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Volume of high-dose regions and likelihood of locoregional control after perioperative high-dose-rate brachytherapy: Do hotter implants work better?

11-jun-2014 | Revista: Brachytherapy

Martínez-Monge R1, Cambeiro 2; Ramos LI2, Olarte A2, Valtueña G2, San-Julián M3, Alcalde J4, Naval-Gías L5, Jurado M6

(1) Department of Radiation Oncology, Clínica Universidad de Navarra, Pamplona, Navarre, Spain.
(2) Department of Radiation Oncology, Clínica Universidad de Navarra, Pamplona, Navarre, Spain.
(3) Department of Orthopedic Surgery, Clínica Universidad de Navarra, Pamplona, Navarre, Spain.
(4) Department of Otolaryngology, Clínica Universidad de Navarra, Pamplona, Navarre, Spain.
(5) Department of Oral Surgery, Clínica Universidad de Navarra, Pamplona, Navarre, Spain.
(6) Department of Gynecology, Clínica Universidad de Navarra, Pamplona, Navarre, Spain.


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PURPOSE
To determine whether perioperative high-dose-rate brachytherapy (PHDRB) implants with larger high-dose regions produce increased locoregional control.

METHODS AND MATERIALS
Patients (n=166) enrolled in several PHDRB prospective studies conducted at the University of Navarre were analyzed. The PHDRB was given to total doses of 16Gy/4 b.i.d. or 24Gy/6 b.i.d. treatments for negative or close/positive margins along with 45Gy/25 Rx of external beam radiation therapy. The histogram-based generalized equivalent uniform dose (EUD) formulism was used to quantify and standardize the dose-volume histogram into 2-Gy equivalents. The region of interest analyzed included: tissue volume encompassed by the prescription isodose of 4Gy (TV100). Routine dose reporting parameters such as physical dose and single-point 2-Gy equivalent dose were used for reference.

RESULTS
After a median followup of 7.4 years (range, 3-12+), 50 patients have failed, and 116 remain controlled at last followup. Overall, EUD was not different in the patients who failed compared with controls (89.1Gy vs. 86.5Gy; p=not significant). When patients were stratified by risk using the University of Navarre Predictive Model, very high-risk patients (i.e., tumors ≥3cm resected with close <1mm/positive margins) had an improved locoregional control with higher EUD values (p=0.028). This effect was not observed in low-, intermediate-, and high-risk University of Navarre Predictive Model categories.

CONCLUSIONS
In very high-risk patients, enlarged high-dose regions can produce a dose-response effect. Routine dose reporting methods such as physical dose and single-point 2-Gy equivalent dose may not show this effect, but it can be revealed by histogram-based EUD assessment.

CITA DEL ARTÍCULO   Brachytherapy. 2014 Jun 11. pii: S1538-4721(14)00542-X. doi: 10.1016/j.brachy.2014.05.015. [Epub ahead of print]