DVH constraints, not dose, impact bowel dysfunction after prostate RT
MedWire News: Rectal dose-volume histogram (DVH) parameters are associated with long-term patient-reported gastrointestinal (GI) quality of life (QoL) after prostate radiation, whereas actual radiation doses are not, report US researchers.
The findings are of clinical importance as they suggest that continued dose escalations may be feasible, provided that the appropriate DVH parameters are observed.
"We evaluated rectal dose-volume parameters in prostate cancer planning because of reports that dose-volume parameters are related to changes in physician-reported toxicity," explain Paul Nguyen (Dana-Farber Cancer Institute and Brigham and Women's Hospital, Boston, Massachusetts) and co-authors.
The team administered a validated QoL questionnaire to 64 men with localized prostate cancer who were treated with either 70.2 or 79.2 Gy external beam radiation therapy and had a minimum 7-year follow-up. DVH parameters of the anterior rectal wall were then correlated with patient-reported long-term GI QoL in 50 eligible patients.
The researchers found no significant difference in long-term bowel QoL scores between those receiving high, and low doses of radiation. However, there was a nonsignificant association between long-term GI dysfunction and higher anterior rectal wall volumes receiving at least 60 Gy (V60, where V=the percentage of the rectum receiving ≥60), 65 Gy (V65), 70 Gy (V70), and 75 Gy (V75).
"This suggests that as the volume of the rectum receiving each dose increased, the level of bowel dysfunction also increased," say Nguyen and team.
To investigate further, the team then dichotomized the DVHs according to their median values. A significant association between anterior rectal wall DVH and long-term bowel dysfunction was seen for patients with a median V60 over 54%, with nonsignificant associations seen for those with a V70 and V75 over 44% and 39%, respectively.
Furthermore, patients with a V60 over 54% had a significantly higher mean bowel symptom score of 10.6 compared with 5.4 for those with a V60 of 54% or below. Among patients with a V65 over 46%, 16.7% reported having diarrhea several times a week or more compared with 0% for those with V65 of 46% or less.
No significant difference was seen in other GI symptoms, including bleeding, cramping, urgency, tenesmus, or pain.
"Further work is needed to validate these findings in larger cohorts," conclude Nguyen et al in the International Journal of Radiation Oncology Biology Physics.
MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010
By Ingrid Grasmo