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The Jacobian of the deformation field of elastic registration between images taken during radiotherapy is a measure of inter-fraction local deformation. The histogram of the Jacobian values (Jac) within an organ was introduced (JVH-Jacobian-volume-histogram) and first applied in quantifying parotid shrinkage. MVCTs of 32 patients previously treated with helical tomotherapy for head-neck cancers were collected. Parotid deformation was evaluated through elastic registration between MVCTs taken at the first and last fractions. Jac was calculated for each voxel of all parotids, and integral JVHs were calculated for each parotid; the correlation between the JVH and the planning dose-volume histogram (DVH) was investigated. On average, 82% (±17%) of the voxels shrinks (Jac < 1) and 14% (±17%) shows a local compression >50% (Jac < 0.5). The best correlation between the DVH and the JVH was found between V10 and V15, and Jac < 0.4-0.6 (p < 0.01). The best constraint predicting a higher number of largely compressing voxels (Jac0.5

PURPOSE/OBJECTIVE: Whole pelvis irradiation with IMRT (WPRT-IMRT) after prostatectomy is efficient in reducing acute toxicity: however, a number of patients still experience moderate acute bowel toxicity. MATERIALS AND METHODS: Ninety-six patients treated with WPRT-IMRT after prostatectomy with adjuvant or salvage intent were analysed. A number of parameters were individually recovered, including the DVHs of the intestinal cavity outside PTV and of the loops referred to both the WPRT phase and the whole treatment. Correlation between clinical-dosimetric parameters and acute bowel toxicity was investigated by logistic analyses. Best predictive cut-off values for continuous variables were assessed by ROC curves. RESULTS: 15/96 (15.6%) Patients experienced grade 2 toxicity (no grade 3). Best dose-volume predictors were the fraction of loops receiving more than 45, 50 and 55Gy (respectively, V45TL50cc, V50TL13cc, V55TL3cc; p-values ranging from 0.005 to 0.027). Age, GU acute toxicity, rectal acute toxicity and time between prostatectomy and IMRT were also predictors of acute bowel toxicity. Multivariate analysis showed that the most predictive independent parameters were age (OR: 1.13; 95%CI: 1.02-1.25; p=0.021) and V50TL (13cc, OR: 8.2; 95%CI: 1.7-40; p=0.009). CONCLUSIONS: The risk of moderate acute uGI toxicity during WPRT-IMRT for post-operatively treated patients increases with age; the risk is substantially reduced in patients with small overlap between PTV and loops.

BACKGROUND AND PURPOSE: Image-guided helical tomotherapy (HT) is a new modality for delivering intensity modulated radiation therapy (IMRT) with helical irradiation: the slip ring continuously rotates while the couch moves into the bore. The radiation source (Linac, 6MV) is collimated into a fan beam and modulated by means of a binary multileaf collimator (MLC). A xenon detector array, opposite the radiation source, allows a megavoltage-CT (MVCT) acquisition of patient images for set-up verification. The aim of this paper is to report the results of a two-year quality control (QC) program for the physical and dosimetric characterization of an HT unit installed at our Institute and clinically activated in November 2004, in order to monitor and verify the stability and the reliability of this promising radiation treatment unit. MATERIALS AND METHODS: Conventional Linac acceptance protocols (ATP) and QC protocols were adapted to HT with the addition of specific items reflecting important differences between the two irradiation modalities. QC tests can be summarized as: (a) mechanical and geometrical characterization of the system's components: evaluation of alignment among radiation source-gantry rotation plan-jaws-MLC-MVCT; (b) treatment beam configuration in static condition: depth dose curves (PDD) and profiles, output factors, output reproducibility and linearity; (c) dynamic component characterization: accuracy and reproducibility of MLC positioning; rotational output reproducibility and linearity, leaf latency, couch movement constancy; (d) gantry-couch and MLC-gantry synchronization; and (e) MVCT image quality. Peculiar periodicity specific tolerance and action levels were defined. Ionization chambers (Exradin A1SL 0.056cc), films (XOmat-V/EDR2), water and solid water phantoms were used to perform quality assurance measurements. RESULTS: Over a two-year period the final average output variation after possible beam output adjustment was -0.2+/-1% for the static condition and equal to 0+/-1% for the rotational condition: around 98% of the collected output data was within the action level compared to 94% if no beam output adjustment was considered. An average energy variation of -0.4+/-0.4% was found. The daily absolute dose verification of IMRT plans showed a dose reproducibility of -0.5+/-1.2% and -0.4+/-2.2%, for low and high dose gradient regions, respectively. Source-jaws-MLC and MVCT alignment results and jaw and leaf positioning accuracy were +/-1mm. Couch-gantry-MLC synchrony tests showed good stability level (+/-2mm). CONCLUSIONS: QC results indicated good reproducibility of all HT mechanical-dosimetric performance.

