Adaptive image-guided radiation therapy may improve bladder preservation

The use of adaptive image-guided radiation therapy as part of trimodality therapy for bladder preservation in patients with localized bladder cancer yielded good oncological outcomes with low rates of acute and late toxicities, according to prospective study results.

Trimodality treatments — consisting of transurethral resection of the bladder tumor, radiation and chemotherapy — for bladder preservation have shown equivalent oncologic outcomes as radical cystectomy. The development of intensity-modulated, image-guided and adaptive radiation techniques may further lessen acute and late toxicities associated with the approach.

“Although a number of investigators have conceived and developed a variety of adaptive radiation therapy techniques, there are few clinical outcome data to validate this dosimetric concept,” Vedang Murthy, MD, radiation oncologist at Tata Memorial Centre in Mumbai, India, said in a press release. “The present proof-of-concept prospective study was conducted with the aim of establishing the safety, efficacy and feasibility of image-guided, intensity-modulated adaptive radiation therapy in clinical practice.”

The analysis included data from 44 patients (median age, 64 years; interquartile range [IQR], 55-72; 88% men) with localized bladder cancer. Patients underwent trimodality treatment with maximal safe surgical resection and concurrent platinum-based chemotherapy followed by adaptive image-guided radiation therapy. Sixteen patients (36%) received neoadjuvant chemotherapy.

The researchers used a plan-of-the-day approach involving megavoltage imaging to choose the most appropriate planning target volumes encompassing the bladder for the particular day.

Radiation therapy planning included three (n = 34) or six (n = 10) concentrically grown planning target volumes. Patients received 64 Gy in 32 fractions to the whole bladder and 55 Gy to pelvic nodes.

Seventy-three percent of patients received prophylactic nodal irradiation and 55% received a simultaneous integrated boost (68 Gy) to the tumor bed.

Median follow-up was 30 months (IQR, 10-57).

Overall, the 3-year locoregional control rate was 78%. Sixty-seven percent of patients achieved 3-year OS and 66% achieved 3-year DFS.

Of the 34 patients alive after 3 years, all but two were disease free. Among patients who died, three died of comorbidities and were disease free at the time of death.

The bladder preservation rate at 3 years was 83%.

An insignificantly greater proportion of patients who received the 68 Gy escalation doserather than the 64 Gy dose achieved 3-year locoregional control (87% vs. 68%) and OS (74% vs. 60%).

Five patients who received dose escalation (11%) and two who did not (4%) experienced grade 3 genitourinary toxicity. No patients experienced acute or late grade 3 or worse gastrointestinal toxicity. Receipt of the higher, 68-Gy dose did not appear to impact rate of acute and late genitourinary and GI toxicities.

The researchers acknowledged the study’s relatively brief follow-up period, as well as their lack of quality of life data, as limitations.

“These results provide proof of concept of using adaptive image-guided radiation therapy in the clinic,” Murthy said. “This will hopefully lead to more and more suitable patients undergoing bladder preservation around the world.” – by Cameron Kelsall

Disclosure: The researchers report no relevant financial disclosures.