Stereotactic Radiosurgery and Stereotactic Body Radiation Therapy by Daniel M. Trifiletti & Samuel T. Chao & Arjun Sahgal & Jason P. Sheehan

Author:Daniel M. Trifiletti & Samuel T. Chao & Arjun Sahgal & Jason P. Sheehan
Language: eng
Format: epub
ISBN: 9783030169244
Publisher: Springer International Publishing

Dosimetric

One of the earliest dosimetric comparisons was published by the group in Vienna, Austria, in 2008 and evaluated plans for 12 patients with early-stage lung lesions using the following techniques: 3D-conformal radiation therapy (3D-CRT), passively scattered proton therapy (PSPT), and intensity-modulated proton therapy (IMPT) [29]. Plans were compared on CT datasets with shallow breathing and abdominal compression in place, as well as with patients assuming deep inspiratory breath hold (DIBH). For all patients, the clinical target volume was a margin of 2–3 mm around the gross lesion (GTV). For shallow breathing/abdominal compression conditions, a 4–10 mm PTV margin was applied depending on the location of the lesion and the degree of respiratory excursion. For the DIBH plans, an isotropic 5 mm PTV margin was applied. No significant differences were noted in maximum (D1%), minimum (D99%) and mean PTV doses between 3D-CRT, PSPT, and IMPT for either respiratory condition. For organs at risk, DIBH improved dose-volume distributions irrespective of treatment modality used. For both respiratory conditions, the ipsilateral lung V2Gy was on average 6–8% lower with both PSPT and IMPT in comparison with 3D-CRT. For the ipsilateral lung 4Gy, only the IMPT approach had a significant reduction in comparison to 3D-CRT (p = 0.049). In contrast, the ipsilateral lung V6Gy and V12Gy were equivalent for all three techniques. For the contralateral lung, both PSPT and IMPT had complete organ sparing in both respiratory conditions, whereas the 3D-CRT plan had a contralateral lung maximum dose of approximately 2Gy. Similarly, both PSPT and IMPT provided superior heart sparing in comparison to 3D-CRT, with significantly lower D1%, V2Gy, and V4Gy values. These results confirm the dosimetric benefits of proton-based SBRT techniques in reducing the low-dose bath on the ipsilateral and contralateral lungs and heart.

Similarly, the group from Mayo Clinic conducted their respective dosimetric comparison of eight patients with Stage I inoperable peripheral NSCLC using the following techniques: 3D-CRT, PSPT, and IMPT [30]. For all patients, the GTV was defined as the gross volume, with an internal target volumes (ITV) created to account for tumor motion. A uniform 5 mm axial and 10 mm longitudinal expansion on the ITV was added to create the PTV. The prescription dose for all patients was 60Gy in three fractions. Both proton plans exhibited lower maximum doses and higher minimum doses in the PTV compared to 3D-CRT. Additionally, the mean dose 2 cm from the PTV was significantly lower for both proton plans as compared to 3D-CRT. With respect to total lung tissue, both PSPT and IMPT achieved lower V5Gy values as compared to 3D-CRT, with only IMPT achieving a lower mean total lung dose than 3D-CRT. On the contrary, while the V20Gy was equivalent between 3D-CRT and IMPT techniques, it was significantly worse with PSPT. Median values for the spinal cord, heart, bronchial tree, esophagus, skin and ribs were all lower with PSPT and IMPT as opposed to 3D-CRT.

With the increasing utilization of IMRT-based lung SBRT treatments, the group from University of Florida (UF) dosimetrically compared plans for

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