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IMRT, 3D-CRT confer similar patient-reported outcomes in prostate cancer
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Intensity-modulated radiation therapy was not associated with improved patient-reported bowel, bladder and sexual function outcomes compared with 3-dimensional conformal radiation therapy given in similar doses for prostate cancer, according to study results.
“There is evidence suggesting that [intensity-modulated radiation therapy] may achieve higher [radiation therapy] doses with no increase or even with a lower dose to normal critical structures, such as bowel and bladder, compared with [3-dimensional conformal radiation therapy],” Deborah W. Bruner, RN, PhD, of the Nell Hodgson Woodruff School of Nursing at Emory University, and colleagues wrote. “However, the cost of [intensity-modulated radiation therapy] may be more than twice that of [3-dimensional conformal radiation therapy] because of increased treatment planning.”
No study had yet directly compared outcomes for patients with prostate cancer who received similar doses of intensity-modulated radiation therapy (IMRT) and 3-dimensional conformal radiation therapy (3D-CRT), according to study background.
Bruner and colleagues evaluated data from 763 men with histologically confirmed prostate adenocarcinoma who were assigned to the high-dose arm of the phase 3 Radiation Therapy Oncology Group (RTOG) 0126 trial. The trial sought to compare high-dose 3D-CRT/IMRT — given in 79.2 Gy in 44 fractions — with 70.2 Gy in 39 fractions.
Patients in the 3D-CRT group received 55.8 Gy to the prostate and proximal seminal vesicles followed by 23.4 Gy to the prostate only. Patients in the IMRT group received 79.2 Gy to the prostate and proximal seminal vesicles.
Patient-reported outcomes were assessed at baseline, 3 months, 6 months, 12 months and 24 months using the Functional Alterations due to Changes in Elimination (FACE) instrument — which assessed bladder and bowel function — and International Index of Erectile Function (IIEF). Researchers evaluated data from patients who completed all items on the FACE and IIEF. If patients completed 13 out of 15 items, researchers conducted an imputed data analysis by replacing the missing item response with the average item response.
Overall, 551 patients completed all minimum FACE data, with data imputed from an additional 78 patients (n = 595). A total of 505 patients completed the minimum IIEF data, and researchers imputed data from an additional 72 patients (n = 577).
Researchers observed no statistically significant differences in erectile function for patients receiving IMRT or 3D-CRT. IMRT patients received a significantly lower penile bulb dose than patients in the 3D-CRT group (P < .0001); however, bulb dose was not significantly linked to IIEF outcomes in either univariate or multivariate sensitivity analyses. These findings persisted even for men aged younger than 70 years, the researchers noted.
The data also indicated that there were no significant differences between IMRT and 3D-CRT in bowel or urinary patient-reported symptoms at all of the time points in the computed and imputed analyses.
The researchers acknowledged the lack of randomization to the IMRT or 3D-CRT treatment arms may be a possible limitation to these findings due to the potential for sampling bias. Rectal bleeding also was not included on the FACE questionnaire as a potential treatment-related outcome.
“The benefit of IMRT over 3D-CRT in terms of bowel, bladder and sexual functions reported by patients themselves has not been supported,” Bruner and colleagues concluded. “It seems reasonable to continue to push for a higher radiotherapy dose to the tumor with a decreasing dose to normal tissues in the experimental setting to determine whether a threshold can be reached that maintains or improves tumor control but decreases treatment-related symptoms to the point at which patients are able to experience a noticeable improvement.”
Advances in technology used in radiation oncology have not necessarily led to reduced toxicity, W. Robert Lee, MD, MS, Med, of the department of radiation oncology at Duke University Medical Center, wrote in an accompanying editorial.
“As the first decade of widespread use of IMRT in prostate cancer ends, the promised dramatic differences in toxicity between IMRT and 3D-CRT are not evident; the effect seems to be much smaller than had been hoped,” Lee wrote. “It is possible that there is a learning curve with IMRT and that the results achievable with more current methods would demonstrate a greater advantage. Whether the increased total dose achievable with IMRT will reduce mortality from prostate cancer with an acceptable increase in acute and late [gastrointestinal/genitourinary] toxicities awaits the publication of RTOG 0126.” – by Cameron Kelsall
Disclosure: Bruner reports no relevant financial disclosures. Lee reports membership on the NCI Genitourinary Steering Committee. Please see the full study for a list of all other authors’ relevant financial disclosures.
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