Commissioning and validation of commercial deformable image registration software for adaptive contouring.

PURPOSE: To report the commissioning and validation of deformable image registration(DIR) software for adaptive contouring. METHODS: DIR (SmartAdapt®v13.6) was validated using two methods namely contour propagation accuracy and landmark tracking, using physical phantoms and clinical images of various disease sites. Five in-house made phantoms with various known deformations and a set of 10 virtual phantoms were used. Displacement in lateral, anterio-posterior (AP) and superior-inferior (SI) direction were evaluated for various organs and compared with the ground truth. Four clinical sites namely, brain (n = 5), HN (n = 9), cervix (n = 18) and prostate (n = 23) were used. Organs were manually delineated by a radiation oncologist, compared with the deformable image registration (DIR) generated contours. 3D slicer v4.5.0.1 was used to analyze Dice Similarity Co-efficient (DSC), shift in centre of mass (COM) and Hausdorff distances Hf95%/avg. RESULTS: Mean (SD) DSC, Hf95% (mm), Hfavg (mm) and COM of all the phantoms 1-5 were 0.84 (0.2) mm, 5.1 (7.4) mm, 1.6 (2.2) mm, and 1.6 (0.2) mm respectively. Phantom-5 had the largest deformation as compared to phantoms 1-4, and hence had suboptimal indices. The virtual phantom resulted in consistent results for all the ROIs investigated. Contours propagated for brain patients were better with a high DSC score (0.91 (0.04)) as compared to other sites (HN: 0.84, prostate: 0.81 and cervix 0.77). A similar trend was seen in other indices too. The accuracy of propagated contours is limited for complex deformations that include large volume and shape change of bladder and rectum respectively. Visual validation of the propagated contours is recommended for clinical implementation. CONCLUSION: The DIR algorithm was commissioned and validated for adaptive contouring.

Characterization of commercial MOSFET detectors and their feasibility for in-vivo HDR brachytherapy.

AIM: The present study was to investigate the use of MOSFET as an vivo dosimeter for the application of Ir-192 HDR brachytherapy treatments. MATERIAL AND METHODS: MOSFET was characterized for dose linearity in the range of 50-1000 cGy, depth dose dependence from 2 to 7 cm, angular dependence. Signal fading was checked for two weeks. RESULT AND DISCUSSION: Dose linearity was found to be within 2% in the dose range (50-1000 cGy). The response varied within 8.07% for detector-source distance of 2-7 cm. The response of MOSFET with the epoxy side facing the source (0 degree) is the highest and the lowest response was observed at 90 and 270 degrees. Signal was stable during the study period. CONCLUSION: The detector showed high dose linearity and insignificant fading. But due to angular and depth dependence, care should be taken and corrections must be applied for clinical dosimetry.

Uncertainties of deformable image registration for dose accumulation of high-dose regions in bladder and rectum in locally advanced cervical cancer.

PURPOSE: To compare the dose accumulation for bladder and rectum by deformable image registration (DIR) and direct addition (DA) of dose volume histogram parameters in magnetic resonance image-guided adaptive brachytherapy (IGABT). Two DIR algorithms, contour- and intensity-based, also have been analyzed. METHODS AND MATERIALS: Patients (n = 21) treated with IGABT for carcinoma cervix under the IntErnational study on MRI-guided BRachytherapy in locally Advanced CErvical cancer protocol were analyzed. Each patient underwent two HDR-BT applications, 1-week apart with two fractions of 7 Gy each delivered per application. For each application, magnetic resonance imaging, volume delineation, reconstruction, treatment planning (BT1 and BT2), and dose evaluation were carried out. BT1 and BT2 images were registered using an intensity-based DIR, followed by deformable dose accumulation (DDA), which was then compared with DA. To compare the intensity-based DIR to other DIR approaches, nine patients were further evaluated using an in-house contour-based DIR algorithm for bladder dose accumulation. RESULTS: Mean (±standard deviation; range) percentage variation between DA and DDA was found to be 2.4% (±3.3;-1.8, 11.5) and 5.2% (±5.1;-1.7, 16.5) for the rectum and bladder, respectively. The differences between the DA and DDA were found to be statistically significant for both rectum (p = 0.008) and bladder (p = 0.0003). Intensity-based DIR algorithm resulted in a larger mean deviation between DDA and DA as compared with contour-based DIR, although statistically insignificant (p = 0.32). The difference between DDA and DA was 2.4 ± 2.0% and 1.3 ± 1.2%, for intensity- and contour-based DIR, respectively. CONCLUSIONS: DA of dose volume histogram parameters provides a good estimate to the dose to the organs at risk; DIR based on image intensities may lead to systematic underestimation of dose due to implausible DIR.

