Dosimetric comparison of radiotherapy techniques for left-sided breast cancer after breast conserving surgery

Najpogostejši neželeni učinki obsevanja so zgodnje spremembe na koži in v področju žleznega tkiva dojke, redkejši pa pozne reakcije na koži, pljučih ali srcu. Stopnja srčne okvare je s sodobnim načrtovanjem obsevanja sicer nizka, vendar je ob vse daljši pričakovani življenjski dobi in sočasni višji prevalenci raka dojk vse več žensk izpostavljenih morebitnim poznim posledicam zdravljenja. Srčna obolenja, pogosteje povzročena z dopolnilnim obsevanjem leve strani prsnega koša, postajajo eden izmed glavnih vzrokov smrti pri ozdravljenih bolnicah z rakom dojk. Z raziskavo smo primerjali dozno-volumske parametre tarčnih volumnov in zdravih organov za tri različne obsevalne tehnike in želeli ugotoviti najbolj primerno tehniko za bolnice z različno velikimi obsevalnimi volumni. Za izbrane bolnice po operaciji zaradi raka leve dojke, smo primerjali tridimenzionalno konfromno obsevanje (3D-CRT), tangencialno obliko intenzitetne modulirane terapije (T-IMRT) in hibridno obliko, ki predstavlja kombinacijo tehnik 3D-CRT ter IMRT (H-IMRT). Dodatni cilj je bila poglobljena analiza dozno-volumskih parametrov srčnih votlin in koronarnih arterij. V analizo smo vključili 60 CT-posnetkov bolnic, ki so se med letoma 2014 in 2015 zdravile z obsevanjem po operaciji raka leve dojke. Na vsak set CT-slik smo vrisali kritične zdrave organe, vključno s posameznimi strukturami srca ter tarčne volumne. Analizirali smo 180 obsevalnih načrtov. CT-posnetke smo razvrstili v skupino z majhnim, srednjim in velikim kliničnim tarčnim volumnom (CTV). V prvi skupini je srednja velikost CTV znašala 425,7 cm3, v drugi 867 cm3 in v tretji 1586,8 cm3. 95-odstotna pokritost načrtovalnega tarčnega volumna za oceno doze (PTVeval)je s tehnikama 3D-CRT in H-IMRT znašala 100 % in s T-IMRT v 88,3 %. Relativni deleži odvečne predpisane doze v načrtovalnem tarčnem volumnu PTVeval (V105–107 %) so bili najnižji s 3D-CRT, absolutni deleži pa s T-IMRT ali H-IMRT. Vrednosti indeksov konfomnosti, homogenosti ter konformacijskega števila so bile najbolj optimalne pri tehniki H-IMRT. Za celotno skupino obsevalnih načrtov smo potrdili prednost dozne razporeditve v strukturi koža za obe IMRT tehniki. Izkazalo se je, da tehnika obsevanja pomembno vpliva tudi na povprečno absorbirano dozo srca (srce Dmean). Najnižje vrednosti smo beležili pri tehniki 3D-CRT, in sicer 1,9 Gy, sledila je T-IMRT z 2,3 Gy in kot najslabša se je izkazala H-IMRT s 3,1 Gy povprečne absorbirane doze srca (p < 0,0005). Nasprotno pa smo najnižje vrednosti visokodoznih območij za parametra srce (V35–40 Gy) ter za levo sprednjo koronarno arterijo (angl. left anterior descending coronary artery, LADCA) (V40 Gy) zabeležili prav pri tehniki H-IMRT. Naši rezultati nakazujejo, da so lahko razlike v povprečni absorbirani dozi srca ali levega prekata posledica uporabljene tehnike obsevanja ali pa telesne konstitucije bolnice. Tudi ob zelo nizki vrednosti srce Dmean (< 2,5 Gy) pa lahko posamezni srčni segmenti, predvsem srednji in distalni segment LADCA ter apikalni in sprednji predel levega prekata, prejmejo bistveno višje doze, celo 30–40 Gy. Pri analizi povprečne absorbirane doze priležnega pljučnega krila smo ugotovili, da najnižje srednje vrednosti dosegamo s tehniko 3D-CRT, in sicer 5,6 Gy, višje pri T-IMRT s 5,7 Gy in najvišje ponovno pri tehniki H-IMRT z 8,7 Gy (p = 0,012). Obsevalna tehnika izbire za večino bolnic po ohranitveni operaciji zaradi raka leve dojke je 3D-CRT, saj smo z njo pri večini obsevalnih načrtov dosegli potrebne zahteve pri načrtovanju. Predvsem za bolnice s srednje velikimi tarčnimi volumni je optimalna