Total ablative stereotactic body radiotherapy to primary and oligometastatic renal cell carcinoma in medically inoperable cases: An institutional analysis.

Introduction: Stereotactic body radiotherapy (SBRT) has been found to be an effective and safe modality with excellent oncological outcome in medically inoperable primary renal cell carcinoma (RCC) and oligometastases. There is scarcity of data on the synchronous delivery of SBRT to primary and oligometastatic RCC in patients unfit for nephrectomy. Here, we report the findings of a retrospective study of prospectively collected data on "total ablative SBRT." Methods: Oligometastatic RCC patients with intact primary tumors were enrolled between May 2021 and June 2022. SBRT was synchronously delivered to the primary tumor and metastases. Demographics, treatment, oncologic outcomes, and toxicity were assessed. Kaplan-Meier estimates were generated for oncologic outcomes. The primary endpoint of this study was feasibility and tolerability. Results: Eleven patients were enrolled between May 2021 and June 2022. One patient died at 2 months after SBRT due to viral pneumonitis (possibly COVID pneumonia). Nine patients (82%) had metastatic disease, while 2 (18%) were stage II. The average maximal diameter of primary was 68.7 mm (range, 23-128 mm). The SBRT doses for primary and metastasis ranged from 40 to 55 Gray (Gy) in 5 to 7 fractions and 22 to 40Gy in 2 to 5 fractions, respectively. The median follow-up period was 10.5 months (Range: 4-15 months). Response assessment was available for ten patients. Local control, marginal control, regional control and initial oligometastatic control (OMC) rates were 100%. OMC declined to 87.5% as one patient had recurrence in irradiated subcarinal lymphnode at 7 months. The metastatic control rate was 80% and loco-regional progression-free survival was 8 months (range, 4-15 months). Toxicities were minimal and manageable. At the last follow-up, 7 of 11 patients were alive with an overall survival of 63.5%. Six patients received systemic therapy after SBRT. Conclusions: Synchronous delivery of SBRT to primary and oligometastatic sites in patients unfit for nephrectomy was feasible and tolerable with good locoregional control. The total ablative SBRT strategy needs to be explored in similar cohorts.

Optimal Combination of Pitch, Modulation Factor and Dosimetric Considerations in Treatment Planning for Total Body Irradiation Using Helical Tomotherapy.

OBJECTIVE: The aim of this study is to makethe standard total body irradiation (TBI) protocol for Helical tomotherapy© (HT) and to analyze the optimal pitch and modulation factor (MF) with respect to dose homogeneity index (HI), target dose coverage, target overdose, beam on time (BOT) and mean lung dose. MATERIALS AND METHODS: Ten patients who underwent high-dose TBI were taken for this study. For each patient, 35 dose plans were created by different combination of pitch and MF. The optimal pitch and MF were deduced using scatter plot and regression methodology based on target coverage, HI, target volume receiving 103%(V103%), 105%(V105%) and 107% (V107%) of the prescription dose and BOT. Using these optimal pitch and MF, the final dose plan was made and the planning aim and achieved dose was compared using two tailed student's t-test. Radiochromic films and ionization chambers were used to measure the delivered dose using anthropomorphic phantom on various points for the head and pelvis regions to verify the skin flash margin and its effect on skin dose. RESULTS: The optimal pitch and MF value were 0.287 and 2.4 respectively. Based on optimal pitch and MF, the mean BOT was 1692 seconds with optimal inhomogeneity (7.4%). For target, D95 and D98 were 97.09% (range:94.7-99.6%, p=0.002) and 93.9% (range:91.5-94.4%,p=0.007) respectively, and mean D2 was within 107% with SD of ±1.22% (p=0.04). The mean of PTV receiving V103, V105 and V107 was 24.48% (range=7.7-36.6%, p=0.03), 5.76% (range=1.4-12.1%, SD=±3.3%), 1.93% (range=0.1-4.6%, p=0.008) respectively. Our measurements show that the flash margin did not increase the skin dose. CONCLUSION: In our study, the optimal combination of pitch value of 0.287 and MF value of 2.4 provided acceptable plans for all patients planned for TBI in HT. The flash margin can provide adequate coverage during patient position uncertainty without increasing the skin dose.

