladder CTV. An anterior block may be considered to reduce small-bowel dose. Contouring pelvic nodes is recommended to confirm that standard fields truly encompass the intended lymphatics at risk and to allow border adjustment when needed. |
| Whole-bladder field | The whole-bladder CTV includes the entire bladder and any gross tumor volume (GTV). The whole-bladder PTV is generated with a 0.5 cm isotropic expansion on the CTV, except for 1.5 cm superiorly. Field design may use a four-field box or opposed laterals to optimize target coverage and organ-at-risk sparing, with multi-leaf collimation used to improve conformality. |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 26.2)
The randomized study cited in the chapter compared standard whole-bladder radiotherapy with reduced high-dose volume radiation therapy (RHDVRT). It found no significant reduction in late toxicity and demonstrated non-inferiority in locoregional control for RHDVRT versus whole-bladder treatment. That keeps two reduction strategies on the table: a two-phase sequential boost or a single-phase concomitant boost. Figures 26.1 and 26.2 support that discussion by showing the DRRs for the small pelvic field and the cone down or SIB layouts.
Intensity-modulated radiation therapy (IMRT)
When the chapter turns to IMRT, it does not redefine the targets from scratch. The volumes remain similar to 3D-CRT and include the whole bladder, the prostate and prostatic urethra in men, and the proximal urethra in women, with or without nodal coverage. What changes is the technical burden. Daily variability in bladder motion creates uncertainty that has to be absorbed by PTV margin, daily setup, and consistent image guidance.
The text is careful not to treat that uncertainty as a bladder-only problem. It explicitly asks the reader to assess day-to-day variation in adjacent organs at risk, especially small and large bowel in the superior, anterior, and lateral directions, and large bowel, sigmoid, and rectum in the posterior and lateral directions. In practical terms, the plan is only as robust as the team’s ability to understand what structures move around the bladder from one fraction to the next.
That is where IMRT earns its role. The chapter highlights reduced dose to organs at risk immediately adjacent to the high-dose PTV, particularly small and large bowel. It also creates an opportunity to spare uninvolved bladder during partial bladder or reduced-volume irradiation, which may support dose escalation to the TURBT bed. The conventional prescriptions cited are 64-66.6 Gy delivered in 32-37 fractions. Elective treatment of regional nodes, including the bladder CTV, is generally 39.6-45 Gy in 1.8 Gy fractions before a sequential bladder boost of 19.8-21.6 Gy, also in 1.8 Gy fractions.
Table 26.3. Field design for selective bladder preservation with IMRT
The IMRT table moves from concept to contouring. It separates the initial pelvic field from the bladder-boost field and makes the expansions for bladder, pelvis, and gross disease explicit.
| Field | Definition and volumes |
|---|---|
| Initial pelvic field | Designed to cover the whole bladder and regional pelvic nodes, as well as the prostate/prostatic urethra in men. GTV = any gross disease and/or tumor bed defined by fiducials or post-TURBT imaging. CTV bladder = whole bladder (including GTV) + prostate/prostatic urethra in men or proximal urethra in women. PTV bladder = CTV bladder + 1.5 cm. CTV pelvis = bilateral pelvic nodal regions (perivesical, internal iliac, external iliac, presacral, distal common iliac). PTV pelvis = CTV pelvis + 8-10 mm on the vessels, corresponding to the nodal regions. If pelvic nodes are treated, combine PTV bladder + PTV pelvis to create the composite PTV for the initial pelvic field. |
| Bladder-boost field | GTV/CTV bladder boost = any gross disease and/or tumor bed defined by fiducials or post-TURBT imaging. PTV bladder boost = CTV + 1 cm isotropic expansion. |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 26.3)
Figures 26.3 through 26.5 show what that logic looks like in actual cases: an initial pelvic IMRT field, a sequential bladder boost, and a bladder-only IMRT approach during concurrent chemoradiation. Their value is practical. They show that the choice between whole-pelvis treatment and bladder-only treatment changes the contours, the PTV, and the relationship to rectum, prostate, and bowel loops.
Simulation and planning
The simulation section is short but decisive. CT-based simulation is recommended with the patient supine and using an appropriate pelvic immobilization device. That sounds operational, yet the chapter ties immobilization directly to the ability to deliver IGRT safely in muscle-invasive bladder cancer.
The other non-negotiable point is bladder filling reproducibility. The text states explicitly that reproducible filling and image-guided verification are critical for effective and safe IGRT delivery. Image guidance may vary by institution, but the workflow described is concrete. During the initial phase, daily KV imaging matched to bone is used together with at least weekly CBCT to verify bladder position. During the boost phase, daily KV imaging matched to fiducials and/or daily CBCT is appropriate. When fiducials are absent, daily CBCT is recommended for the boost phase.
MSKCC guidelines
The Memorial Sloan Kettering Cancer Center section translates the chapter into a very practical workflow. Definitive trimodality therapy generally begins with maximal TURBT, bladder mapping, and placement of gold fiducial markers at the periphery of the TUR bed. That detail matters because it turns the boost from a largely inferred target into a better localized one.
After TUR with fiducial placement, CT-based simulation is performed with an empty bladder. The reasons are stated plainly: consistency and reduction of the initial target volume. Oral contrast is used to delineate bowel, while intravenous contrast should be used with caution in patients with impaired renal function or in those expected to receive nephrotoxic chemotherapy. Then, during week 3-4 of concurrent chemoradiation, CT re-simulation is performed with a full bladder to plan the cone down phase. Here the rationale changes. A full bladder helps displace bowel and uninvolved bladder wall away from the boost target.
The initial phase prescription is 4500 cGy delivered in 25 daily fractions of 180 cGy. Targets for that phase are the whole bladder, the prostate/prostatic urethra, and the regional pelvic nodes: obturators/perivesical, external iliac, internal iliac, presacral, and common iliac nodes up to the aortic bifurcation. The cone down phase delivers 2160 cGy in 12 daily fractions, for a cumulative dose of 6660 cGy in 37 fractions to the boost PTV. The target in that second phase is the TURBT bed defined by fiducials plus a 1 cm margin.
The chapter also leaves room for selected patients. Hypofractionated regimens of 55 Gy in 20 fractions may be used. In that setting, target volumes include the bladder/prostatic urethra and any gross tumor with a 1.5 cm circumferential margin, together with daily CBCT for image guidance. Radiosensitizing chemotherapy is used when clinically appropriate. The patients mentioned here include those with poor performance status, the very elderly, cystectomy-ineligible patients with multifocal disease, and patients receiving palliation for locally advanced disease.
For node-positive patients, the initial phase may incorporate a simultaneous integrated boost to gross adenopathy. The institutional reference is 5625 cGy in 25 daily fractions of 225 cGy to gross nodal disease, with PTV defined as GTV + 5 mm and normal tissue tolerance respected. Figures 26.6 and 26.7 close the chapter with exactly this kind of case, showing how planning changes when disease extends beyond the bladder wall and into visible nodal disease.
If you want the wider perspective from this book, from field design to disease-site recommendations, return to the complete clinical guide. For bladder cancer, the chapter leaves little doubt: local control and organ preservation depend less on any single technique than on consistency among contouring, bladder filling, daily imaging, and boost logic.
