Witt, 46, shared a post on social media from when she finished her last treatment, when she was awarded a certificate of completion and was able to ring the ceremonial gong.
Witt said she was just starting her treatments when her parents were found dead in their home in Worcester, Massachusetts, People magazine reported.
Witt is still unsure if she’s “completely healed” from the breast cancer treatments, which included a mastectomy. She also thanked the medical professionals who kept her health issues private until she decided to disclose them.
Robert and Diane Witt’s deaths were attributed to “probable cardiac dysrhythmia” from exposure to cold, The Telegram & Gazette and The Associated Press reported.
They were found after the actor hadn’t heard from them for several days and had asked a relative to check on them. Police said their heating system was not working at the time of their deaths.
“Every time I offered to have something repaired for them, they refused to allow workers into their house,” Alicia Witt said, according to the AP. “I begged, cried, tried to reason with them, tried to convince them to let me help them move — but every time, they became furious with me, telling me I had no right to tell them how to live their lives and that they had it all under control.”
Photos: Alicia Witt through the years Here are some memorable photos of actress and singer Alicia Witt through the years. (Charles Sykes/Invision/AP)
Photos: Alicia Witt through the years 1999: Alicia Witt attends the premiere of "Deep Blue Sea" on July 26, 1999. (James Peterson/Getty Images)
Photos: Alicia Witt through the years 2000: Alicia Witt attends the world premiere of "The Replacements" in Los Angeles on Aug. 7, 2000. (Kevin Winter/ImageDirect via Getty Images)
Photos: Alicia Witt through the years 2001: Actress Alicia Witt attends the premiere of the film "Vanilla Sky" on December 10, 2001, at the Chinese Theatre in Hollywood, California. (Vince Bucci/Getty Images)
Photos: Alicia Witt through the years 2002: Alicia Witt, Hugh Grant and Sandra Bullock at the premiere of "Two Weeks Notice" at the Bruin Theatre in Westwood, California, on Wednesday, Dec. 18, 2002. (Kevin Winter/ImageDirect via Getty Images)
Photos: Alicia Witt through the years 2003: Actress Alicia Witt attends the 10th annual Race to Erase MS at the Century Plaza Hotel on May 9, 2003, in Century City, California. (Robert Mora/Getty Images)
Photos: Alicia Witt through the years 2004: Actress Alicia Witt attends "Young Hollywood Votes" at the Esquire House Los Angeles on October 13, 2004, in Beverly Hills, California. (Vince Bucci/Getty Images)
Photos: Alicia Witt through the years 2005: Actress Alicia Witt arrives at the Los Angeles Film Festival premiere of "Nine Lives" at the Academy Theater on June 21, 2005, in Beverly Hills, California. (Kevin Winter/Getty Images)
Photos: Alicia Witt through the years 2006: Actress Alicia Witt attend the eighth annual Costume Designers Guild Awards held at the Beverly Hilton Hotel on February 25, 2006, in Beverly Hills, California. (Frazer Harrison/Getty Images)
Photos: Alicia Witt through the years 2007: Actress Alicia Witt arrives to the NBC All-Star Party held during the 2007 Summer Television Critics Association Press Tour at the Beverly Hilton hotel on July 17, 2007, in Beverly Hills, California. (Kevin Winter/Getty Images)
Photos: Alicia Witt through the years 2008: Actor Al Pacino (left) and actress Alicia Witt attend the after party for the world premiere of TriStar Pictures' movie "88 Minutes" at Prive Las Vegas inside the Planet Hollywood Resort & Casino on April 16, 2008, in Las Vegas. (Ethan Miller/Getty Images)
Photos: Alicia Witt through the years 2009: Actress Alicia Witt (left) and guest arrive at the 61st Primetime Emmy Awards held at the Nokia Theatre on September 20, 2009, in Los Angeles. (Frazer Harrison/Getty Images)
Photos: Alicia Witt through the years 2010: Actress Alicia Witt arrives at the Art of Elysium's third annual Black Tie Charity Gala "Heaven" on January 16, 2010, in Beverly Hills, California. (Jason Merritt/Getty Images)
Photos: Alicia Witt through the years 2011: Actress Alicia Witt arrives at the 2011 Art of Elysium "Heaven" Gala held at the California Science Center on January 15, 2011, in Los Angeles. (John Shearer/Getty Images for Art of Elysium)
Photos: Alicia Witt through the years 2012: Actress Alicia Witt attends Vanity Fair, L’Oréal Paris & Fiat-hosted D.J. Night in support of the Pablove Foundation on Saturday on February 25, 2012, in Hollywood, California. (Michael Buckner/Getty Images for VF)
Photos: Alicia Witt through the years 2013: Singer-songwriter Ben Folds and actress Alicia Witt attend the "About Time" premiere during the 51st New York Film Festival at Alice Tully Hall at Lincoln Center on October 1, 2013, in New York City. (Jemal Countess/Getty Images)
Photos: Alicia Witt through the years 2014: Musician Ben Folds and actress Alicia Witt attend the Art of Elysium's seventh annual Heaven Gala presented by Mercedes-Benz at Skirball Cultural Center on January 11, 2014, in Los Angeles. (Mike Windle/Getty Images for Art of Elysium)
Photos: Alicia Witt through the years 2015: Actress Alicia Witt attends the eighth annual Heaven Gala presented by Art of Elysium and Samsung Galaxy at Hangar 8 on January 10, 2015, in Los Angeles. (Jason Merritt/Getty Images for Art of Elysium)
Photos: Alicia Witt through the years 2016: Actress Alicia Witt attends the Art of Elysium 2016 Heaven Gala presented by Vivienne Westwood & Andreas Kronthaler at 3LABS on January 9, 2016, in Culver City, California. (Jason Merritt/Getty Images for Art of Elysium)
Photos: Alicia Witt through the years 2017: Alicia Witt attends the premiere of Showtime's "Twin Peaks" at the Theatre at Ace Hotel on May 19, 2017, in Los Angeles. (Alberto E. Rodriguez/Getty Images)
Photos: Alicia Witt through the years 2018: Actress Alicia Witt attends the 52nd annual CMA Awards at the Bridgestone Arena on November 14, 2018, in Nashville, Tennessee. (Jason Kempin/Getty Images)
Photos: Alicia Witt through the years 2019: Alicia Witt attends the "Orange Is the New Black" Season 7 world premiere screening and after-party on July 25, 2019, in New York City. (Dia Dipasupil/Getty Images for Netflix)
Photos: Alicia Witt through the years 2020: Alicia Witt attends the Art of Elysium's 13th annual Celebration - Heaven at Hollywood Palladium on January 4, 2020, in Los Angeles. (Randy Shropshire/Getty Images for the Art of Elysium)