Current status and future readiness of Indian radiation oncologists to embrace prostate high-dose-rate brachytherapy: An Indian Brachytherapy Society survey.

Purpose: This survey aimed to understand the practice pattern and attitude of Indian doctors towards prostate brachytherapy. Material and methods: A 21-point questionnaire was designed in Google form and sent to radiation oncologists practicing in India, using texts, mails, and social media. Responses were collated, and descriptive statistical analysis was performed. Results: A total of 212 radiation oncologists from 136 centers responded to the survey questionnaire, with majority (66%) being post-specialty training > 6 years. We found that about 44.3% (n = 94) of respondents do not practice interstitial brachytherapy for any site, and majority (83.3%, n = 175) do not practice high-dose-rate (HDR) prostate brachytherapy. Only 2.8% (n = 6) of doctors preferred boost by brachytherapy compared with 38.1% (n = 80) of respondents, who favored stereotactic body radiation therapy (SBRT) boost. When asked about the indication of HDR prostate brachytherapy in Indian setting, 32.5% (n = 67) of respondents favored monotherapy, 46.1% (n = 95) of oncologists thought boost as a good indication, and 21.4% (n = 44) preferred re-irradiation/salvage setting. The most cited reason for prostate brachytherapy not being popularly practiced in India was lack of training (84.8%, n = 179). It was also noted that out of 80 respondents who practiced SBRT for prostate boost, 37 would prefer HDR brachytherapy boost if given adequate training and facilities. Conclusions: The present survey provided insight on practice of prostate brachytherapy in India. It is evident that majority of radiation oncologists do not practice HDR prostate brachytherapy due to lack of training and infrastructure. Indian physicians are willing to learn and start prostate brachytherapy procedures if dedicated training and workshops are organized.

Nidus delineation and dosimetric comparison in arteriovenous malformation in stereotactic radiosurgery by using MRI and 3DCT angiography.

Purpose/Objectives: Accurate delineation of target is key to any successful radiosurgery. C-arm Dyna CT/ 3DCT angiography (3DCTA) has the potential of improving the accuracy of nidus delineation in intracranial arteriovenous malformations (AVM) due to high temporo-spatial resolution of vessel architecture. Here, we present a comparison of nidus delineation and dosimetric parameters between digital 3DCTA and MRI. Materials/Methods: Ten consecutive patients treated for intracranial AVMs were included in this study. All patients underwent MRI/MRA, and 3DCTA and all images were co-registered. AVM were delineated using 3DCTA (GTV3DCTA) and contrast enhanced MRI/MRA (GTVMRI). Hausdorff distance (HD) matrices and dice similarity coefficient (DSC) matrices were analysed. Stereotactic radiosurgery plans were developed for both the volumes for all patients and statistical analysis were performed with T-test. Results: Mean volumes of GTV3DCTA and GTVMRI were 1.771 cc (SD 1.794cc, range 0.124-4.191cc) and 2.183cc (SD 2.16cc, range 0.221-6.133cc), respectively. Significant deviation (p=0.018) was found when taking GTVMRI as a primary and comparing it to GTV3DCTA (MD=0.723cc±0.816cc). Similar result was observed with GTV3DCTA as primary and GTVMRI as secondary (MD=0.188cc, SD=0.193cc, p=0.024). Maximum HD was in the range of 1.71 to 7.44mm (mean=4.27mm, SD=1.56). For GTV3DCTA based plans, significant deviation was found between GTVMRI and GTV3DCTA in dose coverage and the mean difference was 22.17% (SD 16.73). In GTVMRI based plans, the mean CIRTOG deteriorated from 1.33 to 2.18 for GTVMRI and GTV3DCTA, respectively. Significant deviation was found in CIRTOG (0.005) and mean deviation was 0.86(SD=0.72) when comparing GTVMRI and GTV3DCTA. Highly significant (p=0.002) deviation was found in CIPaddick between GTVMRI and GTV3DCTA for GTVMRI based plans with mean difference of 0.26(SD=0.4, for GTVMRI=0.3, GTV3DCTA=0.46). Conclusion: Nidus volume was significantly altered with the use of 3DCTA compared to that of MRA/MRI images. Multimodality imaging is crucial for accurate target delineation, and successful radiosurgical obliteration of nidus.