A multicentre comparison of the dosimetric impact of inter- and intra-fractional anatomical variations in fractionated cervix cancer brachytherapy.

BACKGROUND AND PURPOSE: To compare the dosimetric impact of organ and target variations relative to the applicator for intracavitary brachytherapy by a multicentre analysis with different application techniques and fractionation schemes. MATERIAL AND METHODS: DVH data from 363 image/contour sets (120 patients, 6 institutions) were included for 1-6 fractions per patient, with imaging intervals ranging from several hours to ∼20 days. Variations between images acquired within one (intra-application) or between consecutive applicator insertions (inter-application) were evaluated. Dose plans based on a reference MR or CT image series were superimposed onto subsequent image sets and D(2cm(3)) for the bladder, rectum and sigmoid and D(90) for HR CTV were recorded. RESULTS: For the whole sample, the systematic dosimetric variations for all organs at risk, i.e. mean variations of D(2cm(3)), were found to be minor (<5%), while random variations, i.e. standard deviations were found to be high due to large variations in individual cases. The D(2cm(3)) variations (mean±1SD) were 0.6±19.5%, 4.1±21.7% and 1.6±26.8%, for the bladder, rectum and sigmoid. For HR CTV, the variations of D90 were found to be -1.1±13.1% for the whole sample. Grouping of the results by intra- and inter-application variations showed that random uncertainties for bladder and sigmoid were 3-7% larger when re-implanting the applicator for individual fractions. No statistically significant differences between the two groups were detected in dosimetric variations for the HR CTV. Using 20% uncertainty of physical dose for OAR and 10% for HR CTV, the effects on total treatment dose for a 4 fraction HDR schedule at clinically relevant dose levels were found to be 4-8 Gy EQD2 for OAR and 3 Gy EQD2 for HR CTV. CONCLUSIONS: Substantial variations occur in fractionated cervix cancer BT with higher impact close to clinical threshold levels. The treatment approach has to balance uncertainties for individual cases against the use of repetitive imaging, adaptive planning and dose delivery.

Inter-application variation of dose and spatial location of D(2cm(3)) volumes of OARs during MR image based cervix brachytherapy.

PURPOSE: Evaluation of Inter-application variation of doses and spatial location of D(2cm(3)) volumes of OARs during MR-image based cervix brachytherapy. MATERIALS AND METHODS: Twenty-seven patients treated with EMBRACE protocol were analyzed. Every patient had two applications, one week apart. For each application patient had undergone MR-imaging (MR-1 and MR-2), volume delineation, reconstruction, treatment planning (plan-1 and plan-2) and dose evaluation. Both the image series were then co-registered with applicator as the reference coordinate system (Eclipse planning system v8.6.14). Inter-application dose, volume and spatial location of D(2cm(3)) variation were evaluated. RESULTS: The largest inter-application systematic and random dose variations were observed for sigmoid as compared to rectum and bladder. The mean (±SD) of the relative D(2cm(3)) variations were 0.6(±15.1)%, 0.9(±13.1)% and 11.9(±37.5)% for rectum, bladder and sigmoid respectively. The overlap of D(2cm(3)) volumes was more than 50% in 16(59%), 8(30%) and 3(11%) patients for rectum, bladder and sigmoid, respectively. CONCLUSION: The 2cm(3) volumes between the applications/fractions are quite stable in topography for bladder and rectum, and hence the current practice of cumulative addition of D(2cm(3)) dose is expected to be valid for bladder and rectum. For sigmoid, significant topographical changes were seen, which need further validation in a larger patient population and in multi-centric settings.

