AN A319 CREW; WHILE PARKING THE ACFT AT BOS; EXPERIENCED ACFT MOVEMENT AFTER ACFT WHEEL CHOCKS WERE IN PLACE.

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UPON REACHING THE STOP POINT FOR GATE AS INDICATED BY THE GND MARSHAL; I STOPPED THE ACFT WITH FOOT BRAKES AND SET THE PARKING BRAKE TO 'ON.' THE MARSHAL WENT FROM THE 'FULL STOP' SIGNAL TO A 'CHOCKS IN' SIGNAL ALMOST IMMEDIATELY. AS MY HAND WAS STILL ON THE PARKING BRAKE HANDLE; I PROCEEDED TO SET THE PARKING BRAKE TO 'OFF.' I THEN WENT ABOUT MY OTHER COCKPIT DUTIES. VERY SHORTLY THEREAFTER; I NOTICED THAT THE ACFT WAS MOVING. I QUICKLY APPLIED FOOT BRAKES AND STOPPED THE ACFT. I THEN RESET THE PARKING BRAKE TO 'ON' AND SECURED BOTH ENGS. WHEN APPLYING THE FOOT BRAKES; I FELT SOMETHING BENEATH THE ACFT. AFTER DEPLANING PAX; I INSPECTED THE NOSE AREA OF THE ACFT AND IT APPEARED THAT THERE WAS SLIGHT DAMAGE SUSTAINED TO THE FORWARD AVIONICS COMPARTMENT DOOR AND TO THE #1 DME ANTENNA. THERE WAS A PUSHBACK TRACTOR IN CLOSE VICINITY THAT WAS POSITIONED FOR THE NEXT DEP. I ASKED THE GND MARSHAL WHAT HAD HAPPENED AND HE STATED THAT THE SMALL RUBBER CHOCK THAT HAD BEEN PLACED ON THE L NOSEWHEEL HAD SLIPPED ON THE WET; PAINTED RAMP; THAT THE CHOCK HAD ENDED UP TO THE SIDE AND BEHIND WHERE THE NOSEWHEELS HAD ENDED UP. UPON RETURNING TO THE CABIN OF THE ACFT; I ASKED THE 'A' FLT ATTENDANT IF ANYONE WAS HURT DURING THE SUDDEN STOPPING OF THE ACFT. FLT ATTENDANT INFORMED ME THAT 1 FEMALE PAX HAD FALLEN; BUT HAD STATED THAT SHE WAS ALRIGHT BEFORE EXITING THE ACFT. I ASKED THE OTHER 2 FLT ATTENDANTS IF THEY WERE ALRIGHT AND ONE FLT ATTENDANT STATED THAT SHE HAD FALLEN; BUT WAS OK. THE OTHER FLT ATTENDANT STATED THAT SHE WAS OK ALSO. I MADE AN APPROPRIATE LOGBOOK ENTRY. RECOMMEND CHANGE OF SOP AND KEEP PARKING BRAKE SET FOR ALL ARRS.