Dosimetric comparison between carbon, proton and photon radiation for renal retroperitoneal soft tissue sarcoma recurrence or metastasis after radical nephrectomy

Objective To compare the dosimetric difference between various modalities in the radiation treatment for renal retroperitoneal soft tissue sarcoma recurrence or metastasis (RRSTSRM) after radical nephrectomy, and assess the dosimetric advantage on protecting the organs at risk (OARs) in the carbon and proton radiotherapy for the patients with a single kidney. Methods A total of 12 patients with RRSTSRM who underwent radical nephrectomy were enrolled in this study. Carbon, proton, and photon radiotherapy were implemented for treatment planning. The prescription dose was fulfilled by simultaneously integrated boosting technique, with giving the planning target volume-1 (PTV-1) 51Gy (RBE) and planning target volume-2 (PTV-2) 60 Gy (RBE). Doses in the patient's spinal cord, stomach, duodenum, bowel, colon, and contralateral kidney were evaluated. The normal tissue complication probability (NTCP) of the duodenum, bowel, colon, and contralateral kidney was derived under Lyman-Kutcher-Burman (LKB) estimation. Results In the carbon plans, the percentage volume of 95% prescription dose (V95%) covering PTV-1 (PTV-2) was 95.93% +/- 3.42% (95.61% +/- 4.26%). No significant dosimetric difference on the target was obtained between the four radiation modalities (P > .05). The percentage volume of receiving 40 Gy (RBE) [V40Gy (RBE)] in the duodenum could be reduced from 12.94% +/- 15.99% in the IMRT plans to 6.36% +/- 8.79% (8.44% +/- 12.35%) in the carbon (proton) plans (P < .05). The V40Gy (RBE) in the bowel could be reduced from 13.48% +/- 13.12% in the IMRT plans to 7.04% +/- 9.32% (7.34% +/- 9.89%) in the carbon (proton) plans (P < .05). The mean value of NTCP for the duodenum was 0.43 +/- 0.47 (0.45 +/- 0.48) by using carbon (proton) radiation. The value was 0.05 (0.03) lower than the IMRT plans on average, with a reduction of 0.20 (0.13) for the patients with lesions <5 mm away from the duodenum. The mean doses of the contralateral kidney were 0.28 +/- 0.37 Gy (RBE) [0.28 +/- 0.40 Gy (RBE)] in the IMCT (IMPT) plans, which was 92.43% (92.43%) lower than the value in the IMRT plans respectively (P < .05). Conclusion Compared to the conventional radiation techniques, particle radiotherapy of carbon and proton could significantly spare more OARs in the treatment for RRSTSRM after radical nephrectomy. Patients, especially those whose residuals are close to the duodenum would potentially benefit from the particle radiation therapy for RRSTSRM on the decrease in radiation-related side-effect.