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Analysis of Dose Delivery Error in Conformal Arc Therapy Depending on Target Positions and Arc Trajectories

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°­¹Î¿µ ( Kang Min-Young ) - °Ç±¹´ëÇб³º´¿ø ¹æ»ç¼±Á¾¾çÇаú

À̺¸¶÷ ( Lee Bo-Ram ) - °í·Á´ëÇб³ ¹æ»ç¼±Çаú
±èÀ¯Çö ( Kim You-Hyun ) - °í·Á´ëÇб³ º¸°Ç°úÇдëÇÐ ¹æ»ç¼±Çаú
ÀÌÁ¤¿ì ( Lee Jeong-Woo ) - °Ç±¹´ëÇб³º´¿ø ¹æ»ç¼±Á¾¾çÇаú

Abstract

º» ¿¬±¸ÀÇ ¸ñÀûÀº ȸÀüÁ¶»ç ½Ã Ç¥ÀûÁ¾¾çÀÇ À§Ä¡º¯À§¿Í °µÆ®¸®ÀÇ Á¶»ç¹Ý°æ¿¡ ÀÇÇÑ Ä¡·á±íÀÌ º¯È­¿¡ µû¸¥ ¸ðÀÇÄ¡·á°èȹ °á°ú¿Í ¼±·®Àü´Þ °á°ú»óÀÇ ¿ÀÂ÷¸¦ ºÐ¼®ÇϰíÀÚ ÇÏ¿´´Ù. ±íÀÌ º¯À§°¡ °¡Àå ÀÌ»óÀûÀÎ °æ¿ì, Áï ÆÒÅÒÀÇ Á߽ɿ¡ Ç¥ÀûÀÌ À§Ä¡ÇÑ °æ¿ì¿Í ÇÑÂÊÀ¸·Î 2.5 cm, 5 cm¾¿ Ä¡¿ìÄ£ °æ¿ì·Î ³ª´©¾î ¸ðÀǽÇÇèÇÏ¿´´Ù. Ç¥ÀûÀÇ À§Ä¡ º¯È­¿¡ µû¸¥ ¸ðÀÇÄ¡·á°èȹÀ» ½Ç½ÃÇϱâ À§ÇÏ¿© IMRT Body ÆÒÅè(I¡¯mRT Phantom, Wellhofer Dosimetry, Germany)¸¦ ÀÌ¿ëÇÏ¿© Àü»êÈ­´ÜÃþÃÔ¿µÀåÄ¡(Computed Tomography, Light speed 16, GE, USA)·Î µ¥ÀÌÅ͸¦ ȹµæÇÏ¿´´Ù. ȹµæµÈ ¿µ»óÀ» ÀÌ¿ëÇÏ¿© Ä¡·á°èȹÀåÄ¡(Treatment Planning System, Eclipse, ver. 6.5, VMS, Palo Alto, USA)¸¦ ÀÌ¿ëÇÏ¿© Á¤Áß¾Ó, 2.5 cm, 5 cm¿¡ °¡»óÀÇ Ä¡·áÇ¥ÀûÀ» ¸¸µé¾î ¸ðÀÇÄ¡·á°èȹÀ» ¼ö¸³ÇÏ¿´´Ù. ¼±Çü°¡¼Ó±â(CL21EX, VMS, Palo Alto, USA)ÀÇ 6 MV ±¤ÀÚ¼±°ú ÃÖ±Ù °³¹ßµÈ Gafchromic Çʸ§(EBT2, ISP, Wayne, USA)À» ÀÌ¿ëÇÏ¿© ¼±·®ºÐÆ÷¸¦ ÃøÁ¤ÇÏ¿´°í, ¼±·®ºÐ¼®ÇÁ·Î±×·¥(OmniPro-IMRT, ver. 1.4, Wellhofer Dosimetry, Germany)À» ÀÌ¿ëÇÏ¿© ¸ðÀÇÄ¡·á°èȹ µ¥ÀÌÅÍ¿Í ÃøÁ¤ µ¥ÀÌÅ͸¦ Á¤·®ÀûÀ¸·Î ºÐ¼®ÇÏ¿´´Ù. ºÐ¼®ÇÁ·Î±×·¥À¸·Î ȾÃà¹æÇâ ¼±·®ºÐÆ÷ ÇÁ·ÎÆÄÀÏ(Cross-plane profile)°ú ¼±·®ºÐÆ÷¸¦ Á¤·®ÀûÀ¸·Î ºÐ¼®Çϱâ À§ÇÏ¿© °¨¸¶À妽º(DD: 3%, DTA: 2 mm) È÷½ºÅä±×¶÷À» ÀÌ¿ëÇÏ¿´´Ù. Ç¥Àû°ú Ç¥ÀûÁÖº¯ÀÇ ¼±·®ºÐÆ÷´Â Conformity index(CI), Homogeneity index(HI)¸¦ ÀÌ¿ëÇÏ¿© Á¤·®ÀûÀ¸·Î ºÐ¼®ÇÏ¿´´Ù. Ä¡·áÇ¥Àû ÀüüüÀû¿¡ ´ëÇÑ 100% ¼±·®ºÐÆ÷¿¡ Æ÷ÇԵǴ üÀûÀ» ºñ±³ÇÏ¿© ºÐ¼®ÇÏ¿´´Ù. Ç¥ÀûÀÇ À§Ä¡°¡ 5 cm ¿¡ ÀÖ´Â °æ¿ì ´Ù¹®µ¿ÀûȸÀüÁ¶»ç(Multiple Conformal Arc Therapy, MCAT)´Â 23.8%, ´ÜÀϵ¿ÀûȸÀüÁ¶»ç(Single Conformal Arc Therapy, SCAT)´Â 35.6%, °íÁ¤Á¶»ç´Â 37%¿´°í, Ç¥ÀûÀÌ 2.5 cm¿¡ ÀÖ´Â °æ¿ì MCAT 61%, SCAT 21.5%, °íÁ¤Á¶»ç 14.2%·Î ºÐ¼®µÇ¾ú´Ù. Ç¥ÀûÀÇ À§Ä¡°¡ Áß¾Ó¿¡ ÀÖ´Â °æ¿ì MCAT 70.5%, SCAT 14.1%, °íÁ¤Á¶»ç 36.3%·Î ³ªÅ¸³µ´Ù. Ç¥ÀûÀÇ À§Ä¡°¡ 5 cm Ä¡¿ìÃÄ ÀÖ´Â °æ¿ì¸¦ Á¦¿ÜÇϰí MCATÀÇ 100% ¼±·®ºÐÆ÷¿¡ Æ÷ÇԵǴ üÀûÀÌ °¡Àå Å©°Ô ³ªÅ¸³µ´Ù. °¨¸¶À妽º È÷½ºÅä±×·¥ ºÐ¼®°á°ú, SCATÀÇ °æ¿ì 37.1, 27.3, 29.2·Î MCATÀÇ °æ¿ì 9.2, 8.4, 10.3¿¡ ºñÇØ ÃÖ¼Ò 2.8¹è, ÃÖ´ë 4¹è ¿ÀÂ÷°¡ Å©°Ô ³ªÅ¸³µ´Ù. °á·ÐÀûÀ¸·Î, µ¿ÀûÁ¶ÇüȸÀüÁ¶»ç ½Ã Ç¥ÀûÁ¾¾çÀÇ À§Ä¡º¯ÀÌ¿Í Á¶»ç¹Ý°æÀÇ º¯È­¿¡ µû¶ó ¼±·®Àü´Þ¿À·ùÀÇ °¡´É¼ºÀ» ¾Ë ¼ö ÀÖ¾úÀ¸¸ç Ä¡·áÇ¥ÀûÀÇ À§Ä¡°¡ Á¤Áß¾ÓÀÌ ¾Æ´Ò °æ¿ì, ±íÀÌ¿Í È¸Àü¹Ý°æÀ» ÃÖÀûÈ­ÇÔÀ¸·Î½á Á¤È®ÇÑ ¼±·® Àü´ÞÀ» ÇÒ ¼ö ÀÖ´Ù°í »ý°¢ÇÑ´Ù.