Comparison of IPSA with dose-point optimization and manual optimization for interstitial template brachytherapy for gynecologic cancers.

PURPOSE: To compare inverse planning simulated annealing (IPSA) algorithm with the dose-point 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. Dose-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=0.006) as compared with DPO plan (83.7%; p=0.62). Similarly, mean D(90) was same in both GrO plan and IPSA, 3.96±0.23 and 3.96±0.15Gy, respectively. DPO plans were homogeneous with homogeneity index being 0.82 as compared with 0.68±0.05 of GrO plan and 0.71±0.04 of IPSA. However, IPSA resulted in high conformity with conformity index of 0.78 as compared with 0.72 (p=0.001) and 0.68 (p≤0.001) for GrO and DPO plans, respectively. The dose to rectum (3.3±1.06Gy) and bladder (3.17±0.5Gy) was generally high for DPO plan. GrO plan reduced the dose to the rectum (2.91±0.63; p=0.011) and bladder (2.89±0.63Gy; p=0.003) significantly. IPSA resulted in a further reduction of the dose to rectum (2.79±0.67Gy; p=0.046) and bladder (2.81±0.67Gy; p=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.

Quantitative estimation of doses to salivary glands from using brachytherapy in head and neck cancers.

PURPOSE: To quantify the percentage doses received by salivary glands (SGDs) in head and neck interstitial brachytherapy (BT). METHODS AND MATERIALS: The study included 43 patients who underwent high-dose rate iridium-192 implant for oral cavity and oropharyngeal lesions treated with BT as a boost. BT dose varied with disease stage and external radiation dose, with the total mean dose of 66±4Gy. Patients were divided into two groups, midline and lateralized, based on anatomic implant location. Different dose parameters such as D(max), D(mean), DV(30%) of individual glands were derived from dose volume histogram representing the percentage maximum dose, mean dose, and dose received by 30% volume of individual SGDs, respectively. For better perception of the impact of BT on individual SGDs, the doses received are extrapolated to radical BT dose of 60Gy. RESULTS: For lateralized implants, the highest dose received by ipsilateral parotid (PTD) was 12.3% seen in tonsillar implants. The contralateral PTD receives minimal doses. As expected, the ipsilateral submandibular gland (SMG) received high doses in the range of 80% of the total prescribed dose, whereas contralateral SMG received 10% of ipsilateral dose. For the midline implants, the mean dose range for PTD was 7-11% of the total prescribed dose and for SMG between 17% and 56%, depending on the location. CONCLUSIONS: The study quantifies the percentage doses received by the individual SGDs in interstitial head and neck BT for use in future planning of the BT procedures and for salivary functional studies, prediction of damage, and quality-of-life parameters.

Comparison of DVH parameters and loading patterns of standard loading, manual and inverse optimization for intracavitary brachytherapy on a subset of tandem/ovoid cases.

PURPOSE: Comparison of inverse planning with the standard clinical plan and with the manually optimized plan based on dose-volume parameters and loading patterns. MATERIALS AND METHODS: Twenty-eight patients who underwent MRI based HDR brachytherapy for cervix cancer were selected for this study. Three plans were calculated for each patient: (1) standard loading, (2) manual optimized, and (3) inverse optimized. Dosimetric outcomes from these plans were compared based on dose-volume parameters. The ratio of Total Reference Air Kerma of ovoid to tandem (TRAK(O/T)) was used to compare the loading patterns. RESULTS: The volume of HR CTV ranged from 9-68 cc with a mean of 41(±16.2) cc. Mean V100 for standard, manual optimized and inverse plans was found to be not significant (p=0.35, 0.38, 0.4). Dose to bladder (7.8±1.6 Gy) and sigmoid (5.6±1.4 Gy) was high for standard plans; Manual optimization reduced the dose to bladder (7.1±1.7 Gy p=0.006) and sigmoid (4.5±1.0 Gy p=0.005) without compromising the HR CTV coverage. The inverse plan resulted in a significant reduction to bladder dose (6.5±1.4 Gy, p=0.002). TRAK was found to be 0.49(±0.02), 0.44(±0.04) and 0.40(±0.04) cGy m(-2) for the standard loading, manual optimized and inverse plans, respectively. It was observed that TRAK(O/T) was 0.82(±0.05), 1.7(±1.04) and 1.41(±0.93) for standard loading, manual optimized and inverse plans, respectively, while this ratio was 1 for the traditional loading pattern. CONCLUSIONS: Inverse planning offers good sparing of critical structures without compromising the target coverage. The average loading pattern of the whole patient cohort deviates from the standard Fletcher loading pattern.