Commissioning and Dosimetric Results of an Indigenously Developed Intra-Vaginal Template for Interstitial Plus Intracavitary High dose Rate Image-Guided Brachytherapy of Advanced Cervix Cancer.

Aim: The goal of this study is to discuss the commissioning and dosimetric parameters achieved during the clinical implementation of an indigenously developed intracavitary (IC) plus interstitial (IS) template for high dose rate (HDR) image-guided brachytherapy (IGBT) in cancer (Ca) cervix. We want to discuss our achieved values of cumulative equi-effective doses (EQD2) for high-risk clinical target volume (HRCTV) and organ at risk (OAR) and compare it with available published results. Materials and Methods: Medanta anterior oblique/lateral oblique template has a total of 19 needles including the central tandem. For commissioning the template with needles, the indigenously made acrylic phantom was used. Oblique and straight needles were placed inside the acrylic phantom and a computed tomography (CT) scan was performed. Sixteen patients were treated in HDR IGBT using this template after external-beam radiotherapy. The IGBT plans were evaluated based on EQD2 of target coverage i.e., dose received by 98% (D98%_HRCTV), 90% (D90%_HRCTV), and 50% (D50%_HRCTV) volume of HRCTV, and dose received by 2 cc (D2cc) and 0.1 cc (D0.1cc) of OAR using linear quadratic (LQ) radiobiological model. Results: The autoradiographic in radiochromic film shows that the distance between the needle tip and the middle of the source position is 6 mm. The mean D98%_HRCTV and D90%_HRCTV was 76.8 Gy (range: 70-87.7 Gy, P < 0.01) and 84.49 Gy (range: 76.6-96.7 Gy, P < 0.01), respectively. Mean EQD2 of D2cc of the bladder, rectum, and sigmoid was 85.6 Gy (range: 77.5-99.6 Gy, P < 0.03), 74.3 Gy (range: 70.9-76.7 Gy, P < 0.05), and 58.3 Gy (range: 50.6-67.9 Gy, P = 0.01), respectively. The mean total reference air kerma at a 1 m distance is 0.489cGy (range: 0.391-0.681cGy). Conclusions: The indigenously developed template could attain satisfactory standards in terms of set parameters for commissioning and acceptable dose volume relations in our clinical use for treating the advanced Ca cervix patients who need IC + IS type of HDR IGBT. The comparative analysis with contemporary applicators was acceptable.

Dosimetric Comparison of Robotic and Linear Accelerator Multi-Leaf Collimator-Based Stereotactic Radiosurgery for Arteriovenous Malformation.

PURPOSE: To investigate the dosimetric comparison of different collimators which are used in robotic radiosurgery (cyberknife-CK) and linear accelerator (LINAC) for stereotactic radiosurgery (SRS) in arteriovenous malformation (AVM). MATERIALS AND METHODS: Twenty-five AVM patients were planned in CK using FIXED cone, IRIS collimator, and multi-leaf collimator (MLC) based in LINAC. Dosimetric comparison was performed using Paddick conformity index (CIPaddick) and International Commission on Radiation Units and measurements (ICRU) homogeneity index (HIICRU), gradient score (GS), normal brain dose received by 10cc (D10cc) and critical structure (brain stem, optic chiasma, optic nerves) doses. Paired sample t-test was used for statistical analysis. RESULTS: Mean treatment volume was 3.16cc (standard deviation ± 4.91cc). No significant deviation (P =0.45, 0.237 for FIXED vs. IRIS and FIXED vs. MLC, respectively) was found in target coverage. For CIPaddick, the mean difference (MD) between FIXED- and MLC-based plans was 0.16(P = 0.001); For HIICRU, difference between FIXED and IRIS was insignificant (0.5, P = 0.823); but, when FIXED versus MLC, the deviation was 7.99% (P = 0.002). In FIXED- and MLC-based plans, significant difference was found in GS70 and GS40 (P < 0.041 and 0.005, respectively). MD between FIXED- and MLC-based plans for normal brain for 5Gy, 10Gy, 12Gy, and 20Gy were 36.08cc (P = 0.009), 7.12cc (P = 0.000), 5.84cc (P = 0.000) and 1.56cc (P = 0.000), respectively. AVM volume <0.7cc should be treated with CK FIXED and >0.7cc were treated by using FIXED or IRIS collimators. AVM volume > 1.4cc can be treated by either LINAC MLC-based SRS or CK. CONCLUSION: Our study shows CK collimator (IRIS and FIXED) could be able to treat brain AVMs in any size. Linac MLC-based SRS has some limitations in terms of conformity and low-dose spillage, and advantages like reduced treatment time and MU.

