MULTIPLE ABORTS AND A GAR WERE THE RESULT OF A GND CONFLICT AT BOS ARPT.

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WE WERE TOLD TO POS AND HOLD ON RWY 9 IN BOS. AS WE WERE COMPLETING THE BEFORE TKOF CHKLIST; WE HEARD ACFT XYZ; OUR CALL SIGN; CLRED FOR IMMEDIATE TKOF. THE FO ACKNOWLEDGED THIS CLRNC; SO WITHOUT FURTHER RADIO XMISSIONS; I ADVANCED THE PWR LEVERS. AS WE STARTED OUR ROLL; THE FO SAID THERE WAS AN ACR B737 ON RWY 4R; WHICH I JUST SAW AS HE SAID IT. I INITIATED AN ABORTED TKOF. IT WAS BEFORE 70 KTS; AND THE CTLR SHOUTED 'ACFT XYZ STOP!' I STOPPED THE ACFT SHORT OF THE INTXN. ACR ALSO ABORTED THEIR TKOF. WE WERE TOLD TO TAXI BACK TO THE THRESHOLD AND GIVEN A NUMBER TO CALL UPON ARR AT OUR DEST. WE DEPARTED BOS WITHOUT FURTHER INCIDENT. WHEN I CALLED THE TWR IN BOS; I WAS TOLD BY THE SUPVR THAT ACR YYZ WAS CLRED FOR TKOF ON RWY 4; NOT US. HE SAID THAT UPON REVIEW OF THE TWR TAPES; OUR READBACK AND ACR READBACK HAD BEEN BLOCKED BY EACH OTHER. THE CTLR READ BACK OUR INSTRUCTIONS; WHICH WE NEVER HEARD; POSSIBLY DUE TO COCKPIT NOISE AND HIGH WORKLOAD AT THE INITIATION OF OUR TKOF. OBVIOUSLY; THE 2 SIMILAR SOUNDING CALL SIGNS WERE A CONTRIBUTING FACTOR TO THIS SIT; ALONG WITH THE USE OF INTERSECTING RWYS FOR TKOF. SUPPLEMENTAL INFO FROM ACN 421174: WHILE CAPT WAS INITIATING TKOF WE SAW ANOTHER ACR ACFT ROLLING ON RWY 4R FOR PURPOSE OF TKOF. THOSE 2 RWYS CROSS EACH OTHER IN THE FIRST 1000 FT. WE IMMEDIATELY CALLED FOR ABORT; AND AT THE SAME TIME THE CTLR SAID ON THE RADIO 'ACFT XYZ STOP; STOP!' WE STOPPED THE ACFT WITHOUT XING ANOTHER RWY. AFTER TALKING ON THE TELEPHONE TO TWR; WE WERE TOLD THAT ACR YYZ WAS ORIGINALLY CLRED FOR TKOF AND IT WAS A MISUNDERSTANDING; SO ACR PLT AND MYSELF READ BACK THE CLRNC IN SAME TIME; WHICH CREATED A BLOCK ON THE RADIO AND THAT WAS A REASON WHY WE DID NOT HEAR ANY FURTHER INSTRUCTIONS. SUPPLEMENTAL INFO FROM ACN 421372: OUR ACFT IN POS FOR TKOF ON RWY 4R. TFC CLRING AT THE END. TWR SAID 'BE READY FOR AN IMMEDIATE.' IN POS FOR TKOF ON RWY 9. TWR CTLR IS VERY BUSY; TALKING TO SEVERAL ACFT INCLUDING US; BUT THIS IS NORMAL FOR BOSTON. WE SEE TFC CLR OUR RWY AT THE FAR END AFTER LNDG; AND WE KNOW THIS DC10 IS BEHIND US. TWR CLRS US FOR TKOF; FO ACKNOWLEDGES TKOF CLRNC FOR RWY 4R AS WE ADVANCE THROTTLES. TWR SAYS; 'I DIDN'T HEAR YOU ACKNOWLEDGE;' SO I ACKNOWLEDGED THE CLRNC. WHEN FO POINTED AT THE ACFT ROLLING TOWARDS US AT THE INTXN OF RWYS 9 AND 4R; TWR TOLD THEM TO ABORT; BUT I INITIATED ABORT AS WELL; UNSURE OF THEIR ABILITY AND/OR INTENTION TO STOP. BOTH ACFT STOPPED PRIOR TO THE INTXN. IF AT NIGHT OR REDUCED VISIBILITY; THERE ALMOST CERTAINLY WOULD HAVE BEEN A COLLISION. APPARENTLY; OTHER ACFT ACCEPTED OUR TKOF CLRNC; BUT TWR DIDN'T KNOW. ALL THE TWR KNEW WAS OUR INITIAL READBACK WAS UNREADABLE.