Total body irradiation: Significant dose sparing of lung tissue achievable by helical tomotherapy

PurposeTotal body irradiation (TBI) is an important procedure in the conditioning for bone marrow and hematopoietic stem cell transplantation. Doses up to 12 Gy are delivered in hyperfractionated regimes. TBI performed with helical Tomotherapy® (Accuray, Madison, Wisconsin, USA) is an alternative to conventional techniques to deliver dose in extended target volumes with the possibility of simultaneous dose sparing to organs at risk. In this study we focused on maximum dose reduction to the lungs in TBI using helical Tomotherapy®.Material and methodsForty treatment plans of patients who received TBI were calculated with TomoH® (Accuray, Madison, Wisconsin, USA, Version 2.0.4) with a dose of 12 Gy delivered in six equal fractions (2 × 2 Gy/day). Planning iterations necessary to accomplish ICRU 83 report should be less than 250. Treatment time should be practicable in daily routine (<60 min.). Besides the usual contouring of organs at risk special contouring was required for optimization processes which focused on maximum dose sparing in the central lung tissue. Dose constraints (D2, D98, D99) were predefined for target volumes (i.e. PTV TBI D99: 90% of prescribed dose). Homogeneity index <0.15 was defined for acceptability of the treatment plan.ResultsFor all patients acceptable treatment plan fulfilling the predefined constraints were achievable. An average time of 46 min is required for treatment. Thirty-four of forty patients fulfilled D2 in the PTV TBI. Four patients failed D2 due to a high BMI >28 (maximum dose 13.76 Gy = 114.7%). The D98 in the PTV TBI was not reached by 2/40 patients due to BMI > 31 (minimum dose 11.31 Gy = dose coverage of 94.2%). Also these two patients failed the homogeneity index <0.15. The mean lung dose over all patients of the right lung was 7.18 Gy (range 6.4–9.5 Gy). The left lung showed a median (D50) dose of 7.9 Gy (range 6.7–9.3 Gy). Central lung dose showed a mean dose (D50) of 5.16 Gy (range 4.02–7.29 Gy). The D80 of the central lung showed an average dose of 3.87 Gy.ConclusionsTotal body irradiation using helical Tomotherapy® can be delivered with maximum lung tissue sparing (<6 Gy) but without compromise in adjacent PTV TBI structures (i.e. ribs, heart). High conformity and homogeneity in extended radiation volumes can be reached with this technique in an acceptable planning and treatment time. Limitations may occurred in patients with high body mass index.     

Preliminary Results of Helical Tomotherapy in Patients with Complex-Shaped Meningiomas Close to the Optic Pathway

Meningiomas are the most common benign intracranial tumor. Meningiomas close to the optic pathway represent a treatment challenge both for surgery and radiotherapy. The aim of this article is to describe early results of helical tomotherapy treatment in complex-shaped meningiomas close to the optic pathway. Twenty-eight patients were consecutively treated. All patients were immobilized with a thermoplastic head mask and planned with the aid of a magnetic resonance imaging–computed tomography fusion. All treatments included daily image guidance. Pretreatment symptoms and acute toxicity were recorded. Median age was 57.5 years, and 92.8% patients had Eastern Cooperative Oncology Group performance status scale ≤1. The most common localizations were the sella turcica, followed by the cavernous sinus and the sphenoid. The most common symptoms were derived from cranial nerve deficits. Tomotherapy was administered as primary treatment in 35.7% of patients, as an adjuvant treatment in 32.4%, and as a rescue treatment after postsurgical progression in 32.1% patients. Most patients were either inoperable or Simpson IV. Total dose varied between 5000 and 5400 cGy; fractionation varied between 180 and 200 cGy. Median dose to the planning target volume was 51.7 Gy (range, 50.2–55.9 Gy). Median coverage index was 0.89 (range, 0.18–0.97). Median homogeneity index was 1.05 (range, 1–1.12). Acute transient toxicity was grade 1 and included headache in 35.7% patients, ocular pain/dryness in 28.5%, and radiation dermatitis in 25%. Thus far, with a maximal follow-up of 3 years, no late effects have been seen and all patients have a radiological stabilization of the disease. Helical tomotherapy offered a safe and effective therapeutic alternative for patients with inoperable or subtotally resected complex-shaped meningiomas close to the optic pathway. Acceptable coverage and homogeneity indexes were achieved with appropriate values for maximal doses delivered to the eyes, lenses, and chiasm, despite the proximity of the tumor to these structures.     

