G. Valtueña

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

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.

Stereotactic body radiotherapy (SBRT) for the treatment of inoperable stage I non-small cell lung cancer patients

IntroductionLung cancer is the most frequent neoplasm in humans. Surgery is considered the best therapeutic approach for stage I non-small lung cell cancer (NSCLC). However, a remarkable amount of patients are considered as inoperable. Stereotactic body radiotherapy (SBRT) has risen as an option for those patients, rendering excellent results in quality of life and survival.Materials and methodsWe analyzed clinical studies published between 2002 and 2015 which included SBRT as a treatment modality. Our own clinical series was analyzed as well. The patterns of failure following SBRT were investigated, together with the outcomes and the toxicity observed.ResultsSBRT has proven to maintain an excellent local control. The analysis showed the tumor size and the histology as determinant factors for the response to treatment.ConclusionAccording to the published evidence as well as our own experience, SBRT is a safe and feasible approach for early NSCLC. Its results may be comparable with surgery treatment.

PO-1012: Comparative study of surgery with or without intraoperative multicatheter breast implant for PBI

The data indicate low sensitivity to thermal neutrons, while for fast neutrons, an increase in the SEU cross section with energy was observed. At high energies the results indicate that the cross section levels off. Conclusions: The energy dependence of the SEU mechanism has been investigated for several SRAM memories. A 16 Mbit SRAM from the vendor Cypress was found to be the best candidate for a neutron detector. The characterization results provide a basis for estimating neutron fluence and dose from measurements with the SRAM detector.

Time to loading and locoregional control in perioperative high-dose-rate brachytherapy: The tumor bed effect revisited.

PURPOSE To determine whether the time to loading (TTL) affects locoregional control. METHODS AND MATERIALS Locoregional control status was determined in 301 patients enrolled in several perioperative high-dose-rate brachytherapy (PHDRB) prospective studies conducted at the University of Navarre. The impact of the time elapsed from catheter implantation to the first PHDRB treatment (TTL) was analyzed. Patients treated with PHDRB alone (n = 113), mainly because of prior irradiation, received 32 Gy in eight twice-a-day treatments or 40 Gy in 10 twice-a-day treatments for negative or close/positive margins, respectively. Patients treated with PHDRB + external beam radiation therapy (EBRT) (n = 188) received 16 Gy in four twice-a-day treatments or 24 Gy in six twice-a-day treatments for negative or close/positive margins followed by 45 Gy of EBRT in 25 treatments. RESULTS After a median followup of 6.5 years (range, 2-13.6+), 113 patients have failed (37.5%), 65 in the PHDRB-alone group (57.5%) and 48 in the combined PHDRB + EBRT group (25.5%). Patients who started PHDRB before Postoperative Day 5 had a 10-year locoregional control rate of 66.7% and patients who started PHDRB on Postoperative Day 5 or longer had a 10-year locoregional control rate of 51.8% (p = 0.009). Subgroup analysis detected that this difference was only observed in the recurrent cases treated with PHDRB alone (Subset 2; n = 99; p = 0.004). No correlation could be detected between locoregional control rate and TTL in the other patient subsets although a trend toward a decreased locoregional control rate after a longer TTL was observed when they were grouped together (p = 0.089). CONCLUSIONS Patients should start PHDRB as soon as possible to maximize locoregional control especially in those recurrent cases treated with PHDRB alone. The time effect in other disease scenarios is less clear.