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Purpose
To calculated projected second tu
mor rates and dose to organs at risk (OAR) in patients with benign intracranial
meningio
ma (BM), according to dosi
metric co
mparisons between proton radiotherapy (PRT) and photon radiotherapy (XRT) treat
ment plans.
Methods and Materials
Ten patients with BM treated at Massachusetts General Hospital during 2006-2010 with PRT were replanned with XRT (intensity-modulated or three-dimensional conformal radiotherapy), optimizing dose to the tumor while sparing OAR. Total dose was 54?Gy in 1.8 Gy per fraction for all plans. We calculated equivalent uniform doses, normal tissue complication probabilities, and whole brain-based estimates of excess risk of radiation-associated intracranial second tumors.
Results
Excess risk of second tumors was significantly lower among PRT compared with XRT plans (1.3 vs. 2.8 per 10,000 patients per year, m>pm> < 0.002). Mean equivalent uniform doses were lower among PRT plans for the whole brain (19.0 vs. 22.8 Gy, m>pm> < 0.0001), brainstem (23.8 vs. 35.2?Gy, m>pm> = 0.004), hippocampi (left, 13.5 vs. 25.6 Gy, m>pm> < 0.0001; right, 7.6 vs. 21.8 Gy, m>pm>?=?0.001), temporal lobes (left, 25.8 vs. 34.6 Gy, m>pm> = 0.007; right, 25.8 vs. 32.9 Gy, m>pm>?=?0.008), pituitary gland (29.2 vs. 37.0 Gy, m>pm> = 0.047), optic nerves (left, 28.5 vs. 33.8?Gy, m>pm> = 0.04; right, 25.1 vs. 31.1 Gy, m>pm> = 0.07), and cochleas (left, 12.2 vs. 15.8 Gy, m>pm> = 0.39; right,1.5 vs. 8.8 Gy, m>pm> = 0.01). Mean normal tissue complication probability was <1 % for all structures and not significantly different between PRT and XRT plans.
Conclusions
Compared with XRT, PRT for BM decreases the risk of RT-associated second tumors by half and delivers significantly lower doses to neurocognitive and critical structures of vision and hearing.