Comparison of dosimetry with magnetic resonance and computed tomography imaging delineation of surgical bed volume in breast cancer irradiation.

Background: Postoperative radiotherapy after conservative surgery for patients with breast cancer usually includes focal over-irradiation (boost) to the surgical bed (SB). Irradiation planning using computed tomography (CT) is difficult in many cases because of insufficient intrinsic soft tissue contrast. To ensure appropriate radiation to the tumor, large boost volumes are delineated, resulting in a higher dose to the normal tissue. Magnetic resonance imaging (MRI) provides superior soft tissue contrast than CT and can better differentiate between normal tissue and the SB. However, for SB delineation CT images alone remain the pathway followed in patients undergoing breast irradiation. This study aimed to evaluate the potential advantages in boost dosimetry by using MRI and CT as pre-treatment imaging. Methods: Eighteen boost volumes were drawn on CT and MRI and elastically co-registered using commercial image registration software. The radiotherapy treatment plan was optimized using the CT volumes as the baseline. The dose distributions of the target volumes on CT and MRI were compared using dose-volume histogram cutoff points. Results: The radiation volumes to the SB varied considerably between CT and MRI (conformity index between 0.24 and 0.67). The differences between the MRI and CT boost doses in terms of the volume receiving 98% of the prescribed dose (V98%) varied between 10% and 30%. Smaller differences in the V98% were observed when the boost volumes were delineated using MRI. Conclusion: Using MRI to delineate the volume of the SB may increase the accuracy of boost dosimetry.

Improving dose delivery accuracy with EPID in vivo dosimetry: results from a multicenter study.

PURPOSE: To investigate critical aspects and effectiveness of in vivo dosimetry (IVD) tests obtained by an electronic portal imaging device (EPID) in a multicenter and multisystem context. MATERIALS AND METHODS: Eight centers with three commercial systems-SoftDiso (SD, Best Medical Italy, Chianciano, Italy), Dosimetry Check (DC, Math Resolution, LCC), and PerFRACTION (PF, Sun Nuclear Corporation, SNC, Melbourne, FL)-collected IVD results for a total of 2002 patients and 32,276 tests. Data are summarized for IVD software, radiotherapy technique, and anatomical site. Every center reported the number of patients and tests analyzed, and the percentage of tests outside of the tolerance level (OTL%). OTL% was categorized as being due to incorrect patient setup, incorrect use of immobilization devices, incorrect dose computation, anatomical variations, and unknown causes. RESULTS: The three systems use different approaches and customized alert indices, based on local protocols. For Volumetric Modulated Arc Therapy (VMAT) treatments OTL% mean values were up to 8.9% for SD, 18.0% for DC, and 16.0% for PF. Errors due to "anatomical variations" for head and neck were up to 9.0% for SD and DC and 8.0% for PF systems, while for abdomen and pelvis/prostate treatments were up to 9%, 17.0%, and 9.0% for SD, DC, and PF, respectively. The comparison among techniques gave 3% for Stereotactic Body Radiation Therapy, 7.0% (range 4.7-8.9%) for VMAT, 10.4% (range 7.0-12.2%) for Intensity Modulated Radiation Therapy, and 13.2% (range 8.8-21.0%) for 3D Conformal Radiation Therapy. CONCLUSION: The results obtained with different IVD software and among centers were consistent and showed an acceptable homogeneity. EPID IVD was effective in intercepting important errors.

Improvement in clinical evaluation of PET/CT images with high resolution algorithms.

AIM: Positron emission tomography/computed tomography (PET/CT) diagnosis relies on quality of the reconstructed images which strongly depends on the algorithms used. The aim of this work was to assess if the introduction of high resolution algorithms allows a better identification of reduced diameter lesions, leading to improved diagnosis in clinical setting. METHODS: The performances of a Siemens Biograph6 True Point PET/CT used for this work were checked for both standard and high resolution algorithms. Clinical studies of thirteen patients referred for PET/CT were selected and grouped according to the metabolic tumor volume and their position in the FOV and then reconstructed with both algorithms; clinical studies were estimated in terms of geometric characteristics and uptake values (SUVmax, SUVmean) of the lesions. RESULTS: FWHM, spatial resolution, contrast ratio and image quality of the PET/CT scanner used for this work are in agreement with the performances declared by the manufacturers. For the clinical studies, the results obtained using TrueX algorithm showed an increase in SUVmax and SUVmean of 20% and 10% respectively for lesions with volume higher than 2 cm3 and of about 26% and 15% for smaller lesions. The enhancement of SUVmean was around 10% for in axis lesions and of about 12% for off axis lesions. For SUVmax the increase was 23% for both the positions. For small lesions TrueX algorithm led to a metabolic volume higher than with the iterative one while no significant differences were found for big lesions. CONCLUSION: The advances in 3D PET reconstruction algorithms lead to images with improved quantitative accuracy and image quality performance.

A mathematical approach for evaluating the influence of dose heterogeneity on TCP for prostate cancer brachytherapy treatment.

The low-dose-rate brachytherapy technique has proven suitable for the management of prostate cancer. However, published data generally report the clinical outcome and the minimum peripheral dose (mPD) to the target volume and not the actual dose distribution in patients. To this end, modern guidelines recommend the use of specific dose and volume indices describing dose distribution throughout the target. The introduction of a method, based on the standard linear quadratic model and Poisson statistics, entitled the F-factor allows the TCP from different DVHs to be calculated, by using the TCP from a uniform dose distribution as the reference. The F-factor sensitivity against radiobiological parameters and influence of the DVH were evaluated. We applied the F-formula on the post-plan DVHs of 58 patients treated with (125)I permanent seed implant brachytherapy for localized prostate cancer. F shows a strong correlation with dosimetric parameters already reported as significant predictors of the biochemical outcome.