Treatment planning of epithelial ovarian cancers using helical tomotherapy.

Whole Abdomen Radiotherapy (WAR) for epithelial ovarian cancer though effective has been used sparingly due to inadequate target coverage and poor sparing of Organ At Risk (OAR) leading to significantly higher toxicities. Newer radiation techniques have shown potential for significant improvement in the therapeutic ratio. The purpose of this study was to evaluate Helical Tomotherapy(HT) for WAR. The objective parameters were to obtain uniform and adequate target coverage with maximum OAR sparing. HT plans were generated for five patients with field-width of 5.0/2.5 cm, modulation factor of 3.5/3.0, and a pitch of 0.3. A dose of 25 Gy in 25 fractions was prescribed to the abdomen with a simultaneous boost of 45 Gy in 25 fractions to the pelvis. Dose-volume parameters and various indices were analyzed and compared. Mean volume (standard-deviation) of abdominal and pelvic PTV (planning target volume) was 6630 +/-450 cm3 and 1235 +/-98 cm3 respectively. Mean length of PTV in cranio-caudal direction was 41+/-4 cm. Volume receiving 95% and 107% of the prescription dose, (V95% and V107%) was 95.6+/-2.7% and 2.6+/-0.5% for abdominal-PTV, and 95.7+/-2.4% and 0% for pelvic-PTV respectively. Homogeneity and Conformity indices were 17.5+/-1.7, 1.2+/-0.03 for abdominal PTV, and 5.2+/-0.7, 1.1+/-0.02 for pelvic-PTV respectively. Median dose received by the kidneys, liver and bone marrow were 9.6+/-1.2 Gy, 17+/-2.7 Gy and 22+/-1.4 Gy respectively. HT achieves an excellent coverage of WAR target with simultaneous pelvic boost and better organ (kidneys and liver) sparing. HT for WAR has the potential as consolidative therapy which is being evaluated further in a phase II cohort study in epithelial ovarian cancers.

Treatment outcome with low-dose-rate interstitial brachytherapy in early-stage oral tongue cancers.

PURPOSE: Although radical radiotherapy is known to be equally effective for early-stage oral tongue cancers (T1-2 N0) with the added advantage of organ and function preservation, surgery remains the preferred treatment. We present outcome of patients treated with brachytherapy (BT) either radical or boost. MATERIALS AND METHODS: Fifty-seven patients (T1/T2 31/26) were studied. Seventeen patients (30%) were treated with radical BT (50-67 Gy) while 40 (70%) with external beam radiation therapy (EBRT) + BT (36-56 Gy + 15-38 Gy]. Low-dose-rate (LDR) BT was delivered with 192 Ir wires, using plastic bead technique with varied dose rates (<60 cGy/h in 29 patients, 60-90 cGy/h in 17, and >90 cGy/h in 11). RESULTS: The overall local control (LCR) was achieved in 59.7% (34/57) patients. LCR for T1 and T2 was 67.8% and 50%, respectively. A total of 23 patients had failures [local: 20 (T1: 8; T2: 12 patients), node: 5 (T1:2; T2: 3), and local + nodal: 3]. Overall 5-year disease-free survival and overall survival (OAS) were 51% and 67%, respectively and those for T1 and T2 was 64.5/77.4% and 38.5/54% respectively (P = 0.002). All 16 patients were salvaged. Median survival after salvage treatment was 13.5 months (6-100 months). Soft tissue necrosis was observed in 12.3% (7/57) and osteoradionecrosis in two patients. CONCLUSION: BT, as an integral part of radical radiation therapy in early-stage tongue cancers, appears to be an effective alternative treatment modality with preservation of the organ and function without jeopardizing the outcome.

