Verification dosimetry during treatment for helical tomotherapy using radiographic film

First experience of total body irradiation in conditioning regimes for allogenic hematopoietic stem cells transplantation in children with acute lymphoblastic leukemia in Saint Petersburg

Background. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an effective treatment method of refractory and recurrent forms of acute leukemia in children, while the question of choosing a conditioning regimen in order to achieve the best treatment results remains debatable. Conditioning based on total body irradiation (TbI) was confirmed to be most effective in some trials, but there are still issues of overcoming early and late toxicity, as well   as difficulties in planning and routing patients.Aim. To share the experience of interdisciplinary patient management during the conditioning period with TbI inclusion in Saint petersburg, to evaluate the feasibility, toxicity and effectiveness of the method.Materials and methods. patients undergoing allo-HSCT for high risk acute lymphoblastic leukemia conditioned either with TbI (n = 12) or chemotherapy (n = 10) were included. Medical data were retrospectively analyzed with an assessment of the following transplant outcomes: HSCT-associated toxicity, the frequency and severity of infectious complications, graft versus host disease, as well as overall and event-free survival rates. we have evaluated radiotherapy plans in order to assess the compliance of radiation exposure with acceptable values for critical organs.Results. All patients with acute lymphoblastic leukemia in both groups received appropriate myeloablative conditioning. According to the study results, despite the lack of significance, we obtained differences in HSCT-associated mortality (8.3 and 30 %; p = 0.151), 2-years overall and event-free survival (66 ± 13.6 and 36 ± 16.1 %; p = 0.122) in group with TbI and HdCT respectively. It should be noted that there was a trend towards a decrease of toxic reactions frequency in case of TbI-containing regimens; however we didn’t reveal any significant differences in the number of infectious complications during post-transplant period. The median follow-up was 24.2 months and there were no signs of delayed toxicity.Conclusion. TbI-based conditioning was well tolerated with a low incidence of early and delayed toxicity, better overall and event-free survival. based on feasibility of TbI in Saint petersburg hospitals it is possible to recommend the method in routine practice, taking into account clinical indications.

Fast, simple, and informative patient-specific dose verification method for intensity modulated total marrow irradiation with helical tomotherapy

Background

Patient-specific dose verification for treatment planning in helical tomotherapy is routinely performed using a homogeneous virtual water cylindrical phantom of 30 cm diameter and 18 cm length (Cheese phantom). Because of this small length, treatment with total marrow irradiation (TMI) requires multiple deliveries of the dose verification procedures to cover a wide range of the target volumes, which significantly prolongs the dose verification process. We propose a fast, simple, and informative patient-specific dose verification method which reduce dose verification time for TMI with helical tomotherapy.

Methods

We constructed a two-step solid water slab phantom (length 110 cm, height 8 cm, and two-step width of 30 cm and 15 cm), termed the Whole Body Phantom (WB phantom). Three ionization chambers and three EDR-2 films can be inserted to cover extended field TMI treatment delivery. Three TMI treatment plans were conducted with a TomoTherapy HiArt Planning Station and verified using the WB phantom with ion chambers and films. Three regions simulating the head and neck, thorax, and pelvis were covered in a single treatment delivery. The results were compared to those with the cheese phantom supplied by Accuray, Inc. following three treatment deliveries to cover the body from head to pelvis.

Results

Use of the WB phantom provided point doses or dose distributions from head and neck to femur in a single treatment delivery of TMI. Patient-specific dose verification with the WB phantom was 62% faster than with the cheese phantom. The average pass rate in gamma analysis with the criteria of a 3-mm distance-to-agreement and 3% dose differences was 94% ± 2% for the three TMI treatment plans. The differences in pass rates between the WB and cheese phantoms at the upper thorax to abdomen regions were within 2%. The calculated dose agreed with the measured dose within 3% for all points in all five cases in both the WB and cheese phantoms.

Conclusions

Our dose verification method with the WB phantom provides simple and rapid quality assurance without limiting dose verification information in total marrow irradiation with helical tomotherapy.

Tomotherapy as a tool in image-guided radiation therapy (IGRT): theoretical and technological aspects

Helical tomotherapy (HT) is a novel treatment approach that combines Intensity-Modulate Radiation Therapy (IMRT) delivery with in-built image guidance using megavoltage (MV) CT scanning. The technique utilises a 6 MV linear accelerator mounted on a CT type ring gantry. The beam is collimated to a fan beam, which is intensity modulated using a binary multileaf collimator (MLC). As the patient advances slowly through the ring gantry, the linac rotates around the patient with a leaf-opening pattern optimised to deliver a highly conformal dose distribution to the target in the helical beam trajectory. The unit also allows the acquisition of MVCT images using the same radiation source detuned to reduce its effective energy to 3.5 MV, making the dose required for imaging less than 3 cGy. This paper discusses the major features of HT and describes the advantages and disadvantages of this approach in the context of the commercial Hi-ART system.