tehnika izbire tudi T-IMRT. Za bolnice z izjemno velikimi ali kompleksneje oblikovanim tarčnimi volumni pa sta tehniki izbire 3D-CRT in izjemoma tudi H-IMRT. Pri bolnicah, pri katerih ugotovimo višjo absorbirano dozo na posamezne srčne segmente, pri mlajših bolnicah in pri tistih s pridruženimi dejavniki tveganja za okvaro srca, svetujemo skrbnejše sledenje morebitnih okvar na srcu.Breast cancer is typically treated with lumpectomy, where the tumor is removed with safety margins, followed by adjuvant radiotherapy. Combined treatment allows excellent local control rates and improves survival. In the past years, improvements in multimodal therapy have contributed to increased overall survival rates and prevalence. Most common acute radiotherapy side effects include radiodermatitis and reactions affecting breast tissue. The long-term sequelae of radiation treatment, affecting lung and heart, are rare, and cumulative incidences of cardiovascular diseases after breast radiotherapy are relatively low but must be considered in the context of global increases in the number of breast cancer survivors. Today, one of the biggest challenges in breast cancer adjuvant radiotherapy is to maintain at least the same rates of the locoregional control and at the same time limiting the incidential radiation to healthy normal tissues. Cardiovascular diseases are becoming the most critical competing mortality risk in women with early breast cancer treated with contemporary radiotherapy. We aimed to compare target volume coverage and healthy tissue dose exposure, using three radiotherapy techniques to establish an optimal solution for women with different breast sizes. We compared three-dimensional conformal radiotherapy (3D-CRT), tangential intensity modulated radiotherapy (T-IMRT) and hybrid technique (H-IMRT) after left-sided breast cancer conserving surgery. Sixty patients treated at our institute between 2014 and 2015 were included. On every simulation CT set, we delineated target volumes and organs at risk, including cardiac substructures. Regarding the size of the clinical target volume (CTV), we separately investigated the group with small, medium and large target volumes. In total, 180 treatment plans were evaluated and analysed. Median volumes of the CTV were 425.7 cm3, 867 cm3 and 1586.8 cm3 for the small, medium and large group, respectively. For all three analyzed techniques, we have demonstrated good coverage of the planning target volume for evaluation (PTVeval). The proportion of plans, meeting PTVeval V95%>95% objective was 100% (3D-CRT), 88.3% (T-IMRT) and 100% (H-IMRT). The lowest volumes of relative excessive PTVeval dose (V105–107 %) were generated with 3D-CRT, compared to the lowest absolute volumes, which were generated with T-IMRT or H-IMRT. Best plan quality indexes, such as conformity index, homogeneity index, and confirmation number were demonstrated with H-IMRT. The lowest excessive dose to the skin was achieved with both IMRT techniques. Median heart mean (heart-Dmean) values were 1.9 Gy, 2.3 Gy and 3.1 Gy for 3D-CRT, T-IMRT and H-IMRT, respectively (p30–40 Gy. Higher radiation doses to segments may lead to a higher probability of cardiac injury. Ipsilateral lung dose was similarly reduced by 3D-CRT (5.6 Gy) as compared to T-IMRT (5.7 Gy) or H-IMRT (8.7 Gy) (p=0.012). For breast cancer patients after conservative surgery with an average body habitus, 3D-CRT is the treatment of choice. T-IMRT is also an optimal technique for the group of patients with medium-sized CTV. 3D-CRT also seems viable technique for large target volumes CTV. With H-IMRT, it is possible to achieve the best target coverage in patients with largest and complexly shaped CTV