Dose optimization of intra-operative high dose rate interstitial brachytherapy implants for soft tissue sarcoma (original) (raw)
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Medical Physics, 2000
We have studied the accuracy of statistical parameters of dose distributions in brachytherapy using actual clinical implants. These include the mean, minimum and maximum dose values and the variance of the dose distribution inside the PTV ͑planning target volume͒, and on the surface of the PTV. These properties have been studied as a function of the number of uniformly distributed sampling points. These parameters, or the variants of these parameters, are used directly or indirectly in optimization procedures or for a description of the dose distribution. The accurate determination of these parameters depends on the sampling point distribution from which they have been obtained. Some optimization methods ignore catheters and critical structures surrounded by the PTV or alternatively consider as surface dose points only those on the contour lines of the PTV. D min and D max are extreme dose values which are either on the PTV surface or within the PTV. They must be avoided for specification and optimization purposes in brachytherapy. Using D mean and the variance of D which we have shown to be stable parameters, achieves a more reliable description of the dose distribution on the PTV surface and within the PTV volume than does D min and D max . Generation of dose points on the real surface of the PTV is obligatory and the consideration of catheter volumes results in a realistic description of anatomical dose distributions.
Journal of Applied Clinical Medical Physics, 2010
HDR brachytherapy treatment planning often involves optimization methods to calculate the dwell times and dwell positions of the radioactive source along specified afterloading catheters. The purpose of this study is to compare the dose distribution obtained with geometric optimization (GO) and volume optimization (VO) combined with isodose reshaping. This is a retrospective study of 10 cervix HDR interstitial brachytherapy implants planned using geometric optimization and treated with a dose of 6 Gy per fraction. Four treatment optimization plans were compared: geometric optimization (GO), volume optimization (VO), geometric optimization followed by isodose reshape (GO_IsoR), and volume optimization followed by isodose reshape (VO_IsoR). Dose volume histogram (DVH) was analyzed and the four plans were evaluated based on the dosimetric parameters: target coverage (V 100), conformal index (COIN), homogeneity index (HI), dose nonuniformity ratio (DNR) and natural dose ratio (NDR). Good target coverage by the prescription dose was achieved with GO_ IsoR (mean V 100 of 88.11%), with 150% and 200% of the target volume receiving 32.0% and 10.4% of prescription dose, respectively. Slightly lower target coverage was achieved with VO_IsoR plans (mean V 100 of 86.11%) with a significant reduction in the tumor volume receiving high dose (mean V 150 of 28.29% and mean V 200 of 7.3%). Conformity and homogeneity were good with VO_ IsoR (mean COIN = 0.75 and mean HI = 0.58) as compared to the other optimization techniques. VO_IsoR plans are superior in sparing the normal structures while also providing better conformity and homogeneity to the target. Clinically acceptable plans can be obtained by isodose reshaping provided the isodose lines are dragged carefully.
Medical Dosimetry, 2015
The aim of this study was to compare the clinical benefits of inverse planning simulated annealing (IPSA)-based optimization over volume-based optimization for high-dose rate (HDR) cervix interstitial implants. Overall, 10 patients of cervical carcinoma were considered for treatment with HDR interstitial brachytherapy. Oncentra Master Plan brachytherapy planning system was used for generating 3-dimensional HDR treatment planning for all patients. All patient treatments were planned using volume-based optimization and inverse planning optimization (IPSA). The parameters V 100 , V 150 , and V 200 for the target; D 2 cm 3 of bladder, rectum, and sigmoid colon; and V 80 and V 100 for bladder, rectum, and sigmoid colon were compared using dose-volume histograms (DVHs). The conformity index (CI), relative dose homogeneity index, overdose volume index (ODI), and dose nonuniformity index (DNR) were computed from cumulative DVHs. Good target coverage for prescription dose was achieved with volume-based optimization as compared with IPSA-based dose optimization. Homogeneity was good with the IPSA-based technique as compared with the volume-based dose optimization technique. Volume-based optimization resulted in a higher CI (with a mean value of 0.87) compared with the IPSAbased optimization (with a mean value of 0.76). ODI and DNR are better for the IPSA-based plan as compared with the volume-based plan. Mean doses to the bladder, rectum, and sigmoid colon were least with IPSA. IPSA also spared the critical organs but with considerable target conformity as compared with the volume-based plan. IPSA significantly reduces overall treatment planning time with improved reduced doses to the organs at risk compared with the volume-based optimization treatment planning method.