The Medanta AOLO template for locally advanced cancer cervix brachytherapy: design and clinical implementation.

PURPOSE: In advanced cervical cancers, improved techniques using both intracavitary and interstitial brachytherapy (IC + IS) should be used to adequately cover the residual tumor volume, resulting in better clinical results. Confronted with some limitation in implementing available applicators, we devised our own indigenous template that would also serve as an applicator. MATERIAL AND METHODS: First, a graphical design was drawn, keeping in mind the extent of volumes that need to be targeted in various brachytherapy scenarios. It was validated in a computer system and a physical template was manufactured. The template underwent modified versions through iterative dosimetric and planning exercises. The final model was successfully implemented in a clinical scenario. RESULTS: Cylindrical templates of diameter 3, 4, and 5 cm were produced with central aperture for central tandem, combining surrounding holes spaced at pre-planned points. The instrument can be used for IC + IS brachytherapy in cervical cancers. This easy to use applicator/template can direct needles to treat a distance of 4.5 cm laterally at the level of point A. In two initial applications 55 and 54 cc of high-risk clinical target volumes (HRCTV) were treated, and 90% of the HRCTV was covered by 96% and 97% of prescribed doses, respectively. Additionally, the needles guided by the template helped in sculpting the dose from bladder and rectum. CONCLUSIONS: We have developed an easy to use IC + IS type of template/applicator, which was successfully implemented in our clinical practice.

Study of Variation in Dose Calculation Accuracy Between kV Cone-Beam Computed Tomography and kV fan-Beam Computed Tomography.

Cone-beam computed tomography (CBCT) images are presently used for geometric verification for daily patient positioning. In this work, we have compared the images of CBCT with the images of conventional fan beam CT (FBCT) in terms of image quality and Hounsfield units (HUs). We also compared the dose calculated using CBCT with that of FBCT. Homogenous RW3 plates and Catphan phantom were scanned by FBCT and CBCT. In RW3 and Catphan phantom, percentage depth dose (PDD), profiles, isodose distributions (for intensity modulated radiotherapy plans), and calculated dose volume histograms were compared. The HU difference was within ± 20 HU (central region) and ± 30 HU (peripheral region) for homogeneous RW3 plates. In the Catphan phantom, the difference in HU was ± 20 HU in the central area and peripheral areas. The HU differences were within ± 30 HU for all HU ranges starting from -1000 to 990 in phantom and patient images. In treatment plans done with simple symmetric and asymmetric fields, dose difference (DD) between CBCT plan and FBCT plan was within 1.2% for both phantoms. In intensity modulated radiotherapy (IMRT) treatment plans, for different target volumes, the difference was <2%. This feasibility study investigated HU variation and dose calculation accuracy between FBCT and CBCT based planning and has validated inverse planning algorithms with CBCT. In our study, we observed a larger deviation of HU values in the peripheral region compared to the central region. This is due to the ring artifact and scatter contribution which may prevent the use of CBCT as the primary imaging modality for radiotherapy treatment planning. The reconstruction algorithm needs to be modified further for improving the image quality and accuracy in HU values. However, our study with TG-119 and intensity modulated radiotherapy test targets shows that CBCT can be used for adaptive replanning as the recalculation of dose with the anisotropic analytical algorithm is in full accord with conventional planning CT except in the build-up regions. Patient images with CBCT have to be carefully analyzed for any artifacts before using them for such dose calculations.