Corinna Melchert

Interstitial biodegradable balloon for reduced rectal dose during prostate radiotherapy: results of a virtual planning investigation based on the pre- and post-implant imaging data of an international multicenter study.

PURPOSE To evaluate dose reduction caused by the implantation of an interstitial inflatable and biodegradable balloon device aiming to achieve lower rectal doses with virtual 3D conformal external beam radiation treatment. MATERIALS AND METHODS An inflatable balloon device was placed, interstitially and under transrectal ultrasound guidance, into the rectal-prostate interspace prior treatment initiation of 26 patients with localized prostate cancer, who elected to be treated with radiotherapy (3D CRT or IMRT). The pre- and post-implant CT imaging data of twenty two patients were collected (44 images) for the purpose of the 3D conformal virtual planning presented herein. RESULTS The dorsal prostate-ventral rectal wall separation resulted in an average reduction of the rectal V70% by 55.3% (± 16.8%), V80% by 64.0% (± 17.7%), V90% by 72.0% (± 17.1%), and V100% by 82.3% (± 24.1%). In parallel, rectal D2 ml and D0.1 ml were reduced by 15.8% (± 11.4%) and 3.9% (± 6.4%), respectively. CONCLUSIONS Insertion of the biodegradable balloon into the prostate-rectum interspace is similar to other published invasive procedures. In this virtual dose distribution analysis, the balloon insertion resulted in a remarkable reduction of rectal volume exposed to high radiation doses. This effect has the potential to keep the rectal dose lower especially when higher than usual prostate dose escalation protocols or hypo-fractionated regimes are used. Further prospective clinical investigations on larger cohorts and more conformal radiation techniques will be necessary to define the clinical advantage of the biodegradable interstitial tissue separation device.

External beam boost versus interstitial high-dose-rate brachytherapy boost in the adjuvant radiotherapy following breast-conserving therapy in early-stage breast cancer: a dosimetric comparison

Purpose This study aims to compare the dosimetric data of local tumors bed dose escalation (boost) with photon beams (external beam radiation therapy – EBRT) versus high-dose-rate interstitial brachytherapy (HDR-BT) after breast-conserving treatment in women with early-stage breast cancer. Material and methods We analyzed the treatment planning data of 136 irradiated patients, treated between 2006 and 2013, who underwent breast-conserving surgery and adjuvant whole breast irradiation (WBI; 50.4 Gy) and boost (HDR-BT: 10 Gy in one fraction [n = 36]; EBRT: 10 Gy in five fractions [n = 100]). Organs at risk (OAR; heart, ipsilateral lung, skin, most exposed rib segment) were delineated. Dosimetric parameters were calculated with the aid of dose-volume histograms (DVH). A non-parametric test was performed to compare the two different boost forms. Results There was no difference for left-sided cancers regarding the maximum dose to the heart (HDR-BT 29.8% vs. EBRT 29.95%, p = 0.34). The maximum doses to the other OAR were significantly lower for HDR-BT (Dmax lung 47.12% vs. 87.7%, p < 0.01; rib 61.17% vs. 98.5%, p < 0.01; skin 57.1% vs. 94.75%, p < 0.01; in the case of right-sided breast irradiation, dose of the heart 6.00% vs. 16.75%, p < 0.01). Conclusions Compared to EBRT, local dose escalation with HDR-BT presented a significant dose reduction to the investigated OAR. Only left-sided irradiation showed no difference regarding the maximum dose to the heart. Reducing irradiation exposure to OAR could result in a reduction of long-term side effects. Therefore, from a dosimetric point of view, an interstitial boost complementary to WBI via EBRT seems to be more advantageous in the adjuvant radiotherapy of breast cancer.

Quality assurance during interstitial brachytherapy: in vivo dosimetry using MOSFET dosimeters

Purpose Brachytherapy procedure may result in acute tissue reactions like edema, causing deviations between planned and measured doses. The rationale for in vivo dosimetry in interstitial brachytherapy is to assess the accuracy of the delivered dose in comparison with the dose calculated by the treatment planning system (TPS). Material and methods One single computer tomography (CT) dataset was used for brachytherapy planning, taken within 24 hours after implantation. In vivo interstitial measurements with micro-MOSFET-detectors (metal oxide semiconductor field effect transistor) were performed in 12 patients with different anatomic locations of cancers, including thorax-wall, head and neck, breast, and different types of implantations (monoplanar, loops, and multiplanar). Results Measured values for the thorax-wall tumor patient showed a good agreement with the calculated data, with average deviation of –2.7% in 8 mm distance to the closest dwell position of the source. The deviation of the measured dose value of the head and neck patient was +55.6% in the first fraction and +8.5% in the last fraction. In the ten breast cancer patients, measured doses depended on the proximity of the detector to the irradiated volume PTV. Conclusions The deviations between planned and measured dose values were markedly influenced by the proximity of the detector to the PTV because where the edema exerts, the greatest influence on the tube applicator geometry. The positioning of the patient during irradiation must correspond to the positioning in the planning CT. Further studies are needed to investigate the role of in vivo dosimetry during interstitial brachytherapy as a routine procedure.