The aim of the study is to analyze the dose delivery error depending on the depth variation according to target positions and arc trajectories by comparing the simulated treatment planning with the actual dose delivery in conformal arc therapy. We simulated the conformal arc treatment planning with the three target positions (center, 2.5 cm, and 5 cm in the phantom). For the experiments, IMRT body phantom (I¡¯mRT Phantom, Wellhofer Dosimetry, Germany) was used for treatment planning with CT (Computed Tomography, Light speed 16, GE, USA). The simulated treatment plans were established by three different target positions using treatment planning system (Eclipse, ver. 6.5, VMS, Palo Alto, USA). The radiochromic film (Gafchromic EBT2, ISP, Wayne, USA) and dose analysis software (OmniPro-IMRT, ver. 1.4, Wellhofer Dosimetry, Germany) were used for the measurement of the planned arc delivery using 6 MV photon beam from linear accelerator (CL21EX, VMS, Palo Alto, USA). Gamma index (DD: 3%, DTA: 2 mm) histogram and dose profile were evaluated for a quantitative analysis. The dose distributions surrounded by targets were also compared with each plans and measurements by conformity index (CI), and homogeneity index (HI). The area covered by 100% isodose line was compared to the whole target area. The results for the 5 cm-shifted target plan show that 23.8%, 35.6%, and 37% for multiple conformal arc therapy (MCAT), single conformal arc therapy (SCAT), and multiple static beam therapy, respectively. In the 2.5 cm-shifted target plan, it was shown that 61%, 21.5%, and 14.2%, while in case of center-located target, 70.5%, 14.1%, and 36.3% for MCAT, SCAT, and multiple static beam therapy, respectively. The values were resulted by most superior in the MCAT, except the case of the 5 cm-shifted target. In the analysis of gamma index histogram, it was resulted of 37.1, 27.3, 29.2 in the SCAT, while 9.2, 8.4, 10.3 in the MCAT, for the target positions of center, shifted 2.5 cm and 5 cm, respectively. The fail proportions of the SCAT were 2.8 to 4 times as compared to those of the MCAT. In conclusion, dose delivery error could be occurred depending on the target positions and arc trajectories. Hence, if the target were located in the biased position, the accurate dose delivery could be performed through the optimization of depth according to arc trajectory.

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multiple conformal arc therapy (MCAT); single conformal arc therapy (SCAT); and multiple static beam therapy; gamma index
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