High-dose-rate brachytherapy boost for carcinoma of external auditory canal.

PURPOSE: To report dosimetry and outcome in a case of early stage carcinoma of external ear (T1N0M0) treated with radical radiotherapy alone using a combination of external beam radiotherapy (EBRT) and intracavitary irradiation with a high-dose-rate (HDR) (192)Ir remote afterloading system. METHODS AND METHODS: A 64-year-old gentleman who was diagnosed as T1N0M0 carcinoma of external ear was treated with combination of external beam radiation therapy followed by brachytherapy (BRT). A total dose of 40Gy was delivered by EBRT, following which a 6-Fr catheter for the HDR (192)Ir remote afterloader, fixed by a customized acrylic mold, was inserted into the external auditory canal (EAC) and a total intracavitary radiation dose of 22.5Gy (4.5Gy/F) was given. RESULTS: Evaluation at the completion of treatment and at the end of 4-year followup revealed no evidence of the disease. CONCLUSIONS: In the radical treatment of early stage EAC carcinoma, combination of external beam radiation therapy and BRT may be a modality of choice for its efficacy, less severe side effects, and better cosmetic results.

Dosimetric validation of first helical tomotherapy Hi-Art II machine in India.

A Helical Tomotherapy (HT) Hi-Art II machine, Hi ART (TomoTherapy, Inc., Madison, WI, USA) was installed at our center in July 2007, and was the first machine in India. Image-guided HT is a new modality for delivering intensity modulated radiotherapy (IMRT). Dosimetric tests done include (a) primary beam alignment (b) secondary beam alignment (c) water tank measurements (profiles and depth doses) (d) dose rate measurements (e) IMRT verification, and (f) Mega voltage Computed Tomography (MVCT) dose. Primary and secondary beam alignment revealed an acceptable linear accelerator (linac) alignment in both X and Y axes. In addition, it was observed that the beam was aligned in the same plane as gantry and the jaws were not twisted with respect to gantry. The rotational beam stability was acceptable. Multi-leaf collimators (MLC) were found to be stable and properly aligned with the radiation plane. The jaw alignment during gantry rotation was satisfactory. Transverse and longitudinal profiles were in good agreement with the "Gold" standard. During IMRT verification, the variation between the measured and calculated dose for a particular plan at the central and off-axis was found to be within 2% and 1mm in position, respectively. The dose delivered during the TomoImage scan was found to be 2.57 cGy. The Helical Tomotherapy system is mechanically stable and found to be acceptable for clinical treatment. It is recommended that the output of the machine should be measured on a daily basis to monitor the fluctuations in output.

Dose optimization of intra-operative high dose rate interstitial brachytherapy implants for soft tissue sarcoma.

OBJECTIVE: A three dimensional (3D) image-based dosimetric study to quantitatively compare geometric vs. dose-point optimization in combination with graphical optimization for interstitial brachytherapy of soft tissue sarcoma (STS). MATERIALS AND METHODS: Fifteen consecutive STS patients, treated with intra-operative, interstitial Brachytherapy, were enrolled in this dosimetric study. Treatment plans were generated using dose points situated at the "central plane between the catheters", "between the catheters throughout the implanted volume", at "distances perpendicular to the implant axis" and "on the surface of the target volume" Geometrically optimized plans had dose points defined between the catheters, while dose-point optimized plans had dose points defined at a plane perpendicular to the implant axis and on the target surface. Each plan was graphically optimized and compared using dose volume indices. RESULTS: Target coverage was suboptimal with coverage index (CI = 0.67) when dose points were defined at the central plane while it was superior when the dose points were defined at the target surface (CI=0.93). The coverage of graphically optimized plans (GrO) was similar to non-GrO with dose points defined on surface or perpendicular to the implant axis. A similar pattern was noticed with conformity index (0.61 vs. 0.82). GrO were more conformal and less homogeneous compared to non-GrO. Sum index was superior for dose points defined on the surface of the target and relatively inferior for plans with dose points at other locations (1.35 vs. 1.27). CONCLUSIONS: Optimization with dose points defined away from the implant plane and on target results in superior target coverage with optimal values of other indices. GrO offer better target coverage for implants with non-uniform geometry and target volume.

