In Silico Comparison of Photon Versus Proton Based Stereotactic Body Radiotherapy With Increasing Maximum Peak Dose for Treatment of Primary Renal Cell Carcinoma.

PURPOSE: Photon based Stereotactic Body Radiotherapy (PH-SBRT) has emerged as a promising option for treatment of primary renal cell carcinoma (RCC), however is associated with decrements in long-term kidney function and toxicity to adjacent organs at risk (OARs).

MATERIALS AND

METHODS

We compared proton (PT) based SBRT versus PH-SBRT regarding target coverage, OARs, and maximum peak doses of 125% and 142%. All variables were compared using student t-tests.

RESULTS

Target coverage was comparable between plans for gross tumor volume (GTV) and clinical target volume (CTV). OARs were greatly spared by PT-SBRT including small bowel; V5 Gy to V25 Gy and maximum dose (10.47, 20.22, P = .02), large bowel; V5 Gy to V25 Gy and maximum dose (16.16, 23.90, P = .03), all volumes of uninvolved ipsilateral kidney and maximum dose to heart, lungs, esophagus, stomach, duodenum, ipsilateral ureter, and spinal canal. The ratio of ipsilateral kidney V50%/Vtot (volume receiving 50% of the dose/total volume), which is correlated with glomerular filtration rate loss in prospective trials, was significantly lower with PT-SBRT for both maximum dose of 125% (25.41, 19.97, P < .01) and 142% (23.33, 19.18, P < .01). Integral dose was significantly lower with protons. PT-SBRT with higher peak dose allowed for additional sparing of OARs: stomach V 10 Gy, liver V 25 Gy, large bowel V 30 Gy, V 35 Gy, ipsilateral kidney cortex.

CONCLUSION

PT-SBRT improved target coverage while reducing dose to the involved kidney and adjacent OARs. Protons allow delivery of maximum peak dose escalated plans without exceeding the normal tissues limit and have the potential to better preserve renal function. Prospective studies are warranted to validate these findings and potential clinical benefits.