In LSI, a finite number of small SOBPs are accumulated along the beam direction, contributing to dose reduction to normal tissues at the region near the entrance ( Figure 1B). To overcome this issue, layer-stacking irradiation (LSI) was developed ( 3). This effect becomes greater in bulky tumors irradiated using long-length SOBPs, which increase the risk of toxicity to normal tissues. However, CPI methods have several shortcomings: i.e., normal tissues located at the entrance of the target receive excessive doses because the SOBP length is fixed by the diameter of the target ( Figure 1A). This enables dose distribution that is highly conformal to tumors. ![]() In conventional passive irradiation (CPI) with carbon ions, treatment beams are broadened in the lateral direction using a pair of wobbler magnets and a scatterer, and the Bragg peaks are broadened along the beam direction using a ridge filter to form a spread-out Bragg peak (SOBP) ( 2). Current evidence suggests that carbon ion radiotherapy is more effective for tumor control than standard care ( 1). LSI was associated with a significant trend toward dose reduction at the skin area irradiated with a higher dose by CPI ( P < 0.001).Ĭonclusions: LSI achieved better skin sparing than CPI without sacrificing target volume coverage in parotid tumor patients.Ĭarbon ion radiotherapy holds great promise in cancer treatment. S10–S60 (in increments of 10) were significantly lower for LSI than for CPI ( P < 0.001 for all parameters). ![]() D50% and D98% were slightly higher for CPI however, the absolute difference between the two methods was <3%. Results: For CTV1 and CTV2, there were no significant differences in D2% between LSI and CPI. Skin dose was assessed by SX, which is the skin surface area receiving at least X Gy (RBE). CTV coverage was assessed by DX%, which is the dose covering at least X% of the target volume. CTV1 and CTV2 received 36 Gy (RBE: relative biological effectiveness) in nine fractions and 64 Gy (RBE) in 16 fractions, respectively, using either LSI or CPI. The clinical target volume (CTV) 1 and CTV2 encompassed the parotid grand and the tumor, respectively. Methods: Twenty-one parotid tumors were analyzed. Here, we compared LSI with CPI using the same treatment planning-computed tomography images used for carbon ion radiotherapy (CIRT). Although the superiority of LSI to conventional passive irradiation (CPI) regarding normal tissue sparing is theoretically evident, the clinical benefit of LSI has not been demonstrated.
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