Abstract
Patients with angiosarcoma of the scalp (AS) have an extremely unfavorable prognosis. As local recurrence is one of the main causes of failure, radiotherapy is established as an integral component of the treatment for AS. Delivering an adequate dose to the target while limiting the dose to the surrounding organs at risk (OARs) such as the brain is challenging. We aimed to compare treatment plans among the newest version of tomotherapy (Tomo), volumetric-modulated arc therapy (VMAT), and intensity-modulated proton therapy (IMPT) for AS patients. We created radiotherapy plans using Tomo, VMAT, and IMPT for 19 AS patients treated at our institution and conducted a pilot study comparing the three methods. The clinical target volume (CTV) 1 included the gross tumor volume plus 3.0 cm and CTV2 was defined as the total scalp. The planning target volume (PTV) 1 and PTV2 were defined as CTV1 plus 0.5 cm and CTV2 plus 0.5 cm other than PTV1, respectively. For IMPT, a setup robustness of ± 0.2 cm was used for the setting of PTV. 70 Gy and 56 Gy were prescribed to D95% (i.e., dose to 95% volume of PTV) of PTV1 and PTV2, respectively, using the simultaneous integrated boost technique. Other constraint goals and acceptable ranges of PTV1, PTV2, and OARs were also set. PTV1 and PTV2 with Tomo, VMAT, and IMPT met the dose constraints of D95% and D98% at least within acceptable ranges for all patients. D95% and D98% of PTV1 and PTV2 were similar among the three methods. D2% of PTV1 and PTV2 were significantly higher in IMPT than in Tomo and VMAT. HI for the IMPT plans was significantly higher than for the other plans; HI was 1.22±0.10 (SD) for the IMPT plans, 1.13±0.04 for the Tomo plans, and 1.14±0.04 for the VMAT plans (p < 0.001). D1% and Dmean of the spinal cord (planning organ at risk volume, PRV), brain, brainstem (PRV), optic pathway (PRV), and both inner ears were significantly lower in IMPT than in Tomo and VMAT. Dmax of the spinal cord (PRV) and optic pathway (PRV) and Dmean of the brain, brainstem (PRV), and optic pathway (PRV) were lower in VMAT than in Tomo. Dmean of the brain was 37.4±6.6 Gy in Tomo, 29.7±3.6 Gy in VMAT, and 17.9±2.0 Gy in IMPT (p < 0.001). The three methods could provide adequate coverage of the PTV while compromising the dose constraint of OARs. Although the dose homogeneity within the PTV was worse in IMPT than in Tomo and VMAT, the three methods could provide a well acceptable homogeneity. Among the three methods, IMPT achieved the best OAR sparing, especially for the brain.
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