Total marrow and lymphoid irradiation with helical tomotherapy: A practical implementation report

Objective To standardize the technique and resources for total marrow and lymphoid irradiation (TMLI) as part of the conditioning regimen before allogenic bone marrow transplantation (ABMT) using helical tomotherapy.Methods We used this technique in our first 5 patients requiring TMLI. Patients were immobilized using a mask and a whole-body vacuum cushion. CT scanning was performed in head first supine (HFS) and feet first supine (FFS) orientations with an overlap at mid-thigh. Target consisted of the entire skeleton, spleen, sanctuary sites and major lymphatics whereas lungs, kidneys, aero-digestive tract, bowel, parotids, heart and liver were defined as organs at risk (OAR). Treatment was performed in two parts based on 2 different plans generated in HFS and FFS orientations with an overlap at the mid thigh. Patients along with the immobilization device were manually rotated by 180° to change the orientation after the delivery of HFS plan. The dose at the junction was contributed by a complementary dose gradient from each of the plans. Plan was to deliver 95% of 12Gy to 98% of CTV with dose heterogeneity < 10% and pre-specified OAR doe constraints. Megavoltage-CT was used for position verification before each fraction. Patient specific quality assurance and an in-vivo film dosimetry to verify junction dose were performed in all patients.Results Treatment was delivered in two daily fractions of 2Gy each for 3 days with at least 8-hours gap between each fraction. The target coverage goals were met in all the patients. The average person-hours per patient were 16.5, 21.5 and 25.75 for radiation oncologist, radiation therapist and medical physicist respectively. Average in-room time per patient was 9.25 hours with an average beam-on time of 3.32 hours for all the six fractions. Conclusion This report comprehensively describes technique and resource requirements for TMLI and would serve as a practical guide for departments keen to start this service. Despite being time and labor intensive, it can be implemented safely and robustly. We will be using this methodology in a prospective phase II trial to study safety and feasibility of dose escalated TMLI as part of conditioning regimen before ABMT.

Effect of Changing Phantom Thickness on Helical Radiotherapy Plan: Dosimetric Analysis

Purpose: The aim of this study is to investigate the effect of changing phantom thickness on high dose region of interest (HD_ROI) and low dose ROI’s (LW_ROI’s) doses during helical radiotherapy (RT) by utilizing Adaptive RT (ART) technique. Materials and Methods: The cylindrical phantom (CP) is wrapped with different thickness boluses and scanned in the kilovoltage computed tomography (KVCT). HD_ROI and LW_ROI’s were created in contouring system and nine same plans (1.8 Gy/Fr) were made with images of different thicknesses CP. The point dose measurements were performed using ionization chamber in Helical Tomotherapy (HT) treatment machine. For detecting thickness reduction effect, CP was irradiated using bolus-designed plans and it was irradiated using without bolus plan. The opposite of this scenario was applied to determine the thickness increase. KVCT and megavoltage CT (MVCT) images were used for dose comparison. The HT Planned Adaptive Software was used to see the differences in the planning and verification doses at dose volume histograms (DVH). Results: Point dose measurements showed a 4.480% dose increase in 0.5 cm depth reduction for HD_ROI. These differences reached 8.508% in 2 cm depth and 15,279% in 5 cm depth. At the same time, a dose reduction of 0.665% was determined for a 0.5cm depth increase, a dose reduction of 1.771% was determined for a 2 cm depth increase, a dose reduction of 5.202% was determined for a 5 cm depth increase for the HD_ROI. The ART plan results show that the dose changes in the HD_ROI was greater than the LW_ROI’s. Conclusion: Phantom thicknesses change can lead to a serious dose increase or decrease in the HD_ROI and LW_ROI’s.

Image Guided Intensity Modulated Helical Radiation (Tomotherapy) Used as a Radiosurgical Tool

Introduction: Tomotherapy (HT) is a Linear accelerator mounted on a Computerized Tomography (CT), it is helical in nature, its application implies a megavoltage CT image acquisition which is fused daily to the radiosurgical plan that has been done previously (Image Guided Intensity Modulated Radiosurgery). This technology is new worldwide; to our knowledge this is the first report of intracranial radiosurgery in Latinamerica with HT. We describe dose distribution in a small target, as well as normal case flow and our initial intracranial experience. Methods: For the analysis of irradiation of a small target (PTV), one 10 mm spherical (0.51cc volume) target was elaborated. The PTVs where placed in the isocenter and 100 mm above the isocenter, the PTV received a 6 Gy prescription to the 85% isodose line, with a maximum dose of 9.0 Gy and a minimum of 4.7 Gy. We describe normal patient flow and retrospectively report our early experience from February 2011 to August 2011of intracranial radiosurgical cases. Results: The results of our Quality Assurance (DQA) on phantom studies show a very conformal (CI) 1.14, and homogeneous (HI) 1.51 dose behavior with a fall-off to 50% with regards to PTV of 4.6 mm, thirteen patients had been treated receiving 36 radiosurgical sessions. Conclusions: Radiosurgery with HT, it is a highly conformal,homogeneous with steep dose falloff, comparable to other stereotactic radiosurgical (SRS) tools, it is non invasive and it usually is a very low time consumption technique.