Predictors of Local Control with Palliative Radiotherapy for Multiple Myeloma

PURPOSE/OBJECTIVE(S)

Palliative radiotherapy (RT) is employed for patients with multiple myeloma to improve or prevent symptoms. However, the optimal dose fractionation is not well defined. The role of cytogenetics in informing RT warrants further study. We performed an institutional analysis of patients with multiple myeloma receiving palliative RT and assessed factors associated with local progression, with a focus on dose fractionation and cytogenetic abnormalities.

MATERIALS/METHODS

We queried a prospectively maintained, departmental database for consecutive patients who received palliative RT for multiple myeloma at our institution from 2015 to 2020. Double- and triple-hit were defined as the presence of two and three high-risk cytogenetic abnormalities. RT dose fractionation data were extracted from the database. Follow-up imaging was used to evaluate for progression.

RESULTS

A total of 239 patients with 362 treated lesions were included. Twenty-five patients (10.4%) with 39 lesions had double-hit cytogenetics, and 4 patients (1.7%) with 7 lesions were triple-hit. Patients had the following number of lesions treated with RT: 1 (156, 65.3%), 2 (53, 22.2%), 3 (17, 7.1%), or >3 (13, 5.4%). The most commonly targeted sites were spine (125, 34.5%), abdomen/pelvis (67, 18.5%), and lower extremity (53, 14.6%). Most lesions received doses of 20 Gy/5 fx (132, 36.5%), 8 Gy/1 fx (93, 25.7%), or 30 Gy/10 fx (48, 13.3%). RT equivalent dose in 2 Gray fractions (EQD2) was <2000 cGy for 126 lesions (34.8%) and ≥2000 cGy for 236 lesions (65.2%). At a median follow-up of 4.3 years, the risk of local progression on a per lesion basis at 1 and 4 years was 7.8% (95% CI: 5.5-11.1) and 13.4% (10.3-17.5), respectively. No cytogenetic abnormalities were correlated with local progression. Factors significant on univariate analysis included female sex [hazard ratio (HR): 1.94 (1.02-3.71), p = .045], LDH at diagnosis [HR per 10 units/liter: 1.04 (1.09-1.08), p = .016], and number of treated lesions [HR per lesion: 1.38 (1.02-1.89), p = .039]. These three covariates were included on multivariable analysis, and the only covariate to approach significance was number of treated lesions [HR for >3 versus 1: 2.43 (0.88-6.74), p = .059]. In the overall cohort, EQD2 did not impact risk of progression. Among those with >3 treated lesions, EQD2 ≥2000 cGy was associated with a significantly lower risk of progression [HR: 0.05 (0.01-0.23), p<.001]. Double- and triple-hit status were not correlated with progression. Median overall survival in all patients was 4.1 years versus 1.5 and 0.6 years in those with double- and triple-hit disease, respectively.

CONCLUSION

In this large, institutional study of patients with multiple myeloma, palliative RT achieves durable long-term local control. Patients with high disease burden may be at increased risk of progression at treated sites. This group may benefit from an EQD ≥2000 cGy. Cytogenetics, including double- and triple-hit status, do not appear to influence RT response.

Change in Blood Counts after Palliative Radiotherapy for Multiple Myeloma

PURPOSE/OBJECTIVE(S)

Radiation therapy (RT) can provide effective palliation and prevent symptomatic local progression of multiple myeloma (MM). However, RT is sometimes avoided due to concerns for secondary impact to bone marrow, potentially decreasing blood cell counts and precluding ability to receive future systemic therapies. We reviewed a series of MM patients who received palliative RT to assess changes in blood counts from pre-RT to post-RT, hypothesizing that blood counts would not significantly decline after treatment with modern RT volumes and techniques.

MATERIALS/METHODS

We utilized a prospectively maintained departmental database and included patients who received palliative RT for MM from 2015 to 2020. Lab values immediately pre-RT (within one month of RT start date) and post-RT (within three months of RT completion) including hemoglobin, lymphocytes, neutrophils, and platelets were collected. Statistical differences from pre-RT to post-RT were assessed using t-tests. ANOVA was used to compare change in blood counts between common dose fractionation regimens (30 Gy in 10 Fractions, 20 Gy in 5, and 8 Gy in 1).

RESULTS

A total of 334 MM patients receiving 424 courses of RT were included in this analysis. The median age at start of first treatment was 67 (IQR: 60-76) years. One-hundred ninety-five (58%) were male. Median RT dose was 20 (IQR: 8-24.5) Gy delivered over a median 5 (IQR: 1-5) fractions. Between pre-RT and post-RT, there was no significant change in hemoglobin (+0.1 g/dL (IQR: -0.8, +0.5), p = .076), lymphocyte counts (-0.3*10^9 cells/L (IQR: -0.6, 0), p = .435), or neutrophil counts (-0.1*10^9 cells/L (IQR: -1.1, +0.9), p = .310). In contrast, platelet counts significantly decreased from pre-RT (median 165*10^9 cells/L, IQR: 112-210) to post-RT (median 146, IQR: 93-194) by a median of 17.5 *10^9 cells/L (IQR: -52.5, +14.0, p<0.0001). There were no differences in changes in hemoglobin, neutrophils, or platelets between the common dose fractionations. However, there was a significantly greater drop in lymphocytes after 30 Gy in 10 fractions (p = .039, mean lymphocyte count change (in 10^9 cells/L) for 30 Gy in 10: -0.87, 20 Gy in 5: -0.47, and 8 Gy in 1: -0.27).

CONCLUSION

In this large dataset of patients receiving modern palliative RT for MM, hemoglobin, lymphocytes, and neutrophils did not significantly decline from pre-RT to post-RT. In contrast, there was a statistically significant drop in platelet count by a median 17.5*10^9 cells/L from pre-RT to post-RT, which may or may not be clinically significant depending on clinical context. Patients receiving 30 Gy in 10 fractions had greater drops in lymphocytes than those receiving lower doses. Further analyses will be performed to determine clinical, dosimetric, and volumetric predictors of decline in blood counts after radiation.