Dosimetric evaluation of rectum and bladder using image-based CT planning and orthogonal radiographs with ICRU 38 recommendations in intracavitary brachytherapy.

The purpose is to compare CT-based dosimetry with International Commission on Radiation Units and Measurements (ICRU 38) bladder and rectum reference points in patients of carcinoma of uterine cervix treated with intracavitary brachytherapy (ICA). Twenty-two consecutive patients were evaluated. Orthogonal radiographs and CT images were acquired and transferred to PLATO planning system. Bladder and rectal reference points were identified according to ICRU 38 recommendations. Dosimetry was carried out based on Manchester system. Patient treatment was done using (192)Iridium high dose rate (HDR) remote after-loading machine based on the conventional radiograph-based dosimetry. ICRU rectal and bladder point doses from the radiograph plans were compared with D(2), dose received by 2 cm(3) of the organ receiving maximum dose from CT plan. V(2), volume of organ receiving dose more than the ICRU reference point, was evaluated. The mean (+/-standard deviation) volume of rectum and bladder was 60 (+/-28) cm(3) and 138 (+/-41) cm(3) respectively. The mean reference volume in radiograph and CT plan was 105 (+/-7) cm(3) and 107 (+/-7) cm(3) respectively. It was found that 6 (+/-4) cm(3) of rectum and 16 (+/-10) cm(3) of bladder received dose more than the prescription dose. V(2) of rectum and bladder was 7 (+/-1.7) cm(3) and 20.8 (+/-6) cm(3) respectively. Mean D(2) of rectum and bladder was found to be 1.11 (+/-0.2) and 1.56 (+/-0.6) times the mean ICRU reference points respectively. This dosimteric study suggests that comparison of orthogonal X-ray-based and CT-based HDR ICA planning is feasible. ICRU rectal point dose correlates well with maximum rectal dose, while ICRU bladder point underestimates the maximum bladder dose.

Treatment planning comparison of electron arc therapy and photon intensity modulated radiotherapy for Askin's tumor of chest wall.

BACKGROUND AND PURPOSE: A dosimetric study to quantitatively compare radiotherapy treatment plans for Askin's tumor using Electron Arc (EA) vs. photon Intensity Modulated Radiotherapy (IMRT). MATERIALS AND METHODS: Five patients treated with EA were included in this study. Treatment plans were generated for each patient using EA and IMRT. Plans were compared using dose volume histograms (DVH) of the Planning Target Volume (PTV) and Organs at Risk (OAR). RESULTS: IMRT resulted in superior PTV coverage, and homogeneous dose distribution compared to EA. For EA, 92% of the PTV was covered to 85% of the dose compared to IMRT in which 96% was covered to 95% of the dose. V(107) that represents the hot spot within the PTV was more in IMRT compared to EA: 7.4(+/-2)% vs. 3(+/-0.5)%, respectively. With PTVs located close to the spinal cord (SC), the dose to SC was more with EA, whereas for PTVs located away from the SC, the dose to SC was more with IMRT. The cardiac dose profile was similar to that of SC. Ipsilateral lung received lower doses with IMRT while contralateral lung received higher dose with IMRT compared to EA. For non-OAR normal tissues, IMRT resulted in large volumes of low dose regions. CONCLUSIONS: IMRT resulted in superior PTV coverage and sparing of OAR compared to EA plans. Although IMRT seems to be superior to EA, one needs to keep in mind the volume of low dose regions associated with IMRT, especially while treating young children.

