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BACKGROUND To evaluate the impact of the planning target volume (PTV) density on treatment planning for lung Stereotactic Body Radiation Therapy (SBRT). MATERIAL AND METHODS The PTV coverage was analyzed in two groups of 40 lung SBRT patients. One group had PTV density 0.5 g/cm3. The treatments were planned in Pinnacle 9.10, using the collapsed cone convolution (CCC) algorithm. The prescribed dose was 60 Gy to the PTV in 4-8 fractions. Respecting constraint for the PTV coverage (D98% > 95%), we compared changes in the isodose line prescription, the number of monitor units (MU), maximum dose (Dmax), irradiated volume covered with 30 Gy (V30Gy), and the optimization planning volume (OPV). RESULTS For the same median values of the PTV coverage (98.3%), the differences are presented with median values between lower and higher density than 0.5 g/cm3. The isodose line prescription was 83 vs. 90% (p

Background The use of imaging is indispensable in modern radiation therapy, both for simulation and treatment delivery. For safe and sure utilization, dose delivery from imaging must be evaluated. Objective This study aims to investigate the dose to organ at risk (OAR) delivered by imaging during lung stereotactic body radiation therapy (SBRT) and to evaluate its contribution to the treatment total dose. Material and methods In this retrospectively study, imaging total dose to organs at risk (OARs) (spinal cord, esophagus, lungs, and heart) and effective dose were retrospectively evaluated from 100 consecutive patients of a single institution who had lung SBRT. For each patient, dose was estimated using Monte-Carlo convolution for helical computed tomography (helical CT), Four-Dimensional CT (4D-CT), and kilovoltage Cone-Beam CT (kV-CBCT). Helical CT and kV-CBCT dose were evaluated for the entire thorax acquisition, while 4D-CT dose was analyzed on upper lobe (UL) or lower lobe (LL) acquisition. Treatment dose was extracted from treatment planning system and compared to imaging total dose. Results Imaging total dose maximum values were 117 mGy to the spinal cord, 127 mGy to the esophagus, 176 mGy to the lungs and 193 mGy to the heart. The maximum effective dose was 19.65 mSv for helical CT, 10.62 mSv for kV-CBCT, 25.95 mSv and 38.45 mSv for 4D-CT in UL and LL regions, respectively. Depending on OAR, treatment total dose was higher from 1.7 to 8.2 times than imaging total dose. Imaging total dose contributed only to 0.3% of treatment total dose. Conclusion Imaging dose delivered with 4D-CT to the OARs is higher than those of others modalities. The heart received the highest imaging dose for both UL and LL. Total imaging dose is negligible since it contributed only to 0.3% of treatment total dose.

Purpose: To evaluate the breathing amplitude, tumor motion, patient positioning, and treatment volumes among consecutive four-dimensional computed tomography (4D-CT) scans, during the simulation for lung stereotactic body radiation therapy (SBRT). Material and methods: The variation and shape of the breathing amplitude, patient positioning, and treatment volumes were evaluated for 55 lung cancer patients after consecutive 4D-CT acquisitions, scanned at one-week intervals. The impact of variation in the breathing amplitude on lung tumor motion was determined for 20 patients. The gross tumor volume (GTV) was contoured from a free-breathing CT scan and at ten phases of the respiratory cycle, for both 4D-CTs (440 phases in total). Results: Breathing amplitude decreased by 3.6 (3.4-4.9) mm, tumor motion by 3.2 (0.4-5.0) mm while breathing period increased by 4 (2-6) s, inter-scan for 20 patients. Intra-scan variation was 4 times greater for the breathing amplitude, 5 times for the breathing period, and 8 times for the breathing cycle, comparing irregular versus regular breathing patterns for 55 patients. Using coaching, the breathing amplitude increases 3 to 8 mm, and the breathing period 2 to 6 s. Differences in the contoured treatment volumes were less than 10% between consecutive scans. Patient positioning remained stable, with a small inter-scan difference of 1.1 (0.6-1.4) mm. Conclusion: Decreasing the inter-scan breathing amplitude decreases the tumor motion reciprocally. When the breathing amplitude decreases, the breathing period increases at inter- and intra-scan, especially during irregular breathing. Coaching improves respiration, keeping the initial shape of the breathing amplitude. Contoured treatment volumes and patient positioning were reproducible through successive scans.