Appropriate treatment planning method for field joint dose in total body irradiation using helical tomotherapy

Total body irradiation (TBI) using helical tomotherapy (HT) has advantages over the standard linear accelerator-based approach to the conditioning regimen for hematopoietic cell transplantation. However, the radiation field has to be divided into two independent irradiation plans to deliver a homogeneous dose to the whole body. A clinical target volume near the skin increases the skin surface dose; therefore, high- or low-dose regions arise depending on the set-up position accuracy because the two radiation fields are somewhat overlapped or separated. We aimed to determine an adequate treatment planning method robust to the set-up accuracy for the field joint dose distribution using HT-TBI. We calculated treatment plans reducing target volumes at the interface between the upper and lower body irradiations and evaluated these joint dose distributions via simulation and experimental studies. Target volumes used for the optimization calculation were reduced by 0, 0.5, 1.0, 2.0, 2.5, and 3.0 cm from the boundary surface on the upper and lower sides. Combined dose distributions with set-up error simulated by modifying coordinate positions were investigated to find the optimal planning method. In the ideal set-up position, the target volume without a gap area caused field junctional doses of up to approximately 200%; therefore, target volumes reduced by 2.0–3.0 cm could suppress the maximum dose to within 150%. However, with set-up error, high-dose areas exceeding 150% and low-dose areas below 100% were found with 2.0 and 3.0 cm target volume reduction. Using the dynamic jaw (DJ) system, dose deviations caused by set-up error reached approximately 20%, which is not suitable for HT-TBI. Moreover, these dose distributions can be easily adjusted when combined with the intensity modulation technique for field boundary regions. The results of a simulation and experimental study using a film dosimetry were almost identical, which indicated that reducing the target volume at the field boundary surface by 2.5 cm produces the most appropriate target definition.     

Dose–volume and biological-model based comparison between helical tomotherapy and (inverse-planned) IMAT for prostate tumours

BACKGROUND AND PURPOSE: Helical tomotherapy (HT) and intensity-modulated arc therapy (IMAT) are two arc-based approaches to the delivery of intensity-modulated radiotherapy (IMRT). Through plan comparisons we have investigated the potential of IMAT, both with constant (conventional or IMAT-C) and variable (non-conventional or IMAT-NC, a theoretical exercise) dose-rate, to serve as an alternative to helical tomotherapy. MATERIALS AND METHODS: Six patients with prostate tumours treated by HT with a moderately hypo-fractionated protocol, involving a simultaneous integrated boost, were re-planned as IMAT treatments. A method for IMAT inverse-planning using a commercial module for static IMRT combined with a multi-leaf collimator (MLC) arc-sequencing was developed. IMAT plans were compared to HT plans in terms of dose statistics and radiobiological indices. RESULTS: Concerning the planning target volume (PTV), the mean doses for all PTVs were similar for HT and IMAT-C plans with minimum dose, target coverage, equivalent uniform dose (EUD) and tumour control probability (TCP) values being generally higher for HT; maximum dose and degree of heterogeneity were instead higher for IMAT-C. In relation to organs at risk, mean doses and normal tissue complication probability (NTCP) values were similar between the two modalities, except for the penile bulb where IMAT was significantly better. Re-normalizing all plans to the same rectal toxicity (NTCP=5%), the HT modality yielded higher TCP than IMAT-C but there was no significant difference between HT and IMAT-NC. The integral dose with HT was higher than that for IMAT. CONCLUSIONS: with regards to the plan analysis, the HT is superior to IMAT-C in terms of target coverage and dose homogeneity within the PTV. Introducing dose-rate variation during arc-rotation, not deliverable with current linac technology, the simulations result in comparable plan indices between (IMAT-NC) and HT.     

