S.Sadiq, ¹ S.Siddique, ¹R.N.Maken, ¹ N.Amjad, ¹& R.I.Mahmood²
¹INMOL Hospital,Lahore,Pakistan ²MidlineCity Hospital,Dubai, UnitedArabEmirates
OBJECTIVES:
To evaluate the effectiveness of cone-beam CT (CBCT) in adaptive radiotherapy (ART) for muscle-invasive bladder cancer (MIBC).
- To address challenges posed by the bladder’s variable anatomy, which affects treatment precision.
- To assess whether daily CBCT-based image guidance with a plan-of-the-day (POD) approach improves target coverage accuracy.
- To determine if this approach can reduce geographical misses and enhance overall treatment accuracy in bladder radiotherapy.
METHODS: - Eighteen patients with localized muscle-invasive bladder cancer (T2– T4aN0M0) were treated with 55 Gy in 20 fractions alongside concurrent chemotherapy (cisplatin or 5-FU/mitomycin).
- CT simulation was performed under an empty bladder protocol to define two planning target volumes (PTVs): Small PTV: CTV + 5 mm Large PTV: CTV + 15 mm
- Corresponding radiotherapy plans were generated for each PTV.
- Daily CBCT was used for plan selection based on bladder volume changes.
- Offline evaluations were conducted to assess geographical misses.
- Primary endpoint: Target coverage and bowel volume spared using ART.
- Secondary endpoints: Bladder movement patterns, acute toxicities, and treatment response.
RESULTS:
- Treatment delivery and geometry
- Geographical misses: 26 out of 360 fractions (7.2%)
- Most misses occurred in the superior direction (17 cases; mean displacement 0.49 cm) Small bowel dose:
- Small PTV plan: mean V50 = 16.18 cc
- Large PTV plan: mean V50 = 36.68 cc Plan usage: Small PTV used in 251/360 fractions (71%), preserving a mean 324.03 cc of bowel volume per patient (SD: 280.34) Predominant bladder movement: superior, anterior, and posterior directions
- Toxicity and clinical outcomes
- Acute grade 2 genitourinary toxicity: 5 patients
- Grade 2 gastrointestinal toxicity: 2 patients
- No grade ≥3 radiation-related toxicity observed
- Response rates:
- Complete response: 11 patients
- Partial response: 7 patients
CONCLUSIONS:
CBCT-guided ART enables precise, individualized radiotherapy for MIBC, significantly improving treatment accuracy while minimizing radiation exposure to surrounding healthy tissues. The plan-of-the-day approach effectively mitigates the impact of bladder volume variations, enhancing therapeutic outcomes. These findings underscore the potential of ART as a viable alternative to more invasive interventions such as radical cystectomy, emphasizing its role in optimizing bladder cancer management.