Brachytherapy boost: a novel approach for epiglottic carcinoma.

PURPOSE: Epiglottic (epilaryngeal) carcinoma has been treated conventionally by radical external beam radiotherapy or partial laryngectomy. The aim of this study is to evaluate the role of brachytherapy boost as a novel approach for lingual epiglottic lesions. METHODS AND MATERIALS: Twenty-three patients with T(2-3)N(0-1) lingual epiglottic carcinoma (SCC) were treated with curative intent between January 1990 and December 2001 using low dose rate interstitial (192)Ir implant boost, moderate dose of 25Gy at 0.5cm (mean dose rate, 50.5 cGy/h) 3 weeks after moderate dose of external beam radiotherapy (mEBRT) of 46Gy/23#/28-31d. RESULTS: Complete response after mEBRT was observed in 18 of the 23 patients (78%) and partial response was seen in 5 of the 23 patients (22%). After implant, all patients had complete response. Locoregional control was seen in 19 of the 23 patients (82.6%). Two patients developed distant metastases. Disease-free survival and overall survival at 5 years were 68.3% and 66.7%, respectively. Disease-free survival at 5 years showed a trend toward better outcome for biologically equivalent doses >85Gy compared with biologically equivalent doses <85Gy (80% vs. 68%) (p=0.18). All patients had minimal to acceptable xerostomia. CONCLUSIONS: Interstitial boost with mEBRT is feasible, effective, and a novel approach for lingual epiglottic lesions.

Dosimetric comparison of inverse optimization with geometric optimization in combination with graphical optimization for HDR prostate implants.

The purpose of this study is to compare geometric optimization (GO) with anatomy based inverse optimization (ABIO). Five patients of carcinoma prostate treated with HDR interstitial brachytherapy had been studied. Post implant CT scans of 5 mm slice thickness were obtained; target volume and other critical structures rectum, bladder and urethra were drawn by the clinician. Plans were obtained with geometric optimization and anatomy based inversed optimization. Anatomy based inverse planning implemented currently in PLATO BPS version 14.2, is based on geometric and dose point optimization and designed to account for the critical structures. Graphical optimization (GrO) is used to fine-tune the distribution ie to reduce the dose to critical structures and to improve the target coverage in both geometric optimization and anatomy based inverse optimization plans. DVH of target, rectum, bladder and urethra were evaluated and compared, dose homogeneity index and conformity index were also evaluated for all the plans. The mean target coverage was 93.9±7%, 90.3±4%, 82±13%, 91.6±3 for different optimization techniques GO, GO_gr, ABIO and ABIO_gr respectively. The target coverage in ABIO is not clinically acceptable. Maximum dose, dose to 2% of the volume of urethra D(2%,U) was 137±12%, 123.2±2%, 111.5±9, 122.7±4 for GO, GO_gr, ABIO and ABIO_gr respectively. The mean conformity index values were 0.71, 0.76, 0.65, 0.82 for GO, GO_gr, ABIO, ABIO_gr respectively. ABIO_gr has a good conformity over all other optimization techniques. However the difference is not very significant between GO and GO_gr. The mean values of DHI are 0.81, 0.77, 0.65 and 0.75 for GO, GO_gr, ABIO and ABIO_gr respectively. Geometric optimization is highly homogenous compared to all other optimization techniques.To conclude, target coverage in ABIO is not clinically acceptable. However ABIO followed by graphical optimization is much superior in sparing of critical structures and conformity compared to geometrical optimization. Target coverage is marginally better in GO compared to ABIO_gr. Homogeneity is superior in GO compared to ABIO_gr. However ABIO_gr plans were clinically acceptable with respect to homogeneity. Further, dose escalation to the target is possible with ABIO, without exceeding the tolerance dose to urethra. Clinical correlation of genitourinary toxicity has to be studied.