Strahlentherapie und Onkologie, 2005
Recently, the use of brachytherapy for partial breast irradiation has increased significantly. The aim of this study was to make dosimetric comparisons between conventional (CONV) and CT-based optimized dosimetry systems applied to breast implants. Patients and Methods: 17 patients treated with high-dose-rate (HDR) interstitial brachytherapy were selected for the study. Two patients had two-plane and 15 three-plane implants. Treatment planning was based on conventional two isocentric radiographs and dose point optimization (CONV). For each patient postimplant CT scans were taken, and the target volume (lumpectomy cavity with 1 cm margin) was outlined in all axial slices. The treatment planning was repeated using CT images. The dose distributions were analyzed by dose-volume histograms. To quantify the dose distributions, volume (V90, V100, V150, V200) and dose (D90, D min , mean central dose [MCD]) parameters, along with the dose nonuniformity ratio (DNR), dose homogeneity index (DHI), external volume index (EI) and conformal index (COIN) were used. For each implant, three more virtual treatment plans were created using the Paris dosimetry system (PDS), geometrically optimized system (GOS) and conformal system (CONF). Dose and volume parameters were calculated and compared. Results: The median number of catheters amounted to ten (range: 6 to 13) and the average volume of planning target volume to 63.4 cm 3 (range: 17.7-122 cm 3 ). The mean target coverage was 70%, 61%, 57% and 87%; the D90 72%, 64%, 60% and 94%; the DNR 0.35, 0.25, 0.25 and 0.55; the EI 0.62, 0.54, 0.08 and 0.15; the COIN 0.40, 0.34, 0.50 and 0.74 for the CONV, PDS, GOS and CONF systems, respectively. Conclusion: With CT-based optimized dose planning the target coverage can be significantly increased compared to the conventional dosimetry systems, but the target dose distribution will be more inhomogeneous. To improve the quality of brachytherapy implants, the image-based three-dimensional information should be used not only for dose plan evaluation, but also previously, for planning the geometry of the catheter positions and performing the insertions.
Brachytherapy, 2011
PURPOSE: To compare inverse planning simulated annealing (IPSA) algorithm with the dosepoint optimized (DPO) plan and manual/graphically optimized (GrO) plan for interstitial template brachytherapy for gynecologic cancers. METHODS AND MATERIALS: The data set of 10 consecutive patients was selected for this dosimetric study. For each patient, three plans were calculated: DPO, GrO, and IPSA. Dosee volume parameters from the three plans were compared to analyze the dosimetric outcome. RESULTS: Coverage of the clinical target volume (CTV) with GrO plan and IPSA algorithm was significantly better (mean V 100 of 88.8% and 89.1%; p 5 0.006) as compared with DPO plan (83.7%; p 5 0.62). Similarly, mean D 90 was same in both GrO plan and IPSA, 3.96 AE 0.23 and 3.96 AE 0.15 Gy, respectively. DPO plans were homogeneous with homogeneity index being 0.82 as compared with 0.68 AE 0.05 of GrO plan and 0.71 AE 0.04 of IPSA. However, IPSA resulted in high conformity with conformity index of 0.78 as compared with 0.72 ( p 5 0.001) and 0.68 ( p # 0.001) for GrO and DPO plans, respectively. The dose to rectum (3.3 AE 1.06 Gy) and bladder (3.17 AE 0.5 Gy) was generally high for DPO plan. GrO plan reduced the dose to the rectum (2.91 AE 0.63; p 5 0.011) and bladder (2.89 AE 0.63 Gy; p 5 0.003) significantly. IPSA resulted in a further reduction of the dose to rectum (2.79 AE 0.67 Gy; p 5 0.046) and bladder (2.81 AE 0.67 Gy; p 5 0.035), however with no statistical significance as compared with GrO plan. CONCLUSION: IPSA resulted in significant sparing of normal tissues without compromising CTV coverage as compared with DPO plan. However, IPSA did not show any significant improvement either in CTV coverage or in normal tissue sparing as compared with GrO plan. IPSA was found to be superior in terms of homogeneity and conformity as compared with GrO plan.
