Feasibility of electronic brachytherapy in cervix cancer-A dosimetric comparison of different brachytherapy techniques.

INTRODUCTION: This study analyzes cases in which electronic brachytherapy (eBT) led to acceptable treatment plans in cervical cancer. Findings were compared with dosimetry values obtained in 192Ir-based treatments according to the high-risk clinical target volume (HR-CTV) and the disease stage. MATERIAL AND METHODS: We retrospectively analyzed 48 patients with cervical cancer from two centers. The patients were treated with 192Ir based on MRI. It was possible to use interstitial needles via an Utrecht-type applicator. Dosimetry was simulated using eBT and the parameters D90 and D98 (HR-CTV) and D2cc, D1cc, and D0.1cc (bladder, rectum, and sigmoid colon) were evaluated. The Mann-Whitney U test was used for comparison. The overall cohort of patients was analyzed, as were the sub-cohorts based on stage (FIGO stages I+IIA, IIB and III-IV). Finally, the dosimetry of the eBT plans was evaluated, and the plans obtained were classified as "good", "acceptable", or "poor". RESULTS: Statistically significant differences were found between the eBT and 192Ir plans for D98 (HR-CTV), D1cc and D0.1cc (bladder), and D1cc and D0.1cc (sigmoid colon). A total of 31 cases (64.6%) were considered good, seven (14.6%) were considered acceptable, and 10 (20.8%) were considered poor. For volumes <30 cc, all the plans were good or acceptable; for volumes >30 cc, 54.3% were good, and 71.4% were good or acceptable. By stage, eBT plans for patients with stage IB-IIA disease were good in 100%, whereas those for patients with stage IIB were good in 70.6% and III-IV disease were good in 50%. CONCLUSIONS: eBT provides appropriate dosimetry for treatment of cervical cancer in selected cases.

Consensus statement from the Spanish Brachytherapy Group (GEB) on accelerated partial breast irradiation using multicatheter interstitial brachytherapy.

AIM: To establish consensus guidelines for a safe clinical practice of accelerated partial breast irradiation (APBI) interstitial multicatheter brachytherapy (BT). BACKGROUND: APBI with interstitial multicatheter BT has proved to be effective in the treatment of early stage breast cancer. This paradigm shift in the approach to early breast cancer conservative treatment, along with the existing controversies on the clinical practice of APBI, prompted the Spanish Brachytherapy Group (GEB) of the Spanish Societies of Radiation Oncology (SEOR) and Medical Physics (SEFM) to address BT APBI in a consensus meeting. MATERIALS AND METHODS: Prior to the meeting, a survey with 27 questions on indication, inclusion criteria, BT modality, implant technique, image guidance and simulation, CTV and OAR definition, dose prescription and fractionation, dose calculation, implant quality metrics and OAR dose constrains was distributed. Items not reaching a level of agreement of 70% were discussed and voted during the meeting. RESULTS: 26 Institutions completed the survey, 60% of them perform APBI procedures. The analysis of the survey showed consensus reached on approximately half the questions. An expert panel discussed the remaining items; thereafter, a voting established the definite consensus. CONCLUSIONS: This document summarizes the consensus guidelines agreed during the meeting of the Spanish Brachytherapy Group SEOR-SEFM. Institutions with BT facilities available should offer interstitial BT APBI as a treatment option to patients fulfilling the inclusion criteria. Institutions willing to implement interstitial BT APBI are encouraged to follow the consensus guidelines established herein.

Evaluation of MLC performance in VMAT and dynamic IMRT by log file analysis.

PURPOSE: This multi-institution study assessed the positioning accuracy of multileaf collimators (MLC) by analyzing log files. It determined the main machine parameters that affect MLC positioning errors for pre-TrueBeam (Clinac) and TrueBeam linacs. METHODS: Around 30,000 dIMRT and VMAT log files belonging to 6 linacs from 4 different centers were analyzed. An in-house software was used to calculate 95th percentile and RMS error values and their correlation with certain parameters such as maximum leaf speed, mean leaf speed and gantry angle. The effect of MLC communication delay on error statistics was assessed in Clinac linacs. To that end MLC positioning error statistics were calculated with and without the delay effect. RESULTS: For dIMRT treatments in Clinac linacs the mean leaf RMS error was 0.306mm with and 0.030mm without the delay effect. Leaf RMS error was closely linked to maximum and mean leaf speeds, but without the delay effect that link was weaker. No trend was observed between bank RMS error and gantry angle. Without the delay effect larger bank RMS errors were obtained for gantry angles with leaf movements against gravity. For VMAT treatments in TrueBeam linacs the mean leaf RMS error was 0.038mm. A link was also observed between leaf RMS error and maximum and mean leaf speeds. CONCLUSION: TrueBeam MLC positioning errors are substantially lower than those of Clinac linacs. In Clinac machines the analysis of dynalogs without the delay effect allows us to study the influence of factors that are masked by the delay effect.