Radiation Treatment breaks

My dad has SCLC. He was receiving both chemo and radiation at the same time before his white blood cell count became too low. He's had 5 (out of a possible 6) rounds of chemo and his onc has said "no more" as she believes his body has reached its max. My dad did 20 radiation treatments than was off for 2 weeks because of his low blood count. He still has 13 radiation treatments left. He just re-started again this past Tues. and Wed. before he's had to take 2 days off because of a mishap at the radialogists office (they are moving offices and all my dads radiation #'s were lost in cyberspace when they converted to the new office location). They are hoping they'll be able to start his radiation again this coming Mon. My concern is do too many radiation breaks lessen its effectiveness? Has anyone else had as many or as long of breaks? He feels good and his spirits are high so am thankful for that! God bless.