Superiority of Equivalent Uniform Dose (EUD)-Based Optimization for Breast and Chest Wall*
Medical Dosimetry, 2010
We investigate whether IMRT optimization based on generalized equivalent uniform dose (gEUD) objectives for organs at risk (OAR) results in superior dosimetric outcomes when compared with multiple dose-volume (DV)-based objectives plans for patients with intact breast and postmastectomy chest wall (CW) cancer. Four separate IMRT plans were prepared for each of the breast and CW cases (10 patients). The first three plans used our standard in-house, physician-selected, DV objectives (phys-plan); gEUD-based objectives for the OARs (gEUD-plan); and multiple, "very stringent," DV objectives for each OAR and PTV (DV-plan), respectively. The fourth plan was only beam-fluence optimized (FO-plan), without segmentation, which used the same objectives as in the DV-plan. The latter plan was to be used as an "optimum" benchmark without the effects of the segmentation for deliverability. Dosimetric quantities, such as V 20Gy for the ipsilateral lung and mean dose (D mean ) for heart, contralateral breast, and contralateral lung were used to evaluate the results. For all patients in this study, we have seen that the gEUD-based plans allow greater sparing of the OARs while maintaining equivalent target coverage. The average ipsilateral lung V 20Gy reduced from 22 ؎ 4.4% for the FO-plan to 18 ؎ 3% for the gEUD-plan. All other dosimetric quantities shifted towards lower doses for the gEUD-plan. gEUD-based optimization can be used to search for plans of different DVHs with the same gEUDs. The use of gEUD allows selective optimization and reduction of the dose for each OAR and results in a truly individualized treatment plan.
Calculation of mean central dose in interstitial brachytherapy using Delaunay triangulation
Medical Physics, 2001
In 1997 the ICRU published Report 58 “Dose and Volume Specification for Reporting Interstitial Therapy” with the objective of addressing the problem of absorbed dose specification for reporting contemporary interstitial therapy. One of the concepts proposed in that report is “mean central dose.” The fundamental goal of the mean central dose (MCD) calculation is to obtain a single, readily reportable and intercomparable value which is representative of dose in regions of the implant “where the dose gradient approximates a plateau.” Delaunay triangulation (DT) is a method used in computational geometry to partition the space enclosed by the convex hull of a set of distinct points P into a set of nonoverlapping cells. In the three‐dimensional case, each point of P becomes a vertex of a tetrahedron and the result of the DT is a set of tetrahedra. All treatment planning for interstitial brachytherapy inherently requires that the location of the radioactive sources, or dwell positions in ...
Medical Physics, 1999
In conventional dose optimization algorithms, in brachytherapy, multiple objectives are expressed in terms of an aggregating function which combines individual objective values into a single utility value, making the problem single objective, prior to optimization. A multiobjective genetic algorithm ͑MOGA͒ was developed for dose optimization based on an a posteriori approach, leaving the decision-making process to a planner and offering a representative trade-off surface of the various objectives. The MOGA provides a flexible search engine which provides the maximum of information for a decision maker. Tests performed with various treatment plans in brachytherapy have shown that MOGA gives solutions which are superior to those of traditional dose optimization algorithms. Objectives were proposed in terms of the COIN distribution and differential volume histograms, taking into account patient anatomy in the optimization process.
Journal of the Egyptian National Cancer Institute, 2021
The number of people with implanted hip prosthesis has grown worldwide. For radiotherapy planning of patients with hip implants, few main challenges are encountered. The aim of the present study was to evaluate the feasibility of different planning algorithms in the presence of high-density metallic implant in the treatment of patients with carcinoma cervix. It was found that D98% were 44.49 ± 0.11, 44.51 ± 0.13, 44.39 ± 0.22, and 44.45 ± 0.16 Gy for 4FMC6MV (4-field technique calculated with Monte-Carlo algorithm and 6 MV photon energy), 4FMC6MV_WP (4-field technique calculated with Monte-Carlo algorithm and 6 MV photon energy without prosthesis), 4FCC6MV (4-field technique calculated with collapse-cone-convolution algorithm and 6 MV photon energy), and 4FCC6MV_WP (4-field technique calculated with collapse-cone-convolution algorithm and 6 MV photon energy without prosthesis) respectively. Similarly, D2% were 49.40 ± 0.84, 49.05 ± 0.76, 48.97 ± 0.91, and 48.57 ± 0.85 Gray (Gy) for ...