PURPOSE: To assess setup and organ motion error by means of analysis of daily megavoltage computed tomography (MVCT) of patients treated with hypofractionated helical tomotherapy (71.4-74.2 Gy in 28 fractions). METHODS AND MATERIALS: Data from 21 patients were analyzed. Patients were instructed to empty the rectum carefully before planning CT and every morning before therapy by means of a self-applied rectal enema. The position of the prostate was assessed by means of automatic bone matching (BM) with the planning kilovoltage CT (BM, setup error) followed by a direct visualization (DV) match on the prostate. Deviations between planning and therapy positions referred to BM and BM + DV were registered for the three main axes. In case of a full rectum at MVCT with evident shift of the prostate, treatment was postponed until after additional rectal emptying procedures; in this case, additional MVCT was performed before delivering the treatment. Data for 522 fractions were available; the impact of post-MVCT procedure was investigated for 17 of 21 patients (410 fractions). RESULTS: Prostate motion relative to bony anatomy was limited. Concerning posterior-anterior shifts, only 4.9% and 2.7% of fractions showed deviation of 3 mm or greater of the prostate relative to BM without and with consideration of post-MVCT procedures, respectively. Interobserver variability for BM + DV match was within 0.8 mm (1 SD). CONCLUSIONS: Daily MVCT-based correction is feasible. The BM + DV matching was found to be consistent between operators. Rectal emptying using a daily enema is an efficient tool to minimize prostate motion, even for centers that have not yet implemented image-guided radiotherapy.

PURPOSE: To explore the potential of helical tomotherapy (HT) in the treatment of nasopharynx cancer. PATIENTS AND METHODS: Six T1-4 N1-3 patients were considered. A simultaneous integrated boost (SIB) technique was planned with inversely optimized conventional intensity-modulated radiotherapy (IMRT; dynamic multileaf collimator using the Eclipse-Helios Varian system) and HT. The prescribed (median) doses were 54 Gy, 61.5 Gy, and 64.5 Gy delivered in 30 fractions to PTV1 (planning target volume), PTV2, and PTV3, respectively. The same constraints for PTV coverage and for parotids, spinal cord, mandible, optic structures, and brain stem were followed in both modalities. The planner also tried to reduce the dose to other structures (mucosae outside PTV1, larynx, esophagus, inner ear, thyroid, brain, lungs, submental connective tissue, bony structures) as much as possible. RESULTS: The fraction of PTV receiving > 95% of the prescribed dose (V95%) increased from 97.6% and 94.3% (IMRT) to 99.6% and 97% (HT) for PTV1 and PTV3, respectively (p < 0.05); median dose to parotids decreased from 30.1 Gy for IMRT to 25.0 Gy for HT (p < 0.05). Significant gains (p < 0.05) were found for most organs at risk (OARs): mucosae (V30 decreased from 44 cm(3) [IMRT] to 18 cm(3) [HT]); larynx (V30: 25 cm(3) vs. 11 cm(3)); thyroid (mean dose: 48.7 Gy vs. 41.5 Gy); esophagus (V45: 4 cm(3) vs. 1 cm(3)); brain stem (D1%: 45.1 Gy vs. 37.7 Gy). CONCLUSION: HT improves the homogeneity of dose distribution within PTV and PTV coverage together with a significantly greater sparing of OARs compared to linac five-field IMRT.

PURPOSE: In order to explore the potential of helical Tomotherapy in the treatment of head and neck cancers (HNC), a planning study comparing our routinely delivered IMRT technique (dynamic MLC Varian 600CD Linac, inversely optimised by the Helios/Eclipse system) against two different Tomotherapy planning approaches was performed. MATERIALS AND METHODS: In the first Tomotherapy plan (TOMO-a), we merely applied the same constraints used for the IMRT-Linac technique; in the second one (TOMO-b), we tried to stress the sparing of parotids and mandible while keeping PTV coverage and spinal cord Dmax similar to their values in the TOMO-a plan. Five patients with locally advanced oropharinx (n=3), hypopharinx (n=1) and larynx (n=1) cancer were considered. For each patient, CTV1 including neck nodes and the tumour was defined and was expanded with a margin of 0.5 cm (PTV1); then, CTV2 including high risk nodes and CTV3 including only T were defined and the corresponding PTV2/PTV3 were defined by a 0.5 cm expansion. IMRT and Tomotherapy planning were optimised to deliver 54 Gy in 30 fractions on PTV1 and 16.2 Gy in 9 fractions on PTV3; in the case a PTV2 was defined, 15 Gy were concomitantly delivered while delivering 16.2 Gy on PTV3. Separated plans for the two phases (Phase 1: first 30 fractions; Phase 2: last 9 fractions) were compared in terms of dose-volume histograms (DVH) and dose statistics on PTVs and OARs. RESULTS: When considering Phase 1, Tomotherapy improved the homogeneity of the dose distribution within PTV1 while delivering the same prescribed dose (assessed to be the median dose to PTV): the fraction of PTV1 receiving more than 95% of the prescribed dose (V95%) increased from 90% (IMRT) to 96-97% for Tomotherapy plans. Dmax within PTV1 decreased from 60.3 Gy (IMRT) to 57.4 Gy (TOMO-a) and 58.7 Gy (TOMO-b). Spinal cord Dmax decreased from 31.6 Gy (IMRT) to 26.5 Gy (TOMO-a) and 24.6 Gy (TOMO-b). No attempts to further reduce spinal cord Dmax were done. Mean dose to the parotids decreased from 26.1 Gy (IMRT) to 25.1 Gy (TOMO-a) and 20.8 Gy (TOMO-b). Mandible was significantly better spared with Tomotherapy: mean dose decreased from 34.9 Gy (IMRT) to 34.0 Gy (TOMO-a) and 30.7 Gy (TOMO-b).When considering phase 2, the average gains (TOMO-b vs IMRT) were more modest and depended on the location of PTV2/PTV3. CONCLUSIONS: Preliminary findings obtained in a sequential approach for HNC suggest that Tomotherapy has the potential to significantly improve the therapeutic ratio with respect to a conventional IMRT delivery method.