ABSTRACT
BACKGROUND: In unresectable hepatocellular carcinoma several local ablative treatments are available. Among others, radiation based treatments such as stereotactic body radiotherapy (SBRT) and high-dose rate interstitial brachytherapy (HDR BT) have shown good local control rates. METHODS: We conducted a dose comparison between actually performed HDR BT versus virtually planned SBRT to evaluate the respective clinically relevant radiation exposure to uninvolved liver tissue. Moreover, dose coverage and conformity indices were assessed. RESULTS: Overall, 46 treatment sessions (71 lesions, 38 patients) were evaluated. HDR BT was applied in a single fraction with a dose prescription of 1 × 15 Gy. D98 was 17.9 ± 1.3 Gy, D50 was 41.8 ± 8.1 Gy. The SBRT was planned with a prescribed dose of 3 × 12.5 Gy (65%-Isodose), D98 was 50.7 ± 3.1 Gy, D2 was 57.0 ± 2.3 Gy, and D50 was 55.2 ± 2.3 Gy. Regarding liver exposure Vliver10GyBT was compared to Vliver15.9GySBRT, Vliver16.2GySBRT (EQD2 equivalent doses), and Vliver20GySBRT (clinically relevant dose), all results showed significant differences (p < .001). In a case by case analysis Vliver10GyBT was smaller than Vliver20GySBRT in 38/46 cases (83%). Dmean of the liver was significantly smaller in BT compared to SBRT (p < .001). GTV volume was correlated to the liver exposure and showed an advantage of HDR BT over SBRT in comparison of clinically relevant doses, and for EQD2 equivalent doses. The advantage was more pronounced for greater liver lesions The Conformity Index (CI) was significantly better for BT, while Healthy Tissue Conformity Index (HTCI) and Conformation Number (CN) showed an advantage for SBRT (p < .001). CONCLUSION: HDR BT can be advantageous in respect of sparing of normal liver tissue as compared to SBRT, while providing excellent target conformity.
Subject(s)
Brachytherapy/mortality , Carcinoma, Hepatocellular/mortality , Liver Neoplasms/mortality , Liver/pathology , Organs at Risk/radiation effects , Radiosurgery/mortality , Radiotherapy Planning, Computer-Assisted/methods , Aged , Carcinoma, Hepatocellular/pathology , Carcinoma, Hepatocellular/radiotherapy , Carcinoma, Hepatocellular/surgery , Female , Humans , Image Processing, Computer-Assisted/methods , Liver/diagnostic imaging , Liver/radiation effects , Liver/surgery , Liver Neoplasms/pathology , Liver Neoplasms/radiotherapy , Liver Neoplasms/surgery , Male , Prognosis , Radiotherapy Dosage , Radiotherapy, Image-Guided , Radiotherapy, Intensity-Modulated/methods , Retrospective Studies , Survival Rate , Tomography, X-Ray Computed/methodsABSTRACT
PURPOSE: To validate the collapsed cone (CC) algorithm against Monte Carlo (MC) simulations for model-based dose calculations in high-dose-rate (HDR) liver brachytherapy. METHODS AND MATERIALS: Doses for liver brachytherapy treatment plans of 10 cases were retrospectively recalculated with a model-based approach using Monte Carlo n-Particle Code (MCNP) 6 (Dm,m-MC) and Oncentra Brachy ACE (Dm,m-ACE). Tissue segmentation consisted of assigning uniform compositions and mass densities to predefined Hounsfield Unit (HU) thresholds. Resulting doses were compared according to dose volume histogram parameters typical for clinical routine. These included the percentage liver volume receiving 5 Gy (V5Gy) or 10 Gy (V10Gy), the maximum dose to one cubic centimeter (D1cc) of organs at risk, the clinical target volume (CTV) fractions receiving 150% (V150), 100% (V100), 95% (V95) and 90% (V90) of the prescribed dose and the absolute doses to 95% (D95) and 90% (D90) of the CTV volumes. RESULTS: Doses from Oncentra Brachy ACE agreed well with MC simulations. Differences were seen far from the source, in low-density regions and bone structures. Median percentage deviations were 1.1% for the liver V5Gy and 0.4% for the liver V10Gy, with deviations of largest magnitude amounting to 2.2% and 1.0%, respectively. Organs at risk had median deviations ranging from 0.3% to 1.5% for D1cc, with outliers ranging up to 4.6%. CTV volume parameter deviations ranged between -1.5% and 0.5%, dose parameter deviations ranged mostly between -2% and 1%, with two outliers at -4.0% and -3.4% for a small CTV.
Subject(s)
Brachytherapy , Algorithms , Brachytherapy/methods , Humans , Liver/diagnostic imaging , Monte Carlo Method , Radiotherapy Dosage , Radiotherapy Planning, Computer-Assisted , Retrospective StudiesABSTRACT
PURPOSE: To compare treatment plans for interstitial high dose rate (HDR) liver brachytherapy with 192Ir calculated according to current-standard TG-43U1 protocol with model-based dose calculation following TG-186 protocol. METHODS: We retrospectively evaluated dose volume histogram (DVH) parameters for liver, organs at risk (OARs) and clinical target volumes (CTVs) of 20 patient cases diagnosed with hepatocellular carcinoma (HCC) or metastatic colorectal cancer (mCRC). Dose calculations on a homogeneous water geometry (TG-43U1 surrogate) and on a computed tomography (CT) based geometry (TG-186) were performed using Monte Carlo (MC) simulations. The CTs were segmented based on a combination of assigning TG-186 recommended tissues to fixed Hounsfield Unit (HU) ranges and using organ contours delineated by physicians. For the liver, V5Gy and V10Gy were analysed, and for OARs the dose to 1 cubic centimeter (D1cc). Target coverage was assessed by calculating V150, V100, V95 and V90 as well as D95 and D90. For every DVH parameter, median, minimum and maximum values of the deviations of TG-186 from TG-43U1 were analysed. RESULTS: TG-186-calculated dose was found to be on average lower than dose calculated with TG-43U1. The deviation of highest magnitude for liver parameters was -6.2% of the total liver volume. For OARs, the deviations were all smaller than or equal to -0.5 Gy. Target coverage deviations were as high as -1.5% of the total CTV volume and -3.5% of the prescribed dose. CONCLUSIONS: In this study we found that TG-43U1 overestimates dose to liver tissue compared to TG-186. This finding may be of clinical importance for cases where dose to the whole liver is the limiting factor.
