Skin and lung toxicity in synchronous bilateral breast cancer treated with volumetric-modulated arc radiotherapy: a mono-institutional experience.

PURPOSE: To evaluate acute and late skin/subcutaneous toxicities and radiation-induced lung fibrosis (RILF) in patients treated with adjuvant radiotherapy (RT) for synchronous bilateral breast cancers (SBBC), after conservative surgery. METHODS/PATIENTS: Twenty-five patients were treated with volumetric-modulated arc therapy (VMAT/RapidArc®) on both breasts, and checked clinically for detecting RT toxicities during and after treatment. A high-resolution computed tomography (HRCT) was performed, for detecting RILF during follow-up. RESULTS: We registered acute Grade-1 skin toxicity in 18 patients (72%), while six patients (24%) experienced Grade-2 toxicity. No breath symptoms were reported during and after RT. Late Grade-1 subcutaneous toxicity and late Grade-2 skin toxicity were registered in four patients (16%) and one patient (4%), respectively, at a mean follow-up of 36 months. Grade-1 RILF was detected in six patients (30%). The median volume of fibrosis area was 6.5 cc (range 1.3-21.5 cc). The partial volumes receiving a specified dose (V20, V30, V40, and V50) in patients who developed lung fibrosis were significantly bigger than who did not (p < 0.01). We showed that the mean volume of the tumour boost of patients who developed fibrosis (77.7 cc) was not significantly different from the other patients (90.8 cc) (p = 0.5). CONCLUSION: The clinical impact of this technique is favourable, and this is the first clinical study showing RILF by HRCT in a setting of SBBC. Further study with larger accrual is mandatory.

Clinical application of MOSkin dosimeters to rectal wall in vivo dosimetry in gynecological HDR brachytherapy.

PURPOSE: Three MOSkins dosimeters were assembled over a rectal probe and used to perform in vivo dosimetry during HDR brachytherapy treatments of vaginal cancer. The purpose of this study was to verify the applicability of the developed tool to evaluate discrepancies between planned and measured doses to the rectal wall. MATERIALS AND METHODS: MOSkin dosimeters from the Centre for Medical Radiation Physics are particularly suitable for brachytherapy procedures for their ability to be easily incorporated into treatment instrumentation. In this study, 26 treatment sessions of HDR vaginal brachytherapy were monitored using three MOSkin mounted on a rectal probe. A total of 78 measurements were collected and compared to doses determined by the treatment planning system. RESULTS: Mean dose discrepancy was determined as 2.2±6.9%, with 44.6% of the measurements within ±5%, 89.2% within ±10% and 10.8% higher than ±10%. When dose discrepancies were grouped according to the time elapsed between imaging and treatment (i.e., group 1: ≤90min; group 2: >90min), mean discrepancies resulted in 4.7±3.6% and 7.1±5.0% for groups 1 and 2, respectively. Furthermore, the position of the dosimeter on the rectal catheter was found to affect uncertainty, where highest uncertainties were observed for the dosimeter furthest inside the rectum. CONCLUSIONS: This study has verified MOSkin applicability to in-patient dose monitoring in gynecological brachytherapy procedures, demonstrating the dosimetric rectal probe setup as an accurate and convenient IVD instrument for rectal wall dose verification. Furthermore, the study demonstrates that the delivered dose discrepancy may be affected by the duration of treatment planning.

SU-D-BRCD-04: Validation of Film Dosimetry in the Dose Build-Up Region.

PURPOSE: To establish a film dosimetric method for high-resolution measurement in the dose build-up region. METHODS: Percent depth dose (PDD) curves were measured in water for TomoTherapy using Gafchromic EBT2 films. Depth dose measurements were also performed using Standard Imaging A1SL and PTW PinPoint ionization chambers, as well as a PTW DiodeE detector. The film and detector measurements were then compared to Monte Carlo (MC) simulation data computed using PENELOPE. An in- house support apparatus was constructed to hold the films parallel to the beam central axis while being suspended in the water, simultaneously demarcating the water surface on the film. The films were converted to dose using a corrected net optical density method involving the red and blue color channels of an Epson Expression 10000XL scanner. Film analysis was performed using ImageJ software and MATLAB code developed in clinic. RESULTS: In our film method, a systematic shift of 1.2mm downstream is seen for the sample of five films, with good reproducibility within the sample (s=0.3mm). The film measurements showed a mean PDD difference of 0.3% (s=0.4%) with a maximum of 1.3% from that of MC between depths of 0.5mm to 20mm. The average film dose measured at the water surface (d=0mm) was 13.1% greater than that calculated by MC. EBT2 film shows much better agreement with MC in the dose build-up region than the ionization chamber and detector measurements. CONCLUSIONS: This study demonstrates the capability of EBT2 films for simple and accurate superficial dose measurements. A suspected reason for the systematic shift in film alignment is attributed to difficulty in determining water surface due to the meniscus that forms at the film. Funded by SSRMP Research Grant 2011.