To evaluate the amplitude of lung tumor motion and impact of tumor motion on dose delivered to the organs at risk (OARs) during lung stereotactic body radiation therapy (SBRT). This study included 55 patients (30 males and 25 females) with lung cancer who had a small gross tumor volume (GTV). SBRT lung cancer patients were treated with a prescribed dose of 60 Gy in 4 to 8 fractions. Radiotherapy plans were planned in Pinnacle 9.10 with two partial dynamic conformal arcs (DCAs) for the peripheral region (PR) and three to four partial DCAs for the central region (CR). The amplitude of tumor motion and their impact on the maximum dose delivered (Dmax) to the OARs were evaluated in the upper lobe (UL) and lower lobe (LL) in cases of CR and PR tumor’s localizations. The median tumor motions between CR and PR were 4.5 vs 2.2 mm in the UL and 12.5 vs 7.0 mm in the LL. Max dose delivered to the OARs between CR and PR in the UL and LL were as follows: 6.7 vs 8.9 Gy and 9.1 vs 11.7 Gy for the spinal cord; 15.2 vs 0.6 Gy and 22.4 vs 7.6 Gy for the heart; and 11.7 vs 10.8 Gy and 14.8 vs 9.8 Gy for the esophagus, respectively. The dose received by the OARs depends on the amplitude of tumor motion and is relative to the OAR’s location and motion, due to patient respiration and heart contribution.

In this paper, a dosimetric end-to-end test of respiratory gated radiation therapy (RGRT) applied in lung cancer stereotactic body radiation therapy (SBRT) was performed. The test was performed from treatment simulation to treatment delivery using a QUASAR phantom, for regular, slightly irregular and irregular breathing patterns in phase- and amplitude-gated modes. A mechanical and dosimetric verification was performed to evaluate all steps of the proposed treatment workflow. Dose measurements were performed using a PinPoint ion chamber and GafChromic EBT3 films. Mechanical verification confirmed good function of the chosen systems. Dosimetric verification showed good agreement between planned and measured doses, for the phase-gated versus amplitude-gated modes: 1.4 ± 0.4% versus 1.2 ± 0.2% for regular, 2.8 ± 0.3% versus 3.0 ± 0.3% for slightly irregular, and 6.2 ± 0.7% versus 7.4 ± 0.5% for irregular breathing patterns. The gamma passing rates for 3%/3 mm and 2%/2 mm criteria, comparing phase- versus amplitude-gated modes, were 99.0 ± 0.3% versus 99.5 ± 0.2% and 95.2 ± 0.2% versus 96.1 ± 0.2% for the regular, 97.4 ± 0.8% versus 98.0 ± 0.6% and 91.7 ± 0.5% versus 92.4 ± 0.4% for the slightly irregular, and 96.4 ± 0.5% versus 95.3 ± 0.7% and 86.4 ± 0.5% versus 84.6 ± 0.7% for the irregular breathing patterns, respectively. It is concluded that using equipment and workflow for the treatment of lung cancer by means of SBRT in RGRT mode is safe and efficient, for regular and slightly irregular breathing patterns.

International audience; Background/Aim. For patients with left-sided breast cancer, a major concern is the dose of radiation delivered to the heart, because of increased risk of exposure and consequently increased risk of major coronary events and side effects. In order to reduce the dose to the heart during breast irradiation, deep inspiration breath-hold (DIBH) technique was implemented in our institution. The aim of this retrospective study was to compare dosimetric parameters of DIBH on the heart, left anterior descending artery (LAD) and ipsilateral lung (IL), compared with free breathing (FB) technique. Methods. Twenty patients who underwent radiotherapy with DIBH at our institution were retrospectively analyzed. Two computed tomography (CT) scans were acquired for each patient, FB-CT and DIBH-CT. Plans consisted of two opposed tangential segmented beams and one direct beam with small dose contribution. Doses to the heart, LAD, and IL were assessed. Results. Dosimetric comparison between FB and DIBH for mean dose to the heart was 5.17 Gy vs. 3.68 Gy, respectively (p < 0.0001), and the mean percentage of the volume receiving 25 Gy was 4.63% vs. 0.85%, respectively (p < 0.0001). Mean dose for LAD was 26.09 Gy vs. 11.89 Gy, respectively (p = 0.00014). Mean percentage of the volume receiving 20 Gy for the IL was 15.16% vs. 13.26% (p = 0.0007) for FB and DIBH, respectively. Conclusion. Implementation of DIBH technique in radiotherapy treatment of patients with left-sided breast cancer statistically significantly reduces the dose delivered to the surrounding organs at risk, particularly to the heart and LAD, with optimal target coverage.