Intensity-modulated radiotherapy (IMRT)/Tomotherapy following neoadjuvant chemotherapy in stage IIB-IVA/B undifferentiated nasopharyngeal carcinomas (UCNT): a mono-institutional experience

To evaluate the outcome of Undifferentiated Nasopharyngeal Carcinomas (UCNT) treated with intensity-modulated radiation therapy with Simultaneous Integrated Boost (SIB), following induction chemotherapy. Between January 2006 and June 2009, 52 patients with stage II B-IVA/B UCNT were treated either with linac-IMRT or Tomotherapy. All patients were scheduled to receive three cycles of cisplatin based neoadjuvant chemotherapy. With a median follow-up of 38.5 months (range 12.3–64.1), 3 year overall survival (OS), disease-free survival (DFS), and DFS by T2a–2b and T3–T4-stage were 95.0%, 84.6%, 89.0%, and 78.0%, respectively. At multivariate analysis, none of the examined prognostic factors reported statistical significance. N-classification was not a significant predictive factor for either OS or development of distant metastases. T-stage alone had a borderline effect on DFS and development of metastases. No difference between Tomotherapy and linac-IMRT emerged in terms of loco-regional control and development of severe, acute, and late toxicities. The most significant severe, acute toxicities were grade 3 (32.7%) and grade 4 (7.7%) mucositis. No grades 3 and 4 late toxicities were observed. The most commonly observed late effect was xerostomia, 11.5% patients complained grade 2 xerostomia. The severity of grade 2 xerostomia diminished over time with only four patients not improving salivation. IMRT-SIB following neoadjuvant chemotherapy was very satisfactory in terms of local control, regional control, DFS and OS rates in patients with stage IIB to IVB UCNT. In our experience, adding concurrent chemotherapy to IMRT after neoadjuvant chemotherapy in loco-regional widespread disease resulted to be the indicated approach.     

Distribution of brain metastases in relation to the hippocampus: implications for neurocognitive functional preservation

PURPOSE: With the advent of intensity-modulated radiotherapy, the ability to limit the radiation dose to normal tissue offers an avenue to limit side effects. This study attempted to delineate the distribution of brain metastases with relation to the hippocampus for the purpose of exploring the viability of tomotherapy-guided hippocampal sparing therapy potentially to reduce neurocognitive deficits from radiation. METHODS AND MATERIALS: The pre-radiotherapy T1-weighted, postcontrast axial MR images of 100 patients who received whole brain radiotherapy, stereotactic radiosurgery, or a radiosurgical boost following whole brain radiotherapy between 2002 and 2006 were examined. We contoured brain metastases as well as hippocampi with 5-, 10-, and 15-mm expansion envelopes. RESULTS: Of the 272 identified metastases, 3.3% (n = 9) were within 5 mm of the hippocampus, and 86.4% of metastases were greater than 15 mm from the hippocampus (n = 235). The most common location for metastatic disease was the frontal lobe (31.6%, n = 86). This was followed by the cerebellum (24.3%, n = 66), parietal lobe (16.9%, n = 46), temporal lobe (12.9%, n = 35), occipital lobe (7.7%, n = 21), deep brain nuclei (4.0%, n = 11), and brainstem (2.6%, n = 7). CONCLUSIONS: Of the 100 patients, 8 had metastases within 5 mm of the hippocampus. Hence, a 5-mm margin around the hippocampus for conformal avoidance whole brain radiotherapy represents an acceptable risk, especially because these patients in the absence of any other intracranial disease could be salvaged using stereotactic radiosurgery. Moreover, we developed a hippocampal sparing tomotherapy plan as proof of principle to verify the feasibility of this therapy in the setting of brain metastases.     

3D treatment planning on helical tomotherapy delivery system

The helical tomotherapy is a technologically advanced radiation dose delivery system designed to perform intensity-modulated radiation therapy (IMRT). It is mechanistically unique, based on a small 6-MV linear accelerator mounted on a ring gantry that rotates around the patient while the patient moves through a bore, ultimately yielding a helical path of radiation dose delivery. The helical pattern of dose delivery differentiated tomotherapy from other contemporary radiation therapy systems at the time of its inception. The accompanying 3-dimensional (3D) treatment planning system has been developed to solely support this specific type of dose delivery system. The treatment planning system has 2 modules identified as TomoHelical and TomoDirect to perform IMRT and conformal radiation therapy, respectively. The focus of this work within the scope of this special issue on 3D treatment planning systems is to assess the use of planning tools to generate treatment plans for helical tomotherapy. Clinical examples are used throughout to demonstrate the quality and differences of various clinical scenarios planned with tomotherapy.